Mitigated membrane fouling and enhanced removal of extracellular antibiotic resistance genes from wastewater effluent via an integrated pre-coagulation and microfiltration process

Sensitivity and consistency of long- and short-read metagenomics and epicPCR for the detection of antibiotic resistance genes and their bacterial hosts in wastewater

Wastewater surveillance is a powerful tool to assess the risks associated with antibiotic resistance in communities. One challenge is selecting which analytical tool to deploy to measure risk indicators, such as antibiotic resistance genes (ARGs) and their respective bacterial hosts. Although metagenomics is frequently used for analyzing ARGs, few studies have compared the performance of long-read and short-read metagenomics in identifying which bacteria harbor ARGs in wastewater. Furthermore, for ARG host detection, untargeted metagenomics has not been compared to targeted methods such as epicPCR. Here, we 1) evaluated long-read and short-read metagenomics as well as epicPCR for detecting ARG hosts in wastewater, and 2) investigated the host range of ARGs across the wastewater treatment plant (WWTP) to evaluate host proliferation. Results highlighted long-read revealed a wider range of ARG hosts compared to short-read metagenomics. Nonetheless, the ARG host range detected by long-read metagenomics only represented a subset of the hosts detected by epicPCR. The ARG-host linkages across the influent and effluent of the WWTP were characterized. Results showed the ARG-host phylum linkages were relatively consistent across the WWTP, whereas new ARG-host species linkages appeared in the WWTP effluent. The ARG-host linkages of several clinically relevant species found in the effluent were identified.

Removal of RNA viruses from swine wastewater using anaerobic membrane bioreactor: Performance and mechanisms

The effective removal of viruses from swine wastewater using anaerobic membrane bioreactor (AnMBR) is vital to ecological safety. However, most studies have focused only on disinfectants, whereas the capabilities of the treatment process have not been investigated. In this study, the performance and mechanism of an AnMBR in the removal of porcine hepatitis E virus (HEV), porcine kobuvirus (PKoV), porcine epidemic diarrhea virus (PEDV), and transmissible gastroenteritis coronavirus (TGEV) are systematically investigated. The results show that the AnMBR effectively removes the four viruses, with average removal efficiencies of 1.62, 3.05, 2.41, and 1.34 log for HEV, PKoV, PEDV and TGEV, respectively. Biomass adsorption contributes primarily to the total virus removal in the initial stage of reactor operation, with contributions to HEV and PKoV removal exceeding 71.7 % and 68.2 %, respectively. When the membrane is fouled, membrane rejection dominated virus removal. The membrane rejection contribution test shows the significant contribution of membrane pore foulants (23-76 %). Correlation analysis shows that the surface characteristics and size differences of the four viruses contribute primarily to their different effects on biomass adsorption and membrane rejection. This study provides technical guidance for viral removal during the treatment of high-concentration swine wastewater using an AnMBR.

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.

An advanced treatment process for 3-high wastewater discharged from crude oil storage tanks

The wastewater discharged from crude oil storage tanks (WCOST) contains high concentrations of salt and metal iron ions, and high chemical oxygen demand (COD). It belongs to "3-high" wastewater, which is difficult for purification. In this study, WCOST treatments were comparatively investigated via an advanced pretreatment and the traditional coagulation-microfiltration (CMF) processes. After WCOST was purified through the conventional CMF process, fouling occurred in the microfiltration (MF) membrane, which is rather harmful to the following reverse osmosis (RO) membrane unit, and the effluent featured high COD and UV254 values. The analysis confirmed that the MF fouling was due to the oxidation of ferrous ions, and the high COD and UV254 values were mainly attributable to the organic compounds with small molecular sizes, including aromatic-like and fulvic-like compounds. After the pretreatment of the advanced process consisting of aeration, manganese sand filtration, and activated carbon adsorption in combination with CMF process, the removal efficiencies of organic matter and total iron ions reached 97.3% and 99.8%, respectively. All the water indexes of the effluent, after treatment by the advanced multi-unit process, meet well the corresponding standard. The advanced pretreatment process reported herein displayed a great potential for alleviating the MF membrane fouling and enhanced the lifetime of the RO membrane system in the 3-high WCOST treatment.

Synergistic removal of pharmaceuticals and antibiotic resistance from ultrafiltered WWTP effluent: Free-floating ARGs exceptionally susceptible to degradation

