Mechanisms and Strategies of Advanced Oxidation Processes for Membrane Fouling Control in MBRs: Membrane-Foulant Removal versus Mixed-Liquor Improvement

Membrane bioreactors (MBRs) are well-established and widely utilized technologies with substantial large-scale plants around the world for municipal and industrial wastewater treatment. Despite their widespread adoption, membrane fouling presents a significant impediment to the broader application of MBRs, necessitating ongoing research and development of effective antifouling strategies. As highly promising, efficient, and environmentally friendly chemical methods for water and wastewater treatment, advanced oxidation processes (AOPs) have demonstrated exceptional competence in the degradation of pollutants and inactivation of bacteria in aqueous environments, exhibiting considerable potential in controlling membrane fouling in MBRs through direct membrane foulant removal (MFR) and indirect mixed-liquor improvement (MLI). Recent proliferation of research on AOPs-based antifouling technologies has catalyzed revolutionary advancements in traditional antifouling methods in MBRs, shedding new light on antifouling mechanisms. To keep pace with the rapid evolution of MBRs, there is an urgent need for a comprehensive summary and discussion of the antifouling advances of AOPs in MBRs, particularly with a focus on understanding the realizing pathways of MFR and MLI. In this critical review, we emphasize the superiority and feasibility of implementing AOPs-based antifouling technologies in MBRs. Moreover, we systematically overview antifouling mechanisms and strategies, such as membrane modification and cleaning for MFR, as well as pretreatment and in-situ treatment for MLI, based on specific AOPs including electrochemical oxidation, photocatalysis, Fenton, and ozonation. Furthermore, we provide recommendations for selecting antifouling strategies (MFR or MLI) in MBRs, along with proposed regulatory measures for specific AOPs-based technologies according to the operational conditions and energy consumption of MBRs. Finally, we highlight future research prospects rooted in the existing application challenges of AOPs in MBRs, including low antifouling efficiency, elevated additional costs, production of metal sludge, and potential damage to polymeric membranes. The fundamental insights presented in this review aim to elevate research interest and ignite innovative thinking regarding the design, improvement, and deployment of AOPs-based antifouling approaches in MBRs, thereby advancing the extensive utilization of membrane-separation technology in the field of wastewater treatment.

An overview of the occurrence, impact of process parameters, and the fate of antibiotic resistance genes during anaerobic digestion processes

Antibiotic resistance genes (ARGs) have emerged as a significant global health threat, contributing to fatalities worldwide. Wastewater treatment plants (WWTPs) and livestock farms serve as primary reservoirs for these genes due to the limited efficacy of existing treatment methods and microbial adaptation to environmental stressors. Anaerobic digestion (AD) stands as a prevalent biological treatment for managing sewage sludge and manure in these settings. Given the agricultural utility of AD digestate as biofertilizers, understanding ARGs' fate within AD processes is essential to devise effective mitigation strategies. However, understanding the impact of various factors on ARGs occurrence, dissemination, and fate remains limited. This review article explores various AD treatment parameters and correlates to various resistance mechanisms and hotspots of ARGs in the environment. It further evaluates the dissemination and occurrence of ARGs in AD feedstocks and provides a comprehensive understanding of the fate of ARGs in AD systems. This review explores the influence of key AD parameters such as feedstock properties, pretreatments, additives, and operational strategies on ARGs. Results show that properties such as high solid content and optimum co-digestion ratios can enhance ARG removal, while the presence of heavy metals, microplastics, and antibiotics could elevate ARG abundance. Also, operational enhancements, such as employing two-stage digestion, have shown promise in improving ARG removal. However, certain pretreatment methods, like thermal hydrolysis, may exhibit a rebounding effect on ARG levels. Overall, this review systematically addresses current challenges and offers future perspectives associated with the fate of ARGs in AD systems.

Enhancing pollutants removal in hospital wastewater: Comparative analysis of PAC coagulation vs. bio-contact oxidation, highlighting the impact of outdated treatment plants

While the effectiveness of Poly-Aluminum Chloride (PAC) coagulation for pollutant removal has been documented across various wastewater scenarios, its specific application in hospital wastewater (HWW) treatment to remove conventional pollutants and hazardous genetic pollutants has not been studied. The research compared three hospital wastewater treatment plants (HWTPs) to address a knowledge gap, including the PAC coagulation-sodium hypochlorite disinfection process (PAC-HWTP), the biological contact oxidation-precipitation-sodium hypochlorite process (BCO-HWTP), and a system using outdated equipment with PAC coagulation (ODE-PAC-HWTP). Effluent compliance with national discharge standards is assessed, with BCO-HWTP meeting standards for direct or indirect discharge into natural aquatic environments. ODE-PAC-HWTP exceeds pretreatment standards for COD and BOD5 concentrations. PAC-HWTP effluent largely adheres to national pretreatment standards, enabling release into municipal sewers for further treatment. Metagenomic analysis reveals that PAC-HWTP exhibits higher removal efficiencies for antibiotic resistance genes, metal resistance genes, mobile genetic elements, and pathogens compared to BCO-HWTP and ODE-PAC-HWTP, achieving average removal rates of 45.13%, 57.54%, 80.61%, and 72.17%, respectively. These results suggests that when discharging treated HWW into municipal sewers for further processing, the use of PAC coagulation process is more feasible and cost-effective compared to BCO technologies. The analysis emphasizes the urgent need to upgrade outdated equipment HWTPs.

Physicochemical methods for disinfection of contaminated surfaces - a way to control infectious diseases

This paper represents the reviews of recent advancements in different physicochemical methods for disinfecting contaminated surfaces, which are considered to be responsible for transmitting different bacterial, viral, and fungal infectious diseases. Surface disinfection can be achieved by applying chemicals, UV-based processes, ionization radiation (gamma-ray, X-ray and electron beam), application of self-disinfecting surfaces, no-touch room disinfection methods, and robotic disinfection methods for built-in settings. Application of different chemicals, such as alcohols, hydrogen peroxide, peracetic acid, quaternary ammonium salts, phenol, and iodine solution, are common and economical. However, the process is time-consuming and less efficient. The use of UVC light (wavelength: 200-280 nm, generated by low vapor mercury lamps or pulse xenon light) has gained much attention for disinfecting fomites worldwide. In recent times, the combination of UV and H2O2, based on the principle of the advanced oxidation process, has been applied for disinfecting inanimate surfaces. The process is very efficient and faster than chemical and UV processes. Heavy metals like copper, silver, zinc, and other metals can inactivate microbes and are used for surface modification to produce self-disinfecting surfaces and used in healthcare facilities. In combination with UVB (280-315 nm) and UVA (315-400 nm), titanium oxide has been utilized for disinfecting contaminated surfaces. Ionization radiation, one of the advanced methods, can be used in disinfecting medical devices and drugs. Post-COVID-19 pandemic, the no-touch and robotic disinfection methods utilizing chemicals or UVC lights have received much importance in built-in settings. Among these methods, surface disinfection by applying chemicals by fogging/vaporization and UV radiation methods has been widely reported in the literature compared to other methods.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40201-024-00893-2.

Insight into environmental adaptability of antibiotic resistome from surface water to deep sediments in anthropogenic lakes by metagenomics

The escalating antibiotic resistance threatens the long-term global health. Lake sediment is a vital hotpot in transmitting antibiotic resistance genes (ARGs); however, their vertical distribution pattern and driving mechanisms in sediment cores remain unclear. This study first utilized metagenomics to reveal how resistome is distributed from surface water to 45 cm sediments in four representative lakes, central China. Significant vertical variations in ARG profiles were observed (R2 = 0.421, p < 0.001), with significant reductions in numbers, abundance, and Shannon index from the surface water to deep sediment (all p-values < 0.05). ARGs also has interconnections within the vertical profile of the lakes: twelve ARGs persistently exist all sites and depths, and shared ARGs (e.g., vanS and mexF) were assembled by diverse hosts at varying depths. The 0-18 cm sediment had the highest mobility and health risk of ARGs, followed by the 18-45 cm sediment and water. The drivers of ARGs transformed along the profile of lakes: microbial communities and mobile genetic elements (MGEs) dominated in water, whereas environmental variables gradually become the primary through regulating microbial communities and MGEs with increasing sediment depth. Interestingly, the stochastic process governed ARG assembly, while the stochasticity diminished under the mediation of Chloroflexi, Candidatus Bathyarcaeota and oxidation-reduction potential with increasing depth. Overall, we formulated a conceptual framework to elucidate the vertical environmental adaptability of resistome in anthropogenic lakes. This study shed on the resistance risks and their environmental adaptability from sediment cores, which could reinforce the governance of public health issues.

Pseudomonas aeruginosa and related antibiotic resistance genes as indicators for wastewater treatment

This review aims to examine the existence of Pseudomonas aeruginosa (P. aeruginosa) and their antibiotic resistance genes (ARGs) in aquatic settings and the alternative treatment ways. P. aeruginosa in a various aquatic environment have been identified as contaminants with impacts on human health and the environment. P. aeruginosa resistance to multiple antibiotics, such as sulfamethoxazole, ciprofloxacin, quinolone, trimethoprim, tetracycline, vancomycin, as well as specific antibiotic resistance genes including sul1, qnrs, blaVIM, blaTEM, blaCTX, blaAIM-1, tetA, ampC, blaVIM. The development of resistance can occur naturally, through mutations, or via horizontal gene transfer facilitated by sterilizing agents. In addition, an overview of the current knowledge on inactivation of Pseudomonas aeruginosa and ARG and the mechanisms of action of various disinfection processes in water and wastewater (UV chlorine processes, catalytic oxidation, Fenton reaction, and ozonation) is given. An overview of the effects of nanotechnology and the resulting wetlands is also given.

