UV-A based photocatalytic disinfection of secondary effluent from a wastewater treatment plant using Ag-ZnO: Effect of antibiotic presence, catalyst concentration, lamp and persulfate addition

UV-A based photocatalytic disinfection of secondary effluent from a wastewater treatment plant using Ag-ZnO: Effect of antibiotic presence, catalyst concentration, lamp and persulfate addition | 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 UV-A based photocatalytic disinfection of secondary effluent from a wastewater treatment plant using Ag-ZnO: Effect of antibiotic presence, catalyst concentration, lamp and persulfate addition Dinkar Parashar, Gopal Achari, Mathava Kumar This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6790617/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 this study, applicability of UV-A based photocatalytic disinfection of secondary effluent from a sewage treatment plant (STP) was investigated. Three bacterial strains from the biological treatment effluent namely Stenotrophomonas nematodicola, Frediandcohnia salidurans and Shigella felxneri were isolated, cultured and plated for further experiments in the presence of a model antibiotic, metronidazole (MNZ). Silver doped zinc-oxide (Ag-ZnO) and titanium di-oxide (TiO 2 ) were used as photocatalysts for the disinfection experiments where the former showed better disinfection kinetics under UV-A lamp. Out of the three microbial strains, Shigella flexneri strain showed maximum resistance towards photocatalytic disinfection. Increasing the catalyst dose to 3 g/L increased the disinfection kinetics. However, above 3 g/L, the rate of disinfection decreased due to agglomeration of nano-catalysts, and the increase in residual turbidity. Effect of shigella flexneri concentration showed that disinfection kinetics decreased with increase in bacteria concentration from 1x10 4 to 1x10 9 CFU/mL. In 2 and 3 h, complete removal of 1x10 6 and 1x10 8 CFU/mL was achieved under optimum conditions respectively. In visible region, the activity decreased slightly with a decrease in pseudo-first-order kinetics by ~1.9 times because of the polychromatic visible light. Further, the addition of persulfate in small amount of 200 mg/L increased the disinfection kinetics by ~1.5 times due to generation of persulfate radicals. The presence of MNZ with the shigella flexneri showed that there was a decrease in removal efficiency for both the antibiotic and bacteria with both photocatalysts. This was caused by the competitive antagonistic effect between the antibiotic and bacteria for the reactive oxygen species generated on the photocatalyst surface. Overall, Ag-ZnO showed good photocatalytic disinfection towards wastewater microbes under UV-A. Photocatalytic disinfection wastewater treatment antibiotic removal disinfection kinetics Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 1. Introduction Water borne diseases due to microbial contamination has been increasing over the decades. As per the World Health Organisation (WHO) report, around 2.2 million people die globally because of waterborne diseases and nearly one billion individuals globally lack access to safe water sources (Yao et al. 2024 , Yang et al. 2023 ). Anti-microbial resistance (AMR) is becoming a major concern with around 700,000 deaths occurring due to it per year (Yang et al. 2023 ). Moreover, around 20 lakhs death are predicted to occur in India alone by 2050 because of AMR (Sasikaladevi et al. 2020 ). It has been noted that conventional biological treatment in wastewater treatment plants is not able to completely remove these AMR bacteria and genes (Li et al. 2020 ). Conventional disinfection technologies such as chlorination, ozonation and UV light irradiation while being effective, have certain challenges such as high cost, carcinogenic by-product formation, incomplete microbial inactivation, microbial reactivation after disinfection, increased bacterial resistance, and high energy consumption. Hence, there is a need to research and develop a more effective disinfection technology that can address some of the concerns. Advanced oxidation processes (AOP), with their strong oxidative radicals can completely disinfect and kill a wide range of microbes. Among these photocatalysis has been extensively studied and has promises of being efficient (Qiu et al. 2023 , Yang et al. 2023 , Xia et al. 2016 ). In 1985, the first photocatalytic disinfection study was reported (Matsunaga et al., 1985 ). They used platinum-doped TiO 2 as photocatalysts. After that continuous development and research has led to disinfection via photocatalysis. Photocatalysts which have been reported for the degradation of microbes include TiO 2 (Kumaravel et al. 2021 ), ZnO (Brindha et al. 2024 ), Cu 2 O (Arasavilli et al. 2024 ), g-C 3 N 4 (Yang et al. 2023 ), BiVO 4 (Ye et al. 2021 ) and In 2 O 3 (Chen et al. 2024 ). Among these TiO 2 and ZnO have been identified as leading photocatalysts because of their comparatively high activity, unique band-gap and excellent stability (Parashar et al. 2024 , Parashar et al. 2023 , Zhu and Zhou. 2019). However, single semiconductor photocatalysis has certain drawbacks such as high charge recombination and less stability causing less recyclability. Doping with noble metals is a way to improve single semiconductor photocatalytic activity (Kanakaraju et al. 2022 ). Silver has been identified as a good dopant because of its unique Fermi level, high surface plasmon resonance capability and efficient charge separation ability (Xue et al. 2020 ). The present study explores the disinfection potential of AMR microbes using silver doped ZnO and compares it with that of TiO 2 . To the best of our knowledge, almost all the research work are being conducted on E. coli or other major indicator organisms. It is worth pointing out that the absence of E. coli does not ensure that water is pathogen free. To the best of our knowledge, there have been no studies that have reported on disinfection of anti-microbial resistant microbes in real wastewater. Moreover, the disinfection of microbes varies from strain to strain and knowing the potential of treatment technologies for the environmentally found microbial strains is necessary. The aim and novelty of the current study is to identify the major microbes present in treated wastewater effluents which reach the water bodies, and to estimate the extent of their disinfection via photocatalysis. 2. Materials and methods The antibiotic, i.e., MNZ (C 6 H 9 N 3 O 3 ), zinc acetate and silver nanoparticles were purchased from Sigma Aldrich®. Sodium hydroxide pellets (97% purity) were purchased from Merck India®. Ethanol was purchased from Hayman®, UK. Acetonitrile (HPLC grade) was purchased from Rankem®, India. Luria broth and Agar-agar were supplied from SRL and HIMEDIA brand respectively. All chemicals were of analytical grade and were used as such. UV-A lamps (8 W, Phillips, Poland), were purchased from a hardware store in Chennai, Tamil Nadu, India. Distilled water was used to make the antibiotic solution for all the experiments. Sterilization for all the materials for disinfection experiments were done in 120 o C autoclave at the heating rate of ~ 3 o C/min and at 1 kg/cm 2 pressure for 20 min (Krithish Scientific Company). Bacterial strain identification was done using 16 s ribosomal RNA sequencing (Applied Biosystems). 2.1. Catalyst preparation The catalyst was prepared by thermal decomposition method, as reported in our previous work (Parashar et al. 2024 ). In brief, ZnO was first prepared by grinding zinc acetate using mortar and pestle to make it a fine powder. The fine powder was thermally heated in an alumina crucible in a muffle furnace at 500 o C for 3 h at a heating rate of 15 o C/min. Silver doping in ZnO was done by mixing silver nanoparticles before keeping in muffle furnace. 40% by weight of zinc in zinc acetate was mixed with zinc acetate which had given the best results in our previous study. The mixture was then ground in mortar and pestle followed by annealing in muffle furnace at 500 o C for 3 h. Finally, the catalyst was further ground obtain a uniform powdered catalyst. For comparison with TiO 2 , pure anatase nanoparticles were used (Parashar et al. 2023 ). 2.2. Experimental set-up The experimental set-up consisted of 5 monochromatic UV-A lamps (each of 8 W) having maximum wavelength of 367 nm were placed at the top of reactor. A magnetic stirrer with a glass beaker of 100 mL capacity is placed at the bottom. At the back a cooling fan was provided to dissipate the heat generated in UV-A lamps and to maintain constant working temperature during the experiment. For comparison purposes, visible lamps were also used. For this, 8 visible lamps each 5 W were placed. The wavelength spectra of both the lamps and the schematic diagram of the reactor are provided as supplementary information (Fig. S1 and Fig. S2). 2.3. Microbe culture The IIT Madras sewage treatment plant with a sequential batch reactor (SBR) as secondary treatment unit, treats the domestic sewage generated on campus. Sludge sample was obtained after the SBR treatment. A schematic of the plant and the sampling location is shown in Figure S3. The sample was then cultured in glass petri plates with appropriate dilutions. The antibiotic MNZ was added to the nutrient media to make sure only antibiotic-resistant genes grow. From the culture, three isolated colonies were taken using nichrome wire inside a horizontal air flow laminar hood. These isolated colonies were cultured in separate petri dishes. Further to ensure pure bacterial colonies, the single colonies were cultured in subsequent three glass test tubes and in three glass petri plates. From the final cultured petri dish, bacterial screening analysis was conducted to identify the strain of bacteria present. All subsequent experiments were conducted using pure single strain colonies. All experimental work were conducted inside the horizontal air flow laminar hood near the flame inside the hood to minimize any type of outside contamination. 2.4. Disinfection study Milli and micro pipette tips, centrifuge tips, bacteria culturing nutrient media and solid nutrient media for petri dish plating, as well as the saline solution were all sterilised in the autoclave before initiating any experiment. For the photocatalytic disinfection experiments, initial bacterial concentration of 10 8 CFU/mL was taken by checking the optical density at 600 nm (OD 600 ). A working volume of 20 mL was placed in a 100 mL glass beaker. The catalyst was then added and mixed thoroughly with the bacterial culture by stirring. The samples were then irradiated. Samples were taken at appropriate time interval and were plated on sterilised plastic petri dishes using spread plating method. Samples were serially diluted in saline solution (0.85–0.9% NaCl solution). 80 µL of the serially diluted sample was inoculated on nutrient agar plates and incubated in BOD incubator for 24 h at 37 o C. Colonies formed were counted manually with a colony counter. Colonies forming unit (CFU) per unit sample volume (mL) was calculated according to Eq. ( 1 ). $$\:CFU/mL\:=\:\:\frac{Number\:of\:colonies\:X\:Dilution\:factor}{Volume\:inoculated\:on\:plate}$$ 1 The kinetic results were fitted using the pseudo-first-order kinetic model as shown in Eq. ( 2 ). $$\:\text{ln}\left(\frac{{C}_{t}}{{C}_{o}}\right)=\:-\text{k}\text{*}\text{t}$$ 2 where, C t and C o are the number of colonies at time t and at time 0. k is the pseudo-first-order kinetic rate constant. For the analysis of MNZ, liquid chromatography mass spectroscopy (LC-MS) was used (Agilent Technologies 1260 Infinity coupled with 6120 Quadrapole). Mobile phase for analysing MNZ was a mixture of millipore water and acetonitrile in the ratio of 70:30. The mobile phase was send into the column at a flow rate of 0.4 mL/min. The calibration plot for antibiotic MNZ with different concentration in the LC-MS instrument is shown in Fig. S4. 3. Results and discussion 3.1. Sequencing analysis of microbial strains The three isolated bacterial strains were cultured separately in pure media. The media was having MNZ antibiotic to make sure only ARB will grow on it. Furthermore, single colonies were taken from each of the three petri plates and was streaked on new plates. This procedure was repeated six consecutive times to obtain pure isolated colonies. 16s ribosomal RNA sequencing was conducted on the three bacterial strains. The analysis results matched more than 99% with the database library. The blast results showed the three strains as Stenotrophomonas nematodicola, Frediandcohnia salidurans and Shigella felxneri . All three strains were studied under a microscope to analyse the surface texture of their colonies. The microscopic image of the three pure colonies is shown in Fig. S5. All three colonies were almost spherical with Stenotrophomonas nematodicola showing hairy structure on its surface. Very less research information is available for the disinfection of these three strains present in the environment. However, Stenotrophomonas specie is chlorine tolerant and is observed in treated wastewater (Shekhawat et al. 2021 ). Shigella felxneri is commonly present in wastewater and has been reported as having resistance to multiple antibiotics (Ahamed et al. 2019 , Mecha et al. 2019 , Mecha et al. 2017 ). Further, this strain is also resistant to very low pHs (Rahman et al. 2020 , Zaika. 2001). 