High removal efficiencies of antibiotics and low accumulation of antibiotic resistant genes obtained in microbial fuel cell-constructed wetlands intensified by sponge iron

Iron-dependent autotrophic denitrification as a novel microbial driven and iron-mediated denitrification process: A critical review

Based on previous research results, iron-dependent autotrophic denitrification (IDAD) was evaluated in an all-around way to provide a theoretical basis for further research. First, this review systematically and comprehensively summarizes the development of IDAD technology and describes the physiological properties of relevant functional microorganisms and their potential mechanisms from different perspectives. Second, the possible Fe-N pathways involved in the reaction of different iron-based materials are discussed in detail. Then, the theoretical advantages of the IDAD process and potential problems are described, and the corresponding control strategies are summarized. The influence of key factors on denitrification is discussed in terms of operational and water quality parameters. In addition, the application and research direction of this technology in engineering are summarized. Finally, the latest development trends and prospects for future applications are discussed to promote an in-depth understanding of IDAD and its practical application in sewage treatment.

Iron-carbon enhanced constructed wetland microbial fuel cells for tetracycline wastewater treatment: Efficacy, power generation, and the role of iron-carbon

Tetracycline (TC) antibiotics wastewater is a serious threat to human health and environment. In this study, four groups of laboratory-scale constructed wetlands (CWs) with different configurations were constructed to evaluate the removal efficiency of iron-carbon (Ic) coupled constructed wetland microbial fuel cells (CW-MFC) system for different pollutants removal and bioelectricity production. The results showed that the addition of Ic significantly promoted the removal of contaminants. The maximum removal rates of COD, TN, NH4+-N, and TP were 86.13 %, 81.60 %, 79.07 %, and 97.35 %, respectively. In particular, the removal rates of TC reached 100 %. 3D-EEM analysis further confirmed the role of Ic in promoting organic degradation. The Ic-CW-MFC system also showed superiority in power generation performance with peak power density of 7.90 mW/m2 (internal resistance is 10 Ω), 88.07 % higher than the traditional CW-MFC, while the internal resistance was 68.21 % lower. Therefore, when Ic is used as the substrate of CW-MFC system, its decontamination and electricity generation performance is the best. Analysis of RDA was used to elucidate the relationship of four CWs, dominant strains and environmental factors (pH, ORP and DO). The performance of traditional CWs decreased significantly after TC addition (5-20 mg/L), but Ic-CW-MFC could effectively alleviate the inhibition effect caused by high-concentration TC wastewater. The working mechanism of Ic-CW-MFC in TC wastewater was further analyzed through typical cycle experiment and characterization. The results showed that Ic-CW-MFC is an efficient and economical wastewater treatment technology, which has great potential application value in the treatment of wastewater containing TC.

Performance of electro-assisted ecological floating bed in antibiotics and conventional pollutants degradation: Mechanisms and microbial response

Electro-assisted technology is promising for enhancing plant activity, optimizing functional microbial communities, and significantly strengthening pollutant removal efficiency. In this study, four reactors were designed as control group (CG), Hydrocotyle vulgaris L. ecological floating bed (PEFB), microbial fuel cell (MFC), and Hydrocotyle vulgaris L. ecological floating bed-microbial fuel cell (PEFB-MFC) to investigate the efficiency and mechanisms for the synchronous removal of conventional and antibiotic contaminants. Results showed that PEFB-MFC hold superior removal performance for sulfamethoxazole (61%), tetracycline (61%), CODCr (65%), NH4+-N (86%), TN (41%), and TP (51%). High-throughput sequencing indicated that Pseudomonadota and Actinomycetota were the predominant phyla in the different reactors. Metagenomic sequencing results showed that pollutant degradation-related metabolic functions, such as those involved in carbohydrate and amino acid metabolism in PEFB-MFC exhibited superior abundance compared to the other reactors. LC-MS analysis revealed sulfamethoxazole degradation occurred through active-site cleavage, and tetracycline underwent demethylation, aldehyde formation, dehydroxylation. This study offers a deeper insight into electro-enhanced PEFB on decontamination performance and functional microbial communities.

