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Nitrite-dependent anaerobic methane-oxidation (n-damo) is a potential novel technology for nitrogen removal in anaerobic wastewater treatment. In this study, Geobacter sulfurreducens (G) was applied to stimulate n-damo activity. Conductive materials such as nano-magnetite (M) or aggregating agents such as hydroxylapatite (H) were co-added with G. sulfurreducens to further investigate the enhancement effect. Results showed that the nitrite reduction activity of the n-damo culture was promoted by G. sulfurreducens , with 1.71–2.38 times higher in treatment G, G + M, and G + H than that in the control, but was inhibited by the single addition of hydroxylapatite. N-damo bacterial abundances based on the qPCR of the n-damo-specific pmoA gene increased in treatments with G. sulfurreducens , compared with that of the control. High-throughput sequencing analysis revealed the enrichment of uncultured phylum WPS-2 in treatments with G. sulfurreducens. Fluorescence in situ hybridization verified the co-occurrence pattern of n-damo bacteria (NC10), G. sulfurreducens , and type-I aerobic methanotrophs (Methylomonas spp.). The above results corroborated the microbial interspecies electron transfer (MIET) potentiality of the n-damo enrichment. Our study provides a novel pathway for enhancing MIET to stimulate n-damo process. Unlabelled Image • N-damo was enhanced via application with Geobacter sulfurreducens. • Co-adding of G. sulfurreducens and hydroxylapatite enhanced the most significantly. • Uncultured WPS-2 was selectively enriched by addition with G. sulfurreducens. • Co-existence of NC-10, Geobacter , and Methylomonas was detected. [ABSTRACT FROM AUTHOR]

Malodorous surface water is an important worldwide environmental concern. Current remediation methods, such as aeration or the addition of chemicals, are not eco-friendly due to their high energy consumption or secondary pollution. This study proposed a modified columnar air-cathode microbial fuel cell as a sustainable and effective remediation module to improve water quality. The excellent and economic sheet air-cathode (activated carbon and carbon black as the catalyst layer) and a carbon brush anode were applied in the columnar air-cathode microbial fuel cell (MFC). The results after 48 h showed that by providing the anode as an electron acceptor and enriching electrochemically-active bacteria, MFCs with different external resistances (5 k Ω, 30 Ω, and 2 Ω) exhibited the much better capacity to improve water quality than the Blank group. The maximum COD and sulfide removal rates in the MFCs were approximately 86.3% and 100%, respectively, which were higher than those of the Blank group by 30% and 35%, respectively. The MFCs also showed maximum sulfate increments from 28 mg L−1 to 98 mg L−1 compared with the sulfate reduction to 10 mg L−1 in the Blank group. The oxidation reduction potential (ORP) of the MFCs dramatically increased from −281.2 mV to −135.7 mV after 24 h, whereas the ORP of the Blank group decreased to −287.7 mV. The enrichment of the aerobic bacteria Acinetobacter on the anodes and chemolithoautotrophic sulfide oxidation bacteria Sulfuricurvum, Thiovirga and Thiobacillus in the MFCs could also contribute to COD and sulfide removal. Cathode reduction, which could produce small amounts of hydroxyl radicals, might assist with the ORP elevation and the complete oxidation of dissolved sulfide to sulfate. Unlabelled Image • A modified columnar air-cathode MFC is designed for remediation of overlying water in malodorous surface water. • MFC significantly improves COD and sulfide removal rates with sulfate accumulation. • MFC elevates ORP in simulated overlying water dramatically. • MFC enhances the enrichment of chemolithoautotrophic sulfide oxidation bacteria. • Hydroxyl radicals detected in MFC is one possible contributor for remediation. [ABSTRACT FROM AUTHOR]