3.2. Bacterial species disinfection using TiO 2 and Ag-ZnO For comparison study, all three bacterial strains namely Stenotrophomonas nematodicola , Frediandcohnia salidurans and Shigella felxneri were first tested for photocatalytic disinfection studies under UV-A light using Ag-ZnO catalyst. The disinfection curve and pseudo-first-order kinetic curve are shown in Fig. 1 , and the log-reduction values at various times has been presented in Table 1 . The pseudo-first-order kinetic rate obtained for the three strains were 0.082, 0.074 and 0.055 min − 1 respectively under similar experimental conditions. Shigella flexneri was found to be the most difficult to disinfect. The reason maybe the strain has been shown to develop multi-drug resistance and has stability over a wide pH range and temperature, which makes it more difficult to kill compared to other two strains (Rahman et al. 2020 , Ahamed et al. 2019 ). Henceforth, further experiments were conducted on shigella flexneri strain bacteria. TiO 2 was studied for knowing its disinfection potential for the shigella flexneri strain and for its comparison with Ag-ZnO. The result is shown in Fig. 2 . Photolysis using UV-C lamp showed good removal of 0.5 log within the first 30 min. However, after the initial log reduction, there was slow bacterial degradation and only 0.9 log removal was noted after 180 min. Further, under similar experimental conditions, it was noted that Ag-ZnO showed better disinfection than TiO 2 . This is because of the efficient charge separation in Ag-ZnO with silver acting as charge separator which decreased the charge recombination in ZnO. In case where TiO 2 was used with no dopant similar result was also obtained. Table 1 Log reduction of three bacterial strains using Ag-ZnO at different time intervals and the pseudo-first-order kinetic rate constant Bacteria Log reduction Kinetic rate obtained (min − 1 ) 0 min 30 min 60 min 90 min 120 min Stenotrophomonas nematodicola 0 0.6 2.0 3.3 4.4 0.082 Frediandcohnia salidurans 0 1.7 1.8 2.4 4.1 0.072 Shigella felxneri 0 0.5 1.7 2.2 2.7 0.055 3.3. Control experiments on shigella flexneri Ag and Ag-ZnO were tested for the bacterial strain shigella flexneri in presence and in absence of UV-A light. The results are presented in Fig. 3 . It was observed that bacterial disinfection was higher while using Ag alone compared to Ag-ZnO composite. The reason being Ag has higher disinfection activity than ZnO because of its interaction and uptake inside the bacteria cells and as it attaches itself to cell membranes causing cell disruption and death. The doping of Ag inside ZnO lattice causes less Ag available for disinfection. This caused a decrease in activity of Ag-ZnO when compared to Ag alone (Fabrega et al. 2009 ). However, photocatalysis with Ag-ZnO under UV-A light gave considerably higher activity than without light because of the generation of reactive oxygen species (ROS) which have a high potential for microbial disinfection. The pseudo-first-order rate constant for Ag, Ag-ZnO and Ag-ZnO in UV-A light were 0.031, 0.018 and 0.055 min − 1 , respectively. 3.4. Effect of initial bacterial concentration on bacterial disinfection Shigella flexneri with different initial concentration was further tested for photocatalytic activity using Ag-ZnO under similar experimental conditions. The results obtained is presented in Fig. 4 . It was observed that with an increase in initial bacterial concentration, there was a decrease in kinetic rate, as evident from the steep slope of the curves shown in Fig. 4 . The reason behind this is that with an increase in bacterial concentration, the number of radicals available is less and hence the lower disinfection. In addition, there is a decrease in light penetration inside the solution because of increase in turbidity of solution. 3.5. Effect of catalyst dosage on rate of bacterial disinfection The effect of varying catalyst dosage was investigated and the results are presented in Fig. 5 . The results indicate the disinfection activity increased with increase in catalyst dosage. This is expected as a higher catalyst dosage leads to an increased generation of reactive radicals. However, above a 3 g/L dosage, a decrease was observed in the disinfection activity. This was due to agglomeration of the nanoparticles in the solution leading to a decrease in total active surface area. Additionally, an increase in catalyst dosage led to an increase in turbidity of solution causing a decrease in light penetration inside the solution. This caused less light incidence on the catalyst surface and consequently lower activity. (Ch-Th et al. 2021 ). The pseudo first-order kinetic rate constant for different catalyst dosage is included in Table 2 . Table 2 Pseudo first-order kinetic rate constant for bacterial disinfection with different catalyst dose Catalyst dose Kinetic rate (min − 1 ) 0.5 0.032 1 0.059 2 0.094 3 0.126 4 0.094 3.6. Effect of persulfate addition on rate of bacterial disinfection In recent studies the use of persulfate (PS) has attracted significant attention because of production of high redox potential specie generation. PS radicals have higher redox potential and longer half-life than hydroxyl radical (Ekande and Kumar. 2021). However, the generation of sulphate ions after the study creates secondary pollution. To overcome this, PS addition in amounts of 200 mg/L which is within the permissible limit of Indian standard code was used (BIS 10500. 2012). The results are shown in Fig. 6 . Interestingly, in the first 15 min there was an increase in the bacterial disinfection. The increase in pseudo-first-order kinetics was about 1.5 times (Fig. 6 c). The reason for this increment is the generation of PS radicals (see Eq. 3–6), which along with hydroxyl radicals improved the disinfection activity (Parashar et al. 2023 , Ekande and Kumar, 2021 ). PS radicals can generate hydroxyl radicals either by production of hydrogen peroxide or by reacting with water or hydroxide anions (Waclawek et al. 2017 ). However, after the initial 15 min, there was a slight decrease in the bacterial disinfection. This is due to the quick generation of PS radicals in the beginning which enhanced the bacterial decay rate. However, after a certain period, the generation of PS radicals stopped because of its low concentration. Furthermore, the generated sulphate ions from bacterial oxidation caused by PS radicals interfered with hydroxyl radicals thereby decreasing further bacterial disinfection. This is evident from the later part of curve shown in Fig. 6 b. S 2 O 8 2− + e − → SO 4 − . + SO 4 − (3) SO 4 −. + OH − /H 2 O → OH. + SO 4 2− (+ H + ) (4) S 2 O 8 2− + 2 H 2 O → 2 SO 4 2− + OOH − + 3 H + (5) S 2 O 8 2− + OOH − → SO 4 −. + SO 4 2− + H + + O 2 −. (6) 3.7. Effect of visible light on rate of bacterial disinfection Maximum spectrum of sunlight falls under the visible region of 400–700 nm. For this reason, visible light was studied under similar conditions to check the efficiency of catalyst in visible region. The visible lamp used in the present study had two major peaks mainly, a narrow peak at 454 nm and a broad peak at 532 nm. The lamp was polychromatic covering full visible region spectrum from 400 to 700 nm. The comparison between visible and UV-A lamp is shown in Fig. 7 . Compared to UV-A lamp, the activity of visible lamp was ~ 1.9 times lesser (Fig. 7 c). The reason was, UV-A lamp being monochromatic had a high energy of 3.37 eV which was greater than the band gap of ZnO (3.1 eV) (Parashar et al. 2024 ).The lamp being monochromatic produced high intensity at 367 nm causing better generation of charges in ZnO as compared to visible polychromatic light. Interestingly, there was good activity seen in visible light as well, although, the energy corresponding to the 2 major peaks are 2.73 and 2.33 eV, respectively. This photon energy is not sufficient to generate charge separation in ZnO because of its higher band gap of 3.1 eV. The activity observed in the present study is due to surface plasmon resonance (SPR) effect of silver nanoparticles in visible region. Depending on the need of semiconductor, Ag nanoparticles can either behave as charge separator or shows SPR (Ye et al. 2012 ). In the present case, ZnO can’t get excited by visible light and so, the generation of charges occur in Ag nanoparticles by the visible light. The electron generated on Ag surface got separated into the CB of nearby ZnO causing efficient ROS formation and disinfection. 3.8. Simultaneous treatment for MNZ destruction and bacterial disinfection 3.8.1. Under TiO 2 photocatalysis Removal of MNZ and bacteria in a mixture was studied using the catalyst TiO 2 and the results obtained are shown in Fig. 8 a and b. Removal of MNZ was having an antagonistic effect by the presence of bacteria i.e. the removal was antibiotic was negatively affected because of the presence of bacteria. It is due to competition by the bacteria for the generated ROS. Similar results were obtained for bacterial disinfection also. The removal of bacteria was also negatively affected by the presence of antibiotic. In the beginning of 30 min there was an increase in removal, however overall there was a decrease in the bacterial disinfection. Similar kind of behaviour have been observed previously in case of multi-antibiotic conditions (Parashar et al. 2023 ). Similarly, antagonistic behaviour with TiO 2 was seen for the removal of antibiotics and bacteria presence together (Jimenez-Tototzintle et al. 2018 , Moncayo-Lasso et al. 2012 ). 3.8.2. Under Ag-ZnO photocatalysis Removal of MNZ was affected by the presence of bacteria as shown in Fig. 8 (c). However, the removal efficiency was higher than when TiO 2 was used. This showed that the activity of Ag-ZnO was better than TiO 2 . The reason for increase in activity of Ag-ZnO compared to TiO 2 has been discussed earlier in section 3.2 . In case of multi-component, the decrease in removal of antibiotic was mostly because of the competitive effect of bacteria, which consumed the generated radicals leading to less availability of radicals for MNZ to get oxidized. Similarly, the removal of Shigella flexneri was affected by the presence of MNZ. However, the antagonistic effect felt by bacteria was less compared to MNZ as evident in Fig. 8 (d). This is because of higher concentration of bacteria compared to MNZ. Similar antagonism has been observed in a previous work (Rahman et al. 2020 ). 3.9. Disinfection mechanism The disinfection of shigella flexneri at different time interval is shown in Fig. 9 . The figure shows the plating of microbial sample at different time intervals with appropriate dilutions. As seen in Fig. 9 g, complete bacterial removal occurred in 180 min. Cell membrane rupture has been reported to be the mechanism for bacterial disinfection (Xia et al. 2017 ). The primary mechanism involved in the bacterial disinfection is outer cell wall distortion by the generated radicals on photocatalyst surface. Shigella flexneri being a gram-negative bacteria is characterized by a thin outer membrane made up of polysaccharides. The reactive oxygen species (ROS) generated on catalyst surfaces having very high redox potential, causes the disintegration of thin cell membranes (Rahman et al. 2020 ). This is followed by intracellular organelles coming out of the cell causing microbe killing (Brindha et al. 2024 ). Moreover, the photocatalyst can also stick on the bacterial surface by cell proliferation and endocytosis. This will also cause cell death through cell membranes rupture by organ permeability (Baaloudj et al. 2021 ). As reported in our earlier work, in the UV region, maximum photocatalytic degradation occurs by hydroxyl radicals followed by superoxide radicals and then by holes (Parashar et al. 2024 ). Silver in UV light act as both SPR and as charge separator to effectively generate ROS which easily disinfects the microbes. However, in the study conducted with the visible light having wavelength spectra in only visible region, zinc oxide can’t produce reactive radicals because of large band gap. However, silver nanoparticles showing SPR effect in visible region is responsible for the generation of radicals and causing disinfection. The proposed disinfection mechanism under UV and visible light is shown in Fig. 10 . 3.10. Comparison with previous major studies Most of the disinfection studies had been conducted on E. coli or some indicator organism. Very few studies have been conducted on bacterial strains present in treated wastewaters. Table 3 shows a comparison study on bacterial disinfection work done in the recent past. As observed from the table, the presently obtained kinetic rate constant was higher compared to most of other studies. The present study was conducted on less power lamp compared to other studies. Still the kinetic rate obtained was comparable and higher than most of the studies. The major reason for this was the usage of monochromatic lamp for the excitation of ZnO, whose band-gap is close to the wavelength of light used. Another reason is the proper design of reactor and usage of aluminium foils in the inner walls which facilitates maximum light to remain in the reactor through internal reflection. Shigella flexneri had been studied by a number of authors earlier. Silver, copper and iron doped TiO 2 had been studied under UV light for this strain (Mecha et al. 2019 ). The maximum obtained kinetic rate was 0.067 min − 1 for all the three dopants. The reason for a decrease in the results compared to the silver doped ZnO is because the catalyst synthesis technique. MWCNT/BiVO 4 had been studied and was found to completely disinfect Shigella flexneri in 180 min (Ye et al. 2021 ). However, the kinetic rate had not been mentioned. Moreover, the study used solar power which had higher power compared to the present study. ZnO/ Gypsum @ alginate beads was also studied (Misra et al. 2022 ). Five log removal was observed in 120 min. However, the lamp power and kinetic removal rate were not discussed. Studies on other strains had showed lesser kinetic rate constant as observed in Table 3 . Although the previous work had been conducted at high lamp power, their reaction rate constant and bacterial removal was less than that reported here. Heterostructure formed from g-C 3 N 4 quantum dots combined with g-C 3 N 4 nanosheets had been studied for Staphylococcus aureus (Yang et al. 2023 ). The work was conducted at higher lamp power, however, complete disinfection was not achieved in 120 min. Similarly, lanthanum doped CeO 2 had been studied for Bacillus licheniformis (Chatterjee et al. 2023 ). However, the results obtained were not up to the mark. E. coli studied by other authors in past by various catalysts had not shown remarkable photo catalytic activity. The composite CeO 2 and g-C 3 N 4 had showed 7 log removal of E. coli in 180 min (Huang et al. 2021 ). G-C 3 N 4 alone showed 5 log removal in 120 min (Zhang et al. 2021 ). However, the power requirement was very high. Similarly, GO-TiO 2 -BiVO 4 showed 3 log removal in 180 min (Ch-Th et al. 2021 ). Sulphur doped carbon quantum dot with gC 3 N 4 showed very good activity under visible light (Wang et al. 2019 ). Ag doped ZnO nanorods prepared by solvothermal- co-precipitation method showed about 2 log removal in 120 min (Brindha et al. 2024 ). This showed the superiority of prepared photo-composite by the present method. In conclusion, the present study on microbes found in real environmental water samples had been closer to practical field applications and the obtained results were superior than the previous results reported. Table 3 Photocatalytic comparison of Ag-ZnO with other commonly reported photocatalysts in the recent past. Photocatalyst Microbe specie Lamp (Power) Catalyst dose (g/L) Bacteria initial conc. (CFU/mL) Time taken (min) Bacteria Log removal Kinetic rate (min − 1 ) Ref Ag-TiO 2 Shigella flexneri UV (150 W) 0.5 10 6 60 6 0.067 Mecha et al. 2019 MWCNT/BiVO 4 Shigella flexneri Solar power 0.5 10 7 180 7 - Ye et al. 2021 ZnO/ Gypsum @ alginate beads Shigella flexneri Visible LED 