Synergetic influence of different additives on hydrogen and methane generation from food waste

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Jena, Saroj Kumar Acharya, Sarita Mishra This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5841927/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract In order to co-digest food waste along with cow dung to produce hydrogen and methane, the effects were experimentally assessed in distinct batch reactors for calcium carbonate (CaCO 3 ), copper oxide (CuO), zinc oxide (ZnO), and calcium peroxide (CaO 2 ) as additives in this study. The maximum hydrogen generation using CaO 2 was found to be 115.59 mLg − 1 total solid (TS), which was 8.6% lead by the standard specimen with no additives. In contrast, ZnO reduced lead by 10.4%. In comparison to the control sample, the generation of methane was 161.2 and 129.06. mLg − 1 TS, showing a 40 and 25% increase with CaO 2 and CaCO 3 , whereas it dropped to 62.65 and 76.23 mLg − 1 TS, depicting a 35 and 21% decrease with CuO and ZnO respectively. The addition of CaO 2 and CaCO 3 increased biogas generation by 32.1 and 15.1%, respectively, while the addition of CuO and ZnO decreased it by 31.4 and 24.3%. Ultimately, the digestate's physicochemical characteristics showed an improvement in organic nutrients following co-digestion, making it a useful biofertilizer for use in agriculture. Methane hydrogen biogas digestate anaerobic co-digestion Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Introduction With around 180 million tons produced annually worldwide, the quantity of food waste (FW) that comes from residential and commercial kitchens is increasing yearly [ 1 ]. Finding a different way to utilize FW is essential due to the disposal issue, bacterial infection, and unfavourable surroundings. Anaerobic digestion (AD), which generates biogas as a substitute energy source, is a successful technique for recycling and minimizing FW. The primary energy carriers in biogas that can meet the energy demand given global energy consumption are methane and hydrogen [ 2 ]. Nevertheless, AD has a few well-known drawbacks, including a low rate of energy conversion and fuel degrading efficiency. As a result, ongoing research is being done to improve methane and hydrogen generation by using various technologies. Utilizing additives, co-digesting different feedstocks, and preparation of the substrate and inoculum are some strategies to improve the AD process's performance [ 3 ]. Researchers have extensively researched the use of additives to enhance AD performance. Of the additions, metal oxides, both in bulk and as nanomaterials, demonstrated a potential effect in boosting the production of hydrogen and methane [ 4 ]. The metal oxide is a better option than the other additives because of its higher surface to volume ratio, which facilitated electron transfer during co-digestion and increased the digestate's nutritional value [ 5 ]. In recent years, a variety of metal oxides have been employed to enhance the production of biogas. The synthesis of biohydrogen during the AD of wheat straw has been significantly improved by the successful application of the compounds calcium peroxide (CaO 2 ) and calcium oxide (CaO) [ 6 ]. By eliminating the trichloroethylene from groundwater, the nanoscale CaO 2 proved to be more efficient than the traditional CaO 2 , revealing it as a very useful substrate for AD [ 7 ]. Wang et al. [ 8 ] during their experiment noticed an increased methane production as CaO 2 dosage increased because of the increased breakdown of resistant organics like lignocellulose and humus from waste sludge. According to a different study by Ping et al. [ 9 ], methane generation was higher at higher temperatures, including those with CaO 2 augmentation, than at room temperature. Fu et al. [ 10 ] also noted that the fermentation of corn straw increased the rate of hydrolysis with CaO 2 , which resulted in a greater methane output. Numerous researchers have also examined the impact of zinc oxide (ZnO) and copper oxide (CuO) on the anaerobic digesting process. Chen et al. [ 11 ] found that employing ZnO and CuO significantly decreased the production of biogas and the overall effectiveness of solid removal from sewage sludge. Furthermore, it was shown that ZnO's toxic action prevented the synthesis of biogas from the activated sludge and also affects the formation of volatile fatty acids [ 12 ]. A lower concentration of CuO had no discernible impact on the spread of antibiotic-resistant bacteria created the compounds CaO 2 and CaO according to a different study by Huang et al. [ 13 ]. An extended duration of CuO and ZnO biofouling was noted by Cheng et al. [ 14 ], which limited the development of antibiotic-resistant bacteria and led to improved system performance. Additionally, several types of calcium carbonate (CaCO 3 ) have been added to boost the fermentation of methane and hydrogen. Because of its increased alkalinity and process stability all through the AD of FW, Zhang and Wang [ 15 ] reported better hydrogen production while employing CaCO 3 . Similarly, it was discovered that adding carbonate increased the formation of volatile fatty acids by limiting the repressive action of Ca 2+ on the process, which resulted in an improved hydrogen yield [ 16 ] (Liu et al., 2012). Other investigations have showed similar interpretations regarding the creation of hydrogen [ 17 , 18 ]. Methane production was found to be higher than the control in the kinetic investigation of CaCO 3 addition on wollastonite AD [ 19 ]. It was discovered that adding metal oxide to the feedstock could enhance its breakdown during AD. Therefore, it was thought that using different additives to co-digest FW and cow dung (CD) could improve the fermentation of methane and hydrogen. Although many additives have been employed in AD before, the studies have only looked at the fermentation of hydrogen or methane; little is known about the collective generation of methane and hydrogen from a single-stage AD. Furthermore, no research has been done to assess the efficiency of methane and hydrogen generation using FW and CD as the feedstock with various additions. Therefore, in order to improve the production of methane and hydrogen, an experimental inquiry is needed to examine the effects of different additives. The current work's uniqueness in meeting the technical requirements of the AD method using CD and FW for an environment that uses less energy is established by this exploration divergence. This study aimed to investigate the effects of supplementing with CaO 2 , CuO, ZnO, and CaCO 3 during AD process in order to improve the fermentation of hydrogen and methane. The goal of the study was to choose the optimum addition that could generate the most energy during the process and to enhance the methane and hydrogen inception in comparison to the control sample. Utilizing additions that can be utilized as an enhanced bio-fertilizer for agricultural uses like farming and cultivation, it was also meant to enhance the digestate's physicochemical characteristics. It was expected that the results would provide a clear understanding of how different additives affected system performance, leading to an increase in agriculture productivity and energy efficiency advantages. Materials and Methodology The hostel canteen was the source of the FW. To make the slurry, non-biodegradable materials including plastic, eggshells, and bones were separated by hand and then blended in a household blender. CD was taken from a neighbouring cow shed. By diluting with 10 to 15 millilitres of regular water, the effluent of FW and CD was created. The wastewater treatment facility in Bhubaneswar, India, is where the sludge solution (SS) was obtained. SS served as the experiment's inoculum, while the substrate was made by combining equal volumes of FW and CD slurry. The physicochemical properties of the inoculum and substrate employed in the procedure are shown in Table 1. Table 1. Essential quality of FW, CD, and Sludge solution. Parameter Substrate Inoculum FW CD Sludge solution Total solid (%) 10.2 ± 0.05 68.47 ± 0.09 9.7 ± 0.04 Volatile solid (%) 8.6 ± 0.15 34.81 ± 0.24 7.2 ± 0.07 pH 4.3 ± 0.1 6.7 ± 0.2 7.1 ± 0.1 Carbon (%) 48.7 ± 0.31 41.64 ± 0.43 24.38 ± 0.18 Oxygen (%) 32.56 ± 0.26 37.48 ± 0.41 49.74 ± 0.34 Nitrogen (%) 3.26 ± 0.17 2.81 ± 0.08 1.84 ± 0.10 Hydrogen (%) 6.4 ± 0.14 3.47 ± 0.36 3.19 ± 0.21 Potassium (%) 1.2 ± 0.05 0.04 ± 0.006 0.36 ± 0.02 Sulphur (%) 0.3 ± 0.04 0.07 ± 0.003 0.71 ± 0.03 Phosphorus (%) 0.7 ± 0.02 0.06 ± 0.03 0.24 ± 0.06 Moisture content (%) 82.4 ± 0.46 79.75 ± 0.52 98.7 ± 0.67 Ash (%) 5.19 ± 0.12 12.68 ± 0.23 46.5 ± 0.30 Fixed carbon (%) 12.19 ± 0.09 10.74 ± 0.11 8.63 ± 0.21 Cellulose (% TS) 0.85 ± 0.03 2.197 ± 0.07 ND Hemicellulose (% TS) 0.36 ± 0.04 2.028 ± 0.06 ND Lignin (% TS) 0.27 ± 0.07 3.263 ± 0.05 ND Note: “ND” signifies the value was not determined. Experimental method The trials were carried out using a 600 mL SS as the feedstock in batch reactors together with an inoculum prepared of 100 mL FW mixed with 100 mL CD slurry with a volume of 1 L. The fermentation of hydrogen and methane took place in several reactors. While hydrogen was produced in the fermentative reactor, methane was made in the methanogenic reactor. For optimal system performance, the feedstock to slurry ratio was kept at 1:3 (v/v) [20]. According to earlier research, calcium carbonate (CaCO 3 ), CaO 2 , CuO, and ZnO were added to the batch reactors in amounts of 3 mgL -1 [21,22]. In the fermentative and methanogenic reactors, each additive (99% pure) was utilized in equal amounts to create hydrogen and methane (CH 4 ) independently. While the methanogenic reactors were monitored for 50 days, the fermentative reactors were run for 25 days. By supplying 6 M NaOH and HCl solution, the methanogenic and fermentative reactors' internal pH values were kept at 5.5 and 7, respectively [23]. To support the anaerobic environment, nitrogen was added to the reactors for three to four minutes after homogenous mixing was confirmed. Next, as seen in Fig. 1, the batch reactors were placed on the magnetic stirrer and properly sealed with a rubber stopper. The reactor temperature was maintained at 37±1 0 C using a PT 100 thermostatic explore is in charge of the hot water circulation system. Three samples were put in each type of reactor for greater accuracy, and the average result was applied for analysis of the result. Analytical method : Carbon, nitrogen, hydrogen, oxygen, and sulphur were identified in the final analysis using the CHNS elemental analyser (Nario EL III). The American Public Health Association's standard protocol for measuring pH, total solid (TS), and volatile solid (VS) was followed APHA [24]. An Agilent ICP-MS 8800 TripleQ inductively coupled plasma mass spectrometry was used to determine the composition of potassium (K) and phosphorus (P). The approach proposed by Sluiter et al. [25] was used to measure the lignocellulosic fraction, which includes cellulose, hemicellulose, and lignin. The microstructural arrangement of the additives was examined using a 15 kV accelerating voltage scanning electron microscope (SEM, JSM-JEOL 6360) with an auto coater that changed the sample's coating automatically. The biogas was drawn from the reactor headspace by using an air-tight syringe (VICI, USA). A gas chromatograph (GC-2010, CIC, Baroda) with a thermal conductivity detector and a 2 m × 3 mm stainless steel column (Porapak Q) packed with molecular sieve 5A was used to measure the hydrogen and methane concentrations. With the oven, detector, and injector temperatures set at 50 0 C, 150 0 C, and 50 0 C, respectively, the nitrogen flow rate was adjusted to 20 mL min -1 . The water replacement method was used to precisely produce the biogas, and the constituents of gas samples was controlled every day. Results and discussion 3.1. Characteristics of feedstock and inoculum The inoculum and feedstocks were significantly enhanced with natural materials needed or the co-digestion of anaerobic, as shown in Table 1. CD had the highest total solid and volatile solid (VS) values, whereas sludge solution had the lowest. The findings presented in the literature review [26, 27, 28] were in close agreement with these values. In keeping with the findings of Duman et al. [29], the results of the ultimate and proximate analyses indicated an appropriate range of organic matter to yield maximum possible hydrogen and CH 4 during each batch process. Additionally, the substrate and inoculum were found to have an ideal pH range that is necessary for the system to function at its best [30]. Larger carbohydrate and lower lignin concentration were found in the lignocellulosic fraction of FW, CD, and sludge solution. This is advantageous for microbial breakdown, which leads to a larger accumulation of volatile fatty acids. An analogous finding regarding the feedstock's cellulose, hemicellulose, and lignin composition was validated by Xing et al. [31]. 3.2. Daily biogas synthesis under the influence of additives The microbe later exploited the volatile fatty acids that had collected throughout the hydrolysis and acidification to produce biogas. Fig. 2 shows the methanogenic reactor's daily production of biogas. The degradation of organic materials in the feedstock is represented by the different peaks that are visible in the picture. While the other peaks were ascribed to the breakdown of protein, fat, etc., the first peak, which emerged after four to five days of digestion, reflects the breakdown of carbohydrates. This observation demonstrated that because microorganisms were more likely to distinguish carbs from other elements, the breakdown of carbohydrates happened considerably earlier [32]. In the control sample, the average daily biogas output was recorded to be 2.9 mL g -1 TS. In comparison to the control reactor, it was raised by 3.4 and 4.3 mL g -1 TS, respectively employing CaCO 3 and CaO 2 . Conversely, with ZnO and CuO, it was decreased to 2.1 and 2 mL g -1 TS, respectively. The daily biogas yield for CaO 2 and CaCO 3 was continuously greater than that for the control during the operation. It was consistently lower for CuO and ZnO. When water and CaO 2 react, intermediate products such H 2 O 2 and ·OH are released, which encourages hydrolysis and acidification and increases the amount of biogas produced [10]. In a similar vein, the addition of CaCO 3 significantly increased the process's alkalinity and buffer capacity, which increased the buildup of volatile fatty acids [33]. However, adding CuO and ZnO had a negative effect because it produced toxic Cu 2+ and Zn 2+ ions, which damage the surface of the substrates by generating sensitive oxidation species and reducing the amount of biogas generated [34]. The authors recorded the highest average daily biogas output of 5.36 mL g -1 as mentioned in the previous publication [20]. The FW is co-digested by TS using CaO 2 as a catalyst. Chen et al. [11] investigated the AD of sludge collected from local sewage using ZnO and CuO as conductive nanomaterials, producing the most every day. 3.3. Influence of additives on cumulative biogas synthesis The cumulative biogas synthesis trend was framed using daily production over a period of 50 days. (Fig. 3). For 35–38 days, the biogas generation climbed linearly; however, after that, it practically ceased, as seen by the flat line in the Fig. 3 for days 38–50. It shows that over the first 38 days, the microbes broke down the organic materials, generating the most biogas. The base sample reactor generated a total biogas output of 147.62 mL g -1 TS. The same with use of CaO 2 and CaCO 3 were recorded as 217.41 and 174.02 mL g -1 TS with regard to the control reactor, indicating an increase of 32.1% and 15.1%, respectively. The addition of CaO 2 and CaCO 3 increased the oxidation of the organic matter by releasing Ca 2+ , while the generation of H 2 O 2 and OH within the reacting medium increased the production of biogas [6]. In contrast to the control sample, these values were determined to be 101.25 and 111.72 mL g -1 TS, with CuO and ZnO exhibiting reductions of 31.4 and 24.3%, respectively. This could be the consequence of increased toxicity brought on by the release of Cu 2+ and Zn 2+ , which limit the buildup of VFAs by rupturing the organic matter's during the early phases of AD [34]. The current study's findings are consistent with those of Fu et al. [10], who found that tetracycline, which inhibits microbial development during the co-digestion of maize straw and chicken dung, was effectively removed through the calculation of CaO 2 . In a similar vein, Zhang and Wang [15] observed enhanced biogas synthesis from the AD of FW due to a shorter lag phase with CaCO 3 addition. Chen et al. [11] discovered that, in comparison to the control reactor, the cumulative biogas output was reduced by 17.3% and 90.2%, respectively, when CuO and ZnO were used as nano-additives. 3.4. Concentration of CH 4 under the influence of additives The amount of CH 4 in the biogas is the most imperative determinant of its quality. Biogas with a higher methane content will have a higher heating value. The methane content for each sample during a 50-day digestion period is displayed in Figure 4. Due to the hydrogenase enzyme's dominant role in hydrolysis and acidification, 16.21% was found to be the maximum methane concentration. indicating very little presence at first for all samples for ten to fifteen days [35]. The methane content significantly increased as the co-digestion progressed into the methanogenic stage, peaking between 33 and 37 days of digestion. Following this, all samples, with the exception of the reactor containing CaCO 3 , showed a declining nature for the remainder of the period. Because of its higher alkalinity and larger buffer capacity, the reactor containing CaCO 3 had an earlier peak in the CH 4 level. The control sample had the greatest methane level, 45.63%, but CaO 2 and CaCO 3 raised the amount to 59.6% and 49.79%, respectively. This is explained by the fact that CaO 2 causes organic feedstock to decompose more quickly, which increases the amount of biodegradable material that can be used to ferment methane [8]. Methanogenic bacterial activity is favoured by the carbonate ion formed with CaCO 3 , which raises the concentration of methane [19]. Since the reactor's toxicity prevents methanogenic bacteria from growing during co-digestion, the samples' peak methane concentrations never surpass 23.49% and 27.35%, respectively, indicating the negative effects of CuO and ZnO addition [22,36]. Furthermore, as associated with the base results, the CH 4 content of the generated biogas was reduced by a maximum of 36.1% when using CuO 2 , whereas it was raised by up to 14% when using CaO 2 . The results of the current study were consistent with those of previous studies. According to Fu et al. [10], methane concentrations varied between 49.4% and 66.8% as a result of variations in CaO 2 dosage. Salek et al. [19] demonstrated that the usage of CaCO 3 increased the concentration of methane by 52% due to the generation of carbonate ions. According to Cheng et al. [14], using CuO and ZnO, respectively, dramatically decreased the adenosine triphosphate content by up to 43.5 and 22.4% when cross verified with respect to the base results, which resulted in a substantial decrease in CH 4 production. 