The fate of antibiotic resistance genes in wastewater containing microalgae treated by chlorination, ultra-violet, and Fenton reaction

Antibiotic resistance genes (ARGs) and bacteria (ARBs) in the effluent of wastewater treatment plants (WWTPs) are of utmost importance for the dissemination of ARGs in natural aquatic environments. Therefore, there is an urgent need for effective technologies to eliminate WWTP ARGs/ARBs and mitigate the associated risks posed by the discharged ARG in aquatic environments. To test the effective technology for eliminating ARGs/ARBs, we compared the removal of ARGs and ARBs by three different tertiary treatments, namely ultra-violet (UV) disinfection, chlorination disinfection, and Fenton oxidation. Then, the treated wastewater was co-cultured with Chlorella vulgaris (representative of aquatic biota) to investigate the fate of discharged ARGs into the aquatic environment. The results demonstrated that chlorination (at a chlorine concentration of 15 mg/L) and Fenton (at pH 2.73, with 0.005 mol/L Fe2+ and 0.0025 mol/L H2O2) treatment showed higher efficacy in ARG removal (1.8 - 4.17 logs) than UV treatment (15 min) (1.29 - 3.87 logs). Moreover, chlorine at 15 mg/L and Fenton treatment effectively suppressed ARB regeneration while UV treatment for 15 min could not. Regardless of treatments tested in this study, the input of treated wastewater to the Chlorella system increased the number of ARGs and mobile genetic elements (MGEs), indicating the potential risk of ARG dissemination associated with WWTP discharge. Among the wastewater-Chlorella co-culture systems, chlorination resulted in less of an increase in the number of ARGs and MGEs compared to Fenton and UV treatment. When comparing the wastewater systems to the co-culture systems, it was observed that Chlorella vulgaris reduced the number of ARGs and MGEs in chlorination and UV-treated wastewater; however, Chlorella vulgaris promoted ARG survival in Fenton-treated water, suggesting that aquatic microalgae might act as a barrier to ARG dissemination. Overall, chlorination treatment not only effectively removes ARGs and inhibits ARB regeneration but also shows a lower risk of ARG dissemination. Therefore, chlorination is recommended for practical application in controlling the spread of discharged ARGs from WWTP effluent in natural aquatic environments.

Molecular level removal of antibiotic resistant bacteria and genes: A review of interfacial chemical in advanced oxidation processes

As a kind of novel and persistent environmental pollutants, antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) have been frequently detected in different aquatic environment, posing potential risks to public health and ecosystems, resulting in a biosecurity issue that cannot be ignored. Therefore, in order to control the spread of antibiotic resistance in the environment, advanced oxidation technology (such as Fenton-like, photocatalysis, electrocatalysis) has become an effective weapon for inactivating and eliminating ARB and ARGs. However, in the process of advanced oxidation technology, studying and regulating catalytic active sites at the molecular level and studying the adsorption and surface oxidation reactions between catalysts and ARGs can achieve in-depth exploration of the mechanism of ARGs removal. This review systematically reveals the catalytic sites and related mechanisms of catalytic antagonistic genes in different advanced oxidation processes (AOPs) systems. We also summarize the removal mechanism of ARGs and how to reduce the spread of ARGs in the environment through combining a variety of characterization methods. Importantly, the potential of various catalysts for removing ARGs in practical applications has also been recognized, providing a promising approach for the deep purification of wastewater treatment plants.

Proteomic profiling of antibiotic-resistant Escherichia coli GW-AmxH19 isolated from hospital wastewater treated with physical plasma

Microorganisms which are resistant to antibiotics are a global threat to the health of humans and animals. Wastewater treatment plants are known hotspots for the dissemination of antibiotic resistances. Therefore, novel methods for the inactivation of pathogens, and in particular antibiotic-resistant microorganisms (ARM), are of increasing interest. An especially promising method could be a water treatment by physical plasma which provides charged particles, electric fields, UV-radiation, and reactive species. The latter are foremost responsible for the antimicrobial properties of plasma. Thus, with plasma it might be possible to reduce the amount of ARM and to establish this technology as additional treatment stage for wastewater remediation. However, the impact of plasma on microorganisms beyond a mere inactivation was analyzed in more detail by a proteomic approach. Therefore, Escherichia coli GW-AmxH19, isolated from hospital wastewater in Germany, was used. The bacterial solution was treated by a plasma discharge ignited between each of four pins and the liquid surface. The growth of E. coli and the pH-value decreased during plasma treatment in comparison with the untreated control. Proteome and antibiotic resistance profile were analyzed. Concentrations of nitrite and nitrate were determined as long-lived indicative products of a transient chemistry associated with reactive nitrogen species (RNS). Conversely, hydrogen peroxide served as indicator for reactive oxygen species (ROS). Proteome analyses revealed an oxidative stress response as a result of plasma-generated RNS and ROS as well as a pH-balancing reaction as key responses to plasma treatment. Both, the generation of reactive species and a decreased pH-value is characteristic for plasma-treated solutions. The plasma-mediated changes of the proteome are discussed also in comparison with the Gram-positive bacterium Bacillus subtilis. Furthermore, no effect of the plasma treatment, on the antibiotic resistance of E. coli, was determined under the chosen conditions. The knowledge about the physiological changes of ARM in response to plasma is of fundamental interest to understand the molecular basis for the inactivation. This will be important for the further development and implementation of plasma in wastewater remediation.

Influence of Amino Acid Substitutions in Capsid Proteins of Coxsackievirus B5 on Free Chlorine and Thermal Inactivation

The sensitivity of enteroviruses to disinfectants varies among genetically similar variants and coincides with amino acid changes in capsid proteins, although the effect of individual substitutions remains unknown. Here, we employed reverse genetics to investigate how amino acid substitutions in coxsackievirus B5 (CVB5) capsid proteins affect the virus' sensitivity to free chlorine and heat treatment. Of ten amino acid changes observed in CVB5 variants with free chlorine resistance, none significantly reduced the chlorine sensitivity, indicating a minor role of the capsid composition in chlorine sensitivity of CVB5. Conversely, a subset of these amino acid changes located at the C-terminal region of viral protein 1 led to reduced heat sensitivity. Cryo-electron microscopy revealed that these changes affect the assembly of intermediate viral states (altered and empty particles), suggesting that the mechanism for reduced heat sensitivity could be related to improved molecular packing of CVB5, resulting in greater stability or altered dynamics of virus uncoating during infection.

Performance evaluation for the inactivation of multidrug-resistant bacteria in wastewater effluent by different disinfection technologies

The escalating presence of antibiotic-resistant bacteria (ARB) in aquatic ecosystems underscores the critical role of wastewater treatment plants (WWTPs) in mitigating antibiotic resistance. Disinfection is the final, pivotal step in WWTPs, and it is essential to control the dissemination of ARB before water discharge. This study utilized both phenotypic analysis and transcriptome (RNA-seq) approach to investigate the efficiency and mechanisms of disinfection using chlorination, ultraviolet (UV), and peracetic acid (PAA) on multidrug-resistant bacteria (MRB). Our results demonstrated that the use of 100 mg min L-1 of chlorine, 8.19 mJ cm-2 of UV irradiation or 50 min mg L-1 of PAA significantly reduced the abundance of MRB. Intriguingly, RNA-seq clarified distinct mechanisms of chlorination and UV disinfection. UV radiation triggered the SOS response to cope with DNA damage, induced the expression of multi-drug resistance genes by increasing the expression of efflux pump transporters. UV radiation also promoted the absorption of iron through chelation and transportation to participate in various cell life processes. Chlorination, on the other hand, significantly up-regulated osmotic response elements, including the synthesis of glycine betaine, iron-sulfur clusters, and related transporters. Both chlorination and UV significantly down-regulated key metabolic pathways (P < 0.05), inhibiting the process of amino acid synthesis and energy metabolism. Imbalance in energy homeostasis was the most important factor leading to cytotoxicity. These results provide useful insights into optimizing the wastewater disinfection process in order to prevent the dissemination of ARB in aquatic environment.

