Dynamics of antibiotic resistance genes in microbial fuel cell-coupled constructed wetlands treating antibiotic-polluted water

Removal of chloramphenicol and resistance gene changes in electric-integrated vertical flow constructed wetlands

The performance of an electric-integrated vertical flow constructed wetland (E-VFCW) for chloramphenicol (CAP) removal, changes in microbial community structure, and the fate of antibiotic resistance genes (ARGs) were evaluated. CAP removal in the E-VFCW system was 92.73% ± 0.78% (planted) and 90.80% ± 0.61% (unplanted), both were higher than the control system which was 68.17% ± 1.27%. The contribution of anaerobic cathodic chambers in CAP removal was higher than the aerobic anodic chambers. Plant physiochemical indicators in the reactor revealed electrical stimulation increased oxidase activity. Electrical stimulation enhanced the enrichment of ARGs in the electrode layer of the E-VFCW system (except floR). Plant ARGs and intI1 levels were higher in the E-VFCW than in the control system, suggesting electrical stimulation induces plants to absorb ARGs, reducing ARGs in the wetland. The distribution of intI1 and sul1 genes in plants suggests that horizontal transfer may be the main mechanism dispersing ARGs in plants. High throughput sequencing analysis revealed electrical stimulation selectively enriched CAP degrading functional bacteria (Geobacter and Trichlorobacter). Quantitative correlation analysis between bacterial communities and ARGs confirmed the abundance of ARGs relates to the distribution of potential hosts and mobile genetic elements (intI1). E-VFCW is effective in treating antibiotic wastewater, however ARGs potentially accumulate.

Tea polyphenols and catechins postpone evolution of antibiotic resistance genes and alter microbial community under stress of tetracycline

Relying on the high mobility of water flow, the dissemination of antibiotic resistance genes (ARGs) in the water tends to be exacerbated and enlarged. It caused negative impacts on a wider scope of the environment. The ARGs dissemination monitoring and the methods efficiently reducing their concentration in water became the focus of interest. Green chemicals with antibacterial effects such as tea polyphenols (TPs) and catechins (CA) have been considered as auxiliary disinfectants for ARGs removal in the water environment. However, the antibacterial performance of TPs and CA under the stress of external antibiotics still lacks sufficient research. The results show that more operational taxonomic units can be observed in water samples with TPs and CA than in those without the ingredients under pressure of tetracycline. An unexpected increase along with the increase of ARGs concentrations and the diversity of microbial communities under the low-concentration TPs or CA (1 mg/L). Besides, under the stress of tetracycline, the inhibition of TPs was detected to be strengthened for increase of inti1 and tetC but weakened towards for the increase of tetA. Whilst CA substantially diminished abundances of tetC and tetA under tetracycline pressure. This research demonstrated that TPs and CA are able to assuage development of ARGs under the pressure of antibiotic in water system.

Curbing per- and polyfluoroalkyl substances (PFASs): First investigation in a constructed wetland-microbial fuel cell system

The presence of per- and polyfluoroalkyl substances (PFASs) in water environments has been linked to a slew of negative health effects in both animals and humans, but the green and eco-sustainable removal technologies remain largely unknown. Constructed wetland coupled microbial fuel cell (CW-MFC) is termed a "green process" to control pollutants and recover energy. However, so far, no study has investigated the removal of PFASs and their effects on the performance of the CW-MFC systems. Here, we investigated the removal performance of PFOA and PFOS in the CW-MFC systems both in the absence and presence of electricity circuit, and explored the distribution and fate of PFASs and their interactions with other elements in the systems. Our findings demonstrated excellent removal efficiency of >96% PFOA and PFOS in CW-MFC systems. PFOA and PFOS were distributed throughout the system via wastewater flow, while electrode material and plants are the main enrichment sites in which MFC enhanced up to 10% PFASs removal. However, a loss of 7.2-13.5% of nitrogen removal and a decrease of 7.3% in bioelectricity output were observed when PFASs were introduced in the system. The driven force led to the loss of nitrogen removal and bioelectricity generation lies in the accumulation of PFASs in system composition, which affected microbial activity and community composition, damaging the health of the plant, and in turn reducing CW-MFC's functioning. No doubt, CW-MFC systems provide an alternative technique for PFASs removal, alleviating some limitations to the physical and chemical techniques, but further investigation is highly needed.