3.5. Cumulative CH 4 generation under the influence of additives The organic components in the feedstock that were broken down during the methanogenesis process boost the cumulative CH 4 production rate. Because of their minimal loss qualities and the fact that the microbe reused them during the methane synthesis, it was thought that the additives would not change after the initial phases of co-digestion. Fig. 5 illustrates how additives affect cumulative methane output. For all samples, continuous methane generation is seen for up to 40–42 days. In the additive-free control sample, the cumulative methane output was 96.13 mL g -1 TS. The CH 4 yield with CaO 2 and CaCO 3 as additive was recoded to be 40 and 25% greater, than compared to the control reactor. An intermediate product (H 2 O 2 and ·OH) was created when water and CaO 2 were combined, which aided in the more efficient breakdown of cellulose and hemicellulose. This resulted in the creation of more volatile fatty acids, which increased the amount of biodegradable matter for the bacterium [33]. Moreover, greater biological disintegration during the methane fermentation was the consequence of the anaerobic digestion with CaO 2 and CaCO 3 's increased buffer capacity and alkalinity [10]. Compared to the control sample, the methane yield with CuO and ZnO was 35% and 21% lower, respectively, at 62.65 and 76.23 mL g -1 TS. Lower methane yield was mostly caused by greater toxicity brought on by the release of Cu 2+ and Zn 2+ ions. This was because the feedstock's microbial activity and volatile fatty acid production were suppressed [37]. The literature review previously reported similar findings. According to Wang et al. [8], the cumulative methane output from sewage sludge with different proportions of CaO 2 ranged from 146.3 to 215.9 g g -1 volatile suspended solids (VSS). Luna-delRisco et al. [38] found that utilizing varying dosages of CuO reduced methane generation from sewage sludge and calf dung by 19% to 60%. According to observations of Mu et al. [22], the highest cumulative CH 4 generation from the AD of activated sludge was 99.5 mL g -1 VSS, reduced by 22.8% with respect to the base results. 3.6. Influence of the additives on hydrogen concentration Fig. 6 displays the trend of change in concentration of hydrogen due to additive additions. All of the samples' hydrogen fermentation was completed in the first 8–10 days, with the highest concentration occurring in the first 3–5 days of digestion. It suggests that the hydrogenase enzyme's microbial activity was significant during the hydrolysis and acidification processes, which caused the organic matter to decompose quickly. The control sample's maximum hydrogen content was 17.3% on the fifth day of co-digestion. Over the same time period, the value was raised by 26.34, 19.37, 19.86, and 20.72%, respectively, by CaO 2 , CuO, ZnO, and CaCO 3 . The biggest improvement with CaO 2 was 9% but with CuO as the additive, the least enhancement was nearly comparable to the control reactor. During the AD process, it was found that adding additives increased the hydrogen content overall when compared to the control reactor. This could be because the additives' increased microbial activity leads to a better breakdown of the feedstock. The increased hydrogen content in the presence of CaO 2 is caused by the release of OHˉ and ·O 2 ˉ together with alkali, which jointly encourage the formation of amino acids and improved substrate breakdown during AD [35]. The addition of CaCO 3 enhanced the system's buffer capacity, which ensued in a minor rise in hydrogen concentration, but not as much as CaO 2 [18]. The study's results were consistent with other findings that had already been reported in the literature. Hydrogen concentrations ranged from 12% to 26% when FW was digested anaerobically, according to Wainaina et al. [39]. 3.7. Influence of the additives on cumulative hydrogen synthesis The total hydrogen production in the presence of CaO 2 and CaCO 3 reactors was higher than that from the base inoculum, despite the fact that the reactors that received CuO and ZnO additions produced less hydrogen overall (Fig. 7). It illustrates how the toxicity caused by the use of CuO and ZnO as additive led to a decrease in hydrogen generation during the operation. The total amount of hydrogen produced by the control reactor after 25 days was 105.59 mL g -1 TS. It reduced to 96.6 and 94.84 mL g -1 TS in presence of ZnO and CuO as additive respectively, while presence of CaO 2 and CaCO 3 the hydrogen content augmented to 115.59 and 109.58 mL g -1 TS respectively. The addition of ZnO depicted a maximum reduction of 10.4%, whereas CaO 2 increased the production of hydrogen by 8.6%. The hike in hydrogen synthesis with CaO 2 is caused by the creation of alkali, ·OH, and ·O2ˉ, which enhanced the acidity and there by accelerating the hydrolysis process to augment hydrogen synthesis [40]. Furthermore, adding CaCO 3 upsurges the alkalinity of the inoculum and upholds the pH value at the optimal range, which promotes the growth of hydrogenase bacteria and increases the output of hydrogen [16]. Though Cu 2+ and Zn 2+ have higher toxicity, CuO and ZnO occupy the microbial development within the inoculum, resulting in decrease in hydrogen synthesis [38]. The maximal cumulative hydrogen synthesis from wheat straw was determined to be 114 mL g -1 TS, which is comparable to the quantity obtained in the current investigation [6]. Conclusions While CuO and ZnO reduced the biogas synthesis, CH 4 , and hydrogen fermentation processes of AD process, the addition of CaO 2 and CaCO 3 enhanced these processes in comparison to the control reactor. It was shown that adding CuO and ZnO reduced the biogas generation by 31.4% and 24.3%, respectively, while adding CaO 2 and CaCO 3 raised it by 32.1% and 15.1%, respectively, when compared to the control sample. Additionally, methane production decreased by 35% and 21% with CuO and ZnO, respectively, but augmented by 40% and 25% with CaO 2 and CaCO 3 . Furthermore, the addition of ZnO decreased the hydrogen generation by 10.4% while the addition of CaO 2 increased it by 8.6% when compared to the control. Additionally, the digestate's physicochemical characterization during anaerobic co-digestion revealed a developed nutrient composition that can be used as improved fertilizer. Ultimately, it can be concluded that while the use of CuO and ZnO as additives during the co-digestion process had the opposite effect, the inclusion of CaO 2 and CaCO 3 enhanced the fermentation of CH 4 and hydrogen. It is recommended that future studies evaluate the AD process using other substrates or the synergistic effect of adding many additives to improve efficiency of AD process. Declarations Acknowledgements The authors acknowledge the support received from the Alternative Fuel and Energy Lab of S ‘O’A deemed to be University. Author contributions Conceptualization and design of the experiments, CD, and SPJ; analysis of the data, writing—the original draft, CD and SM; visualization, reviewing and editing, SPJ and SKA; All authors have read and agreed to the published version of the manuscript. Funding The authors have not received any fundings from any source for this research work. Ethics approval and consent to participate Not applicable. Competing of interest The authors declare that they do not have any competing interest. References Melikoglu M, Lin CSK, and Webb C. Analysing global food waste problem: pinpointing the facts and estimating the energy content. Central European Journal of Engineering. 2013; 3(2): 157–164. https://doi.org/10.2478/s13531-012-0058-5 Deheri C, Acharya SK, Thatoi DN, and Mohanty AP. A review on performance of biogas and hydrogen on diesel engine in dual fuel mode. 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Water research. 2020; 168: 115099. https://doi.org/10.1016/j.watres.2019.115099 Forster-Carneiro T, Riau V, and Pérez M. Mesophilic anaerobic digestion of sewage sludge to obtain class B biosolids: Microbiological methods development. Biomass and Bioenergy. 2010; 34(12): 1805-1812. https://doi.org/10.1016/j.biombioe.2010.07.010 Wu H, Gao J, Yang D, Zhou Q, and Liu W. Alkaline fermentation of primary sludge for short-chain fatty acids accumulation and mechanism. Chemical Engineering Journal. 2010; 160(1): 1-7. https://doi.org/10.1016/j.cej.2010.02.012 Xia T, Kovochich M, Liong M, Madler L, Gilbert B, Shi H, Yeh JI, Zink JI, and Nel AE. Comparison of the mechanism of toxicity of zinc oxide and cerium oxide nanoparticles based on dissolution and oxidative stress properties. ACS nano. 2008; 2(10): 2121-2134. Dahiya S, Sarkar O, Swamy YV, and Mohan SV. Acidogenic fermentation of food waste for volatile fatty acid production with co-generation of biohydrogen. Bioresource technology. 