3 10 5 120 5 - Misra et al. 2022 g-C 3 N 4 quantum dots- g-C 3 N 4 nanosheets Staphylococcus aureus Visible (350 W) 2 3*10 6 120 5.3 - Yang et al. 2023 La- CeO 2 E. coli Visible 4 10 7 150 4.3 - Chatterjee et al. 2023 Bacillus licheniformis Visible 4 10 7 150 5.3 - CeO 2 / g-C 3 N 4 E. coli (K-12 strain) Visible (300 W) 0.2 10 7 180 7 0.085 Huang et al. 2021 g-C 3 N 4 E. coli Visible (300 W) 0.1 (PMS = 0.15 g/L) 10 5 120 5 - Zhang et al. 2021 GO-TiO 2 -BiVO 4 E. coli (K-12 strain) Solar simulator light (500 W/m 2 ) 1.05 10 7 30 3 - Ch-Th et al., 2021 S- carbon quantum dot- gC 3 N 4 E. coli Visible (300 W) 0.6 3*10 7 40 6.88 0.029 Wang et al. 2019 Ag-ZnO E. coli Simulated sunlight (150 W) 0.05 - 120 1.98 0.027 Brindha et al. 2024 TiO 2 Shigella flexneri UV-A (40 W) 1 10 8 180 3.7 0.045 Present study Ag-ZnO Stenotrophomonas nematodicola UV-A (40 W) 1 10 8 120 4.4 0.082 Frediandcohnia salidurans UV-A (40 W) 1 10 8 120 4.1 0.074 Shigella flexneri UV-A (40 W) 3 10 8 180 8 0.126 3.11. Practical application of present work and future perspectives Environmental problems and human death associated with AMR have been increasing continuously over the years. The presence of antibiotics in water matrices and their combination with microbes has become a powerful combination which needs to be treated at WWTP before they are released into the environment. In this scenario, the results reported here has high significance. Photocatalysts have good disinfection efficiency of microbial strains present in treated wastewater. The results reported here showed good efficiency under UV-A light of AMR microbes. In visible light as well, the photocatalyst showed good activity which shows its potential for field applications. The photocatalysts presented here have higher kinetic rate of disinfection than those reported in past studies. However, the previous studies were mostly conducted at higher power lamps, as discussed in the Table. The studied photocatalysts had good removal for all the three bacterial strains found in WWTP effluents. Addition of PS within the drinking water permissible limits showed good increment in the photocatalytic disinfection activity. This shows the controllable disinfection kinetic rate when used for on-site usage. Moreover, the catalyst showed good removal for both bacterial disinfection and antibiotic degradation at same time. This indicates promise for field application as tertiary treatment in WWTP. The future scope of the present research work are: (i) studying the applicability of catalyst for treated wastewater effluents; (ii) investigate the effect of co-contaminants such as nutrients and phosphates which are also present in treated wastewater along with microbes and antibiotics; (iii) study the disinfection of all three bacterial strains in a combined system; (iv) all the present experiments has been conducted as batch study, future study can be conducted on continuous flow reactor; (v) energy, cost and life cycle assessment of the system. 4. Conclusions In the present study, Ag-ZnO and TiO 2 were studied for the disinfection of microbes present in real wastewater. The study showed that Ag-ZnO showed better activity compared to TiO 2 . The three bacterial strains identified in the biological treated STP sludge were Stenotrophomonas nematodicola, Frediandcohnia salidurans and Shigella felxneri , and it was found that Shigella felxneri has maximum resistance to disinfection. Bacterial concentration had inverse relation to its removal kinetics. Disinfection kinetics increased with an increase in catalyst dosage and after an optimum dose it decreased. Visible light had a decrease in activity compared to UV-A light because of the former being polychromatic and having less photocatalyst excitation energy. Addition of PS showed an increase in activity because of the formation of PS radicals and an increased formation of hydroxyl radicals. Combined study of antibiotic and bacteria showed little decrease in the removal of both because of competitive antagonistic effect for ROS generated. Overall, the catalyst showed very good disinfection for the bacterial strains along with antibiotics and has high potential for practical applications. Declarations Acknowledgments The authors greatly appreciate the funding provided by Shastri Indo-Canadian Institute for conducting this research. Funding The authors have received the funding from Shastri Indo-Canadian Institute (SICRG-2019–20-R2–1401) for conducting this research. Authors’ contribution Dinkar Parashar: Conceptualization, execution of experiments, data collection, formal analysis and writing original draft of manuscript. Gopal Achari: Formal analysis and evaluation, editing and reviewing of manuscript. Mathava Kumar: Conceptualization, formal analysis and evaluation, editing and reviewing of manuscript, fund acquisition, and overall supervision. Ethical Approval This is not applicable Consent to Participate This is not applicable Consent to Publish This is not applicable Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Data availability Statement The data associated with the manuscript will be available on request. References Ahamed ST, Roy B, Basu U, Dutta S, Ghosh AN, Bandyopadhyay B, Giri N (2019). Genomic and proteomic characterizations of Sfin-1, a novel lytic phage infecting multidrug-resistant Shigella spp. and Escherichia coli C. Front Microbiol 10:1876. https://doi.org/10.3389/fmicb.2019.01876 Arasavilli S, Taksal PA, Das BK, Chowdhury S, Bhattacharya J (2024). Green graphene supported Cu 2 O-Ag 2 O S-scheme photocatalyst with high disinfection activity for prevention of urinary tract infection in toilets: A metagenomic analysis. J Environ Chem Eng 12(3):112703. https://doi.org/10.1016/j.jece.2024.112703 Baaloudj O, Assadi I, Nasrallah N, El Jery A, Khezami L, Assadi AA (2021). Simultaneous removal of antibiotics and inactivation of antibiotic-resistant bacteria by photocatalysis: A review. J Water Process Eng 42:102089. https://doi.org/10.1016/j.jwpe.2021.102089 BIS (Bureau of Indian standards), 2012. Indian Standard drinking water. specification, 10500. http://cgwb.gov.in/documents/wq-standards.pdf Brindha B, Okla MK, Kokilavani S, Sabariselvan L, Al-Amri SS, Abdel-Maksoud MA, Harini G, Alshuwaish R, Alsakkaf WA, Khan SS (2024). Dynamic Ag-mediated electron transfer confined ZnO nanorods for boosted photocatalytic bacterial disinfection. J Clean Prod 451:141908. https://doi.org/10.1016/j.jclepro.2024.141908 Chatterjee M, Mondal M, Sukul T, Mal S, Ghosh K, Das S, Pradhan SK (2023). Superior photocatalytic performance and photo disinfection of bacteria of solvothermally synthesized mesoporous La-doped CeO 2 under simulated visible light irradiation for wastewater treatment. J Alloys Compd 942:169135. https://doi.org/10.1016/j.jallcom.2023.169135 Chen X, Jin Y, Huang P, Zheng Z, Li LP, Lin CY, Chen X, Ding R, Liu J, Chen R (2024). Solar driven photocatalytic disinfection by Z-scheme heterojunction of In 2 O 3 /g-C 3 N 4 : Performance, mechanism and application. Appl Catal B 340:123235. https://doi.org/10.1016/j.apcatb.2023.123235 Ch-Th T, Manisekaran R, Santoyo-Salazar J, Schoefs B, Velumani S, Castaneda H, Jantrania A (2021). Graphene oxide decorated TiO 2 and BiVO 4 nanocatalysts for enhanced visible-light-driven photocatalytic bacterial inactivation. J Photochem Photobiol A Chem 418:113374. https://doi.org/10.1016/j.jphotochem.2021.113374 Ekande OS, Kumar M (2021). Facile synthesis of graphitic carbon nitride from acetic acid pretreatment to activate persulfate in presence of blue light for photocatalytic removal of metronidazole. Chemosphere 276:130171. https://doi.org/10.1016/j.chemosphere.2021.130171 Fabrega J, Fawcett SR, Renshaw JC, Lead JR. (2009). Silver nanoparticle impact on bacterial growth: effect of pH, concentration, and organic matter. Environ Sci Technol 43(19):7285-7290. https://doi.org/10.1021/es803259g Huang W, Ruan S, Zhao M, Xu R, Chen Z, Zhihong G, Song H (2021). Visible-light-driven photocatalytic inactivation of Escherichia coli by 0D/2D CeO 2 /g-C 3 N 4 heterojunction: bactericidal performance and mechanism. J Environ Chem Eng 9(6):106759. https://doi.org/10.1016/j.jece.2021.106759 Jimenez-Tototzintle M, Ferreira IJ, Da Silva Duque S, Barrocas PRG, Saggioro EM (2018). Removal of contaminants of emerging concern (CECs) and antibiotic-resistant bacteria in urban wastewater using UVA/TiO 2 /H 2 O 2 photocatalysis. Chemosphere 210:449-457. https://doi.org/10.1016/j.chemosphere.2018.07.036 Kanakaraju D, Anak Kutiang FD, Lim YC, Goh PS (2022). Recent progress of Ag/TiO 2 photocatalyst for wastewater treatment: Doping, co-doping, and green materials functionalization. Appl Mater Today 27:101500. https://doi.org/10.1016/j.apmt.2022.101500 Kumaravel V, Nair KM, MathewS, Bartlett J, Kennedy JE, Manning HG, Whelan BJ, Leyland NS, Pillai SC (2021). Antimicrobial TiO 2 nanocomposite coatings for surfaces, dental and orthopaedic implants. Chem Eng J 416:129071. https://doi.org/10.1016/j.cej.2021.129071 Li H, Zhang Z, Duan J, Li N, Li B, Song T, Sardar MF, Lv X, Zhu C (2020). Electrochemical disinfection of secondary effluent from a wastewater treatment plant: Removal efficiency of ARGs and variation of antibiotic resistance in surviving bacteria. Chem Eng J 392:123674. https://doi.org/10.1016/j.cej.2019.123674 Matsunaga T, Tomoda R, Nakajima T, Wake H (1985). Photoelectrochemical sterilization of microbial cells by semiconductor powders. FEMS Microbiol Lett 29(1-2):211-214. Mecha AC, Onyango MS, Ochieng A, Momba MNB (2019). UV and solar photocatalytic disinfection of municipal wastewater: inactivation, reactivation and regrowth of bacterial pathogens. Int J Environ Sci Technol 16:3687-3696. https://doi.org/10.1007/s13762-018-1950-1 Mecha AC, Onyango MS, Ochieng A, Momba MN (2017). Evaluation of synergy and bacterial regrowth in photocatalytic ozonation disinfection of municipal wastewater. Sci Total Environ 601:626-635. https://doi.org/10.1016/j.scitotenv.2017.05.204 Misra AJ, Basu A, Behera SK, Mishra A, Lundborg CS, Tripathy SK (2022). Point-of-use photocatalytic device for water disinfection under visible light using ZnO/Gypsum@ alginate beads. J Environ Chem Eng 10(3):107520. https://doi.org/10.1016/j.jece.2022.107520 Moncayo-Lasso A, Mora-Arismendi LE, Rengifo-Herrera JA, Sanabria J, Benitez N, Pulgarin C (2012). The detrimental influence of bacteria (E. coli, Shigella and Salmonella) on the degradation of organic compounds (and vice versa) in TiO 2 photocatalysis and near-neutral photo-Fenton processes under simulated solar light. Photochem Photobiol Sci 11(5):821-827. https://doi.org/10.1039/C2PP05290C Parashar D, Achari G, Kumar M (2024). Facile synthesis of silver doped ZnO nanoparticles by thermal decomposition method for photocatalytic degradation of metronidazole under visible light. J Environ Chem Eng 113205. https://doi.org/10.1016/j.jece.2024.113205 Parashar D, Achari G, Kumar M (2023). Multi-antibiotics removal under UV-A light using sol-gel prepared TiO 2 : Central composite design, effect of persulfate addition and degradation pathway study. Chemosphere 341:140025. https://doi.org/10.1016/j.chemosphere.2023.140025 Qiu P, Zhu J, Zhang C, Liu T, Fang H, Shen L, Zhang S (2023). Visible light-supported efficient photocatalytic disinfection using a robust silver-doped boron photocatalyst. J Environ Chem Eng 11(5):111058. https://doi.org/10.1016/j.jece.2023.111058 Rahman AH, Dash S, Mohanty PS, Mishra A, Lundborg CS, Tripathy SK (2020). Sonophotocatalytic disinfection of Shigella species under visible light irradiation: Insights into its molecular mechanism, antibacterial resistance and biofilm formation. Environ Res 187:109620. https://doi.org/10.1016/j.envres.2020.109620 Sasikaladevi R, Kiruthika Eswari V, Nambi IM (2020). Antibiotic resistance and sanitation in India: current situation and future perspectives. Antibiotic Resistance in the Environment: A Worldwide Overview 217-244. https://doi.org/10.1007/698_2020_608 Shekhawat SS, Gupta AB, Kulshreshtha NM, Prakash R (2021). UV disinfection studies on chlorine tolerant bacteria recovered from treated sewage. J Environ Chem Eng 9(3):105253. https://doi.org/10.1016/j.jece.2021.105253 Waclawek S, Lutze HV, Grubel K, Padil VV, Cernik M, Dionysiou DD (2017). Chemistry of persulfates in water and wastewater treatment: a review. Chem Eng J 330:44-62. https://doi.org/10.1016/j.cej.2017.07.132 Wang W, Zeng Z, Zeng G, Zhang C, Xiao R, Zhou C, Xiong W, Yang Y, Lei L, Liu Y, Huang D, Cheng M, Yang Y, Fu Y, Luo H, Zhou Y (2019). Sulfur doped carbon quantum dots loaded hollow tubular g-C 3 N 4 as novel photocatalyst for destruction of Escherichia coli and tetracycline degradation under visible light. Chem Eng J 378:122132. https://doi.org/10.1016/j.cej.2019.122132 Xia D, An T, Li G, Wang W, Zhao H, Wong PK (2016). Synergistic photocatalytic inactivation mechanisms of bacteria by graphene sheets grafted plasmonic Ag-AgX (X= Cl, Br, I) composite photocatalyst under visible light irradiation. Water Res 99:149-161. https://doi.org/10.1016/j.watres.2016.04.055 Xia D, Wang W, Yin R, Jiang Z, An T, Li G, Zhao H, Wong PK (2017). Enhanced photocatalytic inactivation of Escherichia coli by a novel Z-scheme g-C 3 N 4 /m-Bi 2 O 4 hybrid photocatalyst under visible light: the role of reactive oxygen species. Appl Catal B 214:23-33. https://doi.org/10.1016/j.apcatb.2017.05.035 Xue W, Huang D, Wen X, Chen S, Cheng M, Deng R, Li B, Yang Y, Liu X (2020). Silver-based semiconductor Z-scheme photocatalytic systems for environmental purification. J Hazard Mater 390:122128. https://doi.org/10.1016/j.jhazmat.2020.122128 Yang H, He D, Liu C, Zhou X, Qu J (2023). Magnetic photocatalytic antimicrobial materials for water disinfection. Sep Purif Technol 124697. https://doi.org/10.1016/j.seppur.2023.124697 Yao L, Bai Y, Ding L, Hu Y, Zhang Z, Zhang Y, Chen R, Xie H, Wang J, Wang R (2024). Low oxygen adsorption energy barrier architectures to facilitate microenvironmental photocatalytic disinfection in Wei River. Chem Eng J 498:155468. https://doi.org/10.1016/j.cej.2024.155468 Ye L, Liu J, Gong C, Tian L, Peng T, Zan L (2012). Two different roles of metallic Ag on Ag/AgX/BiOX (X= Cl, Br) visible light photocatalysts: surface plasmon resonance and Z-scheme bridge. ACS Catal 2(8):1677-1683. https://doi.org/10.1021/cs300213m Ye S, Xu Y, Huang L, Lai W, Deng L, Lin Z, Peng H, Zhou X, Xie G (2021). MWCNT/BiVO 4 photocatalyst for inactivation performance and mechanism of Shigella flexneri HL, antibiotic-resistant pathogen. Chem Eng J 424:130415. https://doi.org/10.1016/j.cej.2021.130415 Zaika LL (2001). The effect of temperature and low pH on survival of Shigella flexneri in broth. J Food Prod 64(8):1162-1165. https://doi.org/10.4315/0362-028X-64.8.1162 Zhang C, Li Y, Wang C, Zheng X (2021). Different inactivation behaviors and mechanisms of representative pathogens (Escherichia coli bacteria, human adenoviruses and Bacillus subtilis spores) in g-C 3 N 4 -based metal-free visible-light-enabled photocatalytic disinfection. Sci Total Environ 755:142588. https://doi.org/10.1016/j.scitotenv.2020.142588 Zhu D, Zhou Q (2019). Action and mechanism of semiconductor photocatalysis on degradation of organic pollutants in water treatment: A review. Environ Nanotechnol Monit Manag 12:100255. https://doi.org/10.1016/j.enmm.2019.100255 Supplementary Files SUPPLEMENTARYINFORMATION.docx 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. 