Metagenomic insights on promoting the removal of resistome in aerobic composting pig manure by lightly burned modified magnesite

The antibiotic resistance genes (ARGs) have become a serious issue facing public health. In this study, light-burned magnesite with a high specific surface area at 650 °C (MS650) was used for aerobic composting, evaluating its effect on the resistome during pig manure composting. Different concentrations of MS650 reduced the abundance of the resistome, including seven high-risk ARGs, class two metal and biocide resistance genes (MBRGs), and human pathogenic bacteria (HPBs). The addition of 2.5 % MS650 (L1) in the composting had the best reduction effect on ARGs, MBRGs and HPBs. ARG and microbial community assembly are deterministic processes. Proteobacteria and Actinobacteria was the main factor associated with the decrease in ARGs, followed by virulence factor genes (VFGs, 44.2 %). The reduction in MBRGs by MS650 mainly suppressed HGT by reducing the Isfinder abundance. To summarize, MS650 is an effective method to improve emission reduction of ARGs and MBRGs. This study provided a theoretical basis for improving the engineering application potential of MS650.

Insights to the cooperation of double-working potential electroactive biofilm for performance of sulfamethoxazole removal: ARG fate and microorganism communities

Bioelectrochemical systems (BESs) have shown great potential in enhancing sulfamethoxazole (SMX) removal. However, electroactive biofilms (EBs) constructed with single potentials struggle due to limited biocatalytic activity, hindering deep SMX degradation. Here, we constructed a double-working potential BES (BES-D) to investigate its ability to eliminate SMX and reduce the levels of corresponding antibiotic resistance genes (ARGs). The preferable electrochemical activity of EB in BES-D was confirmed by electrochemical characterization, EPS analysis, physical structure, viability of the biofilm, and cytochrome content. BES-D exhibited a notably greater SMX removal efficiency (94.2 %) than did the single-working potential BES (BES-S) and the open-circuit group (OC). Degradation pathway analysis revealed that the cooperative EB could accelerate the in-depth removal of SMX. Moreover, EB interaction in BES-D decreased the relative abundance of ARGs in biofilms compared to that in BES-S, although the absolute number of ARG copies increased in BES-D effluents. Compared to those in BES-S and OC, more complex cross-niche microbial associations in the EB of BES-D were observed by network analysis of the bacterial community and ARG hosts, enhancing the degradation efficiency of SMX. In conclusion, BES-D has significant potential for SMX removal and the enhancement of EB activity. Nonetheless, the risk of ARG dissemination in effluent remains a concern.

Sponge iron enriches autotrophic/aerobic denitrifying bacteria to enhance denitrification in sequencing batch reactor

Sponge iron (SFe) coupled with a sludge system has great potential for improving biological denitrification; however, the underlying mechanism is not yet fully understood. In this study, the denitrification performance and microbial characteristics of ordinary sludge and SFe-sludge systems were investigated. Overall, the SFe-sludge reactor had faster ammonium degradation rate (94.0 %) and less nitrate accumulation (1.5-53.3 times lower) than ordinary reactor during the complete operation cycle of sequencing batch reactors. The addition of SFe increased the activities of nitrate and nitrite reductases. The total relative abundance of autotrophic denitrifying bacteria (Acidovorax, Arenimonas, etc.) in the SFe-sludge system after 38 days of operation was found to be 10.6 % higher than that in the ordinary sludge reactor. The aerobic denitrifying bacteria (Dokdonella, Phaeodactylibacter, etc.) was 5.3 % higher than ordinary sludge. The SFe-sludge system improved denitrification by enriching autotrophic/aerobic denitrifying bacteria in low carbon-to-nitrogen ratio wastewater treatment.

Synergistic reduction of pollution and carbon mitigation in constructed wetlands-microbial fuel cell using sludge-derived biochar

Integrating microbial fuel cells (MFC) into constructed wetland systems (CW) has been an efficient wastewater treatment to improve the pollutants removal and regenerate power energy. This study fabricated a sludge biochar material (SBM) to sequestrate the carbon of residual sludge. Thereafter used SBM and modified SBM as the substrate materials to construct three groups of CW-MFC for decreasing the greenhouse gas (GHG) emission. The water quality improvement in removal efficiency achieved (2.59 %, 3.10 %, 5.21 % for COD; 3.31 %, 3.60 %, 6.71 % for TN; 1.80 %, 7.38 %, 4.93 % for TP) by the application of MFC, SBM, and modified SBM in wastewater treatment, respectively. Additionally, the reduction in global warming potential (GWP) realized 17.2 %, 42.2 %, and 64.4 % resulting from these applications. The carbon flow and fate diagrams showed MFC shifted the gas phase‑carbon flow from CH4 to CO2, and SBM promoted this shift trends. Microbial diversity indicated enrichment of electrochemically active bacteria (EAB), denitrifying bacteria, and phosphate accumulating organisms (PAOs) by SBM. Metabolic pathways analysis showed that introduction of MFC and SBM exhibited significant increases of key functional genes in metabolic pathway of anaerobic oxidation of methane (AOM). This study highlights the benefit of CW-MFC in and provides a new strategy for removing pollutants and abating GHG emissions in wastewater treatment.

