Combined membrane filtration and 265 nm UV irradiation for effective removal of cell free antibiotic resistance genes from feed water and concentrate

The fate of intracellular and extracellular antibiotic resistance genes during ultrafiltration-ultraviolet-chlorination in a full-scale wastewater treatment plant

Effluent from wastewater treatment plants (WWTPs) is recognized as a significant source of antibiotic resistance genes (ARGs) in the environment. Advanced treatment processes such as ultrafiltration (UF), ultraviolet (UV) light disinfection, and chlorination have emerged as promising approaches for ARG removal. However, the efficacy of sequential disinfection processes, such as UF-UV-chlorination on intracellular (iARGs) and extracellular ARGs (eARGs), remains largely unknown. This study investigates the impact of this sequential disinfection process on the fate of iARGs, eARGs, and a crucial mobile genetic element (intI1) within a full-scale WWTP. Our findings revealed that the UF-UV-chlorination process effectively reduced the overall absolute abundance of detected ARGs in the effluent by 1.93 log, and intI1 by 0.86 log, compared to secondary effluent. The majority of these removals was achieved due to the UF and UV disinfection, while chlorination showed negligible impact on the absolute abundance of ARGs in the final effluent. Notably, five genera were identified as potential hosts for intI1 and eight iARGs, including aac(6')-Ib-cr, drfA1, sul1, sul2, ermB, mefA, tetA, and tetX, suggesting a high potential for horizontal gene transfer involving these ARGs. Overall, this study demonstrated that UF-UV-chlorination is a highly effective method for reducing ARGs in effluent from WWTPs.

Space heterogeneity of nitrogen removal functional genes, nitrogen transformation pathways and mechanisms in MEBR treating mariculture wastewater

Membrane Electro-Bioreactor (MEBR), exhibited excellent nitrogen removal in mariculture wastewater treatment. However, the differences of microbial community and nitrogen transformation pathways on spatial scale caused by the mass transfer of reactive chlorine species (RCS) generated by electrooxidation were unclear. This study provided new insights into the space heterogeneity of ammonia transformation pathways and mechanisms. The results demonstrated an increase in the reduction of nitrate to nitrite through partial denitrification on the membrane. Coupling with dissimilatory nitrate reduction to ammonium and RCS, higher nitrate (0.3 mgN/L) and TN removal (2.6 mgN/L) was obtained in MEBR. Higher relative abundance of narGHI and nirB were obtained. Ammonia oxidation by biofilters was enhanced in MEBR, that ammonia removal contributed by biofilters was 32.0 %, 5.2 times higher than the membrane. Relative abundance of amoABC and Nitrosomonas in biofilters were the highest. The results will provide theoretical basis for reactor configuration and operation optimization.

Photocatalysis Inhibits the Emergence of Multidrug-Resistant Bacteria in an Antibiotic-Resistant Bacterial Community in Aquatic Environments

Bacterial antibiotic resistance has recently attracted increasing amounts of attention. Here, an artificially antibiotic-resistant bacterial community (ARBC) combined with five different constructed antibiotic-resistant bacteria (ARB) with single antibiotic resistance, namely, kanamycin (KAN), tetracycline (TET), cefotaxime (CTX), polymyxin B (PB), or gentamicin (GEM), was studied for the stress response to photocatalysis. With photocatalytic inactivation, the transfer and diffusion of antibiotic resistance genes (ARGs) in the ARBC decreased, and fewer multidrug-resistant bacteria (MDRB) emerged in aquatic environments. After several days of photocatalytic inactivation or Luria broth cultivation, >90% ARB were transformed to antibiotic-susceptible bacteria by discarding ARGs. Bacteria with double antibiotic resistance were the dominant species (99%) of residual ARB. The changes in ARG abundance varied, decreasing for the GEM and TET resistance genes and increasing for the KAN resistance genes. The change in the antibiotic resistance level was consistent with the change in ARG abundance. Correspondingly, point mutations occurred for the KAN, CTX and PB resistance genes after photocatalytic inactivation, which might be the reason why these genes persisted longer in the studied ARBC. In summary, photocatalytic inactivation could reduce the abundance of some ARGs and inhibit the emergence of MDRB as well as block ARG transfer in the bacterial community in aquatic environments. This work highlights the advantages of long-term photocatalytic inactivation for controlling antibiotic resistance and facilitates a better understanding of bacterial communities in real aquatic environments.