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

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

Emerging technologies for enhanced removal of residual antibiotics from source-separated urine and wastewaters: A review

Antibiotic residues are of significant concern in the ecosystem because of their capacity to mediate antibiotic resistance development among environmental microbes. This paper reviews recent technologies for the abatement of antibiotics from human urine and wastewaters. Antibiotics are widely distributed in the aquatic environment as a result of the discharge of municipal sewage. Their existence is a cause for worry due to the potential ecological impact (for instance, antibiotic resistance) on bacteria in the background. Numerous contaminants that enter wastewater treatment facilities and the aquatic environment, as a result, go undetected. Sludge can act as a medium for some chemicals to concentrate while being treated as wastewater. The most sewage sludge that has undergone treatment is spread on agricultural land without being properly checked for pollutants. The fate of antibiotic residues in soils is hence poorly understood. The idea of the Separation of urine at the source has recently been propagated as a measure to control the flow of pharmaceutical residues into centralized wastewater treatment plants (WWTPs). With the ever increasing acceptance of urine source separation practices, visibility and awareness on dedicated treatement technologies is needed. Human urine, as well as conventional WWTPs, are point sources of pharmaceutical micropollutants contributing to the ubiquitous detection of pharmaceutical residues in the receiving water bodies. Focused post-treatment of source-separated urine includes distillation and nitrification, ammonia stripping, and adsorption processes. Other reviewed methods include physical and biological treatment methods, advanced oxidation processes, and a host of combination treatment methods. All these are aimed at ensuring minimized risk products are returned to the environment.

Nitrogen and sulfamethoxazole removal in a partially saturated vertical flow constructed wetland treating synthetic mariculture wastewater

This study investigated the removal of nitrogen and sulfamethoxazole (SMX), and the microbial communities in a partially saturated vertical flow constructed wetland (PS-VFCW) fed with synthetic mariculture wastewater operated at different saturated zone depths (SZDs), i.e. 51, 70, and 60 cm. Removal efficiencies were 99.8%-100.0% for COD, 34.1%-100.0% for NH4+-N, 67.8%-97.3% for total inorganic nitrogen (TIN), and 29.8%-57.2% for SMX. Excellent nitrification performance was achieved at the SZDs of 51 and 60 cm. Denitrification performed well at 70 and 60 cm SZDs. The highest TIN removal efficiency (97.3%) was achieved as the SZD was 60 cm. SMX removal was significantly influenced by SZD and was promoted by higher SZD. The removal of organics, nitrogen, and SMX mainly occurred in the unsaturated zone. Ammonia-oxidizing bacteria, nitrite-oxidizing bacteria, denitrifying bacteria, and SMX-degrading bacteria were detected in the unsaturated and saturated zones, and showed an increasing trend in abundance along the depth.

An Analysis of the Colony Structure of Prokaryotes in the Jialing River Waters in Chongqing

At present, research on the influence of human activities (especially urbanization) on the microbial diversity, structural composition, and spatial distribution of rivers is limited. In this paper, to explore the prokaryotic community structure and the relationship between the community and environmental factors in the Jialing River Basin of Chongqing, so as to provide a basis for monitoring microorganisms in the watershed. The V3–V4 region of the 16 S rRNA gene was analyzed by high-throughput sequencing and the microbial community of the waters of the Jialing River was analyzed for the diversity and composition of the prokaryotic community as well as the species difference of four samples and correlations with environmental factors. The main results of this study were as follows: (1) The diversity index showed that there were significant differences in the biodiversity among the four regions. At the genus level, Limnohabitans, unclassified_f_Comamonadaceae, and Hgcl_clade were the main dominant flora with a high abundance and evenness. (2) A Kruskal–Wallis H test was used to analyze the differences of species composition among the communities and the following conclusions were drawn: each group contained a relatively high abundance of Limnohabitans; the Shapingba District had a higher abundance of Limnohabitans, the Hechuan District had a wide range of unclassified_f_Comamonadaceae, and the Beibei District had a higher Hgcl_clade. (3) Through the determination of the physical and chemical indicators of the water—namely, total nitrogen, total phosphorus, chemical oxygen demand, chlorophyll A, and an analysis by an RDA diagram, the results demonstrated that the distribution of microbial colonies was significantly affected by the environmental factors of the water. Chemical oxygen demand and ammonia nitrogen had a significant influence on the distribution of the colonies. Different biological colonies were also affected by different environmental factors.

