Assessing the Efficiency and Microbial Diversity of H2S-removing Biotrickling Filters at Various pH Conditions

Assessing the Efficiency and Microbial Diversity of H2S-removing Biotrickling Filters at Various pH Conditions | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Assessing the Efficiency and Microbial Diversity of H 2 S-removing Biotrickling Filters at Various pH Conditions Abbas Abbas Rouhollahi, Minoo Giyahchi, Seyed Mohammad Mehdi Dastgheib, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3831762/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 10 You are reading this latest preprint version Abstract Reduced sulfur compounds such as H2S are extremely toxic and highly corrosive, produced in many industrial activities. The biological desulfurization process has been established to be a technically and economically effective alternative to traditional physicochemical processes. This study aimed to investigate the operation of three parallel biotrickling filters (BTFs) in removing H2S at different pH conditions (haloalkaliphilic, neutrophilic, and acidophilic) and their associated microbial population in the biodesulfurization process. BTF columns were inoculated with enriched inoculum and experiments were performed by gradually reducing Empty Bed Retention Time (EBRT) and increasing inlet concentration (Ci). The maximum Removal Efficiency (RE) and Maximum Elimination Capacity (EC) in EBRT 60s for haloalkaline, neutral and acidic conditions were, 91% and 179.5 g S-H2S m-3 h-1, 85.7%, and 141 g S-H2S m-3 h-1, 88% and 145 g S-H2S m-3 h-1 respectively. For visualizing the attached microbial biofilms on pall rings, Scanning Electron Microscopy (SEM) was used and microbial community structure analysis by NGS showed that the most abundant phyla in haBTF, nBTF, and aBTF belong to gammaproteobacteria, betaproteobacteria, and acidithiobacillia, respectively. The alpha analysis according to the Shannon and Simpson indexes showed a lower diversity of bacteria in the aBTF reactor than that of nBTF and haBTF and beta analysis indicated a different composition of bacteria in haBTF compared to the other two filters. These results indicated that the proper performance of BTF under haloalkaliphilic (natron) conditions is the most effective way for H2S removal from air pollutants of different industries. Biofilm Biodesulfurization Biotrickling filter Hydrogen sulfide Microbial biofilm Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 1. Introduction Many industrial activities such as wastewater treatment, petrochemical and natural gas refineries, biogas, composting, pulp and paper, and food production discharge a significant amount of volatile sulfur compounds (VSCs) to the environment [1, 2] The simplest VSC, hydrogen sulfide (H 2 S), is a colourless, flammable, and potentially explosive, heavier than air, highly poisonous and lethal at 600 ppm, severely corrosive, odour nuisance with rotten egg smell, and a very low odour threshold value [1, 3] Fossil fuels, the main energy source around the world, contain sulfur compounds that generate oxidated sulfur mixtures during the burning process. These compounds are precursors of acid rain that destroy the natural environments and architecture [4, 5]. Hence, sulfur removal from fuels is necessary and sometimes challenging. Massive research has been carried out in the field of removing H 2 S from gaseous fuels and off-gases, but still, new innovative research and new technologies are required to improve the performance of biological technologies and to elucidate the role of microbial communities in their functionality [6–9]. Traditional physicochemical technologies have been employed for the treatment of gaseous emissions containing VSCs of waste and/or sour gas streams. However, these methods in contrast to biological methods (biodesulfurization) [2, 10], which are based on the oxidation of H 2 S by sulfide oxidizing bacteria (SOB), are not very environmentally friendly and cost-effective due to high energy consumption for operating at high pressure and temperature [6, 11]. Biodesulfurization processes (BDS) of gas streams are usually carried out by four types of conventional bioreactors: biofilters, bioscrubbers, biotrickling filters (BTF), and bubble column bioreactors [12–14]. Although all of them can effectively remove hydrogen sulfide from contaminated gaseous streams, BTFs have some advantages over others. In BTF aqueous nutrient phase is trickled over the packing bed and the gas phase is forced upward through the vessel. The contaminants are absorbed and biodegraded by the microbes growing on the packing surfaces as biofilm. This technology has been scaled up at industrial scales for removal of up to 12000 ppm H 2 S concentrations [15] and unlike bioscrubber and bubble column bioreactors, the processes of absorption, biodegradation of contaminating compounds, and regeneration occur simultaneously in a single column. In comparison to biofilters, BTFs are more effective in removing compounds that recalcitrant to degradation or generate acidic by-products [16–18] and environmental conditions such as humidity, temperature, pH, and discharge of toxic substances can be better controlled. The choice of the type of bioreactor depends on the nature and loading rate of contaminated gases [19–21]. In BTFs, the autotrophic Sulfide oxidizing bacteria (SOB) have the primary role in the detoxification of VSCs. Thus, the activity and composition of autotrophic and heterotrophic microbial communities have a significant impact on the efficiency and removal rate. On the other hand, environmental factors such as pH have a basic role both in the diversity of the microbial community and solubility of sulfidic compounds. The effects of pH as a critical factor in the formation of bacterial community structures have been emphasized by various researchers including Tu et al. 2016 [22], Omri 2011 [23], and Chouari 2015 [24]. At different pH, varying autotrophic and heterotrophic microbial groups become active and dominant [25]. The selective pressure imposed by environmental conditions such as pH and concentrations of pollutants drastically changes the population structure and its diversity and ultimately affects system performance [26]. The results of Tu's 2017 research also showed that the biofilm thickness and stability are greatly affected by the inlet loading rate and pH [27]. This work aimed to investigate the effect of three different pH-adjusted conditions on the performance and microbial community in three parallel biodesulfurizing BTFs working in the same operational condition. For robust long-term operation, a new method of periodic relative starvation was used to control reactor clogging. Moreover, to elucidate the effect of pH on H 2 S utilizing bacterial community, the bacterial community composition of BTFs' attached biofilm was studied by next-generation sequencing (NGS) of the 16S rRNA gene (high throughput DNA sequencing technology). 2. Materials and methods 2.1. Culture media composition The nutrient solutions of recirculating and enrichment cultures were the mineral salt media (MSM) (Table S1 ). MSM ha , MSM n, and MSM a were used in haloalkaline biotrickling filter (haBTF), neutral biotrickling filter (nBTF), and acidic biotrickling filter (aBTF), respectively. All chemicals were of analytical grade with more than 99.5% purity and were purchased from Merck. During the enrichment and start-up periods, the sole sulfur source for the SOB growth was supplied by Na 2 S 2 O 3 .5H 2 O solution (10 g L − 1 ), and H 2 S mix gas was used during the acclimatization and the experimental phases. 2.2. Enrichment, acclimatization and immobilization of SOB consortia For acquiring diverse and active microbial sulfur-oxidizing consortia as initial inoculum, the SOB community was enriched from a mixture of the following materials: activated sludge of urban and industrial wastewater treatment plants (petrochemical and leather processing industries). At the beginning of the enrichment process, 350 g of the above-mentioned mixture was mixed with 2 liters of MSM n and MSM ha culture media individually and supplemented with Na 2 S 2 O 3 .5H 2 O (10 g L − 1 ) as the sole energy source. Enrichment cultures were continuously aerated for about 6 weeks and the pH values of MSM n , MSM ha , and MSM a were automatically controlled at 7, 8.5, and 1.5 to 2 respectively using 0.5 M NaHCO 3 when necessary and the temperature was controlled at 30°C. At this phase, 30% of the culture media was replaced by fresh media every week and the process continued for 6 weeks until the density of the enriched microbial consortium increased to 10 7 -10 8 CFU ml − 1 . At the immobilization period (startup period), BTFs were inoculated with 500 mL of enriched media harboring 10 7 -10 8 CFU mL − 1 of bacteria. Sodium thiosulfate was replaced by H 2 S as the sole source of energy and to allow the development of biofilm on the packing media, H 2 S concentration was gradually increased stepwise from 100 to 2000 ppmv over 62 days with an empty bed residence of 120s. 2.3. Biotrickling filter setup As shown in the schematic drawing of the experimental setup (Fig. 1 ), three identical lab-scale BTFs were operated to study the performance of H 2 S removal under haloalkaline, neutral, and acidic conditions. The BTF glass columns had an internal diameter and a height of 8 and 60 cm respectively and were packed with polypropylene 16 mm Pall rings to the height of 50 cm (Pall Ring Company, UK). The column temperature was controlled at 30 o C by continuous water circulation in the external jacket (Lauda RC6-CS, Germany). There were three sampling ports in the inlet, outlet, and middle sections of the column. In each BTF, the MSM was fed and recirculated over the packing media by using a peristaltic pump (Watson-Marlow Inc WM603s, USA) through a spray nozzle located at the top of BTFs. The trickling liquid velocity (TLV) During the startup stage was set to 0.9 m h − 1 and during all experiments was set to 7 m h − 1 . Before recycling culture media to the reactor, the coarse sulfur particles were separated by gravity sedimentation in 200 mL sludge traps. To prevent any release of H 2 S gas, the outlet gas of BTFs passed through the NaOH trap. The pressure drops of reactors (∆P) due to biofilm growth were monitored with U-tube water manometers connected to the bottom and top sections of the columns. The air supplied by a compressor was filtered and passed through a thermal mass flow controller (MFC) (BROOKS Instruments USA, type 6250s). Nitrogen flow gas (N 2 , 99.995%) was controlled by Digital MFC) BRONKHORST Instruments Netherlands, type EL-FLOW-201CV (. Air and nitrogen were humidified by passing through a water bubble column. A cylinder of H 2 S gas (5%, balanced N 2 ) was used for supplying hydrogen sulfide and a Digital MFC (UNIT Instruments USA, type UFC-1661) was used to control the flow of gas. Synthetic polluted air was created by combining H 2 S with humidified N 2 and air mixture, in a mixing chamber and divided equally into three flows using a three-way distributer, the mixed gas flow rate was controlled by rotameters before entering each reactor. The gas current was supplied from the bottom of BTFs through a diffuser and the treated gas discharged from the upper end of the column. During the operation times, to prevent the toxic effects of by-products and supply fresh nutrient sources, 15% of spent liquid media was replaced with fresh MSM daily. The pH of MSM n and MSM a in the nBTF and aBTF were monitored and controlled at set-points of 7 ± 0.1 and 2.5 ± 0.5 respectively by automatic addition of 2 N NaOH by pH controller and dosing pump (Hanna BL 7916, USA). The pH and alkalinity of MSM ha in haBTF were adjusted at a value of 8.5 ± 0.1 and 0.4 M, respectively using the addition of make-up fresh medium. If the pH of the MSM ha was higher than 8.5, carbon dioxide gas was used to adjust the pH. Compensation for evaporated water in bioreactors was done by adding water weekly. In all designed experiments, the amount of circulating dissolved oxygen (DO) was considered to be higher than the requirement for complete sulfide oxidation. If the DO of the recirculating medium was reduced compared to the saturated state, excess oxygen was purged to the recirculation medium in the MSM reservoir. 2.4. Analytical Methods H 2 S concentration was monitored online in the sampling port at the inlet, outlet, and middle sections of reactors using electrochemical and photoionization detectors (PID). A portable electrochemical sensor (SP2nd SI-100 SENKO, Korea) was used to measure H 2 S concentration from 0 to 100 ppmv, and at a concentration from 100 to 4000 ppmv, a fixed TVOC system contained PID detector (Ion Science, UK) was used. The precision of online sensor measurement was confirmed monthly by gas chromatographic (GC) analysis. The GC instrument was an Agilent Technologies (model 6890N Network GC System, USA) equipped with a flame photometric detector (FPD) and HP-1 capillary column (0.25Ò 3000 mm; Hewlett Packard, USA). The initial, mild, and final oven temperature was 50, 120, and 250°C, with temperature ramping 5°C min –1 and 20°C min –1 . Nitrogen was used as the carrier gas at a flow rate of 1.5 ml min − 1 and the temperature in the oven, injector, and detector were fixed at 250°C, 100°C, and 250°C, respectively. The concentration of sulfide and sulfate were measured using ion chromatography (Waters, USA) equipped with an IC- Pak anion HC column (4.6 4.6 x 150 mm; Waters) and a conductivity detector (Waters 432). Eluent consisted of 1.7 mM sodium carbonate and 1.8 mM sodium bicarbonate solution with a flow rate of 0.9 ml min − 1 . Dissolved oxygen (DO) and pH were monitored online in a liquid medium by (HQ40d, HACH) and (HANNA HI98191, USA), respectively. At the enrichment phase for the enumeration of total culturable chemolithotrophic SOB, samples were taken from the liquid medium, and the standard plate count method was used, dilutions of suspensions were then plated in appropriate MSM agar medium which was supplemented by Na 2 S 2 O 3 .5H 2 O 10 g L − 1 (Table S1 ). The plates were incubated at 30°C and the colonies were counted after 1 month. 2.5. Electron microscopy analysis Scanning electron microscopy (SEM) images were used for the identification of microbial biofilm formation on the Pall Rings surfaces. The samples were taken from different heights of the BTF column and submerged in ringer solution for removal of planktonic cells. Then samples were fixed for 2 hours in an aqueous solution of 2% osmium tetroxide and washed with water and subsequently postfixed with a solution of 2.5% glutaraldehyde in phosphate buffer for 1.5 h at 4 ◦C and washed in the water again. The graded series of Ethanol solutions (25, 50, 75, 100%) were used for dehydration and finally, the samples were freeze-dried for 1 day. For SEM ( ZEISS 960A, Germany) examination, replicas were produced by shadowing with a layer of gold in a sputter coater (Balzers SCD 004, Lichtenstein) [28]. 2.6. Microbial diversity analysis 2.6.1. DNA extraction At the end of experiments, to evaluate the changes in microbial communities as a function of the BTFs pH values, 30 g of packed bed with attached biomass was collected from top, middle, and bottom sections along the length of the reactors in aseptic condition. Total Genomic DNA was extracted and purified from biomass, using Fast DNA® Spin Kit for Soil (MP Biomedicals, USA) following the manufacturer's instructions, but the binding time of DNA to a silica matrix was modified to 20 min. For each sample, all the above-mentioned operations were performed in triplicate. The quantity and quality of the extracted DNA were analyzed by NanoDrop UV-VIS Spectrophotometer (Thermo Fisher Scientific, NanoDrop ONE, USA). Structural DNA integrity was evaluated by gel electrophoresis analysis (concentration of agarose gel: 1%, voltage: 150 V, electrophoresis time: 40 min). 2.6.2. NGS analysis DNA samples were sent to Beijing Genomics Institute (BGI, Hong Kong NGS Lab) for bacterial diversity analysis based on BGI protocols. Briefly, DNA sample quality control was done by Qubit Fluorometer, NanoDrop, and gel electrophoresis. Then, three libraries of the V3-V4 hypervariable regions (approximately ~ 460 bp) of 16S rRNA genes amplicon were constructed and qualified. Libraries were pair-end sequenced on a MiSeq System (Illumina, San Diego, CA, USA) using the PE300 (PE301 + 8 + 8 + 301) sequencing strategy. The primers used in the PCR reaction were 341 F (5′-ACTCCTACGGGAGGCAGCAG-3′) and 806 R (5′-GGACTACHVG GGTWTCTAA T-3′) (Report of BGI, Hong Kong, NGS lab). 