Anoxic biodegradation of triclosan and the removal of its antimicrobial effect in microbial fuel cells

Unveiling microbial degradation of triclosan: Degradation mechanism, pathways, and catalyzing clean energy

Emerging organic contaminants present in the environment can be biodegraded in anodic biofilms of microbial fuel cells (MFCs). However, there is a notable gap existing in deducing the degradation mechanism, intermediate products, and the microbial communities involved in degradation of broad-spectrum antibiotic such as triclosan (TCS). Herein, the possible degradation of TCS is explored using TCS acclimatized biofilms in MFCs. 95% of 5 mgL-1 TCS are been biodegraded within 84 h with a chemical oxygen demand (COD) reduction of 62% in an acclimatized-MFC (A-MFC). The degradation of TCS resulted in 8 intermediate products including 2,4 -dichlorophenol which gets further mineralized within the system. Concurrently, the 16S rRNA V3-V4 sequencing revealed that there is a large shift in microbial communities after TCS acclimatization and MFC operation. Moreover, 30 dominant bacterial species (relative intensity >1%) are identified in the biofilm in which Sulfuricurvum kujiense, Halomonas phosphatis, Proteiniphilum acetatigens, and Azoarcus indigens significantly contribute to dihydroxylation, ring cleavage and dechlorination of TCS. Additionally, the MFC was able to produce 818 ± 20 mV voltage output with a maximum power density of 766.44 mWm-2. The antibacterial activity tests revealed that the biotoxicity of TCS drastically reduced in the MFC effluent, signifying the non-toxic nature of the degraded products. Hence, this work provides a proof-of-concept strategy for sustainable mitigation of TCS in wastewaters with enhanced bioelectricity generation.

Carbide lime as substrates to boost energy recuperation and dyestuff removal in constructed wetland-microbial fuel cell integrated with copper oxide/carbon cloth cathode

Methylene blue (MB) was regarded as a highly toxic and hazardous substance owing to its irreparable hazard and deplorable damage on the ecosystem and the human body. The treatment of this colorant wastewater appeared to be one of the towering challenges in wastewater treatment. In this study, a microbial fuel cell coupled with constructed wetland (CW-MFC) with effective MB elimination and its energy recuperation concurrently based on the incorporation of carbide lime as a substrate in a new copper oxide-loaded on carbon cloth (CuO/CC) cathode system was studied. The crucial influencing parameters were also delved, and the MB degradation and chemical oxygen demand (COD) removal efficiencies were correspondingly incremented by 97.3% and 89.1% with maximum power output up to 74.1 mW m-2 at optimal conditions (0.2 g L-1 carbide lime loading and 500 Ω external resistance). The carbide lime with high calcium ion content was greatly conducive for the enrichment of critical microorganism and metabolic activities. The relative abundances of functional bacteria including Proteobacteria and Actinobacteriota were vividly increased. Moreover, the impressive results obtained in printed ink wastewater treatment with a COD removal efficiency of 81.3% and a maximum power density of 58.2 mW m-2, which showcased the potential application of CW-MFC.

Application of dissimilatory iron-reducing bacteria for the remediation of soil and water polluted with chlorinated organic compounds: Progress, mechanisms, and directions

Chlorinated organic compounds are widely used as solvents, but they are pollutants that can have adverse effects on the environment and human health. Dissimilatory iron-reducing bacteria (DIRB) such as Shewanella and Geobacter have been applied to treat a wide range of halogenated organic compounds due to their specific biological properties. Until now, there has been no systematic review on the mechanisms of direct or indirect degradation of halogenated organic compounds by DIRB. This work summarizes the discussion of DIRB's ability to enhance the dechlorination of reaction systems through different pathways, both biological and biochemical. For biological dechlorination, some DIRB have self-dechlorination capabilities that directly dechlorinate by hydrolysis. Adjustment of dechlorination genes through genetic engineering can improve the dechlorination capabilities of DIRB. DIRB can also adjust the capacity for the microbial community to dechlorinate and provide nutrients to enhance the expression of dechlorination genes in other bacteria. In biochemical dechlorination, DIRB bioconverts Fe(III) to Fe(II), which is capable of dichlorination. On this basis, the DIRB-driven Fenton reaction can efficiently degrade chlorinated organics by continuously maintaining anoxic conditions to generate Fe(II) and oxic conditions to generate H2O2. DIRB can drive microbial fuel cells due to their electroactivity and have a good dechlorination capacity at low levels of energy consumption. The contribution of DIRB to the removal of pesticides, antibiotics and POPs is summarized. Then the DIRB electron transfer mechanism is discussed, which is core to their ability to dechlorinate. Finally, the prospect of future work on the removal of chlorine-containing organic pollutants by DIRB is presented, and the main challenges and further research directions are suggested.

Biological treatment of triclosan using a novel strain of Enterobacter cloacae and introducing naphthalene dioxygenase as an effective enzyme

In recent years, triclosan (TCS) has been widely used as an antibacterial agent in personal care products due to the spread of the Coronavirus. TSC is an emerging contaminant, and due to its stability and toxicity, it cannot be completely degraded through traditional wastewater treatment methods. In this study, a novel strain of Enterobacter cloacae was isolated and identified that can grow in high TCS concentrations. Also, we introduced naphthalene dioxygenase as an effective enzyme in TCS biodegradation, and its role during the removal process was investigated along with the laccase enzyme. The change of cell surface hydrophobicity during TCS removal revealed that a glycolipid biosurfactant called rhamnolipid was involved in TCS removal, leading to enhanced biodegradation of TCS. The independent variables, such as initial TCS concentration, pH, removal duration, and temperature, were optimized using the response surface method (RSM). As a result, the maximum TCS removal (97%) was detected at a pH value of 7 and a temperature of 32 °C after 9 days and 12 h of treatment. Gas chromatography-mass spectrometry (GC/MS) analysis showed five intermediate products and a newly proposed pathway for TCS degradation. Finally, the phytotoxicity experiment conducted on Cucumis sativus and Lens culinaris seeds demonstrated an increase in germination power and growth of stems and roots in comparison to untreated water. These results indicate that the final treated water was less toxic.

