Labile carbon-induced soil organic matter turnover in a subtropical forest under different redox conditions.

Labile organic carbon (LOC) input strongly affects soil organic matter (SOM) dynamics, including gains and losses. However, it is unclear how redox fluctuations regulate these processes of SOM decomposition and formation induced by LOC input. The objective of this study was to explore the impacts of LOC input on SOM turnover under different redox conditions. Soil samples were collected in a subtropical forest. A single pulse of 13C-labeled glucose (i.e., LOC) was applied to the soil. Soil samples were incubated for 40 days under three redox treatments, including aerobic, anoxic, and 10-day aerobic followed by 10-day anoxic conditions. Results showed that LOC input affected soil priming and 13C-SOM accumulation differently under distinct redox conditions by altering the activities of various microorganisms. 13C-PLFAs (phospholipid fatty acids) were analyzed to determine the role of microbial groups in SOM turnover. Increased activities of fungi and gram-positive bacteria (i.e., the K-strategists) by LOC input could ingest metabolites or residues of the r-strategists (e.g., gram-negative bacteria) to result in positive priming. Fungi could use gram-negative bacteria to stimulate priming intensity via microbial turnover in aerobic conditions first. Reduced activities of K-strategists as a result of the aerobic to anoxic transition decreased priming intensity. The difference in LOC retention in SOM under different redox conditions was mainly attributable to 13C-particulate organic carbon (13C-POC) accumulation. Under aerobic conditions, fungi and gram-positive bacteria used derivatives from gram-negative bacteria to reduce newly formed POC. However, anoxic conditions were not conducive to the uptake of gram-negative bacteria by fungi and gram-positive bacteria, favoring SOM retention. This work indicated that redox-regulated microbial activities can control SOM decomposition and formation induced by LOC input. It is extremely valuable for understanding the contribution of soil affected by redox fluctuations to the carbon cycle.

Enhanced CO2 reduction and acetate synthesis in autotrophic biocathode by N-Hexanoyl-L-homoserine lactone (C6HSL)-based quorum-sensing regulation.

The aim of this study was to investigate the ecological role of quorum-sensing signaling molecule on the autotrophic biocathode for CO2 reduction and acetate synthesis. As a typical quorum-sensing signaling molecule, N-Hexanoyl-L-homoserine lactone (C6HSL) was used to regulate the construction of cathode biofilm. Results showed that the maximum acetate production from CO2 reduction improved by 94.8%, and the maximum Faraday efficiency of the microbial electrosynthesis system enhanced by 71.7%, with the regulation of C6HSL. Electrochemical analyses indicated that higher electrochemical activity and lower charge resistance of biocathode were obtained with C6HSL than without C6HSL. Confocal laser scanning microscopy and electron inhibitor experiment suggested that exogenous C6HSL increased living biomass in the biofilm and facilitated the electron transfer pathway related to NADH dehydrogenase-CoQ and proton motive force. With the C6HSL regulation, the relative abundance of hydrogen producers (e.g., Desulfovibrio and Desulfomicrobium) increased, contributing to the improved performance of autotrophic biocathode.

High current density with spatial distribution of Geobacter in anodic biofilm of the microbial electrolysis desalination and chemical-production cell with enlarged volumetric anode.

The aim of this study was to establish the relationship between spatial distribution of Geobacter and electric intensity in the microbial electrolysis desalination and chemical-production cell (MEDCC) and to investigate the effect of enlarged volumetric anode on the performance of MEDCC. The MEDCC was constructed with nine carbon brush anodes (length × diameter = 11 cm × 3 cm) as enlarged volumetric anode, and operated by feeding with 1 g/L acetate as substrate and 35 g/L NaCl as artificial seawater under the applied voltages of 1.2-4.5 V. Spatial distribution of Geobacter in the anodic biofilm was determined according to the bacterial community analysis on 27 biofilm samples from the top, middle and bottom layers of anodes (i.e., with distance of 4.5, 10, and 15.5 cm to the cathode, respectively). Results showed that the enlarged volumetric anode significantly improved the performance of MEDCC. The maximum desalination rate and current density reached 338.5 ± 21.8 mg/L∙h and 55.7 ± 3.7 A/m2 in the MEDCC, respectively. The electric intensity values decreased with the distance from the anode to the cathode and formed an uneven distribution in the anode chamber. The samples in the top layer of anodes had the highest average 16S rRNA gene copy number of Geobacter of 1.55 × 107 copies/µL, which was 18 times higher than that in the bottom layer of anodes. A linear relation was established between the spatial distribution of Geobacter and electric intensity (R2 = 0.994-0.999). The electric intensity gradient created the uneven spatial distribution of Geobacter in the biofilms of volumetric anode. Results from this study could be useful to enrich Geobacter in the anodic biofilm thus to improve the performance of MEDCC.

