Solar light and the photo-Fenton process against antibiotic resistant bacteria in wastewater: A kinetic study with a Streptomycin-resistant strain

Application of heterogeneous Fenton-like reaction with modified zeolite for removal of antibiotics, antibiotic-resistant bacteria, and antibiotic-resistant genes from swine farm wastewater

The heterogeneous Fenton-like reaction with modified zeolite was introduced for the removal of antibiotics, antibiotic-resistant bacteria (ARB), and antibiotic-resistant genes (ARGs) to reduce environmental impact of the substance residues in swine farm effluent. The heterogeneous Fenton-like reaction with 100 g/L of the modified zeolite and 2 mM H2O2 could completely remove amoxicillin (AMX), tetracycline (TC), and tiamulin (TIA) in the swine farm effluent within 30 min. However, the antibiotic removal in the swine farm effluent was slower than in the ultrapure water. The heterogeneous Fenton-like reaction removed approximately 45-60% of dissolved organic carbon (DOC) and reduced the dissolved organic matter (DOM) sizes in the swine farm effluent. The large molecular size humic-like DOM co-existing in the swine farm effluent could probably decelerate the antibiotic removal via competitive adsorption and oxidation. To inactivate high-tolerant AMX-resistant E. coli, the heterogeneous Fenton-like reaction required 3-fold less exposure time than the H2O2 oxidation. No regrowth of the high-tolerant AMX-resistant E. coli was observed when the exposure time of the heterogeneous Fenton-like reaction was longer than 6 h. The heterogeneous Fenton-like reaction required the exposure time of 24 h to reduce the blaTEM genes, the AMX-resistant genes, of the high-tolerant AMX-resistant E. coli to the level of lower than the limit of detection. The results suggest that different reaction times are required for the removal of antibiotics (within 30 min), ARB (over 6 h), and ARGs (within 24 h). Furthermore, the heterogeneous Fenton-like reaction with the modified zeolite is a promising technology for sequential and efficient removal of antibiotics, ARB, and ARGs residues in swine farm effluent before being discharged into the environment.

Water disinfection and disinfection by products

For ecological safety and public health, it is essential to identify the causes of pollution in water sources and the effects of both natural and human activities. A class of secondary pollutants known as disinfection byproducts (DBPs) is produced when water is treated with disinfectant. Global problems include DBP formation, monitoring, and health effects in drinkable water. Because of the negative health effects of drinking chlorinated water and some DBPs, water manufacturers have made an attempt to balance pathogen elimination with DBP monitoring. The primary obstacles to managing DBPs are their low concentrations and the viability of their extensive use from a technical and economic perspective. Adsorption on activated carbons, ion exchange, membrane processes, and reducing precursors like NOMs are some of the techniques that may be used in controlling DBPs. The application of both new and conventional disinfection technologies in the removal of ARB and ARGs is also summarized in this review, with an emphasis on bacterial inactivation mechanisms like ozonation, chlorination, ultraviolet (UV), sunlight, sunlight-dissolved organic matter (DOM), and photocatalysis/photoelectrocatalysis (PEC).

ZnO-based Cu metal-organic framework (MOF) nanocomposite for boosting and tuning the photocatalytic degradation performance

Although metal-organic frameworks (MOFs) are a viable choice for photocatalysts with large surface area and tunable pore structure, the rapid recombination of excited photogenerated charges results in low activity towards photodegradation. Aiming at improving the photocatalytic activities of MOFs, different strategies to incorporate MOF with light-harvesting semiconductors have been developed. In this research, we report an effective photocatalyst designed by incorporating Cu-MOF with ZnO for the photocatalytic degradation of Rose Bengal exhibiting excellent degradation efficiency of 97.4% in 45 min under natural sunlight with catalyst dosage of 320 mg/L. The optical, morphology and surface characteristics of the prepared nanocomposite were studied using scanning electron microscopy (SEM-EDX), high-resolution transmission electron microscopy (HRTEM), powder X-ray diffraction (PXRD), Brunauer-Emmett-Teller (BET) analysis, thermogravimetric (TGA) analysis, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and ultraviolet diffused reflectance spectroscopy (UV-DRS) techniques. Further studies showed that the degradation followed first-order kinetics with a rate constant of 0.077869 min-1. The degradation mechanism was investigated by photoluminescence (PL) study, XPS, zeta potential and quenching experiment in presence of different scavengers. Meanwhile, the fabricated composite displayed good recovery and reuse properties up to 5 cycles as revealed by XRD analysis proving itself a potential MOF-based photocatalyst towards environmental remediation process.