2.6.3. High-throughput sequence data analysis Bioinformatic data analysis was conducted by the following software. Paired-end reads with sequencing adapters, N base, poly base, low quality, etc were filtered out then clean paired-end reads were overlapped and combined to generate the consensus sequences (tags) by FLASH (V1.2.11). The tags were clustered to Operational Taxonomic Unit (OTU) with 97% pairwise identity by UPARSE-OTU algorithm in USEARCH (v7.0.1090). To calculate the abundance of each OTU, the USEARCH global method was used and the representative OTU sequence was selected according to the most abundant sequence of each OTU. OTU representative sequences were taxonomically classified using Ribosomal Database Project (RDP) Classifier v.2.2 trained on the Greengenes database, using 0.8 confidence values as the cutoff. To analyze and compare the diversity and structure of bacterial communities, alpha diversity indices (Observed species, Ace, Chao1, Shannon, and Simpson) were calculated by Mothur (V1.31.2), and beta-diversity (Principal Component Analysis) was studied using the package ade4 of software R (V3.1.1). OTU's rank curve, rarefaction curves, alpha diversity indexes, and OTU's heat map analysis were done by software R (V3.1.1). 2.7. Experimental conditions and methodology After 62 days and establishing stable conditions in all three bioreactors, E1, E2, and E3 experiments were conducted to evaluate and compare the performance of BTFs with each other, the conditions of conducting these experiments are shown in Table 1 . Experiments E1 and E2 were designed and carried out in two periods of 11 days and experimentE3 in 15 days. By measuring inlet (C in ), outlet concentration (C out ) and using EBRT retention time and flow rate (Q), system performance evaluation parameters, including load retention (LR), removal capacity (EC), and removal efficiency (RE) were calculated. By decreasing (EBRT) while keeping (C in ) constant or by increasing (C in ) and keeping (EBRT) constant, the contamination load of bioreactors can be increased and the behaviour of BTFs can be studied (see the following equation): LR = Q. C i / V r = C i / EBRT Table 1 Experimental conditions for the biotrickling filters (haBTF, nBTF, aBTF) Experiment C i (ppm v ) LR (gS-H 2 S m _3 h _1 ) EBRT (s) Duration (d) previous operation (d) E1 2000 82.19 120 2 31 89.16 110 2 98.63 100 2 109.59 90 2 123.29 80 2 140.90 70 2 164.38 60 2 197.26 50 2 246.58 40 2 328.77 30 2 493.16 20 2 E2 1000 82.19 20 2 53 1090 89.16 20 2 1200 98.63 20 2 1333 109.59 20 2 1500 123.29 20 2 1714 140.90 20 2 2000 164.38 20 2 2400 197.26 20 2 3000 246.58 20 2 4000 328.77 20 2 6000 493.16 20 2 E3 200 65.76 15 1 75 49.32 20 1 24.66 40 1 12.33 80 1 8.22 120 1 1000 328.8 15 1 80 246.6 20 1 123.3 40 1 61.65 80 1 41.1 120 1 2000 665.76 15 1 85 499.32 20 1 249.66 40 1 124.83 80 1 83.22 120 1 2.8. EBRT reduction experiments During the 22 days of E1 experiments, EBRT was stepwise reduced from 120 seconds to 20 seconds and C in (2000 ppm) was kept constant, so LR increased from 82 to 493 g m − 3 h − 1 . In order to achieve stability in the performance, each period was kept for 48 hours. The details of the E1 experiments' conditions are shown in Table 1 . At the end of each stage of EBRT change, the concentration of inlet and outlet hydrogen sulfide was measured, EC and RE values were calculated, and critical parameters (EC critical and EBRT critical ). Critical EC and EBRT were determined at the points where the RE reached 97%. The calculation of maximum EC and critical EBRT can provide important information about bioreactor modeling, performance, and design. The third experiment (E3) was carried out in three C in (200, 1000, and 2000 ppm) to evaluate the effect of a decrease in EBRT (from 120 to 15s) on removal efficiency (RE) (Table 1 ). 2.9. Inlet concentration increase experiments According to the results obtained in the E1 experiments, in E2 experiments, EBRT was kept constant at 60 seconds, and C in was gradually increased from 1000 to 6000 ppm in 22 days (LR 82 to 493 g m − 3 h − 1 ). In the design of BTFs, the reduction of EBRT can lead to a reduction in the height of the column and the reduction of the initial construction costs. To achieve stable conditions in performance, each period of increased LR was continued for 48 hours. The details of the test conditions are shown in Table 1 . 3. Results and Discussions 3.1. BTFs Performance in Experimental Conditions The results of the E1 experiment in which the C i were instant at 2000 ppm with a gradual decrease of EBRT from 120 to 20s revealed the success of haBTF in H 2 S removal over nBTF and aBTF, as this filter reached its maximum EC (179.8 g m − 3 h − 1 ) in less EBRT (50s) with 91.14% EC which is 5.44 and 2.94% more than that of nBTF and aBTF, respectively that reached their maximum RE in 60s of EBRT (Figs. 2 and Figure S1 ). The superiority of haBTF is also revealed by comparing the critical EC in which 97% of inlet H 2 S is removed by the systems. In the condition that C i was constant, this parameter was determined to be 31.1 and 17.5 g m − 3 h − 1 more than nBTF and aBTF's EC, respectively. This rate was achieved in a higher H 2 S loading rate because of removing the higher amount of this gas in less retention time (see Table 2 ) which in conclusion shows the higher efficiency and rate of H 2 S removal by haBTF filter in this experiment. Table 2 Biotrickling filters' performance in the E1 and E2 experiments with E1 experiment in constant C in at 2000 ppm and decreasing EBRT from 120 to 20s and E2 experiment in constant EBRT at 60s and increasing C in from 1000 to 6000 ppm Exp E1 (Constant C in ) BTFs Critical EC g m − 3 h − 1 EBRT s H 2 S LR g S-H 2 S m − 3 h − 1 Maximum EC g m − 3 h − 1 RE % EBRT s H 2 S LR g S-H 2 S m − 3 h − 1 haBTF 137.6 70 140.9 179.8 91.14 50 197.2 nBTF 106.5 90 109.6 141 85.7 60 164.3 aBTF 120.1 80 123.3 145 88.2 60 164.3 Exp E2 (Constant EBRT) BTFs Critical EC g m − 3 h − 1 EBRT s H 2 S LR g S-H 2 S m − 3 h − 1 Maximum EC g m − 3 h − 1 RE % EBRT s H 2 S LR g S-H 2 S m − 3 h − 1 haBTF 167.8 60 173 210.6 64 60 328.7 nBTF 137.5 60 141 150.8 76.4 60 197.2 aBTF 144.6 60 149.1 174.3 53 60 328.7 haBTF E1 : Critical EC that guaranteeing RE 97% of inlet H 2 S was determined to be 137.6 g m − 3 h − 1 & EBRT 70s & Loading Rate (inlet load) is 140.9 g m − 3 h − 1 , maximmum EC 179.8 g m − 3 h − 1 , RE 91.14% & EBRT 50 s, Loading Rate is 197 g m − 3 h − 1 nBTF E1 : Critical EC that guaranteeing RE 97% of inlet H 2 S was determined to be 106.5 g m − 3 h − 1 & EBRT 90s & Loading Rate is 109.6 g m − 3 h − 1 , maximmum EC 141 g m − 3 h − 1 , RE 85.7% & EBRT 60s, Loading Rate is 164.3 g m − 3 h − 1 aBTF E1 : Critical EC that guaranteeing RE 97% of inlet H 2 S was determined to be 120.1 g m − 3 h − 1 & EBRT 80s & Loading Rate is 123.3 g m − 3 h − 1 , maximmum EC 145 g m − 3 h − 1 , RE 88.2% & EBRT 60s, Loading Rate is 164.3 g m − 3 h − 1 haBTF E2 : Critical EC that guaranteeing RE 97% of inlet H 2 S was determined to be 167.8 g m − 3 h − 1 & EBRT 60s & Loading Rate is 173 g m − 3 h − 1 , maximmum EC 210.6 g m − 3 h − 1 , RE 64% & EBRT 60s & Loading Rate is 328.7 g m − 3 h − 1 nBTF E2 : Critical EC that guaranteeing RE 97% of inlet H2S was determined to be 137.5 g m − 3 h − 1 & EBRT 60s & Loading Rate is 141 g m − 3 h − 1 , maximmum EC 150.8 g m − 3 h − 1 , RE 76.4% & EBRT 60s, Loading Rate is 197.2 g m − 3 h − 1 aBTF E2 : Critical EC that guaranteeing RE 97% of inlet H 2 S was determined to be 144.6 g m − 3 h − 1 & EBRT 60s & Loading Rate is 149.1 g m − 3 h − 1 , maximmum EC 174.3 g m − 3 h − 1 , RE 53% & EBRT 60s, Loading Rate is 328.7 g m − 3 h − 1 Comparing the operation of the three filters in the E2 experiment which was followed up at constant EBRT (60s), but this time in rising C i (from 1000 to 6000 ppm) showed almost the same algorithm as the E1 results (see Table 1 ) with haBTF reached the maximum EC of 210.6 g m − 3 h − 1 that was 59.8 and 36.3 g m − 3 h − 1 higher than that of nBTF and aBTF, respectively; higher critical EC (167.8 g m − 3 h − 1 ) were also detected in this system compare to the nBTF and aBTF. While the highest EC rate was achieved with haBTF in the E2 conditions, the RE of the system was recorded at its highest point (91.14%) in the E1 experiment of the same reactor (Table 2 ). Altogether, these results indicated the haBTF system could remove a higher rate of H 2 S than the other two reactors and in both experiments, aBTF had a slight advantage over nBTF. In E3 experiments, the effect of reducing EBRT from 120 seconds to 15 seconds on RE was investigated at three constant and independent input concentrations of 200, 1000, and 2000 ppm of hydrogen sulfide in bioreactors. The results in Figure S2 show that reducing EBRT from 120 seconds to 80 seconds in haBTF at the three mentioned concentrations has no effect on the reduction of RE, and even when the inlet concentration is 1000 ppm, by reducing the time to 40 seconds, only 4% of RE is reduced. On the other hand, in general, the slope of the removal efficiency reduction curves in the three mentioned concentrations in haBTF is always lower than that in aBTF and nBTF, which means that the process of reducing the removal efficiency with the reduction of EBRT in haBTF is slower than the others and independent of the inlet concentration. According to the results, it can be said that aBTF has a better performance than nBTF. Throughout all of the experiments, the oxygen-to-sulfide ratio was maintained at or above 25, which is higher than the requirement for the complete oxidation of sulfide. This limitation in sulfide provides the optimum condition for complete sulfide oxidation and sulfate production. From a bioenergetic point of view, sulfate provides more energy for biomass development than relative oxidation and biosulfur production. The lower portion of oxygen compared to sulfide will cause the formation of biosulfur and increase its density on the packing bed which will cause the pressure drop and eventually lead to the blockage of the system [29]. Moreover, biofilm formation on packing media will lower oxygen penetration which needs more oxygen supply in aerobic biodegradation systems [18, 30]. Generally, sulfide to sulfate oxidation was almost complete during the experiments (more than 88% and 12% of applied sulfide converted to sulfate and biosulfur, respectively). Also, 81–90%, 75–87%, and 78–88% of H 2 S were removed at alkaline, neutral, and acidic conditions, respectively and were assessed by measuring the outlet concentration of hydrogen sulfide placed at the first half of the column height, showing that the most of the H 2 S removes at this part. Since hydrogen sulfide (H 2 S) is a weak acid (pKa = 7), the pH of the MSM solution may have an impact on its mass transfer from the gas to the liquid phase. This effect is less pronounced at acidic, medium at neutral, and strong in alkaline circumstances. As a result, mass transfer from the gas phase to the liquid phase is less affected by a change in retention time under alkaline conditions than it is under acidic or neutral pH settings. Due to its higher concentration, hydrogen sulfide will transfer more mass than oxygen under conditions of constant hydrogen sulfide concentration and declining EBRT. As a result, in the absence of sufficient oxygen content for complete sulfide oxidation, the sulfur to sulfate ratio will rise (Wu et al., 2020). The ratio of O 2 :H 2 S gradually falls as the input pollution load rises, and with less oxygen present in the recycling medium, the oxidation of HS − is incomplete, leading to an increase in the proportion of elemental sulfur in place of sulfate. On the other hand, EBRT decrement declines gas to liquid mass transfer and hydrogen sulfide concentration increment will increase biosulfur production because of the biological potential limitation in HS − to SO 4 2− which is the consequence of oxygen decrement content in the recycling medium and incomplete HS − oxidation [31]. 3.2. Scanning Electron Microscopy Scanning electron micrographs were utilized to track the development of biofilm on pallrings after 90 days of experiments (Fig. 3 ). The analyses revealed the presence of a complex community of bacteria in the haBTF samples (Figs. 3 A and 3 B), including filamentous bacilli that were 1.5 µm in diameter and 4 µm in length, rod-shaped bacteria that were 0.4 µm in diameter and 1 µm in length, and cocobacilli that were 0.5 µm in diameter and 1 µm in length. In addition to bacterial aggregation, biosulfur sediments are shown in Fig. 3 B. In nBTF samples (Fig. 3 C, 3 D), there are bacteria with diameters ranging from 0.34 to 0.9 µm and lengths ranging from 0.9 to 9 µm, biosulfur accumulations produced by SOB secretions with diameters ranging from 1.4 to 7 µm (pointed with an arrow), and a nematode (nearly 5 µm in diameter and 35 µm in length), in addition to various sized bacteria. Even though the experiment used lethal levels of hydrogen sulfide, the existence of nematodes and other protozoa in neutral pH biofilters was unexpected. Amorphous fouling and spherical accumulations of biosulfur (diameter 8–10 µm) were also seen in the microgram of an aBTF sample (Figs. 3 F and 3 E) 3.3. Bacterial community diversity analysis After ending all experiments (90 days), to investigate the correlation of various bacterial populations on the efficiency of H 2 S removal, an analysis of bacterial community and structure was carried out using three amplicon libraries: haBTF, nBTF, and aBTF. After deleting the wrong identified or low-quality sequences, a total of 160632 tags (69% of initial) were identified with an average length of 424 bp, which comprised 61264 tags in the library of haBTF, 50216 tags in library nBTF and 49152 tags in library aBTF. The clustering of all tags to OTU was investigated at 97% similarity and the relative abundance data was calculated for each library. A total of 290 bacterial OTUs were obtained from three amplicon libraries and 119, 134, and 37 OTUs were assigned to haBTF, nBTF, and aBTF, respectively. At the phylum level, (data has not been shown) proteobacteria were the most dominant phylum in all samples, so more than 70% of the total read sequences in three BTFs were classified in this taxon. The other most abundant phyla were Bacteroidetes (18%, nBTF) and actinobacteria (30%, aBTF). The relative abundances and population structures of the bacterial communities at the taxonomical class level are shown in Figure S3. In haBTF, the most abundant classes were Alphaproteobacteria and Gammaproteobacteria (20.9% and 73.7%, respectively), in nBTF Alphaproteobacteria , Betaproteobacteria , Gammaproteobacteria and Flavobacteria (3.7, 59.6%, 15% and 16.6%, respectively) were more important and in aBTF sample Acidithiobacillia and Actinobacteria (65.4% and 30.4%, respectively) were the most prevalent classes. In terms of phylogeny, Acidithiobacillia is classified as an independent class of in the Proteobacteria , but previously its type order Acidithiobacillales was classified in the Gammaproteobacteria . The beta - proteobacteria includes the most abundant sulfur-oxidizing bacteria, but it has been reported that in very harsh environmental conditions most SOB belongs to the Gammaproteobacteria [32] and in extremophile acidic conditions, Acidithiobacillia play a key role. Table S2 lists the number of OTUs predicted in the data set per taxon. The results of molecular studies (Fig. 4 ) showed that in the alkaline condition of haBTF, the gamma and alpha proteobacteria are the most abundant classes (73.7% and 20.9% respectively). In neutral and acidic pH conditions the frequency of these taxa decreased so the abundance of Gammaproteobacteria decreased to 15% and 1.15% and for alphaproteobacteria to 3.7% and 1.4%, respectively. Under acidic pH conditions, the most abundant classes were Acidithiobacillia and Actinobacteria with 65.4% and 30.4%, respectively. In nBTF, the Betaproteobacteria , Flavobacteria , and Gammaproteobacteria were the most abundant classes, respectively. In the present study, contrary to the results of Omri et al., 2011 [23] and Chouari et al., 2015 [24], the lowest ecological diversity was observed at acidic pH, and in accordance with the results of Tu et al 2016 [22], the microbial diversity at neutral pH is higher than that of acidic pH. Acidithiobacillus was the most abundant group of bacteria in the mentioned study which is in agreement with the results of the relative abundance of different bacterial groups in three tested conditions of the present study. As shown in Table 3 , Acidithiobacillus and Thiobacillus are the most abundant genera of bacteria in aBTF and nBTF, respectively and haBTF was abundant with unclassified groups of bacteria. In aBTF after the Acidithiobacillus the most abundant acidophilic microorganism is Mycobacterium with an abundance of 27%, which is most likely mixotrophic SOB, and consistent with the results of Jia et al. 2022 [33], the abundance of mixotrophic SOB Mycobacterium was 78.4%. in aBTF with extremely acidic conditions. Table 3 Phylogenetic classification up to class level and relative abundances (%) of species (Underlined genus and/or species correspond to known SOB species) Taxonomical affiliation Relative abundance (%) Class Family Species haABTF nBTF aBTF Alphaproteobacteria