Occurrence and distribution of antibiotic pollution and antibiotic resistance genes in seagrass meadow sediments based on metagenomics

Seagrass meadows are one of the most important coastal ecosystems that provide essential ecological and economic services. The contamination levels of antibiotic and antibiotic resistance genes (ARGs) in coastal ecosystems are severely elevated owing to anthropogenic disturbances, such as terrestrial input, aquaculture effluent, and sewage discharge. However, few studies have focused on the occurrence and distribution of antibiotics and their corresponding ARGs in this habitat. Thus, we investigated the antibiotic and ARGs profiles, microbial communities, and ARG-carrying host bacteria in typical seagrass meadow sediments collected from Swan Lake, Caofeidian shoal harbor, Qingdao Bay, and Sishili Bay in the Bohai Sea and northern Yellow Sea. The total concentrations of 30 detected antibiotics ranged from 99.35 to 478.02 μg/kg, tetracyclines were more prevalent than other antibiotics. Metagenomic analyses showed that 342 ARG subtypes associated with 22 ARG types were identified in the seagrass meadow sediments. Multidrug resistance genes and RanA were the most dominant ARG types and subtypes, respectively. Co-occurrence network analysis revealed that Halioglobus, Zeaxanthinibacter, and Aureitalea may be potential hosts at the genus level, and the relative abundances of these bacteria were higher in Sishili Bay than those in other areas. This study provided important insights into the pollution status of antibiotics and ARGs in typical seagrass meadow sediments. Effective management should be performed to control the potential ecological health risks in seagrass meadow ecosystems.

Biochar and zero-valent iron alleviated sulfamethoxazole and tetracycline co-stress on the long-term system performance of bioretention cells: Insights into microbial community, antibiotic resistance genes and functional genes

Antibiotics and antibiotic resistance genes (ARGs), known as emerging contaminants, have raised widespread concern due to their potential environmental and human health risks. In this study, a conventional bioretention cell (C-BRC) and three modified bioretention cells with biochar (BC-BRC), microbial fuel cell coupled/biochar (EBC-BRC) and zero-valent iron/biochar (Fe/BC-BRC) were established and two antibiotics, namely sulfamethoxazole (SMX) and tetracycline (TC), were introduced into the systems in order to thoroughly investigate the co-stress associated with the long-term removal of pollutants, dynamics of microbial community, ARGs and functional genes in wastewater treatment. The results demonstrated that the SMX and TC co-stress significantly inhibited the removal of total nitrogen (TN) (C-BRC: 37.46%; BC-BRC: 41.64%; EBC-BRC: 55.60%) and total phosphorous (TP) (C-BRC: 53.11%; BC-BRC: 55.36%; EBC-BRC: 62.87%) in C-BRC, BC-BRC and EBC-BRC, respectively, while Fe/BC-BRC exhibited profoundly stable and high removal efficiencies (TN: 89.33%; TP: 98.36%). Remarkably, greater than 99% removals of SMX and TC were achieved in three modified BRCs compared with C-BRC (SMX: 30.86 %; TC: 59.29%). The decreasing absolute abundances of denitrifying bacteria and the low denitrification functional genes (nirK: 2.80 × 105-5.97 × 105 copies/g; nirS: 7.22 × 105-1.69 × 106 copies/g) were responsible for the lower TN removals in C-BRC, BC-BRC and EBC-BRC. The amendment of Fe/BC successfully detoxified SMX and TC to functional bacteria. Furthermore, the co-stress of antibiotics stimulated the propagation of ARGs (sulI, sulII, tetA and tetC) in substrates of all BRCs and only Fe/BC-BRC effectively reduced all the ARGs in effluent by an order of magnitude. The findings contribute to developing robust ecological wastewater treatment technologies to simultaneously remove nutrients and multiple antibiotics.