High sensitivity is essential for the application of bioelectrochemical system-based sensor (BES sensor) in water quality early-warning, where the electroactive biofilm is of vital importance as it delivers a responsive electric signal to toxic substances. This study artificially designed the morphology of a naturally formed biofilm by employing a serrated knife to scrape the biofilm and thus obtained a reduced thickness and roughness. Then it was further cut by half to halve the biomass. BES sensors equipped with control and processed biofilms were operated under constant anode potential (CAP) and tested at different Cu(II) concentrations to study their sensitivities. Results revealed that the scraped biofilms delivered much increased sensitivity towards Cu(II) shock, which was attributed to a reduced thickness as illustrated by macroscopic and microscopic morphology analysis. Another finding was that biomass per unit interfacial area, rather than the biomass, also affected the sensitivity. To further describe how the inner biofilm responded the toxicity after morphology design, a one-dimension mass transfer model was developed to simulate the mass transfer of Cu(II) in the biofilms with different thicknesses. The relative threshold value of inlet Cu(II) concentration was employed to fit the modeling and experimental results, indicating that decreased biofilm thickness was beneficial for improving the sensitivity. Unlabelled Image • Biofilm's morphology design leads to reduced thickness and roughness. • Scraping the biofilm raises the sensitivity by 34%. • Biofilm's thickness is recognized essential factor on sensitivity. • Biomass per unit interfacial area affects the sensitivity. • One-dimension model simulates the Cu(II) transfer in biofilm. [ABSTRACT FROM AUTHOR]

In this study, bacterial mercury (Hg) methylation was investigated under the influence of red-tide algae of Skeletonema costatum (S. costatum). The distribution and speciation of total mercury (THg) and methylmercury (MeHg) were profiled by employing Geobacter metallireducens (G. metallireducens GS-15) as the methylating bacteria. G. metallireducens GS-15 showed different capabilities in methylating different inorganic forms of Hg(II) (HgCl 2) and Hg(II)-Algae (HgCl 2 captured by S. costatum) to MeHg. In the absence of S. costatum , a maximum methylation efficiency of 4.31 ± 0.47% was achieved with Hg(II) of 1–100 μg L−1, while accelerated MeHg formation rate was detected at a higher initial Hg(II) concentration. In the presence of S. costatum , there were distinct changes in the distribution of THg and MeHg by altering the bioavailability of Hg(II) and Hg(II)-Algae. A larger proportion of THg tended to be retained by a higher algal biomass, resulting in decreased methylation efficiencies. The methylation efficiency of Hg(II) decreased from 3.01 ± 0.10% to 1.01 ± 0.01% with 10-mL and 250-mL algal media, and that of Hg(II)-Algae decreased from 0.83 ± 0.13% to 0.22 ± 0.01% with 10-mL and 250-mL Hg(II)-Algae media. Fourier transform infrared spectrometry, surface charge properties and elemental compositions of S. costatum were used to infer that amine, carboxyl and sulfonate functional groups were most likely to interact with Hg(II) through complexation and/or electrostatic attraction. These results suggest that red-tide algae may be an influencing factor on bacterial Hg methylation in eutrophic water bodies. Unlabelled Image • Bacterial Hg methylation was investigated in the Hg-algae-bacteria system. • Bacterial MeHg yield and methylation efficiency depended on algal biomass. • Higher algal biomass reduced the potential risk of bacterial Hg methylation. • S. costatum exerted significant influences on Hg distribution and speciation. • Various functional groups in algal cells were involved in Hg-algae interactions. [ABSTRACT FROM AUTHOR]