Disinfection of treated urban effluents for reuse by combination of coagulation/flocculation and Fenton processes

In this study, a combination of coagulation/flocculation and Fenton processes was studied as tertiary treatment in order to generate treated water susceptible to reuse. The combination of both processes has never been applied in disinfection of real urban wastewater. The best removals of turbidity and enterobacteria were achieved when applying a coagulant (FeCl₃) dosage of 120 mg/L and the natural pH of the effluent (7.14). The following Fenton reaction presented the maximal enterobacteria inactivation after 120 min at 25 °C, when using hydrogen peroxide and added iron concentrations of 100 mg/L and 7 mg/L, respectively. The abundance of antibiotic resistant (amoxicillin and sulfamethoxazole) enterobacteria and total enterobacteria, enterococci, and heterotrophs, and antibiotic resistance genes - ARG - (sul1, bla_TEM and qnrS) was evaluated before and after each step of the treatment. Values below 10 CFU/100 mL were achieved for total and resistant cultivable enterobacteria immediately after treatment and after storage for 72 h, therefore meeting the strictest limit imposed for E. coli. Physico-chemical parameters also met the established limits for water reuse. Despite harbouring a rich and diverse bacterial community, the final stored disinfected wastewater contained high relative abundance of potentially hazardous bacteria. Such results point out the need of a deep microbiological characterization of treated wastewater to evaluate the risk of its reuse in irrigation.

Simultaneous Removal of Antibiotic Resistant Bacteria, Antibiotic Resistance Genes, and Micropollutants by FeS2@GO-Based Heterogeneous Photo-Fenton Process

The co-occurrence of various chemical and biological contaminants of emerging concerns has hindered the application of water recycling. This study aims to develop a heterogeneous photo-Fenton treatment by fabricating nano pyrite (FeS₂) on graphene oxide (FeS₂@GO) to simultaneously remove antibiotic resistant bacteria (ARB), antibiotic resistance genes (ARGs), and micropollutants (MPs). A facile and solvothermal process was used to synthesize new pyrite-based composites. The GO coated layer forms a strong chemical bond with nano pyrite, which enables to prevent the oxidation and photocorrosion of pyrite and promote the transfer of charge carriers. Low reagent doses of FeS₂@GO catalyst (0.25 mg/L) and H₂O₂ (1.0 mM) were found to be efficient for removing 6-log of ARB and 7-log of extracellular ARG (e-ARG) after 30 and 7.5 min treatment, respectively, in synthetic wastewater. Bacterial regrowth was not observed even after a two-day incubation. Moreover, four recalcitrant MPs (sulfamethoxazole, carbamazepine, diclofenac, and mecoprop at an environmentally relevant concentration of 10 μg/L each) were completely removed after 10 min of treatment. The stable and recyclable composite generated more reactive species, including hydroxyl radicals (HO^•), superoxide radicals (O₂^• -), singlet oxygen (¹O₂). These findings highlight that the synthesized FeS₂@GO catalyst is a promising heterogeneous photo-Fenton catalyst for the removal of emerging contaminants.

A new solar photo-Fenton strategy for wastewater reclamation based on simultaneous supply of H2O2 and NaOCl

This study presents, for the first time, the concurrent supply of the oxidants H₂O₂ and NaOCl in solar-driven Fenton-like processes at neutral pH with ferric nitrilotriacetate (Fe³⁺-NTA) for wastewater reclamation. Simultaneous Escherichia coli (E. coli) inactivation and the removal of the antibiotic sulfamethoxazole (SMX) at 50 μg/L in municipal effluents were investigated in 5-cm deep raceway pond reactors. First, the individual effects of reagent concentrations (1.47, 2.94 and 4.41 mM for H₂O₂; 0.134, 0.269 and 0.403 mM for NaOCl; 0.1 and 0.2 mM for Fe³⁺-NTA) on the economic efficiency (in terms of mass of SMX eliminated per Euro and per hour to attain complete E. coli inactivation and more than 50% of SMX removal) were considered. The highest economic efficiencies were 141 mg_SMX/€·h with H₂O₂ and 222 with NaOCl, the reaction times being 105 and 60 min, respectively. Second, a new strategy for solar photo-Fenton with the combination of the most cost-effective conditions (1.47 mM H₂O₂ - 0.134 mM NaOCl - 0.1 mM Fe³⁺-NTA) was carried out in secondary effluents from two treatment plants with different technologies. Economic efficiency was substantially affected by wastewater composition, ranging from 178 to 1131 mg_SMX/€·h with treatment times between 60 and 10 min, significantly improving the reported results for conventional solar photo-Fenton to date.