Hyphomonadaceae Oceanicaulis sp. 2 1.3 0 0 Rhodobacteraceae Rhodobaca sp. 1 10 0 0 Rhizobiaceae Shinella sp. 2 0.1 0.8 < 0.1 Sphingomonadaceae Sphingomonas 5 sp. 0 < 0.1 < 0.1 Sphingomonas wittichii 0 0 1.3 Betaproteobacteria Hydrogenophilaceae Thiobacillus 3 sp. 0 56.5 1 - Thiomonas 5 sp. < 0.1 2.2 0 Gammaproteobacteria - Alkalimonas amylolytica 4 6.9 0 0 - Alkalimonas delamerensis4 1.5 0 0 Rhodanobacteraceae Dyella 5 sp. 0 1.2 < 0.1 Halomonadaceae Halomonas 4 sp. 1.4 0 0 Halomonas campisalis 3.4 0 0 Halothiobacillaceae Halothiobacillus 3 sp. 0.4 2.3 0 Alteromonadaceae Marinobacter 4 sp. 1 0 0 Lysobacteraceae Stenotrophomonas 4 sp. < 0.1 0.3 0 Stenotrophomonas acidaminiphila < 0.1 2.8 0 Thermomonas 4 sp. 0 1.3 0 Ectothiorhodospiraceae Thioalkalivibrio sulfidophilus 3 1.1 0 0 Acidithiobacillia Acidithiobacillaceae Acidithiobacillus 3 0 1.3 62.5 A. albertensis < 0.1 0.8 2.9 Actinobacteria Mycobacteriaceae Mycobacterium 5 sp. 0 < 0.1 27 Mycobacterium arupense 0 < 0.1 3.3 Flavobacteriia Flavobacteriaceae Chryseobacterium 4 sp. < 0.1 14 0 Sphingobacteriia Chitinophagaceae Sediminibacterium 4 sp. 0 0.7 0 Mollicutes Acholeplasmataceae Acholeplasma 4 sp. 0.8 0 0 Erysipelotrichia Erysipelotrichaceae PSB-M-3 4 0.8 0 0 Total 29 84.7 98.2 Unclassified 69.7 11.7 0.5 Others (< 0.5%) 1.3 3.6 1.3 Total 1. Uncultured bacterium, 2. Unclassified Bacteria, 3. Autotrophic, 4. Heterotrophic, 5. Mixotrophic 3.3.1. OTU rank curve The species diversity of a population depends on two factors: species richness and evenness. Increasing species richness (X-axis) simultaneously with uniform distribution of abundances (Y-axis log scale) can dramatically increase species diversity. OTU rank abundance curve can visually depict two factors at the same time. As can be seen in Fig. 5 in terms of species richness, nBTF has the highest and aBTF has the lowest richness. The steep slope of the OUT curve indicates the lack of uniform distribution of abundance in aBTF so that a limited number of OUTs ranks have the highest frequency and more numbers have the lowest frequency. The curves of haBTF and nBTF, at first start with steep slopes and then vary gently downward parallel, so the two BTFs are similarly distributed in terms of species evenness, and both have more evenness than the aBTF. Overall, according to OTU rank curves, haBTF and nBTF have the same species diversity and more than the aBTF. 3.3.2. Rarefaction curves Based on observed OTUs with increasing sequencing, it was shown that the three rarefaction curves tend to be smooth. This suggests that the produced data is enough to cover the diversity of all species in the community. The other rarefaction curves based on the Chao1 and ACE values also confirmed these results (Figure S4). 3.3.3. Heat map analysis Heat map analysis was done based on the relative abundance of each genus in each sample. To minimize the differences degree of the relative abundance value, the values were all log-transformed. The gradation of green shows the relative abundance of the three samples, -3 (light red) being the minimum and 3 (light green) the abundance of maximum considered. As shown in the heat map (Fig. 6 A), haBTF contained a more diverse group of bacteria in comparison to the two other reactors. This may be because of the formation of a pH gradient in haBTF which provides an adverse niche for different genera. The pH gradient may also be formed in nBTF but in less adverse value than that of haBTF. The most abundant known genera in aBTF, nBTF, and haBTF were Acidithiobacillus , Thiobacillus , and Rhodobaca , respectively. The effect of pH on the formation of different microbial communities has been reported in previous reports by Chouari et al., 2015 [24] and Tu et al., 2016 [22] in which they corroborated changing pH from neutral to acidic conditions will cause alteration in microbial population and both insisted on attendance and abundance of Acidithiobacillus in (extremely) acidic biofilters 3.3.4. Alpha diversity According to results in Table 4 , the value of observed species and indexes of Chao1and ACE showed species richness at neutral pH of nBTF is considerably higher than the others, and also the species richness at the haloalkaline condition (pH 8.5) is higher than the acidic pH (2- 3.5). Severe acidic conditions as selective pressure decreased species richness, but despite the relatively high salt concentration and slight alkalinity in haBTF, seemingly these limiting factors had less effect on species richness. Table 4 Diversity indexes. Observed species (Sobs) value, chao1, ACE indexes reflect the species richness of the community, Shannon and Simpson indexes reflect species diversity Sample Name Sobs Chao1 ACE Shannon Simpson haBTF 119 121.3 122.2 2.35 0.23 nBTF 134 134 134.1 2.26 0.23 aBTF 37 37.4 39 1.25 0.44 Shannon value (H) and Simpson index (D) estimators can reflect the diversity (richness and evenness species) of the community. Shannon value is influenced more by rare abundant species while the Simpson index (D) is affected by dominant and even species. According to the results of Shannon's value, the community diversity of haBTF is greater than the other samples and aBTF is in the lowest level of diversity, but Simpson's index indicated species diversities of haBTF and nBTF are the same and they are greater than aBTF due to its much less evenness and richness. 3.3.5. OTU PCA analysis To display the differences in OTU composition in three BTF samples, Principal Component Analysis (PCA) was used to construct a 2-D graph to summarize factors mainly responsible for this difference. Figure 6 B, based on principal component analysis, showed that along the PC1 axis, the samples could be divided into two separate groups, and along the PC2 axis, they could be separated into two other groups. The composition of OTUs in haBTF is significantly different from that of aBTF and nBTF, and according to the distribution of aBTF and nBTF along the vertical axis of PC2, it could be concluded that these two populations are more similar in terms of OTU structure. These results showed that the bacterial populations of haBTF have a significant difference compared to the other two BTFs, and on the other hand, the bacterial populations formed in aBTF and nBTF are more similar to each other. Conclusions Assessing the effect of pH conditions (haloalkaliphilic, neutrophilic, and acidophilic) on the efficiency of H 2 S removal in the BTF system, three parallel experiments were performed in which removal-determining parameters showed 91.14% RE and 179.8 gS-H 2 S m − 1 EC in haBTF when EBRT was 60s. These values differed in nBTF and aBTF with 85.7% and 88.2% RE; 141 and 145 gS-H 2 S m − 1 EC, respectively, demonstrated better performance of haloalkaliphilic BTF in H 2 S removal with distinct bacterial diversity in comparison with nBTF and aBTF, as NGS results showed, while despite less bacterial diversity, acidic condition performed slightly better compared to the neutral system. Declarations Funding The funding agencies had no role in study design, data collection, data analysis and preparation of the manuscript. Contributions Abbas Abbas Rouhollahi carried out the experiment; Abbas Abbas Rouhollahi and Minoo Giyahchi wrote the original draft of the manuscript; The work was supervised and designed by Mohammad Mehdi Dastgheib and Hamid Moghimi; and all authors read and approved the final version of the manuscript. Ethics approval and consent to participate Not applicable. Consent for publication Not applicable. Competing interests The authors declare no competing interests. References Guerrero L, Montalvo S, Huiliñir C, Campos JL, Barahona A, Borja R:Advances in the biological removal of sulphides from aqueous phase in anaerobic processes: A review. Environmental Reviews.24(1):84-100; doi: 10.1139/er-2015-0046 (2016) Syed M. SG, Falletta P., Béland M.:Removal of hydrogen sulfide from gas streams using biological processes - A review. CANADIAN BIOSYSTEMS ENGINEERING.48; (2006) Vikrant K, Kailasa SK, Tsang DCW, Lee SS, Kumar P, Giri BS, et al.:Biofiltration of hydrogen sulfide: Trends and challenges. Journal of Cleaner Production.187:131-47; doi: 10.1016/j.jclepro.2018.03.188 (2018) Chaiprapat S, Charnnok B, Kantachote D, Sung S:Bio-desulfurization of biogas using acidic biotrickling filter with dissolved oxygen in step feed recirculation. Bioresour Technol.179:429-35; doi: 10.1016/j.biortech.2014.12.068 (2015) Leerdam RCv:Anaerobic degradation of methanethiol in a process for Liquefied Petroleum Gas (LPG) biodesulfurization. (2007) de Rink R, Klok JBM, van Heeringen GJ, Keesman KJ, Janssen AJH, Ter Heijne A, Buisman CJN:Biologically enhanced hydrogen sulfide absorption from sour gas under haloalkaline conditions. J Hazard Mater.383:121104; doi: 10.1016/j.jhazmat.2019.121104 (2020) Roman P, Lipinska J, Bijmans MFM, Sorokin DY, Keesman KJ, Janssen AJH:Inhibition of a biological sulfide oxidation under haloalkaline conditions by thiols and diorgano polysulfanes. Water Res.101:448-56; doi: 10.1016/j.watres.2016.06.003 (2016) Wu H, Yan H, Quan Y, Zhao H, Jiang N, Yin C:Recent progress and perspectives in biotrickling filters for VOCs and odorous gases treatment. J Environ Manage.222:409-19; doi: 10.1016/j.jenvman.2018.06.001 (2018) Wu J, Jiang X, Jin Z, Yang S, Zhang J:The performance and microbial community in a slightly alkaline biotrickling filter for the removal of high concentration H(2)S from biogas. Chemosphere.249:126127; doi: 10.1016/j.chemosphere.2020.126127 (2020) Zytoon MA, AlZahrani AA, Noweir MH, El-Marakby FA:Bioconversion of high concentrations of hydrogen sulfide to elemental sulfur in airlift bioreactor. ScientificWorldJournal.2014:675673; doi: 10.1155/2014/675673 (2014) Cano PI, Colón J, Ramírez M, Lafuente J, Gabriel D, Cantero D:Life cycle assessment of different physical-chemical and biological technologies for biogas desulfurization in sewage treatment plants. Journal of Cleaner Production.181:663-74; doi: 10.1016/j.jclepro.2018.02.018 (2018) Allegue B. L. HJ:Biogas upgrading Evaluation of methods for H2S removal. Danish technological institude. (2014) de Rink R, Klok JBM, van Heeringen GJ, Sorokin DY, Ter Heijne A, Zeijlmaker R, et al.:Increasing the Selectivity for Sulfur Formation in Biological Gas Desulfurization. Environ Sci Technol.53(8):4519-27; doi: 10.1021/acs.est.8b06749 (2019) Mudliar S, Giri B, Padoley K, Satpute D, Dixit R, Bhatt P, et al.:Bioreactors for treatment of VOCs and odours - a review. J Environ Manage.91(5):1039-54; doi: 10.1016/j.jenvman.2010.01.006 (2010) Khoshnevisan B. TP, Alfaro N., Díaz I., Fdz-Polanco M., Rafiee Sh., Angelidaki I. :A review on prospects and challenges of biological H2S removal from biogas with focus on biotrickling filtration and microaerobic desulfurization. Biofuel research journal doi: 10.18331/BRJ2016.4.4.6 (2017) Cox H, Deshusses M:Combined Removal of H2S and Toluene in a Single-Stage Biotrickling Filter. (2000) Mpanias CJ, Baltzis BC:An experimental and modeling study on the removal of mono-chlorobenzene vapor in biotrickling filters. Biotechnol Bioeng.59(3):328-43; doi: 10.1002/(sici)1097-0290(19980805)59:33.0.co;2-d (1998) Schiavon M, Ragazzi M, Rada EC, Torretta V:Air pollution control through biotrickling filters: a review considering operational aspects and expected performance. Crit Rev Biotechnol.36(6):1143-55; doi: 10.3109/07388551.2015.1100586 (2016) Giri BS, Kim KH, Pandey RA, Cho J, Song H, Kim YS:Review of biotreatment techniques for volatile sulfur compounds with an emphasis on dimethyl sulfide. Process Biochemistry.49(9):1543-54; doi: 10.1016/j.procbio.2014.05.024 (2014) Gospodarek M, Rybarczyk P, Szulczyński B, Gębicki J:Comparative Evaluation of Selected Biological Methods for the Removal of Hydrophilic and Hydrophobic Odorous VOCs from Air. Processes.7(4); doi: 10.3390/pr7040187 (2019) Rybarczyk P, Szulczyński B, Gębicki J, Hupka J:Treatment of malodorous air in biotrickling filters: A review. Biochemical Engineering Journal.141:146-62; doi: 10.1016/j.bej.2018.10.014 (2019) Tu X, Li J, Feng R, Sun G, Guo J:Comparison of Removal Behavior of Two Biotrickling Filters under Transient Condition and Effect of pH on the Bacterial Communities. PLoS One.11(5):e0155593; doi: 10.1371/journal.pone.0155593 (2016) Omri I, Bouallagui H, Aouidi F, Godon JJ, Hamdi M:H2S gas biological removal efficiency and bacterial community diversity in biofilter treating wastewater odor. Bioresour Technol.102(22):10202-9; doi: 10.1016/j.biortech.2011.05.094 (2011) Chouari R, Dardouri W, Sallami F, Rais MB, Le Paslier D, Sghir A:Microbial Analysis and Efficiency of Biofiltration Packing Systems for Hydrogen Sulfide Removal from Wastewater Off Gas. Environmental Engineering Science.32(2):121-8; doi: 10.1089/ees.2014.0290 (2015) Jin Y, Veiga MC, Kennes C:Effects of pH, CO2, and flow pattern on the autotrophic degradation of hydrogen sulfide in a biotrickling filter. Biotechnol Bioeng.92(4):462-71; doi: 10.1002/bit.20607 (2005) Soupramanien A, Malhautier L, Dumont E, Andrès Y, Rocher J, Fanlo J-L:Biological treatment of a mixture of gaseous sulphur reduced compounds: identification of the total bacterial community's structure. Journal of Chemical Technology & Biotechnology.87(6):817-23; doi: 10.1002/jctb.3729 (2012) Tu X, Guo J, Yang Y, Feng R, Sun G, Li J:Biofilms formed within the acidic and the neutral biotrickling filters for treating H2S-containing waste gases. RSC Advances.7(41):25475-82; doi: 10.1039/c7ra04053a (2017) Bozzola JJ, Russell LD. Electron Microscopy: Principles and Techniques for Biologists. Jones and Bartlett (1999). Janssen A. J. H. SR, van der Kaa C., Jochemsen A., Bontsema J., Lettinga G. :Biological Sulphide Oxidation in a Fed-Batch Reactor. Biotechnology and Bioengineering.47(3):327-33; (1995) M. Deshusses DG. Biotrickling Filter Technology. In: Zarook Shareefdeen AS, editor. Biotechnology for Odor and Air Pollution Control. Springer. p. 147-66 (2005). Montebello AM, Fernández M, Almenglo F, Ramírez M, Cantero D, Baeza M, Gabriel D:Simultaneous methylmercaptan and hydrogen sulfide removal in the desulfurization of biogas in aerobic and anoxic biotrickling filters. Chemical Engineering Journal.200-202:237-46; doi: 10.1016/j.cej.2012.06.043 (2012) Montebello AM, Bezerra T, Rovira R, Rago L, Lafuente J, Gamisans X, et al.:Operational aspects, pH transition and microbial shifts of a H2S desulfurizing biotrickling filter with random packing material. Chemosphere.93(11):2675-82; doi: 10.1016/j.chemosphere.2013.08.052 (2013) Jia T, Zhang L, Sun S, Zhao Q, Peng Y:Adding organics to enrich mixotrophic sulfur-oxidizing bacteria under extremely acidic conditions-A novel strategy to enhance hydrogen sulfide removal. Sci Total Environ.854:158768; doi: 10.1016/j.scitotenv.2022.158768 (2022) Additional Declarations No competing interests reported. Supplementary Files Supplementarydatafile.docx Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 04 Mar, 2024 Reviews received at journal 25 Jan, 2024 Reviewers agreed at journal 15 Jan, 2024 Reviews received at journal 15 Jan, 2024 Reviewers agreed at journal 05 Jan, 2024 Reviewers agreed at journal 04 Jan, 2024 Reviewers invited by journal 04 Jan, 2024 Editor assigned by journal 04 Jan, 2024 Submission checks completed at journal 04 Jan, 2024 First submitted to journal 03 Jan, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-3831762","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":265762017,"identity":"53c67505-0ac9-4fe0-8fbc-02b5e2e5c98c","order_by":0,"name":"Abbas Abbas Rouhollahi","email":"","orcid":"","institution":"University of Tehran","correspondingAuthor":false,"prefix":"","firstName":"Abbas","middleName":"Abbas","lastName":"Rouhollahi","suffix":""},{"id":265762018,"identity":"a820f4a2-7713-4dc7-8b4e-7b8ecf534624","order_by":1,"name":"Minoo Giyahchi","email":"","orcid":"","institution":"University of Tehran","correspondingAuthor":false,"prefix":"","firstName":"Minoo","middleName":"","lastName":"Giyahchi","suffix":""},{"id":265762019,"identity":"d6f43a33-01cb-4c96-a51e-bae651e42985","order_by":2,"name":"Seyed Mohammad Mehdi Dastgheib","email":"","orcid":"","institution":"Research Institute of Petroleum Industry","correspondingAuthor":false,"prefix":"","firstName":"Seyed","middleName":"Mohammad Mehdi","lastName":"Dastgheib","suffix":""},{"id":265762020,"identity":"12561e6f-e751-407b-8e04-438654407394","order_by":3,"name":"Hamid Moghimi","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAtklEQVRIiWNgGAWjYBACAyBmBpI8/FABHuK1SDYwk6QFxDjATKTDzMUOH35dULBNxvhG/gGGHzUMMuYNBLRYzk5Ls55hcJvH7EYyA2PPMQYemQOEHHY7x8yYB6qFgbeBgUeCkMPgWoxnAG35S6QW48cgLQYSyQzMRNqSlsYM0iJx5rHBYZljEsRoST78mefPbXv+9sSHD9/U2NgT1AIEbHBFBxgYiNEAjMkPRCkbBaNgFIyCkQsA96M1rp57kd8AAAAASUVORK5CYII=","orcid":"","institution":"University of Tehran","correspondingAuthor":true,"prefix":"","firstName":"Hamid","middleName":"","lastName":"Moghimi","suffix":""}],"badges":[],"createdAt":"2024-01-03 12:14:40","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3831762/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3831762/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":49324167,"identity":"662ead80-adaa-48d1-a436-1114c9668612","added_by":"auto","created_at":"2024-01-08 17:14:57","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":418159,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic of BTFs system. 