Bioelectrochemical stability improvement by Ce-N modified carbon-based cathode in high-salt stress and mechanism research

Although microbial fuel cells (MFCs) have potential for high-salt wastewater treatment, their application is limited by poor salt tolerance, deactivation and unstable catalytic performance. This study designed Ce-C, N-C, and Ce-N modified activated carbon (Ce-N-C) based on the catalytic mechanism and salt tolerance performance of Ce and N elements to address these limitations. With activated carbon (AC) as the control, this study analyzed the stability of the four cathodes under different salinity environments using norfloxacin (NOR) as a probe to assess the effect of cathodes and salinity on MFC degradation performance. After three months, comparing with other three cathodes, the Ce-N-C cathode demonstrated superior and stable electrochemical and power generation performance. In particular, the advantages of Ce-N-C in high-salt (600 mM NaCl) environment is more significant than no-salt or low-salt. The potential of Ce-N-C-End at current density of 0 was 14.0% higher than AC-End, and the power density of the MFC with Ce-N-C cathode was 105.7 mW/m², which was 3.1 times higher than AC. Also, the stability of NOR removal under the function of Ce-N-C improved with the increase of NaCl concentration or operation time. The CeO₂(111) crystal form, N-Ce-O bond and pyridine N might be the key factors in improving the catalytic performance and salt tolerance of the Ce-N modified carbon-based cathode using XPS and XRD analysis.

Evaluation of the Respective Contribution of Anode and Cathode for Triclosan Degradation in a Bioelectrochemical System

In this work, the bioelectrochemical system (BES) is a feasible alternative for successfully degrading typical refractory emerging contaminant triclosan (TCS). A single-chamber BES reactor with an initial TCS concentration of 1 mg/L, an applied voltage of 0.8 V, and a solution buffered with 50 mM PBS degraded 81.4±0.2% of TCS, exhibiting TCS degradation efficiency improvement to 90.6±0.2% with a biocathode formed from a reversed bioanode. Both bioanode and biocathode were able to degrade TCS with comparable efficiencies of 80.8±4.9% and 87.3±0.4%, respectively. Dechlorination and hydrolysis were proposed as the TCS degradation pathway in the cathode chamber, and another hydroxylation pathway was exclusive in the anode chamber. Microbial community structure analysis indicated Propionibacteriaceae was the predominant member in all electrode biofilms, and the exoelectrogen Geobacter was enriched in anode biofilms. This study comprehensively revealed the feasibility of operating BES technology for TCS degradation.

Interpreting the degradation mechanism of triclosan in microbial fuel cell by combining analysis microbiome community and degradation pathway

Microbes play a dominant role for the transformation of organic contaminants in the environment, while a significant gap exists in understanding the degradation mechanism and the function of different species. Herein, the possible bio-degradation of triclosan in microbial fuel cell was explored, with the investigation of degradation kinetics, microbial community, and possible degradation products. 5 mg/L of triclosan could be degraded within 3 days, and an intermediate degradation product (2,4-dichlorophen) could be further degraded in system. 32 kinds of dominant bacteria (relative intensity >0.5%) were identified in the biofilm, and 10 possible degradation products were identified. By analyzing the possible involved bioreactions (including decarboxylation, dehalogenation, dioxygenation, hydrolysis, hydroxylation, and ring-cleavage) of the dominant bacteria and possible degradation pathway of triclosan based on the identified products, biodegradation mechanism and function of the bacteria involved in the degradation of triclosan was clarified simultaneously. This study provides useful information for further interpreting the degradation mechanism of organic pollutants in mixed flora by combining analysis microbiome community and degradation pathway.

Mechanism of visible light enhances microbial degradation of Bisphenol A

Bisphenol A (BPA) is a toxic endocrine disruptor detected in various environments. Microbial metabolic/enzymatic degradation has been thought to be the main pathway for BPA attenuation in natural environments. In this study, we found that under visible light conditions, superoxide produced by bacteria was the main reason for the rapid removal of BPA, accounting for 57 % of the total removal rate. With visible light, the bacteria degraded BPA at a rate of 0.22 mg/L/d, and the total removal within 8 days reached 85 %, which is 4.7 times compared with that of dark culture. The intermediate product 4-iso-propenylphenol, which was considered as an end-product of microbial degradation of BPA in previous reports, was detected in large quantities at 24 h in culture but gradually decreased in our experiment. Community analysis suggested bacteria with aromatic hydrocarbon degradation ability were more enriched under light incubation. Moreover, the bacteria showed well degradation ability to various pharmaceutically active but nonbiodegradable compounds including diclofenac and fluoxetine, with a removal rate of 88 % and 20 %, respectively. Our study revealed the organic pollutant transformation pathway under the combined action of light and microorganisms, providing new insights into the microbial treatment of aromatic hydrocarbon pollutants.