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-6790617","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":473333214,"identity":"65fbbed1-b4be-41a4-ab24-2065c2be9471","order_by":0,"name":"Dinkar Parashar","email":"","orcid":"","institution":"Indian Institute of Technology Madras","correspondingAuthor":false,"prefix":"","firstName":"Dinkar","middleName":"","lastName":"Parashar","suffix":""},{"id":473333215,"identity":"febbb035-38a2-4668-93b0-178f4a099e52","order_by":1,"name":"Gopal Achari","email":"","orcid":"","institution":"University of Calgary","correspondingAuthor":false,"prefix":"","firstName":"Gopal","middleName":"","lastName":"Achari","suffix":""},{"id":473333216,"identity":"1a3ec8fe-ddd3-4f2d-8afa-9a463ba971e7","order_by":2,"name":"Mathava Kumar","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAtklEQVRIiWNgGAWjYHACNiC24WGD8niI0MEMUpzGw8ZGopbDEMuIArrt5489+Nl2XoZPvjuB4UcNg4w5IS1mZ5LZDXvbbgMdxruBsecYA49lAyEtB5LZJHjOQLQw8DYw8BgcIKTl/GM2yT9nzkFs+UuUlhvJbNI8FQfAWpiJs+XGYzNpmYpkoJbcDYdljkkQ47DEZ5JvDOzs5ZvPbnz4psbGnqAWFABULEGK+lEwCkbBKBgFuAAAMZg1LAmQZrMAAAAASUVORK5CYII=","orcid":"https://orcid.org/0000-0002-4124-4605","institution":"Indian Institute of Technology Madras","correspondingAuthor":true,"prefix":"","firstName":"Mathava","middleName":"","lastName":"Kumar","suffix":""}],"badges":[],"createdAt":"2025-05-31 11:19:48","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6790617/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6790617/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":85227735,"identity":"c93ecd9f-2aff-48f8-9cbf-e90fdf7e4b10","added_by":"auto","created_at":"2025-06-23 15:33:19","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":132755,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Photo catalytic log reduction curve for three bacterial strains using Ag-ZnO and, (b) pseudo-first-order kinetic results.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6790617/v1/b9b1e4091fba18e9ac39fe79.png"},{"id":85229375,"identity":"b4082931-34cc-4e9a-9c8f-7b0dd846264d","added_by":"auto","created_at":"2025-06-23 15:41:19","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":58273,"visible":true,"origin":"","legend":"\u003cp\u003ePhotocatalytic kinetic degradation study of \u003cem\u003eshigella flexneri \u003c/em\u003eusing Ag-ZnO and TiO\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6790617/v1/485f3703ae7d22c7015229d4.png"},{"id":85227739,"identity":"6a08e59b-4423-49d0-b7e4-9ca81944aeab","added_by":"auto","created_at":"2025-06-23 15:33:19","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":66041,"visible":true,"origin":"","legend":"\u003cp\u003e(\u003cstrong\u003ea\u003c/strong\u003e) Kinetic curve, and (\u003cstrong\u003eb\u003c/strong\u003e) log reduction curve for the degradation of \u003cem\u003eshigella flexneri\u003c/em\u003e by Ag and Ag-ZnO in the presence and absence of light.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-6790617/v1/c1b430f273307ac68f14becc.png"},{"id":85229974,"identity":"6ebebc8e-4fec-4412-a94d-b33b0ab03ae9","added_by":"auto","created_at":"2025-06-23 15:49:19","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":65421,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of different initial bacterial concentration (CFU/mL) on the photocatalytic degradation of \u003cem\u003eshigella flexneri\u003c/em\u003e using Ag-ZnO.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-6790617/v1/32c3e37e4a4fb64bdacf5cde.png"},{"id":85229377,"identity":"b668e509-4d6a-4840-913a-81fb72e286bf","added_by":"auto","created_at":"2025-06-23 15:41:19","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":85124,"visible":true,"origin":"","legend":"\u003cp\u003e(\u003cstrong\u003ea\u003c/strong\u003e) The effect of different catalyst dosage on the photocatalytic degradation of \u003cem\u003eshigella flexneri\u003c/em\u003e using Ag-ZnO with time, and (\u003cstrong\u003eb\u003c/strong\u003e) first order kinetic results.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-6790617/v1/2b2baaa14af9e55c0ead3887.png"},{"id":85229976,"identity":"ac201b1b-b334-451f-9d1c-4f00282ee993","added_by":"auto","created_at":"2025-06-23 15:49:19","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":121550,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(a) \u003c/strong\u003eEffect of PS addition along with catalyst on the photocatalytic degradation of \u003cem\u003eshigella flexneri\u003c/em\u003e using Ag-ZnO, (\u003cstrong\u003eb\u003c/strong\u003e) log reduction of \u003cem\u003eshigella flexneri\u003c/em\u003e disinfection with time and (\u003cstrong\u003ec\u003c/strong\u003e) pseudo-first-order kinetic results (Initial bacterial conc. = 10\u003csup\u003e5\u003c/sup\u003e CFU/mL, catalyst dose = 1 g/L, PS dose = 0.2 g/L).\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-6790617/v1/e7c9ea0cba469a5799fe75f7.png"},{"id":85229378,"identity":"6c439c42-43d7-4a23-b4ba-76aa641df8ee","added_by":"auto","created_at":"2025-06-23 15:41:19","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":91980,"visible":true,"origin":"","legend":"\u003cp\u003e(\u003cstrong\u003ea\u003c/strong\u003e) Comparison of photocatalytic disinfection of \u003cem\u003eshigella flexneri\u003c/em\u003e under UV-A and visible light using Ag-ZnO, (\u003cstrong\u003eb\u003c/strong\u003e) log reduction of \u003cem\u003eshigella flexneri\u003c/em\u003e disinfection and (\u003cstrong\u003ec\u003c/strong\u003e) pseudo-first-order kinetic results (Experimental Conditions: solution volume – 50mL, initial bacteria concentration – 10\u003csup\u003e4\u003c/sup\u003e CFU/mL, catalyst dose – 1 g/L, lamp power – 40 W)\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-6790617/v1/21e29f5dae7a461d87b50844.png"},{"id":85229380,"identity":"668b498a-af17-4d08-a06b-c9ff24afdbef","added_by":"auto","created_at":"2025-06-23 15:41:19","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":118489,"visible":true,"origin":"","legend":"\u003cp\u003e(\u003cstrong\u003ea\u003c/strong\u003e) Removal of MNZ in presence of \u003cem\u003eshigella flexneri\u003c/em\u003e using TiO\u003csub\u003e2\u003c/sub\u003e, and (\u003cstrong\u003eb\u003c/strong\u003e) \u003cem\u003eshigella flexneri\u003c/em\u003e disinfection in presence of MNZ using TiO\u003csub\u003e2\u003c/sub\u003e. (\u003cstrong\u003ec\u003c/strong\u003e) Removal of MNZ in presence of \u003cem\u003eshigella flexneri\u003c/em\u003e using Ag-ZnO, and (\u003cstrong\u003ed\u003c/strong\u003e) \u003cem\u003eshigella flexneri\u003c/em\u003e disinfection in presence of MNZ using Ag-ZnO. (Experimental Conditions: solution volume – 50 mL, initial bacteria concentration – 10\u003csup\u003e8\u003c/sup\u003e CFU/mL, initial MNZ concentration – 10 mg/L, catalyst dose – 1 g/L)\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-6790617/v1/877dbfb6abb2255ff7797b76.png"},{"id":85229973,"identity":"83a8ebb7-9c04-4c8e-91b5-051d96827497","added_by":"auto","created_at":"2025-06-23 15:49:19","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":343192,"visible":true,"origin":"","legend":"\u003cp\u003eImages of petri plates of \u003cem\u003eshigella flexneri\u003c/em\u003e disinfection experiment at different time interval (\u003cstrong\u003ea\u003c/strong\u003e) 0 min, (\u003cstrong\u003eb\u003c/strong\u003e) 30 min, (\u003cstrong\u003ec\u003c/strong\u003e) 60 min, (\u003cstrong\u003ed\u003c/strong\u003e) 90 min, (\u003cstrong\u003ee\u003c/strong\u003e) 120 min, (\u003cstrong\u003ef\u003c/strong\u003e) 150 min, and (\u003cstrong\u003eg\u003c/strong\u003e) 180 min (Experimental conditions: solution volume – 50 mL, initial bacteria concentration – 10\u003csup\u003e8\u003c/sup\u003e CFU/mL, catalyst Ag-ZnO dose – 3 g/L, UV-A lamps – 5*8 W)\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-6790617/v1/9afc750fa79992d2d1c1f8bd.png"},{"id":85229382,"identity":"257c9da3-2018-42a0-b9a0-f0bf6da9dd76","added_by":"auto","created_at":"2025-06-23 15:41:19","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":85987,"visible":true,"origin":"","legend":"\u003cp\u003eProposed photocatalytic bacterial disinfection mechanism under (\u003cstrong\u003ea\u003c/strong\u003e) UV light, (\u003cstrong\u003eb\u003c/strong\u003e) visible light.\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-6790617/v1/e59c80a61f0c4b5a907b4d78.png"},{"id":85746650,"identity":"e7cd34ac-99bd-4fb0-a105-9c441715e400","added_by":"auto","created_at":"2025-07-01 09:33:42","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2338588,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6790617/v1/cd6889fe-17d3-4646-8348-acb94e2c04c9.pdf"},{"id":85227754,"identity":"7f276aca-2919-4f44-a51f-48eeed4e0d05","added_by":"auto","created_at":"2025-06-23 15:33:19","extension":"docx","order_by":5,"title":"","display":"","copyAsset":false,"role":"supplement","size":2018902,"visible":true,"origin":"","legend":"","description":"","filename":"SUPPLEMENTARYINFORMATION.docx","url":"https://assets-eu.researchsquare.com/files/rs-6790617/v1/3702c2e76cc406f926710f20.docx"}],"financialInterests":"","formattedTitle":"UV-A based photocatalytic disinfection of secondary effluent from a wastewater treatment plant using Ag-ZnO: Effect of antibiotic presence, catalyst concentration, lamp and persulfate addition","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eWater borne diseases due to microbial contamination has been increasing over the decades. As per the World Health Organisation (WHO) report, around 2.2\u0026nbsp;million people die globally because of waterborne diseases and nearly one billion individuals globally lack access to safe water sources (Yao et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2024\u003c/span\u003e, Yang et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Anti-microbial resistance (AMR) is becoming a major concern with around 700,000 deaths occurring due to it per year (Yang et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Moreover, around 20 lakhs death are predicted to occur in India alone by 2050 because of AMR (Sasikaladevi et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIt has been noted that conventional biological treatment in wastewater treatment plants is not able to completely remove these AMR bacteria and genes (Li et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Conventional disinfection technologies such as chlorination, ozonation and UV light irradiation while being effective, have certain challenges such as high cost, carcinogenic by-product formation, incomplete microbial inactivation, microbial reactivation after disinfection, increased bacterial resistance, and high energy consumption. Hence, there is a need to research and develop a more effective disinfection technology that can address some of the concerns.\u003c/p\u003e \u003cp\u003eAdvanced oxidation processes (AOP), with their strong oxidative radicals can completely disinfect and kill a wide range of microbes. Among these photocatalysis has been extensively studied and has promises of being efficient (Qiu et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2023\u003c/span\u003e, Yang et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2023\u003c/span\u003e, Xia et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). In 1985, the first photocatalytic disinfection study was reported (Matsunaga et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e1985\u003c/span\u003e). They used platinum-doped TiO\u003csub\u003e2\u003c/sub\u003e as photocatalysts. After that continuous development and research has led to disinfection via photocatalysis. Photocatalysts which have been reported for the degradation of microbes include TiO\u003csub\u003e2\u003c/sub\u003e (Kumaravel et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), ZnO (Brindha et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2024\u003c/span\u003e), Cu\u003csub\u003e2\u003c/sub\u003eO (Arasavilli et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2024\u003c/span\u003e), g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e (Yang et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), BiVO\u003csub\u003e4\u003c/sub\u003e (Ye et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) and In\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (Chen et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Among these TiO\u003csub\u003e2\u003c/sub\u003e and ZnO have been identified as leading photocatalysts because of their comparatively high activity, unique band-gap and excellent stability (Parashar et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2024\u003c/span\u003e, Parashar et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2023\u003c/span\u003e, Zhu and Zhou. 2019). However, single semiconductor photocatalysis has certain drawbacks such as high charge recombination and less stability causing less recyclability. Doping with noble metals is a way to improve single semiconductor photocatalytic activity (Kanakaraju et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Silver has been identified as a good dopant because of its unique Fermi level, high surface plasmon resonance capability and efficient charge separation ability (Xue et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The present study explores the disinfection potential of AMR microbes using silver doped ZnO and compares it with that of TiO\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003eTo the best of our knowledge, almost all the research work are being conducted on \u003cem\u003eE. coli\u003c/em\u003e or other major indicator organisms. It is worth pointing out that the absence of \u003cem\u003eE. coli\u003c/em\u003e does not ensure that water is pathogen free. To the best of our knowledge, there have been no studies that have reported on disinfection of anti-microbial resistant microbes in real wastewater. Moreover, the disinfection of microbes varies from strain to strain and knowing the potential of treatment technologies for the environmentally found microbial strains is necessary. The aim and novelty of the current study is to identify the major microbes present in treated wastewater effluents which reach the water bodies, and to estimate the extent of their disinfection via photocatalysis.