2015; 182: 103-113. http://dx.doi.org/10.1016/j.biortech.2015.01.007 Su Y, Chen Y, Zheng X, Wan R, Huang H, Li M, and Wu L. Using sludge fermentation liquid to reduce the inhibitory effect of copper oxide nanoparticles on municipal wastewater biological nutrient removal. Water research. 2016; 99: 216-224. http://dx.doi.org/10.1016/j.watres.2016.04.066 Zhang L, He X, Zhang Z, Cang D, Nwe KA, Zheng L, Li Z, and Cheng S. Evaluating the influences of ZnO engineering nanomaterials on VFA accumulation in sludge anaerobic digestion. Biochemical Engineering Journal. 2017; 125: 206-211. http://dx.doi.org/doi:10.1016/j.bej.2017.05.008 Luna-delRisco M, Orupõld K, and Dubourguier HC. Particle-size effect of CuO and ZnO on biogas and methane production during anaerobic digestion. Journal of hazardous materials. 2011; 189(1-2): 603-608. https://doi.org/10.1016/j.jhazmat.2011.02.085 Wainaina S, Awasthi MK, Horváth IS, and Taherzadeh MJ. Anaerobic digestion of food waste to volatile fatty acids and hydrogen at high organic loading rates in immersed membrane bioreactors. Renewable Energy. 2020; 152: 1140-1148. https://doi.org/10.1016/j.renene.2020.01.138 Li Y, Wang J, Zhang A, and Wang L. Enhancing the quantity and quality of short-chain fatty acids production from waste activated sludge using CaO 2 as an additive. Water research. 2015; 83: 84-93. https://doi.org/10.1016/j.watres.2015.06.021 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted 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. 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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-5841927","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":403484329,"identity":"2a938e6a-5d4e-43c3-8796-4926b3937c55","order_by":0,"name":"Chinmay Deheri","email":"","orcid":"","institution":"Vikash Institute of Technology","correspondingAuthor":false,"prefix":"","firstName":"Chinmay","middleName":"","lastName":"Deheri","suffix":""},{"id":403484330,"identity":"f99dd546-2736-4649-9a7d-a482efbe12de","order_by":1,"name":"Shakti P. Jena","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA4klEQVRIiWNgGAWjYDACCQZmBgYDNiCL+QBUiLGBsJYDYC1sCaRoAbN4DIhzl/zs5sfGHwr45MzZz3z+8KGGQZ6/gbntAT4tBneOGScAHWZs2ZO7TXLGMQbDGQcY2/HaZyCRYHwAqCVxw4Hcbcw8bAyMGxgY2yTwOmxG+meQlvoN5988/szzj8GeoBaGGzlghyUY3MhhkOZtY0gkqAWostjgjAGb4YYbz8wkZ/ZJJM84TNhhmyUq/hyTNzif/PjDh282tv3t7c/wOwwCjsEYQMXMRKgHghrilI2CUTAKRsHIBAAP0Uib7qDUAQAAAABJRU5ErkJggg==","orcid":"","institution":"Siksha O Anusandhan University","correspondingAuthor":true,"prefix":"","firstName":"Shakti","middleName":"P.","lastName":"Jena","suffix":""},{"id":403484331,"identity":"45827e8c-cc7e-4705-91bc-78a4384007ec","order_by":2,"name":"Saroj Kumar Acharya","email":"","orcid":"","institution":"Siksha O Anusandhan University","correspondingAuthor":false,"prefix":"","firstName":"Saroj","middleName":"Kumar","lastName":"Acharya","suffix":""},{"id":403484332,"identity":"08d0f47a-4175-4808-a834-881b6ee50757","order_by":3,"name":"Sarita Mishra","email":"","orcid":"","institution":"Vikash Institute of Technology","correspondingAuthor":false,"prefix":"","firstName":"Sarita","middleName":"","lastName":"Mishra","suffix":""}],"badges":[],"createdAt":"2025-01-16 12:38:29","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5841927/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5841927/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":74206569,"identity":"20cd1fe9-0d80-4132-88d9-f481b2e2cd42","added_by":"auto","created_at":"2025-01-20 03:52:16","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":100425,"visible":true,"origin":"","legend":"\u003cp\u003eIllustration of the lab scale experimental arrangement.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-5841927/v1/85544d0e6f78705c1e44bb27.png"},{"id":74207211,"identity":"72fd2be7-aa6c-4327-a8ef-d7d7e43b937d","added_by":"auto","created_at":"2025-01-20 04:00:16","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":167259,"visible":true,"origin":"","legend":"\u003cp\u003eDaily biogas synthesis concerning to time.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-5841927/v1/46358f4c5326c7828eb71125.png"},{"id":74208185,"identity":"90a2b77c-81b3-40c7-acf6-351f8dea99ec","added_by":"auto","created_at":"2025-01-20 04:16:16","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":164107,"visible":true,"origin":"","legend":"\u003cp\u003eCumulative biogas synthesis concerning to time.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-5841927/v1/f7005b4ef15fa1ed9178916e.png"},{"id":74206575,"identity":"2836ddef-0255-472f-b638-fb8cc0a2f48d","added_by":"auto","created_at":"2025-01-20 03:52:16","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":179727,"visible":true,"origin":"","legend":"\u003cp\u003eChange in CH\u003csub\u003e4\u003c/sub\u003e concentration concerning to digestion time.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-5841927/v1/1089c6aa881a359ba1557296.png"},{"id":74206576,"identity":"05cba828-293d-4333-9015-969219ac4189","added_by":"auto","created_at":"2025-01-20 03:52:16","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":155605,"visible":true,"origin":"","legend":"\u003cp\u003eCumulative CH\u003csub\u003e4 \u003c/sub\u003egeneration concerning to digestion time.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-5841927/v1/6c0ac32a2fcefba68480fc5a.png"},{"id":74206580,"identity":"b57a7154-9b0c-4ea2-aa40-bf3f89644db3","added_by":"auto","created_at":"2025-01-20 03:52:16","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":145177,"visible":true,"origin":"","legend":"\u003cp\u003eChange in concentration of hydrogen concerning to digestion time.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-5841927/v1/0b1ad17dae53fbafd14e388e.png"},{"id":74206570,"identity":"84113d38-6458-458b-8917-97a2d2ed8d16","added_by":"auto","created_at":"2025-01-20 03:52:16","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":131342,"visible":true,"origin":"","legend":"\u003cp\u003eVariation incumulative hydrogen synthesis concerning to digestion time.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-5841927/v1/5b35818c762ce7225a37747d.png"},{"id":74477132,"identity":"81a72526-52ef-4f37-ab37-aee76ff27d42","added_by":"auto","created_at":"2025-01-22 15:49:03","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1684036,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5841927/v1/bfcb8e05-5483-400d-8bbb-4bf893007349.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Synergetic influence of different additives on hydrogen and methane generation from food waste","fulltext":[{"header":"Introduction","content":"\u003cp\u003eWith around 180\u0026nbsp;million tons produced annually worldwide, the quantity of food waste (FW) that comes from residential and commercial kitchens is increasing yearly [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Finding a different way to utilize FW is essential due to the disposal issue, bacterial infection, and unfavourable surroundings. Anaerobic digestion (AD), which generates biogas as a substitute energy source, is a successful technique for recycling and minimizing FW. The primary energy carriers in biogas that can meet the energy demand given global energy consumption are methane and hydrogen [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Nevertheless, AD has a few well-known drawbacks, including a low rate of energy conversion and fuel degrading efficiency. As a result, ongoing research is being done to improve methane and hydrogen generation by using various technologies. Utilizing additives, co-digesting different feedstocks, and preparation of the substrate and inoculum are some strategies to improve the AD process's performance [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Researchers have extensively researched the use of additives to enhance AD performance. Of the additions, metal oxides, both in bulk and as nanomaterials, demonstrated a potential effect in boosting the production of hydrogen and methane [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. The metal oxide is a better option than the other additives because of its higher surface to volume ratio, which facilitated electron transfer during co-digestion and increased the digestate's nutritional value [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. In recent years, a variety of metal oxides have been employed to enhance the production of biogas. The synthesis of biohydrogen during the AD of wheat straw has been significantly improved by the successful application of the compounds calcium peroxide (CaO\u003csub\u003e2\u003c/sub\u003e) and calcium oxide (CaO) [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. By eliminating the trichloroethylene from groundwater, the nanoscale CaO\u003csub\u003e2\u003c/sub\u003e proved to be more efficient than the traditional CaO\u003csub\u003e2\u003c/sub\u003e, revealing it as a very useful substrate for AD [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Wang et al. [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] during their experiment noticed an increased methane production as CaO\u003csub\u003e2\u003c/sub\u003e dosage increased because of the increased breakdown of resistant organics like lignocellulose and humus from waste sludge. According to a different study by Ping et al. [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], methane generation was higher at higher temperatures, including those with CaO\u003csub\u003e2\u003c/sub\u003e augmentation, than at room temperature. Fu