Carbamazepine degradation and genome sequencing of a novel exoelectrogen isolated from microbial fuel cells

Extracellular electron transfer and pharmaceutical products degradation mechanisms of electrochemical active microbial are helpful in optimizing electricity generation and biotoxic contaminants removal for microbial fuel cells (MFCs). An exoelectrogenic bacterial strain (designated as LYK-6) capable of degrading carbamazepine was first isolated from MFCs operated with carbamazepine as unique fuel. The strain LYK-6 was identified as the member of Pseudomonas genus according to morphological characteristics and 16S rRNA gene sequence analysis. Carbamazepine degradation rate of the strain LYK-6 was determined as 56.28% in inorganic salt medium using carbamazepine as sole carbon source. There were two oxidation peaks located at -0.044 V and 0.288 V revealed with differential pulse voltammetry analysis of the strain LQK-6. The maximum voltage of MFCs inoculated the strain LYK-6 reached to 187 mV when the MFCs fed with carbamazepine. The complete genome of the strain LYK-6 was of 4,454,672 bp in length and encoding 4209 protein genes. Genome annotation and functional gene analysis showed that the strain LYK-6 had significant genes encoding proteins responsible for the degradation of carbamazepine. The results demonstrated that the strain LYK-6 was promising application for the treatment of carbamazepine contaminant water by MFCs. This finding increases the known diversity of exoelectrogens.

Effect of Electrode Distances on Remediation of Eutrophic Water and Sediment by Sediment Microbial Fuel Cell Coupled Floating Beds

Efficient and sustainable technologies for cleaning of contaminated water and sediments are in urgent demand. In this study, a new type of sediment microbial fuel cell coupled floating bed (FB-SMFC) was developed to repair eutrophic water and sediment in a cleaner way. The effect of electrode spacing on the power generation capacity and the synchronous remediation of pollutants from eutrophic water and sediment were studied. When the electrode distance was 60 cm, the maximum power generation and pollutant removal effects were obtained. At the end of the experiment, the maximum output voltage was 0.4 V, and the chemical oxygen demand (COD_Cr, potassium dichromate method), total nitrogen (TN), and total phosphorus (TP) contents in the overlying water were 8 mg/L, 0.7 mg/L, and 0.39 mg/L. The corresponding removal rates were 88.2%, 78.8%, and 59.0%, respectively. The removal rates of organic matter and TN in the sediment were 12.8% and 86.4%, respectively, and the fixation rate of TP was 29.2%. Proteobacteria was the dominant phylum of bacteria in the sediment and anode. Many anaerobic bacteria were found in the overlying water, which facilitated denitrification. Overall, the results of this research revealed a highly efficient and reliable strategy for eutrophic water and sediment remediation, aquatic ecosystems restoration, and human health protection.

Assessing the enhanced reduction effect with the addition of sulfate based P inactivating material during algal bloom sedimentation

The typical harm effect of algal bloom sedimentation is to increase sulfides level in surroundings, threatening aquatic organisms and human health; whereas, P inactivating materials containing sulfate are commonly attempted to be used to immobilize reactive P or to flocculate excessive algae in water columns for eutrophication control. In this study, variations in sulfate reduction during algal bloom sedimentation with the addition of sulfate based inactivating materials was comprehensively assessed based on using Al₂(SO₄)₃ with comparison to AlCl₃. The results showed that addition of Al₂(SO₄)₃ had more substantial effect on overlying water and sediment properties compared to those of ACl₃. Al₂(SO₄)₃ can enhance sulfate reduction, resulting in temporary increase of sulfides (p < 0.01) and quick decrease of various Fe (p < 0.01) in overlying water and then promoting the formation of FeS and FeS₂ (determined by EXAFS analysis) in sediments. Most importantly, the increased sulfides, as well as the physical barrier on sediment formed due to Al₂(SO₄)₃ addition, enhanced the transformation of sulfides to odorous contaminants, increasing odorous contaminants (especially methyl thiols) production by approximately one order of magnitude in overlying water. Furthermore, the increased sulfides facilitated to the enrichment of microorganisms related to S cycles (Thiobacillu with relative abundance of 23.8%) and even promoted to enrich bacterial genus potentially with pathogenicity (Treponema) in sediments. The impacts of sulfate tended to be regulated by algae concentration; however, careful management was recommended for sulfate based inactivating materials application to control eutrophication with algal blooms.

Effect of microplastics on microbial dechlorination of a polychlorinated biphenyl mixture (Aroclor 1260)

Microplastics (MPs) and polychlorinated biphenyls (PCBs) generally coexist in the environment, posing risks to public health and the environment. This study investigated the effect of different MPs on the microbial anaerobic reductive dechlorination of Aroclor 1260, a commercial PCB mixture. MP exposure inhibited microbial reductive dechlorination of PCBs, with inhibition rates of 39.43%, 23.97%, and 17.53% by polyethylene (PE), polypropylene (PP), and polystyrene (PS), respectively. The dechlorination rate decreased from 1.63 μM Cl^- d^-1 to 0.99-1.34 μM Cl^- d^-1 after MP amendment. Chlorine removal in the meta-position of PCBs was primarily inhibited by MPs, with no changes in the final PCB dechlorination metabolites. The microbial community compositions in MP biofilms were not significantly different (P > 0.05) from those in suspension culture, although possessing greater Dehalococcoides abundance (0.52-0.81% in MP biofilms; 0.03-0.12% in suspension culture). The co-occurrence network analysis revealed that the presence of MPs attenuated microbial synergistic interactions in the dechlorinating culture systems, which may contribute to the inhibitory effect on microbial PCB dechlorination. These findings are important for comprehensively understanding microbial dechlorination behavior and the environmental fate of PCBs in environments with co-existing PCBs and MPs and for guiding the application of in situ PCB bioremediation.