1. Gas regulator; 2. Mass flow controller; 3. Filter; 4. Compressed air;\u0026nbsp; 5. Humidifier; 6. Gas Mixing chamber; 7. Gas distributor; 8. Soap bubble flowmeter; 9. Inlet H\u003csub\u003e2\u003c/sub\u003eS Gas sensor; 10. NaOH traps; 11. Outlet H\u003csub\u003e2\u003c/sub\u003eS Gas sensor; 12. Gas outlet; 13. Middle Sampling port; 14. Gas inlet; 15. haBTF; 16. nBTF; 17. aBTF;\u0026nbsp; 18. pH controller; 19. MSM reservoir; 20. Recirculation pumps; 21. pH controler pump; 22. NaOH reserve; 23. Biosulfur gravity drain trap; 24. NaHCo\u003csub\u003e3 \u003c/sub\u003ereserve; 25. Water bath circulator\u003c/p\u003e","description":"","filename":"floatimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-3831762/v1/05bfbfd385ccdf35d3b1f126.jpeg"},{"id":49324170,"identity":"af2f7582-e96d-43fa-b1d9-d286536a9381","added_by":"auto","created_at":"2024-01-08 17:14:57","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":7442077,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of BTFs fed load on H\u003csub\u003e2\u003c/sub\u003eS elimination capacities during the treatment of H\u003csub\u003e2\u003c/sub\u003eS. haBTF (A \u0026amp; B), nBTF (C \u0026amp; D), aBTF (E \u0026amp; F).\u0026nbsp; Constant inlet concentration (2000 ppm), EBRT Change from 120s to 20 s (A, C, E). Constant EBRT 60s, inlet concentration changes from 1000 to 6000 ppm (B, D, F)\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-3831762/v1/bfdcf2ca1b858521f83b0de3.png"},{"id":49325260,"identity":"324e2489-f539-4e8a-b2db-5f91dd4e32f2","added_by":"auto","created_at":"2024-01-08 17:22:57","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1188729,"visible":true,"origin":"","legend":"\u003cp\u003eScanning Electron Microscopy images of the packing material after the desulfurizing operation. (haBTF: \u003cstrong\u003eA\u003c/strong\u003e.\u003cstrong\u003e \u003c/strong\u003eX2000, \u003cstrong\u003eB\u003c/strong\u003e.\u003cstrong\u003e \u003c/strong\u003eX5000), (nBTF: \u003cstrong\u003eC\u003c/strong\u003e. X2000, \u003cstrong\u003eD\u003c/strong\u003e. X3000), (aBTF:\u003cstrong\u003e E\u003c/strong\u003e. X1000, \u003cstrong\u003eF\u003c/strong\u003e.\u003cstrong\u003e \u003c/strong\u003eX3000)\u003c/p\u003e","description":"","filename":"floatimage3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-3831762/v1/686d030520937456d2d6b934.jpeg"},{"id":49324168,"identity":"ebfad749-e61a-4916-b631-490ebe8d7f3e","added_by":"auto","created_at":"2024-01-08 17:14:57","extension":"jpeg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":185958,"visible":true,"origin":"","legend":"\u003cp\u003eBacterial community structure and relative abundances at a class level of haBTF, aBTF, and nBTF samples\u003c/p\u003e","description":"","filename":"floatimage4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-3831762/v1/607bf4149104e4fc202f387d.jpeg"},{"id":49324169,"identity":"7cbe0ec9-60ab-4fdc-ac0f-ce3a928e4bb0","added_by":"auto","created_at":"2024-01-08 17:14:57","extension":"jpeg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":103304,"visible":true,"origin":"","legend":"\u003cp\u003eOTU rank\u003cstrong\u003e \u003c/strong\u003ecurves of haBTF, nBTF, and aBTF libraries\u003c/p\u003e","description":"","filename":"floatimage5.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-3831762/v1/e9efc5d39038ee876d2d8fc6.jpeg"},{"id":49324173,"identity":"89ac6b91-6f48-45ed-bfdf-aecbfa4e6be8","added_by":"auto","created_at":"2024-01-08 17:14:57","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":232339,"visible":true,"origin":"","legend":"\u003cp\u003eBacterial community structure and diversity of three BTFs. \u003cstrong\u003eA)\u003c/strong\u003e Bacterial community structures were exhibited by a heat map of abundant bacteria at the genus level. The dendrogram on the longitudinal axis was based on the sequence similarity between phylogenetic trees at the genus level and the horizontal dendrogram shows the proximity of the three bacterial communities, the relative distance was calculated based on the abundance, and the closest ones are placed in one branch and the farthest in a separate branch. The gradation of green represents the level of relative abundance as a base of log10 for all the three samples considered contigs, 0 (white) being the lowest and 7 (dark green) the abundance level of maximum considered. \u003cstrong\u003eB)\u003c/strong\u003e Principal Component Analysis (PCA) based on OTU abundance\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3831762/v1/2ee11ce6b79aabc23b58c7ed.jpg"},{"id":49326235,"identity":"2759e912-53b2-497c-a4f8-bb163d05e9e0","added_by":"auto","created_at":"2024-01-08 17:30:58","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1170541,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3831762/v1/baf80643-145b-4750-967d-63cdd85d0285.pdf"},{"id":49324171,"identity":"20cdec1f-43c5-4eea-a811-cc1c2e5223e1","added_by":"auto","created_at":"2024-01-08 17:14:57","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":760916,"visible":true,"origin":"","legend":"","description":"","filename":"Supplementarydatafile.docx","url":"https://assets-eu.researchsquare.com/files/rs-3831762/v1/5d6075ebb92609c4e37bbba5.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003eAssessing the Efficiency and Microbial Diversity of H\u003csub\u003e2\u003c/sub\u003eS-removing Biotrickling Filters at Various pH Conditions\u003c/p\u003e","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eMany industrial activities such as wastewater treatment, petrochemical and natural gas refineries, biogas, composting, pulp and paper, and food production discharge a significant amount of volatile sulfur compounds (VSCs) to the environment [1, 2] The simplest VSC, hydrogen sulfide (H\u003csub\u003e2\u003c/sub\u003eS), is a colourless, flammable, and potentially explosive, heavier than air, highly poisonous and lethal at 600 ppm, severely corrosive, odour nuisance with rotten egg smell, and a very low odour threshold value [1, 3] Fossil fuels, the main energy source around the world, contain sulfur compounds that generate oxidated sulfur mixtures during the burning process. These compounds are precursors of acid rain that destroy the natural environments and architecture [4, 5]. Hence, sulfur removal from fuels is necessary and sometimes challenging.\u003c/p\u003e \u003cp\u003eMassive research has been carried out in the field of removing H\u003csub\u003e2\u003c/sub\u003eS from gaseous fuels and off-gases, but still, new innovative research and new technologies are required to improve the performance of biological technologies and to elucidate the role of microbial communities in their functionality [6\u0026ndash;9].\u003c/p\u003e \u003cp\u003eTraditional physicochemical technologies have been employed for the treatment of gaseous emissions containing VSCs of waste and/or sour gas streams. However, these methods in contrast to biological methods (biodesulfurization) [2, 10], which are based on the oxidation of H\u003csub\u003e2\u003c/sub\u003eS by sulfide oxidizing bacteria (SOB), are not very environmentally friendly and cost-effective due to high energy consumption for operating at high pressure and temperature [6, 11].\u003c/p\u003e \u003cp\u003eBiodesulfurization processes (BDS) of gas streams are usually carried out by four types of conventional bioreactors: biofilters, bioscrubbers, biotrickling filters (BTF), and bubble column bioreactors [12\u0026ndash;14]. Although all of them can effectively remove hydrogen sulfide from contaminated gaseous streams, BTFs have some advantages over others. In BTF aqueous nutrient phase is trickled over the packing bed and the gas phase is forced upward through the vessel. The contaminants are absorbed and biodegraded by the microbes growing on the packing surfaces as biofilm. This technology has been scaled up at industrial scales for removal of up to 12000 ppm H\u003csub\u003e2\u003c/sub\u003eS concentrations [15] and unlike bioscrubber and bubble column bioreactors, the processes of absorption, biodegradation of contaminating compounds, and regeneration occur simultaneously in a single column. In comparison to biofilters, BTFs are more effective in removing compounds that recalcitrant to degradation or generate acidic by-products [16\u0026ndash;18] and environmental conditions such as humidity, temperature, pH, and discharge of toxic substances can be better controlled. The choice of the type of bioreactor depends on the nature and loading rate of contaminated gases [19\u0026ndash;21].\u003c/p\u003e \u003cp\u003eIn BTFs, the autotrophic Sulfide oxidizing bacteria (SOB) have the primary role in the detoxification of VSCs. Thus, the activity and composition of autotrophic and heterotrophic microbial communities have a significant impact on the efficiency and removal rate. On the other hand, environmental factors such as pH have a basic role both in the diversity of the microbial community and solubility of sulfidic compounds.\u003c/p\u003e \u003cp\u003eThe effects of pH as a critical factor in the formation of bacterial community structures have been emphasized by various researchers including Tu et al. 2016 [22], Omri 2011 [23], and Chouari 2015 [24]. At different pH, varying autotrophic and heterotrophic microbial groups become active and dominant [25]. The selective pressure imposed by environmental conditions such as pH and concentrations of pollutants drastically changes the population structure and its diversity and ultimately affects system performance [26]. The results of Tu's 2017 research also showed that the biofilm thickness and stability are greatly affected by the inlet loading rate and pH [27].\u003c/p\u003e \u003cp\u003eThis work aimed to investigate the effect of three different pH-adjusted conditions on the performance and microbial community in three parallel biodesulfurizing BTFs working in the same operational condition. For robust long-term operation, a new method of periodic relative starvation was used to control reactor clogging. Moreover, to elucidate the effect of pH on H\u003csub\u003e2\u003c/sub\u003eS utilizing bacterial community, the bacterial community composition of BTFs' attached biofilm was studied by next-generation sequencing (NGS) of the 16S rRNA gene (high throughput DNA sequencing technology).\u003c/p\u003e"},{"header":"2. Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n\u003ch2\u003e2.1. Culture media composition\u003c/h2\u003e\n\u003cp\u003eThe nutrient solutions of recirculating and enrichment cultures were the mineral salt media (MSM) (Table \u003cspan class=\"InternalRef\"\u003eS1\u003c/span\u003e). MSM\u003csub\u003eha\u003c/sub\u003e, MSM\u003csub\u003en,\u003c/sub\u003e and MSM\u003csub\u003ea\u003c/sub\u003e were used in haloalkaline biotrickling filter (haBTF), neutral biotrickling filter (nBTF), and acidic biotrickling filter (aBTF), respectively. All chemicals were of analytical grade with more than 99.5% purity and were purchased from Merck.\u003c/p\u003e\n\u003cp\u003eDuring the enrichment and start-up periods, the sole sulfur source for the SOB growth was supplied by Na\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e.5H\u003csub\u003e2\u003c/sub\u003eO solution (10 g L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), and H\u003csub\u003e2\u003c/sub\u003eS mix gas was used during the acclimatization and the experimental phases.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\n\u003ch2\u003e2.2. Enrichment, acclimatization and immobilization of SOB consortia\u003c/h2\u003e\n\u003cp\u003eFor acquiring diverse and active microbial sulfur-oxidizing consortia as initial inoculum, the SOB community was enriched from a mixture of the following materials: activated sludge of urban and industrial wastewater treatment plants (petrochemical and leather processing industries). At the beginning of the enrichment process, 350 g of the above-mentioned mixture was mixed with 2 liters of MSM\u003csub\u003en\u003c/sub\u003e and MSM\u003csub\u003eha\u003c/sub\u003e culture media individually and supplemented with Na\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e.5H\u003csub\u003e2\u003c/sub\u003eO (10 g L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) as the sole energy source. Enrichment cultures were continuously aerated for about 6 weeks and the pH values of MSM\u003csub\u003en\u003c/sub\u003e, MSM\u003csub\u003eha\u003c/sub\u003e, and MSM\u003csub\u003ea\u003c/sub\u003e were automatically controlled at 7, 8.5, and 1.5 to 2 respectively using 0.5 M NaHCO\u003csub\u003e3\u003c/sub\u003e when necessary and the temperature was controlled at 30\u0026deg;C. At this phase, 30% of the culture media was replaced by fresh media every week and the process continued for 6 weeks until the density of the enriched microbial consortium increased to 10\u003csup\u003e7\u003c/sup\u003e-10\u003csup\u003e8\u003c/sup\u003e CFU ml\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eAt the immobilization period (startup period), BTFs were inoculated with 500 mL of enriched media harboring 10\u003csup\u003e7\u003c/sup\u003e-10\u003csup\u003e8\u003c/sup\u003e CFU mL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e of bacteria. Sodium thiosulfate was replaced by H\u003csub\u003e2\u003c/sub\u003eS as the sole source of energy and to allow the development of biofilm on the packing media, H\u003csub\u003e2\u003c/sub\u003eS concentration was gradually increased stepwise from 100 to 2000 ppmv over 62 days with an empty bed residence of 120s.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\n\u003ch2\u003e2.3. Biotrickling filter setup\u003c/h2\u003e\n\u003cp\u003eAs shown in the schematic drawing of the experimental setup (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e), three identical lab-scale BTFs were operated to study the performance of H\u003csub\u003e2\u003c/sub\u003eS removal under haloalkaline, neutral, and acidic conditions. The BTF glass columns had an internal diameter and a height of 8 and 60 cm respectively and were packed with polypropylene 16 mm Pall rings to the height of 50 cm (Pall Ring Company, UK). The column temperature was controlled at 30\u003csup\u003eo\u003c/sup\u003eC by continuous water circulation in the external jacket (Lauda RC6-CS, Germany). There were three sampling ports in the inlet, outlet, and middle sections of the column. In each BTF, the MSM was fed and recirculated over the packing media by using a peristaltic pump (Watson-Marlow Inc WM603s, USA) through a spray nozzle located at the top of BTFs. The trickling liquid velocity (TLV) During the startup stage was set to 0.9 m h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and during all experiments was set to 7 m h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eBefore recycling culture media to the reactor, the coarse sulfur particles were separated by gravity sedimentation in 200 mL sludge traps. To prevent any release of H\u003csub\u003e2\u003c/sub\u003eS gas, the outlet gas of BTFs passed through the NaOH trap. The pressure drops of reactors (∆P) due to biofilm growth were monitored with U-tube water manometers connected to the bottom and top sections of the columns. The air supplied by a compressor was filtered and passed through a thermal mass flow controller (MFC) (BROOKS Instruments USA, type 6250s). Nitrogen flow gas (N\u003csub\u003e2\u003c/sub\u003e, 99.995%) was controlled by Digital MFC) BRONKHORST Instruments Netherlands, type EL-FLOW-201CV (. Air and nitrogen were humidified by passing through a water bubble column.\u003c/p\u003e\n\u003cp\u003eA cylinder of H\u003csub\u003e2\u003c/sub\u003eS gas (5%, balanced N\u003csub\u003e2\u003c/sub\u003e) was used for supplying hydrogen sulfide and a Digital MFC (UNIT Instruments USA, type UFC-1661) was used to control the flow of gas. Synthetic polluted air was created by combining H\u003csub\u003e2\u003c/sub\u003eS with humidified N\u003csub\u003e2\u003c/sub\u003e and air mixture, in a mixing chamber and divided equally into three flows using a three-way distributer, the mixed gas flow rate was controlled by rotameters before entering each reactor. The gas current was supplied from the bottom of BTFs through a diffuser and the treated gas discharged from the upper end of the column. During the operation times, to prevent the toxic effects of by-products and supply fresh nutrient sources, 15% of spent liquid media was replaced with fresh MSM daily. The pH of MSM\u003csub\u003en\u003c/sub\u003e and MSM\u003csub\u003ea\u003c/sub\u003e in the nBTF and aBTF were monitored and controlled at set-points of 7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1 and 2.