Effects of substrate type on variation of sludge organic compounds, bioelectric production and microbial community structure in bioelectrochemically-assisted sludge treatment wetland

A bioelectrochemical assisted sludge treatment wetland (BE-STW) is a promising technology used in the elimination of organic compounds and recovery of bio-energy. In this study, four BE-STW systems were constructed to investigate the effects of some substrates (i.e. graphite particles, zeolite, ceramsite, and gravel) on organic compounds biodegradation and transformation, electricity production, and anodic bacterial community. The maximum output voltages were 0.939, 0.870, 0.741 and 0.835 V, and the maximum power densities were 0.467, 0.143, 0.110, and 0.131 W/m³ for the graphite particles (BS-GP), zeolite (BS-Z), ceramsite (BS-C), and gravel (BS-G) systems, respectively. Also, the dissolved organic carbon (DOC) removal rates were 61.84%, 28.54%, 25.56%, and 18.34% in BS-GP, BS-G, BS-Z, and BS-C, respectively. The degradation of aromatic compounds in sludge extracellular biological organic matter (EBOM) was mainly due to the decrease of hydrophilic fraction (HPI) and transphilic acid fraction (TPI-A) contents. Moreover, aromatic proteins were preferentially removed in BS-Z. For BS-C, the tyrosine-like proteins and humic acid-like substances in TPI-A were totally removed. An excitation-emission matrix (EEM) analysis showed that the fluorescent intensity of the humic acid-like substances was the lowest in BS-GP, and no fluorescence peaks of fulvic acid-like substances were observed. Finally, at the genus level, Longilinea, Terrimonas, Ottowia, and Saccharibacteria_genera_incertae_sedis were the dominant bacteria in BE-STW, and Methylophilus was also only detected in BS-GP. These results confirmed that substrate materials have a significant impact on the preferentially degraded organic matter in BE-STWs, which can provide a theoretical basis for the practical application of STW in the future.

The dynamic of the potential pathogenic bacteria, antibiotic-resistant bacteria, and antibiotic resistance genes in the water at different growth stages of grass carp pond

Pond aquaculture has become the most important and broadest breeding model in China, and an extremely important source of aquatic products, but the potential hazard factors of potential pathogenic bacteria (PPB), antibiotic resistance bacteria (ARB), and antibiotic resistance genes (ARGs) in aquaculture environment are largely invisible. In the present study, the bacterial communities in the larvae, juvenile, rearing, and harvesting culture stages of great grass carp (Ctenopharyngodon idellus) ponds were investigated and the structure of microbial flora analysis showed that the larvae culture stage has the highest abundance and the most dominant phyla were Proteobacteria (27.8%). A total of 123 significant Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway annotations and the relative abundance of nine bacterial phenotypes implied that the larvae culture stage had the most abundance of pathogenic potential and mobile elements. The correlation analyses of environmental factors showed that temperature, stocking density, pH, and transparency showed the significant impacts on both the distribution of microbiome and the PPB. More importantly, a total of 40 ARB were identified, and 16 ARGs have the detection rates of 100%, which revealed that they are widely distributed and highly enriched in the aquaculture production. Notably, this is the first robust report to analyze and understand the PPB, ARB, and ARGs characteristics and dynamic changes in the pond aquaculture.

Insight into the organic matter degradation enhancement in the bioelectrochemically-assisted sludge treatment wetland: Transformation of the organic matter and microbial community evolution

Sludge treatment wetland (STW) has been widely used to dewater and mineralize the various sludge, but the low degradation ability of organic matter can limit its application. Bioelectrochemistry has been proven to accelerate the degradation of organic compounds and recover bioenergy from the sludge. In this study, a bioelectrochemical-assisted sludge treatment wetland (BE-STW) system was constructed to determine the most common types of degraded organic matter and the functional bacterial community. It was found that the bioelectrochemistry process contributed to a further removal of the total chemical oxygen demand (TCOD) by 19% (±0.6) and the additional soluble chemical oxygen demand (SCOD) value was 64.10% (±0.63), with a voltage output of 0.961 V and a power density of 0.351 W/m³. The hydrophilic and hydrophobic acid fractions of the sludge were preferentially removed in BE-STW. The tryptophan-like protein and fulvic acid-like substances were totally removed, whereas, the hydrolysis of aromatic organic compounds in the neutral and hydrophobic acid fractions was enhanced. Also, the enrichment of Longilinea and Methylophilus improved the hydrolysis of organic matter. Moreover, the high relative abundance of Thauera, Dechloromonas, and Syntrophorhabdus could accelerate the degradation of aromatic compounds in the BE-STW system. The bacteria from the genus Geobacter was predominantly detected (2.48%) in the anodic biofilm on BE-STW. The results showed that bioelectrochemistry could improve the sludge stabilization degree in STW, accelerate the organic matter degradation and hydrolysis efficiency, and harvest bioelectricity, simultaneously. This technology can provide a new pathway to increase the efficiency of the traditional STW systems.