Abstract Antibiotic resistance genes (ARGs) discharged through wastewater treatment plants (WWTPs) has aroused growing public concern for its risk to human health and ecological safety. Membrane bioreactor (MBR) has been recognized as an effective approach to remove ARGs in full-scale WWTPs, but its advantage over traditional processes was not clearly quantified. To address this, we investigated four full-scale WWTPs containing parallel MBR and traditional processes (oxidation ditch or sequencing batch reactor) to compare the reduction of eight types of ARGs (bla TEM , ermB , tetW , tetO , sul1 , sul2 , addD , and qnrS) and int1. In general, MBRs reduced the ARGs (1.1–7.3 log removal) better than parallel processes (0.4–4.2 log removal). Notably, the dominant ARGs in the influent, such as ermB , sul1 and int1 (106.39–107.79 copies/mL), were more effectively reduced by MBRs (1.5–7.3 log removal) than traditional processes (0.8–3.4 log removal). Meanwhile, the distribution of those ARGs in activated sludge was not significantly different between aforementioned processes (p > 0.05). The separation coefficient (K sw) was proposed to represent the contribution of solid separation on ARG removal, subsequent analysis revealed surprisingly strong correlation between K sw values of dominant ARGs (ermB , sul1 and int1) and their log removal by MBR (R = 0.79–0.96, p < 0.05), while such correlation was much weaker in traditional process (R = 0.33–0.37), indicating solid separation was the major pathway for removal of dominant ARGs and int1. According to the canonical correlation analysis between process operation and ARG removal in MBR, sludge retention time (SRT) seemed to be the major factor affecting removal of dominant ARGs and int1. This comparative study can be helpful for further understanding and operating MBR process to reduce the ARGs in effluent. Graphical abstract Unlabelled Image Highlights • Four full-scale MBRs were compared with parallel OD and SBRs in ARG removal. • MBR showed 1–3 orders of magnitude higher to remove ARGs than parallel processes. • ARGs in activated sludge were distributed similarly in MBR and the parallel processes. • Separation coefficient was proposed and correlated with ARG removal in MBR process. • Influence of operational parameters on ARG removal in MBR was discussed by CCA. [ABSTRACT FROM AUTHOR]

Based on the new syntrophic methanogenesis route via direct interspecies electron transfer (DIET), a novel bioaugmentation method by adding exoelectrogenic Geobacter species to accelerate methanogenesis was developed in this study. Geobacter sulfurreducens PCA, type exoelectrogenic strain of Geobacter species was chosen for the research. To clarify the effect of G. sulfurreducens on methanogenesis, batch tests of CH 4 production were carried out. Acetate, the most typical precursor of methanogenesis was chosen as the substrate of batch tests. Amendment of G. sulfurreducens accelerated CH 4 production remarkably. The lag phase of CH 4 production was shortened, and the maximum CH 4 production rate was increased by 78%. Fluorescence in situ hybridization showed that G. sulfurreducens closely gathered with methanogens. For the archaeal communities, the high-throughput sequencing results demonstrated that Methanosaetaceae and Methanobacteriaceae were potential bioaugmented methanogens. We speculated that the accelerated methanogenesis by adding G. sulfurreducens may result from the syntrophic association between G. sulfurreducens and methanogens affiliated with Methanosaetaceae and Methanobacteriaceae . This research provides a new route to enhance methanogenesis through the utilization of G. sulfurreducens . Through this study, the role of Geobacter in the anaerobic engineering and carbon cycling of nature should be paid more attention. [ABSTRACT FROM AUTHOR]

Antibiotic resistance genes (ARGs) in environment have become a growing public concern, due to their potential to be obtained by pathogens and their duplication along cell division. Horizontal gene transfer (HGT) was reported to be responsible for ARGs dissemination in microbes, but the HGT feature in environmental biofilm was still unclear due to insufficient assay tools. To address this challenge, we applied a novel microfluidic system to cultivate thin biofilm by continuous supply of nutrients and close contact between cells. Resembling the living state of biofilm in open environment, this chip visualized the transfer of ARG-encoded plasmids RP4 and pKJK5 to the receptors, e.g., activated sludge bacteria. The average plasmid transfer frequency per receptor (T/R) from RP4-hosted Pseudomonas putida KT2440 to activated sludge bacteria was quantified to be 2.5 × 10 −3 via flow cytometry, and T/R for pKJK5-hosted Escherichia coli MG1655 was 8.9 × 10 −3 , while the corresponding average frequencies per donor (T/D) were diverse for the two host strains as 4.3 × 10 −3 and 1.4 × 10 −1 respectively. The difference between T/R and T/D was explained by the plasmid transfer kinetics, implying specific purposes of the two calculations. Finally, we collected the transconjugants by fluorescent activated cell sorting and further sequenced their 16S rDNA. Bacteria from phyla Proteobacteria and Firmicutes were found more susceptible to be transconjugants than those from Bacteroidetes . Our work demonstrated that microfluidic system was advantageous in biofilm HGT study, which can provide more insights into environmental ARG control. [ABSTRACT FROM AUTHOR]