To protect the environment and human health, antibiotic resistance genes (ARGs) and persistent pharmaceuticals need to be removed from WWTP effluent prior to its reuse. However, an efficient process for removing free-floating extracellular DNA (exDNA) in combination with a wide range of pharmaceuticals is yet to be reported for real process conditions. As a possible solution, we treated real ultrafiltered WWTP effluent with UV/H₂O₂ and combined GAC and zeolite sorption. In terms of exDNA, sequencing and high-throughput quantitative PCR (HT-qPCR) showed that exDNA is a potent carrier of numerous ARGs in ultrafiltered WWTP effluent (123 ARGs), including multi-drug efflux pump mexF that became the dominant exARG in GAC effluent over time. Due to the exposure to degradation agents, exDNA was reduced more efficiently than intracellular DNA, and overall levels of ARGs were substantially lowered. Moreover, GAC sorption was particularly effective in the removal of almost all the 85 detected pharmaceutical residues, with fresh GAC demonstrating an efficiency of up to 100%. However, zeolite (Si/Al 0.8) addition was needed to enhance the removal of persistent pollutants such as gabapentin and diclofenac to 57% and up to 100%, respectively. Our combined approach eminently decreases the hazardous effects of pharmaceuticals and antibiotic resistance in the ultrafiltered WWTP effluent, producing effluent suitable for multiple reuse options according to the latest legislation. In addition, we provided similarly promising but less extensive data for surface water and treated greywater.

Solid-liquid interface adsorption of antibiotic resistance plasmids induced by nanoplastics aggravates gene pollution in aquatic ecosystems

Antibiotic resistance genes (ARGs) and nanoplastics (NPs) have been identified as emerging pollutants in water environment; the interactions between antibiotic resistance plasmids (ARPs) and NPs will influence ARG transport in sediments. Herein, the adsorption experiments of a typical ARP onto polystyrene nanoplastics (PS-NPs) in river and lake sediments were conducted to elucidate the adsorption mechanisms and the effects of environmental factors. Results indicated that the adsorption amounts of PS-NPs increased with the dosages while decreased with the particle size of sediments. Multi-layer adsorption of PS-NPs was found to exist mainly in sand and silt sediments, whereas the filling adsorption dominated in the clay. Moreover, the adsorbed PS-NPs enhanced the physisorption of ARPs in sediments through stimulating the intraparticle diffusion of ARPs induced by electrostatic force. Besides, the adsorption amounts of ARPs onto the PS-NPs decreased with the increasing pH and dissolve organic matter due to the enhanced electrostatic repulsion and competitive adsorption. The ion strength played catalytic roles by increasing the electrostatic attraction and adsorption sites of ARPs on PS-NPs. The adsorbed ARPs in sediments were closely related with the ARGs in extra/intracellular DNA of biofilms, influencing the distribution and proliferation of ARGs largely. The findings indicate that ARG-associated pollution might be enhanced by the solid-liquid interface adsorption induced by NPs, which was controlled by pH, ion strength and dissolve organic matter. This study provides supplementary insights into the roles of NPs as carriers of ARP in sediments, and advances our understanding on the risks of NP-ARG co-occurring contamination in aquatic ecosystems.

Antibiotics and antimycotics in waste water treatment plants: Concentrations, removal efficiency, spatial and temporal variations, prediction, and ecological risk assessment

For investigating the spatial, temporal variations and assessing ecological risk of 10 antibiotics and 6 antimycotics, influent sewage water and treated effluent were collected during three different seasons in 19 waste water treatment plants of Tianjin. High performance liquid chromatography tandem mass spectrometry was used to analyze 16 substances. The concentration range of influent samples was not detected (nd) -547.94 ng/L and the concentration range of effluent samples was nd-52.97 ng/L. By calculating the removal efficiency, it was found that Ciprofloxacin (CIP), Ofloxacin (OFL) and Clotrimazole (CTR) were effectively removed. There were significant spatial and temporal differences, the concentration in the dry season was evidently higher than that in the wet and normal seasons, and the northeast was lower than that in the northwest and southeast. By establishing a data set of influent and effluent, the priority features were extracted by feature engineering, which were temperature and NH₃-N. Under the condition of ensuring the best performance of the models, the influent model with 9 features and the effluent model with 4 features were established, and the quantitative relationship between the above features and concentration was obtained through partial dependence analysis. Except for Moxifloxacin (MOX), Norfloxacin (NOR) and OFL in the influent samples, the RQ values for other antibiotics and antimycotics were less than 0.1. Among the effluent samples, only NOR had an RQ value greater than 0.1, and OFL, MOX, and Pefloxacin (PEF) had RQ values between 0.01 and 0.1. Comparing the observations and predictions individual RQ values, the predictions were ideal and matched the observations. This work effectively assessed environmental impact and provided a valuable reference for evaluating antibiotics and antimycotics ecological toxicity.