Removal of METH through Tertiary or Advanced Treatment in a WWTP

METHs are drugs that enter wastewater through the feces and urine of users. Conventional wastewater treatment plants are not capable of removing this type of emerging contaminant, but, in recent years, techniques have been developed to abate drugs of abuse. The present investigation focused on obtaining the technique that keeps the best balance between the comparison criteria considered: efficiency; costs; development stage; and waste generation. That is why a bibliographic review was carried out in the scientific databases of the last eight years, concluding that the six most popular techniques are: SBR, Fenton reaction, mixed-flow bioreactor, ozonation, photocatalysis, and UV disinfection. Subsequently, the Saaty and Modified Saaty methods were applied, obtaining a polynomial equation containing the four comparison criteria for the evaluation of the techniques. It is concluded that the UV disinfection method is the one with the best relationship between the analyzed criteria, reaching a score of 0.8591/1, followed by the Fenton method with a score of 0.6925/1. This research work constitutes a practical and easy-to-use tool for decision-makers, since it allows finding an optimal treatment for the abatement of METHs.

Roles of reactive oxygen species in antibiotic resistant bacteria inactivation and micropollutant degradation in Fenton and photo-Fenton processes

Reactive oxygen species play a critical role in degrading chemical or biological contaminants in advanced oxidation processes. However, it is still not clear whether conventional Fenton and photo-Fenton processes generate different reactive oxygen species, respectively. This study revealed the roles of reactive oxygen species (ROS) for simultaneous removal of antibiotic resistant bacteria (ARB) and recalcitrant micropollutant using three processes, i.e., conventional Fenton, photo-Fenton, and ethylenediamine-N, N'-disuccinic acid (EDDS) modified photo-Fenton. Both chemical scavengers and electron paramagnetic resonance spectroscopy confirmed the generation of various ROS and their contribution towards bacterial inactivation and micropollutant degradation. Results showed ARB and carbamazepine (CBZ) elimination efficiency in the order: EDDS modified photo-Fenton process > photo-Fenton process > Fenton process. The ARB detection limit (6-log ARB) was observed within 10 min at lower doses of 0.1 mM Fe³⁺, 0.2 mM EDDS, and 0.5 mM hydrogen peroxide (H₂O₂). With the same dose, it took longer (60 min) to remove CBZ, while 2.5 times higher H₂O₂ dose (1.25 mM) removed around 99% of CBZ within 10 min treatment. The present study highlighted that the hydroxyl radical (HO^•) plays a dominant role, while singlet oxygen (¹O₂) and superoxide radical anion (O₂^•-) exhibit moderate effects to remove the hazards. Our findings provide mechanistic insights into the role of various reactive oxygen species on degrading micropollutants and inactivating ARB.

Application of iron-activated persulfate for municipal wastewater disinfection

To address the increasing contamination of aquatic environments and incidence of waterborne diseases, advanced oxidation processes with activated persulfate have emerged as tools to inactivate wastewater microorganisms and contaminants. In this work, the disinfection of a secondary effluent from a wastewater treatment plant by iron-based persulfate activation was studied. Experiments in a batch stirred tank reactor were carried out to evaluate the performance along reaction time and the effect of operational parameters in the oxidative process efficiency (oxidant and iron concentration, pH and temperature). After 60 min of reaction, persulfate and iron concentrations of 3 mM and 0.75 mM, respectively, combined with a neutral initial pH (7.5) and a temperature of 40 °C, allowed to reach values below the detection limit (<10 CFU/100 mL) of enterococci and enterobacteria with and without ciprofloxacin resistance, as well as a 91% inactivation of total heterotrophic organisms and a 70% removal of total organic carbon. Regrowth of microorganisms was evaluated 72 h after treatment and it was only noticed a slight increase in total heterotrophs. Evaluation of physico-chemical characteristics of the treated water showed that it meets the requirements imposed by European and Portuguese legislation for its reuse in irrigation and most urban utilities.

Irreversible inactivation of carbapenem-resistant Klebsiella pneumoniae and its genes in water by photo-electro-oxidation and photo-electro-Fenton - Processes action modes