Synergistic effect of bioanode and biocathode on nitrobenzene removal: Microbial community structure and functions.

This study aimed to reveal the synergistic effect of bioanode and biocathode on nitrobenzene (NB) removal with different microbial community structures and functions. Single-chamber bioelectrochemical reactors were constructed and operated with different initial concentrations of NB and glucose as the substrate. With the synergistic effect of biocathode and bioanode, NB was completely removed within 8 h at a kinetic rate constant of 0.8256 h-1, and high conversion rate from NB to AN (92%) was achieved within 18 h. The kinetic rate constant of NB removal was linearly correlated with the maximum current density and total coulombs (R2 > 0.95). Increase of glucose and NB concentrations had significantly positive and negative effects, respectively, on the NB removal kinetics (R2 > 0.97 and R2 > 0.93, respectively). Geobacter sp. and Enterococcus sp. dominated in the bioanode and biocathode, respectively. The presence of Klebsiella pneumoniae in the bioanode was beneficial for Geobacter species to produce electricity and to alleviate the NB inhibition. As one of the dominant species at the biocathode, Methanobacterium formicicum has the ability of nitroaromatics degradation according to KEGG analysis, which played a crucial role for NB reduction. Fermentative bacteria converted glucose into volatile fatty acids or H2, to provide energy sources to other species (e.g., Geobacter sulfurreducens and Methanobacterium formicicum). The information from this study is useful to optimize the bioelectrocatalytic system for nitroaromatic compound removal.

Enhanced sulfur recovery and sulfate reduction using single-chamber bioelectrochemical system.

The aim of this study was to investigate the feasibility of sulfate removal and elemental sulfur (S0) recovery in the single-chamber bioelectrochemical system (S-BES). The performance of S-BES was compared with that of dual-chamber bioelectrochemical system (D-BES). The S-BES was constructed with graphite felt as the anode and graphite brush as the cathode. The D-BES was constructed with proton exchange membrane as the separator between anode and cathode chambers. With an applied voltage of 1.0 V and 1 g/L acetate as the substrate, the S-BES and D-BES were tested by feeding with 480 mg/L SO42- in the phosphate buffer. Results showed that the maximum current density of 37.6 ± 4.5 mA/m3 was reached in the S-BES, which was higher than that in the D-BES (i.e., 22.2 ± 2.6 mA/m3). The SO42- removal was much higher in the S-BES than in the D-BES (99.5% vs. 57.2%). In the effluent and the electrodes of S-BES, S0 was identified with Raman and X- Ray diffraction analyses. The S0 recovery on the anode was 13.7 times of that on the cathode of S-BES, indicating that S0 was mainly produced on the anode. The measured total S0 recovery reached 67.5% in the S-BES. High relative abundance of Desulfurella (47.1%) and Geobacter (26.1%) dominated the community in the anode biofilm of S-BES. The excellent performance of S-BES may be attributed to the neutral pH in the solution and the synergistic reaction between the anode and cathode. Results from this study should be useful to enhance the S-BES applications in treating wastewater containing sulfate.

Hydrogen production in single-chamber microbial electrolysis cell under high applied voltages.

The aim of this study was to investigate the performance of single-chamber MEC under applied voltages higher than that for water electrolysis. With different acetate concentrations (1.0-2.0 g/L), the MEC was tested under applied voltages from 0.8 to 2.2 V within 2600 h (54 cycles). Results showed that the MEC was stably operated for the first time within 20 cycles under 2.0 and 2.2 V, compared with the control MEC with significant water electrolysis. The maximum current density reached 27.8 ± 1.4 A/m2 under 2.0 V, which was about three times as that under 0.8 V. The anode potential in the MEC could be kept at 0.832 ± 0.110 V (vs. Ag/AgCl) under 2.2 V, thus without water electrolysis in the MEC. High applied voltage of 1.6 V combined with alkaline solution (pH = 11.2) could result in high hydrogen production and high current density. The maximum current density of MEC at 1.6 V and pH = 11.2 reached 42.0 ± 10.0 A/m2, which was 1.85 times as that at 1.6 V and pH = 7.0. The average hydrogen content reached 97.2% of the total biogas throughout all the cycles, indicating that the methanogenesis was successfully inhibited in the MEC at 1.6 V and pH = 11.2. With high hydrogen production rate and current density, the size and investment of MEC could be significantly reduced under high applied voltages. Our results should be useful for extending the range of applied voltages in the MEC.