Unveiling the characteristics of free-living and particle-associated antibiotic resistance genes associated with bacterial communities along different processes in a full-scale drinking water treatment plant

Antibiotic resistance genes (ARGs) as emerging contaminants, often co-occur with mobile genetic elements (MGEs) and are prevalent in drinking water treatment plants (DWTPs). In this study, the characteristics of free-living (FL) and particle-associated (PA) ARGs associated with bacterial communities were investigated along two processes within a full-scale DWTP. A total of 13 ARGs and two MGEs were detected. FL-ARGs with diverse subtypes and PA-ARGs with high abundances displayed significantly different structures. PA-MGEs showed a strong positive correlation with PA-ARGs. Chlorine dioxide disinfection achieved 1.47-log reduction of FL-MGEs in process A and 0.24-log reduction of PA-MGEs in process B. Notably, PA-fraction virtually disappeared after treatment, while blaTEM, sul2, mexE, mexF and IntI1 of FL-fraction remained in the finished water. Moreover, Acinetobacter lwoffii (0.04 % ∼ 45.58 %) and Acinetobacter schindleri (0.00 % ∼ 18.54 %) dominated the 16 pathogens, which were more abundant in FL than PA bacterial communities. PA bacteria exhibited a more complex structure with more keystone species than FL bacteria. MGEs contributed 20.23 % and 19.31 % to the changes of FL-ARGs and PA-ARGs respectively, and water quality was a key driver (21.73 %) for PA-ARGs variation. This study provides novel insights into microbial risk control associated with size-fractionated ARGs in drinking water.

Unraveling the nexus: Microplastics, antibiotics, and ARGs interactions, threats and control in aquaculture - A review

In recent years, aquaculture has expanded rapidly to address food scarcity and provides high-quality aquatic products. However, this growth has led to the release of significant effluents, containing emerging contaminants like antibiotics, microplastics (MPs), and antibiotic resistance genes (ARGs). This study investigated the occurrence and interactions of these pollutants in aquaculture environment. Combined pollutants, such as MPs and coexisting adsorbents, were widespread and could include antibiotics, heavy metals, resistance genes, and pathogens. Elevated levels of chemical pollutants on MPs could lead to the emergence of resistance genes under selective pressure, facilitated by bacterial communities and horizontal gene transfer (HGT). MPs acted as vectors, transferring pollutants into the food web. Various technologies, including membrane technology, coagulation, and advanced oxidation, have been trialed for pollutants removal, each with its benefits and drawbacks. Future research should focus on ecologically friendly treatment technologies for emerging contaminants in aquaculture wastewater. This review provided insights into understanding and addressing newly developing toxins, aiming to develop integrated systems for effective aquaculture wastewater treatment.

An evaluation of conventional and nature-based technologies for controlling antibiotic-resistant bacteria and antibiotic-resistant genes in wastewater treatment plants

Antibiotic resistance is a globally recognized health concern which leads to longer hospital stays, increased morbidity, increased mortality, and higher medical costs. Understanding how antibiotic resistance persists and exchanges in environmental systems like soil, water, and wastewater are critically important for understanding the emergence of pathogens with new resistance profiles and the subsequent exposure of people who indirectly/directly come in contact with these pathogens. There are concerns about the widespread application of prophylactic antibiotics in the clinical and agriculture sectors, as well as chemicals/detergents used in food and manufacturing industries, especially the quaternary ammonium compounds which have been found responsible for the generation of resistant genes in water and soil. The rates of horizontal gene transfer increase where there is a lack of proper water/wastewater infrastructure, high antibiotic manufacturing industries, or endpoint users - such as hospitals and intensive agriculture. Conventional wastewater treatment technologies are often inefficient in the reduction of ARB/ARGs and provide the perfect combination of conditions for the development of antibiotic resistance. The wastewater discharged from municipal facilities may therefore be enriched with bacterial communities/pathogens and provide a suitable environment (due to the presence of nutrients and other pollutants) to enhance the transfer of antibiotic resistance. However, facilities with tertiary treatment (either traditional/emerging technologies) provide higher rates of reduction. This review provides a synthesis of the current understanding of wastewater treatment and antibiotic resistance, examining the drivers that may accelerate their possible transmission to a different environment, and highlighting the need for tertiary technologies used in treatment plants for the reduction of resistant bacteria/genes.

