•Nickel foam was used as alternative supporting base to replace expensive carbon cloth in MECs.•The hydrogen production rate and catalytic performance of Pt/NF cathodes were evaluated.•The economic analysis showed a 56% reduction using Pt/NF in place of Pt/carbon cloth.A cheap but efficient electrode material is required to explore and apply to microbial electrolysis cell (MEC) with high hydrogen evolution reaction (HER) efficiency and low over-potential loss. Pt coating carbon cloth (Pt/CC) was one of the most efficient catalyst for hydrogen production in current lab research, but it is difficult to be applied in practice because of expensive cost and week strength from the base material (carbon cloth). Thus a cheap and effective supporting base material is worth to evaluate on hydrogen recovery and loss to methane for the MEC future application. In this study, nickel foam (NF) was used as an alternative to expensive carbon cloth, and NF coated with Pt (Pt/NF) was applied and evaluated through catalytic performance, hydrogen production efficiency and economic assessment in comparison with Pt/CC. The Pt/NF showed a competitive HER performance to Pt/CC. The highest hydrogen yield was reached 0.71 ± 0.03 m3/m3·d by Pt/NF under 0.8 V, which exceeded 6%, 10% over Pt/CC and NF, respectively. The energy efficiency relative to the electrical energy input was 127% for Pt/NF and 123%, 110% for Pt/CC and NF, respectively. For fifteen cycles, the methane content of Pt/NF got the lowest due to its higher hydrogen evolution activity. The economic analysis showed a 56% reduction when using Pt/NF as supporting base in place of carbon cloth to achieve similar performance. The linear sweep voltammetry (LSV) showed the possibility to further reduce input voltage in a long term operation.

The Fenton reagent has recently been verified as being effective for lignocellulose pretreatment. However, the Fenton reaction can only work under acidic conditions, leading to severe environmental pollution and increasing the cost for sewage treatment. This has made identification of iron chelates that could enhance Fenton degradation under neutral conditions important. In this study, citric acid, a non-toxic polyhydroxy carboxylic acid, was introduced as an iron chelate in Fenton pre-treatment of rice straw. Results demonstrated that citric acid has the ability to (i) maintain the oxidation capacity of the Fenton reagent under near-neutral conditions, (ii) enhance the degradation of lignin and reduce the crystallinity of rice straw from 0.41 to 0.21, (iii) promote the saccharification of rice straw (the maximum saccharification ratio of 35.7% was two-fold higher than that for the untreated rice straw), and (iv) elevate the maximum activity of β-glucosidase from 0.33 IU mL−1 to 0.61 IU mL−1. Moreover, the effect of operational parameters such as pH and processing time on the saccharification of rice straw by Fenton pretreatment with and without citric acid has been demonstrated. The findings strongly support Fenton plus citric acid as an efficient and environmentally friendly lignocellulose pretreatment method.

•A hybrid anaerobic reactor with built-in BES was efficient for azo dye removal.•The appropriate volume ratio between anaerobic sludge and cathode was 1:1.•BES module presented higher electron utilization efficiency.A hybrid anaerobic reactor with built-in bioelectrochemical system (BES) has been verified for efficiently treating mixed azo dye wastewater, yet still facing many challenges, such as uncertain reactor construction and insufficient electron donors. In this study, an up-flow hybrid anaerobic reactor with built-in BES was developed for acid orange 7 (AO7) containing wastewater treatment. Cathode and real domestic wastewater both served as electron donor for driving azo dye decolorization. The decolorization efficiency (DE) of AO7 (200 mg/L) in the hybrid reactor was 80.34 ± 2.11% with volume ratio between anaerobic sludge and cathode (VRslu:cat) of 0.5:1 and hydraulic retention time (HRT) of 6 h, which was 15.79% higher than that in BES without sludge zone. DE was improved to 86.02 ± 1.49% with VRslu:cat increased to 1:1. Further increase in the VRslu:cat to 1.5:1 and 2:1, chemical oxygen demand (COD) removal efficiency was continuously improved to 28.78 ± 1.96 and 32.19 ± 0.62%, but there was no obvious DE elevation (slightly increased to 87.62 ± 2.50 and 90.13 ± 3.10%). BES presented efficient electron utilization, the electron usage ratios (EURs) in which fluctuated between 11.02 and 13.06 mol e−/mol AO7. It was less than half of that in sludge zone of 24.73–32.06 mol e−/mol AO7. The present work optimized the volume ratio between anaerobic sludge and cathode that would be meaningful for the practical application of this hybrid system.