et al. [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] also noted that the fermentation of corn straw increased the rate of hydrolysis with CaO\u003csub\u003e2\u003c/sub\u003e, which resulted in a greater methane output. Numerous researchers have also examined the impact of zinc oxide (ZnO) and copper oxide (CuO) on the anaerobic digesting process. Chen et al. [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] found that employing ZnO and CuO significantly decreased the production of biogas and the overall effectiveness of solid removal from sewage sludge. Furthermore, it was shown that ZnO's toxic action prevented the synthesis of biogas from the activated sludge and also affects the formation of volatile fatty acids [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. A lower concentration of CuO had no discernible impact on the spread of antibiotic-resistant bacteria created the compounds CaO\u003csub\u003e2\u003c/sub\u003e and CaO according to a different study by Huang et al. [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. An extended duration of CuO and ZnO biofouling was noted by Cheng et al. [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e], which limited the development of antibiotic-resistant bacteria and led to improved system performance. Additionally, several types of calcium carbonate (CaCO\u003csub\u003e3\u003c/sub\u003e) have been added to boost the fermentation of methane and hydrogen. Because of its increased alkalinity and process stability all through the AD of FW, Zhang and Wang [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e] reported better hydrogen production while employing CaCO\u003csub\u003e3\u003c/sub\u003e. Similarly, it was discovered that adding carbonate increased the formation of volatile fatty acids by limiting the repressive action of Ca\u003csup\u003e2+\u003c/sup\u003e on the process, which resulted in an improved hydrogen yield [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e] (Liu et al., 2012). Other investigations have showed similar interpretations regarding the creation of hydrogen [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Methane production was found to be higher than the control in the kinetic investigation of CaCO\u003csub\u003e3\u003c/sub\u003e addition on wollastonite AD [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. It was discovered that adding metal oxide to the feedstock could enhance its breakdown during AD. Therefore, it was thought that using different additives to co-digest FW and cow dung (CD) could improve the fermentation of methane and hydrogen. Although many additives have been employed in AD before, the studies have only looked at the fermentation of hydrogen or methane; little is known about the collective generation of methane and hydrogen from a single-stage AD. Furthermore, no research has been done to assess the efficiency of methane and hydrogen generation using FW and CD as the feedstock with various additions. Therefore, in order to improve the production of methane and hydrogen, an experimental inquiry is needed to examine the effects of different additives. The current work's uniqueness in meeting the technical requirements of the AD method using CD and FW for an environment that uses less energy is established by this exploration divergence. This study aimed to investigate the effects of supplementing with CaO\u003csub\u003e2\u003c/sub\u003e, CuO, ZnO, and CaCO\u003csub\u003e3\u003c/sub\u003e during AD process in order to improve the fermentation of hydrogen and methane. The goal of the study was to choose the optimum addition that could generate the most energy during the process and to enhance the methane and hydrogen inception in comparison to the control sample. Utilizing additions that can be utilized as an enhanced bio-fertilizer for agricultural uses like farming and cultivation, it was also meant to enhance the digestate's physicochemical characteristics. It was expected that the results would provide a clear understanding of how different additives affected system performance, leading to an increase in agriculture productivity and energy efficiency advantages.\u003c/p\u003e"},{"header":"Materials and Methodology","content":"\u003cp\u003eThe hostel canteen was the source of the FW. To make the slurry, non-biodegradable materials including plastic, eggshells, and bones were separated by hand and then blended in a household blender. CD was taken from a neighbouring cow shed. By diluting with 10 to 15 millilitres of regular water, the effluent of FW and CD was created. The wastewater treatment facility in Bhubaneswar, India, is where the sludge solution (SS) was obtained. SS served as the experiment\u0026apos;s inoculum, while the substrate was made by combining equal volumes of FW and CD slurry. The physicochemical properties of the inoculum and substrate employed in the procedure are shown in Table 1.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 1.\u003c/strong\u003e Essential quality of FW, CD, and Sludge solution.\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"585\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 178px;\"\u003e\n \u003cp\u003eParameter\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 272px;\"\u003e\n \u003cp\u003eSubstrate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 135px;\"\u003e\n \u003cp\u003eInoculum\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003eFW\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 141px;\"\u003e\n \u003cp\u003eCD\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 135px;\"\u003e\n \u003cp\u003eSludge solution\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 178px;\"\u003e\n \u003cp\u003eTotal solid (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003e10.2 \u0026plusmn; 0.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 141px;\"\u003e\n \u003cp\u003e68.47 \u0026plusmn; 0.09\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 135px;\"\u003e\n \u003cp\u003e9.7 \u0026plusmn; 0.04\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 178px;\"\u003e\n \u003cp\u003eVolatile solid (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003e8.6 \u0026plusmn; 0.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 141px;\"\u003e\n \u003cp\u003e34.81 \u0026plusmn; 0.24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 135px;\"\u003e\n \u003cp\u003e7.2 \u0026plusmn; 0.07\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 178px;\"\u003e\n \u003cp\u003epH\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003e4.3 \u0026plusmn; 0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 141px;\"\u003e\n \u003cp\u003e6.7 \u0026plusmn; 0.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 135px;\"\u003e\n \u003cp\u003e7.1 \u0026plusmn; 0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 178px;\"\u003e\n \u003cp\u003eCarbon (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003e48.7 \u0026plusmn; 0.31\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 141px;\"\u003e\n \u003cp\u003e41.64 \u0026plusmn; 0.43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 135px;\"\u003e\n \u003cp\u003e24.38 \u0026plusmn; 0.18\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 178px;\"\u003e\n \u003cp\u003eOxygen (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003e32.56 \u0026plusmn; 0.26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 141px;\"\u003e\n \u003cp\u003e37.48 \u0026plusmn; 0.41\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 135px;\"\u003e\n \u003cp\u003e49.74 \u0026plusmn; 0.34\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 178px;\"\u003e\n \u003cp\u003eNitrogen (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003e3.26 \u0026plusmn; 0.17\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 141px;\"\u003e\n \u003cp\u003e2.81 \u0026plusmn; 0.08\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 135px;\"\u003e\n \u003cp\u003e1.84 \u0026plusmn; 0.10\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 178px;\"\u003e\n \u003cp\u003eHydrogen (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003e6.4 \u0026plusmn; 0.14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 141px;\"\u003e\n \u003cp\u003e3.47 \u0026plusmn; 0.36\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 135px;\"\u003e\n \u003cp\u003e3.19 \u0026plusmn; 0.21\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 178px;\"\u003e\n \u003cp\u003ePotassium (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003e1.2 \u0026plusmn; 0.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 141px;\"\u003e\n \u003cp\u003e0.04 \u0026plusmn; 0.006\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 135px;\"\u003e\n \u003cp\u003e0.36 \u0026plusmn; 0.02\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 178px;\"\u003e\n \u003cp\u003eSulphur (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003e0.3 \u0026plusmn; 0.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 141px;\"\u003e\n \u003cp\u003e0.07 \u0026plusmn; 0.003\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 135px;\"\u003e\n \u003cp\u003e0.71 \u0026plusmn; 0.03\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 178px;\"\u003e\n \u003cp\u003ePhosphorus (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003e0.7 \u0026plusmn; 0.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 141px;\"\u003e\n \u003cp\u003e0.06 \u0026plusmn; 0.