Operational performance of corncobs/sawdust biofilters coupled to microbial fuel cells treating domestic wastewater

Biofilters coupled to microbial fuel cells (MFCs) are the most integral treatment technology that generate water-energy nexus for rural zones sanitation. Moreover, biofilters coupled to MFCs, using organic residues as bed filter have not been studied. Therefore, the aim of this study was comparatively to evaluate biofilters based on corncobs/sawdust coupled to MFCs treating domestic wastewater. Biofilters based on corncobs/sawdust (50%, v/v) as bed filter incorporating microorganisms (BM), earthworms/microorganisms (BEM, Eisenia foetida Savigny), plants/microorganisms (BPM, Canna indica L.), and all organisms (HB) were evaluated. These biofilters were coupled to 2 electrochemical systems based on graphite cathodes with graphite (G)/stainless-steel mesh (M) anodes. Three nominal hydraulic loading rates (0.3, 0.5, and 1 m³ m^-2 d^-1) evaluating removal of organic matter, nutrients and pathogens were monitored. Voltage within electrochemical systems also were registered. Results demonstrated that biofilters based on corncob/wood chips coupled to MFCs reach mean organic matter removal efficiencies over 80% (COD: 86%, BOD₅: 91%). Nevertheless, HB_G was the most efficient (up to 6%) biofiltration technology monitored. The biofiltration typologies studied reported removal efficiencies of nutrients (NH₃-N, PO₄^3-) and pathogens (fecal coliforms) up to 99%. Specifically, BM_G and HB_G were the biofiltration typologies that registered the highest energy recovery (up to 104 mV, 29 mW m^-2). Within all the biofiltration typologies studied, the hybrid biofiltration coupled to MFCs using graphite (HB_G) is the one that offers the best water-energy nexus conditions, thanks to its biological complexity.

Removal of emerging contaminants by emulsion liquid membrane: perspective and challenges

Emerging contaminants (ECs) originated from different agricultural, biological, chemical, and pharmaceutical sectors have been detected in our water sources for many years. Several technologies are employed to minimise EC content in the aqueous phase, including solvent extraction processes, but there is not a solution commonly accepted yet. One of the studied alternatives is based on separation processes of emulsion liquid membrane (ELM) that benefit low solvent inventory and energy needs. However, a better understanding of the process and factors influencing the operating conditions and the emulsion stability of the extraction/stripping process is crucial to enhancing ELM's performance. This article aims to describe the applications of this technique for the EC removal and to comprehensively review the ELM properties and characteristics, phase compositions, and process parameters.

A review of the bioelectrochemical system as an emerging versatile technology for reduction of antibiotic resistance genes

Antibiotic contamination and the resulting resistance genes have attracted worldwide attention because of the extensive overuse and abuse of antibiotics, which seriously affects the environment as well as human health. Bioelectrochemical system (BES), a potential avenue to be explored, can alleviate antibiotic pollution and reduce antibiotic resistance genes (ARGs). This review mainly focuses on analyzing the possible reasons for the good performance of ARG reduction by BESs and potential ways to improve its performance on the basis of revealing the generation and transmission of ARGs in BES. This system reduces ARGs through two pathways: (1) the contribution of BES to the low selection pressure of ARGs caused by the efficient removal of antibiotics, and (2) inhibition of ARG transmission caused by low sludge yield. To promote the reduction of ARGs, incorporating additives, improving the removal rate of antibiotics by adjusting the environmental conditions, and controlling the microbial community in BES are proposed. Furthermore, this review also provides an overview of bioelectrochemical coupling systems including the BES coupled with the Fenton system, BES coupled with constructed wetland, and BES coupled with photocatalysis, which demonstrates that this method is applicable in different situations and conditions and provides inspiration to improve these systems to control ARGs. Finally, the challenges and outlooks are addressed, which is constructive for the development of technologies for antibiotic and ARG contamination remediation and blocking risk migration.

The influence of external resistance on the performance of microbial fuel cell and the removal of sulfamethoxazole wastewater

Microbial fuel cells (MFCs) are promising equipment for simultaneous treatment of sewage and power generation. External resistance (R_ext) plays a crucial impact in the performance of MFCs in antibiotic wastewater treatment and antibiotic resistance genes (ARGs) reduction. In this study, R_ext and whether to add 20 mg/L sulfamethoxazole (SMX) as variables, it was observed that the performance of several chemical properties of MFCs was optimal when R_ext was 1000 Ω. The power density before and after addition of SMX was 1220.5 ± 24.5 mW/m² and 1186.2 ± 9.2 mW/m², respectively; Furthermore, the degradation rate of SMX was as high as 87.52 ± 1.97% within 48 h. High-throughput sequencing results showed that both R_ext and SMX affected the microbial community and relative abundance of the phylum and genera. Meanwhile, the MFCs with 1000 Ω R_ext generated less the targeted ARGs. Experimental results showed that 1000 Ω was the most suitable R_ext for MFCs in the treatment of antibiotic wastewater.