Effect of pH on bacterial distributions within cathodic biofilm of the microbial fuel cell with maltodextrin as the substrate.

The aim of this study was to investigate pH effect on stratification of bacterial community in cathodic biofilm of the microbial fuel cell (MFC) under alkaline conditions. A single-chamber MFC with air-cathode was operated with 0.8 g/L maltodextrin and bicarbonate buffer solutions under pH values of 8.5, 9.5, and 10.5, respectively. The cathodic biofilms were characterized by linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), confocal laser scanning microscopy (CLSM), freezing microtome and high-throughput sequencing analysis on bacterial communities, respectively. Results showed that the maximum power densities in the MFC increased with the pH values and reached 1221 ± 96 mW/m2 at pH = 10.5 during ∼30 d of operation. With different pH values, the composition and relative abundance of bacterial community significantly changed in the bottom (0-50 µm), middle (50-100 µm), and top (100-150 µm) layers of the cathodic biofilm. With pH = 10.5, aerobic bacteria accounted for 12%, 13%, and 34% of the bacterial community in the top, middle, and bottom layers, respectively. The amount of anaerobic bacteria in the top and middle layers (i.e., 52%, and 50% of the bacterial community, respectively) was higher than that in the bottom layer (22%). The distribution of aerobic and anaerobic bacteria showed a "valley-peak" structure within the layers. The high CO32- concentration facilitates the hydroxyl transfer and the neutralization in the anode of the MFC under high alkali conditions. The results from this study should be useful to develop new catalyst and cathode in the MFC.

Sulfate reduction and elemental sulfur recovery using photoelectric microbial electrolysis cell.

Elemental sulfur recover from sulfate-rich environment has great significance for the sustainable development of environment and energy. This study aimed to realize simultaneous sulfate reduction and elemental sulfur recovery using a novel photoelectricity microbial electrolysis cell (PMEC) under low applied voltages. At an applied voltage of 1.2 V, the sulfate reduction rate in the PMEC reached 200 ± 2.3 mg L-1 d-1, and 46.3 ± 7.9% of the reduced sulfate converted to elemental sulfur. With increasing voltages from 0.8 to 1.5 V, the sulfate reduction rates enhanced from 37.8 ± 12.4 to 236 ± 18.1 mg L-1 d-1. The recovery efficiency of elemental sulfur from removed sulfate decreased to 35% at 1.5 V, which was attributed to the higher concentration of dissolved oxygen diffusing from the anode side. Sulfate reducing bacteria (including Desulfovibrio and Desulfomicrobium) cooperated with sulfur oxidizing bacteria (including Thiomonas and Acinetobacter) for recovering elemental sulfur that could be regulated by cathode configuration. The study provided an alternative to apply solar energy in biological sulfur recovery and reduce energy consumption of wastewater treatment.

Carbon quantum dots-decorated TiO2/g-C3N4 film electrode as a photoanode with improved photoelectrocatalytic performance for 1,4-dioxane degradation.

In this study, carbon quantum dots (CQDs) were used to decorate a TiO2/g-C3N4 (TCN) film electrode. The morphological, optical, and electrochemical properties of the TiO2/g-C3N4/CQDs nanorod arrays (TCNC NRAs) film were investigated using transmission electron microscopy (TEM), scanning electron microscopy (SEM), UV-vis diffuse reflectance spectroscopy (DRS), photoluminescence (PL), and electrochemical impedance spectroscopy (EIS). The improved optical properties, photoelectrochemical properties and photoelectrocatalytic (PEC) performance of photoanode can be observed by doping CQDs onto the TCN NRAs film. Compared with TiO2 NRAs and TCN NRAs, the narrower band gap of 2.47 eV and longer lifetime of photoinduced electron-hole pairs were observed in the TCNC NRAs. Under visible light irradiation and a bias voltage of 1.2 V, the photocurrent density and 1,4-dioxane (1,4-D) removal rate of PEC process with TCNC NRAs electrode reached 0.16 mA/cm2 and 77.9%, respectively, which was 2.5 times and 1.5 times of that with TCN NRAs electrode. TCNC NRAs electrode could keep >75% of the 1,4-D removal rate during five cycles tests. High PEC performance with TCNC NRAs electrode could be attributed to the enhanced charge separation and the change of electron transfer mechanism from typical heterojunction to Z-scheme, which may increase the active species production and change the dominant reactive species from O2·- to ·OH. Our experimental results should be useful for studying the degradation of 1,4-D and developing efficient PEC materials.

