Effect of the coexposure of sulfadiazine, ciprofloxacin and zinc on the fate of antibiotic resistance genes, bacterial communities and functions in three-dimensional biofilm-electrode reactors

Mitigation of Triclocarban Inhibition in Microbial Electrolysis Cell-Assisted Anaerobic Digestion

Triclocarban (TCC), as a widely used antimicrobial agent, is accumulated in waste activated sludge at a high level and inhibits the subsequent anaerobic digestion of sludge. This study, for the first time, investigated the effectiveness of microbial electrolysis cell-assisted anaerobic digestion (MEC-AD) in mitigating the inhibition of TCC to methane production. Experimental results showed that 20 mg/L TCC inhibited sludge disintegration, hydrolysis, acidogenesis, and methanogenesis processes and finally reduced methane production from traditional sludge anaerobic digestion by 19.1%. Molecular docking revealed the potential inactivation of binding of TCC to key enzymes in these processes. However, MEC-AD with 0.6 and 0.8 V external voltages achieved much higher methane production and controlled the TCC inhibition to less than 5.8%. TCC in the MEC-AD systems was adsorbed by humic substances and degraded to dichlorocarbanilide, leading to a certain detoxification effect. Methanogenic activities were increased in MEC-AD systems, accompanied by complete VFA consumption. Moreover, the applied voltage promoted cell apoptosis and sludge disintegration to release biodegradable organics. Metagenomic analysis revealed that the applied voltage increased the resistance of electrode biofilms to TCC by enriching functional microorganisms (syntrophic VFA-oxidizing and electroactive bacteria and hydrogenotrophic methanogens), acidification and methanogenesis pathways, multidrug efflux pumps, and SOS response.

Recent progress of particle electrode materials in three-dimensional electrode reactor: synthesis strategy and electrocatalytic applications

With the complete promotion of a green, low-carbon, safe, and efficient economic system as well as energy system, the promotion of clean governance technology in the field of environmental governance becomes increasingly vital. Because of its low energy consumption, great efficiency, and lack of secondary pollutants, three-dimensional (3D) electrode technology is acknowledged as an environmentally beneficial and sustainable way to managing clean surroundings. The particle electrode is an essential feature of the 3D electrode reactor. This study provides an in-depth examination of the most current advancements in 3D electrode technology. The significance of 3D electrode technology is emphasized, with an emphasis on its use in a variety of sectors. Furthermore, the particle electrode synthesis approach and mechanism are summarized, providing vital insights into the actual implementation of this technology. Furthermore, by a metrological examination of the research literature in this sector, the paper expounds on the potential and obstacles in the development and popularization of future technology.

Variations in antibiotic resistance genes during long-term operation of an upflow anaerobic sludge blanket reactor

Antibiotic resistance genes (ARGs) have been widely detected in the environment. Anaerobic digestion (AD) has the potential ability to remove ARGs, and a comprehensive study is needed on the variations in ARGs during AD. In this study, variations in antibiotic resistance genes (ARGs) and microbial communities were investigated during the long-term operation of an upflow anaerobic sludge blanket (UASB) reactor. An antibiotic mixture of erythromycin, sulfamethoxazole and tetracycline was added to the UASB influent and the operation period was 360 days. The abundances of 11 ARGs and class 1 integron-integrase gene were detected in the UASB reactor, and the correlation between the ARGs and the microbial community was analyzed. The composition of ARGs indicated that the main ARGs in the effluent were sul1, sul2, and sul3, whereas the main ARG in the sludge was tetW. Correlation analysis indicated a negative correlation between microorganisms and ARGs in the UASB. In addition, most of ARGs showed a positive correlation with norank_f_Propionibacteriaceae and Clostridum_sensu_stricto_6, which were identified as potential hosts. These findings may help develop a feasible strategy for removing ARGs from aquatic environments during anaerobic digestion.

Response of biofilm-based systems for antibiotics removal from wastewater: Resource efficiency and process resiliency