A taxonomy of design factors in constructed wetland-microbial fuel cell performance: A review

The past decade has seen the rapid development of constructed wetland-microbial fuel cell (CW-MFC) technology in many aspects. The first publication on the combination of constructed wetland (CW) and microbial fuel cell (MFC) appeared in 2012, subsequently, research on the subject has grown exponentially to improve the performance of CW-MFCs in their dual roles of wastewater treatment and power generation. Although significant research has been conducted on this technology worldwide, a comprehensive and critical review of effective controlling parameters is lacking. More broadly, research is needed to draw up-to-date conclusions on recent developments and to identify knowledge gaps for further studies. This review paper systematically enumerates and reviews research studies published in this area to determine the key design factors and their role in CW-MFC performance. Moreover, a taxonomy of all CW-MFC design parameters has been synthesised from the literature. Importantly, this original work provides a comprehensive conceptual framework for future researchers, designers, builders, and users to understand CW-MFC technology. Within the taxonomy, parameters are placed in three main categories (physical/environmental, chemical, and biological/electrochemical) and comprehensive details are given for each parameter. Finally, a comprehensive summary of the parameters has been tabulated showing their impact on CW-MFC operation, design recommendations from literature, and the significant research gaps that this review has identified within the existing literature. It is hoped that this paper will provide a clear and rich picture of this technology at its current stage of development and furthermore, will facilitate a deeper understanding of CW-MFC performance for long-term and large-scale development.

Challenges of aqueous per- and polyfluoroalkyl substances (PFASs) and their foreseeable removal strategies

Per- and polyfluoroalkyl substances (PFASs) are artificial refractory organic pollutants which are widely presented in aqueous environment. Due to the unquiet strength of the highly polarized carbon-fluorine bond (C-F) and their hydrophobic/lipophobic feature as well as biological persistence properties, the remediation and treatment of PFASs is a big challenge. Preliminary studies indicate that a few kinds of technical approaches could remove or transfer PFASs, but the effectiveness is not high as expected or limited while most of the techniques are only tested at laboratory scale. A review of existing treatment technologies was thus conducted for the purpose to outlook these technologies, and more importantly, to propose the foreseeable technique. As such, a constructed wetland-microbial fuel cell (CW-MFC) technology was recommended, which is a newly emerged technology by integrating physical, chemical and enhanced biological processes plus the wetland plants function with strong eco-friendly feature for a comprehensive removal of PFASs. It is expected that the review can strengthen our understanding on PFASs' research and thus can help selecting reasonable technical means of aqueous PFASs control.

Treatment of typical antibiotics in constructed wetlands integrated with microbial fuel cells: Roles of plant and circuit operation mode

This study evaluated the removal efficiencies of sulfamethoxazole (SMX), tetracycline (TC) and their common co-existing contaminants, i.e., chemical oxygen demand (COD) and nitrogen in constructed wetlands integrated with microbial fuel cells (MFC-CWs), as affected by plant, circuit operation mode and influent antibiotic loads. The results demonstrated that MFC-CWs with plant and circuit connection exhibited the best performance in SMX and TC removal. The removal percentages for SMX and TC were 99.70-100% and 99.66-99.85% at HRT of 1 d, respectively, in MFC-CWs with plant and circuit connection when the influent SMX and TC concentrations were 5-100 μg L^-1 and 5-50 μg L^-1. The removal efficiencies of both SMX and TC were mainly enhanced by the circuit connection, compared to the plants. The presence of plant and circuit connection also accelerated the accumulation of SMX and TC in electrode layers, and the residues of both antibiotics in the anode layer were higher than in the cathode layer. Besides, closed-circuit MFC-CWs showed better COD removal performance than open-circuit MFC-CWs, irrespective of the increasing influent COD and antibiotic concentrations. The NH₄⁺-N removal in MFC-CWs was mainly promoted by the presence of plants and decreased with increasing influent antibiotic concentrations. Additionally, the bioelectricity generation of planted MFC-CWs was better than in unplanted systems. The coulombic efficiencies in both planted and unplanted MFC-CWs decreased with increasing influent antibiotic concentrations. In summary, MFC-CWs with plant and circuit connection have potential for the treatment of wastewater containing SMX and TC.