Impact of Plastic Particles on the Horizontal Transfer of Antibiotic Resistance Genes to Bacterium: Dependent on Particle Sizes and Antibiotic Resistance Gene Vector Replication Capacities

Plastic particles impact the propagation of antibiotic resistance genes (ARGs) in environmental media, and their perturbation on the horizontal gene transfer (HGT) of ARGs is recognized as a critical influencing mechanism. However, studies concerning the influence and influencing mechanisms of plastic particles on the HGT of ARGs were limited, particularly for the effect of particle sizes and ARG vector-associated mechanisms. This study explored the impact of polystyrene (PS) particles with sizes of 75, 90, 100, 1000, and 10000 nm on the HGT (via transformation) of ARGs mediated by pUC19, pSTV29, and pBR322 plasmids into Escherichia coli cells. PS particles with sizes ≤100 nm impacted the transformation of ARGs, but large particles (1000 and 10000 nm) showed no obvious effects. Effects of PS particles on the transfer of three plasmids were vastly distinct. For pUC19 with high replication capacities, the transfer was monotonously promoted. However, for pSTV29 and pBR322 with low replication capacities, suppressing effects were observed. This was attributed to two competing mechanisms. The enhancing mechanism was that the direct interaction of PS particles with membrane lipids and the indirect effect associated with bacterial oxidative stress response induced pore formation on the cell membrane and increased membrane permeability, thus enhancing plasmid entrance. The inhibiting mechanism was that PS particles interfered with plasmid replication inside E. coli, thus decreasing the bacterial tranformation. This study deepened our understanding of the environmental dissemination of ARGs in plastic contamination.

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.

Antibiotic-Resistant Gene Behavior in Constructed Wetlands Treating Sewage: A Critical Review

The main objective of this review is to evaluate the performance of constructed wetlands (CWs) used to reduce antibiotic-resistant genes (ARGs) during sewage treatment. To accomplish this objective, statistical and correlation analyses were performed using published data to determine the influence of operational and design parameters on ARG reduction in CWs. The effects of design and operational parameters, such as different CW configurations, seasonality, monoculture and polyculture, support medium, and hydraulic retention time (HRT), on ARG removals, were analyzed. A comparison of ARG reduction under different CW configurations showed that the hybrid configuration of surface flow (SF)–vertical subsurface flow (VSSF) achieved the highest reductions, with values of 1.55 ulog. In this case, aeration is considered an important factor to reduce ARGs in CWs, and it should be considered in future studies. However, statistical analyses showed that the ARG reductions under different CW configurations were not significant (p > 0.05). The same behavior was observed when the effects of operational factors on ARG reductions were analyzed (p > 0.05). The results of this study show that CWs are not optimal technologies to reduce ARGs in sewage. The combination of CWs with advanced wastewater technologies can be a solution for enhancing ARG reduction and reducing the spread of antibiotic resistance.

Interface behavior and removal mechanisms of human pathogenic viruses in anaerobic membrane bioreactor (AnMBR)

Effective removal of human pathogenic viruses is an indispensable yet rarely studied aspect for sustainable treatment of domestic wastewater by anaerobic membrane bioreactor (AnMBR). In this study, the interface behaviors and removal mechanisms of norovirus genogroup I (GI), genogroup II (GII), and rotavirus A from domestic wastewater was systematically investigated in a one-stage AnMBR. On average, norovirus GI, GII and rotavirus were reduced by 4.64, 5.00, and 2.31 logs, respectively. Viruses tended to be transferred to larger-sized suspended solids from sewage influent to the mixed liquor, and the weight-specific concentration of the virus in >100 μm particles of the mixed liquor was significantly higher than that of sewage, indicating a particle scale-dependent affinity with the virus. In-series membrane filtration test showed the main contribution of the membrane retention, which was dominated by the bio-cake layer and the pristine membrane, while the membrane and associated pore foulants can retain viruses in a filtration resistance-efficient way. An unsteady-state mass balance model revealed that free viruses in the bulk liquid of AnMBR were minimally attached to the cake layer but mainly retained by the membrane and pore foulants (>99%). In addition, despite the small virus decay rates in the mixed liquor, the associated contribution increased with run time due to the prolonged sludge retention time. These insights into virus behaviors and removal mechanisms may provide novel regulation strategies for enhanced virus removal by AnMBR.

Potassium ferrate combined with ultrafiltration for treating secondary effluent: Efficient removal of antibiotic resistance genes and membrane fouling alleviation

Antibiotic resistance genes (ARGs) are considered as emerging environmental contaminants, which should be controlled by wastewater treatment plants to prevent their discharge into the environment. However, conventional treatment techniques generally fail to successfully reduce ARGs, and the release of cell-free ARGs was underestimated. In this study, potassium ferrate (Fe(VI)) pretreatment combined with ultrafiltration (UF) process was developed to remove both cell-associated and cell-free ARGs in real secondary effluent, compared to ferric chloride (Fe(III)) and poly-aluminum chloride (PACl) pretreatment processes. It was found that total ARGs especially cell-free ARGs were effectively removed by Fe(VI) oxidation. However, due to the poor settleability of the negatively charged particles formed by Fe(VI) in the secondary effluent, the removal of cell-associated ARGs was less compared to Fe(III) and PACl pretreatments. The combination of Fe(VI) and UF removed the most ARGs (3.26 - 5.01 logs) due to the efficient removal of cell-free ARGs by Fe(VI) (> 2.15 logs) and co-interception of both cell-associated ARGs and Fe(VI) formed particles of the UF. High-throughput sequencing revealed that Fe(VI) decreased the viability and relative abundances of the potential ARGs hosts. Fe(VI)-UF exhibited the best performance on humic-like fluorescent organic matters removal, as well as the least phytotoxicity in the effluent. Moreover, membrane fouling was remarkably alleviated by Fe(VI) pretreatment because (1) Fe(VI) removed macromolecules such as protein-like and polysaccharide-like substances which would block the membrane pores, (2) Fe(VI) improved the hydrophilicity of foulants and reduced the hydrophobic adsorption between foulants and membrane. In short, Fe(VI)-UF is a promising technology to efficiently remove ARGs (especially cell-free ARGs) and alleviate UF membrane fouling in wastewater reclamation.