Biofilm-based systems have efficient stability to cope-up influent shock loading with protective and abundant microbial assemblage, which are extensively exploited for biodegradation of recalcitrant antibiotics from wastewater. The system performance is subject to biofilm types, chemical composition, growth and thickness maintenance. The present study elaborates discussion on different type of biofilms and their formation mechanism involving extracellular polymeric substances secreted by microbes when exposed to antibiotics-laden wastewater. The biofilm models applied for estimation/prediction of biofilm-based systems performance are explored to classify the application feasibility. Further, the critical review of antibiotics removal efficiency, design and operation of different biofilm-based systems (e.g. rotating biological contactor, membrane biofilm bioreactor etc.) is performed. Extending the information on effect of various process parameters (e.g. hydraulic retention time, pH, biocarrier filling ratio etc.), the microbial community dynamics responsible of antibiotics biodegradation in biofilms, the technological problems, related prospective and key future research directions are demonstrated. The biofilm-based system with biocarriers filling ratio of ∼50-70% and predominantly enriched with bacterial species of phylum Proteobacteria protected under biofilm thickness of ∼1600 μm is effectively utilized for antibiotic biodegradation (>90%) when operated at DO concentration ≥3 mg/L. The C/N ratio ≥1 is best suitable condition to eliminate antibiotic pollution from biofilm-based systems. Considering the significance of biofilm-based systems, this review study could be beneficial for the researchers targeting to develop sustainable biofilm-based technologies with feasible regulatory strategies for treatment of mixed antibiotics-laden real wastewater.

Biofilm electrode reactor coupled manganese ore substrate up-flow microbial fuel cell-constructed wetland system: High removal efficiencies of antibiotic, zinc (II), and the corresponding antibiotic resistance genes

A coupled system comprised of a biofilm electrode reactor (BER) and a manganese ore substrate microbial fuel cell-constructed wetland (MFC-CW) system was used to remove co-exposed antibiotic and Zn (II), as well as simultaneously reduce copies of antibiotic resistance genes (ARGs) in the current study. In this system, BER primarily reduced the concentrations of antibiotics and Zn (II), and the effluent was used as the input to the MFC-CW, thereby providing electricity to BER. Co-exposure to a high concentration of Zn (II) decreased the relative abundances (RAs) of ARGs in the BER effluent, whereas the remaining sub-lethal concentration of Zn (II) increased the RAs of ARGs in the MFC-CW effluent. Even though the absolute copies of ARGs in the effluents increased during co-exposure, the total number of target ARG copies in the effluent of MFC-CW was significantly lower than that of BER. Moreover, BER pre-treatment eliminated most of Zn (II), which improved the electrical power generation characteristic of the MFC-CW unit. Correspondingly, the bacterial community and the ARGs hosts were analyzed to demonstrate the mechanism. In conclusion, the coupled system demonstrates significant potential to reduce antibiotics, Zn (II) and environmental risks posed by ARGs.

Enhanced removal of antibiotic and antibiotic resistance genes by coupling biofilm electrode reactor and manganese ore substrate up-flow microbial fuel cell constructed wetland system

Manganese ore substrate up-flow microbial fuel cell constructed wetland (UCW-MFC(Mn)) as an innovative wastewater treatment technology for purifying antibiotics and electricity generation with few antibiotic resistance genes (ARGs) generation has attracted attention. However, antibiotic purifying effects should be further enhanced. In this study, a biofilm electrode reactor (BER) that needs direct current driving was powered by a Mn ore anode (UCW-MFC(Mn)) to form a coupled system without requiring direct-current source. Removal efficiencies of sulfadiazine (SDZ), ciprofloxacin (CIP) and the corresponding ARGs in the coupled system were compared with composite (BER was powered by direct-current source) and anaerobic systems (both of BER and UCW-MFC were in open circuit mode). The result showed that higher antibiotic removal efficiency (94% for SDZ and 99.1% for CIP) in the coupled system was achieved than the anaerobic system (88.5% for SDZ and 98.2% for CIP). Moreover, electrical stimulation reduced antibiotic selective pressure and horizontal gene transfer potential in BER, and UCW-MFC further reduced ARG abundances by strengthening the electro-adsorption of ARG hosts determined by Network analysis. Bacterial community diversity continuously decreased in BER while it increased in UCW-MFC, indicating that BER mitigated the toxicity of antibiotic. Degree of modularity, some functional bacteria (antibiotic degrading bacteria, fermentative bacteria and EAB), and P450 enzyme related to antibiotic and xenobiotics biodegradation genes were enriched in electric field existing UCW-MFC, accounting for the higher degradation efficiency. In conclusion, this study provided an effective strategy for removing antibiotics and ARGs in wastewater by operating a BER-UCW-MFC coupled system.

A review on three-dimensional electrochemical technology for the antibiotic wastewater treatment

The potential genotoxicity and non-biodegradability of antibiotics in the natural water bodies threaten the survival of various living things and cause serious environmental pollution and destruction. Three-dimensional (3D) electrochemical technology is considered a powerful means for antibiotic wastewater treatment as it can degrade non-biodegradable organic substances into non-toxic or harmless substances and even completely mineralize them under the action of electric current. Therefore, antibiotic wastewater treatment using 3D electrochemical technology has now become a hot research topic. Thus, in this review, a detailed and comprehensive investigation was conducted on the antibiotic wastewater treatment using 3D electrochemical technology, including the structure of the reactor, electrode materials, the influence of operating parameters, reaction mechanism, and combination with other technologies. Many studies have shown that the materials of electrode, especially particle electrode, have a great effect on the antibiotic wastewater treatment efficiency. The influence of operating parameters such as cell voltage, solution pH, and electrolyte concentration was very significant. Combination with other technologies such as membrane and biological technologies has effectively increased antibiotic removal and mineralization efficiency. In conclusion, the 3D electrochemical technology is considered as a promising technology for the antibiotic wastewater treatment. Finally, the possible research directions of the 3D electrochemical technology for antibiotic wastewater treatment were proposed.