Carbapenem-resistant Klebsiella pneumoniae is a critical priority pathogen according to the World Health Organization's classification. Effluents of municipal wastewater treatment plants (EWWTP) may be a route for K. pneumoniae dissemination. Herein, the inactivation of this microorganism in simulated EWWTP by the photo-electro-oxidation (PEO) and photo-electro-Fenton (PEF) processes was evaluated. Firstly, the disinfecting ability and action pathways of these processes were established. PEO achieved faster K. pneumoniae inactivation (6 log units in 75 min of treatment) than the PEF process (6 log units in 105 min of treatment). PEO completely inactivated K. pneumoniae due to the simultaneous action of UVA light, electrogenerated H₂O_2, and anodic oxidation pathways. The slower inactivation of K. pneumoniae when using PEF was related to interfering screen effects of iron oxides on light penetration and the diffusion of the bacteria to the anode. However, both PEO and PEF avoided the recovery and regrowth of treated bacteria (with no detectable increase in the bacteria concentration after 24 h of incubation). In addition to the bacteria evolution, the effect of treatment processes on the resistance gene was examined. Despite inactivation of K. pneumoniae by PEF was slower than by PEO, the former process induced a stronger degrading action on the gene, conferring the resistance to carbapenems (PEF had a Ct value of 24.92 cycles after 105 min of treatment, while PEO presented a Ct of 19.97 cycles after 75 min). The results of this research indicate that electrochemical processes such as PEO and PEF are highly effective at dealing with resistant K. pneumoniae in the EWWTP matrix.

Simultaneous bacterial inactivation and microcontaminant removal by solar photo-Fenton mediated by Fe3+-NTA in WWTP secondary effluents

Simultaneous microorganism inactivation and organic microcontaminant removal in municipal wastewater treatment plant (WWTP) secondary effluents by the solar photo-Fenton process mediated by Fe³⁺-NTA is studied in depth. To achieve this objective, different key aspects were addressed: (i) the effect of initial Fe³⁺-NTA concentration at 1:1 molar ratio (0.10-0.30 mM) and H₂O₂ concentration (1.47-5.88 mM), (ii) the effect of initial microorganism load (10³ and 10⁶ CFU/mL) and (iii) the impact of the disinfection target on treatment cost. The first stage of this work was carried out in simulated WWTP effluent spiked with 100 µg/L of imidacloprid (IMD) as model microcontaminant and inoculated with Escherichia coli (E. coli) K-12 as reference strain, in a pilot scale raceway pond reactor with 5-cm of liquid-depth. Secondly, the most cost-effective conditions were validated in actual WWTP effluent. The kinetic analysis revealed that increasing Fe³⁺-NTA concentration over 0.20 mM does not significantly reduce treatment time due to the limited effect caused on the volumetric rate photon absorption. Treatment cost is determined by the disinfection process, since IMD removal was always faster than E. coli inactivation. The most cost-effective strategy to achieve 10 CFU/100 mL of E. coli (Regulation EU 2020/741) was 0.20/4.41 mM Fe³⁺-NTA/H₂O₂, with a cost of 0.32 €/m³. A less restrictive disinfection target, 100 CFU/100 mL, allowed reducing reactant concentration and cost, 0.10/1.47 mM Fe³⁺-NTA/H₂O₂ and 0.15 €/m³, respectively. In both cases, no regrowth at 24 h and more than 90% of IMD removal were observed.

Combat of antimicrobial resistance in municipal wastewater treatment plant effluent via solar advanced oxidation processes: Achievements and perspectives

This review aims to gather main achievements and limitations associated to the application of solar photocatalytic processes with regard to the removal of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) from municipal wastewater treatment plant effluent (MWWTPE). Solar photocatalytic processes were chosen considering the context of developing tropical countries. Among these processes, solar photo-Fenton has been proved effective for the elimination of ARB from MWWTPE at neutral pH in bench and pilot scale and also under continuous flow. Yet, ARG removal varies as according to the gene. Irradiation intensity and matrix composition play a key role on treatment efficiency for this purpose. The use of sulfate radical in modified solar photo-Fenton is still incipient for ARB and ARG removal. Also, investigations related to ARB resistance profile and horizontal gene transfer rates after solar photo-Fenton treatment must be further analyzed. Regarding solar heterogeneous photocatalysis, TiO₂ and TiO₂-composites applied in suspension are the most commonly investigated for the removal of ARB and ARGs. Irradiation intensity, temperature and catalyst dosage affect treatment efficiency. However, most studies were performed in synthetic solutions using reduced sample volumes. Extended exposition times and addition of H₂O₂ to the system (solar/TiO₂/H₂O₂) are required to prevent bacteria regrowth and ensure ARG abatement. In addition, enhancement of TiO₂ with graphene or (semi)metals improved ARB elimination. Differences concerning irradiation intensity, matrix composition, catalyst dosage, and model ARB and ARGs used in studies analyzed in this review hinder the comparison of photocatalysts synthesized by various research groups. Finally, future research should aim at evaluating the efficiency of solar photocatalytic processes in real matrices originated from sewage treatment systems applied in developing countries; determining indicators of antimicrobial resistance in MWWTPE; and investigating ARB mutation rate as well as the removal of cell-free ARGs present in suspension in MWWTPE.