Bioelectrochemical catabolism of triclocarban through the cascade acclimation of triclocarban-hydrolyzing and chloroanilines-oxidizing microbial communities

Chlorinated antimicrobial triclocarban (3,4,4'-trichlorocarbanilide, TCC) is an emerging refractory contaminant omnipresent in various environments. Preferential microbial hydrolysis of TCC to chloroanilines is essential for its efficient mineralization. However, the microbial mineralization of TCC in domestic wastewater is poorly understood. Here, the bioelectrochemical catabolism of TCC to chloroanilines (3,4-dichloroaniline and 4-chloroaniline) and then to CO₂ was realized through the cascade acclimation of TCC-hydrolyzing and chloroanilines-oxidizing microbial communities. The biodegradation of chloroanilines was obviously enhanced in the bioelectrochemical reactors. Pseudomonas, Diaphorobacter, and Sphingomonas were the enriched TCC or chloroanilines degraders in the bioelectrochemical reactors. The addition of TCC enhanced the synergistic effect within functional microbial communities based on the feature of the phylogenetic ecological networks. This study provides a new idea for the targeted domestication and construction of functionally differentiated microbial communities to efficiently remove TCC from domestic wastewater through a green and low-carbon bioelectrochemical method.

Augmentation of chloramphenicol degradation by Geobacter-based biocatalysis and electric field

Electroactive microorganisms and electrochemical technologies have been separately used for environmental remediation such as antibiotics removal, yet the efficiency of coupling these two methods for chlorinated antibiotics removal is poorly known. Here we tested the synergy of Geobacter sulfurreducens PCA, an electroactive bacteria, and an electrical field, on chloramphenicol removal. Removal is increased two-fold by increasing the temperature from 30°C to 37°C. The cyclic voltammograms and chronoamperometry tests demonstrated that G. sulfurreducens PCA catalyzed chloramphenicol chemical reduction with electrode as excusive electron donor. A critical voltage, -0.6 to -0.5 V vs. Ag/AgCl, was discovered for chloramphenicol degradation with an increase of removal rate about 2.62-folds, from 31.06% to 81.41%. Combined removal with both G. sulfurreducens PCA and an electrical field increased the apparent rate constant and reached 82.77% removal at -0.5 V. Specially, the combined removal at -0.5 V even presented more robust removal efficiency compared to -0.6 V (78.64%) without G. sulfurreducens PCA. Mass spectrometry of degradation products indicates the reduction of nitro into amine groups, and dechlorination into less toxic compounds. Overall, combined biocatalysis and an electrical field is a promising method to remove antibiotics from polluted environments.

Organic matter stabilized Fe in drinking water treatment residue with implications for environmental remediation

Fe-based materials used to adsorb P are commonly considered to be limited by the increased Fe lability, while Fe in drinking water treatment residue (DWTR) shows stable P adsorption abilities. Accordingly, this study aimed to gain insight into Fe lability in DWTR as compared to FeCl₃ and Fe₂(SO₄)₃ using Fe fractionation, EXAFS, and high-throughput sequencing technologies. The results showed that compared to Fe₂(SO₄)₃ and FeCl₃, Fe was relatively stable in the DWTR under the effects of organic matter, sulfides, and anaerobic conditions. Typically, the addition of FeCl₃ and Fe₂(SO₄)₃ enhanced Fe mobility in sediment and overlying water, promoting the formation of Fe-humin acid and ferrous sulfides (FeS and FeS₂). However, the addition of DWTR, even at relatively high doses of Fe, has limited impact on Fe mobility. The addition remarkably increased oxidizable Fe in sediment (by approximately 63%), causing Fe to be dominated by oxidizable and residual fractions (like those in raw DWTR); EXAFS analysis also suggested that Fe-humin acid increased substantially with the addition of DWTR, becoming the main Fe species in sediment (with a relative abundance of 50.1%). Importantly, the Fe distributions were stable in sediment with DWTR added, which demonstrated that organic matter stabilized the Fe in the DWTR. Further analysis indicated that all materials promoted the enrichment of bacterial genera potentially related to Fe metabolism (e.g., Bacteroides, Dok59, and Methanosarcina). Fe₂O₃ in the FeCl₃ and Fe₂(SO₄)₃ groups and Fe-HA in the DWTR group were the key species affecting the microbial communities. Overall, the stabilizing effect of organic matter on Fe in DWTR could be used to develop Fe-based materials to enhance Fe stability for environmental remediation.

Comparison of anaerobic, cycling aerobic/anoxic, and sequential anaerobic/aerobic/anoxic digestion to remove triclosan and triclosan metabolites from municipal biosolids

The antimicrobial triclosan (TCS) is a pervasive and persistent environmental micropollutant which can contaminate land, biota, and water through the land application of biosolids. Many existing sludge management techniques have limited effectiveness against TCS and TCS metabolites including triclosan-sulfate (TCS-SO₄). The objective of this study was to evaluate the impacts of different digestion types (anaerobic, aerobic/anoxic, and sequential anaerobic + aerobic/anoxic), temperatures, and digester sludge retention times (SRTs) on the destruction of organic matter, and on TCS/TCS metabolites. Conventional mesophilic anaerobic digesters (AD), room temperature cycling aerobic/anoxic digesters (AERO/ANOX), and sequential AD + AERO/ANOX digesters were all effective in removing organic matter. The optimum single-stage AD, and AERO/ANOX scenarios were both 20-day SRTs which had 52.3 ± 1.4 and 47.1 ± 3.7% chemical oxygen demand (COD) removals, respectively. Sequential AD + AERO/ANOX digesters improved organic matter destruction, removing up to 68.2 ± 2.1% of COD at an 8-day AD + 12-day AERO/ANOX second-stage (mesophilic) SRTs. While AD showed modest levels of TCS removals (all <40%), TCS was substantially more degradable aerobically with AERO/ANOX removing up to 80.3 ± 2.5% of TCS and nearly all TCS-SO₄ entering the digester at a 20-day SRT. Sequential AD + AERO/ANOX removed virtually all TCS-SO₄ entering the system and improved TCS removals from first stage ADs. However, they were less effective than a single-stage AERO/ANOX digester operating at the same overall SRT. These results demonstrate that AERO/ANOX and sequential AD + AERO/ANOX processes could be used to reduce the amount of TCS, TCS-SO₄ and TCS-related compounds in digested sludge, minimizing the environmental burden of the land application of biosolids.