Comparison on removal performance of virus, antibiotic-resistant bacteria, cell-associated and cell-free antibiotic resistance genes, and indicator chemicals by ozone in the filtrated secondary effluent of a sewage treatment plant

Due to the widespread appearance of viruses, antibiotic-resistant bacteria (ARBs), and antibiotic resistance genes (ARGs) in the aquatic environment, more powerful oxidation processes such as ozonation are needed to enhance the efficiency of their inactivation and removal during wastewater treatment. However, information is lacking on the elimination rates of viruses, ARBs, cell-associated ARGs (ca-ARGs), and cell-free ARGs (cf-ARGs) during ozonation. This study examined the kinetics and dose-dependent inactivation of a virus (MS2 coliphage) and an ARB (Ampicillin-resistant [AmpR] E. coli) and the removal of ca- and cf-ARGs (plasmid-encoded blaTEM) by ozonation in a filtered secondary effluent (SE) of a municipal sewage treatment plant (STP). In addition, the ozonation kinetics of carbamazepine (CBZ) and metoprolol (MTP)-ubiquitous organic micropollutants with different removal rate constants-were also investigated in order to monitor their effectiveness as indicators for the abovementioned biological risk factors. Our results showed that ozonation was an efficient way to remove MS2, AmpRE. coli, ARGs, CBZ, and MTP. We investigated the kinetics of their inactivation/removal with respect to exposure in terms of CT (dissolved ozone concentration C and contact time T) value, and found their inactivation/removal constants were in the following order: MS2 (8.66 ×103 M-1s-1) ≈ AmpRE. coli (8.19 ×103 M-1s-1) > cf-ARG (3.95 ×103 M-1s-1) > CBZ (3.21 ×103 M-1s-1) > ca-ARG (2.48×103 M-1s-1) > MTP (8.35 ×102 M-1s-1). In terms of specific ozone dose, > 5-log inactivation of MS2 was observed at > 0.30 mg O3/mg DOC, while > 5-log inactivation of AmpRE. coli was confirmed at 1.61-2.35 mg O3/mg DOC. Moreover, there was almost no removal of ca-ARG when the specific ozone dose was < 0.68 mg O3/mg DOC. However, 2.86-3.42-log removal of ca-ARG was observed at 1.27-1.31 mg O3/mg DOC, while 1.14-1.36-log removal of cf-ARG was confirmed at 3.60-4.30 mg O3/mg DOC. As alternative indicators, > 4-log removal of CBZ was observed at > 1.00 mg O3/mg DOC, while > 2-log removal of MTP was confirmed at > 2.00 mg O3/mg DOC. Thus, it was observed that inactivation of E. coli needs a greater ozone dose to achieve the same level of inactivation of AmpRE. coli; for ARGs, cf-ARG can persist longer than ca-ARG if low dosages of ozone are applied in the filtrated SE, CBZ might act as an indicator with which to monitor the inactivation of viruses and ARBs, while MTP might act as an indicator with which to monitor removal of ARGs. Moreover, cf-ARG cannot be neglected even after ozonation due to the possibility that ca-ARGs can become cf-ARGs during ozonation and be discharged with the final effluent, posing a potential risk to the receiving environment.

The improved resistance of germinated spores to ultraviolet irradiation: Comparison with chlorine

Fungi outbreaks in water will include a series of processes, including spore aggregation, germination, biofilm, and finally present in a mixed state in the aquatic environment. More attention is paid to the control of dispersed fungal spores, however, there was little knowledge of the control of germinated spores. This study investigated the inactivation kinetics and mechanism of ultraviolet (UV) treatment for fungal spores with different germination percentages compared with dormant spores. The results indicated that the inactivation rate constants (k) of spores with 5%-45% germination were 0.0278-0.0299 cm2/mJ for Aspergillus niger and 0.0588-0.0647 cm2/mJ for Penicillium polonicum, which were lower than those of dormant spores. It suggested that germinated spores were more tolerant to UV irradiation than dormant spores, and it may be due to the defensive barrier (upregulated pigments) and some reductive substance (upregulated enoyl reductase) by absorbing UV or reacting with reactive oxygen species according to transcriptome analysis. Compared to dormant spores, the k-UV of germinated spores decreased by 18.17%-26.56% for Aspergillus niger, which was less than k-chlorine (62.33%-69.74%). A slighter decrease in k-UV showed UV irradiation can efficiently control fungi contamination, especially when dormant spores and germinated spores coexisted in actual water systems. This study indicates that more attention should be paid to germinated spores.

Urban wastewater disinfection by iron chelates mediated solar photo-Fenton: Effects on seven pathogens and antibiotic resistance transfer potential

The effects of solar photo-Fenton (SPF) process mediated by the iron chelate Fe3+ imminodisuccinic acid (Fe:IDS) on both the inactivation of seven relevant pathogens and the potential for antibiotic resistance transfer (degradation of antibiotic resistance genes (ARGs) and after treatment regrowth), in real secondary treated urban wastewater, were investigated for the first time. A comparison with results obtained by sunlight/H2O2 process and Fe3+ ethylenediaminedisuccinic acid (Fe:EDDS) SPF was also carried out. ARGs were quantified by polymerase chain reaction (PCR) in samples before and after (3 h) the treatment. The persistence of the selected pathogens and ARGs was also evaluated in regrowth tests (72 h) under environmentally mimicking conditions. Fe:IDS SPF resulted to be more effective (from 1.4 log removal for Staphylococcus spp. to 4.3 log removal for Escherichia coli) than Fe:EDDS SPF (from 0.8 log removal for Pseudomonas aeruginosa to 2.0 log removal for Total coliphages) and sunlight/H2O2 (from 1.2 log removal for Clostridium perfringens to 3.3 log removal for E. coli) processes for the seven pathogens investigated. Potential pathogens regrowth was also severely affected, as no substantial regrowth was observed, both in presence and absence of catalase. A similar trend was observed for ARGs removal too (until 0.001 fold change expression for qnrS after 3 h). However, a poor effect and a slight increase in fold change was observed after treatment especially for gyrA, mefA and intl1. Overall, the effect of the investigated processes on ARGs was found to be ARG dependent. Noteworthy, coliphages can regrow after sunlight/H2O2 treatment unlike SPF processes, increasing the risk of antibiotic resistance transfer by transduction mechanism. In conclusion, Fe:IDS SPF is an attractive solution for tertiary treatment of urban wastewater in small wastewater treatment plants as it can provide effective disinfection and a higher protection against antibiotic resistance transfer than the other investigated processes.

Physico-Chemical Investigation and Antimicrobial Efficacy of Ozonated Oils: The Case Study of Commercial Ozonated Olive and Sunflower Seed Refined Oils

Drug resistance represents one of the great plagues of our time worldwide. This largely limits the treatment of common infections and requires the development of new antibiotics or other alternative approaches. Noteworthy, the indiscriminate use of antibiotics is mostly responsible for the selection of mutations that confer drug resistance to microbes. In this regard, recently, ozone has been raising interest for its unique biological properties when dissolved in natural oils. Ozonated oils have been reported to act in a non-specific way on microorganisms hindering the acquisition of advantageous mutations that result in resistance. Here, we focused on the antimicrobial effect of two commercial olive (OOO) and sunflower seeds (OSO) oils. Nuclear magnetic resonance spectroscopy and thermal analysis showed the change in the chemical composition of the oils after ozonation treatment. Different ozonated oil concentrations were then used to evaluate their antimicrobial profile against Candida albicans, Enterococcus faecalis, Staphylococcus aureus, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Escherichia coli by agar diffusion and broth dilution methods. Cytotoxicity was also evaluated in keratinocytes and epithelial cells. Overall, our results revealed that both OOO and OSO showed a potent microbicidal effect, especially against C. albicans (IC50 = OOO: 0.3 mg/mL and OSO: 0.2 mg/mL) and E. faecalis (IC50 = OOO: 0.4 mg/mL and OSO: 2.8 mg/mL) albeit exerting a certain effect also against S. aureus and E. coli. Moreover, both OOO and OSO do not yield any relevant cytotoxic effect at the active concentrations in both cell lines. This indicates that the ozonated oils studied are not toxic for mammalian cells despite exerting a potent antimicrobial effect on specific microorganisms. Therefore, OOO and OSO may be considered to integrate standard therapies in the treatment of common infections, likely overcoming drug resistance issues.

Performance of sewage sludge treatment for the removal of antibiotic resistance genes: Status and prospects

Wastewater treatment plants (WWTPs) receive wastewater containing antibiotic resistant bacteria (ARB) and antibiotic resistant genes (ARGs), which are predominant contributors to environmental pollution in water and soil. Of these sources, sludge is a more significant contributor than effluent. Knowing how sludge treatment affects the fate of ARGs is vital for managing the risk of these genes in both human and natural environments. This review therefore discusses the sources and transmission of ARGs in the environment and highlights the risks of ARGs in sludge. The effects of co-existing constituents (heavy metals, microplastics, etc.) on sludge and ARGs during treatment are collated to highlight the difficulty of treating sludge with complex constituents in ARGs. The effects of various sludge treatment methods on the abundances of ARGs in sludge and in soil from land application of treated sludge are discussed, pointing out that the choice of sludge treatment method should take into account various potential factors, such as soil and soil biology in subsequent land application. This review offers significant insights and explores the abundances of ARGs throughout the process of sludge treatment and disposal. Unintentional addition of antibiotic residues, heavy metals, microplastics and organic matter in sludge could significantly increase the abundance and reduce the removal efficiency of ARGs during treatment, which undoubtedly adds a barrier to the removal of ARGs from sludge treatment. The complexity of the sludge composition and the diversities of ARGs have led to the fact that no effective sludge treatment method has so far been able to completely eliminate the ecological risk of ARGs. In order to reduce risks resulting by transmission of ARGs, technical and management measures need to be implemented.

Systematic analysis of the scientific-technological production on the use of the UV, H2O2, and/or Cl2 systems in the elimination of bacteria and associated antibiotic resistance genes

This study presents a systematic review of the scientific and technological production related to the use of systems based on UV, H2O2, and Cl2 for the elimination of antibiotic-resistant bacteria (ARB) and genes associated with antibiotic resistance (ARGs). Using the Pro Know-C (Knowledge Development Process-Constructivist) methodology, a portfolio was created and analyzed that includes 19 articles and 18 patents published between 2011 and 2022. The results show a greater scientific-technological production in UV irradiation systems (8 articles and 5 patents) and the binary combination UV/H2O2 (9 articles and 4 patents). It was emphasized that UV irradiation alone focuses mainly on the removal of ARB, while the addition of H2O2 or Cl2, either individually or in binary combinations with UV, enhances the removal of ARB and ARG. The need for further research on the UV/H2O2/Cl2 system is emphasized, as gaps in the scientific-technological production of this system (0 articles and 2 patents), especially in its electrochemically assisted implementation, have been identified. Despite the gaps identified, there are promising prospects for the use of combined electrochemically assisted UV/H2O2/Cl2 disinfection systems. This is demonstrated by the effective removal of a wide range of contaminants, including ARB, fungi, and viruses, as well as microorganisms resistant to conventional disinfectants, while reducing the formation of toxic by-products.