•Bioelectrochemistry significantly regulates the anaerobic digestion process.•Applying voltage has significant influence on fermentation community structure.•Bioelectrochemical reaction positively changes acidogenesis pathway.•It is an energy-favorable strategy to start AD at high voltage but operate at low.Methane production was tested in membrane-less microbial electrolysis cells (MECs) under closed-circuit (RCC) and open-circuit (ROC) conditions, using glucose as a substrate, to understand the regulatory effects of bioelectrochemistry in anaerobic digestion systems. A dynamic model was built to simulate methane productions and microbial dynamics of functional populations, which were colonized in groups RCC and ROC during the start-up stage. The experiment results showed significantly greater methane production in RCC than ROC, the average methane production of RCC was 0.131 m3/m3/d, which was 1.4 times higher than that of ROC (0.055 m3/m3/d). The simulation results revealed that bioelectrochemistry had a significant influence on the abundance of microorganisms involved in acidogenesis and methanogenesis. The abundance of glucose-uptaking microorganisms was 87% of the total biomass in ROC without applied voltage, which was 20% higher than that in RCC (67%) when external voltages were applied between the anode and cathode. The abundance of hydrogenotrophic methanogens in RCC was 6% higher than that in ROC. The simulation results were verified through 16S rDNA high-throughput sequencing analysis. An electron balance analysis revealed that alteration of the acidogenesis type led to more acetate and hydrogen production from glucose fermentation, compared with the situation without bioelectrochemistry. An additional pathway from acetate to hydrogen was introduced by bioelectrolysis. These two factors resulted in significant enhancement of methane production in RCC. Bioelectrolysis process directly contributed to 26% of the total methane production after the start-up stage. When the applied voltages were cut down or decreased, RCC could maintain considerable methane productions, because the microbial communities and electron transfer pathways were already formed. Starting-up with high voltage, but operating under low voltage, could be an energy-favorable strategy for accelerating biogas production in bioelectro-anaerobic bioreactors.Download high-res image (426KB)Download full-size image

•The size and distribution of Pd-cell NPs are affected by the ratio of CDW to Pd.•The quantitative characterization strategy of Pd associate with cell is proposed.•Pd-cell can be used as valid catalyst for the catalytic reduction of NB and 4-CP.•Catalytic activity of suspended Pd-cell catalyst is ruled by exposed area of Pd NP.•The conductivity of electrocatalyst Pd-cell determines its catalytic effectiveness.The palladized cell (Pd-cell) could be used as an efficient catalyst in catalyzing the degradations of a wide variety of environmental contaminants. Nevertheless, when the Pd NPs associate with the bacteria, the catalytic activity likely significantly affected by the biomass. Quantitative indicators that characterize of Pd-cell are necessary and little attention has been paid to investigate how the catalytic efficiency of Pd-cell is affected by the size and distribution of Pd NPs. To fill this gap, we explored the roles of the above-mentioned key factors on the performance of Pd-cell in catalyzing the degradations of two aromatic contaminants (nitrobenzene and p-chlorophenol) in two commonly used scenarios: (1) using Pd-cell as suspended catalyst in solution and (2) using Pd-cell as electrocatalyst directly coated on electrode. In scenario (1), the relationship of exposing area to Pd particle size and distribution factors was established. Based on theoretical estimation and catalytic performance analysis, the results indicated that adjusting the exposing area to a large value (9.3 ± 0.1 × 105 nm2 mg−1 Pd) was extremely effective for improving the catalytic activity of Pd-cell used as a suspension catalyst. In scenario (2), our results showed that the best electrocatalytic performances were achieved on the electrode decorated with Pd-cells with the largest NP size (54.3 ± 16.4 nm), which exerted maximum electrochemical active surface area (10.6 m2 g−1) as well as favorable conductivity. The coverage of deposited Pd NPs (>95%) on the cell surface played a crucial role in boosting the conductivity of biocatalyst, thus determining the possibility of Pd-cell as an efficient electrocatalyst. The findings of this study provide a guidance for the synthesis and application of Pd-cell, which enables the design of Pd-cell to be suitable for different catalysis systems with high catalytic performance.Download high-res image (297KB)Download full-size image