Facilitated bio-mineralization of N,N-dimethylformamide in anoxic denitrification system: Long-term performance and biological mechanism

Due to highly recalcitrant and toxicological nature of N,N-dimethylformamide (DMF), efficient removal of DMF is challenging for biological wastewater treatment. In this study, an anoxic denitrification system was developed and continuously operated for 220 days in order to verify the enhanced DMF biodegradation mechanism. As high as 41.05 mM DMF could be thoroughly removed in the anoxic denitrification reactor at hydraulic residence time (HRT) of 24 h, while the total organic carbon (TOC) and nitrate removal efficiencies were as high as 95.7 ± 2.5% and 98.4 ± 1.1%, respectively. Microbial community analyses indicated that the species related to DMF hydrolysis (Paracoccus, Brevundimonas and Chryseobacterium) and denitrification (Paracoccus, Arenimonas, Hyphomicrobium, Aquamicrobium and Bosea) were effectively enriched in the anoxic denitrification system. Transcriptional analysis coupled with enzymatic activity assay indicated that both hydrolysis and mineralization of DMF were largely enhanced in the anoxic denitrification system. Moreover, the occurrence of microbial denitrification distinctly facilitated carbon source utilization to produce electron and energy, which was rather beneficial for better reactor performance. This study demonstrated that the anoxic denitrification system would be a potential alternative for efficient treatment of wastewater polluted by recalcitrant pollutants such as DMF.

Synthesis and characterization of Ag0(NPs)/TiO2 nanocomposite: insight studies of triclosan removal from aqueous solutions

Nanocomposite mesoporous Ag⁰(NPs)/TiO₂ thin film materials were synthesized and assessed for its efficient application in the elimination of potentially important drug triclosan from aqueous solutions. A template synthesis using the polyethylene glycol was enabled to obtain Ag⁰(NPs)/TiO₂ nanocomposite materials where zerovalent Ag was in situ doped to the titania network. The nanocomposite materials were characterized by the scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscope (TEM), EDX elemental mapping, X-ray diffraction (XRD) analyses and Brunauer-Emmett-Teller (BET) methods. Further, the diffuse reflectance spectroscopy (DRS) was introduced to estimate the band gap of these solids. The thin film materials were subjected to the remediation of water contaminated with triclosan using the UV-A light. The oxidative elimination of triclosan was demonstrated as a function of pH, concentration of triclosan and presence of several co-existing ions. Increase in pH (4.0-10.0) and triclosan concentrations (0.5-15.0 mg/L) had decreased significantly the percentage degradation of triclosan. The pseudo-first-order kinetics was shown in the degradation of triclosan and rate constant was significantly decreased with the increase in pollutant concentration (0.5-15.0 mg/L) and pH (4.0-10.0). The 1000 times presence of scavengers showed that ^•OH were, predominantly, caused the oxidation of triclosan. Moreover, multiple application of nanocomposite Ag⁰(NPs)/TiO₂(B) revealed that the thin film was fairly intact since the photocatalytic efficiency of triclosan removal was almost unaffected.

Biodegradation of sulfonamides in both oxic and anoxic zones of vertical flow constructed wetland and the potential degraders

The pollution of wastewater with antibiotics and antibiotics resistance genes has attracted public concerns about ecosystem and global health. Swine wastewater can contain high concentrations of antibiotics, especially sulfonamides, even after full-scale wastewater treatment. In this study, mesocosm-scale vertical flow constructed wetlands (VF-CWs) were applied to abate nutrients and antibiotics in swine wastewater containing sulfonamides. VF-CWs performed well in the removal of both nutrients and antibiotics. Sulfonamides did not influence total organic carbon (TOC) and total phosphorus (TP) removal, and even slightly enhanced NH₄⁺-N removal. High removal efficiencies (26.42-84.05%) were achieved for sulfadiazine (SDZ), sulfamethoxazole (SMX) and sulfamethazine (SMZ). Together with lab-scale sorption and biodegradation experiments, microbial degradation was found to be the most important removal mechanism for sulfonamides in VF-CWs. Sulfonamides addition increased bacterial alpha-diversity and changed microbial community structure. Moreover, antibiotics promoted antibiotic-resistant or -degrading bacteria. Bacillus, Geobacter and other seven genera were correlated with sulfonamides reduction under either aerobic or anaerobic condition. In summary, VF-CW is a suitable alternative for swine wastewater treatment, and biodegradation plays the key role in sulfonamides abatement. Main findings of the work. This was the first work to combine bacterial community analysis with microcosm experiments to uncover the major removal mechanism of sulfonamides in constructed wetlands.

Dynamic evolution of electrochemical and biological features in microbial fuel cells upon chronic exposure to increasing oxytetracycline dosage

Dynamic changes in power generation and electrochemical properties were compared between the control microbial fuel cells (C-MFC) and an oxytetracycline (OTC)-treated MFC (O-MFC) on days 84, 139, 174, 224, 295, 307 and 353. The results showed that a high concentration of OTC (>5 mg·L^-1) could inhibit microbial activity and result in a decline of voltage output and power density compared with the same C-MFC. However, with the prolongation of incubation time, the inhibitory effect was gradually weakened. Electrochemical analyses demonstrated that long-term OTC acclimation reduced the ohmic and polarisation resistance of the anode, which was conducive to the recovery of electrochemical performance. More than 99% of 10 mg·L^-1 OTC could be removed within 48 h, and the antibacterial activity of the MFC effluent on Escherichia coli DH5α was conclusively eliminated. High-throughput sequencing analysis revealed that the diversity and richness of the microbial community decreased significantly after long-term OTC enrichment. Acinetobacter, Petrimonas, Spirochaetaceae and Delftia were enriched and played a dominant role in C-MFC stability and power generation. The promotion by Cupriavidus, Geobacter and Stenotrophomonas in simultaneous OTC degradation and bioelectricity generation in the O-MFC was demonstrated.