New directions on membranes for removal and degradation of emerging pollutants in aqueous systems

Emerging pollutants (EPs) refer to a group of non-regulated chemical or biological substances that have been recently introduced or detected in the environment. These pollutants tend to exhibit resistance to conventional treatment methods and can persist in the environment for prolonged periods, posing potential adverse effects on ecosystems and human health. As we enter a new era of managing these pollutants, membrane-based technologies hold significant promise in mitigating impact of EPs on the environment and safeguarding human health due to their high selectivity, efficiency, cost-effectiveness and capability for simultaneous separation and degradation. Moreover, these technologies continue to evolve rapidly with the development of new membrane materials and functionalities, advanced treatment strategies, and analyses for effectively treating EPs of more recent concerns. The objective of this review is to present the latest directions and advancements in membrane-based technologies for addressing EPs. By highlighting the progress in this field, we aim to share valuable perspectives with researchers and contribute to the development of future directions in sustainable treatments for EPs.

A review on the effects of discharging conventionally treated livestock waste to the environmental resistome

Globally, animal production has developed rapidly as a consequence of the ongoing population growth, to support food security. This has consequently led to an extensive use of antibiotics to promote growth and prevent diseases in animals. However, most antibiotics are not fully metabolized by these animals, leading to their excretion within urine and faeces, thus making these wastes a major reservoir of antibiotics residues, antibiotic resistance genes (ARGs) and antibiotic resistant bacteria (ARB) in the environment. Farmers normally depend on conventional treatment methods to mitigate the environmental impact of animal waste; however, these methods are not fully efficient to remove the environmental resistome. The present study reviewed the variability of residual antibiotics, ARB, as well as ARGs in the conventionally treated waste and assessed how discharging it could increase resistome in the receiving environments. Wherein, considering the efficiency and environmental safety, an addition of pre-treatments steps with these conventional treatment methods could enhance the removal of antibiotic resistance agents from livestock waste.

Selection of indicator contaminants of emerging concern when reusing reclaimed water for irrigation - A proposed methodology

Organic and microbial contaminants of emerging concern (CECs), even though not yet regulated, are of great concern in reclaimed water reuse projects. Due to the large number of CECs and their different characteristics, it is useful to include only a limited number of them in monitoring programs. The selection of the most representative CECs is still a current and open question. This study presents a new methodology for this scope, in particular for the evaluation of the performance of a polishing treatment and the assessment of the risk for the environment and the irrigated crops. As to organic CECs, the methodology is based on four criteria (occurrence, persistence, bioaccumulation and toxicity) expressed in terms of surrogates (respectively, concentrations in the secondary effluent, removal achieved in conventional activated sludge systems, Log K_ow and predicted-no-effect concentration). It consists of: (i) development of a dataset including the CECs found in the secondary effluent, together with the corresponding values of surrogates found in the literature or by in-field investigations; (ii) normalization step with the assignment of a score between 1 (low environmental impact) and 5 (high environmental impact) to the different criteria based on threshold values set according to the literature and experts' judgement; (iii) CEC ranking according to their final score obtained as the sum of the specific scores; and (iv) selection of the representative CECs for the different needs. Regarding microbial CECs, the selection is based on their occurrence and their highest detection frequency in the secondary effluent and in the receiving water, the antibiotic consumption patterns, and recommendations by national and international organisations. The methodology was applied within the ongoing reuse project SERPIC resulting in a list of 30 indicator CECs, including amoxicillin, bisphenol A, ciprofloxacin, diclofenac, erythromycin, ibuprofen, iopromide, perfluorooctane sulfonate (PFOS), sulfamethoxazole, tetracycline, Escherichia coli, faecal coliform, 16S rRNA, sul1, and sul2.

Reduction of Ultrafiltration Membrane Fouling by the Pretreatment Removal of Emerging Pollutants: A Review

Ultrafiltration (UF) processes exhibit high removal efficiencies for suspended solids and organic macromolecules, while UF membrane fouling is the biggest obstacle affecting the wide application of UF technology. To solve this problem, various pretreatment measures, including coagulation, adsorption, and advanced oxidation, for application prior to UF processes have been proposed and applied in actual water treatment processes. Previously, researchers mainly focused on the contribution of natural macromolecular pollutants to UF membrane fouling, while the mechanisms of the influence of emerging pollutants (EPs) in UF processes (such as antibiotics, microplastics, antibiotic resistance genes, etc.) on membrane fouling still need to be determined. This review introduces the removal efficiency and separation mechanism for EPs for pretreatments combined with UF membrane separation technology and evaluates the degree of membrane fouling based on the UF membrane's materials/pores and the structural characteristics of the cake layer. This paper shows that the current membrane separation process should be actively developed with the aim of overcoming specific problems in order to meet the technical requirements for the efficient separation of EPs.