Deterioration of sludge characteristics and promotion of antibiotic resistance genes spread with the co-existing of polyvinylchloride microplastics and tetracycline in the sequencing batch reactor

With the continuous increase in microplastics (MPs) and tetracycline (TC) entering wastewater treatment plants (WWTPs) along with sewage, the co-existence of MPs and TC in the biological treatment of wastewater has attracted extensive attention. This study investigated the effect of 1 mg/L polyvinyl chloride (PVC) MPs and 100 ng/L TC co-existing on sequencing batch reactors (SBRs) (S2) treating phenol wastewater in contrast to the control with TC alone (S1). The phenol removal efficiency was significantly inhibited by the co-existence of PVC MPs and TC. Sludge characteristics were also distinctively influenced. The decreased zone sludge velocity (ZSV) and increased sludge volume index (SVI) indicated that the combined effect of PVC MPs and TC deteriorated sludge settleability, which had positive and negative linear correlations with extracellular polymeric substances (EPS) content and the protein (PN)/polysaccharide (PS) ratio, respectively. Moreover, the decreased and increased relative abundances of potential phenol-degraders and antibiotic resistance gene (ARG) carriers may elucidate the inhibition of phenol removal and promotion of ARGs propagation with the co-occurrence of PVC MPs and TC. In addition, the enhanced potential ARGs hosts, loss of the EPS protective effect, and increased membrane permeability induced by reactive oxygen species (ROS) jointly promoted ARGs dissemination in the co-existence of PVC MPs and TC. Notably, the co-occurrence of ARGs and mobile genetic element (MGEs) indicated that the co-existence of PVC MPs and TC promoted the spread of some transposase-associated ARGs mediated by horizontal gene transfer (HGT).

Free-floating extracellular DNA (exDNA) in different wastewaters: Status quo on exDNA-associated antimicrobial resistance genes

Wastewater treatment plants (WWTPs) have been reported as major anthropogenic reservoirs for the spread of antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) into the environment, worldwide. While most studies mainly focus on the intracellular DNA (iDNA), extracellular DNA (exDNA) accounting for a significant proportion of the total DNA in wastewater, was usually neglected. Following the One Health approach, this study focuses on wastewaters of municipal, clinical, and livestock origins (n = 45) that undergo different treatment processes (i.e., conventional activated sludge, ultrafiltration, and ozonation). Water samples were analysed for 12 ARGs as indicators of the different compartments associated with iDNA and exDNA by quantitative real-time PCR (qPCR). Taxonomic profiling of exDNA-fractions, obtained using nucleic acid adsorption particles, was conducted by sequencing the V3-V4 hypervariable regions of the 16S rRNA gene. Notified exDNA concentrations varied between on-site WWTPs and treatment stages, and ranged from 314.0 ± 70.2 ng/mL in untreated livestock wastewater down to 0.7 ± 0.1 ng/mL in effluents after ultrafiltration. In general, influents exhibited higher concentrations compared to effluents, while wastewater treated by advanced treatment processes (i.e., ultrafiltration and ozonation) showed the lowest exDNA concentrations. Despite the lower concentrations, free-floating exDNA accounted for up to 80.0 ± 5.8% of the total DNA in effluents. Target ARGs were more common in the iDNA (100%, n = 45/45), compared to the exDNA-fractions (51.1%, n = 23/45), whereas exDNA-ARGs were mostly detected in clinical and slaughterhouse wastewaters as well as in the municipal influents. Compared to the iDNA-ARGs, the concentrations of exDNA-ARGs were in general lower. Nevertheless, significant higher concentrations for exDNA-associated genes were measured in clinical wastewaters for blaNDM (4.07 ± 0.15 log gene copies (GC)/L) and blaVIM-2 (6.0 ± 0.2 log GC/L). Overall, our results suggest that depending on the origin of wastewater and its treatment methods, exDNA represents an important reservoir for ARGs, particularly in clinical wastewater.

Simultaneous removal of antibiotics and antibiotic resistant genes using a CeO2@CNT electrochemical membrane-NaClO system

The simultaneous removal of antibiotic and antibiotic resistance genes (ARGs) are important to inhibit the spread of antibiotic resistance. In this study, a coupled treatment system was developed using a CeO2 modified carbon nanotube electrochemical membrane and NaClO (denoted as CeO2@CNT-NaClO) to treat simulated water samples containing antibiotics and antibiotic-resistant bacteria (ARB). As the mass ratio of CeO2 to CNT was 5:7 and the current density was 2.0 mA/cm2, the CeO2@CNT-NaClO system removed 99% of sulfamethoxazole, 4.6 log sul1 genes, and 4.7 log intI1 genes from the sulfonamide-resistance water samples, and removed 98% of tetracycline, 2.0 log tetA genes, and 2.6 log intI1 genes of the tetracycline-resistance water samples. The outstanding performance of the CeO2@CNT-NaClO system for simultaneously removing antibiotic and ARGs was mainly ascribed to the generation of multiple reactive species, including •OH, •ClO, •O2- and 1O2. Antibiotics can undergo efficient degradation by •OH. However, the reaction between •OH and antibiotics reduces the availability of •OH to permeate into the cells and react with DNA. Nevertheless, the presence of •OH enhancd the effects of •ClO, •O2-, and 1O on ARG degradation. Through the coupled action of •OH, •ClO, •O2-, and 1O2, the cell membranes of ARB experience severe damage, resulting in an increase in intracellular reactive oxygen species (ROS) and a decrease in superoxide dismutase (SOD) activity. Consequently, this coordinated mechanism leads to superior removal of ARGs.

Simultaneous removal of antibiotics and antibiotic resistance genes in wastewater by a novel nonthermal plasma/peracetic acid combination system: Synergistic performance and mechanism

In this study, a novel and green method combining plasma with peracetic acid (plasma/PAA) was developed to simultaneously remove antibiotics and antibiotic resistance genes (ARGs) in wastewater, which achieves significant synergistic effects in the removal efficiencies and energy yield. At a plasma current of 2.6 A and PAA dosage of 10 mg/L, the removal efficiencies of most detected antibiotics in real wastewater exceeded 90 % in 2 min, with the ARG removal efficiencies ranging from 6.3 % to 75.2 %. The synergistic effects of plasma and PAA could be associated with the motivated production of reactive species (including •OH, •CH₃, ¹O₂, ONOO^-, •O₂^- and NO•), which decomposed antibiotics, killed host bacteria, and inhibited ARG conjugative transfer. In addition, plasma/PAA also changed the contributions and abundances of ARG host bacteria and downregulated the corresponding genes of two-component regulatory systems, thus reducing ARG propagation. Moreover, the weak correlations between the removal of antibiotics and ARGs highlights the commendable performance of plasma/PAA in the simultaneous removal of antibiotics and ARGs. Therefore, this study affords an innovative and effective avenue to remove antibiotics and ARGs, which relies on the synergistic mechanisms of plasma and PAA and the simultaneous removal mechanisms of antibiotics and ARGs in wastewater.

The fate of antibiotic resistance genes in the coastal lagoon with multiple functional zones

Coastal lagoons provide many important services to human society, but their year-round use for aquaculture introduces large amounts of sewage. The contamination of antibiotic resistance genes (ARGs) is therefore of great concern. In this study, 50 ARGs subtypes, two integrase genes (intl1, intl2), and 16S rRNA genes were detected by high-throughput quantitative PCR, and standard curves of all target genes were prepared for quantification. The occurrence and distribution of ARGs in a typical coastal lagoon (XinCun lagoon, China) were comprehensively explored. We detected 44 and 38 subtypes of ARGs in the water and sediment, respectively, and discuss the various factors influencing the fate of ARGs in the coastal lagoon. Macrolides-lincosamides-streptogramins B was the primary ARG type, and macB was the predominant subtype. Antibiotic efflux and antibiotic inactivation were the main ARG resistance mechanisms. The XinCun lagoon was divided into eight functional zones. The ARGs showed a distinct spatial distribution owing to the influence of microbial biomass and anthropogenic activity in different functional zones. Fishing rafts, abandoned fish ponds, the town sewage zone, and mangrove wetlands provided a large quantity of ARGs to the XinCun lagoon. Nutrients and heavy metals also significantly correlated with the fate of the ARGs, especially NO₂^--N and Cu, which cannot be ignored. It is noteworthy that lagoon-barrier systems coupled with persistent pollutant inputs result in coastal lagoons acting as a "buffer pool" for ARGs, which can then accumulate and threaten the offshore environment.