Enhanced degradation of diclofenac with Ru/Fe modified anode microbial fuel cell: Kinetics, pathways and mechanisms

A microbial fuel cell (MFC) was constructed with a Ru/Fe-modified-anode prepared by reduction and coating for enhancing diclofenac (DCF) degradation. Results showed that Ru⁰ and Fe⁰ were dispersed uniformly on Ru/Fe-modified-electrode surface, and Ru/Fe existed as an alloy structure. Due to catalysis of Ru/Fe, both electrochemical activity and DCF-degradation performance of Ru/Fe-modified-anode-MFC (Ru/Fe-MFC) were enhanced compared to carbon-felt-anode-MFC (CF-MFC). The maximum power density of Ru/Fe-MFC reached 0.600 W m^-2, and DCF-degradation in Ru/Fe-MFC followed the pseudo-first-order-kinetic model with k_obs of 0.711 d^-1 which was 1.08, 1.34 and 2.21 times higher than that of Ru-modified-anode-MFC (Ru-MFC), Fe-modified-andoe-MFC (Fe-MFC) and CF-MFC, respectively. Results also showed that DCF-degradation and power generation would compete for electrons in Ru/Fe-MFC. Ru/Fe-modified-anode accelerated the enrichment of electro-active bacteria and DCF-degrading bacteria such as Geobacter, Clostridium, Sedimentibacter, Pseudomonas and Desulfovibrionaceae. Stepwise dechlornation occurred for DCF-degradation mainly due to synergistic reaction of Ru/Fe and DCF-degrading bacteria within Ru/Fe-MFC.

Triclosan Removal in Microbial Fuel Cell: The Contribution of Adsorption and Bioelectricity Generation

The occurrence of Triclosan (TCS) in natural aquatic systems has been drawing increasing attention due to its endocrine-disruption effects as well as for the development of antibiotic resistances. Wastewater discharge is the main source of water contamination by TCS. In this study, the removal of TCS in microbial fuel cells (MFCs) was carefully investigated. A 94% removal of TCS was observed with 60 mV electricity generation as well as a slight drop in pH. In addition, we found that adsorption also contributed to the removal of TCS in aqueous solution and 21.73% and 19.92% of the total mass was adsorbed to the inner wall of the reactor and to the electrode, respectively. The results revealed that the attenuation of TCS depends on both biodegradation and physical adsorption in the anode chamber. Thus, the outcomes of our study provide a better understanding of the TCS removal mechanism in MFCs.

Nitrate stimulation of N-Methylpyrrolidone biodegradation by Paracoccus pantotrophus: Metabolite mechanism and Genomic characterization

Due to the toxicological nature of N-methylpyrrolidone (NMP), the conventional anaerobic bioprocess is quite ineffective for NMP removal from wastewater. In order to achieve effective NMP biodegradation under anoxic condition, Paracoccus pantotrophus NJUST38 was isolated for the first time. The supplementation of nitrate into anoxic system resulted in complete removal of 5 mM NMP by NJUST38 within 11 h compared to 24% in the anaerobic control system in the absence of nitrate. Genome characterization revealed that NMP biodegradation catalyzed by several key enzymes/genes, including N-methylhydantoin amidohydrolase (hyuB), methyltransferase (cobA), 4-aminobutyrate-2-oxoglutarate transaminase (gabT), succinate-semialdehyde dehydrogenase (gabD) and so on. NMP biodegradation pathway was proposed based on several intermediates, where NMP was biodegraded mainly for providing electrons and reducing power to support microbial denitrification through tricarboxylic acid (TCA) cycle. The proposed mechanism should aid our mechanistic understanding of NMP biodegradation by Paracoccus pantotrophus and the development of sustainable bioremediation strategies.

NanoFe3O4 accelerates anoxic biodegradation of 3, 5, 6-trichloro-2-pyridinol

3, 5, 6-trichloro-2-pyridinol (TCP) is a widespread organic pollutant with persistent, mobile and high antimicrobial effects. Here, nanoFe₃O₄ was firstly introduced into the anoxic biodegradation of TCP. It was found that nanoFe₃O₄ significantly accelerated TCP biodegradation. The removal rate of TCP (100 mg L^-1) increased from 83.03% to 98.74% within 12 h in the presence of nanoFe₃O₄, and the addition of nanoFe₃O₄ also promoted the accumulation of CO₂. Reductive dechlorination mechanism was involved in anoxic biodegradation of TCP. Molecular approaches further revealed that nanoFe₃O₄ distinctly induced the shifts of bacterial community. The dominant genus Ochrobactrum was converted to genus Delftia in nanoFe₃O₄ treatment, and the relative abundance of Delftia increased from 10.26% to 44.62%. Meanwhile, the total relative abundance of bacteria related to TCP dechlorination and degradation significantly increased in the presence of nanoFe₃O₄. These results indicated that nanoFe₃O₄ induced the enrichment of TCP-degrading bacteria to promote the anoxic biodegradation of TCP.