Using biochar to strengthen the removal of antibiotic resistance genes: Performance and mechanism

In this study, the excess activated sludge was used for pyrolysis to produce biochar with Ce modification. The removal process and mechanism of ampicillin resistance gene (ARG_Amp) by biochar was investigated. The results showed that when pyrolyzing the excess sludge at 400 °C, the organic components in the sludge could be partially pyrolyzed and complexed with Ce. By accepting electrons from phenol or quinone, persistent free radicals (PFRs) were formed on the surface of biochar. On the optimized conditions with the initial ARG_Amp concentration of 41.43 mg/L, the removal ratios of ARG_Amp by adsorption, PFRs, hydroxyl free radicals (·OH) by adding H₂O₂ were 28.37%, 8.26%, and 27.56%. No melted DNA was detected in the treated samples. The oxidation process by PFRs and ·OH can directly destroy the ARG_Amp structure. The phosphodiester bond in the base stacking structure and the phosphate bond in the nucleotide are the possible action sites of PFRs. Treated ARG_Amp products were in the form of base pair residues or short-chain double helix structures. ·OH can be added to the bases of nucleotide molecules to form highly active free radical adducts. They can initiate molecular dehydrogenation and intermolecular proton transfer, resulting in oxidation of the base to the scission of the phosphate sugar backbone.

Mechanism of a double-channel nitrogen-doped lignin-based carbon on the highly selective removal of tetracycline from water

A high-performance nitrogen-doped lignin-based carbon material (ILAC-N) was synthesized using industrial lignin and urea by hydrothermal and activation, as an absorbent of tetracycline hydrochloride (TC). The results showed that the ILAC-N comprises a double-channeled structure with micro and mesopores. It exhibits an excellent adsorption capacity of TC across a wide pH range (pH 2-11), with the highest adsorption capacity of 1396 mg g^-1 at 323 K. Tests in actual wastewater showed that the TC removal rate by ILAC-N exceeded 97.4%. Moreover, it maintained a removal rate of 84% after 10 regeneration cycles, revealing its high reusability. Mechanisms suggested that pore filling and π-π interaction played a critical role in this process. In conclusion, ILAC-N can be broadly applied to livestock manure and pharmaceutical wastewater treatment, owing to its high adsorption capacity, good adsorption properties across a wide pH range, excellent reusability. Furthermore, this research opens a new path for lignin utilization.

Effect of type of coagulants on removal efficiency and removal mechanisms of antibiotic resistance genes in anaerobic digestion of primary sludge produced via a chemically enhanced primary treatment process

The potential impact of the trivalent coagulant cations on the removal mechanisms, removal efficiencies and removal patterns of antibiotic resistance genes (ARGs) during anaerobic digestion (AD) of chemically enhanced primary treatment sludge (CEPTS) was investigated using polyaluminium chloride (PACl), ferric chloride (FeCl₃) and mixed FeCl₃-PACl. The removal efficiency of 23 ARGs and intI1 improved to 72.1% in AD of primary sludge with 100 mg/L FeCl₃ and was lowest (only 54.4 %) in AD of primary sludge with 25 mg/L PACl. The removal of ARGs in AD of CEPTS with addition of single or mixed types of Al-based coagulant began to increase rapidly at the onset of batch operation. On the other hand, both the rapid increase in the removal efficiency of ARGs in AD with FeCl₃ and the maximum removal efficiency were attained later than in the other ADs.

Performance and mechanism in degradation of typical antibiotics and antibiotic resistance genes by magnetic resin-mediated UV-Fenton process

Incomplete removal of antibiotics and antibiotic resistance genes (ARGs) has often been reported in wastewater treatment plants. More efficient treatment processes are needed to reduce their risks to the environment. Herein, we evaluated the degradation of antibiotics and ARGs by using magnetic anion exchange resin (MAER) as UV-Fenton catalyst. Sulfamethoxazole (SMZ), ofloxacin (OFX), and amoxicillin (AMX) were selected as the target compounds. The three antibiotics were almost completely degraded (> 99%) following the MAER UV-Fenton reaction for 30 min. From the degradation mechanism study, it was found that Fe³⁺/Fe²⁺ could be cyclically transferred from the catalyst at permeable interface, and the photo-generated electrons could be effectively separated. The dominant reactive radicals for antibiotics degradation were hydroxide during the MAER UV-Fenton reaction. The degradation pathway for sulfamethoxazole was proposed. In addition, wastewater samples from a wastewater treatment plant were applied to investigate the removal efficiency of antibiotics and their ARGs by the MAER UV-Fenton system. A rapid decrease in antibiotics and ARGs level was observed with this reaction system. The results from this study suggest that the MAER-mediated UV-Fenton reaction could be applied for the effective removal of antibiotics and ARGs in wastewater.