Simultaneous removal of antibiotic resistant bacteria, antibiotic resistance genes, and micropollutants by a modified photo-Fenton process

Although photo-driven advanced oxidation processes (AOPs) have been developed to treat wastewater, few studies have investigated the feasibility of AOPs to simultaneously remove antibiotic resistant bacteria (ARB), antibiotic resistance genes (ARGs) and micropollutants (MPs). This study employed a modified photo-Fenton process using ethylenediamine-N,N'-disuccinic acid (EDDS) to chelate iron(III), thus maintaining the reaction pH in a neutral range. Simultaneous removal of ARB and associated extracellular (e-ARGs) and intracellular ARGs (i-ARGs), was assessed by bacterial cell culture, qPCR and atomic force microscopy. The removal of five MPs was also evaluated by liquid chromatography coupled with mass spectrometry. A low dose comprising 0.1 mM Fe(III), 0.2 mM EDDS, and 0.3 mM hydrogen peroxide (H₂O₂) was found to be effective for decreasing ARB by 6-log within 30 min, and e-ARGs by 6-log within 10 min. No ARB regrowth occurred after 48-h, suggesting that the proposed process is an effective disinfectant against ARB. Moreover, five recalcitrant MPs (carbamazepine, diclofenac, sulfamethoxazole, mecoprop and benzotriazole at an initial concentration of 10 μg/L each) were >99% removed after 30 min treatment in ultrapure water. The modified photo-Fenton process was also validated using synthetic wastewater and real secondary wastewater effluent as matrices, and results suggest the dosage should be doubled to ensure equivalent removal performance. Collectively, this study demonstrated that the modified process is an optimistic 'one-stop' solution to simultaneously mitigate both chemical and biological hazards.

Regrowth of bacteria after light-based disinfection - What we know and where we go from here

Regrowth of bacteria after water/wastewater disinfection is a serious risk to public health, particularly when such pathogens carry antibiotic resistance genes. Despite increasing interest in light-based disinfection using ultraviolet or solar radiation, the mechanism of bacterial regrowth and their concentration upon light exposure (i.e., during storage, or after discharge into rivers or lakes) remain poorly understood. Therefore, we present a focused critical review to 1) elucidate regrowth mechanisms, 2) summarize the pros and cons of available experimental designs and detection techniques for regrowth evaluation, and 3) provide an outlook of key research directions for further investigations of post-disinfection bacterial regrowth. Bacterial regrowth can occur through reactivation from a viable but non-culturable state, repair of photo-induced DNA damage, and reproduction of bacteria surviving disinfection. Many studies have underestimated the degree of actual regrowth because of the use of simple experimental designs and plate count methods, which cannot quantify actual abundance of viable bacteria. Further research should investigate the effects of various factors on bacterial regrowth in realistic conditions in regrowth tests and adopt multiplex detection methods that combine culture-based and culture-independent approaches. An accurate understanding of the mechanisms involved in bacterial regrowth following disinfection is critical for safeguarding public health and aquatic environments.

Persulfate mediated solar photo-Fenton aiming at wastewater treatment plant effluent improvement at neutral PH: emerging contaminant removal, disinfection, and elimination of antibiotic-resistant bacteria

This work investigated an innovative alternative to improve municipal wastewater treatment plant effluent (MWWTP effluent) quality aiming at the removal of contaminants of emerging concern (caffeine, carbendazim, and losartan potassium), and antibiotic-resistant bacteria (ARB), as well as disinfection (E. coli). Persulfate was used as an alternative oxidant in the solar photo-Fenton process (solar/Fe/S₂O₈^2-) due to its greater stability in the presence of matrix components. The efficiency of solar/Fe/S₂O₈^2- at neutral pH using intermittent iron additions is unprecedented in the literature. At first, solar/Fe/S₂O₈^2- was performed in a solar simulator (30 W m^-2) leading to more than 60% removal of CECs, and the intermittent iron addition strategy was proved effective. Then, solar/Fe/S₂O₈^2- and solar/Fe/H₂O₂ were compared in semi-pilot scale in a raceway pond reactor (RPR) and a cost analysis was performed. Solar/Fe/S₂O₈^2- showed higher efficiencies of removal of target CECs (55%), E. coli (3 log units), and ARB (3 to 4 log units) within 1.9 kJ L^-1 of accumulated irradiation compared to solar/Fe/H₂O₂ (CECs, 49%; E. coli, 2 log units; ARB, 1 to 3 log units in 2.5 kJ L^-1). None of the treatments generated acute toxicity upon Allivibrio fischeri. Lower total cost was obtained using S₂O₈^2- (0.6 € m^-3) compared to H₂O₂ (1.2 € m^-3). Therefore, the iron intermittent addition aligned to the use of persulfate is suitable for MWWTP effluent quality improvement at neutral pH.