Enhanced denitrification and power generation of municipal wastewater treatment plants (WWTPs) effluents with biomass in microbial fuel cell coupled with constructed wetland

A microbial fuel cell-constructed wetland (MFC-CW) with water hyacinth is established to remove the nitrogen and organics from municipal wastewater treatment plants (WWTPs) effluents. Because insufficient carbon sources in influent might decrease pollutants removal efficiency and electricity generation, this research aimed to select high-quality and low-cost biomass as additional carbon source to improve the performance of MFC-CW. Cellulose and hemicellulose (xylan) were chosen as the biomass. Results indicated that xylan displayed a higher nitrate removal (above 92%) compared with cellulose (10.9%). With xylan as carbon source, the anode packing removed nitrate above 80%, while the cathode packing only removed around 50%. With glucose as sole carbon source, the maximum total nitrogen (TN) removal of MFC-CW was 87.66 ± 4.23%, which was higher than that of MFC (85.58 ± 4.14%). The chemical oxygen demand (COD) and TN in the effluent of MFC-CW were maintained below 25 mg/L and 1.5 mg/L, respectively, with the COD/TN ratio around 5.4 and hydraulic retention time (HRT) at 48 h. The TN removal reached the maximum efficiency of 88.78 ± 3.98% when glucose and xylan ratio was in 40%:60% as composite carbon sources, and COD and TN in the effluent were below 20 mg/L and 1.5 mg/L, respectively. In addition, xylan as the additional carbon source significantly promoted the power density compared with sole glucose. Microbial community diversity in the MFC-CW was significantly higher than that in the single MFC or CW. Proteobacteria and Cyanobacteria_norank were relatively more dominant in the MFC-CW than those in the single MFC or CW, which accounted for high nitrogen removal and power generation. Findings in this study proved that MFC-CW with biomass addition enhanced nitrogen removal and power generation.

Performance of different macrophytes in the decontamination of and electricity generation from swine wastewater via an integrated constructed wetland-microbial fuel cell process

Plants constitute a major element of constructed wetlands (CWs). In this study, a coupled system comprising an integrated vertical flow CW (IVCW) and a microbial fuel cell (MFC) for swine wastewater treatment was developed to research the effects of macrophytes commonly employed in CWs, Canna indica, Acorus calamus, and Ipomoea aquatica, on decontamination and electricity production in the system. Because of the different root types and amounts of oxygen released by the roots, the rates of chemical oxygen demand (COD) and ammonium nitrogen (NH₄⁺-N) removal from the swine wastewater differed as well. In the unplanted, Canna indica, Acorus calamus, and Ipomoea aquatica systems, the COD removal rates were 80.20%, 88.07%, 84.70%, and 82.20%, respectively, and the NH₄⁺-N removal rates were 49.96%, 75.02%, 70.25%, and 68.47%, respectively. The decontamination capability of the Canna indica system was better than those of the other systems. The average output voltages were 520±42, 715±20, 660±27, and 752±26mV for the unplanted, Canna indica, Acorus calamus, and Ipomoea aquatica systems, respectively, and the maximum power densities were 0.2230, 0.4136, 0.3614, and 0.4964W/m³, respectively. Ipomoea aquatica had the largest effect on bioelectricity generation promotion. In addition, electrochemically active bacteria, Geobacter and Desulfuromonas, were detected in the anodic biofilm by high-throughput sequencing analysis, and Comamonas (Proteobacteria), which is widely found in MFCs, was also detected in the anodic biofilm. These results confirmed the important role of plants in IVCW-MFCs.

Degradation pathways, microbial community and electricity properties analysis of antibiotic sulfamethoxazole by bio-electro-Fenton system

Sulfamethoxazole (SMX) is a general antibiotic that is frequently identified in wastewater and surface water. In this study, the degradation and metabolic pathway of SMX by bio-electro-Fenton systems equipped with a CNT/r-FeOOH cathode were investigated. When initial SMX = 25 mg/L, the removal efficiency of SMX reached 94.66% by the bio-electro-Fenton system. The concentrations of sul1, sul2, sul3, sulA, intI1 and 16S rRNA genes were examined in effluents. Four out of the six ARGs analysed were detected. Among all quantified sul genes, sul1 and sulA were the most abundant. High-throughput sequencing revealed that the microbial communities and relative abundance at the phylum and genus levels were affected by different SMX concentrations. In addition, the intermediates were detected and the possible SMX degradation pathway by the bio-electro-Fenton process in the present system was proposed. Furthermore, the highest power density obtained was 283.32 ± 16.35 mW/m² (SMX = 25 mg/L). This study provides an efficient and cost effective method for degrading antibiotics.