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5 respectively by automatic addition of 2 N NaOH by pH controller and dosing pump (Hanna BL 7916, USA). The pH and alkalinity of MSM\u003csub\u003eha\u003c/sub\u003e in haBTF were adjusted at a value of 8.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1 and 0.4 M, respectively using the addition of make-up fresh medium. If the pH of the MSM\u003csub\u003eha\u003c/sub\u003e was higher than 8.5, carbon dioxide gas was used to adjust the pH. Compensation for evaporated water in bioreactors was done by adding water weekly. In all designed experiments, the amount of circulating dissolved oxygen (DO) was considered to be higher than the requirement for complete sulfide oxidation. If the DO of the recirculating medium was reduced compared to the saturated state, excess oxygen was purged to the recirculation medium in the MSM reservoir.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\n\u003ch2\u003e2.4. Analytical Methods\u003c/h2\u003e\n\u003cp\u003eH\u003csub\u003e2\u003c/sub\u003eS concentration was monitored online in the sampling port at the inlet, outlet, and middle sections of reactors using electrochemical and photoionization detectors (PID). A portable electrochemical sensor (SP2nd SI-100 SENKO, Korea) was used to measure H\u003csub\u003e2\u003c/sub\u003eS concentration from 0 to 100 ppmv, and at a concentration from 100 to 4000 ppmv, a fixed TVOC system contained PID detector (Ion Science, UK) was used. The precision of online sensor measurement was confirmed monthly by gas chromatographic (GC) analysis. The GC instrument was an Agilent Technologies (model 6890N Network GC System, USA) equipped with a flame photometric detector (FPD) and HP-1 capillary column (0.25\u0026Ograve; 3000 mm; Hewlett Packard, USA). The initial, mild, and final oven temperature was 50, 120, and 250\u0026deg;C, with temperature ramping 5\u0026deg;C min\u003csup\u003e\u0026ndash;1\u003c/sup\u003e and 20\u0026deg;C min\u003csup\u003e\u0026ndash;1\u003c/sup\u003e. Nitrogen was used as the carrier gas at a flow rate of 1.5 ml min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and the temperature in the oven, injector, and detector were fixed at 250\u0026deg;C, 100\u0026deg;C, and 250\u0026deg;C, respectively.\u003c/p\u003e\n\u003cp\u003eThe concentration of sulfide and sulfate were measured using ion chromatography (Waters, USA) equipped with an IC- Pak anion HC column (4.6 4.6 x 150 mm; Waters) and a conductivity detector (Waters 432). Eluent consisted of 1.7 mM sodium carbonate and 1.8 mM sodium bicarbonate solution with a flow rate of 0.9 ml min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Dissolved oxygen (DO) and pH were monitored online in a liquid medium by (HQ40d, HACH) and (HANNA HI98191, USA), respectively. At the enrichment phase for the enumeration of total culturable chemolithotrophic SOB, samples were taken from the liquid medium, and the standard plate count method was used, dilutions of suspensions were then plated in appropriate MSM agar medium which was supplemented by Na\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e.5H\u003csub\u003e2\u003c/sub\u003eO 10 g L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Table \u003cspan class=\"InternalRef\"\u003eS1\u003c/span\u003e). The plates were incubated at 30\u0026deg;C and the colonies were counted after 1 month.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\n\u003ch2\u003e2.5. Electron microscopy analysis\u003c/h2\u003e\n\u003cp\u003eScanning electron microscopy (SEM) images were used for the identification of microbial biofilm formation on the Pall Rings surfaces. The samples were taken from different heights of the BTF column and submerged in ringer solution for removal of planktonic cells. Then samples were fixed for 2 hours in an aqueous solution of 2% osmium tetroxide and washed with water and subsequently postfixed with a solution of 2.5% glutaraldehyde in phosphate buffer for 1.5 h at 4 ◦C and washed in the water again. The graded series of Ethanol solutions (25, 50, 75, 100%) were used for dehydration and finally, the samples were freeze-dried for 1 day. For SEM \u003cstrong\u003e(\u003c/strong\u003eZEISS 960A, Germany) examination, replicas were produced by shadowing with a layer of gold in a sputter coater (Balzers SCD 004, Lichtenstein) [28].\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\n\u003ch2\u003e2.6. Microbial diversity analysis\u003c/h2\u003e\n\u003cdiv id=\"Sec9\" class=\"Section3\"\u003e\n\u003ch2\u003e2.6.1. DNA extraction\u003c/h2\u003e\n\u003cp\u003eAt the end of experiments, to evaluate the changes in microbial communities as a function of the BTFs pH values, 30 g of packed bed with attached biomass was collected from top, middle, and bottom sections along the length of the reactors in aseptic condition. Total Genomic DNA was extracted and purified from biomass, using Fast DNA\u0026reg; Spin Kit for Soil (MP Biomedicals, USA) following the manufacturer's instructions, but the binding time of DNA to a silica matrix was modified to 20 min. For each sample, all the above-mentioned operations were performed in triplicate. The quantity and quality of the extracted DNA were analyzed by NanoDrop UV-VIS Spectrophotometer (Thermo Fisher Scientific, NanoDrop ONE, USA). Structural DNA integrity was evaluated by gel electrophoresis analysis (concentration of agarose gel: 1%, voltage: 150 V, electrophoresis time: 40 min).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec10\" class=\"Section3\"\u003e\n\u003ch2\u003e2.6.2. NGS analysis\u003c/h2\u003e\n\u003cp\u003eDNA samples were sent to Beijing Genomics Institute (BGI, Hong Kong NGS Lab) for bacterial diversity analysis based on BGI protocols. Briefly, DNA sample quality control was done by Qubit Fluorometer, NanoDrop, and gel electrophoresis. Then, three libraries of the V3-V4 hypervariable regions (approximately\u0026thinsp;~\u0026thinsp;460 bp) of 16S rRNA genes amplicon were constructed and qualified. Libraries were pair-end sequenced on a MiSeq System (Illumina, San Diego, CA, USA) using the PE300 (PE301\u0026thinsp;+\u0026thinsp;8\u0026thinsp;+\u0026thinsp;8\u0026thinsp;+\u0026thinsp;301) sequencing strategy. The primers used in the PCR reaction were 341 F (5\u0026prime;-ACTCCTACGGGAGGCAGCAG-3\u0026prime;) and 806 R (5\u0026prime;-GGACTACHVG GGTWTCTAA T-3\u0026prime;) (Report of BGI, Hong Kong, NGS lab).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec11\" class=\"Section3\"\u003e\n\u003ch2\u003e2.6.3. High-throughput sequence data analysis\u003c/h2\u003e\n\u003cp\u003eBioinformatic data analysis was conducted by the following software. Paired-end reads with sequencing adapters, N base, poly base, low quality, etc were filtered out then clean paired-end reads were overlapped and combined to generate the consensus sequences (tags) by FLASH (V1.2.11). The tags were clustered to Operational Taxonomic Unit (OTU) with 97% pairwise identity by UPARSE-OTU algorithm in USEARCH (v7.0.1090). To calculate the abundance of each OTU, the USEARCH global method was used and the representative OTU sequence was selected according to the most abundant sequence of each OTU. OTU representative sequences were taxonomically classified using Ribosomal Database Project (RDP) Classifier v.2.2 trained on the Greengenes database, using 0.8 confidence values as the cutoff.\u003c/p\u003e\n\u003cp\u003eTo analyze and compare the diversity and structure of bacterial communities, alpha diversity indices (Observed species, Ace, Chao1, Shannon, and Simpson) were calculated by Mothur (V1.31.2), and beta-diversity (Principal Component Analysis) was studied using the package ade4 of software R (V3.1.1). OTU's rank curve, rarefaction curves, alpha diversity indexes, and OTU's heat map analysis were done by software R (V3.1.1).\u003c/p\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\n\u003ch2\u003e2.7. Experimental conditions and methodology\u003c/h2\u003e\n\u003cp\u003eAfter 62 days and establishing stable conditions in all three bioreactors, E1, E2, and E3 experiments were conducted to evaluate and compare the performance of BTFs with each other, the conditions of conducting these experiments are shown in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. Experiments E1 and E2 were designed and carried out in two periods of 11 days and experimentE3 in 15 days. By measuring inlet (C\u003csub\u003ein\u003c/sub\u003e), outlet concentration (C\u003csub\u003eout\u003c/sub\u003e) and using EBRT retention time and flow rate (Q), system performance evaluation parameters, including load retention (LR), removal capacity (EC), and removal efficiency (RE) were calculated. By decreasing (EBRT) while keeping (C\u003csub\u003ein\u003c/sub\u003e) constant or by increasing (C\u003csub\u003ein\u003c/sub\u003e) and keeping (EBRT) constant, the contamination load of bioreactors can be increased and the behaviour of BTFs can be studied (see the following equation):\u003c/p\u003e\n\u003cp\u003eLR\u0026thinsp;=\u0026thinsp;Q. C\u003csub\u003ei\u003c/sub\u003e / V\u003csub\u003er\u003c/sub\u003e = C\u003csub\u003ei\u003c/sub\u003e / EBRT\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003ctable id=\"Tab1\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eExperimental conditions for the biotrickling filters (haBTF, nBTF, aBTF)\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eExperiment\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eC\u003csub\u003ei\u003c/sub\u003e (ppm\u003csub\u003ev\u003c/sub\u003e)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eLR (gS-H\u003csub\u003e2\u003c/sub\u003eS m\u003csup\u003e_3\u003c/sup\u003e h\u003csup\u003e_1\u003c/sup\u003e)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eEBRT (s)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eDuration (d)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eprevious operation (d)\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd rowspan=\"11\" align=\"left\"\u003e\n\u003cp\u003eE1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd rowspan=\"11\" align=\"char\" char=\".\"\u003e\n\u003cp\u003e2000\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e82.19\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e120\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd rowspan=\"11\" align=\"char\" char=\".\"\u003e\n\u003cp\u003e31\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e89.16\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e110\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e98.63\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e100\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e109.59\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e90\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e123.29\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e80\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e140.90\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e70\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e164.38\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e60\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e197.26\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e50\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e246.58\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e40\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e328.77\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e30\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e493.16\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e20\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd rowspan=\"11\" align=\"left\"\u003e\n\u003cp\u003eE2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1000\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e82.19\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e20\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd rowspan=\"11\" align=\"char\" char=\".\"\u003e\n\u003cp\u003e53\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1090\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e89.16\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e20\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1200\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e98.63\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e20\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1333\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e109.59\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e20\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1500\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e123.29\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e20\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1714\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e140.90\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e20\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2000\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e164.38\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e20\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2400\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e197.26\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e20\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e3000\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e246.58\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e20\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e4000\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e328.77\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e20\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e6000\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e493.16\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e20\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd rowspan=\"15\" align=\"left\"\u003e\n\u003cp\u003eE3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd rowspan=\"5\" align=\"char\" char=\".\"\u003e\n\u003cp\u003e200\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e65.76\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e15\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd rowspan=\"5\" align=\"char\" char=\".\"\u003e\n\u003cp\u003e75\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e49.32\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e20\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e24.66\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e40\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e12.33\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e80\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e8.22\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e120\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd rowspan=\"5\" align=\"char\" char=\".\"\u003e\n\u003cp\u003e1000\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e328.8\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e15\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd rowspan=\"5\" align=\"char\" char=\".\"\u003e\n\u003cp\u003e80\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e246.6\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e20\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e123.3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e40\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e61.65\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e80\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e41.1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e120\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd rowspan=\"5\" align=\"char\" char=\".\"\u003e\n\u003cp\u003e2000\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e665.76\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e15\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd rowspan=\"5\" align=\"char\" char=\".