Positive and negative effects of recirculating aquaculture water advanced oxidation: O3 and O3/UV treatments improved water quality but increased antibiotic resistance genes

Recirculating aquaculture systems (RASs) can be efficiently used for aquaculture, and oxidation treatment is commonly used to improve water quality. However, the effects of oxidation treatments on aquaculture water safety and fish yield in RASs are poorly understood. In this study, we tested the effects of O₃ and O₃/UV treatments on aquaculture water quality and safety during culture of crucian carp. O₃ and O₃/UV treatments reduced the dissolved organic carbon (DOC) concentration by ∼40% and destroyed the refractory organic lignin-like features. There was enrichment of ammonia oxidizing (Nitrospira, Nitrosomonas, and Nitrosospira) and denitrifying (Pelomonas, Methyloversatilis, and Sphingomonas) bacteria, and N-cycling functional genes were enriched by 23% and 48%, respectively, after O₃ and O₃/UV treatments. Treatment with O₃ and O₃/UV reduced NH₄⁺-N and NO₂^--N in RASs. O₃/UV treatment increased fish length and weight as well as probiotics in fish intestine. However, high saturated intermediates and tannin-like features induced antibiotic resistance genes (ARGs) in O₃ and O₃/UV treatments, by 52% and ∼28%, respectively, and also enhanced horizontal transfer of ARGs. Overall, the application of O₃/UV achieved better effects. However, understanding the potential biological risks posed by ARGs in RASs and determining the most efficient water treatment strategies to mitigate these risks should be goals of future work.

Quantification and antibiotic resistance risk assessment of chlorination-residual viable/VBNC Escherichia coli and Enterococcus in on-site hospital wastewater treatment system

On-site hospital wastewater treatment system widely applying chlorination has been regarded as an important barrier to curb the dissemination of antibiotic resistance. Chlorination-residual viable and viable but non-culturable (VBNC) bacteria probably lead to overestimate the effect of disinfection, while their antibiotic resistance risks imported from hospital effluents to municipal pipe network may be ignored. In this study, we quantified viable/VBNC Escherichia coli and Enterococcus in chlorination of an on-site hospital wastewater treatment system and assessed their antibiotic resistance risks. The numbers of viable/VBNC Escherichia coli and Enterococcus in raw wastewater were detected as high as 5.76-6.34/5.76-6.33 and 5.44-5.76/5.44-5.75 log₁₀(cells/mL). Meanwhile, high proportions of antibiotic-resistant Escherichia coli and Enterococcus to culturable Escherichia coli and Enterococcus were observed, especially carrying ampicillin resistance (22.25-41.70 % and 28.09-54.05 %). Chlorination could remove 0.44-1.88-/0.43-1.88- and 0.29-1.29-/0.28-1.28-log of viable/VBNC and complete culturable Escherichia coli and Enterococcus, but cause antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) to be released outside cells, and possibly further enhance the antibiotic resistance of viable bacteria. Low detections of antibiotics suggested that the occurrence of antibiotic-resistant bacteria (ARB) may not be accompanied by the corresponding antibiotics. Different sampling months had some impacts on above results, while the results were basically stable at different sampling times of hospital daily working period. The high release rates (11.26-13.02 and 11.59-12.98 log₁₀(cells/h)) and cumulative amounts (15.41-16.12 and 15.75-16.14 log₁₀(cells)) of chlorination-residual viable/VBNC Escherichia coli and Enterococcus indirectly assessed the potential risks of bacterial antibiotic resistance entering municipal pipe network. Additionally, the contributions from the corresponding antibiotic ceftazidime, ciprofloxacin, and vancomycin with the cumulative amounts of 2.57-4.85, 5.73-7.50, and 5.21-7.14 kg should also be taken seriously. Residual chlorine could serve as an important signal indicator for the risk assessment.

Enhance antibiotic resistance and human health risks in aerosols during the COVID-19 pandemic

Aerosols are an important route for the transmission of antibiotic resistance genes (ARGs). Since the 2019 (COVID-19) pandemic, the large-scale use of disinfectants has effectively prevented the spread of environmental microorganisms, but studies regarding the antibiotic resistance of airborne bacteria remain limited. This study focused on four functional urban areas (commercial areas, educational areas, residential areas and wastewater treatment plant) to study the variations in ARG abundances, bacterial community structures and risks to human health during the COVID-19 pandemic in aerosol. The results indicated the abundance of ARGs during the COVID-19 period were up to approximately 13-fold greater than before the COVID-19 period. Large-scale disinfection resulted in a decrease in total bacterial abundance. However, chlorine-resistant bacteria tended to be survived. Among the four functional areas, the diversity and abundance of aerosol bacteria were highest in commercial aera. Antibiotic susceptibility assays suggested elevated resistance of isolated bacteria to several tested antibiotics due to disinfection exposure. The potential exposure risks of ARGs to human health were 2 times higher than before the COVID-19 pandemic, and respiratory intake was the main exposure route. The results highlighted the elevated antibiotic resistance of bacteria in aerosols that were exposed to disinfectants after the COVID-19 pandemic. This study provides theoretical guidance for the rational use of disinfectants and control of antimicrobial resistance.

Optimizing ozone dose and contact time for removal of antibiotic-resistant P. aeruginosa, A. baumannii, E. coli, and associated resistant genes in effluent of an activated sludge process in a municipal WWTP

This study aimed to investigate the impact of ozonation on inactivation of antibiotic-resistant bacteria (ARB) including E. coli, P. aeruginosa, and A. baumannii, as well as on removal of 16S-rRNA gene and their associated antibiotic-resistant genes (ARGs) indigenously present in effluent of municipal wastewater treatment plant. The Chick-Watson model was used to describe bacterial inactivation rates at specific ozone doses. Maximum reduction of total cultivable A. baumannii, E. coli, and P. aeruginosa were found to be 7.6, 7.1, and 4.7 log, respectively, with the highest ozone dose of 0.48 gO₃/gCOD at 12 min contact time. According to the study results, complete inactivation of ARB and bacterial regrowth was not observed after 72 h incubation. The culture methods overestimated the performance of disinfection processes and propidium monoazide combined with qPCR, and showed the presence of viable but non-culturable bacteria after ozonation. ARGs were more persistent to ozone than ARB. The results of this study highlighted the significance of specific ozone dose and contact time in ozonation process considering the bacterial species and associated ARGs as well as the wastewater physicochemical characteristics, in order to help diminish the entrance of the biological microcontaminants into the environment.

Removal of antibiotic resistant bacteria and plasmid-encoded antibiotic resistance genes in water by ozonation and electro-peroxone process

The electro-peroxone (EP) process is an electricity-based oxidation process enabled by electrochemically generating hydrogen peroxide (H₂O₂) from cathodic oxygen (O₂) reduction during ozonation. In this study, the removal of antibiotic resistant bacteria (ARB) and plasmid-encoded antibiotic resistance genes (ARGs) during groundwater treatment by ozonation alone and the EP process was compared. Owing to the H₂O₂-promoted ozone (O₃) conversion to hydroxyl radicals (•OH), higher •OH exposures, but lower O₃ exposures were obtained during the EP process than ozonation alone. This opposite change of O₃ and •OH exposures decreases the efficiency of ARB inactivation and ARG degradation moderately during the EP process compared with ozonation alone. These results suggest that regarding ARB inactivation and ARG degradation, the reduction of O₃ exposures may not be fully counterbalanced by the rise of •OH exposures when changing ozonation to the EP process. However, due to the rise of •OH exposure, plasmid DNA was more effectively cleaved to shorter fragments during the EP process than ozonation alone, which may decrease the risks of natural transformation of ARGs. These findings highlight that the influence of the EP process on ARB and ARG inactivation needs to be considered when implementing this process in water treatment.

Bacterial inactivation processes in water disinfection - mechanistic aspects of primary and secondary oxidants - A critical review

Water disinfection during drinking water production is one of the most important processes to ensure safe drinking water, which is gaining even more importance due to the increasing impact of climate change. With specific reaction partners, chemical oxidants can form secondary oxidants, which can cause additional damage to bacteria. Cases in point are chlorine dioxide which forms free available chlorine (e.g., in the reaction with phenol) and ozone which can form hydroxyl radicals (e.g., during the reaction with natural organic matter). The present work reviews the complex interplay of all these reactive species which can occur in disinfection processes and their potential to affect disinfection processes. A quantitative overview of their disinfection strength based on inactivation kinetics and typical exposures is provided. By unifying the current data for different oxidants it was observable that cultivated wild strains (e.g., from wastewater treatment plants) are in general more resistant towards chemical oxidants compared to lab-cultivated strains from the same bacterium. Furthermore, it could be shown that for selective strains chlorine dioxide is the strongest disinfectant (highest maximum inactivation), however as a broadband disinfectant ozone showed the highest strength (highest average inactivation). Details in inactivation mechanisms regarding possible target structures and reaction mechanisms are provided. Thereby the formation of secondary oxidants and their role in inactivation of pathogens is decently discussed. Eventually, possible defense responses of bacteria and additional effects which can occur in vivo are discussed.

Overuse of food-grade disinfectants threatens a global spread of antimicrobial-resistant bacteria

Food-grade disinfectants are extensively used for microbial decontamination of food processing equipment. In recent years, food-grade disinfectants have been increasingly used. However, the overuse of disinfectants causes another major issue, which is the emergence and spread of antimicrobial-resistant bacteria on a global scale. As the ongoing pandemic takes global attention, bacterial infections with antibiotic resistance are another ongoing pandemic that often goes unnoticed and will be the next real threat to humankind. Here, the effects of food-grade disinfectant overuse on the global emergence and spread of antimicrobial-resistant bacteria were reviewed. It was found that longtime exposure to the most common food-grade disinfectants promoted resistance to clinically important antibiotics in pathogenic bacteria, namely cross-resistance. Currently, the use of disinfectants is largely unregulated. The mechanisms of cross-resistance are regulated by intrinsic molecular mechanisms including efflux pumps, DNA repair system, modification of the molecular target, and metabolic adaptation. Cross-resistance can also be acquired by mobile genetic elements. Long-term exposure to disinfectants has an impact on the dissemination of antimicrobial resistance in soil, plants, animals, water, and human gut environments.