Significance of water level in affecting cathode potential in electro-wetland

Bioelectricity production is always restricted by the limited cathode performance in integrated constructed wetland-microbial fuel cells (termed as electro-wetlands). Generally, the cathodes are located at the air-water interface for an oxygen-rich environment. However, its performance may still be unsatisfactory, resulting in a low bioelectricity production. After a long term trial in previous study, we recognised that the position of the electron collector in the cathode significantly affected the bioelectricity production in electro-wetlands. In this study, two cathode configurations of electron collector at the air-water interface and above water level for 1.5 cm, respectively, were evaluated for cell voltage and power density in a vertical up-flow electro-wetland. Results showed that maximum total power density was increased from 31 mW/m² to 165 mW/m² when the cathode electron collector was changed from the air-water interface to 1.5 cm above water level, proving that cathode configuration is the key factor in bioelectricity production.

Influence of amoxicillin after pre-treatment on the extracellular polymeric substances and microbial community of anaerobic granular sludge

A combined process coupling a Fe₃O₄ nanoparticles (Fe₃O₄ NPs) heterogeneous Fenton-like reaction and an anaerobic biological technology was investigated in order to effectively treat amoxicillin-containing wastewater. With the increase in the pretreatment degree, the average COD removal rate correspondingly increased from 84.8% to 92.4% using the anaerobic biological treatment, and the biodegradability and COD removal efficiency was improved by the pretreatment processes. During the process of amoxicillin degradation, hydroxyl free radicals tended to attack the lactamide, amide and pentacyclic rings of amoxicillin. In the excitation-emission matrix (EEM) spectra of soluble microbial products (SMPs), the absorption peak of humic acid gradually decreased with application of the pretreatment. The pretreatment products were more beneficial to the characteristics of anaerobic granular sludge. For the microbial community structure, the proportion of Methanothrix and Clostridia increased with addition the heterogeneous Fenton-like pretreatment, which favored conversion of organic contaminants to volatile fatty acids and biogas.

Optimizing the performance of organics and nutrient removal in constructed wetland-microbial fuel cell systems

No studies have reported the operation optimization of constructed wetland-microbial fuel cell (CW-MFC) systems in terms of pollutant removal under the influence of multiple factors. Multifactor orthogonal experiment (L₂₅(5⁵)) was designed in this study to investigate the influence of multiple factors on the CW-MFC performance and determine the optimal operating conditions for the organics and nutrient removal. The tested factors include volume ratio of granular graphite in the substrates (A), dissolved oxygen (DO) concentration in the cathode zone (B), hydraulic retention time (HRT) (C), effluent reflux ratio (D), and external resistance (E). The results showed that the sequence and degree of the influence of the tested factors were C** > B** > E** > D* > A for chemical oxygen demand (COD_Cr) removal, C** > B** > D* > E > A for ammonia nitrogen (NH₃-N) removal, C** > D** > B** > E* > A* for total nitrogen (TN) removal, and C** > D* > B > A > E for total phosphorus (TP) removal (* denotes significant influence (0.01 < p < 0.05) and ** denotes extremely significant influence (p ≤ 0.01)). HRT was found to be the most influential factor for pollutant removal in CW-MFCs with a contribution of over 50% for COD_Cr, NH₃-N and TP removal, and over 45% for TN removal. The optimal operating conditions for COD_Cr, NH₃-N, TN and TP removal in CW-MFCs were quite different from each other. Comprehensively considering the treatment efficiency of pollutant, treatment capacity of wastewater, and energy consumption from artificial aeration, the selected comprehensive optimal operating conditions for CW-MFCs were A = 20%, B = 1.5 mg/L, C = 1.5 days, D = 50%, and E ≤ 250 Ω. Moreover, incorporating the MFC significantly enhanced the organics and nitrogen removal in CWs by 8.72-11.04% COD_Cr and 9.78-12.04% TN.

Azo dye as part of co-substrate in a biofilm electrode reactor-microbial fuel cell coupled system and an analysis of the relevant microorganisms

In general, refractory organics were hardly used as co-substrate in bioelectrochemical system. This study established a coupled bioelectrochemical system composed of a biofilm electrode reactor and a microbial fuel cell for using the azo dye X-3B as part of co-substrate. The two units degraded the azo dye X-3B stepwise while using it as part of co-substrate. Our results indicated that the removal efficiency of X-3B increased 28.5% using the coupled system compared with a control system. Moreover, the addition of the co-substrate glucose, which was necessary for MFC electricity generation, was reduced on the premise of stable removal efficiency in the coupled system to prevent resource waste due to using X-3B as part of co-substrate. The intermediate products of X-3B degradation were further explored using gas chromatography-mass spectrometry and a X-3B degradation pathway was proposed at the same time. Microbial communities were analyzed, illustrating that the mechanism of X-3B degradation was dependent on bioelectrochemistry rather than on microbial degradation.