\"\u003e\n\u003cp\u003e85\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e499.32\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e20\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e249.66\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e40\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e124.83\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e80\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e83.22\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e120\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\n\u003ch2\u003e2.8. EBRT reduction experiments\u003c/h2\u003e\n\u003cp\u003eDuring the 22 days of E1 experiments, EBRT was stepwise reduced from 120 seconds to 20 seconds and C\u003csub\u003ein\u003c/sub\u003e (2000 ppm) was kept constant, so LR increased from 82 to 493 g m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. In order to achieve stability in the performance, each period was kept for 48 hours. The details of the E1 experiments' conditions are shown in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. At the end of each stage of EBRT change, the concentration of inlet and outlet hydrogen sulfide was measured, EC and RE values were calculated, and critical parameters (EC\u003csub\u003ecritical\u003c/sub\u003e and EBRT\u003csub\u003ecritical\u003c/sub\u003e). Critical EC and EBRT were determined at the points where the RE reached 97%. The calculation of maximum EC and critical EBRT can provide important information about bioreactor modeling, performance, and design. The third experiment (E3) was carried out in three C\u003csub\u003ein\u003c/sub\u003e (200, 1000, and 2000 ppm) to evaluate the effect of a decrease in EBRT (from 120 to 15s) on removal efficiency (RE) (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\n\u003ch2\u003e2.9. Inlet concentration increase experiments\u003c/h2\u003e\n\u003cp\u003eAccording to the results obtained in the E1 experiments, in E2 experiments, EBRT was kept constant at 60 seconds, and C\u003csub\u003ein\u003c/sub\u003e was gradually increased from 1000 to 6000 ppm in 22 days (LR 82 to 493 g m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). In the design of BTFs, the reduction of EBRT can lead to a reduction in the height of the column and the reduction of the initial construction costs. To achieve stable conditions in performance, each period of increased LR was continued for 48 hours. The details of the test conditions are shown in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"3. Results and Discussions","content":"\u003cdiv id=\"Sec16\" class=\"Section2\"\u003e\n \u003ch2\u003e3.1. BTFs Performance in Experimental Conditions\u003c/h2\u003e\n \u003cp\u003eThe results of the E1 experiment in which the C\u003csub\u003ei\u003c/sub\u003e were instant at 2000 ppm with a gradual decrease of EBRT from 120 to 20s revealed the success of haBTF in H\u003csub\u003e2\u003c/sub\u003eS removal over nBTF and aBTF, as this filter reached its maximum EC (179.8 g m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) in less EBRT (50s) with 91.14% EC which is 5.44 and 2.94% more than that of nBTF and aBTF, respectively that reached their maximum RE in 60s of EBRT (Figs. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e and Figure \u003cspan class=\"InternalRef\"\u003eS1\u003c/span\u003e). The superiority of haBTF is also revealed by comparing the critical EC in which 97% of inlet H\u003csub\u003e2\u003c/sub\u003eS is removed by the systems. In the condition that C\u003csub\u003ei\u003c/sub\u003e was constant, this parameter was determined to be 31.1 and 17.5 g m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e more than nBTF and aBTF\u0026apos;s EC, respectively. This rate was achieved in a higher H\u003csub\u003e2\u003c/sub\u003eS loading rate because of removing the higher amount of this gas in less retention time (see Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e) which in conclusion shows the higher efficiency and rate of H\u003csub\u003e2\u003c/sub\u003eS removal by haBTF filter in this experiment.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eBiotrickling filters\u0026apos; performance in the E1 and E2 experiments with E1 experiment in constant C\u003csub\u003ein\u003c/sub\u003e at 2000 ppm and decreasing EBRT from 120 to 20s and E2 experiment in constant EBRT at 60s and increasing C\u003csub\u003ein\u003c/sub\u003e from 1000 to 6000 ppm\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth rowspan=\"4\" align=\"left\"\u003e\n \u003cp\u003eExp E1\u003c/p\u003e\n \u003cp\u003e(Constant C\u003csub\u003ein\u003c/sub\u003e)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eBTFs\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCritical EC\u003c/p\u003e\n \u003cp\u003eg m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eEBRT\u003c/p\u003e\n \u003cp\u003es\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eH\u003csub\u003e2\u003c/sub\u003eS LR\u003c/p\u003e\n \u003cp\u003eg S-H\u003csub\u003e2\u003c/sub\u003eS m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMaximum EC\u003c/p\u003e\n \u003cp\u003eg m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eRE\u003c/p\u003e\n \u003cp\u003e%\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eEBRT\u003c/p\u003e\n \u003cp\u003es\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eH\u003csub\u003e2\u003c/sub\u003eS LR\u003c/p\u003e\n \u003cp\u003eg S-H\u003csub\u003e2\u003c/sub\u003eS m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ehaBTF\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e137.6\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e70\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e140.9\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e179.8\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e91.14\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e50\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e197.2\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003enBTF\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e106.5\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e90\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e109.6\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e141\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e85.7\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e60\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e164.3\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eaBTF\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e120.1\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e80\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e123.3\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e145\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e88.2\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e60\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e164.3\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"3\" align=\"left\"\u003e\n \u003cp\u003eExp E2\u003c/p\u003e\n \u003cp\u003e(Constant EBRT)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eBTFs\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCritical EC\u003c/p\u003e\n \u003cp\u003eg m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eEBRT\u003c/p\u003e\n \u003cp\u003es\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eH\u003csub\u003e2\u003c/sub\u003eS LR\u003c/p\u003e\n \u003cp\u003eg S-H\u003csub\u003e2\u003c/sub\u003eS m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eMaximum EC\u003c/p\u003e\n \u003cp\u003eg m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eRE\u003c/p\u003e\n \u003cp\u003e%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eEBRT\u003c/p\u003e\n \u003cp\u003es\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eH\u003csub\u003e2\u003c/sub\u003eS LR\u003c/p\u003e\n \u003cp\u003eg S-H\u003csub\u003e2\u003c/sub\u003eS m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ehaBTF\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e167.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e173\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e210.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e64\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e328.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003enBTF\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e137.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e141\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e150.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e76.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e197.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eaBTF\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e144.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e149.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e174.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e53\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e328.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003ctfoot\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"9\"\u003e\u003cstrong\u003ehaBTF E1\u003c/strong\u003e : Critical EC that guaranteeing RE 97% of inlet H\u003csub\u003e2\u003c/sub\u003eS was determined to be 137.6 g m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e \u0026amp; EBRT 70s \u0026amp; Loading Rate (inlet load) is 140.9 g m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, maximmum EC 179.8 g m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, RE 91.14% \u0026amp; EBRT 50 s, Loading Rate is 197 g m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e \u003cstrong\u003enBTF E1\u003c/strong\u003e : Critical EC that guaranteeing RE 97% of inlet H\u003csub\u003e2\u003c/sub\u003eS was determined to be 106.5 g m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e \u0026amp; EBRT 90s \u0026amp; Loading Rate is 109.6 g m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, maximmum EC 141 g m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, RE 85.7% \u0026amp; EBRT 60s, Loading Rate is 164.3 g m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e \u003cstrong\u003eaBTF E1\u003c/strong\u003e: Critical EC that guaranteeing RE 97% of inlet H\u003csub\u003e2\u003c/sub\u003eS was determined to be 120.1 g m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e \u0026amp; EBRT 80s \u0026amp; Loading Rate is 123.3 g m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, maximmum EC 145 g m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, RE 88.2% \u0026amp; EBRT 60s, Loading Rate is 164.3 g m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"9\"\u003e\u003cstrong\u003ehaBTF E2\u003c/strong\u003e : Critical EC that guaranteeing RE 97% of inlet H\u003csub\u003e2\u003c/sub\u003eS was determined to be 167.8 g m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e \u0026amp; EBRT 60s \u0026amp; Loading Rate is 173 g m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, maximmum EC 210.6 g m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, RE 64% \u0026amp; EBRT 60s \u0026amp; Loading Rate is 328.7 g m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e \u003cstrong\u003enBTF E2\u003c/strong\u003e: Critical EC that guaranteeing RE 97% of inlet H2S was determined to be 137.5 g m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e \u0026amp; EBRT 60s \u0026amp; Loading Rate is 141 g m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, maximmum EC 150.8 g m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, RE 76.4% \u0026amp; EBRT 60s, Loading Rate is 197.2 g m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e \u003cstrong\u003eaBTF E2\u003c/strong\u003e: Critical EC that guaranteeing RE 97% of inlet H\u003csub\u003e2\u003c/sub\u003eS was determined to be 144.6 g m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e \u0026amp; EBRT 60s \u0026amp; Loading Rate is 149.1 g m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, maximmum EC 174.3 g m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, RE 53% \u0026amp; EBRT 60s, Loading Rate is 328.7 g m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tfoot\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003eComparing the operation of the three filters in the E2 experiment which was followed up at constant EBRT (60s), but this time in rising C\u003csub\u003ei\u003c/sub\u003e (from 1000 to 6000 ppm) showed almost the same algorithm as the E1 results (see Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e) with haBTF reached the maximum EC of 210.6 g m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e that was 59.8 and 36.3 g m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e higher than that of nBTF and aBTF, respectively; higher critical EC (167.8 g m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) were also detected in this system compare to the nBTF and aBTF. While the highest EC rate was achieved with haBTF in the E2 conditions, the RE of the system was recorded at its highest point (91.14%) in the E1 experiment of the same reactor (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e). Altogether, these results indicated the haBTF system could remove a higher rate of H\u003csub\u003e2\u003c/sub\u003eS than the other two reactors and in both experiments, aBTF had a slight advantage over nBTF.\u003c/p\u003e\n \u003cp\u003eIn E3 experiments, the effect of reducing EBRT from 120 seconds to 15 seconds on RE was investigated at three constant and independent input concentrations of 200, 1000, and 2000 ppm of hydrogen sulfide in bioreactors. The results in Figure S2 show that reducing EBRT from 120 seconds to 80 seconds in haBTF at the three mentioned concentrations has no effect on the reduction of RE, and even when the inlet concentration is 1000 ppm, by reducing the time to 40 seconds, only 4% of RE is reduced. On the other hand, in general, the slope of the removal efficiency reduction curves in the three mentioned concentrations in haBTF is always lower than that in aBTF and nBTF, which means that the process of reducing the removal efficiency with the reduction of EBRT in haBTF is slower than the others and independent of the inlet concentration. According to the results, it can be said that aBTF has a better performance than nBTF.\u003c/p\u003e\n \u003cp\u003eThroughout all of the experiments, the oxygen-to-sulfide ratio was maintained at or above 25, which is higher than the requirement for the complete oxidation of sulfide. This limitation in sulfide provides the optimum condition for complete sulfide oxidation and sulfate production. From a bioenergetic point of view, sulfate provides more energy for biomass development than relative oxidation and biosulfur production. The lower portion of oxygen compared to sulfide will cause the formation of biosulfur and increase its density on the packing bed which will cause the pressure drop and eventually lead to the blockage of the system [29]. Moreover, biofilm formation on packing media will lower oxygen penetration which needs more oxygen supply in aerobic biodegradation systems [18, 30]. Generally, sulfide to sulfate oxidation was almost complete during the experiments (more than 88% and 12% of applied sulfide converted to sulfate and biosulfur, respectively). Also, 81\u0026ndash;90%, 75\u0026ndash;87%, and 78\u0026ndash;88% of H\u003csub\u003e2\u003c/sub\u003eS were removed at alkaline, neutral, and acidic conditions, respectively and were assessed by measuring the outlet concentration of hydrogen sulfide placed at the first half of the column height, showing that the most of the H\u003csub\u003e2\u003c/sub\u003eS removes at this part. Since hydrogen sulfide (H\u003csub\u003e2\u003c/sub\u003eS) is a weak acid (pKa\u0026thinsp;=\u0026thinsp;7), the pH of the MSM solution may have an impact on its mass transfer from the gas to the liquid phase. This effect is less pronounced at acidic, medium at neutral, and strong in alkaline circumstances. As a result, mass transfer from the gas phase to the liquid phase is less affected by a change in retention time under alkaline conditions than it is under acidic or neutral pH settings. Due to its higher concentration, hydrogen sulfide will transfer more mass than oxygen under conditions of constant hydrogen sulfide concentration and declining EBRT. As a result, in the absence of sufficient oxygen content for complete sulfide oxidation, the sulfur to sulfate ratio will rise (Wu et al., 2020). The ratio of O\u003csub\u003e2\u003c/sub\u003e:H\u003csub\u003e2\u003c/sub\u003eS gradually falls as the input pollution load rises, and with less oxygen present in the recycling medium, the oxidation of HS\u003csup\u003e\u0026minus;\u003c/sup\u003e is incomplete, leading to an increase in the proportion of elemental sulfur in place of sulfate. On the other hand, EBRT decrement declines gas to liquid mass transfer and hydrogen sulfide concentration increment will increase biosulfur production because of the biological potential limitation in HS\u003csup\u003e\u0026minus;\u003c/sup\u003e to SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e which is the consequence of oxygen decrement content in the recycling medium and incomplete HS\u003csup\u003e\u0026minus;\u003c/sup\u003e oxidation [31].\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec17\" class=\"Section2\"\u003e\n \u003ch2\u003e3.2. Scanning Electron Microscopy\u003c/h2\u003e\n \u003cp\u003eScanning electron micrographs were utilized to track the development of biofilm on pallrings after 90 days of experiments (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e). The analyses revealed the presence of a complex community of bacteria in the haBTF samples (Figs.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eA and \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eB), including filamentous bacilli that were 1.5 \u0026micro;m in diameter and 4 \u0026micro;m in length, rod-shaped bacteria that were 0.4 \u0026micro;m in diameter and 1 \u0026micro;m in length, and cocobacilli that were 0.5 \u0026micro;m in diameter and 1 \u0026micro;m in length. In addition to bacterial aggregation, biosulfur sediments are shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eB. In nBTF samples (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eC, \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eD), there are bacteria with diameters ranging from 0.34 to 0.9 \u0026micro;m and lengths ranging from 0.9 to 9 \u0026micro;m, biosulfur accumulations produced by SOB secretions with diameters ranging from 1.4 to 7 \u0026micro;m (pointed with an arrow), and a nematode (nearly 5 \u0026micro;m in diameter and 35 \u0026micro;m in length), in addition to various sized bacteria. Even though the experiment used lethal levels of hydrogen sulfide, the existence of nematodes and other protozoa in neutral pH biofilters was unexpected. Amorphous fouling and spherical accumulations of biosulfur (diameter 8\u0026ndash;10 \u0026micro;m) were also seen in the microgram of an aBTF sample (Figs.