Comparison of the elimination effectiveness of tetracycline and AmpC β-lactamase resistance genes in a municipal wastewater treatment plant using four parallel processes

Municipal wastewater treatment plants (mWWTPs), considered reservoirs of antibiotic resistance genes (ARGs), are selected to compare the contributions of technology and process to ARG removal. Fifteen ARGs (tetA, tetB, tetC, tetE, tetG, tetL, tetM, tetO, tetQ, tetS, tetX, MOX, CIT, EBC, and FOX) and two integron genes (intI1, intI2) were tracked and detected in wastewater samples from a large-scale mWWTP with four parallel processes, including three biological technologies of AAO (anaerobic-anoxic-oxic), AB (adsorption-biodegradation), and UNITANK, two different disinfection technologies, and two primary sedimentation steps. The results showed that ARGs were widely detected, among which tetA and tetM had the highest detection rate at 100%. AAO was the most effective process in removing ARGs, followed by the AB and UNITANK processes, where the separation step was critical: 37.5% AmpC β-lactamase genes were reduced by the secondary clarifier. UV disinfection was more efficient than chlorination disinfection by 47.0% in ARG removal. Both disinfection and primary sedimentation processes could effectively remove integrons, and the swirling flow grit chamber was a more effective primary settling facility in total ARG removal than the aerated grit chamber. The tet genes and AmpC β-lactamase genes were significantly correlated with the water quality indexes of BOD5, CODCr, SS, TP, TOC, pH and NH4+-N (p < 0.05). In addition, the correlation between efflux pump genes and AmpC β-lactamase genes was strongly significant (r2 = 0.717, p < 0.01). This study provides a more powerful guide for selecting and designing treatment processes in mWWTPs with additional consideration of ARG removal.

Evaluating the effect of gradient applied voltages on antibiotic resistance genes proliferation and biogas production in anaerobic electrochemical membrane bioreactor

Anaerobic biological treatment technologies are one of the major hotspots of antibiotic resistance genes (ARGs). Previous studies have applied the electrochemical process to improve biogas production, however, it was challenged that high voltages might promote membrane permeability and reactive oxygen species overproduction to promote ARGs proliferation. Herein, the biogas production and ARGs proliferation in an anaerobic electrochemical membrane bioreactor (AnEMBR) were investigated at the gradient voltages of 0-0.9 V. Results show the reactor performances (average CH₄ production and current generation) were distinctly improved with the increase of applied voltage, and reached the optimum at 0.9 V. However, long-term application (>30 day) of 0.9 V deteriorated the reactor performances. Meanwhile, the relative abundances of most target ARGs in the supernatant and effluent of AnEMBR at 0.9 V increased by 0.68-1.55 and 0.42-1.26 logs compared to those before applying voltage, respectively. After disconnecting the circuit, these ARGs abundances all decreased to the original level. Significant correlations between intlI and ARGs (e.g., tetA, tetQ, sulI, and sulII) were observed, indicating horizontal gene transfer may contribute to the increased ARGs. Moreover, the shift of microbial communities caused by the applied voltage enriched potential ARGs-hosts (e.g., Tolumonas), contributing to the proliferation of ARGs.

Removal of extracellular antibiotic resistance genes using magnetic biochar/quaternary phosphonium salt in aquatic environments: A mechanistic study

The proliferation and spread of antibiotic resistance genes (ARGs) is becoming a worldwide crisis. Extracellular DNA encoding ARGs (eARGs) in aquatic environment plays a critical role in the dispersion of antimicrobial resistance genes. Strategies to control the dissemination of eARGs are urgently required for ecological safety and human health. Towards this goal, magnetic biochar/quaternary phosphonium salt (MBQ), was used to investigate the efficiency and removal mechanism for eARGs. Magnetic biochar modified by quaternary phosphonium salt enhanced the adsorption capacity of extracellular DNA to approximately 9 folds, compared to that of the unmodified. DNA adsorption by MBQ was mainly dominated by chemisorption in heterogeneous systems and was promoted in acidic and low-salt environment. The generation of •OH and MBQ colloid jointly cleaved DNA into fragments, facilitating the adsorption of the phosphate backbone of DNA onto MBQ through electrostatic force as well as the conformational transition of DNA. Furthermore, quantification of extracellular DNA after MBQ was applied in water demonstrated that over 92.7% of resistance genes were removed, indicating a significantly reduced risk of propagation of antimicrobial resistance in aquatic environments. These findings have a practical significance in the application of MBQ in mitigating the spread of ARGs in aquatic environment.