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 135px;\"\u003e\n \u003cp\u003e0.24 \u0026plusmn; 0.06\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 178px;\"\u003e\n \u003cp\u003eMoisture content (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003e82.4 \u0026plusmn; 0.46\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 141px;\"\u003e\n \u003cp\u003e79.75 \u0026plusmn; 0.52\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 135px;\"\u003e\n \u003cp\u003e98.7 \u0026plusmn; 0.67\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 178px;\"\u003e\n \u003cp\u003eAsh (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003e5.19 \u0026plusmn; 0.12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 141px;\"\u003e\n \u003cp\u003e12.68 \u0026plusmn; 0.23\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 135px;\"\u003e\n \u003cp\u003e46.5 \u0026plusmn; 0.30\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 178px;\"\u003e\n \u003cp\u003eFixed carbon (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003e12.19 \u0026plusmn; 0.09\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 141px;\"\u003e\n \u003cp\u003e10.74 \u0026plusmn; 0.11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 135px;\"\u003e\n \u003cp\u003e8.63 \u0026plusmn; 0.21\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 178px;\"\u003e\n \u003cp\u003eCellulose (% TS)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003e0.85 \u0026plusmn; 0.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 141px;\"\u003e\n \u003cp\u003e2.197 \u0026plusmn; 0.07\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 135px;\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 178px;\"\u003e\n \u003cp\u003eHemicellulose (% TS)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003e0.36 \u0026plusmn; 0.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 141px;\"\u003e\n \u003cp\u003e2.028 \u0026plusmn; 0.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 135px;\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 178px;\"\u003e\n \u003cp\u003eLignin (% TS)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003e0.27 \u0026plusmn; 0.07\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 141px;\"\u003e\n \u003cp\u003e3.263 \u0026plusmn; 0.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 135px;\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eNote: \u0026ldquo;ND\u0026rdquo; signifies the value was not determined.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eExperimental method\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe trials were carried out using a 600 mL SS as the feedstock in batch reactors together with an inoculum prepared of 100 mL FW mixed with 100 mL CD slurry with a volume of 1 L. The fermentation of hydrogen and methane took place in several reactors. While hydrogen was produced in the fermentative reactor, methane was made in the methanogenic reactor. For optimal system performance, the feedstock to slurry ratio was kept at 1:3 (v/v) [20]. According to earlier research, calcium carbonate (CaCO\u003csub\u003e3\u003c/sub\u003e), CaO\u003csub\u003e2\u003c/sub\u003e, CuO, and ZnO were added to the batch reactors in amounts of 3 mgL\u003csup\u003e-1\u003c/sup\u003e [21,22].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn the fermentative and methanogenic reactors, each additive (99% pure) was utilized in equal amounts to create hydrogen and methane (CH\u003csub\u003e4\u003c/sub\u003e) independently. While the methanogenic reactors were monitored for 50 days, the fermentative reactors were run for 25 days. By supplying 6 M NaOH and HCl solution, the methanogenic and fermentative reactors\u0026apos; internal pH values were kept at 5.5 and 7, respectively [23]. To support the anaerobic environment, nitrogen was added to the reactors for three to four minutes after homogenous mixing was confirmed. Next, as seen in Fig. 1, the batch reactors were placed on the magnetic stirrer and properly sealed with a rubber stopper. The reactor temperature was maintained at 37\u0026plusmn;1\u003csup\u003e0\u003c/sup\u003eC using a PT 100 thermostatic explore is in charge of the hot water circulation system. Three samples were put in each type of reactor for greater accuracy, and the average result was applied for analysis of the result.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAnalytical method\u003c/strong\u003e:\u003c/p\u003e\n\u003cp\u003eCarbon, nitrogen, hydrogen, oxygen, and sulphur were identified in the final analysis using the CHNS elemental analyser (Nario EL III). The American Public Health Association\u0026apos;s standard protocol for measuring pH, total solid (TS), and volatile solid (VS) was followed APHA [24]. An Agilent ICP-MS 8800 TripleQ inductively coupled plasma mass spectrometry was used to determine the composition of potassium (K) and phosphorus (P). The approach proposed by Sluiter et al. [25] was used to measure the lignocellulosic fraction, which includes cellulose, hemicellulose, and lignin.\u003c/p\u003e\n\u003cp\u003eThe microstructural arrangement of the additives was examined using a 15 kV accelerating voltage scanning electron microscope (SEM, JSM-JEOL 6360) with an auto coater that changed the sample\u0026apos;s coating automatically. The biogas was drawn from the reactor headspace by using an air-tight syringe (VICI, USA). A gas chromatograph (GC-2010, CIC, Baroda) with a thermal conductivity detector and a 2 m \u0026times; 3 mm stainless steel column (Porapak Q) packed with molecular sieve 5A was used to measure the hydrogen and methane concentrations. With the oven, detector, and injector temperatures set at 50\u003csup\u003e0\u003c/sup\u003eC, 150\u003csup\u003e0\u003c/sup\u003eC, and 50\u003csup\u003e0\u003c/sup\u003eC, respectively, the nitrogen flow rate was adjusted to 20 mL min\u003csup\u003e-1\u003c/sup\u003e. The water replacement method was used to precisely produce the biogas, and the constituents of gas samples was controlled every day.\u003c/p\u003e"},{"header":"Results and discussion","content":"\u003cp\u003e\u003cstrong\u003e3.1. Characteristics of feedstock and inoculum\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe inoculum and feedstocks were significantly enhanced with natural materials needed or the co-digestion of anaerobic, as shown in Table 1. CD had the highest total solid and volatile solid (VS) values, whereas sludge solution had the lowest. The findings presented in the literature review [26, 27, 28] were in close agreement with these values. In keeping with the findings of Duman et al. [29], the results of the ultimate and proximate analyses indicated an appropriate range of organic matter to yield maximum possible hydrogen and CH\u003csub\u003e4\u0026nbsp;\u003c/sub\u003eduring each batch process.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAdditionally, the substrate and inoculum were found to have an ideal pH range that is necessary for the system to function at its best [30]. Larger carbohydrate and lower lignin concentration were found in the lignocellulosic fraction of FW, CD, and sludge solution. This is advantageous for microbial breakdown, which leads to a larger accumulation of volatile fatty acids. An analogous finding regarding the feedstock\u0026apos;s cellulose, hemicellulose, and lignin composition was validated by Xing et al. [31].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.2. Daily biogas synthesis under the influence of additives\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe microbe later exploited the volatile fatty acids that had collected throughout the hydrolysis and acidification to produce biogas. Fig. 2 shows the methanogenic reactor\u0026apos;s daily production of biogas. The degradation of organic materials in the feedstock is represented by the different peaks that are visible in the picture. While the other peaks were ascribed to the breakdown of protein, fat, etc., the first peak, which emerged after four to five days of digestion, reflects the breakdown of carbohydrates.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThis observation demonstrated that because microorganisms were more likely to distinguish carbs from other elements, the breakdown of carbohydrates happened considerably earlier [32]. In the control sample, the average daily biogas output was recorded to be 2.9 mL g\u003csup\u003e-1\u003c/sup\u003e TS. In comparison to the control reactor, it was raised by 3.4 and 4.3 mL g\u003csup\u003e-1\u003c/sup\u003e TS, respectively employing CaCO\u003csub\u003e3\u0026nbsp;\u003c/sub\u003eand CaO\u003csub\u003e2\u003c/sub\u003e. Conversely, with ZnO and CuO, it was decreased to 2.1 and 2 mL g\u003csup\u003e-1\u003c/sup\u003e TS, respectively. The daily biogas yield for CaO\u003csub\u003e2\u003c/sub\u003e and CaCO\u003csub\u003e3\u003c/sub\u003e was continuously greater than that for the control during the operation. It was consistently lower for CuO and ZnO. When water and CaO\u003csub\u003e2\u003c/sub\u003e react, intermediate products such H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e and \u0026middot;OH are released, which encourages hydrolysis and acidification and increases the amount of biogas produced [10]. In a similar vein, the addition of CaCO\u003csub\u003e3\u003c/sub\u003e significantly increased the process\u0026apos;s alkalinity and buffer capacity, which increased the buildup of volatile fatty acids [33].