Response of the Intertidal Microbial Community Structure and Metabolic Profiles to Zinc Oxide Nanoparticle Exposure.

The toxicity of nanomaterials to microorganisms is related to their dose and environmental factors. The aim of this study was to investigate the shifts in the microbial community structure and metabolic profiles and to evaluate the environmental factors in a laboratory scale intertidal wetland system exposed to zinc oxide nanoparticles (ZnO NPs). Microbial assemblages were determined using 16S rRNA high-throughput sequencing. Community-level physiological profiles were determined using Biolog-ECO technology. Results showed Proteobacteria was the predominant (42.6%-55.8%) phylum across all the sediments, followed by Bacteroidetes (18.9%-29.0%). The genera Azoarcus, Maribacter, and Thauera were most frequently detected. At the studied concentrations (40 mg·L-1, 80 mg·L-1, 120 mg·L-1), ZnO NPs had obvious impacts on the activity of Proteobacteria. Adverse effects were particularly evident in sulfur and nitrogen cycling bacteria such as Sulfitobacter, unidentified_Nitrospiraceae, Thauera, and Azoarcus. The alpha diversity index of microbial community did not reflect stronger biological toxicity in the groups with high NP concentrations (80 mg·L-1, 120 mg·L-1) than the group with low NP concentration (40 mg·L-1). The average well color development (AWCD) values of periodically submersed groups were higher than those of long-term submersed groups. The group with NP concentration (40 mg·L-1) had the lowest AWCD value; those of the groups with high NP concentrations (80 mg·L-1, 120 mg·L-1) were slightly lower than that of the control group. The beta diversity showed that tidal activity shaped the similar microbial community among the periodically submerged groups, as well as the long-term submerged groups. The groups with high DO concentrations had higher diversity of the microbial community, better metabolic ability, and stronger resistance to ZnO NPs than the groups with a low DO concentration.

Enhanced electron transfer on microbial electrosynthesis biocathode by polypyrrole-coated acetogens.

Extracellular electron transfer (EET) is a significant pathway to transport electrons between bacteria and electrode in microbial electrosynthesis systems (MESs). To enhance EET in the MES, a high-conductivity polymer, polypyrrole (PPy), was coated on the surface of mixed culture acetogens in situ and the PPy-coated bacteria were inoculated on the cathode of MES. The charge transfer resistance of PPy-coated biocathode was 33%-70% of that with PPy-uncoated. Acetate production rate and Faradic efficiency in PPy-coated biocathodes increased by 3 to 6 times. After 960 h operation, Acetobacterium, Desulfovibrio, and Acinetobacter dominate the community on the coated and uncoated biocathode. Quinone loop and NADH dehydrogenase to ubiquinone were involved in electron transfer pathway of biocathode and stimulated by PPy coating. Low-level expression of C-type cytochromes on biocathode indicated its less important role in inward EET. The study provided useful information for applications of high-conductivity chemicals in microbial electrosynthesis.

Influencing pathways of soil microbial attributes on accumulation of heavy metals in brassica (Brassica campestris L. ssp.chinensis var.utilis Tsen et Lee) leaves.