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.

Response of microbial antibiotic resistance to pesticides: An emerging health threat

The spread of microbial antibiotic resistance has seriously threatened public health globally. Non-antibiotic stressors have significantly contributed to the evolution of bacterial antibiotic resistance. Although numerous studies have been conducted on the potential risk of pesticide pollution for bacterial antibiotic resistance, a systematic review of these concerns is still lacking. In the present study, we elaborate the mechanism underlying the effects of pesticides on bacterial antibiotic resistance acquisition as well as the propagation of antimicrobial resistance. Pesticide stress enhanced the acquisition of antibiotic resistance in bacteria via various mechanisms, including the activation of efflux pumps, inhibition of outer membrane pores for resistance to antibiotics, and gene mutation induction. Horizontal gene transfer is a major mechanism whereby pesticides influence the transmission of antibiotic resistance genes (ARGs) in bacteria. Pesticides promoted the conjugation transfer of ARGs by increasing cell membrane permeability and increased the proportion of bacterial mobile gene elements, which facilitate the spread of ARGs. This review can improve our understanding regarding the pesticide-induced generation and spread of ARGs and antibiotic resistant bacteria. Moreover, it can be applied to reduce the ecological risks of ARGs in the future.

Removal behavior and key drivers of antibiotic resistance genes in two full-scale leachate treatment plants

Leachate is a critical reservoir of antibiotic resistance genes (ARGs) and its proper treatment is closely related to human health and ecosystem safety. Here, we used high-throughput qPCR to explore the removal behavior of ARGs in two full-scale leachate treatment plants (LTPs) where biological treatment and membrane filtration processes were integrated. A total of 286 ARGs and 55 mobile genetic elements (MGEs) were detected, with aminoglycoside, multidrug and MLSB resistance genes being the most prevalent and abundant. Anaerobic digestion was found to be an important pretreatment process for leachate, while anoxic/aerobic tanks in membrane bioreactor (MBR) acted as incubators for ARGs due to their significant proliferation effect on ARGs. Integrated membrane filtration (UF-NF-RO) excelled in ARGs removal with absolute abundances reduced by 3 to 6 orders of magnitude, from about 10⁹ copies/mL in raw leachate to 10³-10⁵ copies/mL in effluents. Our results also showed that leachate treatment processes significantly altered the composition of ARGs and bacterial communities. Procrustes analysis and network analysis revealed strong associations between microbes and ARGs, with several hub genes and bacterial genera identified. Structural equation models (SEMs) indicated that bacterial composition, MGEs and basic water properties were the key drivers shaping ARGs dynamics in the raw leachate, biological system and filtration system, respectively. Notably, several pathogens (e.g., Klebsiella, Vibrio, Aeromonas) were closely correlated with ARGs in raw leachate and may amplify the dissemination risks of ARGs. Moreover, insertion sequences in biological systems would accelerate the horizontal gene transfer of ARGs. In short, this study provides new insights into the mechanisms of ARGs removal and dissemination behavior in industrial-scale LTPs.

Removal of antibiotic microbial resistance by micro- and ultrafiltration of secondary wastewater effluents at pilot scale

Low-pressure membrane filtration was investigated at pilot scale with regard to its removal of antimicrobial resistance genes (ARGs) in conventional secondary treated wastewater plant effluents. While operating microfiltration (MF) and ultrafiltration (UF) membranes, key operational parameters for antimicrobial resistance (AMR) studies and key factors influencing AMR removal efficiencies of low-pressure membrane filtration processes were examined. The main factor for AMR removal was the pore size of the membrane. The formation of the fouling layer on capillary membranes had only a small additive effect on intra- and extrachromosomal ARG removal and a significant additive effect on mobile ARG removal. Using feeds with different ARGs abundances revealed that higher ARG abundance in the feed resulted in higher ARG abundance in the filtrate. Live-Dead cell counting in UF filtrate showed intact bacteria breaking through the UF membrane. Strong correlations between 16S rRNA genes (as surrogate for bacteria quantification) and the sul1 gene in UF filtrate indicated ARBs likely breaking through UF membranes.