Effects of sewage sludge-derived biochar and its precursor on the accumulation of metals (Cd, Cu, Pb and Zn) in soil and their uptake by plants in a 1-year field experiment involving corn-radish rotation were comparatively studied. The human health risks were assessed, and the safe application period of biochar were estimated. The application of biochar, compares to sewage sludge, significantly enhanced the radish yield (p < 0.05; not corn yield) and significantly reduced the accumulation of metals in both plants (p < 0.05), especially the annual application at ≤15 t ha−1. The hazard quotient analyses of the metals showed there were no health risks to humans (Hazard Index < 1) in consuming the edible parts of the both plants. The application of sewage sludge at ≥15 t ha−1 resulted in Cd in radish exceeded the threshold for foodstuffs set by China (0.1 mg kg−1). The total contents of Cd, Cu, Pb and Zn in soil increased gradually as the application of sewage sludge or its biochar increased from 7.5 t ha−1 to 30 t ha−1. More metals were found to be introduced to soil by the land application of biochar than by its precursor at the same doses, because the metals were concentrated in biochar during the preparation process. The contamination risk assessment of soil based on the geo-accumulation index, the contamination factor and the pollution load index suggested the application of biochar on farmland should <15 t ha−1. Therefore, taking into account the yield of and metal concentrations in the radish and corn plants and the contamination risks in soil, it is recommended that the continuous safe application period at an application of 7.5 t ha−1 year−1 of biochar should not exceed 15 years, and that of its precursor sewage sludge should not exceed 17 years. Unlabelled Image • The soil-plant-human health risks by application of sludge biochar were assessed. • The safety application years of sludge biochar in farmland were estimated. • Metals in radish and corn were lowered by application of biochar than sludge. • More metals were loaded into soil by application of biochar than sludge. • The max safety application years for biochar was 15 y at a dose of 7.5 t ha−1 y−1. [ABSTRACT FROM AUTHOR]

Sulfur autotrophic denitrification utilizes elemental sulfur as the electron donor for nitrate removal from aquatic environments. Organic carbon could stimulate the conversion of sulfur and facilitates the S0-based denitrification process in the mix-trophic. In this study, the co-cultured system of sulfur reducer (Geobacter sulfurreducens) and Thiobacillus denitrificans was used to investigate that how organic carbon could boost the S0-based denitrification. The results showed that the rate of S0-based denitrification was improved with C/N ratio of 0.13 and this improvement continued even after the acetate was exhausted. Sulfur probe test and Raman analysis suggested that reduced sulfur species (S x 2−) were formed with the addition of organic carbon. The S x 2− could recombine with element sulfur and the bioavailability of S0 would be improved, as a result, the rate of S0-based denitrification increased as well. Nitrate reduction rate could further increase with the C/N ratio of 0.88, but it would decrease significantly when the C/N ratio increased to 1.50 as the high concentration of generated S2−. Our results provided explanations that why organic carbon addition would improve the bioavailability of S0 which could further promote the S0-dominant denitrification process. Unlabelled Image • Organic carbon can boost the S0-based denitrification of co-culture system. • Geobacter sulfurreducens could convert S0 to reduced sulfur species (S x 2−). • Sulfur bioavailability could be improved by the sulfur conversion process. [ABSTRACT FROM AUTHOR]