Biogenetic nanopalladium (bio-Pd) has attracted increasing attention recently due to its economical and environmental friendly synthesis route. However, traditional bacteria suspensions formed palladium (Sus-Pd) is limited to be the electrochemical catalyst owing to the poor conductivity of bacterial cells. Herein, we demonstrated Pd nanoparticles, synthesized by electroactive Geobacter biofilm, can form a three-dimensional conductive network (EAB-Pd) that is beneficial to the electrons transfer. As a result, the EAB-Pd delivered an over 5-fold increase of current compared to the Sus-Pd in hydrogen evolution and the reductive degradation of nitro-, azo- and chloroaromatics. Superior performance of EAB-Pd was also observed in comparison with the commercial Pd catalyst. A good stability of EAB-Pd has been further confirmed under electrochemical and mechanical stresses as well as through the reuse after over 3 months of storage. This novel proposed method enables the direct electrochemical application of bio-Pd without the previous required cell carbonization and chemical binders.Keywords: Conductive 3D network; Electroactive biofilm; In situ fabrication; Nanopalladium; Reductive catalysis

Understanding the microbial community structure relative to enhancement of methane production from digestion of waste-activated sludge (WAS) coupled with a bioelectrochemical system is a key scientific question for the potential application of bioelectrochemistry in biogas production. Little has been known about the influence of electrode on the structure and function of microbial communities, especially methanogens in a bioelectrochemical anaerobic digestion (AD) reactor. Here, a hybrid reactor, which coupled bioelectrolysis and AD, was developed to enhance methane recovery from WAS. The methane production rate reached up to 0.0564 m3 methane/(m3 reactor*d) in the hybrid reactor at room temperature, which was nearly double than that of the control anaerobic reactor (0.0259 m3 methane/(m3reactor*d)) without bioelectrochemical device. Microbial community analysis revealed that hydrogenotrophic methanogen Methanobacterium dominated the cathode biofilm, which was the predominant contributor to accelerate the methane production rate from WAS. While acetoclastic methanogen Methanosaeta was enriched in the sludge phase of all reactors, shifts of the microbial community structure of the biocathode was in significant correlation with the methane production. This study suggested a potential way to utilize a bioelectrochemical system with the regulated microbial community to enhance methane production from WAS.Keywords: Anaerobic digestion (AD); Bioelectrochemical system (BES); Methanogenic community; Waste-activated sludge (WAS)

•A novel integrated upflow microbial electrolysis assisted AD reactor was designed.•Nickel, Stainless steel & Copper were tested as cathode for methane production.•Nickel mesh cathode was identified the best CH4 production for beer wastewater.•Electrochemical activity revealed on CH4 yield, COD removal and current generation.As a reliable source for methane production, the major goal of our research was to design and testify a novel microbial electrolysis assisted upflow anaerobic (Upflow-MEC) reactor for beer wastewater treatment and simultaneous methane production. Three reactors with different cathode materials were constructed and the reactor with Ni cathode had a maximum COD removal of 85%, methane yield of 142.8 mL/gCOD, TOC removal of 83%, Carbohydrate removal of 97%, Protein removal of 62% and current production of 8.6 mA, under 0.8 V applied voltage at HRT of 24 h. It was an application-oriented, membrane-free, continuous reactor and shortening the reaction time and increasing organic content conversion to methane were the key developing targets.