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eF and \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eE)\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec18\" class=\"Section2\"\u003e\n \u003ch2\u003e3.3. Bacterial community diversity analysis\u003c/h2\u003e\n \u003cp\u003eAfter ending all experiments (90 days), to investigate the correlation of various bacterial populations on the efficiency of H\u003csub\u003e2\u003c/sub\u003eS removal, an analysis of bacterial community and structure was carried out using three amplicon libraries: haBTF, nBTF, and aBTF. After deleting the wrong identified or low-quality sequences, a total of 160632 tags (69% of initial) were identified with an average length of 424 bp, which comprised 61264 tags in the library of haBTF, 50216 tags in library nBTF and 49152 tags in library aBTF. The clustering of all tags to OTU was investigated at 97% similarity and the relative abundance data was calculated for each library. A total of 290 bacterial OTUs were obtained from three amplicon libraries and 119, 134, and 37 OTUs were assigned to haBTF, nBTF, and aBTF, respectively. At the phylum level, (data has not been shown) \u003cem\u003eproteobacteria\u003c/em\u003e were the most dominant phylum in all samples, so more than 70% of the total read sequences in three BTFs were classified in this taxon. The other most abundant phyla were \u003cem\u003eBacteroidetes\u003c/em\u003e (18%, nBTF) and \u003cem\u003eactinobacteria\u003c/em\u003e (30%, aBTF). The relative abundances and population structures of the bacterial communities at the taxonomical class level are shown in Figure S3. In haBTF, the most abundant classes were \u003cem\u003eAlphaproteobacteria\u003c/em\u003e and \u003cem\u003eGammaproteobacteria\u003c/em\u003e (20.9% and 73.7%, respectively), in nBTF \u003cem\u003eAlphaproteobacteria\u003c/em\u003e, \u003cem\u003eBetaproteobacteria\u003c/em\u003e, \u003cem\u003eGammaproteobacteria\u003c/em\u003e and \u003cem\u003eFlavobacteria\u003c/em\u003e (3.7, 59.6%, 15% and 16.6%, respectively) were more important and in aBTF sample \u003cem\u003eAcidithiobacillia\u003c/em\u003e and \u003cem\u003eActinobacteria\u003c/em\u003e (65.4% and 30.4%, respectively) were the most prevalent classes. In terms of phylogeny, \u003cem\u003eAcidithiobacillia\u003c/em\u003e is classified as an independent class of in the \u003cem\u003eProteobacteria\u003c/em\u003e, but previously its type order \u003cem\u003eAcidithiobacillales\u003c/em\u003e was classified in the \u003cem\u003eGammaproteobacteria\u003c/em\u003e. The \u003cem\u003ebeta\u003c/em\u003e-\u003cem\u003eproteobacteria\u003c/em\u003e includes the most abundant sulfur-oxidizing bacteria, but it has been reported that in very harsh environmental conditions most SOB belongs to the \u003cem\u003eGammaproteobacteria\u003c/em\u003e [32] and in extremophile acidic conditions, \u003cem\u003eAcidithiobacillia\u003c/em\u003e play a key role. Table S2 lists the number of OTUs predicted in the data set per taxon.\u003c/p\u003e\n \u003cp\u003eThe results of molecular studies (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e) showed that in the alkaline condition of haBTF, the \u003cem\u003egamma\u003c/em\u003e and \u003cem\u003ealpha proteobacteria\u003c/em\u003e are the most abundant classes (73.7% and 20.9% respectively). In neutral and acidic pH conditions the frequency of these taxa decreased so the abundance of \u003cem\u003eGammaproteobacteria\u003c/em\u003e decreased to 15% and 1.15% and for \u003cem\u003ealphaproteobacteria\u003c/em\u003e to 3.7% and 1.4%, respectively. Under acidic pH conditions, the most abundant classes were \u003cem\u003eAcidithiobacillia\u003c/em\u003e and \u003cem\u003eActinobacteria\u003c/em\u003e with 65.4% and 30.4%, respectively. In nBTF, the \u003cem\u003eBetaproteobacteria\u003c/em\u003e, \u003cem\u003eFlavobacteria\u003c/em\u003e, and \u003cem\u003eGammaproteobacteria\u003c/em\u003e were the most abundant classes, respectively.\u003c/p\u003e\n \u003cp\u003eIn the present study, contrary to the results of Omri et al., 2011 [23] and Chouari et al., 2015 [24], the lowest ecological diversity was observed at acidic pH, and in accordance with the results of Tu et al 2016 [22], the microbial diversity at neutral pH is higher than that of acidic pH. \u003cem\u003eAcidithiobacillus\u003c/em\u003e was the most abundant group of bacteria in the mentioned study which is in agreement with the results of the relative abundance of different bacterial groups in three tested conditions of the present study. As shown in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e, \u003cem\u003eAcidithiobacillus\u003c/em\u003e and \u003cem\u003eThiobacillus\u003c/em\u003e are the most abundant genera of bacteria in aBTF and nBTF, respectively and haBTF was abundant with unclassified groups of bacteria. In aBTF after the \u003cem\u003eAcidithiobacillus\u003c/em\u003e the most abundant acidophilic microorganism is \u003cem\u003eMycobacterium\u003c/em\u003e with an abundance of 27%, which is most likely mixotrophic SOB, and consistent with the results of Jia et al. 2022 [33], the abundance of mixotrophic SOB \u003cem\u003eMycobacterium\u003c/em\u003e was 78.4%. in aBTF with extremely acidic conditions.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab3\" border=\"1\"\u003e\n \u003ccaption\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003ePhylogenetic classification up to class level and relative abundances (%) of species (Underlined genus and/or species correspond to known SOB species)\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e\n \u003cth colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003eTaxonomical affiliation\u003c/p\u003e\n \u003c/th\u003e\n \u003cth colspan=\"3\" align=\"left\"\u003e\n \u003cp\u003eRelative abundance (%)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eClass\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eFamily\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSpecies\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ehaABTF\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003enBTF\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eaBTF\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eAlphaproteobacteria\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eHyphomonadaceae\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eOceanicaulis\u003c/em\u003e sp.\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eRhodobacteraceae\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eRhodobaca\u003c/em\u003e sp.\u003csup\u003e1\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eRhizobiaceae\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eShinella\u003c/em\u003e sp.\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eSphingomonadaceae\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eSphingomonas\u003c/em\u003e\u003csup\u003e\u003cem\u003e5\u003c/em\u003e\u003c/sup\u003e sp.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eSphingomonas wittichii\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eBetaproteobacteria\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eHydrogenophilaceae\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eThiobacillus\u003c/em\u003e\u003csup\u003e\u003cem\u003e3\u003c/em\u003e\u003c/sup\u003e sp.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e56.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eThiomonas\u003c/em\u003e\u003csup\u003e\u003cem\u003e5\u003c/em\u003e\u003c/sup\u003e sp.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eGammaproteobacteria\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eAlkalimonas amylolytica\u003c/em\u003e\u003csup\u003e\u003cem\u003e4\u003c/em\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eAlkalimonas delamerensis4\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eRhodanobacteraceae\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eDyella\u003c/em\u003e\u003csup\u003e\u003cem\u003e5\u003c/em\u003e\u003c/sup\u003e sp.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eHalomonadaceae\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eHalomonas\u003c/em\u003e\u003csup\u003e\u003cem\u003e4\u003c/em\u003e\u003c/sup\u003e sp.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eHalomonas campisalis\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eHalothiobacillaceae\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eHalothiobacillus\u003c/em\u003e\u003csup\u003e\u003cem\u003e3\u003c/em\u003e\u003c/sup\u003e sp.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eAlteromonadaceae\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eMarinobacter\u003c/em\u003e\u003csup\u003e\u003cem\u003e4\u003c/em\u003e\u003c/sup\u003e sp.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eLysobacteraceae\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eStenotrophomonas\u003c/em\u003e\u003csup\u003e\u003cem\u003e4\u003c/em\u003e\u003c/sup\u003e sp.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eStenotrophomonas acidaminiphila\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eThermomonas\u003c/em\u003e\u003csup\u003e\u003cem\u003e4\u003c/em\u003e\u003c/sup\u003e sp.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eEctothiorhodospiraceae\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eThioalkalivibrio sulfidophilus\u003c/em\u003e\u003csup\u003e\u003cem\u003e3\u003c/em\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eAcidithiobacillia\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eAcidithiobacillaceae\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eAcidithiobacillus\u003c/em\u003e\u003csup\u003e\u003cem\u003e3\u003c/em\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e62.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eA. albertensis\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eActinobacteria\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eMycobacteriaceae\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eMycobacterium\u003c/em\u003e\u003csup\u003e\u003cem\u003e5\u003c/em\u003e\u003c/sup\u003e sp.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e27\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eMycobacterium arupense\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eFlavobacteriia\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eFlavobacteriaceae\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eChryseobacterium\u003c/em\u003e\u003csup\u003e\u003cem\u003e4\u003c/em\u003e\u003c/sup\u003e sp.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eSphingobacteriia\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eChitinophagaceae\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eSediminibacterium\u003c/em\u003e\u003csup\u003e\u003cem\u003e4\u003c/em\u003e\u003c/sup\u003e sp.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eMollicutes\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eAcholeplasmataceae\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eAcholeplasma\u003c/em\u003e\u003csup\u003e\u003cem\u003e4\u003c/em\u003e\u003c/sup\u003e sp.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eErysipelotrichia\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eErysipelotrichaceae\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePSB-M-3\u003csup\u003e4\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTotal\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e84.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e98.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUnclassified\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e69.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e11.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eOthers (\u0026lt;\u0026thinsp;0.5%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTotal\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003ctfoot\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"6\"\u003e1. Uncultured bacterium, 2. Unclassified Bacteria, 3. Autotrophic, 4. Heterotrophic, 5. Mixotrophic\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tfoot\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec19\" class=\"Section3\"\u003e\n \u003ch2\u003e3.3.1. OTU rank curve\u003c/h2\u003e\n \u003cp\u003eThe species diversity of a population depends on two factors: species richness and evenness. Increasing species richness (X-axis) simultaneously with uniform distribution of abundances (Y-axis log scale) can dramatically increase species diversity. OTU rank abundance curve can visually depict two factors at the same time. As can be seen in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e in terms of species richness, nBTF has the highest and aBTF has the lowest richness. The steep slope of the OUT curve indicates the lack of uniform distribution of abundance in aBTF so that a limited number of OUTs ranks have the highest frequency and more numbers have the lowest frequency. The curves of haBTF and nBTF, at first start with steep slopes and then vary gently downward parallel, so the two BTFs are similarly distributed in terms of species evenness, and both have more evenness than the aBTF. Overall, according to OTU rank curves, haBTF and nBTF have the same species diversity and more than the aBTF.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec20\" class=\"Section3\"\u003e\n \u003ch2\u003e3.3.2. Rarefaction curves\u003c/h2\u003e\n \u003cp\u003eBased on observed OTUs with increasing sequencing, it was shown that the three rarefaction curves tend to be smooth. This suggests that the produced data is enough to cover the diversity of all species in the community. The other rarefaction curves based on the Chao1 and ACE values also confirmed these results (Figure S4).\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec21\" class=\"Section3\"\u003e\n \u003ch2\u003e3.3.3. Heat map analysis\u003c/h2\u003e\n \u003cp\u003eHeat map analysis was done based on the relative abundance of each genus in each sample. To minimize the differences degree of the relative abundance value, the values were all log-transformed. The gradation of green shows the relative abundance of the three samples, -3 (light red) being the minimum and 3 (light green) the abundance of maximum considered. As shown in the heat map (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003eA), haBTF contained a more diverse group of bacteria in comparison to the two other reactors. This may be because of the formation of a pH gradient in haBTF which provides an adverse niche for different genera. The pH gradient may also be formed in nBTF but in less adverse value than that of haBTF. The most abundant known genera in aBTF, nBTF, and haBTF were \u003cem\u003eAcidithiobacillus\u003c/em\u003e, \u003cem\u003eThiobacillus\u003c/em\u003e, and \u003cem\u003eRhodobaca\u003c/em\u003e, respectively. The effect of pH on the formation of different microbial communities has been reported in previous reports by Chouari et al., 2015 [24] and Tu et al., 2016 [22] in which they corroborated changing pH from neutral to acidic conditions will cause alteration in microbial population and both insisted on attendance and abundance of \u003cem\u003eAcidithiobacillus\u003c/em\u003e in (extremely) acidic biofilters\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec22\" class=\"Section3\"\u003e\n \u003ch2\u003e3.3.4. Alpha diversity\u003c/h2\u003e\n \u003cp\u003eAccording to results in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e, the value of observed species and indexes of Chao1and ACE showed species richness at neutral pH of nBTF is considerably higher than the others, and also the species richness at the haloalkaline condition (pH 8.5) is higher than the acidic pH (2- 3.5). Severe acidic conditions as selective pressure decreased species richness, but despite the relatively high salt concentration and slight alkalinity in haBTF, seemingly these limiting factors had less effect on species richness.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab4\" border=\"1\"\u003e\n \u003ccaption\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eDiversity indexes. Observed species (Sobs) value, chao1, ACE indexes reflect the species richness of the community, Shannon and Simpson indexes reflect species diversity\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSample Name\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSobs\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eChao1\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eACE\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eShannon\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSimpson\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ehaBTF\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e119\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e121.