Bacteriophage-based biocontrol technology to enhance the efficiency of wastewater treatment and reduce targeted bacterial biofilms

Wastewater treatment is an essential process for public health and a sustainable ecosystem. Inadequate wastewater treatment can lead to the release of organic and inorganic pollutants and pathogenic bacteria into the receiving waters which could be further utilized for recreation purposes. The interaction between bacteriophage and bacteria in a wastewater treatment plant plays a major role in maintaining the treatment process. Phage therapy has been proposed as an alternative to conventional treatment methods as bacteriophages can be used on specific targets and leave useful bacteria unharmed. The bacterial species, which are responsible for bulking, foaming, and biofilm formation in a wastewater treatment plant (WWTP) have been identified and their respective phages are isolated to control their growth. Phages with lytic life cycles are preferred to lysogenic. Lytic phages can kill the specific target as they lyse the cell, infect most of the hosts, and have an immediate effect on controlling problems caused by bacteria in a WWTP. The bacteriophages such as T7, SPI1, GTE7, PhaxI, MAG1, MAG2, ϕPh_Se01, ϕPh_Se02, and Bxb1 have been investigated for the removal of bacterial biofilms from wastewater. Novel experimental setups have improved the efficiency of phage therapy in small-scale and pilot-scale experiments. Much more in-depth knowledge of the microbial community and their interaction would help promote the usage of phage therapy in large-scale wastewater treatments. This paper has covered the recent advancements in phage therapy as an effective biocontrol of pathogenic bacteria in the wastewater treatment process and has looked at certain shortcomings that have to be improved.

The synergistic mechanism of β-lactam antibiotic removal between ammonia-oxidizing microorganisms and heterotrophs

Nitrifying system is an effective strategy to remove numerous antibiotics, however, the contribution of ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea (AOA) and heterotrophs for antibiotic removal are still unclear. In this study, the mechanism of β-lactam antibiotic (cefalexin, CFX) removal was studied in a nitrifying sludge system. Results showed that CFX was synergistically removed by AOB (Nitrosomonas, played a major role) and AOA (Candidatus_Nitrososphaera) through ammonia monooxygenase-mediated co-metabolism, and by heterotrophs (Pseudofulvimonas, Hydrogenophaga, RB41, Thauera, UTCFX1, Plasticicumulans, Phaeodactylibacter) through antibiotic resistance genes (ARGs)-encoded β-lactamases-mediated hydrolysis. Regardless of increased archaeal and heterotrophic CFX removal with the upregulation of amoA in AOA and ARGs, the system exhibited poorer CFX removal performance at 10 mg/L, mainly due to the inhibition of AOB. This study provides new reference for the important roles of heterotrophs and ARGs, opening the possibilities for the application of ARGs in antibiotic biodegradation.

Seasonal variations of microbial community structure, assembly processes, and influencing factors in karst river

The physicochemical properties and microbial communities have significant annual and seasonal changes in karst aquifers. To explore the changes of microbial community and their relationships with environmental factors, water samples were collected from a typical karst river. Microbial communities in winter (Jan-2017 and Jan-2019) were stable with high similarity in spite of the 2 years sampling interval, but the microbial communities in Aug-2017 was different from that in Aug-2018. In four sampling times, there were 275 shared genera, whose average relative abundance ranging from 89.04 to 96.27%. The winter and summer specific genera were mainly from the recharge of tributary site K6 and discharge of waste water treatment plant (K2 and K3), respectively. The deterministic processes had a more significant effect on the microbial community assembly in winter than that in summer, which was affected by environmental pressure from pollution. Furthermore, antibiotics and inorganic nitrogen pollution affected element cycles of nitrogen and sulfur indirectly through microbial ecological modules in karst river, and the denitrification and desulfurization processes were potentially inhibited. These findings contributed to understand the changes and its assembly mechanism of microbial community, as well as the feedback to environment in polluted karst river.