The search and development of an efficient and cost-effective redox mediator is essential for rapid decolorization of azo dye wastewater. Here, for the first time the electron shuttling activity of different lignite samples was assessed and utilized to promote azo dye reduction by sulfide. Mediated electrochemical reduction and oxidation analysis indicated that the lignite samples possessed a higher electron accepting capacity but negligible electron donating capacity. And the promotion effects of lignite samples seemed to be determined by their electron accepting capacities. It was found that the lignite-mediated decolorization performance increased with the increase of sulfide concentration (0–3.0 mM), lignite dosage (0–300 mg L−1) and salinity (0–6% NaCl). Over 80% decolorization could be kept in eight successive rounds of operation, revealing the persistent acceleration effects of lignite. Measurement and comparison of individual reaction rates not only further confirmed the redox mediator activity of lignite, but also identified the first step, i.e., reduction of lignite by sulfide to be the rate-limiting step of mediated azo dye decolorization. Additionally, redox transformation was observed with lignite's oxygenated moieties and iron components, which were believed to contribute to lignite's redox mediator activity. Based on the findings of this study, redox-active lignite could be used to enhance the treatment of wastewater containing azo dyes and other oxidative pollutants.

Anaerobic fermentation liquid from waste activated sludge with a rich content of organics and phosphate ions is a promising source of carbon and electrolytes for MECs. The effects of three different electrolytes, including phosphate buffer solution (PBS), bicarbonate buffer solution (BBS), and sodium chloride (NaCl), on the performance of an MEC fed with sludge fermentation liquid (SFL) were compared under conditions of similar conductivity. The production yield of hydrogen was 0.92 mL mg−1 COD in an MEC with NaCl, which performed similarly with yields of 1.03 mL mg−1 with BBS and 1.04 mL mg−1 with PBS. The COD removal efficiencies exceeded 50% in all three groups. Although the energy efficiency of 108% with NaCl was lower than that with PBS (121%), the self-buffering system had advantages regarding cost and environment-friendly application over both PBS and BBS. Comparable performance could be obtained in an MEC with NaCl by adjusting the conductivity using SFL as a carbon source and buffer solution.

•Acylhomoserine lactones enhanced bioelectrochemcial activities in MECs.•MEC performances were affected by chain length and concentration of AHLs.•Highest H2 yield was achieved by 3OC6-HSL at an initial concentration of 10 μM.Quorum sensing (QS) has been extensively studied as a cell–cell communication system, where small chemical signal molecules (acylhomoserine lactones, AHLs) can regulate the bacterial communications in bioelectrochemical systems via chemical signaling and electric signaling. In this study, electrochemical activity of bio-anode is substantially promoted by adding two kinds of AHLs with different chain length at the stage of community formation in microbial electrolysis cells (MECs). Hydrogen yield increase is observed by adding of two chain length AHLs, 3-oxo-hexanoyl-homoserine lactone (3OC6-HSL) and 3-oxo-dodecanoyl homoserine lactone (3OC12-HSL). A higher MEC current is acquired with addition of 3OC6-HSL than 3OC12-HSL at a fixed voltage of 0.8 V (vs. SHE). The highest yield is up to 3.8 ± 0.2 mol H2 mol−1 acetate at 10 μM 3OC6-HSL, which is increased 29% over control MECs. Evaluated on applied voltage, energy efficiency is increased to 171.6  ±  21.3% with short chain AHL, however, no significant improvement is performed on energy efficiency and coulombic efficiency with long-chain AHL. The study shows that bioelectrochemical characteristics of MECs varied on the chain length of AHL signal molecules and short-chain AHLs have a more positive effect on electron transfer and energy recovery in MECs.Effects of different chain length of AHLs on anodic biofilm formation to determine bioelectrochemical property on energy recovery in MECs.