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.

Constructed wetlands as neglected fixed source of microplastics and antibiotic resistance genes in natural water bodies?

The pollution status and the harm caused by microplastics and antibiotic resistance genes (ARGs) in aquatic ecosystems have been a growing concern. The presence of microplastics could accelerate the transfer and spread of ARGs. Before sewage reaches natural water bodies, microplastics and ARGs need to be eliminated through specific processes. Constructed wetlands are currently an effective and environmentally friendly wastewater treatment process. Research has shown significant effectiveness in removing microplastics and ARGs. Microplastics and ARGs can be removed through processes such as adsorption, capture, adhesion, and biodegradation. However, long-term continuous operation could lead to constructed wetlands becoming significant reservoirs of microplastics and ARGs. Inflow loads and seasonal variations in constructed wetlands may result in the reintroduction of persistent microplastics and ARGs into the receiving water body, establishing the constructed wetland as a continuous source of these pollutants in the receiving water body. The key to the widespread application of constructed wetlands lies in solving this challenging problem. Therefore, although constructed wetlands serve as a green strategy for removing microplastics and ARGs, there are still many gaps in our knowledge. Based on the current accumulation of microplastics and ARGs in constructed wetlands, this paper summarizes the removal of microplastics and ARGs in existing constructed wetlands and explores the interaction between them. Additionally, it proposes suggestions for optimizing the process and improving the reliability of monitoring microplastics and ARGs in sewage.

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.

Simultaneous passivation of heavy metals and removal of antibiotic resistance genes by calcium peroxide addition during sewage sludge composting

This research evaluated the effects of calcium peroxide (CP) at 0% (CK, w/w), 5% (T1, w/w), and 10% (T2, w/w), on heavy metals (HMs) mobility and prevalence of antibiotic resistance genes (ARGs) during sludge composting. T1 and T2 significantly reduced (p < 0.05) the mobility of Cu (29.34%, and 32.94%, respectively), Ni (24.07%, and 31.48%, respectively) and Zn (33.28%, and 54.11%, respectively) compared to CK after the composting. CP addition resulted in a decrease in mobile genetic elements (MGEs) and ARGs during composting. Together with structural equation model and random forest analysis depicted MGEs had a primary association with total ARGs variations during composting. Microbial analysis indicated CP downregulated the expression of the genes associated with two-component and type IV secretion system, thus reducing the prevalence of ARGs. This study demonstrates that application of CP is a feasible strategy to mitigate both ARGs and HMs hazards during composting.

The dynamics and transmission of antibiotic resistance associated with plant microbiomes

Antibiotic resistance genes (ARGs) have been widely found and studied in soil and water environments. However, the propagation of ARGs in plant microbiomes has attracted insufficient attention. Plant microbiomes, especially the rhizosphere microorganisms, are closely connected with water, soil, and air, which allows ARGs to spread widely in ecosystems and pose a threat to human health after entering the human body with bacteria. Therefore, it is necessary to deeply understand and explore the dynamics and the transmission of ARGs in rhizosphere microorganisms and endophytes of plants. In this review, the transmission and influencing factors of ARGs in the microorganisms associated with plants, especially the influence of root exudates on plant microbiomes, are analyzed. Notably, the role of intrinsic genes of plants in determining root exudates and their potential effects on ARGs are proposed and analyzed. The important role of phyllosphere microorganisms and endophytes in the transmission of ARGs and co-resistance of antibiotics and other substances are also emphasized. The proliferation and transmission of ARGs associated with plant microbiomes addressed in this review is conducive to revealing the fate of ARGs in plant microorganisms and alleviating ARG pollution.

3D porous carbon-embedded nZVI@Fe2O3 nanoarchitectures enable prominent performance and recyclability in antibiotic removal