The elimination of cell-associated and non-cell-associated antibiotic resistance genes during membrane filtration processes: A review

With increasing water reuse as a sustainable water management strategy, antibiotic resistance genes (ARGs) which have been identified as emerging contaminants in wastewater are attracting global attentions. Given that wastewater treatment plants are now well-established as a sink and source of ARGs in both cell-associated and non-cell-associated forms, a need is acknowledged to reduce their proliferation and protect public health. Due to their different characteristics, cell-associated and non-cell-associated ARGs may have distinct responses to membrane filtration processes which are widely used as advanced treatment to the secondary effluent. This review improves the understanding of the abundance of cell-associated and non-cell-associated ARGs in wastewaters and the secondary effluents and compares the elimination of ARGs in cell-associated and non-cell-associated forms by low-pressure and high-pressure membrane filtration processes. The former process reduces the concentration of cell-associated ARGs by more than 2-logs on average. An increase of the retention efficiency of non-cell-associated ARGs is observed with decreasing molecular weight cut-offs in ultrafiltration. The high-pressure membrane filtration (i.e., nanofiltration and reverse osmosis) can effectively eliminate both cell-associated and non-cell-associated ARGs, with averagely more than 4.6-log reduction. In general, the two forms of ARGs can be removed from water by the membrane filtration processes via the effects of size exclusion, adsorption, and electrostatic repulsion. The size and conformation of cell-associated and non-cell-associated ARGs, characteristics of membranes, coexisting substances, and biofilm formation influence ARG retention. Accumulation and potential proliferation of cell-associated and non-cell-associated ARGs in foulants and concentrate and corresponding control strategies warrant future research.

Synthetic organic antibiotics residues as emerging contaminants waste-to-resources processing for a circular economy in China: Challenges and perspective

Synthetic antibiotics have been known for years to combat bacterial antibiotics. But their overuse and resistance have become a concern recently. The antibiotics reach the environment, including soil from the manufacturing process and undigested excretion by cattle and humans. It leads to overburden and contamination of the environment. These organic antibiotics remain in the environment for a very long period. During this period, antibiotics come in contact with various flora and fauna. The ill manufacturing practices and inadequate wastewater treatment cause a severe problem to the water bodies. After pretreatment from pharmaceutical industries, the effluents are released to the water bodies such as rivers. Even after pretreatment, effluents contain a significant number of antibiotic residues, which affect the living organisms living in the water bodies. Ultimately, river contaminated water reaches the ocean, spreading the contamination to a vast environment. This review paper discusses the impact of synthetic organic contamination on the environment and its hazardous effect on health. In addition, it analyzes and suggests the biotechnological strategies to tackle organic antibiotic residue proliferation. Moreover, the degradation of organic antibiotic residues by biocatalyst and biochar is analyzed. The circular economy approach for waste-to-resource technology for organic antibiotic residue in China is analyzed for a sustainable solution. Overall, the significant challenges related to synthetic antibiotic residues and future aspects are analyzed in this review paper.

Fate of antibiotic resistant genes in wastewater environments and treatment strategies - A review

Antibiotic-resistant bacteria (ARB) and antibiotic-resistant genes (ARGs) have emerged in aquatic environments through the discharge of large amounts of antibiotics into wastewater. Well-designed wastewater treatment plants (WWTPs) with effective treatment processes are essential to prevent the release of ARGs directly into the environment. Although some systematic sequential treatment methods are used to remove ARGs, considerable gaps in removal mechanisms will be discussed. Therefore, deep analysis and discussion of various treatment methods are required to understand the ARGs removal mechanisms. In this manuscript, the role of antibiotics and the resistance mechanism of ARB are discussed in depth. In addition, the fate of ARGs in an aquatic environment and detection methods are compared comprehensively and discussed. In particular, the advantages and disadvantages of various methods are summarized and reviewed critically. Finally, combined technologies, such as advanced oxidation process (AOP) with biochemical systems, membrane separation with electrochemical AOP, ultrafiltration (UF) membrane coupled with photocatalytic treatment, and UF membrane separation coupled with sonication, are introduced. Overall, low-energy anaerobic treatment reactors with any of the above combined treatments might reduce the discharge of large quantities of ARGs into the environment. Finally, this review provides valuable insights for better ARG removal technologies by introducing combined effective treatment strategies used in real WWTPs.