Microbial attributes have a great impact on soil heavy metal bioavailability, yet their influencing pathway on heavy metal accumulation in crop plants remains elusive. This study was aimed to analyze the influencing pathways of microbial attributes, including microbial biomass C and N (MBC and MBN), basal soil respiration (BSR) along with the activities of catalase, urease, and sucrase, on heavy metals (i.e., Cd, Cr, Cu, Ni, Pb, and Zn) accumulation by brassica leaves. Based upon a field investigation close to electroplating factory outlets, 45 pairs of soil and brassica samples were analyzed in the laboratory. Concentrations of heavy metals in brassica leaves declined with sampling distances downstream from the outlets. Redundancy analysis indicated that bioavailable concentrations of Cr, Cu, Ni, and MBC along with catalase activity were the major variables influencing heavy metal accumulation in brassica leaves and accounted for 83% of the accumulation. MBC and catalase activity accounted for 17% of the heavy metal accumulation in brassica leaves. Stepwise regression indicated that catalase activity, MBC, and BSR significantly affected heavy metal accumulation in brassica leaves. Based on structural equation modeling, the pathway coefficient of microbial activities-brassica heavy metals and the pathway coefficient of microbial biomass-brassica heavy metals are 0.122 (P < 0.05), suggesting that these microbial attributes (i.e. MBC along with catalase activities and SBR) could affect heavy metal accumulation in brassica leaves directly. The pathway coefficients of microbial activities-bioavailable heavy metals-brassica heavy metals and microbial biomass-bioavailable heavy metals-brassica heavy metal were -0.541 (P < 0.001) and 0.453 (P < 0.001), respectively, indicating that increase of microbial activities inhibited heavy metal accumulation while increase of microbial biomass promoted heavy metal accumulation, in brassica leaves. These results suggested that heavy metal bioavailability played a mediating role in the influencing pathways of soil microbial attributes on heavy metals in brassica leaves.

Development and environmental implication of pedotransfer functions of Cd desorption rate coefficients in historically polluted soils.

The desorption rate is an important factor determining cadmium (Cd) ecotoxicity and pollution remediation in soils. The pedotransfer functions (PTFs) of desorption rate coefficients of fresh Cd in soils have been developed in literature. We hypothesized that the aging of Cd pollution would alter Cd desorption process. Taking historically polluted soils as the object, this study aimed at testing the hypothesis and developing new PTFs of desorption rate coefficients for historical Cd. 15 d batch extraction experiments and 13 kinetic models were employed to define Cd desorption rate coefficients in 27 historically polluted soil samples. Compared with fresh Cd, the desorption rate coefficients of historical Cd were lower, and the break time of biphasic desorption processes was retarded to 3 d (4320 min). Different with the usual models for fresh Cd desorption (e.g. parabolic diffusion and two constant rate models), the best models to mimic the historical Cd desorption processes were the pseudo first order, logarithmic, Elovich, and simple Elovich models. The rate-limiting step controlling Cd desorption was changed from the intraparticle diffusion to the interface reaction with aging of pollution. New PTFs of desorption rate coefficients of historical Cd were established (R2 ≥ 0.71). Cd desorption rate coefficients increased with organic matter and clay contents, but decreased with oxalate extractable Fe content, solution pH, cation exchange capacity, and silt content. The key soil properties influencing desorption rate coefficients were not altered by the aging of pollution. The developed PTFs could guide us to adjusting the ecotoxicity and pollution remediation of Cd in historically polluted field soils.

Biochar amendment effects on the activities of soil carbon, nitrogen, and phosphorus hydrolytic enzymes: a meta-analysis.

The aim of this meta-analysis was to synthesize the effects of biochar amendment on soil enzyme activities (SEAs) related to carbon (C), nitrogen (N), and phosphorus (P) cycling. Based on 401 paired comparisons from 43 published studies, the SEAs and main influential factors were analyzed in response to biochar characteristics, soil properties, and experiment conditions. Results showed that biochar additions to soils overall increased the N- and P-cycling SEAs by 14 and 11%, respectively. The enhancement of the N- and P-cycling SEAs was mainly attributable to the microbial stimulation by biochar properties (i.e., nutrient content and porosity) and soil nutrients (e.g., soil organic C and total N). The enhancement was the most significant under the conditions with biochars produced at low temperatures and using feedstock materials with high nutrient content, and biochar applications in acidic or neutral soils, coarse or fine soils, and farmland soils. Biochar additions to soils overall reduced the C-cycling SEAs by 6.3%. The C-cycling SEAs were greatly suppressed under the conditions with low and very high biochar loads, biochars produced at high temperatures and with feedstock materials of herb and lignocellulose, and biochar applications in alkaline, fine, and forest soils. The results were mainly related to the adsorption and inhibition effects of biochars and soil properties (e.g., liming effect, high biochar porosity and aromatic C content) on fungi and the enzymes. Biochar feedstock, C/N and load, and soil total N were the main influential factors on the SEAs. The results from this study demonstrate that biochar amendment is beneficial to improving soil N and P cycling and C sequestration.

Engineering banana endosphere microbiome to improve Fusarium wilt resistance in banana.