Overcoming the instability and poor recyclability during the practical applications of contaminant scavengers is a challenging topic. Herein, a three-dimensional (3D) interconnected carbon aerogel (nZVI@Fe₂O₃/PC) embedding a core-shell nanostructure of nZVI@Fe₂O₃ was elaborately designed and fabricated via an in-situ self-assembly process. The porous carbon with 3D network architecture exhibits strong adsorption towards various antibiotic contaminants in water, where the stably embedded nZVI@Fe₂O₃ nanoparticles not only serve as magnetic seeds for recycling, but also avoid the shedding and oxidation of nZVI in the adsorption process. As a result, nZVI@Fe₂O₃/PC efficiently captures sulfamethoxazole (SMX), sulfamethazine (SMZ), ciprofloxacin (CIP), tetracycline (TC) and other antibiotics in water. In particular, an excellent adsorptive removal capacity of 329 mg g^-1 and a rapid capture kinetics (99% of removal efficiency in 10 min) under a wide pH adaptability (2-8) are achieved using nZVI@Fe₂O₃/PC as an SMX scavenger. nZVI@Fe₂O₃/PC displays exceptional long-term stability given that it shows excellent magnetic property after it is stored in water solution for 60 d, making it an ideal stable scavenger for contaminants in an etching-resistant and efficient manner. This work would also provide a general strategy to develop other stable iron-based functional architectures for efficient catalytic degradation, energy conversion and biomedicine.

Simultaneous removal of nitrate, lead, and tetracycline by a fixed-biofilm reactor assembled with kapok fiber and sponge iron: Comparative analysis of operating conditions and biotic community

In recent years, under the condition of lack of carbon source, the presence of composite micro-pollutants make the removal of nitrate seriously damaged, and to find a suitable way to solve this problem is imminent. A fixed-biofilm carrier modified by mixing sponge iron (SI) and kapok fiber (KF) combined with strain Zoogloea sp. FY6 was constructed in this study to get a fixed-biofilm reactor with merit denitrification performance. By adjusting the operation parameters, it can be concluded that when the carbon to nitrogen (C/N) ratio was 1.5, the hydraulic retention time (HRT) was 6.0 h, and the pH was 6.0, the nitrate removal efficiency (NRE) of the fixed-biofilm reactor was up to 95.4% (2.95 mg L^-1 h^-1). In addition, the fixed-biofilm reactor constructed in this study can remove lead (Pb²⁺) and tetracycline (TC) excellently in the presence of SI and Zoogloea sp. FY6, and the denitrification performance can still maintain a high level under the influence of different concentrations of Pb²⁺ and TC. Furthermore, the addition of SI not only removes the compound pollutants, but also protects the toxicity of the pollutant inflow in the bioreactor, and the metabolic process of microorganisms in the bioreactor also removes some of the compound pollutants. The high-throughput data showed the abundance of strain Zoogloea sp. FY6 was still the highest value under the influence of various pollutants, and the metagenomic prediction showed that the fixed-biofilm reactor had perfect denitrification process and iron redox cycle benefits. This study provides a valuable reference for sustainable utilization of natural biological resources and reduction of material costs in wastewater treatment plants (WWTPs).

Integration of MFC reduces CH4, N2O and NH3 emissions in batch-fed wetland systems

The combination of microbial fuel cells (MFCs) with constructed wetlands (CWs) for enhancing water purification efficiency and generating bioelectricity has attracted extensive attention. However, the other benefits of MFC-CWs are seldom reported, especially the potential for controlling gaseous emissions. In this study, we have quantitatively compared the pollutant removal efficiency and the emission of multiple gases between MFC-CWs and batch-fed wetland systems (BF CWs). MFC-CWs exhibited significantly (p < 0.01) higher COD, NH₄⁺-N, TN, and TP removal efficiencies and significantly (p < 0.01) lower global warming potential (GWP) than BF CWs. The integration of MFC decreased GWP by 23.88% due to the reduction of CH₄ and N₂O fluxes, whereas the CO₂ fluxes were slightly promoted. The quantitative PCR results indicate that the reduced N₂O fluxes in MFC-CWs were driven by the reduced transcription of the nosZ gene and enhanced the ratio of nosZ/(nirS + nirK); the reduced CH₄ fluxes were related to pomA and mcrA. Additionally, the NH₃ fluxes were reduced by 52.20% in MFC-CWs compared to BF CWs. The integration of MFC promoted the diversity of microbial community, especially Anaerolineaceae, Saprospiraceae and Clostridiacea. This study highlights a further benefit of MFC-CWs and provides a new strategy for simultaneously removing pollutants and abating multiple gas emissions in BF CWs.