This study aims to explore the application of sulfur-based constructed wetlands (CWs) for effective nitrogen (N) removal from wastewater. Two solid sulfur sources namely elemental sulfur (S0) and pyrite (FeS 2) were used as substrates in two CWs, i.e. S-CW and P-CW, respectively. The CWs were vegetated with a common wetland plant Iris pseudacorus , and were operated to investigate the effects of hydraulic retention time (HRT) and temperature on N removal. The use of S0 resulted in the highest denitrification rate (19.0 ± 7.5 g m−2 d−1), whereas up to 20 times slower total inorganic nitrogen (TIN) removal was observed with FeS 2. Different sulfur sources had negligible effects on the growth of I. pseudacorus , but the element contents (e.g., N, S, and P) within the plant tissues were different. Iris roots in S-CW had higher S content compared with those in P-CW, which resulted in the difference in shoots colors. The characteristics of rhizospheric microbial communities were closely related to the sulfur and nitrogen sources. Briefly, denitrifying and sulfur-oxidizing genera (e.g., Denitratisoma , Sulfurimonas , Thiobacillus) were dominating in the S-CW, suggesting the occurrence of both autotrophic and heterotrophic denitrification processes in the wetland. On the other hand, nitrifying bacteria were more abundant (e.g. Nitrospira , Piscinibacter) in the P-CW. S0 layer and rhizosphere accounted for 99.3% of nitrogen removal and the former part most likely played important roles with a decrease in HRT. Low temperature strongly affected the rate and efficiency of denitrification but recovered to 49.2 ± 25.8% when added with 30 mg L−1 sodium acetate. This study broadens the applications of sulfur-based CWs and provides a promising management strategy for denitrification at low temperatures. Unlabelled Image • N removal was better in S-CW (3.4–19.0 g m−2 d−1) than P-CW (0–1.0 g m−2 d−1). • S0/FeS 2 affected element distributions in Iris pseudacorus and shaped rhizospheric microbes accordingly. • Short HRT (6–12 h) is recommended for S-CW operation in case of NH 4 +-N accumulation. • S0 layer and rhizosphere accounted for 99.3% of N removal in S-CW. • NaAC addition recovered N removal of S-CW which was restricted by low temperature. [ABSTRACT FROM AUTHOR]

Anaerobic ammonium oxidation (anammox) is recognized as the most cost-effective process for nitrogen removal from wastewater. In this study, effects of polyethylene plastics, nonwoven fabric, granular activated carbon (GAC) and polyurethane sponge as buoyant carriers were evaluated in lab-scale moving bed biofilm reactors (MBBRs). The overall performance of MBBRs with four types of carriers from priority to inferiority was noticed as, GAC, nonwoven fabrics, polyurethane sponge and polyethylene plastics under the same packing ratio of 20 v% and an average carrier size of 4 × 4 × 4 mm. The hydrophobic surface of GAC could selectively adsorb hydrophobic protein and favor anammox bacteria attachment, which contributed to achieving a total nitrogen removal rate of 0.40 kg-N/(m3·d) in 60 days. In conclusion, our results provide compelling evidence for achieving effective anammox process in an MBBR with GAC carriers and would benefit towards accomplishing a stable partial nitritation-anammox process in the future. Unlabelled Image • Anammox-MBBR with GAC achieved a TNRR 0.40 kg-N/(m3·d) in only 60 days. • GAC and nonwoven fabrics carrier could greatly enhance denitrification efficiency. • High positive correlations among EPS production, amx abundance and performance • Hydrophobic surface of GAC could selectively adsorb hydrophobic protein. • The anammox biofilm on GAC contributes to fast start-up and stable operation. [ABSTRACT FROM AUTHOR]

Changes in the biogeochemical cycling of mercury (Hg) and Hg species were investigated in a typical marine aquaculture area located at Zhoushan island, Zhejiang province, east China. Mercury species were analyzed in different environmental samples collected during a field survey and a simulation batch experiment. The field work comprised both summer and winter collection of water and sediment samples from marine aquaculture sites (MAS) in a field survey and from corresponding reference sites (CRS) located 2500 m from the MAS. THg concentrations in water were 91.3 ± 70.3 and 115 ± 22.6 pmol L−1 in summer and winter, respectively. Particulate Hg accounting for ˃60% of THg and positively correlated with total suspended solid content in water. Dissolved organic carbon in water was positively correlated with dissolved Hg. Significantly higher (p < 0.001, F = 102) total methylmercury (TMeHg) contents were observed in MAS (0.31 ± 0.26 ng g−1) than in CRS (0.06 ± 0.03 ng g−1) in the sediment solid phase. Moreover, MeHg formation rate in MAS was clearly higher than in CRS in the simulation experiment. Both the field survey and the simulation experiment highlighted the readier formation of MeHg in MAS than in CRS. TMeHg levels in blackhead seabream (Acanthopagrus schlegelii), red snapper (Lutjanus campechanus) and perch (Perca fluviatilis) were only 52.7 ± 5.74, 23.7 ± 2.51 and 24.3 ± 3.86 ng g−1, values significantly lower than the safety guideline (1000 ng g−1) established by the World Health Organization. Unlabelled Image • THg concentration in water was 91.3 pmol·L−1 and PHg account for 63.4% of THg. • Fish farming increased THg accumulation and MeHg formation in sediment. • Suspended solid influence the Hg distribution and sedimentation in water. • MeHg concentration in fish tissues was significantly lower than WHO guidelines. [ABSTRACT FROM AUTHOR]