Does light-based tertiary treatment prevent the spread of antibiotic resistance genes? Performance, regrowth and future direction

The common occurrence of antibiotic-resistance genes (ARGs) originating from pathogenic and facultative pathogenic bacteria pose a high risk to aquatic environments. Low removal of ARGs in conventional wastewater treatment processes and horizontal dissemination of resistance genes between environmental bacteria and human pathogens have made antibiotic resistance evolution a complex global health issue. The phenomenon of regrowth of bacteria after disinfection raised some concerns regarding the long-lasting safety of treated waters. Despite the inactivation of living antibiotic-resistant bacteria (ARB), the possibility of transferring intact and liberated DNA containing ARGs remains. A step in this direction would be to apply new types of disinfection methods addressing this issue in detail, such as light-based advanced oxidation, that potentially enhance the effect of direct light interaction with DNA. This study is devoted to comprehensively and critically review the current state-of-art for light-driven disinfection. The main focus of the article is to provide an insight into the different photochemical disinfection methods currently being studied worldwide with respect to ARGs removal as an alternative to conventional methods. The systematic comparison of UV/chlorination, UV/H₂O₂, sulfate radical based-AOPs, photocatalytic processes and photoFenton considering their mode of action on molecular level, operational parameters of the processes, and overall efficiency of removal of ARGs is presented. An in-depth discussion of different light-dependent inactivation pathways, influence of DBP and DOM on ARG removal and the potential bacterial regrowth after treatment is presented. Based on presented revision the risk of ARG transfer from reactivated bacteria has been evaluated, leading to a future direction for research addressing the challenges of light-based disinfection technologies.

Titanium dioxide based nanocomposites - Current trends and emerging strategies for the photocatalytic degradation of ruinous environmental pollutants

Many ruinous pollutants are omnipresent in the environment and among them; pesticides are xenobiotic and pose to be a bio-recalcitrance. Their detrimental ecological and environmental impacts attract attention of environmental excerpts and the surge of stringent regulations have endows the need of a technically feasible treatment. This critical review emphasizes about the occurrence, abundance and fate of structurally distinct pesticides in different environment. The practiced remedial strategies and in particular, the advanced oxidation processes (AOPs) those utilize the photo-catalytic properties of nano-composites for the degradation of pollutants are critically discussed. Photo-catalytic degradation utilizes many composite materials at nano-scale level, wherein synthesis of nano-composites with appropriate precursors and other adjoining functional moieties are of prime importance. Therefore, suitable starter materials along with the reaction conditions are prerequisite for effectively tailoring the nano-composites. The aforementioned aspects and their customized applications are critically discussed. The associated challenges, opportunities and process economics of degradation using photo-catalytic AOP techniques are highlighted and in addition, the review tries to explain how best the photo-degradation can be a stand-alone tool with a societal importance. Conclusively, the future prospects for undertaking new researches in photo-catalytic breakdown of pollutants that can be judiciously sustainable.

Impact of engineered nanoparticles on the fate of antibiotic resistance genes in wastewater and receiving environments: A comprehensive review

Nanoparticles (NPs) and antibiotic resistance elements are ubiquitous in wastewater and consequently, in receiving environments. Sub-lethal levels of engineered NPs potentially result in a selective pressure on antibiotic resistance gene (ARG) propagation in wastewater treatment plants. Conversely, emergent NPs are being designed to naturally attenuate ARGs based on special physical and electrochemical properties, which could alleviate dissemination of ARGs to the environment. The complex interactions between NPs and antibiotic resistance elements have heightened interest in elucidating the potential positive and negative implications. This review focuses on the properties of NPs and ARGs and how their interactions could increase or decrease antibiotic resistance at wastewater treatment plants and in receiving environments. Further, the potential for sub-lethal level NPs to facilitate horizontal gene transfer of ARGs and increase mutagenesis rates, which adds a layer of complexity to combatting antibiotic resistance associated with wastewater management, is discussed. Notably, the literature revealed that sub-lethal exposure of engineered NPs may facilitate conjugative transfer of ARGs by increasing cell membrane permeability. The enhanced permeability is a result of direct damage via NP attachment and indirect damage by generating reactive oxygen species (ROS) and causing genetic changes relevant to conjugation. Finally, current knowledge gaps and future research directions (e.g., deciphering the fate of NPs in the environment and examining the long-term cytotoxicity of NPs) are identified for this emerging field.