Response of sediment bacterial community to triclosan in subtropical freshwater benthic microcosms

The response of sediment bacterial communities in subtropical freshwater benthic microcosms to sediment-associated triclosan (TCS; 28 d exposure) was analysed using Illumina high-throughput sequencing. This study highlights the interactive effects of TCS and the presence of benthic macroinvertebrates (Limnodrilus hoffmeisteri and Viviparidae bellamya) on sediment bacterial communities. Our results show that TCS alone significantly altered the taxonomic composition and decreased alpha diversity of sediment bacterial communities at concentrations ≥80 μg TCS/g dry weight (dw) sediment (sed). Regarding dominant phyla, TCS significantly reduced the relative abundance of Bacteroidetes and Firmicutes at these concentrations, whereas the relative abundance of Chloroflexi and Cyanobacteria increased. In the presence of benthic macroinvertebrates, the sediment bacterial community was affected by 8 μg TCS/g dw sed as well. However, the presence of benthic macroinvertebrates did not cause measurable changes to bacterial community in unspiked (i.e., control) sediment. These results indicate that TCS alone would not alter the sediment bacterial community at environmentally relevant concentrations (up till 8 μg/g dw sed), but may have an effect in combination with the presence of benthic macroinvertebrates. Therefore, we recommend to include benthic macroinvertebrates when assessing the response of sediment bacterial communities during exposure to environmental stress such as organic contaminants.

Comparative study on ferrate oxidation of BPS and BPAF: Kinetics, reaction mechanism, and the improvement on their biodegradability

Bisphenol S (BPS) and bisphenol AF (BPAF) were increasingly consumed and these compounds are resistant to environmental degradation. Herein, ferrate oxidation of BPS and BPAF was investigated, and biodegradability of the oxidation products was examined. The second-order reaction rate constants of ferrate with BPS and BPAF were 1.3 × 10³ M^-1s^-1 and 3 × 10² M^-1s^-1, respectively, at pH 7.0, 25 °C. In the oxidation process, some BPS molecules dimerized, while other BPS molecules were oxidized through oxygen-transfer process, leading to the formation of hydroxylation products and benzene-ring cleavage products. The dominant reaction of BPAF with ferrate was oxygen-transfer process, and BPAF was degraded into lower molecular weight products. The variation of assimilable organic carbon (AOC) suggested that the biodegradability of BPAF and BPS was largely improved after ferrate oxidation. Compared with the BPS oxidation products, the BPAF oxidation products were easier to be bio-consumed. Pure culture test showed that BPAF inhibited the growth of Escherichia coli, while ferrate oxidation completely eliminated this toxic effect. Co-existing humic acid (HA, 1 mg C/L to 5 mg C/L) decreased the removal of BPS and BPAF with ferrate. Compared with BPAF, more oxidation intermediates formed in the ferrate oxidation of BPS may be reduced by HA to the parent molecular. Thus, the inhibition effect of HA on the ferrate oxidation of BPS was more obvious than that on BPAF.

Development of a novel chem-bio hybrid process using biochar supported nanoscale iron sulfide composite and Corynebacterium variabile HRJ4 for enhanced trichloroethylene dechlorination

A sequential chem-bio hybrid process was developed using a novel biochar supported carboxymethyl cellulose-stabilized nanoscale iron sulfide (CMC-FeS@biochar) as a chemical remover and Corynebacterium variabile HRJ4 as a biological agent for trichloroethylene (TCE) degradation. Compared with CMC-FeS, FeS@biochar600, bare FeS and biochar600, the CMC-FeS@biochar600 composite displayed better physiochemical properties (smaller hydrodynamic diameter and higher stability) and demonstrated excellent removal capacity for TCE from aqueous phase. A facultative bacterial strain, Corynebacterium variabile HRJ4, growing well in the presence of CMC-FeS@biochar (added up to 0.25 g L^-1), further enhanced TCE removal after chemical treatment. The dechlorination pathway proposed based on the gas chromatography-mass spectrometry (GC-MS) analysis revealed that TCE was dechlorinated to cis-1,2-dichloroethene (cis-DCE) and acetylene via hydrogenolysis and β-elimination, respectively within 12 h by CMC-FeS@biochar. Addition of HRJ4 strain into the reaction system effectively enhanced the degradation of the residual TCE, cis-DCE and acetylene to ethylene. Acetylene was the main product in chemical process, whereas ethylene was the main product in biological process as strain HRJ4 could reduce acetylene to ethylene effectively. The results of this study signify the potential application of CMC-FeS@biochar600/HRJ4 chem-bio hybrid system for complete degradation of TCE in the anaerobic environment.

Development of a novel anoxic/oxic fed-batch membrane bioreactor (AFMBR) based on gravity-driven and partial aeration modes: A pilot scale study

A novel pilot gravity-driven anoxic/oxic fed-batch membrane bioreactor (AFMBR) was developed to treat real domestic wastewater. In this process, the anoxic and oxic stages created favorable conditions for stable and continuous nitritation-denitritation/denitrification-nitrification links without adding external carbon source. Excellent removals of organic carbon/nitrogen (NH₄⁺-N: 71-97%, COD: 78-96%, UV₂₅₄: 70-95%, TN: 20-60%) and spontaneous permeability recovery were achieved simultaneously. It was assessed at micro levels by characterizing sludge particle morphologies, microbiota functional evolutions, fouling layer properties and energy consumptions. It was demonstrated that the aerobic granular sludge (AGS) was cultivated successfully. Notable differences of microbial diversity were observed in different regions of AFMBR. The SEM and AFM spectra suggested the loose cake layers can shed automatically due to low pressure and continue flushing. The energy consumption in AFMBR was around 0.042 kWh/m³, far lower than that of conventional MBR. Overall, the AFMBR has a potential on improvement of domestic wastewater treatment.