Statistical modeling optimization for antibiotics decomposition by ultrasound/electro-Fenton integrated process: Non-carcinogenic risk assessment of drinking water

The present work proposes an ultrasound (US) assisted electro-Fenton (EF) process for eliminating penicillin G (PNG) and ciprofloxacin (CIP) from aqueous solutions and the process was further optimized by response surface methodology (RSM)- Box-Behnken design (BBD). The impact of pH, hydrogen peroxide (H₂O₂) concentration, applied voltage, initial pollutant concentration, and operating time were studied. The capability application of the electro-Fenton (EF) and US processes was compared separately and in combination under the optimum conditions of pH of 4, a voltage of 15 V, the initial antibiotic concentration of 20.7 mg/L, H₂O₂ concentration of 0.8 mg/L, and the operating time of 75 min. The removal efficiency of PNG and CIP using the sono-electro-Fenton (SEF) process, as the results revealed, was approximately 96% and 98%, respectively. The experiments on two scavengers demonstrated that ^⦁OH contributes significantly to the CIP and PNG degradation by SEF, whereas ^⦁O^-₂ corresponds to only a negligible amount. The total organic carbon (TOC) and chemical oxygen demand (COD) analyses were used to assess the mineralization of CIP and PNG. The efficiency of COD and TOC removal was reached at 73.25% and 62.5% for CIP under optimized operating circumstances, and at 61.52% and 72% for PNG, respectively. These findings indicate that a sufficient rate of mineralization was obtained by SEF treatment for the mentioned pollutants. The reaction kinetics of CIP and PNG degradation by the SEF process were found to follow a pseudo-first-order kinetic model. In addition, the human health risk assessment of natural water containing CIP and PNG that was purified by US, EF, and SEF processes was done for the first time. According to the findings, the non-carcinogenic risk (HQ) caused by drinking purified water by all three systems was calculated in the acceptable range. Thus, SEF is a proper system to remove various antibiotics in potable water and reduces their human health risks.

Current Progress in Natural Degradation and Enhanced Removal Techniques of Antibiotics in the Environment: A Review

Antibiotics are used extensively throughout the world and their presence in the environment has caused serious pollution. This review summarizes natural methods and enhanced technologies that have been developed for antibiotic degradation. In the natural environment, antibiotics can be degraded by photolysis, hydrolysis, and biodegradation, but the rate and extent of degradation are limited. Recently, developed enhanced techniques utilize biological, chemical, or physicochemical principles for antibiotic removal. These techniques include traditional biological methods, adsorption methods, membrane treatment, advanced oxidation processes (AOPs), constructed wetlands (CWs), microalgae treatment, and microbial electrochemical systems (such as microbial fuel cells, MFCs). These techniques have both advantages and disadvantages and, to overcome disadvantages associated with individual techniques, hybrid techniques have been developed and have shown significant potential for antibiotic removal. Hybrids include combinations of the electrochemical method with AOPs, CWs with MFCs, microalgal treatment with activated sludge, and AOPs with MFCs. Considering the complexity of antibiotic pollution and the characteristics of currently used removal technologies, it is apparent that hybrid methods are better choices for dealing with antibiotic contaminants.

Anaerobic electrochemical membrane bioreactor effectively mitigates antibiotic resistance genes proliferation under high antibiotic selection pressure

The spread of antibiotics and antibiotic resistance genes (ARGs) in environments has posed potential threats to public health. Unfortunately, conventional biological wastewater treatment technologies generally show insufficient removal of antibiotics and ARGs. Bioelectrochemical systems, which can effectively degrade refractory organic pollutants via enhancing microbial metabolisms through electrochemical redox reaction, may provide an alternative for the control of antibiotics and ARGs. Herein, an anaerobic electrochemical membrane bioreactor (AnEMBR) was conducted by combining bioelectrochemical system and anaerobic membrane bioreactor to treat antibiotic-containing wastewater. The AnEMBR at open circuit showed stable CH4 production and high removal of COD and chlortetracycline (CTC) in treating 2.5-15 mg/L CTC. However, increasing CTC to 45 mg/L completely inhibited the methanogenesis of AnEMBR at open circuit. After applying external voltage in AnEMBR, the performances of AnEMBR were significantly improved (e.g., increased CH4 production and CTC removal). Moreover, CTC exposure significantly increased the relative abundances of ARGs in sludge, supernatant, and effluent in AnEMBR at open circuit. Applying voltage greatly attenuated the total relative abundances of ARGs in the supernatant and effluent of AnEMBR compared to those at open circuit. This could be attributed to the enrichment of tetracycline degradation gene tetX, which greatly enhanced the removal of CTC by the AnEMBR and thus reduced the selective pressure of CTC on the microorganisms in supernatant and effluent for ARGs proliferation. These results would provide an effective wastewater treatment technology for treating high-level antibiotic-containing wastewater to mitigate the potential risk of ARGs and antibiotics spread in receiving water body.