\u003c/p\u003e"},{"header":"2. Materials and methods","content":"\u003cp\u003eThe antibiotic, i.e., MNZ (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e9\u003c/sub\u003eN\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e), zinc acetate and silver nanoparticles were purchased from Sigma Aldrich\u0026reg;. Sodium hydroxide pellets (97% purity) were purchased from Merck India\u0026reg;. Ethanol was purchased from Hayman\u0026reg;, UK. Acetonitrile (HPLC grade) was purchased from Rankem\u0026reg;, India. Luria broth and Agar-agar were supplied from SRL and HIMEDIA brand respectively. All chemicals were of analytical grade and were used as such. UV-A lamps (8 W, Phillips, Poland), were purchased from a hardware store in Chennai, Tamil Nadu, India. Distilled water was used to make the antibiotic solution for all the experiments. Sterilization for all the materials for disinfection experiments were done in 120 \u003csup\u003eo\u003c/sup\u003eC autoclave at the heating rate of ~\u0026thinsp;3 \u003csup\u003eo\u003c/sup\u003eC/min and at 1 kg/cm\u003csup\u003e2\u003c/sup\u003e pressure for 20 min (Krithish Scientific Company). Bacterial strain identification was done using 16 s ribosomal RNA sequencing (Applied Biosystems).\u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Catalyst preparation\u003c/h2\u003e \u003cp\u003eThe catalyst was prepared by thermal decomposition method, as reported in our previous work (Parashar et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). In brief, ZnO was first prepared by grinding zinc acetate using mortar and pestle to make it a fine powder. The fine powder was thermally heated in an alumina crucible in a muffle furnace at 500 \u003csup\u003eo\u003c/sup\u003eC for 3 h at a heating rate of 15 \u003csup\u003eo\u003c/sup\u003eC/min. Silver doping in ZnO was done by mixing silver nanoparticles before keeping in muffle furnace. 40% by weight of zinc in zinc acetate was mixed with zinc acetate which had given the best results in our previous study. The mixture was then ground in mortar and pestle followed by annealing in muffle furnace at 500 \u003csup\u003eo\u003c/sup\u003eC for 3 h. Finally, the catalyst was further ground obtain a uniform powdered catalyst. For comparison with TiO\u003csub\u003e2\u003c/sub\u003e, pure anatase nanoparticles were used (Parashar et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Experimental set-up\u003c/h2\u003e \u003cp\u003eThe experimental set-up consisted of 5 monochromatic UV-A lamps (each of 8 W) having maximum wavelength of 367 nm were placed at the top of reactor. A magnetic stirrer with a glass beaker of 100 mL capacity is placed at the bottom. At the back a cooling fan was provided to dissipate the heat generated in UV-A lamps and to maintain constant working temperature during the experiment. For comparison purposes, visible lamps were also used. For this, 8 visible lamps each 5 W were placed. The wavelength spectra of both the lamps and the schematic diagram of the reactor are provided as supplementary information (Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e and Fig. S2).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3. Microbe culture\u003c/h2\u003e \u003cp\u003eThe IIT Madras sewage treatment plant with a sequential batch reactor (SBR) as secondary treatment unit, treats the domestic sewage generated on campus. Sludge sample was obtained after the SBR treatment. A schematic of the plant and the sampling location is shown in Figure S3. The sample was then cultured in glass petri plates with appropriate dilutions. The antibiotic MNZ was added to the nutrient media to make sure only antibiotic-resistant genes grow. From the culture, three isolated colonies were taken using nichrome wire inside a horizontal air flow laminar hood. These isolated colonies were cultured in separate petri dishes. Further to ensure pure bacterial colonies, the single colonies were cultured in subsequent three glass test tubes and in three glass petri plates. From the final cultured petri dish, bacterial screening analysis was conducted to identify the strain of bacteria present. All subsequent experiments were conducted using pure single strain colonies. All experimental work were conducted inside the horizontal air flow laminar hood near the flame inside the hood to minimize any type of outside contamination.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4. Disinfection study\u003c/h2\u003e \u003cp\u003eMilli and micro pipette tips, centrifuge tips, bacteria culturing nutrient media and solid nutrient media for petri dish plating, as well as the saline solution were all sterilised in the autoclave before initiating any experiment. For the photocatalytic disinfection experiments, initial bacterial concentration of 10\u003csup\u003e8\u003c/sup\u003e CFU/mL was taken by checking the optical density at 600 nm (OD\u003csub\u003e600\u003c/sub\u003e). A working volume of 20 mL was placed in a 100 mL glass beaker. The catalyst was then added and mixed thoroughly with the bacterial culture by stirring. The samples were then irradiated. Samples were taken at appropriate time interval and were plated on sterilised plastic petri dishes using spread plating method. Samples were serially diluted in saline solution (0.85\u0026ndash;0.9% NaCl solution). 80 \u0026micro;L of the serially diluted sample was inoculated on nutrient agar plates and incubated in BOD incubator for 24 h at 37 \u003csup\u003eo\u003c/sup\u003eC. Colonies formed were counted manually with a colony counter. Colonies forming unit (CFU) per unit sample volume (mL) was calculated according to Eq.\u0026nbsp;(\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:CFU/mL\\:=\\:\\:\\frac{Number\\:of\\:colonies\\:X\\:Dilution\\:factor}{Volume\\:inoculated\\:on\\:plate}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eThe kinetic results were fitted using the pseudo-first-order kinetic model as shown in Eq.\u0026nbsp;(\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$\\:\\text{ln}\\left(\\frac{{C}_{t}}{{C}_{o}}\\right)=\\:-\\text{k}\\text{*}\\text{t}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere, C\u003csub\u003et\u003c/sub\u003e and C\u003csub\u003eo\u003c/sub\u003e are the number of colonies at time t and at time 0. k is the pseudo-first-order kinetic rate constant.\u003c/p\u003e \u003cp\u003eFor the analysis of MNZ, liquid chromatography mass spectroscopy (LC-MS) was used (Agilent Technologies 1260 Infinity coupled with 6120 Quadrapole). Mobile phase for analysing MNZ was a mixture of millipore water and acetonitrile in the ratio of 70:30. The mobile phase was send into the column at a flow rate of 0.4 mL/min. The calibration plot for antibiotic MNZ with different concentration in the LC-MS instrument is shown in Fig. S4.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.1. Sequencing analysis of microbial strains\u003c/h2\u003e \u003cp\u003eThe three isolated bacterial strains were cultured separately in pure media. The media was having MNZ antibiotic to make sure only ARB will grow on it. Furthermore, single colonies were taken from each of the three petri plates and was streaked on new plates. This procedure was repeated six consecutive times to obtain pure isolated colonies. 16s ribosomal RNA sequencing was conducted on the three bacterial strains. The analysis results matched more than 99% with the database library. The blast results showed the three strains as \u003cem\u003eStenotrophomonas nematodicola, Frediandcohnia salidurans\u003c/em\u003e and \u003cem\u003eShigella felxneri\u003c/em\u003e. All three strains were studied under a microscope to analyse the surface texture of their colonies. The microscopic image of the three pure colonies is shown in Fig. S5. All three colonies were almost spherical with \u003cem\u003eStenotrophomonas nematodicola\u003c/em\u003e showing hairy structure on its surface. Very less research information is available for the disinfection of these three strains present in the environment. However, \u003cem\u003eStenotrophomonas\u003c/em\u003e specie is chlorine tolerant and is observed in treated wastewater (Shekhawat et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). \u003cem\u003eShigella felxneri\u003c/em\u003e is commonly present in wastewater and has been reported as having resistance to multiple antibiotics (Ahamed et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2019\u003c/span\u003e, Mecha et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2019\u003c/span\u003e, Mecha et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Further, this strain is also resistant to very low pHs (Rahman et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2020\u003c/span\u003e, Zaika. 2001).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.2. Bacterial species disinfection using TiO\u003csub\u003e2\u003c/sub\u003e and Ag-ZnO\u003c/h2\u003e \u003cp\u003eFor comparison study, all three bacterial strains namely \u003cem\u003eStenotrophomonas nematodicola\u003c/em\u003e, \u003cem\u003eFrediandcohnia salidurans\u003c/em\u003e and \u003cem\u003eShigella felxneri\u003c/em\u003e were first tested for photocatalytic disinfection studies under UV-A light using Ag-ZnO catalyst. The disinfection curve and pseudo-first-order kinetic curve are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, and the log-reduction values at various times has been presented in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The pseudo-first-order kinetic rate obtained for the three strains were 0.082, 0.074 and 0.055 min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e respectively under similar experimental conditions. \u003cem\u003eShigella flexneri\u003c/em\u003e was found to be the most difficult to disinfect. The reason maybe the strain has been shown to develop multi-drug resistance and has stability over a wide pH range and temperature, which makes it more difficult to kill compared to other two strains (Rahman et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2020\u003c/span\u003e, Ahamed et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Henceforth, further experiments were conducted on \u003cem\u003eshigella flexneri\u003c/em\u003e strain bacteria.\u003c/p\u003e \u003cp\u003eTiO\u003csub\u003e2\u003c/sub\u003e was studied for knowing its disinfection potential for the \u003cem\u003eshigella flexneri\u003c/em\u003e strain and for its comparison with Ag-ZnO. The result is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Photolysis using UV-C lamp showed good removal of 0.5 log within the first 30 min. However, after the initial log reduction, there was slow bacterial degradation and only 0.9 log removal was noted after 180 min. Further, under similar experimental conditions, it was noted that Ag-ZnO showed better disinfection than TiO\u003csub\u003e2\u003c/sub\u003e. This is because of the efficient charge separation in Ag-ZnO with silver acting as charge separator which decreased the charge recombination in ZnO. In case where TiO\u003csub\u003e2\u003c/sub\u003e was used with no dopant similar result was also obtained.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eLog reduction of three bacterial strains using Ag-ZnO at different time intervals and the pseudo-first-order kinetic rate constant\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eBacteria\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"5\" nameend=\"c6\" namest=\"c2\"\u003e \u003cp\u003eLog reduction\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eKinetic rate obtained (min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0 min\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e30 min\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e60 min\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e90 min\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003e120 min\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eStenotrophomonas nematodicola\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e4.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.082\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eFrediandcohnia salidurans\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e4.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.072\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eShigella felxneri\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e2.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.055\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.3. Control experiments on \u003cem\u003eshigella flexneri\u003c/em\u003e\u003c/h2\u003e \u003cp\u003eAg and Ag-ZnO were tested for the bacterial strain \u003cem\u003eshigella flexneri\u003c/em\u003e in presence and in absence of UV-A light. The results are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. It was observed that bacterial disinfection was higher while using Ag alone compared to Ag-ZnO composite. The reason being Ag has higher disinfection activity than ZnO because of its interaction and uptake inside the bacteria cells and as it attaches itself to cell membranes causing cell disruption and death. The doping of Ag inside ZnO lattice causes less Ag available for disinfection. This caused a decrease in activity of Ag-ZnO when compared to Ag alone (Fabrega et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). However, photocatalysis with Ag-ZnO under UV-A light gave considerably higher activity than without light because of the generation of reactive oxygen species (ROS) which have a high potential for microbial disinfection. The pseudo-first-order rate constant for Ag, Ag-ZnO and Ag-ZnO in UV-A light were 0.031, 0.018 and 0.055 min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.4. Effect of initial bacterial concentration on bacterial disinfection\u003c/h2\u003e \u003cp\u003e \u003cem\u003eShigella flexneri\u003c/em\u003e with different initial concentration was further tested for photocatalytic activity using Ag-ZnO under similar experimental conditions. The results obtained is presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. It was observed that with an increase in initial bacterial concentration, there was a decrease in kinetic rate, as evident from the steep slope of the curves shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The reason behind this is that with an increase in bacterial concentration, the number of radicals available is less and hence the lower disinfection. In addition, there is a decrease in light penetration inside the solution because of increase in turbidity of solution.