Anodic potentials, electricity generation and bacterial community as affected by plant roots in sediment microbial fuel cell: Effects of anode locations

A planted sediment microbial fuel cell (PSMFC) is a promising new technology for harvesting energy and remediating a contaminated geo-environment. In this study, the effects of roots (of Acorus tatarinowii) on oxygen profiles in sediment, power generation, and anodic bacterial community were investigated in PSMFCs and unplanted SMFCs with different anode locations to roots. The presence of plant did not improve the electricity generation when roots were placed on the surface of an anode because a high amount of oxygen loss from roots increased the redox potential at anode and made aerobic bacteria co-exit and compete with electrochemically active bacteria in substance utilization. It was suggested to place the anode under the roots with a proper distance, where the PSMFCs made use of root-derived organics, avoiding the negative effects of oxygen loss. Oxygen loss could control the diurnal rhythm of power generation in the PSMFCs.

Vertical up-flow constructed wetlands exhibited efficient antibiotic removal but induced antibiotic resistance genes in effluent

The intensive use of antibiotics results in their continuous release into the environment and the subsequent widespread dissemination of antibiotic resistance genes (ARGs), thus posing potential risks for public health. Although vertical up-flow constructed wetlands (VUF-CWs) have been widely used to treat wastewater in remote or rural regions, few studies have assessed the potential risks of ARG dissemination when VUF-CWs are applied to treat wastewaters containing antibiotics. In this study, the removal performance of two typical antibiotics (sulfamethoxazole (SMX) and tetracycline (TC)) and the fate of ARGs were evaluated in three lab-scale VUF-CWs. The results indicated that high removal efficiencies (>98%) could be achieved for both SMX and TC. However, the exposure of antibiotics resulted in harboring abundant ARGs (mainly sul- and tet-related genes), even with increasing abundances with operation time. The abundances of ARGs had a positive correlation with the accumulation of SMX and TC in different layers of VUF-CWs, where the tet and sul genes have the highest abundance in the bottom layer due to the highest antibiotic exposure concentration. Positive correlations were observed between the abundance of tet gene and antibiotic concentration in effluent. Although the effluent had lower abundances of the ARGs than that in the wetland media, the occurrence of ARGs in effluent might still pose risk for public health. Further studies are required to explore effective control strategies to eliminate ARGs from VUF-CWs.

A system composed of a biofilm electrode reactor and a microbial fuel cell-constructed wetland exhibited efficient sulfamethoxazole removal but induced sul genes

The aim of this work was to study sulfamethoxazole (SMX) removal efficiency and fate of corresponding sul genes in a stacked microbial fuel cell-constructed wetland coupled biofilm electrode reactor system (MFC-CW-BER). Findings showed that two stacked MFC-CWs could provide a relatively stable electricity supply to support the biofilm for SMX removal. Excellent SMX removal (>99.29%) was obtained in the BER-MFC-CW. Compared with the 2000 µg L^-1 SMX influent, the relative abundance of the sul genes in biofilm media and effluent was enhanced with continuously high concentrations of SMX (4000 μg L^-1). The relative abundances of sul genes in biofilm media and effluent increased as the hydraulic retention time decreased. However, there was no obvious variation in the relative abundance of sul genes in the effluent from MFC-CWs. No effect could be observe of the direct voltage and bioelectricity on the relative abundance of the sul genes in the BER.

Bioprocessing for elimination antibiotics and hormones from swine wastewater

Antibiotics and hormones in swine wastewater have become a critical concern worldwide due to the severe threats to human health and the eco-environment. Removal of most detectable antibiotics and hormones, such as sulfonamides (SAs), SMs, tetracyclines (TCs), macrolides, and estrogenic hormones from swine wastewater utilizing various biological processes were summarized and compared. In biological processes, biosorption and biodegradation are the two major removal mechanisms for antibiotics and hormones. The residuals in treated effluents and sludge of conventional activated sludge and anaerobic digestion processes can still pose risks to the surrounding environment, and the anaerobic processes' removal efficiencies were inferior to those of aerobic processes. In contrast, membrane bioreactors (MBRs), constructed wetlands (CWs) and modified processes performed better because of their higher biodegradation of toxicants. Process modification on activated sludge, anaerobic digestion and conventional MBRs could also enhance the performance (e.g. removing up to 98% SMs, 88.9% TCs, and 99.6% hormones from wastewater). The hybrid process combining MBRs with biological or physical technology also led to better removal efficiency. As such, modified conventional biological processes, advanced biological technologies and MBR hybrid systems are considered as a promising technology for removing toxicants from swine wastewater.