Simultaneous denitrification and antibiotic degradation of low-C/N-ratio wastewater by a three-dimensional biofilm-electrode reactor: Performance and microbial response

Three-dimensional biofilm-electrode reactors (3D-BERs) were fabricated and used to simultaneously remove nitrate and metronidazole (MNZ) from low-C/N-ratio wastewater. The results showed that 1 mg/L MNZ significantly promoted nitrate removal. After MNZ was added to the reactor, the removal efficiencies of total nitrogen (TN) and NO₃^--N increased significantly from 18.97% and 52.09% to 71.63% and 99.98% within 6 h, respectively. The MNZ-removal kinetics conformed to a pseudo-first-order model, and the removal rate constant reached a maximum value of 0.853 h^-1, which was 4.1 and 2.8 times higher than that of pure microorganisms and pure electrochemical reactors, respectively. This indicated that the 3D-BERs constructed in this study were capable of simultaneous MNZ degradation and denitrification. In the presence of nitrate, six MNZ-degradation intermediates were identified, and four MNZ transformation pathways were proposed, including cleavage of hydroxyethyl groups, reduction of nitro groups, N-denitration, and deprotonation of side-chain hydroxyl groups. High-throughput sequencing revealed that the reactor was rich in various MNZ-degraders and denitrifiers, such as Hydrogenophaga, Methylomonas, Crenohrix, Dechloromonas, and Methylophilus. A function prediction analysis of nitrogen metabolism showed that the 3D-BER reactor with MNZ had higher denitrification activity than the other reactors tested. It was speculated that the intermediates produced by MNZ could act as carbon sources allowing denitrifying bacteria to perform denitrification, which made a nonnegligible contribution to the removal of nitrogen.

Bibliometric analysis of microbial sulfonamide degradation: Development, hotspots and trend directions

Microbial sulfonamide degradation (MSD) is an efficient and safe treatment in both natural and engineered ecosystems. In order to systematically understand the research status and frontier trends of MSD, this study employed CiteSpace to conduct a bibliometric analysis of data from the Web of Science (WoS) and the China National Knowledge Infrastructure (CNKI) published from 2000 to 2021. During this time, China, Germany, Spain, the United States and Australia played leading roles by producing numerous high impact publications, while the Chinese Academy of Sciences was the leading research institution in this interdisciplinary research category. The Chemosphere was the top journal in terms of the number of citations. MSD research has gradually progressed from basic laboratory-based experiments to more complex environmental microbial communities and finally to deeper research on molecular mechanisms and engineering applications. Although multi-omics and synthetic community are the key techniques in the frontier research, they are also the current challenges in this field. A summary of published articles shows that Proteobacteria, Gammaproteobacteria, Burkholderiales and Alcaligenaceae are the most frequently observed MSD phylum, class, order and family, respectively, while Bacillus, Pseudomonas and Achromobacter are the top three MSD genera. To our knowledge, this study is the first to investigate the development and current challenges of MSD research, put forward future perspective, and form a relatively complete list of sulfonamide-degrading microorganisms for reference.

Response behavior of antibiotic resistance genes to zinc oxide nanoparticles in cattle manure thermophilic anaerobic digestion process: A metagenomic analysis

This work investigated the metagenomics-based behavior of antibiotic resistance genes (ARGs) during cattle manure anaerobic digestion with zinc oxide nanoparticles (ZnO NPs) that are commonly used as animal feed additives. The 6.6% decrease in total ARGs abundance while remained unchanged ARGs diversity with ZnO NPs (5 mg/g total solid), suggested ZnO NPs may mitigate ARGs risk by abundance. Also, ZnO NPs affected ARGs with mechanisms specifically of antibiotic inactivation and antibiotic target change, and declined potential hosts' abundance (bacterial genus Ruminiclostridium, Riminococcus, and Paenibacillus) which mainly contributed to the decreased ARGs' abundance. Besides, microbial chemotaxis decreased by 17% with ZnO NPs compared to that without nanoparticles indicated a depression on potential hosts, who could develop the mechanism to adapt to altered digestion conditions, which probably inhibited the ARGs' propagation. These findings are important to promote understanding of the potential ARGs risks in treatments of livestock wastes containing animal feed additives.