Performances and enhanced mechanisms of nitrogen removal in a submerged membrane bioreactor coupled sponge iron system

Sponge iron is a potential material for nitrogen removal, but lack of a study about nitrogen removal in a membrane bioreactor (MBR) coupled with sponge iron. The performances and mechanisms of nitrogen removal of SI-MBR were investigated and compared it with that in GAC-MBR. The results showed that the average rate of organic matter removal in the SI-MBR was 92.74%, which was higher than that in the GAC-MBR (87.48%). And the average effluent NO₂^--N and NO₃^--N concentration in the SI-MBR (0.02 mg/L and 3.73 mg/L) was lower than that in the GAC-MBR (0.05 mg/L and 7.51 mg/L). Meanwhile, the highest nitrification rate and denitrification rate was respectively 3.544 ± 0.25 mg/(g VSS·h) and 6.643 ± 0.2 mg/(g VSS·h) in the SI-MBR, which was higher than that (3.094 ± 0.25 mg/(g VSS·h) and (6.376 ± 0.2 mg/(g VSS·h)) in the GAC-MBR. Additionally, the bacterial activities (e.g., DHA activity and respiratory activity) were obviously enhanced through the iron ion from sponge iron. The bacterial community in the SI-MBR system was more richness and diverse than that in the GAC-MBR. Ultimately, the mechanisms of enhanced biological nitrogen removal with sponge iron in MBR were analyzed. On the surface of sponge iron, the DIRB and FOB could use the iron ion from sponge iron as the electron transfer to improve the nitrogen and organic removal. With sponge iron, there is not only the nitrification bacteria and heterotrophic denitrifying microorganism enriched, but also the autotrophic denitrifying bacteria abounded obviously. The autotrophic denitrifying bacteria could use Fe(II) as an electron donor to achieve denitrification and enhance the nitrogen removal.

Deciphering the role of extracellular polymeric substances in the regulation of microbial extracellular electron transfer under low concentrations of tetracycline exposure: Insights from transcriptomic analysis

Low concentrations of antibiotics can regulate the formation of electroactive biofilms, however, the underlying mechanisms, especially the composition and spatial distribution of extracellular polymeric substances (EPS) and their effects on extracellular electron transfer (EET) process, have not been fully deciphered. Here, the response of EPS of Geobacter sulfurreducens biofilm to low concentrations of tetracycline (μg L^-1 to mg L^-1) was explored, and the impact of such EPS variations on EET efficiency was further elucidated by transcriptomic analysis. Results showed that 0.05 mg L^-1 of tetracycline achieved both beneficial quantitative and spatial regulation of redox-active proteins and non-conducting exopolysaccharides in EPS, while higher concentrations induced negative effects. Moreover, 1 mg L^-1 of tetracycline upregulated multiple exopolysaccharide biosynthesis-related genes, indicating a stress response for cell-protection, while 0.05 mg L^-1 of tetracycline upregulated most direct EET-related gene expressions, resulting in the promoted EET efficiency. Furthermore, 0.05 mg L^-1 of tetracycline selectively enriched Geobacter (45.55% vs 19.55% in control, respectively) from mixed inoculum. This research provides a new insight of how antibiotics at low concentrations regulated EET process through modulation of EPS.

Enhanced performance and microbial interactions of shallow wetland bed coupling with functional biocathode microbial electrochemical system (MES)

It is essential to remediate the polluted urban river, which endangers the aquatic creatures and affected human body's senses. The treatment wetland combined with microbial electrochemical system (MES) used for the remediation is becoming a new research focus due to its ideal pollutants removal efficiency and small footprint. Here this paper provided a kind of novel shallow wetland bed coupling with close-circuit microbial electrochemical system (WB-CMES) to remove pollutants in surface water. In contrast to the shallow wetland bed coupling with open-circuit MES (WB-OMES) and the shallow wetland bed without MES (WB), the enhancing effects and pollutants removal pathway were evaluated. After 62-day operation, average TN removal efficiency in WB-CMES was 87.7%, which was 19.7% and 13.8% higher than that of WB-OMES and WB respectively. The rate coefficient k of NO₃^--N degradation in WB-CMES was 1.6 and 1.8 times higher than that in WB-OMES and WB. The results of chlorophyll, protein and superoxide dismutase (SOD) in WB-CMES were 27.3%, 44.3% and 12.9% higher than those in WB. The microbial community structure analysis indicated that electroactive bacteria on anode like Desulfobulbus could oxidize organics and generate electrons to compensate cathode, meanwhile, cathode could enrich more species of functional bacteria like Rhodobacter, Pirellula, Hyphomicrobium, Thauera, which had a synergistic effect on oxygen reduction, nitrogen removal and plant growth. The results indicated that oxygen produced by submerged plants could be utilized by the oxygen-reducing functional biocathode of MES and the proper aerobic and anoxic environment might enhance nitrate removal mainly through simultaneous nitrification and denitrification (SND), aerobic denitrification and anammox. This research provided a novel technology with advantages of simple operation, flexible configuration, easy scale-up and low cost for application in remediation of highly polluted surface water.