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.5. Effect of catalyst dosage on rate of bacterial disinfection\u003c/h2\u003e \u003cp\u003eThe effect of varying catalyst dosage was investigated and the results are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. The results indicate the disinfection activity increased with increase in catalyst dosage. This is expected as a higher catalyst dosage leads to an increased generation of reactive radicals. However, above a 3 g/L dosage, a decrease was observed in the disinfection activity. This was due to agglomeration of the nanoparticles in the solution leading to a decrease in total active surface area. Additionally, an increase in catalyst dosage led to an increase in turbidity of solution causing a decrease in light penetration inside the solution. This caused less light incidence on the catalyst surface and consequently lower activity. (Ch-Th et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). The pseudo first-order kinetic rate constant for different catalyst dosage is included in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003ePseudo first-order kinetic rate constant for bacterial disinfection with different catalyst dose\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCatalyst dose\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eKinetic rate (min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.032\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.059\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.094\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.126\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.094\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e3.6. Effect of persulfate addition on rate of bacterial disinfection\u003c/h2\u003e \u003cp\u003eIn recent studies the use of persulfate (PS) has attracted significant attention because of production of high redox potential specie generation. PS radicals have higher redox potential and longer half-life than hydroxyl radical (Ekande and Kumar. 2021). However, the generation of sulphate ions after the study creates secondary pollution. To overcome this, PS addition in amounts of 200 mg/L which is within the permissible limit of Indian standard code was used (BIS 10500. 2012). The results are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e. Interestingly, in the first 15 min there was an increase in the bacterial disinfection. The increase in pseudo-first-order kinetics was about 1.5 times (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec). The reason for this increment is the generation of PS radicals (see Eq.\u0026nbsp;3\u0026ndash;6), which along with hydroxyl radicals improved the disinfection activity (Parashar et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2023\u003c/span\u003e, Ekande and Kumar, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). PS radicals can generate hydroxyl radicals either by production of hydrogen peroxide or by reacting with water or hydroxide anions (Waclawek et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). However, after the initial 15 min, there was a slight decrease in the bacterial disinfection. This is due to the quick generation of PS radicals in the beginning which enhanced the bacterial decay rate. However, after a certain period, the generation of PS radicals stopped because of its low concentration. Furthermore, the generated sulphate ions from bacterial oxidation caused by PS radicals interfered with hydroxyl radicals thereby decreasing further bacterial disinfection. This is evident from the later part of curve shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Taba\" border=\"1\"\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e + e\u003csup\u003e\u0026minus;\u003c/sup\u003e \u0026rarr; SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e. + SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(3)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026minus;.\u003c/sup\u003e + OH\u003csup\u003e\u0026minus;\u003c/sup\u003e/H\u003csub\u003e2\u003c/sub\u003eO \u003cb\u003e\u0026rarr;\u003c/b\u003e OH. + SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e (+\u0026thinsp;H\u003csup\u003e+\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(4)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e + 2 H\u003csub\u003e2\u003c/sub\u003eO \u003cb\u003e\u0026rarr;\u003c/b\u003e 2 SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e + OOH\u003csup\u003e\u0026minus;\u003c/sup\u003e + 3 H\u003csup\u003e+\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(5)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e + OOH\u003csup\u003e\u0026minus;\u003c/sup\u003e\u003cb\u003e\u0026rarr;\u003c/b\u003e SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026minus;.\u003c/sup\u003e + SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e + H\u003csup\u003e+\u003c/sup\u003e + O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026minus;.\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(6)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e3.7. Effect of visible light on rate of bacterial disinfection\u003c/h2\u003e \u003cp\u003eMaximum spectrum of sunlight falls under the visible region of 400\u0026ndash;700 nm. For this reason, visible light was studied under similar conditions to check the efficiency of catalyst in visible region. The visible lamp used in the present study had two major peaks mainly, a narrow peak at 454 nm and a broad peak at 532 nm. The lamp was polychromatic covering full visible region spectrum from 400 to 700 nm. The comparison between visible and UV-A lamp is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. Compared to UV-A lamp, the activity of visible lamp was ~\u0026thinsp;1.9 times lesser (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ec). The reason was, UV-A lamp being monochromatic had a high energy of 3.37 eV which was greater than the band gap of ZnO (3.1 eV) (Parashar et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).The lamp being monochromatic produced high intensity at 367 nm causing better generation of charges in ZnO as compared to visible polychromatic light. Interestingly, there was good activity seen in visible light as well, although, the energy corresponding to the 2 major peaks are 2.73 and 2.33 eV, respectively. This photon energy is not sufficient to generate charge separation in ZnO because of its higher band gap of 3.1 eV. The activity observed in the present study is due to surface plasmon resonance (SPR) effect of silver nanoparticles in visible region. Depending on the need of semiconductor, Ag nanoparticles can either behave as charge separator or shows SPR (Ye et al. \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). In the present case, ZnO can\u0026rsquo;t get excited by visible light and so, the generation of charges occur in Ag nanoparticles by the visible light. The electron generated on Ag surface got separated into the CB of nearby ZnO causing efficient ROS formation and disinfection.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e3.8. Simultaneous treatment for MNZ destruction and bacterial disinfection\u003c/h2\u003e \u003cdiv id=\"Sec16\" class=\"Section3\"\u003e \u003ch2\u003e3.8.1. Under TiO\u003csub\u003e2\u003c/sub\u003e photocatalysis\u003c/h2\u003e \u003cp\u003eRemoval of MNZ and bacteria in a mixture was studied using the catalyst TiO\u003csub\u003e2\u003c/sub\u003e and the results obtained are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ea and b. Removal of MNZ was having an antagonistic effect by the presence of bacteria i.e. the removal was antibiotic was negatively affected because of the presence of bacteria. It is due to competition by the bacteria for the generated ROS. Similar results were obtained for bacterial disinfection also. The removal of bacteria was also negatively affected by the presence of antibiotic. In the beginning of 30 min there was an increase in removal, however overall there was a decrease in the bacterial disinfection. Similar kind of behaviour have been observed previously in case of multi-antibiotic conditions (Parashar et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Similarly, antagonistic behaviour with TiO\u003csub\u003e2\u003c/sub\u003e was seen for the removal of antibiotics and bacteria presence together (Jimenez-Tototzintle et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2018\u003c/span\u003e, Moncayo-Lasso et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2012\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section3\"\u003e \u003ch2\u003e3.8.2. Under Ag-ZnO photocatalysis\u003c/h2\u003e \u003cp\u003eRemoval of MNZ was affected by the presence of bacteria as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e (c). However, the removal efficiency was higher than when TiO\u003csub\u003e2\u003c/sub\u003e was used. This showed that the activity of Ag-ZnO was better than TiO\u003csub\u003e2\u003c/sub\u003e. The reason for increase in activity of Ag-ZnO compared to TiO\u003csub\u003e2\u003c/sub\u003e has been discussed earlier in section \u003cspan refid=\"Sec9\" class=\"InternalRef\"\u003e3.2\u003c/span\u003e. In case of multi-component, the decrease in removal of antibiotic was mostly because of the competitive effect of bacteria, which consumed the generated radicals leading to less availability of radicals for MNZ to get oxidized. Similarly, the removal of \u003cem\u003eShigella flexneri\u003c/em\u003e was affected by the presence of MNZ. However, the antagonistic effect felt by bacteria was less compared to MNZ as evident in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e(d). This is because of higher concentration of bacteria compared to MNZ. Similar antagonism has been observed in a previous work (Rahman et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003e3.9. Disinfection mechanism\u003c/h2\u003e \u003cp\u003eThe disinfection of \u003cem\u003eshigella flexneri\u003c/em\u003e at different time interval is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e. The figure shows the plating of microbial sample at different time intervals with appropriate dilutions. As seen in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003eg, complete bacterial removal occurred in 180 min. Cell membrane rupture has been reported to be the mechanism for bacterial disinfection (Xia et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). The primary mechanism involved in the bacterial disinfection is outer cell wall distortion by the generated radicals on photocatalyst surface. \u003cem\u003eShigella flexneri\u003c/em\u003e being a gram-negative bacteria is characterized by a thin outer membrane made up of polysaccharides. The reactive oxygen species (ROS) generated on catalyst surfaces having very high redox potential, causes the disintegration of thin cell membranes (Rahman et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). This is followed by intracellular organelles coming out of the cell causing microbe killing (Brindha et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Moreover, the photocatalyst can also stick on the bacterial surface by cell proliferation and endocytosis. This will also cause cell death through cell membranes rupture by organ permeability (Baaloudj et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). As reported in our earlier work, in the UV region, maximum photocatalytic degradation occurs by hydroxyl radicals followed by superoxide radicals and then by holes (Parashar et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Silver in UV light act as both SPR and as charge separator to effectively generate ROS which easily disinfects the microbes. However, in the study conducted with the visible light having wavelength spectra in only visible region, zinc oxide can\u0026rsquo;t produce reactive radicals because of large band gap. However, silver nanoparticles showing SPR effect in visible region is responsible for the generation of radicals and causing disinfection. The proposed disinfection mechanism under UV and visible light is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003e3.10. Comparison with previous major studies\u003c/h2\u003e \u003cp\u003eMost of the disinfection studies had been conducted on E. coli or some indicator organism. Very few studies have been conducted on bacterial strains present in treated wastewaters. Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e shows a comparison study on bacterial disinfection work done in the recent past. As observed from the table, the presently obtained kinetic rate constant was higher compared to most of other studies. The present study was conducted on less power lamp compared to other studies. Still the kinetic rate obtained was comparable and higher than most of the studies. The major reason for this was the usage of monochromatic lamp for the excitation of ZnO, whose band-gap is close to the wavelength of light used. Another reason is the proper design of reactor and usage of aluminium foils in the inner walls which facilitates maximum light to remain in the reactor through internal reflection. \u003cem\u003eShigella flexneri\u003c/em\u003e had been studied by a number of authors earlier. Silver, copper and iron doped TiO\u003csub\u003e2\u003c/sub\u003e had been studied under UV light for this strain (Mecha et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). The maximum obtained kinetic rate was 0.067 min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for all the three dopants. The reason for a decrease in the results compared to the silver doped ZnO is because the catalyst synthesis technique. MWCNT/BiVO\u003csub\u003e4\u003c/sub\u003e had been studied and was found to completely disinfect \u003cem\u003eShigella flexneri\u003c/em\u003e in 180 min (Ye et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). However, the kinetic rate had not been mentioned. Moreover, the study used solar power which had higher power compared to the present study. ZnO/ Gypsum @ alginate beads was also studied (Misra et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Five log removal was observed in 120 min. However, the lamp power and kinetic removal rate were not discussed. Studies on other strains had showed lesser kinetic rate constant as observed in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eAlthough the previous work had been conducted at high lamp power, their reaction rate constant and bacterial removal was less than that reported here. Heterostructure formed from g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e quantum dots combined with g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanosheets had been studied for \u003cem\u003eStaphylococcus aureus\u003c/em\u003e (Yang et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The work was conducted at higher lamp power, however, complete disinfection was not achieved in 120 min. Similarly, lanthanum doped CeO\u003csub\u003e2\u003c/sub\u003e had been studied for \u003cem\u003eBacillus licheniformis\u003c/em\u003e (Chatterjee et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). However, the results obtained were not up to the mark. \u003cem\u003eE. coli\u003c/em\u003e studied by other authors in past by various catalysts had not shown remarkable photo catalytic activity. The composite CeO\u003csub\u003e2\u003c/sub\u003e and g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e had showed 7 log removal of \u003cem\u003eE. coli\u003c/em\u003e in 180 min (Huang et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). G-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e alone showed 5 log removal in 120 min (Zhang et al. \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). However, the power requirement was very high. Similarly, GO-TiO\u003csub\u003e2\u003c/sub\u003e-BiVO\u003csub\u003e4\u003c/sub\u003e showed 3 log removal in 180 min (Ch-Th et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Sulphur doped carbon quantum dot with gC\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e showed very good activity under visible light (Wang et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Ag doped ZnO nanorods prepared by solvothermal- co-precipitation method showed about 2 log removal in 120 min (Brindha et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). This showed the superiority of prepared photo-composite by the present method. In conclusion, the present study on microbes found in real environmental water samples had been closer to practical field applications and the obtained results were superior than the previous results reported.