Recent development in antimicrobial activity of biopolymer-inorganic nanoparticle composites with water disinfection potential: a comprehensive review

Nowadays, water-borne diseases including hepatitis remain the critical health challenge due to the inadequate supply of potable and safe water for human activities. The major cause is that the pathogenic microorganisms causing diseases have developed resistance against common techniques used by sewage water treatment plants for water disinfection. Therefore, there is a need to improve these conventional water treatment techniques by taking into consideration the application of nanotechnology for wastewater purification. The main aim of this paper is to provide a review on the synthesis of biopolymer-inorganic nanoparticle composites (BINCs), their used as antimicrobial compounds for water disinfection, as well as to elaborate on their antimicrobial mechanism of action. The microbial properties affecting the activity of antimicrobial compounds are also evaluated.

Solar photon-Fenton process eliminates free plasmid DNA harboring antimicrobial resistance genes from wastewater

This work aimed to assess the elimination and inactivation of resistance-conferring plasmids (RCPs) present in suspension in secondary wastewater by solar photo-Fenton as these are important vectors for the dissemination of antimicrobial resistance. Experiments were performed in synthetic secondary wastewater (SWW) and municipal wastewater treatment plant effluent (MWWTPE). Solar photo-Fenton (50 mg L^-1 of H₂O₂ and 30 mg L^-1 of Fe²⁺) was carried out for 60 min at neutral pH by applying the intermittent iron addition strategy. The removal of RCPs was assessed by Real-Time Polymerase Chain Reaction (qPCR). The transformation of competent non-resistant E. coli was used to evaluate the inactivation of target RCPs harboring antibiotic resistance genes (ARGs) to ampicillin (pSB1A2) or kanamycin (pSB1K3) after treatment and controls. Solar photo-Fenton completely removed RCPs initially present in both matrixes (SWW and MWWTPE), showing enhanced performance compared to the dark Fenton process. Both RCPs were inactivated after 30 min of solar photo-Fenton treatment, while 60 min were necessary to achieve the same effect for the dark Fenton reaction under similar conditions. These results indicate the potential of solar photo-Fenton to improve wastewater quality and reduce the spread of antimicrobial resistance in the environment by hampering the discharge of cell-free RCPs present in suspension in MWWTP onto environmental waters.

Synergistic impacts of Cu2+ on simultaneous removal of tetracycline and tetracycline resistance genes by PSF/TPU/UiO forward osmosis membrane

Cu²⁺, tetracycline (TC), and corresponding tetracycline resistance genes (TRGs) are common micropollutants in aquaculture wastewater, which have great impact on environment and human health. In this study, we developed a thin-film nanocomposite (TFN) forward osmosis (FO) membrane with an electrospinning thermoplastic polyurethane/polysulfone (PSF/TPU) substrate and a UiO-66-NH₂ particle interlayer modified active layer. The effects of Cu²⁺ concentration on the synergetic removal of TC and TRGs (e.g., tetA/M/X/O/C, int1, and 16 S rRNA gene) were analyzed to determine the role of Cu²⁺ in FO process. The rejection mechanism was also analyzed in depth. Results demonstrated that the rejection of TC and Cu²⁺ was 99.53% and 97.99%. The rejection of TRGs exceeded 90% (specifically, over 99% for tetC) at a Cu²⁺ concentration of 500 μg/L when 0.5 M (NH₄)₂HPO₄ was used as draw solution. Complexation reaction between Cu²⁺ and TC, electrostatic interaction, and the adsorption of Cu²⁺ on membrane surface were the main contributing factors for the high rejection efficiencies. Altogether, the as-prepared FO membrane holds great potential for simultaneously removing heavy metals, antibiotics, and resistance genes in real wastewater.

Distribution of extracellular and intracellular antibiotic resistance genes in sludge fractionated in terms of settleability

The widespread proliferation of antibiotic resistance genes (ARGs) is a serious environmental and human health issue. Wastewater treatment facilities (WWTFs) are potential sources to spread ARGs to natural environment, for which, the presence state of ARGs in the sludge, as extracellular ones (eARGs) or intracellular ones (iARGs), along with the sludge settleability, are very important factors. The sludge settleability is closely associated with its floc size and density, bacterial activity, and the proportion of intact/damaged bacterial cells that aggregate together to form flocs for separation in the sedimentation process. It is reasonable to hypothesize that the distribution of eARGs and iARGs may differ with the sludge fractions of different settleability, a topic of great academic and practical significance requiring clarification. In this study, sludge samples from the aerobic contact tank of six household WWTFs were fractionated into fractions with different settling velocities: sludge of low settleability (LS), medium settleability (MS) and high settleability (HS); and the distribution of eARGs and iARGs in the obtained fractions for the widely detected tet G, tet M and sul 1 in water environment was evaluated based on the PMA-qPCR method, together with the evaluation for the well reported mobile genomic element intl 1 and total bacterial 16S rDNA. For the LS fractions, which contained more damaged bacterial cells, the distribution percentages of eARGs were generally higher than those of iARGs. For the HS fractions, which contained flocs with larger sizes formed by both intact and damaged bacterial cells, the relative abundances of ARGs and intl 1 were found apparently lower even if the presence percentages of eARGs were comparatively higher. It is thus inferable that sludge fractions of LS may possess higher transfer potential for ARGs and enhancing their settleability through optimization of the operation conditions is important for mitigating the proliferation 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.