Anaerobic digestion is an effective biological treatment process that produces methane by degrading organic compounds in waste/wastewater. It is a complicated microbial process by metabolic interactions among different types of microorganisms. In this process, efficient interspecies electron transfer between secondary fermenting bacteria and methanogens is the critical process for fast and effective methanogenesis. In syntrophic metabolism, hydrogen or formate has been considered as the conventional electron carrier transferring electrons from secondary fermenting bacteria to hydrogenotrophic methanogens. Recently, direct interspecies electron transfer (DIET) without the involvement of dissolved redox mediators is arousing great concerns and has been regarded as a more efficient and thermodynamically favorable interspecies electron transfer pathway for methanogenesis. Interspecies electron exchange through DIET is accomplished via the membrane-bound cytochromes or conductive pili. Several kinds of exogenously-added conductive or semiconductive iron oxides have been discovered to greatly enhance anaerobic methanogenesis through promoting DIET. Different (semi)conductive iron oxides give a boost to DIET through different mechanisms based on the physicochemical properties of the iron oxides and the reciprocal interactions between iron oxides and functional microorganisms. In this review, the current understanding of interspecies electron transfer in syntrophic-methanogenic consortions is summarized, the effects and deep-rooted mechanisms of (semi)conductive iron oxides on methanogenesis and DIET are discussed, and possible future perspectives and development directions are suggested for DIET via (semi)conductive iron oxides in anaerobic digestion. Unlabelled Image • Interspecies electron transfer is the critical step for syntrophic methanogenesis. • H 2 acts as diffusive electron carriers between syntrophic partners in IHT pathway. • DIET is established by biological electrical connections instead of diffusive H 2. • (Semi)conductive iron oxides promote syntrophic methanogenesis by enhancing DIET. • Electric microbial syntrophy network is built by (semi)conductive iron oxides. [ABSTRACT FROM AUTHOR]

Sulfur autotrophic denitrification has been proved feasible for nitrate removal from aquatic environments and it utilizes elemental sulfur as the electron donor. A maximum denitrification rate of 194.57 mg N/L·d was achieved with biogenic sulfur as electron donor in a mixed culture collected from sulfur packed bed reactors; this rate was considerably higher than that delivered by α-S 8 or μ-S in the same mixed culture. The elemental sulfur was also tested in the pure culture of Thiobacillus denitrificans , while a lower denitrification rate was noted than in the mixed culture, bio-S (4.86 mg N/L·d) again outperformed other two elemental sulfur's. X-ray absorption near edge structure spectra were collected to examine possible metabolic intermediates during the sulfur autotrophic denitrification process. The analysis revealed the existence of two major intermediates: DL-cysteine and L-cystine. They were found to not only provide electrons but also play a critical role in promoting the elemental sulfur-mediated sulfur autotrophic denitrification process. In general, we investigated the formation and enhancement effects of sulfur intermediates in the sulfur autotrophic denitrification process. Unlabelled Image • Three forms of sulfurs were used for So-based denitrification process. • Bio-S could achieve the best nitrogen removal performance. • XANES analysis revealed the existence of DL-cysteine and L-cystine in bio-S. • DL-cysteine and L-cystine were able to improve So-based denitrification process. [ABSTRACT FROM AUTHOR]