Using photocatalyzed-peroxonization to disinfect and denature genetic material of bacterial plasmids present in hospital wastewater

The literature reports the presence of multiresistant microorganisms in wastewater discharged from municipal and hospital wastewater treatment plants (WWTPs). This has led to questions concerning the disinfection efficiency of the treatments applied. Thus, this study aimed to assess the efficiency of different chemical oxidation methods to disinfect and to degrade bacterial plasmids present in hospital wastewaters, to avoid the dispersion of antibiotic resistance genes in the environment. The methods tested were UV_254nm alone or associated with an Ag or Ti-photocatalyst in photo-peroxonization (UV_254 nm/H₂O₂/O₃/Ag₂O/Ag₂CO₃@PU or UV_254 nm/H₂O₂/O₃/TiO₂@PU) under different pH conditions (4, 7, and 10). The application of plasmid DNA electrophoresis to hospital wastewater treated using an advanced oxidation process (AOP) achieved the total structural denaturation of microorganism plasmids at the three pH values tested. Also, UV_254 nm alone was partially efficient in the disinfection of hospital wastewater. AOPs performed with the two functionalized catalysts resulted in 100% disinfection after 10 min at the three pH values tested. No intact plasmids were observed after 20 min of treatment with photocatalysis. This study could contribute to the development and improvement of wastewater treatment aimed at mitigating the spread of multiresistant microorganisms in the environment.

Virus inactivation by sequential ultraviolet-chlorine disinfection: Synergistic effect and mechanism

The COVID-19 outbreak has raised concerns about the efficacy of the disinfection process followed in water treatment plants in preventing the spread of viruses. Ultraviolet (UV) and chlorine multi-barrier disinfection processes are commonly used in water treatment plants; however, their effects on virus inactivation are still unclear. In this study, the effects of different disinfection processes (i.e., UV, free chlorine, and their combination) on waterborne viruses were analyzed using bacteriophage surrogates (i.e., MS2 and PR772) as alternative indicators. The results showed that the inactivation rates of PR772 by either UV or free chlorine disinfection were higher than those of MS2. PR772 was approximately 1.5 times more sensitive to UV disinfection and 8.4 times more sensitive to chlorine disinfection than MS2. Sequential UV-chlorine disinfection had a synergistic effect on virus inactivation, which was enhanced by an increase in the UV dose. As compared with single free chlorine disinfection, UV irradiation at 40 mJ cm^-2 enhanced MS2 and PR772 inactivation significantly with a 2.7-fold (MS2) and a 1.7-fold (PR772) increase in the inactivation rate constants on subsequent chlorination in phosphate buffered saline. The synergistic effect was also observed in real wastewater samples, in which the MS2 inactivation rate increased 1.4-fold on subsequent chlorination following UV irradiation at 40 mJ cm^-2. The mechanism of the synergistic effect of sequential UV-chlorine disinfection was determined via sodium dodecyl sulfate-polyacrylamide gel electrophoresis, using MS2 as an indicator. The results showed that the synergistic effect was due to damage to MS2 surface proteins caused by previous UV disinfection, which enhanced the sensitivity of MS2 to chlorination. This study provides a feasible approach for the efficient inactivation of viruses in water supply and drainage.

Transmission of antibiotic resistance genes through mobile genetic elements in Acinetobacter baumannii and gene-transfer prevention

Antibiotic resistance is a major global public health concern. Acinetobacter baumannii is a nosocomial pathogen that has emerged as a global threat because of its high levels of resistance to many antibiotics, particularly those considered as last-resort antibiotics, such as carbapenems. Mobile genetic elements (MGEs) play an important role in the dissemination and expression of antibiotic resistance genes (ARGs), including the mobilization of ARGs within and between species. We conducted an in-depth, systematic investigation of the occurrence and dissemination of ARGs associated with MGEs in A. baumannii. We focused on a cross-sectoral approach that integrates humans, animals, and environments. Four strategies for the prevention of ARG dissemination through MGEs have been discussed: prevention of airborne transmission of ARGs using semi-permeable membrane-covered thermophilic composting; application of nanomaterials for the removal of emerging pollutants (antibiotics) and pathogens; tertiary treatment technologies for controlling ARGs and MGEs in wastewater treatment plants; and the removal of ARGs by advanced oxidation techniques. This review contemplates and evaluates the major drivers involved in the transmission of ARGs from the cross-sectoral perspective and ARG-transfer prevention processes.

Quaternary Ammonium Groups Modified Magnetic Cyclodextrin Polymers for Highly Efficient Dye Removal and Sterilization in Water Purification

Water recovery is a significant proposition for human survival and sustainable development, and we never stop searching for more efficient, easy-operating, low-cost and environmentally friendly methods to decontaminate water bodies. Herein, we combined the advantages of β-cyclodextrin (β-CD), magnetite nanoparticles (MNs), and two kinds of quaternary ammonium salts to synthesize two porous quaternary ammonium groups capped magnetic β-CD polymers (QMCDP1 and QMCDP2) to remove organic pollutants and eradicate pathogenic microorganisms effectively through a single implementation. In this setting, β-CD polymer (CDP) was utilized as the porous substrate material, while MNs endowed the materials with excellent magnetism enhancing recyclability in practical application scenarios, and the grafting of quaternary ammonium groups was beneficial for the adsorption of anionic dyes and sterilization. Both QMCDPs outperformed uncapped MCDPs in their adsorption ability of anionic pollutants, using methyl blue (MB) and orange G (OG) as model dyes. Additionally, QMCDP2, which was modified with longer alkyl chains than QMCDP1, exhibits superior bactericidal efficacy with a 99.47% removal rate for Staphylococcus aureus. Accordingly, this study provides some insights into designing a well-performed and easily recyclable adsorbent for simultaneous sterilization and adsorption of organic contaminants in wastewater.

Removal of antibiotic resistance genes during livestock wastewater treatment processes: Review and prospects

Antibiotic resistance genes (ARGs) are emerging pollutants that have received extensive attention. Many different types of ARGs exist in livestock wastewater. If not effectively treated, they can threaten animal production, public health and the ecological safety of the surrounding environment. To address the high risk of livestock wastewater contamination by ARGs, the effects of different wastewater treatment processes on ARGs and their influencing factors and mechanisms are reviewed herein. Additionally, the current problems associated with removal of ARGs are discussed, and future research is proposed.

The fate of antibiotic resistance genes and their association with bacterial and archaeal communities during advanced treatment of pig farm wastewater

Advanced wastewater treatment plants are widely used in most large-scale pig farms in southern China. However, the fate of antibiotic resistance genes (ARGs) and their association with bacterial and archaeal communities during advanced wastewater treatment remain unclear. In this study, the profiles of ARGs in typical advanced wastewater treatment plants were surveyed using metagenomic analysis. The results showed that 279- 326 different subtypes of ARGs were detected in raw wastewater, with a total abundance of 5.98 ± 0.48 copies per bacterial cell. During the advanced wastewater treatment, the abundance and number of ARGs were significantly reduced. Microbial communities (bacteria and archaea) contributed the most to the variation in ARG abundance and composition (PCA axis_1), accounting for 10.8 % and 15.7 %, respectively, followed by mobile genetic elements (MGEs) and physicochemical factors. Special attention should be given to potential pathogenic bacteria such as Escherichia, Streptococcus, Enterococcus and Staphylococcus and archaea such as Methanocorpusculum, Candidatus Methanoplasma and Candidatus Methanomethylophilus, which were important potential ARG hosts. Bacterial communities may indirectly affect ARG variation by affecting archaeal communities. These findings indicated that ARG levels in pig farm wastewater can be effectively reduced during advanced treatment and highlighted the important role played by archaea, which should not be ignored.

Water disinfection by the UVA/electro-Fenton process under near neutral conditions: Performance and mechanisms

An efficient and thorough water disinfection is critical for human health. In this study, UVA-LEDs, nitrilotriacetic acid (NTA) and a boron-doped diamond anode were respectively used as the UVA source, the iron chelator and the anode for the UVA/electro-Fenton (E-Fenton) reaction to treat wastewater. The disinfection performance of the UVA/E-Fenton had been investigated. The mechanisms of the E. coli inactivation had been clarified. The results showed that complete disinfection (about 5.6-log removal) could be achieved within 50 min at a certain condition due to the synergistic effort of the UVA, anodic oxidation and the electro-Fenton. The quenching experiments and the electron paramagnetic resonance (EPR) detection indicated that •OH, •O₂^- and ¹O₂ play important roles for inactivating E. coli. The results of SEM images and genomic DNA electrophoresis suggested that both the cell structure and the DNA had been thoroughly destroyed during the UVA/E-Fenton process. Increasing the UVA irradiation, oxygen bubbling could improve the disinfection rate, while it also would increase the energy consumption. The appropriate Fe and NTA ratio was 1:2 to realize an efficient Fenton reaction under near neutral condition. Complete disinfection was also achieved within 50 min when it used for treating real wastewater. Thus, the UVA/E-Fenton process is a satisfied way for water disinfection.