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003ePhotocatalytic comparison of Ag-ZnO with other commonly reported photocatalysts in the recent past.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"9\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePhotocatalyst\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMicrobe specie\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLamp (Power)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCatalyst dose (g/L)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eBacteria initial conc. (CFU/mL)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eTime taken (min)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eBacteria Log removal\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eKinetic rate (min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eRef\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAg-TiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eShigella flexneri\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eUV (150 W)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e10\u003csup\u003e6\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.067\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eMecha et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2019\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMWCNT/BiVO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eShigella flexneri\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSolar power\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e10\u003csup\u003e7\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e180\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eYe et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2021\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZnO/ Gypsum @ alginate beads\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eShigella flexneri\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eVisible LED\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e10\u003csup\u003e5\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eMisra et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2022\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eg-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e quantum dots- g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanosheets\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eStaphylococcus aureus\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eVisible (350 W)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e3*10\u003csup\u003e6\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e5.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eYang et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2023\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eLa- CeO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eE. coli\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eVisible\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e10\u003csup\u003e7\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e150\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e4.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eChatterjee et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2023\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eBacillus licheniformis\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eVisible\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e10\u003csup\u003e7\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e150\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e5.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCeO\u003csub\u003e2\u003c/sub\u003e/ g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eE. coli (K-12 strain)\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eVisible (300 W)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e10\u003csup\u003e7\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e180\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.085\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eHuang et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2021\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eg-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eE. coli\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eVisible (300 W)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.1 (PMS\u0026thinsp;=\u0026thinsp;0.15 g/L)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e10\u003csup\u003e5\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eZhang et al. \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2021\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGO-TiO\u003csub\u003e2\u003c/sub\u003e-BiVO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eE. coli (K-12 strain)\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSolar simulator light (500 W/m\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e10\u003csup\u003e7\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eCh-Th et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2021\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS- carbon quantum dot- gC\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eE. coli\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eVisible (300 W)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e3*10\u003csup\u003e7\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e6.88\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.029\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eWang et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2019\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAg-ZnO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eE. coli\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSimulated sunlight (150 W)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1.98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.027\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eBrindha et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2024\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eShigella flexneri\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eUV-A (40 W)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e10\u003csup\u003e8\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e180\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e3.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.045\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003ePresent study\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eAg-ZnO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eStenotrophomonas nematodicola\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eUV-A (40 W)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e10\u003csup\u003e8\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e4.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.082\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eFrediandcohnia salidurans\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eUV-A (40 W)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e10\u003csup\u003e8\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e4.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.074\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eShigella flexneri\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eUV-A (40 W)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e10\u003csup\u003e8\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e180\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.126\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003e3.11. Practical application of present work and future perspectives\u003c/h2\u003e \u003cp\u003eEnvironmental problems and human death associated with AMR have been increasing continuously over the years. The presence of antibiotics in water matrices and their combination with microbes has become a powerful combination which needs to be treated at WWTP before they are released into the environment.\u003c/p\u003e \u003cp\u003eIn this scenario, the results reported here has high significance. Photocatalysts have good disinfection efficiency of microbial strains present in treated wastewater. The results reported here showed good efficiency under UV-A light of AMR microbes. In visible light as well, the photocatalyst showed good activity which shows its potential for field applications. The photocatalysts presented here have higher kinetic rate of disinfection than those reported in past studies. However, the previous studies were mostly conducted at higher power lamps, as discussed in the Table. The studied photocatalysts had good removal for all the three bacterial strains found in WWTP effluents. Addition of PS within the drinking water permissible limits showed good increment in the photocatalytic disinfection activity. This shows the controllable disinfection kinetic rate when used for on-site usage. Moreover, the catalyst showed good removal for both bacterial disinfection and antibiotic degradation at same time. This indicates promise for field application as tertiary treatment in WWTP.\u003c/p\u003e \u003cp\u003eThe future scope of the present research work are: (i) studying the applicability of catalyst for treated wastewater effluents; (ii) investigate the effect of co-contaminants such as nutrients and phosphates which are also present in treated wastewater along with microbes and antibiotics; (iii) study the disinfection of all three bacterial strains in a combined system; (iv) all the present experiments has been conducted as batch study, future study can be conducted on continuous flow reactor; (v) energy, cost and life cycle assessment of the system.\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eIn the present study, Ag-ZnO and TiO\u003csub\u003e2\u003c/sub\u003e were studied for the disinfection of microbes present in real wastewater. The study showed that Ag-ZnO showed better activity compared to TiO\u003csub\u003e2\u003c/sub\u003e. The three bacterial strains identified in the biological treated STP sludge were \u003cem\u003eStenotrophomonas nematodicola, Frediandcohnia salidurans\u003c/em\u003e and \u003cem\u003eShigella felxneri\u003c/em\u003e, and it was found that \u003cem\u003eShigella felxneri\u003c/em\u003e has maximum resistance to disinfection. Bacterial concentration had inverse relation to its removal kinetics. Disinfection kinetics increased with an increase in catalyst dosage and after an optimum dose it decreased. Visible light had a decrease in activity compared to UV-A light because of the former being polychromatic and having less photocatalyst excitation energy. Addition of PS showed an increase in activity because of the formation of PS radicals and an increased formation of hydroxyl radicals. Combined study of antibiotic and bacteria showed little decrease in the removal of both because of competitive antagonistic effect for ROS generated. Overall, the catalyst showed very good disinfection for the bacterial strains along with antibiotics and has high potential for practical applications.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors greatly appreciate the funding provided by Shastri Indo-Canadian Institute for conducting this research.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors have received the funding from Shastri Indo-Canadian Institute (SICRG-2019–20-R2–1401) for conducting this research.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors’ contribution\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDinkar Parashar:\u003c/strong\u003e Conceptualization, execution of experiments, data collection, formal analysis and writing original draft of manuscript. \u003cstrong\u003eGopal Achari:\u003c/strong\u003e Formal analysis and evaluation, editing and reviewing of manuscript. \u003cstrong\u003eMathava Kumar:\u003c/strong\u003e Conceptualization, formal analysis and evaluation, editing and reviewing of manuscript, fund acquisition, and overall supervision.