Are iron chelates suitable to perform photo-Fenton at neutral pH for secondary effluent treatment?

There have been concerns about which iron chelate is most suitable for application in the photo-Fenton process as well as the fate of these chelates after application. In this study, five chelating agents, i.e. citric acid (CA), oxalic acid (OA), ethylenediamine disuccinic acid (EDDS), ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), representing the most used iron chelates were assessed for suitability of application in homogeneous photo-Fenton-like process at pH of 7. The efficiency of the iron chelates were assessed in the disinfection of secondary effluent. The results for the disinfection and bacteria regrowth followed the order EDTA>OA>NTA>CA>OA. All the iron chelates were observed to have increased the COD of the effluent with EDDS having the highest COD contribution. The ability of the chelates to remove aromaticity was measured by the UV₂₅₄ measurement. The efficiency of the chelates to remove aromaticity decreased in the order CA>EDDS>NTA>CA>OA. To determine the fate of the chelates, toxicity tests were conducted on the chelates before and after irradiation and the results revealed a decrease in toxicity after photoirradiation, implying the chelates were degraded and the products/intermediates produced were of less toxicity as compared to the parent compounds.

Efficient inactivation of antibiotic resistant bacteria and antibiotic resistance genes by photo-Fenton process under visible LED light and neutral pH

Antibiotic resistance has been recognized as a major threat to public health worldwide. Inactivation of antibiotic resistant bacteria (ARB) and degradation of antibiotic resistance genes (ARGs) are critical to prevent the spread of antibiotic resistance in the environment. Conventional disinfection processes are effective to inactivate water-borne pathogens, yet they are unable to completely eliminate the antibiotic resistance risk. This study explored the potential of the photo-Fenton process to inactivate ARB, and to degrade both extracellular and intracellular ARGs (e-ARGs and i-ARGs, respectively). Using Escherichia coli DH5α with two plasmid-encoded ARGs (tetA and bla_TEM-1) as a model ARB, a 6.17 log ARB removal was achieved within 30 min of applying photo-Fenton under visible LED and neutral pH conditions. In addition, no ARB regrowth occurred after 48-h, demonstrating that this process is very effective to induce permanent disinfection on ARB. The photo-Fenton process was validated under various water matrices, including ultrapure water (UPW), simulated wastewater (SWW) and phosphate buffer (PBS). The higher inactivation efficiency was observed in SWW as compared to other matrices. The photo-Fenton process also caused a 6.75 to 8.56-log reduction in eARGs based on quantitative real-time PCR of both short- and long amplicons. Atomic force microscopy (AFM) further confirmed that the extracellular DNA was sheared into short DNA fragments, thus eliminating the risk of the transmission of antibiotic resistance. As compared with e-ARGs, a higher dosage of Fenton reagent was required to damage i-ARGs. In addition, the tetA gene was more easily degraded than the bla_TEM-1 gene. Collectively, our results demonstrate the photo-Fenton process is a promising technology for disinfecting water to prevent the spread of antibiotic resistance.

Inactivation and change of tetracycline-resistant Escherichia coli in secondary effluent by visible light-driven photocatalytic process using Ag/AgBr/g-C3N4

Control of antibiotic-resistant bacteria (ARB) and their related genes in secondary effluents has become a serious issue because of increased awareness of their health risks. A considerable number of techniques have been developed in recent years, particularly in relation to advanced oxidation. However, limited information is known about cellular behavior and resistance characteristic change during photocatalytic treatment. In this study, the inactivation of tetracycline (TC)-resistant Escherichia coli (TC-E. coli), removal of TC-resistant genes (TC-RGs), and antibiotic susceptibility were evaluated by employing photocatalytic treatment using Ag/AgBr/g-C₃N₄ with visible light irradiation. The effects of light intensity, photocatalyst dosage, and reaction ambient temperature on photocatalysis were modelled and investigated. The rate of TC-E. coli removal was also optimized. Results demonstrated that the optimal conditions for TC-E. coli removal included light intensity of 96.0 mW/cm², photocatalyst dosage of 211.0 mg/L, and reaction ambient temperature of 23.7 °C. Under such conditions, the ARB removal rate was 6.1 log after 90 min and the related TC-RG removal rates were 49%, 86%, 69%, and 86% for tetA, tetM, tetQ, and intl1, respectively. The minimum inhibitory concentration test after photocatalysis shows that the antibiotic resistance of TC-E. coli was enhanced, which may be mainly due to the changes in the membrane potential and resulted in difficulty in destroying the bacteria through antibiotic contact. Hence, photocatalytic treatment could be an ideal method for ARB and antibiotic-resistant gene (ARG) control in wastewater, but the health risks of the remaining ARB and ARG should be investigated further.