New insights into the role of molecular structures on the fate and behavior of antibiotics in an osmotic membrane bioreactor

Osmotic membrane bioreactors (OMBRs) have been applied to enhance removal of antibiotics, however, information on the effects of molecular structures on the behavior of antibiotics is still lacking. Herein, adsorption kinetics, transformation pathways, and membrane rejection mechanisms of OMBRs were investigated by adding two typical antibiotics (i.e., sulfadiazine, SDZ, and tetracycline hydrochloride, TC-HCl). 80.70-91.12% of TC-HCl was removed by adsorption and biodegradation, while 17.50-75.14% of SDZ was removed by membrane rejection; this depended on its concentration due to reduced electrostatic interactions and hydrophobic adsorption. The adsorption capacity of TC-HCl (i.e., 1.34±0.01 mg/g) was significantly higher than that of SDZ (i.e., 0.18±0.03 mg/g) due to enhanced π-π interactions, hydrogen bonding and improved electrostatic interactions. The abundant production of polysaccharide-like substances from TC-HCl biodegradation contributed to microbial metabolism and thus enhanced microbial function during TC-HCl biotransformation. The primary degradation pathways were determined by microbial function analysis, and the primary intermediates from TC-HCl degradation were less toxic than those from SDZ degradation due to the different reactions of amino groups. These results and the corresponding mechanism provide a theoretical foundation for the further development of OMBR technology for highly efficient treatment of antibiotic wastewater.

Response of antibiotic resistance to the co-exposure of sulfamethoxazole and copper during swine manure composting

Heavy metals driven co-selection of antibiotic resistance in soil and water bodies has been widely concerned, but the response of antibiotic resistance to co-existence of antibiotics and heavy metals in composting system is still unknown. Commonly used sulfamethoxazole and copper were individually and jointly added into four reactors to explore their effects on antibiotic resistance genes (ARGs), mobile genetic elements (MGEs), heavy metal resistance genes (MRGs) and bacterial community structure. The abundance of total ARGs and MGEs were notably decreased by 68.64%-84.95% and 91.27-97.38%, respectively, after the composting. Individual addition of sulfamethoxazole, individual addition of copper, simultaneously addition of sulfamethoxazole and copper increased the abundance of ARGs and MGEs throughout the composting period. Co-exposure of sulfamethoxazole and copper elevated the total abundance of ARGs by 1.17-1.51 times by the end of the composting compared to individual addition of sulfamethoxazole or copper. Network analysis indicated that the shifts in potential host bacteria determined the ARGs variation. Additionally, MGEs and MRGs had significant effects on ARGs, revealing that horizontal gene transfer and heavy metals induced co-resistance could promote ARGs dissemination.

Three-dimensional biofilm electrode reactors (3D-BERs) for wastewater treatment

Three-dimensional biofilm electrode reactors (3D-BERs) are highly efficient in refractory wastewater treatment. In comparison to conventional bio-electrochemical systems, the filled particle electrodes act as both electrodes and microbial carriers in 3D-BERs. This article reviews the conception and basic mechanisms of 3D-BERs, as well as their current development. The advantages of 3D-BERs are illustrated with an emphasis on the synergy of electricity and microorganisms. Electrode materials utilized in 3D-BERs are systematically summarized, especially the critical particle electrodes. The configurations of 3D-BERs and their integration with wastewater treatment reactors are introduced. Operational parameters and the adaptation of 3D-BERs to varieties of wastewater are discussed. The prospects and challenges of 3D-BERs for wastewater treatment are then presented, and the future research directions are proposed. We believe that this timely review will help to attract more attentions on 3D-BERs investigation, thus promoting the potential application of 3D-BERs in wastewater treatment.

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.

Response of antibiotic and heavy metal resistance genes to tetracyclines and copper in substrate-free hydroponic microcosms with Myriophyllum aquaticum

Constructed wetlands for antibiotics and heavy metals removal have become important reservoirs of antibiotic resistance genes (ARGs) and heavy metal resistance genes (MRGs), especially in the substrates. Here, substrate-free hydroponic microcosms of Myriophyllum aquaticum were established; tetracyclines (TCs) and Cu(II) were added to evaluate the behaviours of ARGs and MRGs in the microcosms. Several ARGs, MRGs, and mobile genetic elements (MGE) were detected in the biofilms attached to the plants, ranging from 0.5 to 2.3 × 10⁸ copies/g dry weight. ARGs and MRGs exhibited higher relative abundances in the effluent suspended solids (SS); however, their absolute amounts were much lower than those in conventionally constructed wetlands. Microcosms with TCs and Cu(II) exhibited a higher level of resistant genes than those with compound added singularly owing to co-selection pressure. The existence of TCs and copper significantly changed the microbial communities in the microcosms. The exogenous input of TC/Cu(II) and microbial community structure were the factors driving the occurrence of ARGs, whereas MRGs were more correlated with the copper addition. Thus, reducing the exogenous inputs of antibiotics /heavy metals and SS of the effluent is suggested for the mitigation of resistant genes in phytoremediation technologies working in the absence of conventional substrates.