Development, current state and future trends of sludge management in China: Based on exploratory data and CO2-equivaient emissions analysis

This study statistically reported the current state of sludge treatment/disposal in China from the aspects of sources, technical routes, geographical distribution, and development by using observational data after 1978. By the end of 2019, 5476 municipal wastewater treatment plants were operating in China, leading to an annual sludge productivity of 39.04 million tons (80% water content). Overall, 29.3% of the sludge in China was disposed via land application, followed by incineration (26.7%) and sanitary landfills (20.1%). Incineration, compost, thermal hydrolysis and anerobic digestion were the mainstream technologies for sludge treatment in China, with capacities of 27,122, 11,250, 8342 and 6944 t/d in 2019, respectively. Incineration and drying were preferentially constructed in East China. In contrast, sludge compost was most frequently used in Northeast China (46.5%), East China (22.4%) and Central China (12.8%), while anaerobic digestion in East China, North China and Central China. The capacities of sludge facilities exhibited a sharp increase in 2009-2019, with an overall greenhouse gas emissions in China in 2019 reached 108.18 × 10⁸ kg CO₂-equivaient emissions, and the four main technical routes contributed as: incineration (45.11%) > sanitary landfills (23.04%) > land utilization (17.64%) > building materials (14.21%). Challenges and existing problems of sludge disposal in China, including high CO₂ emissions, unbalanced regional development, low stabilization and land utilization levels, were discussed. Finally, suggestions regarding potential technical and administrative measures in China, and sustainable sludge management for developing countries, were also given.

Extracellular DNA (eDNA): Neglected and Potential Sources of Antibiotic Resistant Genes (ARGs) in the Aquatic Environments

Over the past decades, the rising antibiotic resistance bacteria (ARB) are continuing to emerge as a global threat due to potential public health risk. Rapidly evolving antibiotic resistance and its persistence in the environment, have underpinned the need for more studies to identify the possible sources and limit the spread. In this context, not commonly studied and a neglected genetic material called extracellular DNA (eDNA) is gaining increased attention as it can be one of the significant drivers for transmission of extracellular ARGS (eARGs) via horizontal gene transfer (HGT) to competent environmental bacteria and diverse sources of antibiotic-resistance genes (ARGs) in the environment. Consequently, this review highlights the studies that address the environmental occurrence of eDNA and encoding eARGs and its impact on the environmental resistome. In this review, we also brief the recent dedicated technological advancements that are accelerating extraction of eDNA and the efficiency of treatment technologies in reducing eDNA that focuses on environmental antibiotic resistance and potential ecological health risk.

Ferrate effectively removes antibiotic resistance genes from wastewater through combined effect of microbial DNA damage and coagulation

The widespread of antibiotic resistance genes (ARGs) in the environment can pose severe threats to public health. The wastewater treatment plant (WWTP) is regarded as an important hotspot of ARGs in the urban environment, but the removal of ARGs through conventional treatment techniques has been proven not sufficient. In this study, ferrate (Fe(VI)) was applied for the first time to remove intracellular ARGs from the secondary effluent of the WWTP. The results showed that Fe(VI) treatment could effectively remove 15 ARGs covering eight different types as well as intI1, the most common integron important to ARGs horizontal transfer. The removal efficiencies of tested genes could reach 1.10-4.37 log at the Fe(VI) dosage of 10 mg-Fe/L, which is significantly higher than those achieved through traditional disinfection methods. The DNA gel electrophoresis suggested that Fe(VI) could induce microbial DNA damage and consequently resulted in ARGs elimination. The presence of ARGs in settled residues indicated that coagulation initiated by Fe(VI) reduction products also contributed to ARGs removal from wastewater. In addition, the viability and relative abundances of potential ARGs hosts in the wastewater were decreased after Fe(VI) treatment. This study suggested a promising prospect for applying Fe(VI) to efficiently remove ARGs from wastewater, and consequently to control their proliferation and transfer in the environment.

Emerging pollutants-Part II: Treatment

Emerging pollutants (EPs) refer to a class of pollutants, which are emerging in the environment or recently attracted attention. EPs mainly include pharmaceutical and personal care products (PPCPs), endocrine-disrupting chemicals (EDCs), and antibiotic resistance genes (ARGs). EPs have potential threats to human health and ecological environment. In recent years, the continuous detections of EPs in surface and ground water have brought huge challenges to water treatment and also made the treatment of EPs become an international research hotspot. This paper summarizes some research results on EPs treatment published in 2019. This paper may be helpful to understand the current situations and development trends of EP treatment technologies.