Membrane bioreactor followed by solar photo-Fenton oxidation: Bacterial community structure changes and bacterial reduction

The removal of antibiotic resistance genes (ARGs) and taxon-specific markers, the bacterial community structure changes and the permanent inactivation of total bacteria including their antibiotic-resistant counterparts (ARB) in actual wastewater during a Membrane BioReactor (MBR) application followed by solar photo-Fenton oxidation at bench- and then pilot-scale under solar irradiation, were investigated. The presence of enterococci- and pseudomonad-specific taxon markers and of sul1 and ampC ARGs in the MBR effluent was confirmed, indicating the challenge of such processes, for the removal of biological molecules. On the other hand, >99 % reduction of all types of cultivable bacteria examined was observed after MBR treatment, with a 5-log reduction of E. coli and 6-log reduction of P. aeruginosa and Klebsiella spp. There was a shift in the bacterial community structure in the MBR effluent after the bench- and pilot-scale solar photo-Fenton oxidation. Notably, thermotolerant bacterial genera like Ignavibacterium and Thermomonas were prevalent during the pilot-scale process operated at a high ambient temperature, while the most prevalent genera were Mycobacterium, Nocardioides and Mesorhizobium, which are primarily not pathogenic and plant-related. In agreement, a different bacterial community structure according to the G-C content after DGGE analysis was noted between the MBR and solar photo-Fenton oxidation-treated effluents, but interestingly also between the bench- and pilot-scale oxidation-treated effluents. There was complete absence of ARGs after the bench-scale solar photo-Fenton oxidation application but not after the pilot-scale treatment (1.56 and 1.53 log₁₀ CE 100 ng^-1 DNA, of sul and ermB, respectively). Taxon-specific markers were found in both oxidation setups. Inactivation of cultivable Escherichia coli, Pseudomonas aeruginosa and Klebsiella spp. (including ARB) was achieved during both oxidation setups, with no further re-activation observed.

Presence of bromide and iodide promotes the horizontal transfer of antibiotic resistance genes during chlorination: A preliminary study

Chlorination was reported to have a great potential to increase horizontal gene transfer (HGT) of antibiotic resistance genes (ARGs), which poses a great threat to global human health. Bromide (Br^-) and iodide (I^-) ions are widely spread ions in water and wastewater. In chlorination, Br^- and I^- can be oxidized to active bromine and iodine species. The influence of the co-existing different halogen oxidants (chlorine + bromine or iodine species) on HGT of ARGs were rarely investigated. In this study, the conjugative transfer of ARGs between a donor strain E. coli K12 and a recipient strain E. coli HB101 was investigated in chlorination without/with the presence of Br^- or I^-. Immediately after the addition of sodium hypochlorite, 53-88 % of the dosed chlorine was rapidly consumed, 10 %-42 % fast transformed into organic combined chloramines, and only low levels of free chlorine (0.02-0.8 mg/L as Cl₂) left in the diluted cultural medium. Conjugative transfer mediated by the RP4 plasmid was not significantly enhanced in chlorination without the presence of Br^- or I^-. With the presence of Br^- (0.5-5.0 mg/L) or I^- (0.05-0.5 mg/L) in chlorination, the co-existing free halogen oxidants and their organic combined ones up-regulated the mRNA expression of the oxidative stress-regulatory gene (rpoS), outer membrane protein gene (ompC), and conjugation-relevant genes (trbBp and trfAp), and caused more damage to cell entirety. As a result, the co-existing reactive halogen oxidants enhanced the HGT of ARGs probably via conjugative transfer and transformation. This study showed that the presence of Br^- and I^- of common levels in aquatic environment promoted HGT of ARGs in chlorination, thus accelerating the transmission and prevalence of ARGs.

Application of Nucleotide-Based Kinetic Modeling Approaches to Predict Antibiotic Resistance Gene Degradation during UV- and Chlorine-Based Wastewater Disinfection Processes: From Bench- to Full-Scale

This study investigated antibiotic resistance gene (ARG) degradation kinetics in wastewaters during bench- and full-scale treatment with UV light and chlorine─with the latter maintained as free available chlorine (FAC) in low-ammonia wastewater and converted into monochloramine (NH₂Cl) in high-ammonia wastewater. Twenty-three 142-1509 bp segments (i.e., amplicons) of seven ARGs (blt, mecA, vanA, tet(A), ampC, bla_NDM, bla_KPC) and the 16S rRNA gene from antibiotic resistant bacteria (ARB) strains Bacillus subtilis, Staphylococcus aureus, Enterococcus faecium, Escherichia coli, Pseudomonas aeruginosa, and Klebsiella pneumoniae were monitored as disinfection targets by qPCR. Rate constants for ARG and 16S rRNA gene amplicon degradation by UV, FAC, and NH₂Cl were measured in phosphate buffer and used to expand and validate several recently developed approaches to predict DNA segment degradation rate constants based solely on their nucleotide contents, which were then applied to model ARG degradation during bench-scale treatment in buffer and wastewater matrixes. Kinetics of extracellular and intracellular ARG degradation by UV and FAC were well predicted up to ∼1-2-log₁₀ elimination, although with decreasing accuracy at higher levels for intracellular genes, while NH₂Cl yielded minimal degradation under all conditions (agreeing with predictions). ARB inactivation kinetics varied substantially across strains, with intracellular gene degradation lagging cell inactivation in each case. ARG degradation levels observed during full-scale disinfection at two wastewater treatment facilities were consistent with bench-scale measurements and predictions, where UV provided ∼1-log₁₀ ARG degradation, and chlorination of high-ammonia wastewater (dominated by NH₂Cl) yielded minimal ARG degradation.

Advanced wastewater treatment with ozonation and granular activated carbon filtration: Inactivation of antibiotic resistance targets in a long-term pilot study

The inactivation of antibiotic resistant bacteria (ARB) and genes (ARGs) in an advanced plant combining ozonation and granular activated carbon (GAC) filtration applied for effluent after conventional activated sludge treatment at a full-scale urban wastewater treatment plant was investigated for over 13 consecutive months. The nitrite compensated specific ozone dose ranged between 0.4 and 0.7 g O₃/g DOC with short-time sampling campaigns (0.2-0.9 g O₃/g DOC). Samples were analysed with culture-dependent methods for bacterial targets and with qPCR for genes. The log removal values were correlated with a decrease of the matrix UV absorption at 254 nm (ΔUV₂₅₄) and indicated a range of ΔUV₂₅₄ that corresponds to a sufficient membrane damage to affect DNA. For trimethoprim/sulfamethoxazole resistant E. coli, sul1, ermB and tetW, this phase was observed at ΔUV₂₅₄ of ~30 % (~0.5 g O₃/g DOC). For ampicillin resistant E. coli and bla_TEM-1, it was observed around 35-40 % (~0.7 g O₃/g DOC), which can be linked to mechanisms related to oxidative damages in bacteria resistant to bactericidal antibiotics. GAC treatment resulted in a further abatement for trimethoprim/sulfamethoxazole E. coli, sul1 and tetW, and in increase in absolute and relative abundance of ermB and bla_TEM-1.

How multi-walled carbon nanotubes in wastewater influence the fate of coexisting antibiotic resistant genes in the subsequent disinfection process

Wastewater treatment plants (WWTPs) are important hubs for the spread of antibiotic resistance genes (ARGs). Engineered nanoparticles, which was inevitably released to WWTPs, could change environmentally sensitive of antibiotic resistant bacteria (ARB). This would influence the fate of ARGs in subsequent disinfection process and consequent health risk. In this study, the ARGs fate of the effluent in conventional sodium hypochlorite (NaClO) disinfection process was investigated as multi-walled carbon nanotubes (MWCNTs) existed in sequencing batch reactor (SBR). The results showed the existence of MWCNTs in SBR could enhance the removal efficiency of intracellular 16S rRNA gene and intI1, extracellular intI1, sul2 and tetX in the effluent by NaClO. This is mainly due to the variation of bacterial physiological status, bacterial population structure and the activation of NaClO under the role of MWCNTs. MWCNTs in SBR could increase in membrane permeability of bacterial cells, which would be conducive to the penetration of chlorination to cytoplasm. MWCNTs in SBR also could change the bacterial population structure and induce the chlorine-sensitive bacteria; thus the potential hosts of ARGs in the effluent would be more easily inactivated by NaClO. Moreover, the residual MWCNTs in the effluent could activate NaClO to generate various free radical, which would enhance the oxidizing capacity of chlorination.

Tap water as a natural vehicle for microorganisms shaping the human gut microbiome

Fresh potable water is an indispensable drink which humans consume daily in substantial amounts. Nonetheless, very little is known about the composition of the microbial community inhabiting drinking water or its impact on our gut microbiota. In the current study, an exhaustive shotgun metagenomics analysis of the tap water microbiome highlighted the occurrence of a highly genetic biodiversity of the microbial communities residing in fresh water and the existence of a conserved core tap water microbiota largely represented by novel microbial species, representing microbial dark matter. Furthermore, genome reconstruction of this microbial dark matter from water samples unveiled homologous sequences present in the faecal microbiome of humans from various geographical locations. Accordingly, investigation of the faecal microbiota content of a subject that daily consumed tap water for 3 years provides proof for horizontal transmission and colonization of water bacteria in the human gut.

Detection and various environmental factors of antibiotic resistance gene horizontal transfer

Bacterial antibiotic resistance in water environments is becoming increasingly severe, and new antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) have also attracted the attention of researchers. The horizontal transfer of ARGs in water environments is considered one of the main sources of bacterial resistance in the natural environment. Horizontal gene transfer (HGT) mainly includes conjugation, natural transformation, and transduction, and conjugation has been investigated most. Several studies have shown that there are a large number of environmental factors that might affect the horizontal transfer of ARGs in water environments, such as nanomaterials, various oxidants, and light; however, there is still a lack of systematic and comprehensive reviews on the detection and the effects of the influence factors of on ARG horizontal transfer. Therefore, this study introduced three HGT modes, analysed the advantages and disadvantages of current methods for monitoring HGT, and then summarized the influence and mechanism of various factors on ARG horizontal transfer, and the possible reasons for the different effects caused by similar factors were mainly critically discussed. Finally, existing research deficiencies and future research directions of ARG horizontal transfer in water environments were discussed.