Reponses of microbial community and antibiotic resistance genes to the selection pressures of ampicillin, cephalexin and chloramphenicol in activated sludge reactors

High concentrations of antibiotics can exert strong selection pressures on the microbial community and promote the emergence and dissemination of antibiotic resistance genes (ARGs). The activated sludge reactors treating ampicillin, cephalexin and chloramphenicol production wastewater were established to investigate the responses of microbial community, ARGs and mobile genetic elements (MGEs) to antibiotics. Antibiotic selection pressures significantly declined the microbial diversity and changed microbial community structures. Based on metagenomic analysis, a total of 500 ARG subtypes affiliated with 18 ARG types were identified and 63 ARGs were shared by all samples. The substantial increase of ARG abundance and the shifts of ARG profiles were significantly correlated with antibiotic types and concentrations. The evident enrichment of non-corresponding ARG types suggested the strong co-selection effects of the target antibiotics. Additionally, metagenomic analysis revealed the occurrence of 104 MGEs belonging to various types and the five dominant MGEs were tnpA, intI1, tniA, tniB and IS91. The ARG-MGE co-occurrence associations implied the potential mobility of ARGs. Network analysis also demonstrated that five ARG types (aminoglycoside, beta-lactam, chloramphenicol, multidrug and tetracycline resistance genes) tended to co-occur internally and the obvious co-occurrence patterns among different ARG types indicated the potential for resistance co-selection. Moreover, 15 bacterial genera were speculated as the hosts of diverse ARGs. This study provides a comprehensive overview of the occurrence of ARGs and MGEs and is valuable for the risk assessment and management of antibiotic resistance.

Bioaugmentation of Moving Bed Biofilm Reactor (MBBR) with Achromobacter JL9 for enhanced sulfamethoxazole (SMX) degradation in aquaculture wastewater

This study investigated whether bioaugmentation improves sulfamethoxazole (SMX) degradation and nitrogen removal in the Moving Bed Biofilm Reactor (MBBR) system. The effects of the C/N ratio on SMX degradation and nitrogen removal were also evaluated. Using MBBR system operation experiments, the bioaugmented reactor was found to perform more effectively than the non-bioaugmentation reactor, with the highest SMX, nitrate-N, and ammonia-N removal efficiencies of 80.49, 94.70, and 96.09%, respectively. The changes in the sulfonamide resistance genes and bacterial communities were detected at various operating conditions. The results indicate that the diversity of the bacterial communities and the abundance of resistance genes were markedly influenced by bioaugmentation and the C/N ratio, with Achromobacter among the dominant genera in the MBBR system. The bio-toxicity of samples, calculated as the inhibition percentage (IP) toward Escherichia coli, was found to decrease to non-toxic ranges after treatment.

Behaviors and related mechanisms of Zn resistance and antibiotic resistance genes during co-composting of erythromycin manufacturing wastes and pig manure

This study explored the fate of Zn- resistance genes (ZRGs), antibiotic- resistance genes (ARGs) and related mechanisms associated with bacterial communities during co-composting of erythromycin manufacturing wastes (EMW) and pig manure (PM) at the ratio of 0% (control), 5% (L) and 20% (H) (PM basis). The relative abundance (RAs) of erm genes in most treatments were decreased by 77.75-99.97% after composting. But total RA of czc genes were increased by 8.34, 15.86 and 12.03 times in control, L and H treatment respectively. The higher EMW in H showed a negative impact on removing of erm genes and aggravated the enrichment of ZRGs compared with control and L. Redundancy analysis showed that Firmicutes accounted for the highest explanation of ARGs and ZRGs variations, and Zn in EMW had significant impact on the succession of bacterial community.

Microbial communities responded to tetracyclines and Cu(II) in constructed wetlands microcosms with Myriophyllum aquaticum

Combined antibiotic and heavy metal pollution has generated considerable concern. Constructed wetlands (CWs) have been shown to efficiently remove pollutants; however, the microbial community responses to combined pollutants remain enigmatic. In this study, seven microcosm CWs were planted with Myriophyllum aquaticum, spiked with tetracyclines (TCs) (300-30,000 μg/L), alone or with Cu(II), to investigate the response of plant-associated microbial communities. TCs and the Cu/TC ratio greatly affected the performance of CWs. Tetracyclines led to higher microbial diversity, evenness and richness, while UniFrac distances and principal coordinate (PC_O) and redundancy analyses revealed that the co-presence of TCs and Cu(II) led to variations in bacterial communities. Proteobacteria, Cyanobacteria and Bacteroidetes were the dominant microbial phyla and Cloacibacterium, Hydrogenophaga, Rheinheimera and Denitratisoma accounted for 6.2-21.0% of all genera. Therefore, the co-occurrence of heavy metals should be considered when judging the removal potential of TCs in phytoremediation.