The combined effect of an integrated reclaimed water system on the reduction of antibiotic resistome

The reuse of urban reclaimed water is conducive to alleviate the current serious shortage of water resources. However, antibiotic resistance genes (ARGs) in reclaimed water have received widespread attention due to their potential risks to public health. Deciphering the fate of ARGs in reclaimed water benefits the development of effective strategies to control resistome risk and guarantees the safety of water supply of reclaimed systems. In this study, the characteristics of ARGs in an integrated reclaimed water system (sewage treatment plant-constructed wetland, STP-CW) in Beijing (China) have been identified using metagenomic assembly-based analysis, as well as the combined effect of the STP-CW system on the reduction of antibiotic resistome. Results showed a total of 29 ARG types and 813 subtypes were found in the reclaimed water system. As expected, the STP-CW system improved the removal of ARGs, and about 58% of ARG subtypes were removed from the effluent of the integrated STP-CW system, which exceeded 43% for the STP system and 37% for the CW system. Although the STP-CW system had a great removal on ARGs, abundant and diverse ARGs were still found in the downstream river. Importantly, network analysis revealed the co-occurrence of ARGs, mobile genetic elements and virulence factors in the downstream water, implying potential resistome dissemination risk in the environment. Source identification with SourceTracker showed the STP-effluent was the largest contributor of ARGs in the downstream river, with a contribution of 45%. Overall, the integrated STP-CW system presented a combined effect on the reduction of antibiotic resistome, however, the resistome dissemination risk was still non-negligible in the downstream reclaimed water. This study provides a comprehensive analysis on the fate of ARGs in the STP-CW-river system, which would benefit the development of effective strategies to control resistome risk for the reuse of reclaimed water.

Antibiotics and antibiotic resistant bacteria/genes in urban wastewater: A comparison of their fate in conventional treatment systems and constructed wetlands

There is a growing concern that the use and misuse of antibiotics can increase the detection of antibiotic resistant genes (ARGs) in wastewater. Conventional wastewater treatment plants provide a pathway for ARGs and antibiotic resistant bacteria (ARB) to be released into natural water bodies. Research has indicated that conventional primary and secondary treatment systems can reduce ARGs/ARB to varying degrees. However, in developing/low-income countries, only 8-28% of wastewater is treated via conventional treatment processes, resulting in the environment being exposed to high levels of ARGs, ARB and pharmaceuticals in raw sewage. The use of constructed wetlands (CWs) has the potential to provide a low-cost solution for wastewater treatment, with respect to removal of nutrients, pathogens, ARB/ARGs either as a standalone treatment process or when integrated with conventional treatment systems. Recently, CWs have also been employed for the reduction of antibiotic residues, pharmaceuticals, and emerging contaminants. Given the benefits of ARG removal, low cost of construction, maintenance, energy requirement, and performance efficiencies, CWs offer a promising solution for developing/low-income countries. This review promotes a better understanding of the performance efficiency of treatment technologies (both conventional systems and CWs) for the reduction of antibiotics and ARGs/ARB from wastewater and explores workable alternatives.

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.

A Review of Stand-Alone and Hybrid Microbial Electrochemical Systems for Antibiotics Removal from Wastewater

The growing concern about residual antibiotics in the water environment pushes for innovative and cost-effective technologies for antibiotics removal from wastewater. In this context, various microbial electrochemical systems have been investigated as an alternative to conventional wastewater technologies that are usually ineffective for the adequate removal of antibiotics. This review article details the development of stand-alone and hybrid or integrated microbial electrochemical systems for antibiotics removal from wastewater. First, technical features, antibiotics removal efficiencies, process optimization, and technological bottlenecks of these systems are discussed. Second, a comparative summary based on the existing reports was established to provide insights into the selection between stand-alone and hybrid systems. Finally, research gaps, the relevance of recent progress in complementary areas, and future research needs have been discussed.