Interpreting the effects of natural organic matter on antimicrobial activity of Ag2S nanoparticles with soft particle theory

Natural organic matter (NOM) ubiquitously exists in natural waters and would adsorb onto the particle surface. Previous studies showed that NOM would alleviate the toxicity of nanomaterials, while the mechanism is seldom quantitatively interpreted. Herein, the effects of humic substances [Suwannee River fulvic acid (SRFA) and Suwannee River humic acid (SRHA)] and biomacromolecules [alginate and bovine serum albumin (BSA)] on the aggregation and antimicrobial effects of silver sulfide nanoparticles (Ag₂S-NPs) were investigated. The aggregation kinetics of Ag₂S-NPs in electrolyte solutions were in agreement with the results based on Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The dynamic light scattering (DLS) results showed that the SRFA, SRHA, alginate and BSA molecules coated on the Ag₂S-NPs surfaces. The NOM coating layer prevented salt-induced coagulation of Ag₂S-NPs, and the effects of BSA and SRHA on Ag₂S-NPs stabilizing were more obvious than that of SRFA and alginate. Flow cytometry analysis results suggested that BSA and SRHA were more effective on alleviating the Ag₂S-NPs induced cell (Escherichia coli) membrane damage than SRFA and alginate. After interpreting the electrophoretic mobility (EPM) data of the NOM coated Ag₂S-NPs by Ohshima's soft particle theory, it was found that the thickness of the NOM coating layers followed the orders of BSA > SRHA > alginate > SRFA. The E.coli cell membrane damage level was negatively correlated with the thickness and softness of the coating layer. NOM coating may physically alleviate the contact between NPs and E. coli cells and thus attenuate the extent of cell membrane damage caused by the NP-cell interaction. This work provides a new perspective for quantitatively interpreting the influence of NOM on the environmental behaviors and risks of nanomaterials.

Biodegradation of sulfadiazine in microbial fuel cells: Reaction mechanism, biotoxicity removal and the correlation with reactor microbes

Sulfadiazine (SDZ) is a high priority sulfonamide antibiotic and was always detected in environmental samples. This study explored the removal of SDZ in microbial fuel cells (MFCs), in terms of MFC operation, degradation products, reaction mechanism, SDZ biotoxicity removal, and the correlation between microbial community and SDZ removal. SDZ would greatly impact the activity of reactor microbes, and longtime acclimation is required for the biodegradation of SDZ in MFCs. After acclimation, 10 mg/L of SDZ could be removed within 48 h. Liquid chromatographic-mass spectroscopic analysis showed that SDZ could be degraded into 2-aminopyrimidine, 2-amino-4-hydroxypyrimidine and benzenesulfinic acid. Compared with published SDZ biodegradation mechanism, we found that the sulfanilamide part (p-Anilinesulfonic acid) of SDZ would be degraded into benzenesulfinic acid in the system. The effects of background constituents on SDZ biodegradation were explored, and co-existed humic acid (HA) and fulvic acid (FA) could accelerate the removal of SDZ in MFCs. After analyzing the reactor microbial community and the removal of SDZ at different operation cycles, it was found that the relative abundance of Methanocorpusculum, Mycobacterium, Clostridium, Thiobacillus, Enterobacter, Pseudomonas, and Stenotrophomonas was highly correlated with the removal of SDZ throughout the experiment.

Sulfate-reducing mixed communities with the ability to generate bioelectricity and degrade textile diazo dye in microbial fuel cells

The biotreatment of recalcitrant wastes in microbial fuel cells (MFCs) rather than chemical, physical, and advanced oxidation processes is a low-cost and eco-friendly process. In this study, sulfate-reducing mixed communities in MFC anodic chamber were employed for simultaneous electricity generation, dye degradation, and sulfate reduction. A power generation of 258 ± 10 mW/m² was achieved under stable operating conditions in the presence of electroactive sulfate-reducing bacteria (SRB). The SRBs dominant anodic chambers result in dye, chemical oxygen demand (COD), and sulfate removal of greater than 85% at an initial COD (as lactate)/SO₄^2- mass ratio of 2.0 and dye concentration of 100 mg/L. The effects of the COD/SO₄^2- ratio (5.0:1.0-0.5:1.0) and initial diazo dye concentration (100-1000 mg/L) were studied to evaluate and optimize the MFC performance. Illumina Miseq technology for bacterial community analysis showed that Proteobacteria (89.4%), Deltaproteobacteria (52.7%), and Desulfovibrio (48.2%) were most dominant at phylum, class, and genus levels, respectively, at the MFC anode. Integration of anaerobic SRB culture in MFC bioanode for recalcitrant chemical removal and bioenergy generation may lead to feasible option than the currently used technologies in terms of overall pollutant treatment.

Copper removal and microbial community analysis in single-chamber microbial fuel cell

In this study, copper removal and electricity generation were investigated in a single-chamber microbial fuel cell (MFC). Result showed that copper was efficiently removed in the membrane-less MFC with removal efficiency of 98.3% at the tolerable Cu²⁺ concentration of 12.5 mg L^-1, the corresponding open circuit voltage and maximum power density were 0.78 V and 10.2 W m^-3, respectively. The mechanism analysis demonstrated that microbial electrochemical reduction contributed to the copper removal with the products of Cu and Cu₂O deposited at biocathode. Moreover, the microbial community analysis indicated that microbial communities changed with different copper concentrations. The dominant phyla were Proteobacteria and Bacteroidetes which could play key roles in electricity generation, while Actinobacteria and Acidobacteria were also observed which were responsible for Cu-resistant and copper removal. It will be of important guiding significance for the recovery of copper from low concentration wastewater through single-chamber MFC with simultaneous energy recovery.