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical Approval\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis is not applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Participate\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis is not applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Publish\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis is not applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting Interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability Statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data associated with the manuscript will be available on request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eAhamed ST, Roy B, Basu U, Dutta S, Ghosh AN, Bandyopadhyay B, Giri N (2019). Genomic and proteomic characterizations of Sfin-1, a novel lytic phage infecting multidrug-resistant Shigella spp. and Escherichia coli C. Front Microbiol 10:1876. https://doi.org/10.3389/fmicb.2019.01876\u003c/li\u003e\n \u003cli\u003eArasavilli S, Taksal PA, Das BK, Chowdhury S, Bhattacharya J (2024). Green graphene supported Cu\u003csub\u003e2\u003c/sub\u003eO-Ag\u003csub\u003e2\u003c/sub\u003eO S-scheme photocatalyst with high disinfection activity for prevention of urinary tract infection in toilets: A metagenomic analysis. J Environ Chem Eng 12(3):112703. https://doi.org/10.1016/j.jece.2024.112703\u003c/li\u003e\n \u003cli\u003eBaaloudj O, Assadi I, Nasrallah N, El Jery A, Khezami L, Assadi AA (2021). Simultaneous removal of antibiotics and inactivation of antibiotic-resistant bacteria by photocatalysis: A review. J Water Process Eng 42:102089. https://doi.org/10.1016/j.jwpe.2021.102089\u003c/li\u003e\n \u003cli\u003eBIS (Bureau of Indian standards), 2012. Indian Standard drinking water. specification, 10500. http://cgwb.gov.in/documents/wq-standards.pdf\u003c/li\u003e\n \u003cli\u003eBrindha B, Okla MK, Kokilavani S, Sabariselvan L, Al-Amri SS, Abdel-Maksoud MA, Harini G, Alshuwaish R, Alsakkaf WA, Khan SS (2024). Dynamic Ag-mediated electron transfer confined ZnO nanorods for boosted photocatalytic bacterial disinfection. J Clean Prod 451:141908. https://doi.org/10.1016/j.jclepro.2024.141908\u003c/li\u003e\n \u003cli\u003eChatterjee M, Mondal M, Sukul T, Mal S, Ghosh K, Das S, Pradhan SK (2023). Superior photocatalytic performance and photo disinfection of bacteria of solvothermally synthesized mesoporous La-doped CeO\u003csub\u003e2\u003c/sub\u003e under simulated visible light irradiation for wastewater treatment. J Alloys Compd 942:169135. https://doi.org/10.1016/j.jallcom.2023.169135\u003c/li\u003e\n \u003cli\u003eChen X, Jin Y, Huang P, Zheng Z, Li LP, Lin CY, Chen X, Ding R, Liu J, Chen R (2024). Solar driven photocatalytic disinfection by Z-scheme heterojunction of In\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e: Performance, mechanism and application. Appl Catal B 340:123235. https://doi.org/10.1016/j.apcatb.2023.123235\u003c/li\u003e\n \u003cli\u003eCh-Th T, Manisekaran R, Santoyo-Salazar J, Schoefs B, Velumani S, Castaneda H, Jantrania A (2021). Graphene oxide decorated TiO\u003csub\u003e2\u003c/sub\u003e and BiVO\u003csub\u003e4\u003c/sub\u003e nanocatalysts for enhanced visible-light-driven photocatalytic bacterial inactivation. J Photochem Photobiol A Chem 418:113374. https://doi.org/10.1016/j.jphotochem.2021.113374\u003c/li\u003e\n \u003cli\u003eEkande OS, Kumar M (2021). Facile synthesis of graphitic carbon nitride from acetic acid pretreatment to activate persulfate in presence of blue light for photocatalytic removal of metronidazole. Chemosphere 276:130171. https://doi.org/10.1016/j.chemosphere.2021.130171\u003c/li\u003e\n \u003cli\u003eFabrega J, Fawcett SR, Renshaw JC, Lead JR. (2009). Silver nanoparticle impact on bacterial growth: effect of pH, concentration, and organic matter. Environ Sci Technol 43(19):7285-7290. https://doi.org/10.1021/es803259g\u003c/li\u003e\n \u003cli\u003eHuang W, Ruan S, Zhao M, Xu R, Chen Z, Zhihong G, Song H (2021). Visible-light-driven photocatalytic inactivation of Escherichia coli by 0D/2D CeO\u003csub\u003e2\u003c/sub\u003e/g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e heterojunction: bactericidal performance and mechanism. J Environ Chem Eng 9(6):106759. https://doi.org/10.1016/j.jece.2021.106759\u003c/li\u003e\n \u003cli\u003eJimenez-Tototzintle M, Ferreira IJ, Da Silva Duque S, Barrocas PRG, Saggioro EM (2018). Removal of contaminants of emerging concern (CECs) and antibiotic-resistant bacteria in urban wastewater using UVA/TiO\u003csub\u003e2\u003c/sub\u003e/H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e photocatalysis. Chemosphere 210:449-457. https://doi.org/10.1016/j.chemosphere.2018.07.036\u003c/li\u003e\n \u003cli\u003eKanakaraju D, Anak Kutiang FD, Lim YC, Goh PS (2022). Recent progress of Ag/TiO\u003csub\u003e2\u003c/sub\u003e photocatalyst for wastewater treatment: Doping, co-doping, and green materials functionalization. Appl Mater Today 27:101500. https://doi.org/10.1016/j.apmt.2022.101500\u003c/li\u003e\n \u003cli\u003eKumaravel V, Nair KM, MathewS, Bartlett J, Kennedy JE, Manning HG, Whelan BJ, Leyland NS, Pillai SC (2021). Antimicrobial TiO\u003csub\u003e2\u003c/sub\u003e nanocomposite coatings for surfaces, dental and orthopaedic implants. Chem Eng J 416:129071. https://doi.org/10.1016/j.cej.2021.129071\u003c/li\u003e\n \u003cli\u003eLi H, Zhang Z, Duan J, Li N, Li B, Song T, Sardar MF, Lv X, Zhu C (2020). Electrochemical disinfection of secondary effluent from a wastewater treatment plant: Removal efficiency of ARGs and variation of antibiotic resistance in surviving bacteria. Chem Eng J 392:123674. https://doi.org/10.1016/j.cej.2019.123674\u003c/li\u003e\n \u003cli\u003eMatsunaga T, Tomoda R, Nakajima T, Wake H (1985). Photoelectrochemical sterilization of microbial cells by semiconductor powders. FEMS Microbiol Lett 29(1-2):211-214.\u003c/li\u003e\n \u003cli\u003eMecha AC, Onyango MS, Ochieng A, Momba MNB (2019). UV and solar photocatalytic disinfection of municipal wastewater: inactivation, reactivation and regrowth of bacterial pathogens. Int J Environ Sci Technol 16:3687-3696. https://doi.org/10.1007/s13762-018-1950-1\u003c/li\u003e\n \u003cli\u003eMecha AC, Onyango MS, Ochieng A, Momba MN (2017). Evaluation of synergy and bacterial regrowth in photocatalytic ozonation disinfection of municipal wastewater. Sci Total Environ 601:626-635. https://doi.org/10.1016/j.scitotenv.2017.05.204\u003c/li\u003e\n \u003cli\u003eMisra AJ, Basu A, Behera SK, Mishra A, Lundborg CS, Tripathy SK (2022). Point-of-use photocatalytic device for water disinfection under visible light using ZnO/Gypsum@ alginate beads. J Environ Chem Eng 10(3):107520. https://doi.org/10.1016/j.jece.2022.107520\u003c/li\u003e\n \u003cli\u003eMoncayo-Lasso A, Mora-Arismendi LE, Rengifo-Herrera JA, Sanabria J, Benitez N, Pulgarin C (2012). The detrimental influence of bacteria (E. coli, Shigella and Salmonella) on the degradation of organic compounds (and vice versa) in TiO\u003csub\u003e2\u003c/sub\u003e photocatalysis and near-neutral photo-Fenton processes under simulated solar light. Photochem Photobiol Sci 11(5):821-827. https://doi.org/10.1039/C2PP05290C\u003c/li\u003e\n \u003cli\u003eParashar D, Achari G, Kumar M (2024). Facile synthesis of silver doped ZnO nanoparticles by thermal decomposition method for photocatalytic degradation of metronidazole under visible light. J Environ Chem Eng 113205. https://doi.org/10.1016/j.jece.2024.113205\u003c/li\u003e\n \u003cli\u003eParashar D, Achari G, Kumar M (2023). Multi-antibiotics removal under UV-A light using sol-gel prepared TiO\u003csub\u003e2\u003c/sub\u003e: Central composite design, effect of persulfate addition and degradation pathway study. Chemosphere 341:140025. https://doi.org/10.1016/j.chemosphere.2023.140025\u003c/li\u003e\n \u003cli\u003eQiu P, Zhu J, Zhang C, Liu T, Fang H, Shen L, Zhang S (2023). Visible light-supported efficient photocatalytic disinfection using a robust silver-doped boron photocatalyst. J Environ Chem Eng 11(5):111058. https://doi.org/10.1016/j.jece.2023.111058\u003c/li\u003e\n \u003cli\u003eRahman AH, Dash S, Mohanty PS, Mishra A, Lundborg CS, Tripathy SK (2020). Sonophotocatalytic disinfection of Shigella species under visible light irradiation: Insights into its molecular mechanism, antibacterial resistance and biofilm formation. Environ Res 187:109620. https://doi.org/10.1016/j.envres.2020.109620\u003c/li\u003e\n \u003cli\u003eSasikaladevi R, Kiruthika Eswari V, Nambi IM (2020). Antibiotic resistance and sanitation in India: current situation and future perspectives. Antibiotic Resistance in the Environment: A Worldwide Overview 217-244. https://doi.org/10.1007/698_2020_608\u003c/li\u003e\n \u003cli\u003eShekhawat SS, Gupta AB, Kulshreshtha NM, Prakash R (2021). UV disinfection studies on chlorine tolerant bacteria recovered from treated sewage. J Environ Chem Eng 9(3):105253. https://doi.org/10.1016/j.jece.2021.105253\u003c/li\u003e\n \u003cli\u003eWaclawek S, Lutze HV, Grubel K, Padil VV, Cernik M, Dionysiou DD (2017). Chemistry of persulfates in water and wastewater treatment: a review. Chem Eng J 330:44-62. https://doi.org/10.1016/j.cej.2017.07.132\u003c/li\u003e\n \u003cli\u003eWang W, Zeng Z, Zeng G, Zhang C, Xiao R, Zhou C, Xiong W, Yang Y, Lei L, Liu Y, Huang D, Cheng M, Yang Y, Fu Y, Luo H, Zhou Y (2019). Sulfur doped carbon quantum dots loaded hollow tubular g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e as novel photocatalyst for destruction of Escherichia coli and tetracycline degradation under visible light. Chem Eng J 378:122132. https://doi.org/10.1016/j.cej.2019.122132\u003c/li\u003e\n \u003cli\u003eXia D, An T, Li G, Wang W, Zhao H, Wong PK (2016). Synergistic photocatalytic inactivation mechanisms of bacteria by graphene sheets grafted plasmonic Ag-AgX (X= Cl, Br, I) composite photocatalyst under visible light irradiation. Water Res 99:149-161. https://doi.org/10.1016/j.watres.2016.04.055\u003c/li\u003e\n \u003cli\u003eXia D, Wang W, Yin R, Jiang Z, An T, Li G, Zhao H, Wong PK (2017). Enhanced photocatalytic inactivation of Escherichia coli by a novel Z-scheme g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e/m-Bi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e hybrid photocatalyst under visible light: the role of reactive oxygen species. Appl Catal B 214:23-33. https://doi.org/10.1016/j.apcatb.2017.05.035\u003c/li\u003e\n \u003cli\u003eXue W, Huang D, Wen X, Chen S, Cheng M, Deng R, Li B, Yang Y, Liu X (2020). Silver-based semiconductor Z-scheme photocatalytic systems for environmental purification. J Hazard Mater 390:122128. https://doi.org/10.1016/j.jhazmat.2020.122128\u003c/li\u003e\n \u003cli\u003eYang H, He D, Liu C, Zhou X, Qu J (2023). Magnetic photocatalytic antimicrobial materials for water disinfection. Sep Purif Technol 124697. https://doi.org/10.1016/j.seppur.2023.124697\u003c/li\u003e\n \u003cli\u003eYao L, Bai Y, Ding L, Hu Y, Zhang Z, Zhang Y, Chen R, Xie H, Wang J, Wang R (2024). Low oxygen adsorption energy barrier architectures to facilitate microenvironmental photocatalytic disinfection in Wei River. Chem Eng J 498:155468. https://doi.org/10.1016/j.cej.2024.155468\u003c/li\u003e\n \u003cli\u003eYe L, Liu J, Gong C, Tian L, Peng T, Zan L (2012). Two different roles of metallic Ag on Ag/AgX/BiOX (X= Cl, Br) visible light photocatalysts: surface plasmon resonance and Z-scheme bridge. ACS Catal 2(8):1677-1683. https://doi.org/10.1021/cs300213m\u003c/li\u003e\n \u003cli\u003eYe S, Xu Y, Huang L, Lai W, Deng L, Lin Z, Peng H, Zhou X, Xie G (2021). MWCNT/BiVO\u003csub\u003e4\u003c/sub\u003e photocatalyst for inactivation performance and mechanism of Shigella flexneri HL, antibiotic-resistant pathogen. Chem Eng J 424:130415. https://doi.org/10.1016/j.cej.2021.130415\u003c/li\u003e\n \u003cli\u003eZaika LL (2001). The effect of temperature and low pH on survival of Shigella flexneri in broth. J Food Prod 64(8):1162-1165. https://doi.org/10.4315/0362-028X-64.8.1162\u003c/li\u003e\n \u003cli\u003eZhang C, Li Y, Wang C, Zheng X (2021). Different inactivation behaviors and mechanisms of representative pathogens (Escherichia coli bacteria, human adenoviruses and Bacillus subtilis spores) in g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e-based metal-free visible-light-enabled photocatalytic disinfection. Sci Total Environ 755:142588. https://doi.org/10.1016/j.scitotenv.2020.142588\u003c/li\u003e\n \u003cli\u003eZhu D, Zhou Q (2019). Action and mechanism of semiconductor photocatalysis on degradation of organic pollutants in water treatment: A review. Environ Nanotechnol Monit Manag 12:100255. https://doi.org/10.1016/j.enmm.2019.100255\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":"Photocatalytic disinfection, wastewater treatment, antibiotic removal, disinfection kinetics","lastPublishedDoi":"10.21203/rs.3.rs-6790617/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6790617/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIn this study, applicability of UV-A based photocatalytic disinfection of secondary effluent from a sewage treatment plant (STP) was investigated. Three bacterial strains from the biological treatment effluent namely \u003cem\u003eStenotrophomonas nematodicola, Frediandcohnia salidurans\u003c/em\u003e and \u003cem\u003eShigella felxneri\u003c/em\u003e were isolated, cultured and plated for further experiments in the presence of a model antibiotic, metronidazole (MNZ). Silver doped zinc-oxide (Ag-ZnO) and titanium di-oxide (TiO\u003csub\u003e2\u003c/sub\u003e) were used as photocatalysts for the disinfection experiments where the former showed better disinfection kinetics under UV-A lamp. Out of the three microbial strains, \u003cem\u003eShigella flexneri\u003c/em\u003e strain showed maximum resistance towards photocatalytic disinfection. Increasing the catalyst dose to 3 g/L increased the disinfection kinetics. However, above 3 g/L, the rate of disinfection decreased due to agglomeration of nano-catalysts, and the increase in residual turbidity. Effect of \u003cem\u003eshigella\u003c/em\u003e \u003cem\u003eflexneri\u003c/em\u003e concentration showed that disinfection kinetics decreased with increase in bacteria concentration from 1x10\u003csup\u003e4\u003c/sup\u003e to 1x10\u003csup\u003e9\u003c/sup\u003e CFU/mL. In 2 and 3 h, complete removal of 1x10\u003csup\u003e6\u003c/sup\u003e and 1x10\u003csup\u003e8\u003c/sup\u003e CFU/mL was achieved under optimum conditions respectively. In visible region, the activity decreased slightly with a decrease in pseudo-first-order kinetics by ~1.9 times because of the polychromatic visible light. Further, the addition of persulfate in small amount of 200 mg/L increased the disinfection kinetics by ~1.5 times due to generation of persulfate radicals. The presence of MNZ with the \u003cem\u003eshigella flexneri\u003c/em\u003e showed that there was a decrease in removal efficiency for both the antibiotic and bacteria with both photocatalysts. This was caused by the competitive antagonistic effect between the antibiotic and bacteria for the reactive oxygen species generated on the photocatalyst surface. Overall, Ag-ZnO showed good photocatalytic disinfection towards wastewater microbes under UV-A.\u003c/p\u003e","manuscriptTitle":"UV-A based photocatalytic disinfection of secondary effluent from a wastewater treatment plant using Ag-ZnO: Effect of antibiotic presence, catalyst concentration, lamp and persulfate addition","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-06-23 15:33:14","doi":"10.21203/rs.3.rs-6790617/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":"d43e5a09-7eb1-4d2f-ba6d-5461d80893f3","owner":[],"postedDate":"June 23rd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-07-01T09:25:33+00:00","versionOfRecord":[],"versionCreatedAt":"2025-06-23 15:33:14","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6790617","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6790617","identity":"rs-6790617","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}