Advances and Applications of Hollow Fiber Nanofiltration Membranes: A Review

Hollow fiber nanofiltration (NF) membranes have gained increased attention in recent years, partly driven by the availability of alternatives to polyamide-based dense separation layers. Moreover, the global market for NF has been growing steadily in recent years and is expected to grow even faster. Compared to the traditional spiral-wound configuration, the hollow fiber geometry provides advantages such as low fouling tendencies and effective hydraulic cleaning possibilities. The alternatives to polyamide layers are typically chemically more stable and thus allow operation and cleaning at more extreme conditions. Therefore, these new NF membranes are of interest for use in a variety of applications. In this review, we provide an overview of the applications and emerging opportunities for these membranes. Next to municipal wastewater and drinking water processes, we have put special focus on industrial applications where hollow fiber NF membranes are employed under more strenuous conditions or used to recover specific resources or solutes.

Effect of preferential UV photolysis on the source control of antibiotic resistome during subsequent biological treatment systems

The environmental spread of antibiotic resistance genes (ARGs) from the direct application of traditional biological treatment systems for antibiotics in water is a potential public health threat. UV photolysis has been proved to be an efficient pretreatment method for antibacterial activity elimination, but the fate of antibiotic resistome in subsequent bioreactors fed with pretreated florfenicol (FLO) in synthetic wastewater is still unknown. Antibacterial activity in synthetic wastewater was effectively eliminated by UV irradiation pretreatment, and the diversity and abundance of detected ARGs in both aerobic and anaerobic bioreactors were significantly lower than those without pretreatment. Meanwhile, UV irradiation pretreatment shaped the structure and composition of sludge microbial communities in the subsequent bioreactors closer to those of the FLO-free groups. The relative abundances of Pseudomonas and Escherichia-Shigella working as the potential hosts of ARGs were significantly reduced in aerobic and anaerobic bioreactors, respectively. The significantly positive correlation between floR and intI1 and the decrease of intI1 abundance in UV photolytic pretreatment groups indicated that the horizontal transfer of floR was decreased. The study provides new insights into the effect of preferential UV photolysis as a pretreatment method on the source control of antibiotic resistome in subsequent biological treatment process.

Calculating expected effects of treatment effectivity and river flow rates on the contribution of WWTP effluent to the ARG load of a receiving river

Concentrations of genetic markers for antibiotic resistance genes (ARGs) were measured in the effluents of three Norwegian wastewater treatment plants (WWTPs) and in a receiving river upstream and downstream of the discharge point of one WWTP. Calculations based on mass balances were carried out to evaluate the impact of river flow rates and treatment effectivity on the WWTP's contribution to the load of genetic markers in the river. At average river flow rates, the WWTP effluent contributes 5-15% to the genetic marker load of the respective river. However, at minimum river flow rates, the WWTP effluent contributes 22-55% to the loads of different genetic markers. Scenarios of an improved or worsened removal of genetic markers in the WWTP showed that a further 1-log removal using additional treatment would be sufficient to improve considerably the river water quality with respect to genetic markers. Then, at an average flow rate, the contribution of the WWTP effluent to the load of the river would be less than 2%. However, in the case of low treatment effectivity or malfunction of the WWTP, the marker load of the river would increase dramatically. Even at average flow rate, 75-92% of the marker load would then originate from the WWTP. The results demonstrate the importance of considering the flow rates and hydrologic characteristics of the recipient water body when deciding on priorities regarding the upgrade of WWTPs for further removal of ARGs.

Removal of antibiotic-resistant genes during drinking water treatment: A review

Once contaminate the drinking water source, antibiotic resistance genes (ARGs) will propagate in drinking water systems and pose a serious risk to human health. Therefore, the drinking water treatment processes (DWTPs) are critical to manage the risks posed by ARGs. This study summarizes the prevalence of ARGs in raw water sources and treated drinking water worldwide. In addition, the removal efficiency of ARGs and related mechanisms by different DWTPs are reviewed. Abiotic and biotic factors that affect ARGs elimination are also discussed. The data on presence of ARGs in drinking water help come to the conclusion that ARGs pollution is prevalent and deserves a high priority. Generally, DWTPs indeed achieve ARGs removal, but some biological treatment processes such as biological activated carbon filtration may promote antibiotic resistance due to the enrichment of ARGs in the biofilm. The finding that disinfection and membrane filtration are superior to other DWTPs adds weight to the advice that DWTPs should adopt multiple disinfection barriers, as well as keep sufficient chlorine residuals to inhibit re-growth of ARGs during subsequent distribution. Mechanistically, DWTPs obtain direct and inderect ARGs reduction through DNA damage and interception of host bacterias of ARGs. Thus, escaping of intracellular ARGs to extracellular environment, induced by DWTPs, should be advoided. This review provides the theoretical support for developping efficient reduction technologies of ARGs. Future study should focus on ARGs controlling in terms of transmissibility or persistence through DWTPs due to their biological related nature and ubiquitous presence of biofilm in the treatment unit.