BACKGROUND: Plant microbiome highlights the importance of endosphere microbiome for growth and health of the host plant. Microbial community analysis represents an elegant way to identify keystone microbial species that have a more central position in the community. The aim of this study was to access the interactions between the keystone bacterial species and plants during banana Fusarium wilt process, by comparing the endophytic bacterial and fungal community in banana roots and shoot tips during growth and wilting processes. The keystone bacterial species were isolated and further engineered to improve banana wilt resistance. RESULTS: Banana endosphere microbiome structure varied during plant growth and wilting processes. Bacterial and fungal diversity in the shoot tips and roots increased with the development of the banana plantlets. The bacterial groups belonging to the Enterobacteriaceae family with different relative abundances were detected in all the samples. The Klebsiella spp. might be the keystone bacteria during the growth of banana plantlets. The relative abundance of Fusarium associated with the wilt disease did not increase during the wilting process. The endophytic Enterobacteriaceae strains Enterobacter sp. E5, Kosakonia sp. S1, and Klebsiella sp. Kb were isolated on Enterobacteriaceae selective medium and further engineered by expressing 1-aminocyclopropane-1-carboxylate (ACC) deaminase on the bacterial cell walls (designated as E5P, S1P, and KbP, respectively). Pot experiments suggested that plants inoculated with strains E5, E5P, S1, and S1P increased resistance to the Fusarium wilt disease compared with the controls without inoculation, whereas the Klebsiella inoculation (Kb and KbP) did not increase the wilt resistance. Compared with the inoculation with the wild strains E5 and S1, the inoculation with engineered strains E5P and S1P significantly increased wilt resistance and promoted plant growth, respectively. The results illustrated that the keystone species in the banana microbiome may not be dominant in numbers and the functional role of keystone species should be involved in the wilt resistance. CONCLUSION: The ACC deaminase activity of engineered bacteria was essential to the Fusarium wilt resistance and growth promotion of banana plants. Engineering keystone bacteria in plant microbiome with ACC deaminase on the cell walls should be a promising method to improve plant growth and disease resistance.

[Impact Mechanisms of Carboxyl Group Modified Cathode on Acetate Production in Microbial Electrosynthesis Systems].

Microbial electrosynthesis systems (MESs) can convert carbon dioxide into added value compounds using microorganisms as catalyst, which is expected to help achieve conversion of greenhouse gases into resources. However, the synthetic efficiency of MESs is far behind the industry requirements. In this study, carbon cloth surfaces were bonded with carboxyl groups by electrochemical reduction of aryl diazonium salts and then used as a cathode in MESs reactors. The results showed that the hydrophilicity of the carbon cloth surfaces improved after the carboxyl groups were modified. However, weaker current of cyclic voltammetry was obtained in the modified cathode. Significant differences were observed between modified (CA-H, CA-M, CA-L) and non-modified cathode (CK) during the start-up period. After 48h, the hydrogen production rate of CA-H, CA-M, CA-L was 21.45, 28.60, and 22.75 times higher than CK. After 120h, the acetate accumulation concentration of CA-H, CA-M, CA-L was 2.01, 2.43, and 1.44 times higher than CK. After 324h, there was little difference in the electrochemical activity of cathodic biofilm and protein content (about 0.47 mg·cm-2) in all groups. The analysis of the community structure of cathodic biofilm showed that, in the genus level, Acetobacterium, Norank_p_Saccharibacteria, and Thioclava were the dominant species, accounting for 59.6% to 82.1%. There was little difference in the relative abundance of Acetobacterium in all groups (31.3% to 40.1%). However, the relative abundance of norank_p_Saccharibacteria in CA-H, CA-M, CA-L, and CK were 16.1%, 24.6%, 31.1%, and 37.5%, respectively. The carboxyl modified cathode had a great influence on the start-up stage of MESs, which could be a new idea for the rapid start-up of MESs.

Efficient reduction of nitrobenzene by sulfate-reducer enriched biocathode in microbial electrolysis cell.