Wastewater Treatment by Advanced Oxidation Process and Their Worldwide Research Trends

Background: Water is a scarce resource and is considered a fundamental pillar of sustainable development. The modern development of society requires more and more drinking water. For this cleaner wastewater, treatments are key factors. Among those that exist, advanced oxidation processes are being researched as one of the sustainable solutions. The main objective of this manuscript is to show the scientific advances in this field. Methods: In this paper, a systematic analysis of all the existing scientific works was carried out to verify the evolution of this line of research. Results: It was observed that the three main countries researching this field are China, Spain, and the USA. Regarding the scientific collaboration between countries, three clusters were detected-one of Spain, one of China and the USA, and one of Italy and France. The publications are grouped around three types of water: industrial, urban, and drinking. Regarding the research, 15 clusters identified from the keywords analyzed the advanced oxidation process (alone or combined with biological oxidation) with the type of wastewater and the target pollutant, removal of which is intended. Finally, the most important scientific communities or clusters detected in terms of the number of published articles were those related to the elimination of pollutants of biological origin, such as bacteria, and of industrial nature, such as pesticides or pharmaceutical products.

Removal of microorganisms and antibiotic resistance genes from treated urban wastewater: A comparison between aluminium sulphate and tannin coagulants

The presence of antibiotic resistant-bacteria (ARB) and antibiotic resistance genes (ARG) in treated effluents of urban wastewater treatment plants (WWTP) may represent a threat to the environment and public health. Therefore, cost-effective technologies contributing to minimize loads of these contaminants in the final effluents of WWTP are required. This study aimed at assessing the capacity of coagulation to reduce the ARB&ARG load in secondary treated urban wastewater (STWW), as well as the impact of the process on the structure and diversity of the bacterial community. Coagulation performance using aluminium sulphate, a synthetic substance, and tannins, a biowaste, was compared. Samples were analysed immediately before (STWW) and after the coagulation treatment (Alu, Tan), as well as after 3-days storage in the dark at room temperature (RSTWW, RAlu, RTan), to assess possible reactivation events. Both coagulants decreased the turbidity and colour and reduced the bacterial load (16S rRNA gene copy number, total heterotrophs (HET), and ARB (faecal coliforms resistant to amoxicillin (FC/AMX) or ciprofloxacin (FC/CIP) up to 1-2 log immediately after the treatment. Both coagulants reduced the load of intl1, but in average, aluminium sulphate was able to decrease the content of the analysed ARGs (bla_TEM and qnrS) to lower levels than tannin. Reactivation after storage was observed mainly in RTan. In these samples the load of the culturable populations and qnrS gene prevalence increased, sometimes to values higher than those found in the initial wastewater. Reactivation was also characterized by an increment in Gammaproteobacteria relative abundance in the bacterial community, although with distinct patterns for RTan and RAlu. Curvibacter, Undibacterium and Aquaspirillum were among the most abundant genera in RAlu and Aeromonas, Pseudomonas and Stenotrophomonas in RTan. These bacterial community shifts were in agreement with the variations in the culturable bacterial counts of HET for RTan and FC/CIP for RAlu. In summary, the overall performance of aluminium sulphate was better than that of tannins in the treatment of treated urban wastewater.

Inactivation of carbapenem-resistant Klebsiella pneumoniae by photo-Fenton: Residual effect, gene evolution and modifications with citric acid and persulfate

The photo-Fenton process application to eliminate carbapenem-resistant Klebsiella pneumoniae, an antibiotic-resistant priority pathogen, was evaluated. Initially, reagents concentration effect was tested and under suitable conditions (5 mg L^-1 of Fe²⁺ and 50 mg L^-1 of H₂O₂) complete bacteria inactivation by action of hydroxyl radical and UVA plus hydrogen peroxide was achieved at 120 min. The process presented a strong residual disinfecting effect when light was turned off at only 20 min. Besides, the cultivability of treated K. pneumoniae in a selective medium containing carbapenem antibiotics was considered. bla-KPC, gene responsible for the resistance, evolution was also assessed. The bacteria response to carbapenem antibiotics was higher as the treatment time increased. In turn, bla-KPC gene remained when K. pneumoniae was completely inactivated (120 min); nevertheless, treatment times longer than 120 min diminished bla-KPC presence. Finally, the photo-Fenton process and its modifications (citric acid addition or persulfate anion instead hydrogen peroxide) were applied to a real hospital wastewater in Colombia. In such complex matrix, the conventional photo-Fenton system reached a moderate disinfection (∼3.5 log-units at 300 min). Meanwhile, in presence of citric acid total inactivation was completed at the same time. Interestingly, the H₂O₂ substitution by persulfate strongly accelerated the microorganism elimination, achieving the 6-log-units reduction after only 60 min of process action. Thus, the effective elimination of K. pneumoniae from water by the modified photo-Fenton evidenced the potential applicability of this process to limit the proliferation of antibiotic resistant bacteria.