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eHowever, adding CuO and ZnO had a negative effect because it produced toxic Cu\u003csup\u003e2+\u003c/sup\u003e and Zn\u003csup\u003e2+\u003c/sup\u003e ions, which damage the surface of the substrates by generating sensitive oxidation species and reducing the amount of biogas generated [34]. The authors recorded the highest average daily biogas output of 5.36 mL g\u003csup\u003e-1\u0026nbsp;\u003c/sup\u003eas mentioned in the previous publication [20]. The FW is co-digested by TS using CaO\u003csub\u003e2\u003c/sub\u003e as a catalyst. Chen et al. [11] investigated the AD of sludge collected from local sewage using ZnO and CuO as conductive nanomaterials, producing the most every day.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.3. Influence of additives on cumulative biogas synthesis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe cumulative biogas synthesis trend was framed using daily production over a period of 50 days. (Fig. 3). For 35\u0026ndash;38 days, the biogas generation climbed linearly; however, after that, it practically ceased, as seen by the flat line in the Fig. 3 for days 38\u0026ndash;50. It shows that over the first 38 days, the microbes broke down the organic materials, generating the most biogas. The base sample reactor generated a total biogas output of 147.62 mL g\u003csup\u003e-1\u003c/sup\u003e TS. The same with use of CaO\u003csub\u003e2\u003c/sub\u003e and CaCO\u003csub\u003e3\u003c/sub\u003e were recorded as 217.41 and 174.02 mL g\u003csup\u003e-1\u003c/sup\u003e TS with regard to the control reactor, indicating an increase of 32.1% and 15.1%, respectively. The addition of CaO\u003csub\u003e2\u003c/sub\u003e and CaCO\u003csub\u003e3\u003c/sub\u003e increased the oxidation of the organic matter by releasing Ca\u003csup\u003e2+\u003c/sup\u003e, while the generation of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e and OH within the reacting medium increased the production of biogas [6]. In contrast to the control sample, these values were determined to be 101.25 and 111.72 mL g\u003csup\u003e-1\u003c/sup\u003e TS, with CuO and ZnO exhibiting reductions of 31.4 and 24.3%, respectively. This could be the consequence of increased toxicity brought on by the release of Cu\u003csup\u003e2+\u003c/sup\u003e and Zn\u003csup\u003e2+\u003c/sup\u003e, which limit the buildup of VFAs by rupturing the organic matter\u0026apos;s during the early phases of AD [34]. The current study\u0026apos;s findings are consistent with those of Fu et al. [10], who found that tetracycline, which inhibits microbial development during the co-digestion of maize straw and chicken dung, was effectively removed through the calculation of CaO\u003csub\u003e2\u003c/sub\u003e. In a similar vein, Zhang and Wang [15] observed enhanced biogas synthesis from the AD of FW due to a shorter lag phase with CaCO\u003csub\u003e3\u003c/sub\u003e addition. Chen et al. [11] discovered that, in comparison to the control reactor, the cumulative biogas output was reduced by 17.3% and 90.2%, respectively, when CuO and ZnO were used as nano-additives.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.4. Concentration of CH\u003csub\u003e4\u0026nbsp;\u003c/sub\u003eunder the influence of additives\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe amount of CH\u003csub\u003e4\u003c/sub\u003e in the biogas is the most imperative determinant of its quality. Biogas with a higher methane content will have a higher heating value. The methane content for each sample during a 50-day digestion period is displayed in Figure 4. Due to the hydrogenase enzyme\u0026apos;s dominant role in hydrolysis and acidification, 16.21% was found to be the maximum methane concentration. indicating very little presence at first for all samples for ten to fifteen days [35]. The methane content significantly increased as the co-digestion progressed into the methanogenic stage, peaking between 33 and 37 days of digestion. Following this, all samples, with the exception of the reactor containing CaCO\u003csub\u003e3\u003c/sub\u003e, showed a declining nature for the remainder of the period. Because of its higher alkalinity and larger buffer capacity, the reactor containing CaCO\u003csub\u003e3\u003c/sub\u003e had an earlier peak in the CH\u003csub\u003e4\u003c/sub\u003e level. The control sample had the greatest methane level, 45.63%, but CaO\u003csub\u003e2\u003c/sub\u003e and CaCO\u003csub\u003e3\u003c/sub\u003e raised the amount to 59.6% and 49.79%, respectively. This is explained by the fact that CaO\u003csub\u003e2\u003c/sub\u003e causes organic feedstock to decompose more quickly, which increases the amount of biodegradable material that can be used to ferment methane [8]. Methanogenic bacterial activity is favoured by the carbonate ion formed with CaCO\u003csub\u003e3\u003c/sub\u003e, which raises the concentration of methane [19]. Since the reactor\u0026apos;s toxicity prevents methanogenic bacteria from growing during co-digestion, the samples\u0026apos; peak methane concentrations never surpass 23.49% and 27.35%, respectively, indicating the negative effects of CuO and ZnO addition [22,36]. Furthermore, as associated with the base results, the CH\u003csub\u003e4\u003c/sub\u003e content of the generated biogas was reduced by a maximum of 36.1% when using CuO\u003csub\u003e2\u003c/sub\u003e, whereas it was raised by up to 14% when using CaO\u003csub\u003e2\u003c/sub\u003e. The results of the current study were consistent with those of previous studies. According to Fu et al. [10], methane concentrations varied between 49.4% and 66.8% as a result of variations in CaO\u003csub\u003e2\u003c/sub\u003e dosage. Salek et al. [19] demonstrated that the usage of CaCO\u003csub\u003e3\u003c/sub\u003e increased the concentration of methane by 52% due to the generation of carbonate ions. According to Cheng et al. [14], using CuO and ZnO, respectively, dramatically decreased the adenosine triphosphate content by up to 43.5 and 22.4% when cross verified with respect to the base results, which resulted in a substantial decrease in CH\u003csub\u003e4\u0026nbsp;\u003c/sub\u003eproduction.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.5. Cumulative CH\u003csub\u003e4\u003c/sub\u003e generation under the influence of additives\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe organic components in the feedstock that were broken down during the methanogenesis process boost the cumulative CH\u003csub\u003e4\u003c/sub\u003e production rate. Because of their minimal loss qualities and the fact that the microbe reused them during the methane synthesis, it was thought that the additives would not change after the initial phases of co-digestion. Fig. 5 illustrates how additives affect cumulative methane output. For all samples, continuous methane generation is seen for up to 40\u0026ndash;42 days. In the additive-free control sample, the cumulative methane output was 96.13 mL g\u003csup\u003e-1\u003c/sup\u003e TS. The CH\u003csub\u003e4\u003c/sub\u003e yield with CaO\u003csub\u003e2\u0026nbsp;\u003c/sub\u003eand CaCO\u003csub\u003e3\u0026nbsp;\u003c/sub\u003eas additive was recoded to be 40 and 25% greater, than compared to the control reactor. An intermediate product (H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e and \u0026middot;OH) was created when water and CaO\u003csub\u003e2\u003c/sub\u003e were combined, which aided in the more efficient breakdown of cellulose and hemicellulose. This resulted in the creation of more volatile fatty acids, which increased the amount of biodegradable matter for the bacterium [33]. Moreover, greater biological disintegration during the methane fermentation was the consequence of the anaerobic digestion with CaO\u003csub\u003e2\u003c/sub\u003e and CaCO\u003csub\u003e3\u003c/sub\u003e\u0026apos;s increased buffer capacity and alkalinity [10]. Compared to the control sample, the methane yield with CuO and ZnO was 35% and 21% lower, respectively, at 62.65 and 76.23 mL g\u003csup\u003e-1\u003c/sup\u003e TS. Lower methane yield was mostly caused by greater toxicity brought on by the release of Cu\u003csup\u003e2+\u003c/sup\u003e and Zn\u003csup\u003e2+\u003c/sup\u003e ions. This was because the feedstock\u0026apos;s microbial activity and volatile fatty acid production were suppressed [37]. The literature review previously reported similar findings. According to Wang et al. [8], the cumulative methane output from sewage sludge with different proportions of CaO\u003csub\u003e2\u003c/sub\u003e ranged from 146.3 to 215.9 g g\u003csup\u003e-1\u003c/sup\u003e volatile suspended solids (VSS). Luna-delRisco et al. [38] found that utilizing varying dosages of CuO reduced methane generation from sewage sludge and calf dung by 19% to 60%. According to observations of Mu et al. [22], the highest cumulative CH\u003csub\u003e4\u003c/sub\u003e generation from the AD of activated sludge was 99.5 mL g\u003csup\u003e-1\u003c/sup\u003e VSS, reduced by 22.8% with respect to the base results.