This study aimed to enhance treatment of wastewater containing nitrobenzene (NB) and sulfate using biocathode enriched with sulfate-reducing bacteria in microbial electrolysis cell (MEC). Artificial wastewater with 50 mg L-1 NB and 200 mg L-1 sulfate was used as the catholyte. With 0.8 V applied voltage, removal efficiencies of NB and sulfate reached 98% and 34%, respectively, within 36 h. Aniline and sulfide were the main reductive products in the catholyte with concentrations increased to 0.32 and 0.51 mM, which accounted for 97% and 78% of the removed NB and sulfate, respectively. Sulfate-reducer Desulfovibrio sp. and Wolinella sp. played the dominant role in the biocathode for the reductions of sulfate and NB. Analyses of scanning electron microscope and X-ray photoelectron spectroscopy showed the formation of elemental S on the biocathode surface. The relative abundance of sulfur-oxidizing bacterium Thioclava sp. reached 24% on the biocathode. The results indicated that the oxidation process from S2- to S0 occurred on the biocathode, which provided electrons to biofilm for NB reduction. The MEC with sulfate-reducer enriched biocathode can be used as an alternative to treat complex wastewater containing NB and sulfate.

Impacting Microbial Communities and Absorbing Pollutants by Canna Indica and Cyperus Alternifolius in a Full-Scale Constructed Wetland System.

Wetland plants that cover the wetlands play an important role in reducing pollutants. The aim of this study was to investigate the effect of two plant species on microbial communities and nitrogen-removal genes and to evaluate the contributions of absorbing pollutants by Canna indica (CI) and Cyperus alternifolius (CA) to the removal performance in both a vertical subsurface flow constructed wetland and a horizontal subsurface flow constructed wetland, which were part of a full-scale hybrid constructed wetland system. The microbial assemblages were determined using 16S rRNA high-throughput sequencing. Results showed that the presence of CI and CA positively affected microbial abundance and community in general and which was positive for the total bacteria and ammonia nitrogen removal in the CWs. The higher abundance of Nitrospirae appeared in the non-rhizosphere sediment (NRS) than that in the rhizosphere sediment (RS). More denitrification genes were found in NRS than in RS. The copy numbers of narG, nirS and nosZ genes for CA were higher than those for CI. Wetland plant species can significantly (P < 0.05) affect the distribution of microbial communities in RS. Plant selection is important to promote the development of microbial communities with a more active and diverse catabolic capability and the contribution of plant absorption to the overall removal rate of wetland system can be neglected.

Enhanced sulfate reduction accompanied with electrically-conductive pili production in graphene oxide modified biocathodes.

This study aimed to investigate the graphene oxide (GO) conversion by the sulfate-reducing biocathode and its modified effects on performance of the microbial electrolysis cell (MEC). Biocathodes were acclimated with autotrophic sulfate-reducing cultures using medium containing 500 mg L-1 sulfate. Sulfate reductive rate in the MEC was 230 and 135 g m-3 d-1, respectively, with and without 30 mg L-1 GO addition. Raman measurements showed that GO was efficiently reduced to graphene by the biocathode within 24 h. Higher electrochemical activity and smaller charge transfer resistance were detected on biofilm with GO affected. With high electrical conductivity of 307 ±â€¯36 µS cm-1, pili substance were observed on GO affected biofilm. As dominated by Desulfovibrio sp., the biocathode could use GO as the sole electron acceptor and maintained high activity. The results from this study should provide useful information for applications of nanomaterials in the biocathode MEC.

Development of microbial community within the cathodic biofilm of single-chamber air-cathode microbial fuel cell.

The aim of this study was to investigate the development of microbial community within the cathodic biofilm of single-chamber air-cathode microbial fuel cell (MFC). To analyze microbial community structures within cathodic biofilm, cathodic biofilm samples were stratified into three layers, i.e., the cathode-side layer (0-40 µm), the middle layer (40-80 µm), and the anolyte-side layer (80-120 µm). After four starting cycles (0-188 h), the maximum power densities of the MFC fed with 1 g/L acetate decreased from 1056 ±â€¯110 to 410 ±â€¯50 mW/m2 within 15 cycles (~30 d) of operation. The relative abundance of Pseudomonas gradually increased from 18.9% in the 1st cycle to 50.2% in the 4th cycle. After 15 cycles, the relative abundance of Pseudomonas became 53.8%, 16.4%, and 8.90% in the middle, anolyte-side, and cathode-side layers, respectively. The aerobic bacteria within the cathodic biofilm increased from 24% in the anodyte-side layer to 43% in the cathode-side layer. The relative abundance of Methanobrevibacter was 42.1% and 37.2% after 3 and 15 cycles, respectively. The bacterial community structures were similar among cycles 2, 3, and 4, but significantly different in the 15th cycle. The results from this study should be useful to understand the mechanism of the cathodic biofilm formation and to develop strategies to enhance performance of the MFC.