Solar-light driven photodegradation of antimicrobials, their transformation by-products and antibiotic resistance determinants in treated wastewater

This study aimed to assess the possibility of using solar light-driven photolysis and TiO₂-based photocatalysis to remove (1) antibiotic residues, (2) their transformation products (TPs), (3) antibiotic resistance determinants, and (4) genes identifying the indicator bacteria in a treated wastewater (secondary effluent). 16 antimicrobials belonging to the different classes and 45 their transformation by-products were selected for the study. The most susceptible to photochemical decomposition was tetracycline, which was completely removed in the photocatalysis process and in more than 80% in the solar light-driven photolysis. 83.8% removal (on average) was observed using photolysis and 89.9% using photocatalysis in the case of the tested genes, among which the genes sul1, uidA, and intI1 showed the highest degree of removal by both methods. The study revealed that applied methods promisingly remove the tested antibiotics, their TPs and genes even in such a complex matrix including treated wastewater and photocatalysis process had a higher removal efficiency of antibiotics, TPs and genes tested. Moreover, the high percentage removal of the intI1 gene (>93%) indicates the possibilities of use of the solar light-driven photolysis and TiO₂-based photocatalysis in minimizing the antibiotic resistance genes transfer by mobile genetic elements.

Pharmaceuticals and other contaminants of emerging concern in Admiralty Bay as a result of untreated wastewater discharge: Status and possible environmental consequences

Considering how the impact of human activity in Antarctica is growing, the aim of this study was to conduct the first assessment of pharmaceuticals and personal care products (PPCPs), other emerging contaminants (ECs), and antibiotic resistance genes present in the western shore of the Admiralty Bay region of King George Island. In total, more than 170 substances were evaluated to assess the potential environmental risks they pose to the study area. The major evaluated source of pollutants in this study is discharged untreated wastewater. The highest PPCP concentrations in wastewater were found for naproxen (2653 ngL^-1), diclofenac (747 ngL^-1), ketoconazole (760 ngL^-1), ibuprofen (477 ngL^-1) and acetaminophen (332 ngL^-1). Moreover, the concentrations of benzotriazole (6340 ngL^-1) and caffeine (3310 ngL^-1) were also high. The Risk Quotient values indicate that azole antifungals (ketoconazole), anti-inflammatories (diclofenac, ibuprofen) and stimulants (caffeine) are the main groups responsible for the highest toxic burden. In addition, antibiotic resistance genes integrons (int 1) and sulphonamide resistance genes (sul 1-2) were detected in wastewater and seawater. These results indicate that regular monitoring of PPCPs and other ECs is of great importance in this environment. Additionally, the following mitigation strategies are suggested: (1) to create a centralised record of the medications prescribed and consumed in situ (to improve knowledge of potential contaminants without analysis); (2) to use more environmentally friendly substitutes both for pharmaceuticals and personal care products when possible (limiting consumption at the source); and (3) to apply advanced systems for wastewater treatment before discharge to the recipient (end-of-pipe technologies as a final barrier).

Multifunctional porous β-cyclodextrin polymer for water purification

Keeping water clean is of vital significance for human health and environmental protection. In order to remove organic micro-pollutants and natural organic substances in water bodies and kill pathogenic microorganisms simultaneously, this study synthesized a multifunctional porous β-cyclodextrin polymer with a high specific surface area by introducing quaternary ammonium groups and rigid benzene rings, respectively, which was then polymerized with crosslinking agent-4,4'-bis (chloromethyl)-1,1'-biphenyl (BCMBP) in an ionic liquid system. The grafting of quaternary ammonium groups was beneficial for the removal of negative-charged humic acid (HA) and sterilization. The introduction of numerous rigid structures during benzylation and Friedel-Crafts alkylation reaction could significantly improve the porosity and specific surface area of the polymer, conducive to the exposure of cyclodextrin binding sites and contaminant adsorption. By changing the proportions of quaternization and benzylation, the structure and surface properties of the polymer could be adjusted, thus further regulating the adsorption performance. Compared with activated carbon, the polymer named BQCD-BP with a huge surface area of 1133 m² g^-1 prepared under optimized conditions showed outstanding adsorption performance and sterilization ability. The pseudo-second-order kinetic constant of BQCD-BP reached 1.2058 g·mg^-1·min^-1, which was approximately 50 times greater than that of activated carbon (0.0256 g·mg^-1·min^-1) under the same experimental condition. The adsorption capacity of BQCD-BP to HA was twice as high as that to AC, and the antibacterial ability of BQCD-BP was significant, achieving 90% at the dosage of 1g L^-1. Moreover, the adsorption process was hardly affected by the hydrochemical conditions, and the polymer was easy to regenerate. In addition, the excellent adsorption and antibacterial performance of the polymer were also identified by natural water treatment. COD was almost completely removed, and the removal efficiency of TP reached 92% after contact with BQCD-BP. The sterilization rate of BQCD-BP to viable bacteria in complex water bodies reached 82%. Undoubtedly, BQCD-BP is a potential multifunctional water treatment material with reasonable design in the actual water purification.

Degradation and inactivation of chromosomal and plasmid encoded resistance genes/ARBs and the impact of different matrices on UV and UV/H2O2 based advanced oxidation process

This study reports a structured investigation on the degradation kinetics of different types (gyrA^R,tetA^R, qnrS^R) and conformational forms (chromosomal, plasmids) of ARGs and mobile genetic elements (intl-1, plasmids) as a function of water matrix (DI water, phosphate buffer, wastewater) with UV and UV/H₂O₂ treatments. Extracellular, intracellular and the free-ARGs fate were tracked to infer the impact of various parameters on the degradation efficacy of the treatment process. The degradation profile of e-ARGs (118-454 bp) showed 1-4 log reductions but did not correlate strongly to amplicon size indicating the importance of active sites distribution and/or types of ARGs for UV induced gene damage. The i-ARGs showed similar degradation rates compared to e-ARGs for UV in phosphate buffer (PBS) but showed (1.3-2 times) slower rates for i-ARGs with UV/H₂O₂ due to scavenging of OH radicals by the cellular components. While the ARB inactivation was effective, but ARG damage was not supplemental as i-ARGs and f-ARGs persisted. In the wastewater matrix, generation of radical species was contributing to improved degradation rates from UV/H₂O₂ treatment, specifically for f-ARGs resulting in significantly improved degradation (p<0.05) compared to PBS. These indicates a non-selective nature of attack from radical species generated from UV irradiation on the effluent organic matter (E_fOM) than sequenced based damage to the genes from UV. For the plasmid degradation, conformational differences pertaining to the supercoiled structures and intracellular forms influenced slower (1.2-2.8 times) UV mediated gene damage rate as opposed to chromosomal ARGs. These results can be useful for better assessing UV based treatment processes for effective ARG removal.

Differentiation of DNA or membrane damage of the cells in disinfection by flow cytometry

Recently, the viabilities changes of fungal spores in the water supply system during different disinfection processes have been revealed. SYBR Green I (SG), a nucleic acid stain, its fluorescence intensity is correlated with the amount of double-stranded DNA. This study established a new method through successive SG-SG-PI staining (PI: Propidium Iodide) with flow cytometry (FCM). It could successfully distinguish DNA damage and membrane damage of fungal spores, clearly elucidating the intrinsic disinfection mechanism during the chemical disinfection. This method was briefly described as follows: firstly, (1) the fungal spores were stained with SG and washed by centrifugation; and then, (2) the washed spores were treated with disinfectants and terminated; after that, (3) the disinfected spores were re-stained with SG and analyzed by FCM; finally, (4) the SG re-stained spores were stained with PI and analyzed by FCM. The percentages of spores with DNA damage and membrane damage were determined by the fluorescence intensity obtained from steps (3) and (4), respectively. The repeatability and applicability of this developed method were confirmed. It was further applied to explore the inactivation mechanism during chlorine-based disinfection, and results demonstrated that chloramine attacked the DNA more seriously than the membrane, while chlorine and chlorine dioxide worked in a reverse way.

The balance between treatment efficiency and receptor quality determines wastewater impacts on the dissemination of antibiotic resistance

This study investigated the balance between treatment efficiency and impact caused by urban wastewater treatment plants (UWTPs) on the dissemination of antibiotic resistance. Four full-scale UWTPs (PT1-PT4) and the receiving river were sampled over four campaigns. The 16 S rRNA gene, two mobile genetic elements (MGEs), eight antibiotic resistance genes (ARGs), and culturable bacteria were monitored over different treatment stages and in hospital effluent. The bacterial and antibiotic resistance load was not significantly different in the inflow of the four UWTPs (p > 0.01). Biological treatment promoted ARGs reduction values up to 2.5 log-units/mL, while UV (PT1, PT2) or sand filtration/ozonation (PT3) led to removal values < 0.6 log-units/mL. The final effluent of PT3, with the highest removal rates and significantly lower ARGs abundance, was not significantly different from the receiving water body. Emerging ARGs (e.g., bla_VIM, bla_OXA-48, and bla_KPC) were sporadically detected in the river, although more frequent downstream. Hospital effluent might contribute for the occurrence of some, but not all these ARGs in the river. A major conclusion was that the impact of the UWTPs on the river was not only determined by treatment efficiency and final effluent quality, but also by the background contamination of the river and/or dilution rate.