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.6. Influence of the additives on hydrogen concentration\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFig. 6 displays the trend of change in concentration of hydrogen due to additive additions. All of the samples\u0026apos; hydrogen fermentation was completed in the first 8\u0026ndash;10 days, with the highest concentration occurring in the first 3\u0026ndash;5 days of digestion. It suggests that the hydrogenase enzyme\u0026apos;s microbial activity was significant during the hydrolysis and acidification processes, which caused the organic matter to decompose quickly. The control sample\u0026apos;s maximum hydrogen content was 17.3% on the fifth day of co-digestion. Over the same time period, the value was raised by 26.34, 19.37, 19.86, and 20.72%, respectively, by CaO\u003csub\u003e2\u003c/sub\u003e, CuO, ZnO, and CaCO\u003csub\u003e3\u003c/sub\u003e. The biggest improvement with CaO\u003csub\u003e2\u003c/sub\u003e was 9% but with CuO as the additive, the least enhancement was nearly comparable to the control reactor. During the AD process, it was found that adding additives increased the hydrogen content overall when compared to the control reactor. This could be because the additives\u0026apos; increased microbial activity leads to a better breakdown of the feedstock. The increased hydrogen content in the presence of CaO\u003csub\u003e2\u003c/sub\u003e is caused by the release of OHˉ and \u0026middot;O\u003csub\u003e2\u003c/sub\u003eˉ together with alkali, which jointly encourage the formation of amino acids and improved substrate breakdown during AD [35]. The addition of CaCO\u003csub\u003e3\u003c/sub\u003e enhanced the system\u0026apos;s buffer capacity, which ensued in a minor rise in hydrogen concentration, but not as much as CaO\u003csub\u003e2\u003c/sub\u003e [18]. The study\u0026apos;s results were consistent with other findings that had already been reported in the literature. Hydrogen concentrations ranged from 12% to 26% when FW was digested anaerobically, according to Wainaina et al. [39].\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.7. Influence of the additives on cumulative hydrogen synthesis\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe total hydrogen production in the presence of CaO\u003csub\u003e2\u003c/sub\u003e and CaCO\u003csub\u003e3\u003c/sub\u003e reactors was higher than that from the base inoculum, despite the fact that the reactors that received CuO and ZnO additions produced less hydrogen overall (Fig. 7). It illustrates how the toxicity caused by the use of CuO and ZnO as additive led to a decrease in hydrogen generation during the operation. The total amount of hydrogen produced by the control reactor after 25 days was 105.59 mL g\u003csup\u003e-1\u003c/sup\u003e TS. It reduced to 96.6 and 94.84 mL g\u003csup\u003e-1\u003c/sup\u003e TS in presence of ZnO and CuO as additive respectively, while presence of CaO\u003csub\u003e2\u003c/sub\u003e and CaCO\u003csub\u003e3\u003c/sub\u003e the hydrogen content augmented to 115.59 and 109.58 mL g\u003csup\u003e-1\u003c/sup\u003e TS respectively. The addition of ZnO depicted a maximum reduction of 10.4%, whereas CaO\u003csub\u003e2\u003c/sub\u003e increased the production of hydrogen by 8.6%. The hike in hydrogen synthesis with CaO\u003csub\u003e2\u003c/sub\u003e is caused by the creation of alkali, \u0026middot;OH, and \u0026middot;O2ˉ, which enhanced the acidity and there by accelerating the hydrolysis process to augment hydrogen synthesis [40]. Furthermore, adding CaCO\u003csub\u003e3\u003c/sub\u003e upsurges the alkalinity of the inoculum and upholds the pH value at the optimal range, which promotes the growth of hydrogenase bacteria and increases the output of hydrogen [16]. Though Cu\u003csup\u003e2+\u003c/sup\u003e and Zn\u003csup\u003e2+\u003c/sup\u003e have higher toxicity, CuO and ZnO occupy the microbial development within the inoculum, resulting in decrease in hydrogen synthesis [38]. The maximal cumulative hydrogen synthesis from wheat straw was determined to be 114 mL g\u003csup\u003e-1\u003c/sup\u003e TS, which is comparable to the quantity obtained in the current investigation [6].\u0026nbsp;\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eWhile CuO and ZnO reduced the biogas synthesis, CH\u003csub\u003e4\u003c/sub\u003e, and hydrogen fermentation processes of AD process, the addition of CaO\u003csub\u003e2\u003c/sub\u003e and CaCO\u003csub\u003e3\u003c/sub\u003e enhanced these processes in comparison to the control reactor. It was shown that adding CuO and ZnO reduced the biogas generation by 31.4% and 24.3%, respectively, while adding CaO\u003csub\u003e2\u003c/sub\u003e and CaCO\u003csub\u003e3\u003c/sub\u003e raised it by 32.1% and 15.1%, respectively, when compared to the control sample. Additionally, methane production decreased by 35% and 21% with CuO and ZnO, respectively, but augmented by 40% and 25% with CaO\u003csub\u003e2\u003c/sub\u003e and CaCO\u003csub\u003e3\u003c/sub\u003e. Furthermore, the addition of ZnO decreased the hydrogen generation by 10.4% while the addition of CaO\u003csub\u003e2\u003c/sub\u003e increased it by 8.6% when compared to the control. Additionally, the digestate's physicochemical characterization during anaerobic co-digestion revealed a developed nutrient composition that can be used as improved fertilizer. Ultimately, it can be concluded that while the use of CuO and ZnO as additives during the co-digestion process had the opposite effect, the inclusion of CaO\u003csub\u003e2\u003c/sub\u003e and CaCO\u003csub\u003e3\u003c/sub\u003e enhanced the fermentation of CH\u003csub\u003e4\u003c/sub\u003e and hydrogen. It is recommended that future studies evaluate the AD process using other substrates or the synergistic effect of adding many additives to improve efficiency of AD process.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors acknowledge the support received from the Alternative Fuel and Energy Lab of S \u0026lsquo;O\u0026rsquo;A deemed to be University.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eConceptualization and design of the experiments, CD, and SPJ; analysis of the data, writing\u0026mdash;the original draft, CD and SM; visualization, reviewing and editing, SPJ and SKA; \u0026nbsp;All authors have read and agreed to the published version of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors have not received any fundings from any source for this research work.\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\u003eCompeting of interest\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they do not have any competing interest.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eMelikoglu M, Lin CSK, and Webb C. 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Journal of hazardous materials. 2011; 189(1-2): 603-608. https://doi.org/10.1016/j.jhazmat.2011.02.085\u003c/li\u003e\n\u003cli\u003eWainaina S, Awasthi MK, Horv\u0026aacute;th IS, and Taherzadeh MJ. Anaerobic digestion of food waste to volatile fatty acids and hydrogen at high organic loading rates in immersed membrane bioreactors. Renewable Energy. 2020; 152: 1140-1148. https://doi.org/10.1016/j.renene.2020.01.138\u003c/li\u003e\n\u003cli\u003eLi Y, Wang J, Zhang A, and Wang L. Enhancing the quantity and quality of short-chain fatty acids production from waste activated sludge using CaO\u003csub\u003e2\u003c/sub\u003e as an additive. Water research. 2015; 83: 84-93. https://doi.org/10.1016/j.watres.2015.06.021\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Methane, hydrogen, biogas, digestate, anaerobic co-digestion","lastPublishedDoi":"10.21203/rs.3.rs-5841927/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5841927/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIn order to co-digest food waste along with cow dung to produce hydrogen and methane, the effects were experimentally assessed in distinct batch reactors for calcium carbonate (CaCO\u003csub\u003e3\u003c/sub\u003e), copper oxide (CuO), zinc oxide (ZnO), and calcium peroxide (CaO\u003csub\u003e2\u003c/sub\u003e) as additives in this study. The maximum hydrogen generation using CaO\u003csub\u003e2\u003c/sub\u003e was found to be 115.59 mLg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e total solid (TS), which was 8.6% lead by the standard specimen with no additives. In contrast, ZnO reduced lead by 10.4%. In comparison to the control sample, the generation of methane was 161.2 and 129.06. mLg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003eTS, showing a 40 and 25% increase with CaO\u003csub\u003e2\u003c/sub\u003e and CaCO\u003csub\u003e3\u003c/sub\u003e, whereas it dropped to 62.65 and 76.23 mLg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e TS, depicting a 35 and 21% decrease with CuO and ZnO respectively. The addition of CaO\u003csub\u003e2\u003c/sub\u003e and CaCO\u003csub\u003e3\u003c/sub\u003e increased biogas generation by 32.1 and 15.1%, respectively, while the addition of CuO and ZnO decreased it by 31.4 and 24.3%. Ultimately, the digestate's physicochemical characteristics showed an improvement in organic nutrients following co-digestion, making it a useful biofertilizer for use in agriculture.\u003c/p\u003e","manuscriptTitle":"Synergetic influence of different additives on hydrogen and methane generation from food waste","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-01-20 03:52:11","doi":"10.21203/rs.3.rs-5841927/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"2efaa6ce-5015-434b-a68d-4788837a7625","owner":[],"postedDate":"January 20th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-01-28T06:23:25+00:00","versionOfRecord":[],"versionCreatedAt":"2025-01-20 03:52:11","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5841927","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5841927","identity":"rs-5841927","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}