Antibiotic resistomes in drinking water sources across a large geographical scale: Multiple drivers and co-occurrence with opportunistic bacterial pathogens

Antibiotic resistance genes (ARGs) can survive the water treatment process. However, the prevalence patterns, key drivers, and relationships with opportunistic pathogens of the antibiotic resistome harbored in drinking water sources remain unclear. Herein, 53 drinking water samples collected across a large geographical scale in China were characterized based on ARGs, mobile genetic elements (MGEs), bacterial communities, antibiotics, and opportunistic bacterial pathogens. A total of 265 unique ARGs and MGEs were detected by high-throughput quantitative polymerase chain reaction (HT-qPCR), and 101 genes were shared among over 50% of samples. ARG abundance was higher in rivers than in reservoirs or groundwater, and ARG similarity showed a distance-decay relationship at the >4 000 km scale. Four out of the five detected opportunistic pathogens (i.e., Escherichia coli, Mycobacterium spp., Clostridium perfringens, and Bacillus cereus group) were potential hosts of ARGs. Based on multivariate statistics, our results demonstrated that the factors influencing the antibiotic resistome in drinking water sources were multiple and interactive. The bacterial community greatly contributed to ARG structure, and antibiotic concentrations and MGEs also affected ARG proliferation. The structural equation model indicated that geographical location and sample types (i.e., river, reservoir, and groundwater) had indirect effects on ARGs by changing the bacterial community and antibiotic concentration. Holistic consideration of natural and anthropogenic factors is recommended to understand antibiotic resistome variation in drinking water sources at a large geographical scale. Furthermore, large-scale diverse samples are suggested to minimize the potential influence of accident or stochasticity. Our findings provide insight into water quality risks induced by drinking water antibiotic resistomes.

Comparison of novel functionalized nanofiber forward osmosis membranes for application in antibacterial activity and TRGs rejection

Antibiotic resistance genes (ARGs) are serious pollutants in municipal sewage treatment plants and may cause significant harm to ecological systems, microbial fouling is also inevitable in membrane process. Herein, novel forward osmosis (FO) membranes made of electrospun nanofibers (TFN0) and further impregnated with titanium dioxide (TiO₂) (TFN1) nanoparticles and titanium dioxide/silver composite nanoparticles (TiO₂/AgNPs) (TFN2). The FO membranes were used to compare the antimicrobial performance and rejection of tetracycline-resistant genes (TRGs). Characterizations revealed that the TiO₂/AgNPs were evenly scattered in the polysulfone (PSf) nanofibers and resulted in a TFN2 membrane that exhibited excellent physicochemical properties, filtration, and antibiofouling performance in real wastewater. The cell viability analysis revealed that the antibacterial effect of the TFN2 membranes was significantly better than that of TFN1, as indicated by about 65 % of E. coli cells killed after contact with the TFN2 membrane. TFN2 membranes had greater rejection rates of TRB and TRGs than TFN1. The TRG permeation rates of the TFN2 membrane in the FO mode (active layer facing the feed solution) were 39.62 % and 33.02 % lower than the TFN0 and TFN1 membranes, respectively. FO membranes modified by the TiO₂/AgNPs nanocomposites hold promise to remove ARGs and pathogens from wastewater treatment plant effluents.

Strong improvement of nanofiltration performance on micropollutant removal and reduction of membrane fouling by hydrolyzed-aluminum nanoparticles

Increasing attention has been focused on the removal of micropollutants from contaminated drinking source water. However, low rejection efficiency and membrane fouling still inhibit further application of nanofiltration membrane in this field. Interesting results were found that the residual hydrolyzed-aluminum nanoparticles from supernatant after coagulation and sedimentation strongly improved the nanofiltration performance for micropollutant removal. A simulated raw water containing humic acids, micropollutants and kaolinite clay was employed to investigate the factors of water matrix affecting the nanoparticle-enhanced nanofiltration for micropollutant removal. Results of experiments showed that these hydrolyzed-aluminum nanoparticles easily induced the aggregation of bisphenol-A (BPA) and humic acids in the supernatant. The enhancement of BPA removal was mainly attributed to the repelling interaction between the Al-BPA-DOC complexity and in situ-modified membrane surface during nanofiltration. 'This in situ surface modification by the hydrolyzed-aluminum nanoparticles improved membrane hydrophilicity, roughness and positively-charging capacity. For the treatment of River Songhua water spiked with micropollutant, the percentage removal of BPA was improved to be 88.5%, much more than the case of single nanofiltration without coagulation (60.7%). Meanwhile, the membrane fouling was reduced by 2.13 times than the case of single nanofiltration without the dynamically deposited-layer of nanoparticles. This in situ modification of nanofiltration membrane by hydrolyzed-aluminum nanoparticles achieved excellent removal efficiency for micropollutants from River Songhua water background.