Pyophage cocktail for the biocontrol of membrane fouling and its effect in aerobic microbial biofilm community during the treatment of antibiotics

Membrane bioreactor systems face an inevitable challenge that is biofouling, which not only hinders the operation of the system, but also poses an environmental and medical concern caused by the increased antibiotic resistance in bacterial biofilms. This study investigates the disruption of membrane fouling using bacteriophage cocktail (Pyophage) in an aerobic membrane bioreactor for treatment of wastewater containing high non-lethal concentration of erythromycin, tetracycline and sulfamethoxazole, while also considering the effect of the cocktail on performance. The results indicate that Pyophage cocktail contributes significantly to the decrease (45%) in transmembrane pressure while also suppressing biofilm-producing bacteria compared to the control reactors. It also reconstructed biodegradation mechanism of antibiotics especially increasing the relative abundance of gram-negative bacteria by enhancement the removal rate of erythromycin and sulfamethoxazole from the aerobic system to 99%.

Variation and distribution of antibiotic resistance genes and their potential hosts in microbial electrolysis cells treating sewage sludge

Microbial electrolysis cells (MECs) system is an emerging pollution control technology. However, information on the variation of antibiotic resistance genes (ARGs) in MECs treating sewage sludge is still very limited. In this study, the fate of ARGs and their correlation with microbes in MECs under different applied voltages (0-1.5 V) were studied. Most target ARGs were effectively removed, but tetB, tetM and tetQ were enriched up to 2.05 log units in suspended sludge. Most ARGs were mainly distributed on electrodes, except tetQ and tetM enriched in suspended sludge. The selective pressure of residual antibiotics in the sewage sludge was negligible. Horizontal gene transfer was validated for the spread of sul1, sul2, tetA and tetC in MECs. Network analysis revealed that the potential hosts of ARGs mainly belonged to Bacteroidetes, Firmicutes and Proteobacteria. Some genera related to electron transfer were newly found to be the potential ARGs hosts in MECs.

Antibiotic resistance genes, bacterial communities, and functions in constructed wetland-microbial fuel cells: Responses to the co-stresses of antibiotics and zinc

The effects of the continuous accumulation of Zinc (Zn) on the fate of antibiotic resistance genes (ARGs) in constructed wetland-microbial fuel cells (CW-MFCs) remain unclear. In this study, the impacts of Zn addition and a circuit mode on antibiotic removal, occurrence of ARGs, the bacterial community, and bacterial functions were investigated in three groups of CW-MFCs. The results showed that continuous Zn exposure enriched the target ARGs during the initial stage, while excessive Zn accumulation decreased antibiotic removal and the abundance of ARGs. A principal component analysis demonstrated that ARGs and the bacterial community distribution characteristics were significantly impacted by the mass accumulation of antibiotics and Zn, as well as the circuit mode. A redundancy analysis, partial least squares path modeling, and Procrustes analysis revealed that the accumulation of antibiotics and Zn, the composition of the bacterial community, the circuit mode, and the abundance of intI associated with horizontal gene transfer jointly contributed to the distributions of ARGs in the electrodes and effluent. Moreover, continuous exposure to Zn decreased the bacterial diversity and changed the composition and function of the bacterial community predicted using PICRUSt tool. The co-occurrence of ARGs, their potential hosts and bacterial functions were further revealed using a network analysis. A variation partition analysis also showed that the accumulation of target pollutants and the circuit mode had a significant impact on the bacterial community composition and functions. Therefore, the interaction among ARGs, the bacterial community, bacterial functions, and pollutant accumulations in the CW-MFC was complex. This study provides useful implications for the application of CW-MFCs for the treatment of wastewater contaminated with antibiotics and heavy metals.

Effect of extracellular polymer substances on the tetracycline removal during coagulation process

In this study, the effect of extracellular polymer substances on the tetracycline removal under hydroxyl aluminium treatment was investigated, and the molecular mechanisms of extracellular polymeric substances mediated coagulation of tetracycline were also explored. The results show that the presence of extracellular polymeric substances could significantly enhance the removal efficiency of tetracycline in hydroxyl aluminium coagulation. Findings suggest that tyrosine and tryptophan in extracellular proteins acted as binding sites to capture tetracycline. Evidences provided by the density functional theory calculations in combination with spectroscopy analysis indicated that two main mechanisms accounted for tetracycline removal in the presence of extracellular polymeric substances and polyaluminum chloride: (1) amino group in proteins and carbonyl in tetracycline were bridged by Al³⁺; (2) benzene rings in tryptophan and tyrosine were π-π stacked with tetracycline, and the amino group in complexes were further coordinated with Al³⁺.