Degradation of the Nonsteroidal Anti-Inflammatory Drug Piroxicam by Iron Activated Persulfate: The Role of Water Matrix and Ultrasound Synergy

This work examined the oxidation of Piroxicam (PIR), a representative nonsteroidal anti-inflammatory drug using iron activated persulfate. The effect of persulfate dosing was vital for the efficiency of the process. The addition of 20 mg/L sodium persulfate (SPS) eliminated 500 μg/L of PIR in less than 20 min at natural pH. PIR decomposition followed pseudo-first-order kinetics, and the observed kinetic constant increased by 2.1 times when the initial concentration of PIR decreased from 2000 to 250 μg/L. Acidic pH favored the PIR destruction, while both sulfate and hydroxyl radicals are involved in PIR destruction at natural pH. The effect of inorganic ions like bicarbonate and chlorides was almost insignificant on PIR removal. The presence of humic acid reduced PIR removal from 100% to 67% after 20 min of treatment with 2 mg/L Fe2+ and 20 mg/L SPS. The experiment that was performed with bottled water showed similar efficiency with ultrapure water, while in the case of secondary effluent, PIR removal decreased by 26% after 30 min of treatment. The Fe2+/SPS/ultrasound hybrid process showed a low degree of synergy (18.3%). The ecotoxicity of aqueous solution using the Vibrio fischeri as an indicator was reduced during the treatment, although with a different trend from the removal of PIR, possibly due to byproducts derived from the oxidation of secondary effluent and PIR.

Solar photo-Fenton disinfection of 11 antibiotic-resistant bacteria (ARB) and elimination of representative AR genes. Evidence that antibiotic resistance does not imply resistance to oxidative treatment

The emergence of antibiotic resistance represents a major threat to human health. In this work we investigated the elimination of antibiotic resistant bacteria (ARB) by solar light and solar photo-Fenton processes. As such, we have designed an experimental plan in which several bacterial strains (Staphylococcus aureus, Escherichia coli and Klebsiella pneumoniae) possessing different drug-susceptible and -resistant patterns and structures (Gram-positive and Gram-negative) were subjected to solar light and the photo-Fenton oxidative treatment in water. We showed that both solar light and solar photo-Fenton processes were effective in the elimination of ARB in water and that the time necessary for solar light disinfection and solar photo-Fenton disinfection were similar for antibiotic-susceptible and antibiotic-resistant strains (mostly 180-240 and 90-120 min, respectively). Moreover, the bacterial structure did not significantly affect the effectiveness of the treatment. Similar regrowth pattern was observed (compared to the susceptible strain) and no development of bacteria with higher drug-resistance values was found in waters after any treatment. Finally, both processes were effective to reduce AR genes (ARGs), although solar photo-Fenton was more rapid than solar light. In conclusion, the solar photo-Fenton process ensured effective disinfection of ARB and elimination of ARGs in water (or wastewater) and is a potential mean to ensure limitation of ARB and ARG spread in nature.

Analogies and differences among bacterial and viral disinfection by the photo-Fenton process at neutral pH: a mini review

Over the last years, the photo-Fenton process has been established as an effective, green alternative to chemical disinfection of waters and wastewaters. Microorganisms' inactivation is the latest success story in the application of this process at near-neutral pH, albeit without clearly elucidated inactivation mechanisms. In this review, the main pathways of the combined photo-Fenton process against the most frequent pathogen models (Escherichia coli for bacteria and MS2 bacteriophage for viruses) are analyzed. Firstly, the action of solar light is described and the specific inactivation mechanisms in bacteria (internal photo-Fenton) and viruses (genome damage) are presented. The contribution of the external pathways due to the potential presence of organic matter in generating reactive oxygen species (ROS) and their effects on microorganism inactivation are discussed. Afterwards, the effects of the gradual addition of Fe and H₂O₂ are assessed and the differences among bacterial and viral inactivation are highlighted. As a final step, the simultaneous addition of both reagents induces the photo-Fenton in the bulk, focusing on the differences induced by the homogeneous or heterogeneous fraction of the process and the variation among the two respective targets. This work exploits the accumulated evidence on the mechanisms of bacterial inactivation and the scarce ones towards viral targets, aiming to bridge this knowledge gap and make possible the further application of the photo-Fenton process in the field of water/wastewater treatment.