Removal of tetracycline-resistant Escherichia coli and its genes through ultrasound treatment combined with ultraviolet light emitting diodes

Antibiotic resistance has gained increasing attention worldwide, and wastewater treatment plants have been regarded as hotspots for antibiotic-resistant bacteria and antibiotic-resistant genes (ARGs). In this study, we evaluated the removal of tetracycline-resistant Escherichia coli and its related genes through ultrasound (US) treatment with different input levels of US-specific energy combined with ultraviolet light emitting diodes (UV-LEDs). Simultaneous US with UV-LEDs effectively eliminated tetracycline-resistant E. coli with the normal suggested UV-LEDs dosage (below 30 mJ/cm²). The removal efficiency increased with the addition of US (specific input energy of 8-16 kJ/L), and simultaneous US treatment with UV-LEDs was relatively more effective than US pretreatment. Analyses of cell damage by K⁺ leakage and flow cytometry showed that the cell wall kept its integrity during the applied treatment conditions. Consequently, the removal efficiencies of 16 S rRNA, tet M, and tet Q were unsatisfactory because less than 1 log reduction was achieved. Increasing the US energy remarkably damaged the cell wall and potentially promoted the reaction. The removal of ARGs increased four times when using US-specific input energy at 330 kJ/L with 5 mJ/cm² compared with UV-LEDs alone. The US treatment combined with UV-LEDs is a novel process that does not require chemicals. Results of this research can provide theoretical support for the removal of ARGs.

Intracellular versus extracellular antibiotic resistance genes in the environment: Prevalence, horizontal transfer, and mitigation strategies

Antibiotic resistance genes (ARGs) are present as both intracellular and extracellular fractions of DNA in the environment. Due to the poor yield of extracellular DNA in conventional extraction methods, previous studies have mainly focused on intracellular ARGs (iARGs). In this review, we evaluate the prevalence/persistence and horizontal transfer of iARGs and extracellular ARGs (eARGs) in different environments, and then explore advanced mitigation strategies in wastewater treatment plants (WWTPs) for preventing the spread of antibiotic resistance in the environment. Although iARGs are the main fraction of ARGs in nutrient-rich environments, eARGs are predominant in receiving aquatic environments. In such environments, natural transformation of eARGs occurs with a comparable frequency to conjugation of iARGs. Further, eARGs can be adsorbed by soil and sediments particles, protected from DNase degradation, and consequently persist longer than iARGs. Collectively, these characteristics emphasize the crucial role of eARGs in the spread of antibiotic resistance in the environment. Fate of iARGs and eARGs through advanced treatment technologies (disinfection and membrane filtration) indicates that different mitigation strategies may be required for each ARG fraction to be significantly removed. Finally, comprehensive risk assessment is needed to evaluate/compare the effect of iARGs versus eARGs in the environment.

An alternative material for an effective treatment technique proposal in the light of bibliometric profile of global scientific research on antibiotic resistance and Escherichia coli

Antibiotic resistance is considered by the countries to be a global health issue and a huge threat to public health. The reduction of resistant microorganisms from water/wastewater is of importance in environmental sciences since they are resistant in the aquatic environment. In this study, a bibliometric analysis of literature from the field of environmental science in water ecosystems from 2015 to 2019 was carried out using the keywords "Antibiotic Resistance (AR)" and "Escherichia coli". Furthermore, using the keywords of "Fresh Water," "Sea Water," and "Waste Water," 155, 52, and 57 studies were discovered, respectively. It is found that 217 studies of the total 2115 studies investigated on AR are mostly performed in the "Waste Water" by considering human health. Given the studies, an up-to-date solution should be proposed since the release of antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) from wastewater treatment plants needs to be mitigated. For this reason, it is obvious that working on micro and macro ecosystems will increase the probability of solutions in antibiotic resistance. A discussion of removal techniques for coliform bacteria, particularly antibiotic resistant Escherichia coli, was presented. One of the unique values of this study is to offer an innovative solution that removing them by metal-organic frameworks (MOFs) are emerging crystalline hybrid materials. MOFs are used for environmental, biological, and food antimicrobial substances efficiently. Therefore, we can give inspiration to the future studies of antimicrobial resistance removal via adsorption using MOFs as adsorbents. Graphical Abstract.