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e122.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.23\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003enBTF\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e134\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e134\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e134.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.23\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eaBTF\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e37.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e39\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.44\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003eShannon value (H) and Simpson index (D) estimators can reflect the diversity (richness and evenness species) of the community. Shannon value is influenced more by rare abundant species while the Simpson index (D) is affected by dominant and even species. According to the results of Shannon\u0026apos;s value, the community diversity of haBTF is greater than the other samples and aBTF is in the lowest level of diversity, but Simpson\u0026apos;s index indicated species diversities of haBTF and nBTF are the same and they are greater than aBTF due to its much less evenness and richness.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec23\" class=\"Section3\"\u003e\n \u003ch2\u003e3.3.5. OTU PCA analysis\u003c/h2\u003e\n \u003cp\u003eTo display the differences in OTU composition in three BTF samples, Principal Component Analysis (PCA) was used to construct a 2-D graph to summarize factors mainly responsible for this difference. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003eB, based on principal component analysis, showed that along the PC1 axis, the samples could be divided into two separate groups, and along the PC2 axis, they could be separated into two other groups. The composition of OTUs in haBTF is significantly different from that of aBTF and nBTF, and according to the distribution of aBTF and nBTF along the vertical axis of PC2, it could be concluded that these two populations are more similar in terms of OTU structure. These results showed that the bacterial populations of haBTF have a significant difference compared to the other two BTFs, and on the other hand, the bacterial populations formed in aBTF and nBTF are more similar to each other.\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e"},{"header":"Conclusions","content":"\u003cp\u003eAssessing the effect of pH conditions (haloalkaliphilic, neutrophilic, and acidophilic) on the efficiency of H\u003csub\u003e2\u003c/sub\u003eS removal in the BTF system, three parallel experiments were performed in which removal-determining parameters showed 91.14% RE and 179.8 gS-H\u003csub\u003e2\u003c/sub\u003eS m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e EC in haBTF when EBRT was 60s. These values differed in nBTF and aBTF with 85.7% and 88.2% RE; 141 and 145 gS-H\u003csub\u003e2\u003c/sub\u003eS m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e EC, respectively, demonstrated better performance of haloalkaliphilic BTF in H\u003csub\u003e2\u003c/sub\u003eS removal with distinct bacterial diversity in comparison with nBTF and aBTF, as NGS results showed, while despite less bacterial diversity, acidic condition performed slightly better compared to the neutral system.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe funding agencies had no role in study design, data collection, data analysis and preparation of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eContributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAbbas Abbas Rouhollahi carried out the experiment; Abbas Abbas Rouhollahi and Minoo Giyahchi wrote the original draft of the manuscript; The work was supervised and designed by Mohammad Mehdi Dastgheib and Hamid Moghimi; and all authors read and approved the final version of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eGuerrero L, Montalvo S, Huili\u0026ntilde;ir C, Campos JL, Barahona A, Borja R:Advances in the biological removal of sulphides from aqueous phase in anaerobic processes: A review. Environmental Reviews.24(1):84-100; doi: 10.1139/er-2015-0046 (2016)\u003c/li\u003e\n\u003cli\u003eSyed M. SG, Falletta P., B\u0026eacute;land M.:Removal of hydrogen sulfide from gas streams using biological processes - A review. CANADIAN BIOSYSTEMS ENGINEERING.48; (2006)\u003c/li\u003e\n\u003cli\u003eVikrant K, Kailasa SK, Tsang DCW, Lee SS, Kumar P, Giri BS, et al.:Biofiltration of hydrogen sulfide: Trends and challenges. Journal of Cleaner Production.187:131-47; doi: 10.1016/j.jclepro.2018.03.188 (2018)\u003c/li\u003e\n\u003cli\u003eChaiprapat S, Charnnok B, Kantachote D, Sung S:Bio-desulfurization of biogas using acidic biotrickling filter with dissolved oxygen in step feed recirculation. Bioresour Technol.179:429-35; doi: 10.1016/j.biortech.2014.12.068 (2015)\u003c/li\u003e\n\u003cli\u003eLeerdam RCv:Anaerobic degradation of methanethiol in a process for Liquefied Petroleum Gas (LPG) biodesulfurization. (2007)\u003c/li\u003e\n\u003cli\u003ede Rink R, Klok JBM, van Heeringen GJ, Keesman KJ, Janssen AJH, Ter Heijne A, Buisman CJN:Biologically enhanced hydrogen sulfide absorption from sour gas under haloalkaline conditions. J Hazard Mater.383:121104; doi: 10.1016/j.jhazmat.2019.121104 (2020)\u003c/li\u003e\n\u003cli\u003eRoman P, Lipinska J, Bijmans MFM, Sorokin DY, Keesman KJ, Janssen AJH:Inhibition of a biological sulfide oxidation under haloalkaline conditions by thiols and diorgano polysulfanes. Water Res.101:448-56; doi: 10.1016/j.watres.2016.06.003 (2016)\u003c/li\u003e\n\u003cli\u003eWu H, Yan H, Quan Y, Zhao H, Jiang N, Yin C:Recent progress and perspectives in biotrickling filters for VOCs and odorous gases treatment. J Environ Manage.222:409-19; doi: 10.1016/j.jenvman.2018.06.001 (2018)\u003c/li\u003e\n\u003cli\u003eWu J, Jiang X, Jin Z, Yang S, Zhang J:The performance and microbial community in a slightly alkaline biotrickling filter for the removal of high concentration H(2)S from biogas. Chemosphere.249:126127; doi: 10.1016/j.chemosphere.2020.126127 (2020)\u003c/li\u003e\n\u003cli\u003eZytoon MA, AlZahrani AA, Noweir MH, El-Marakby FA:Bioconversion of high concentrations of hydrogen sulfide to elemental sulfur in airlift bioreactor. ScientificWorldJournal.2014:675673; doi: 10.1155/2014/675673 (2014)\u003c/li\u003e\n\u003cli\u003eCano PI, Col\u0026oacute;n J, Ram\u0026iacute;rez M, Lafuente J, Gabriel D, Cantero D:Life cycle assessment of different physical-chemical and biological technologies for biogas desulfurization in sewage treatment plants. Journal of Cleaner Production.181:663-74; doi: 10.1016/j.jclepro.2018.02.018 (2018)\u003c/li\u003e\n\u003cli\u003eAllegue B. L. HJ:Biogas upgrading Evaluation of methods for H2S removal. Danish technological institude. (2014)\u003c/li\u003e\n\u003cli\u003ede Rink R, Klok JBM, van Heeringen GJ, Sorokin DY, Ter Heijne A, Zeijlmaker R, et al.:Increasing the Selectivity for Sulfur Formation in Biological Gas Desulfurization. Environ Sci Technol.53(8):4519-27; doi: 10.1021/acs.est.8b06749 (2019)\u003c/li\u003e\n\u003cli\u003eMudliar S, Giri B, Padoley K, Satpute D, Dixit R, Bhatt P, et al.:Bioreactors for treatment of VOCs and odours - a review. J Environ Manage.91(5):1039-54; doi: 10.1016/j.jenvman.2010.01.006 (2010)\u003c/li\u003e\n\u003cli\u003eKhoshnevisan B. TP, Alfaro N., D\u0026iacute;az I., Fdz-Polanco M., Rafiee Sh., Angelidaki I. :A review on prospects and challenges of biological H2S removal from biogas with focus on biotrickling filtration and microaerobic desulfurization. Biofuel research journal doi: 10.18331/BRJ2016.4.4.6 (2017)\u003c/li\u003e\n\u003cli\u003eCox H, Deshusses M:Combined Removal of H2S and Toluene in a Single-Stage Biotrickling Filter. (2000)\u003c/li\u003e\n\u003cli\u003eMpanias CJ, Baltzis BC:An experimental and modeling study on the removal of mono-chlorobenzene vapor in biotrickling filters. Biotechnol Bioeng.59(3):328-43; doi: 10.1002/(sici)1097-0290(19980805)59:3\u0026lt;328::aid-bit9\u0026gt;3.0.co;2-d (1998)\u003c/li\u003e\n\u003cli\u003eSchiavon M, Ragazzi M, Rada EC, Torretta V:Air pollution control through biotrickling filters: a review considering operational aspects and expected performance. Crit Rev Biotechnol.36(6):1143-55; doi: 10.3109/07388551.2015.1100586 (2016)\u003c/li\u003e\n\u003cli\u003eGiri BS, Kim KH, Pandey RA, Cho J, Song H, Kim YS:Review of biotreatment techniques for volatile sulfur compounds with an emphasis on dimethyl sulfide. Process Biochemistry.49(9):1543-54; doi: 10.1016/j.procbio.2014.05.024 (2014)\u003c/li\u003e\n\u003cli\u003eGospodarek M, Rybarczyk P, Szulczyński B, Gębicki J:Comparative Evaluation of Selected Biological Methods for the Removal of Hydrophilic and Hydrophobic Odorous VOCs from Air. Processes.7(4); doi: 10.3390/pr7040187 (2019)\u003c/li\u003e\n\u003cli\u003eRybarczyk P, Szulczyński B, Gębicki J, Hupka J:Treatment of malodorous air in biotrickling filters: A review. Biochemical Engineering Journal.141:146-62; doi: 10.1016/j.bej.2018.10.014 (2019)\u003c/li\u003e\n\u003cli\u003eTu X, Li J, Feng R, Sun G, Guo J:Comparison of Removal Behavior of Two Biotrickling Filters under Transient Condition and Effect of pH on the Bacterial Communities. PLoS One.11(5):e0155593; doi: 10.1371/journal.pone.0155593 (2016)\u003c/li\u003e\n\u003cli\u003eOmri I, Bouallagui H, Aouidi F, Godon JJ, Hamdi M:H2S gas biological removal efficiency and bacterial community diversity in biofilter treating wastewater odor. Bioresour Technol.102(22):10202-9; doi: 10.1016/j.biortech.2011.05.094 (2011)\u003c/li\u003e\n\u003cli\u003eChouari R, Dardouri W, Sallami F, Rais MB, Le Paslier D, Sghir A:Microbial Analysis and Efficiency of Biofiltration Packing Systems for Hydrogen Sulfide Removal from Wastewater Off Gas. Environmental Engineering Science.32(2):121-8; doi: 10.1089/ees.2014.0290 (2015)\u003c/li\u003e\n\u003cli\u003eJin Y, Veiga MC, Kennes C:Effects of pH, CO2, and flow pattern on the autotrophic degradation of hydrogen sulfide in a biotrickling filter. Biotechnol Bioeng.92(4):462-71; doi: 10.1002/bit.20607 (2005)\u003c/li\u003e\n\u003cli\u003eSoupramanien A, Malhautier L, Dumont E, Andr\u0026egrave;s Y, Rocher J, Fanlo J-L:Biological treatment of a mixture of gaseous sulphur reduced compounds: identification of the total bacterial community\u0026apos;s structure. Journal of Chemical Technology \u0026amp; Biotechnology.87(6):817-23; doi: 10.1002/jctb.3729 (2012)\u003c/li\u003e\n\u003cli\u003eTu X, Guo J, Yang Y, Feng R, Sun G, Li J:Biofilms formed within the acidic and the neutral biotrickling filters for treating H2S-containing waste gases. RSC Advances.7(41):25475-82; doi: 10.1039/c7ra04053a (2017)\u003c/li\u003e\n\u003cli\u003eBozzola JJ, Russell LD. Electron Microscopy: Principles and Techniques for Biologists. Jones and Bartlett (1999).\u003c/li\u003e\n\u003cli\u003eJanssen A. J. H. SR, van der Kaa C., Jochemsen A., Bontsema J., Lettinga G. :Biological Sulphide Oxidation in a Fed-Batch Reactor. Biotechnology and Bioengineering.47(3):327-33; (1995)\u003c/li\u003e\n\u003cli\u003eM. Deshusses DG. Biotrickling Filter Technology. In: Zarook Shareefdeen AS, editor. Biotechnology for Odor and Air Pollution Control. Springer. p. 147-66 (2005).\u003c/li\u003e\n\u003cli\u003eMontebello AM, Fern\u0026aacute;ndez M, Almenglo F, Ram\u0026iacute;rez M, Cantero D, Baeza M, Gabriel D:Simultaneous methylmercaptan and hydrogen sulfide removal in the desulfurization of biogas in aerobic and anoxic biotrickling filters. Chemical Engineering Journal.200-202:237-46; doi: 10.1016/j.cej.2012.06.043 (2012)\u003c/li\u003e\n\u003cli\u003eMontebello AM, Bezerra T, Rovira R, Rago L, Lafuente J, Gamisans X, et al.:Operational aspects, pH transition and microbial shifts of a H2S desulfurizing biotrickling filter with random packing material. Chemosphere.93(11):2675-82; doi: 10.1016/j.chemosphere.2013.08.052 (2013)\u003c/li\u003e\n\u003cli\u003eJia T, Zhang L, Sun S, Zhao Q, Peng Y:Adding organics to enrich mixotrophic sulfur-oxidizing bacteria under extremely acidic conditions-A novel strategy to enhance hydrogen sulfide removal. Sci Total Environ.854:158768; doi: 10.1016/j.scitotenv.2022.158768 (2022)\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"microbial-cell-factories","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"micf","sideBox":"Learn more about [Microbial Cell Factories](http://microbialcellfactories.biomedcentral.com/)","snPcode":"12934","submissionUrl":"https://submission.nature.com/new-submission/12934/3","title":"Microbial Cell Factories","twitterHandle":"@BioMedCentral","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Biofilm, Biodesulfurization, Biotrickling filter, Hydrogen sulfide, Microbial biofilm","lastPublishedDoi":"10.21203/rs.3.rs-3831762/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3831762/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eReduced sulfur compounds such as H2S are extremely toxic and highly corrosive, produced in many industrial activities. The biological desulfurization process has been established to be a technically and economically effective alternative to traditional physicochemical processes. This study aimed to investigate the operation of three parallel biotrickling filters (BTFs) in removing H2S at different pH conditions (haloalkaliphilic, neutrophilic, and acidophilic) and their associated microbial population in the biodesulfurization process. BTF columns were inoculated with enriched inoculum and experiments were performed by gradually reducing Empty Bed Retention Time (EBRT) and increasing inlet concentration (Ci). The maximum Removal Efficiency (RE) and Maximum Elimination Capacity (EC) in EBRT 60s for haloalkaline, neutral and acidic conditions were, 91% and 179.5 g S-H2S m-3 h-1, 85.7%, and 141 g S-H2S m-3 h-1, 88% and 145 g S-H2S m-3 h-1 respectively. For visualizing the attached microbial biofilms on pall rings, Scanning Electron Microscopy (SEM) was used and microbial community structure analysis by NGS showed that the most abundant phyla in haBTF, nBTF, and aBTF belong to gammaproteobacteria, betaproteobacteria, and acidithiobacillia, respectively. The alpha analysis according to the Shannon and Simpson indexes showed a lower diversity of bacteria in the aBTF reactor than that of nBTF and haBTF and beta analysis indicated a different composition of bacteria in haBTF compared to the other two filters. These results indicated that the proper performance of BTF under haloalkaliphilic (natron) conditions is the most effective way for H2S removal from air pollutants of different industries.\u003c/p\u003e","manuscriptTitle":"Assessing the Efficiency and Microbial Diversity of H2S-removing Biotrickling Filters at Various pH Conditions","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-01-08 17:14:52","doi":"10.21203/rs.3.rs-3831762/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-03-04T11:07:31+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-01-25T17:36:13+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"fdf349fd-a364-4da4-9b75-d445da50bd95","date":"2024-01-15T19:32:53+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-01-15T06:01:47+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"6dc972d4-40fa-4119-bbdd-86a378bac82a","date":"2024-01-06T04:45:51+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"8e72d83e-ecd1-4e5b-a741-f5388f6ab227","date":"2024-01-05T00:32:25+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-01-05T00:15:23+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-01-04T17:01:36+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-01-04T17:01:36+00:00","index":"","fulltext":""},{"type":"submitted","content":"Microbial Cell Factories","date":"2024-01-03T12:03:00+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"microbial-cell-factories","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"micf","sideBox":"Learn more about [Microbial Cell Factories](http://microbialcellfactories.biomedcentral.com/)","snPcode":"12934","submissionUrl":"https://submission.nature.com/new-submission/12934/3","title":"Microbial Cell Factories","twitterHandle":"@BioMedCentral","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"f3f451e7-538c-478a-a998-adbc012413ab","owner":[],"postedDate":"January 8th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2024-05-16T21:25:36+00:00","versionOfRecord":[],"versionCreatedAt":"2024-01-08 17:14:52","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-3831762","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3831762","identity":"rs-3831762","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}