Several anaerobic systems have been established for mineralizing halogenated aromatics (HACs) by construction of dehalogenation and oxidative degradation consortia. However, functional interplay of bacterial and genetic activity during HAC mineralization is poorly understood. In this study, the temporal distributions of potential dehalogenators, oxidative degraders and relevant functional genes were investigated in an anaerobic consortium for mineralizing HACs. The consortium held wide mineralization potential, and was able to mineralize various types of HACs with halogens in the ortho- and meta-positions, such as 4-chlorophenol (4-CP) and 2,4,6-trichlorophenol (2,4,6-TCP). Copy numbers of the potential dehalogenators (Dehalobacterium and Sulfurospirillum spp.) and phenol degraders (Geobacter spp.) proliferated enormously (10–102 copies per ml) and remained at a high level (105 to 107 copies per ml) throughout the 4-CP and 2,4,6-TCP mineralization processes (60 days). Meanwhile, the growth of two functional genes, putative chlorophenol reductive dehalogenase cprA and benzoyl-CoA reductase bamB genes showed similar trends, with numbers increased by over 10 copies per ml on average. In comparison, without the addition of HAC, no significant growth of potential dehalogenators, degraders and functional genes was observed. The distribution trends of functional bacteria and genes revealed simultaneous satisfaction of the redox niches of both dehalogenation and oxidative degradation by the enriched consortium. This study proposed the complete mineralization of a wide range of HACs by supplying one consortium containing multiple functional microbes and a simple nutrient supplement under anaerobic conditions.

In this study, a novel technology named pretreatment coupled with anaerobic digestion–microbial electrolysis cells (AD–MECs) for waste activated sludge (WAS) reduction and renewable bioenergy recovery has been investigated. The results showed that, compared with the control pretreatment, the three pretreatment methods used greatly enhanced the performance of the AD–MECs process, and efficient sludge reduction was achieved, especially in heat-alkaline pretreatment, 36.9% and 46.7% for total suspended solid (TSS) and volatile suspended solid (VSS) removal in 6 days. MECs fed with fermented WAS, displayed positive potential for bioenergy recovery, and the highest bio-hydrogen yield was 20.30 mg H2/g VSS. Kinetic models indicated that with initial concentrations of soluble organic matter increasing, the bio-hydrogen yields of MECs increased linearly (R2 = 0.8903–0.9742). The results above suggested that the novel technology proposed in this work showed attractive potential for renewable bioenergy recovery and sludge reduction.

The environment-friendly biosynthesis of gold nanoparticles and reduced graphene oxide nanohybrid (bio-AuNPs/rGO) was achieved with Shewanella oneidensis MR-1 under ambient and growing conditions. Both MR-1 cells and its metabolites were vital for the synthesis of bio-AuNPs/rGO, which showed comparable structural features to the chemically synthesized counterpart (chem-AuNPs/rGO). Compared to chem-AuNPs/rGO, bio-AuNPs, bio-rGO and their mixture, bio-AuNPs/rGO not only exhibited better catalytic activity and reusability towards the chemical reduction of 4-nitrophenol, but also showed higher stimulating effect on microbial reduction of nitrobenzene. These might be due to the good morphology/structure properties, introduction of N-doping and synergistic effects between AuNPs and rGO. The MR-1 cells could attach themselves closely to bio-AuNPs/rGO, which might facilitate the transfer of electrons from cells to nitrobenzene during reduction. Moreover, bio-AuNPs/rGO could also enhance the nitrobenzene bioreduction by some MR-1 mutant strains lacking components of the Mtr pathway (ΔcymA, ΔmtrA and ΔmtrB), whereas no stimulating effect on nitrobenzene reduction by ΔomcA/ΔmtrC mutant strain was observed. This study provided a simple and eco-friendly method to synthesize graphene-based nanohybrid capable of stimulating reductive transformation of environmental pollutants.

In microbial electrolysis cells (MECs), the hydrogen production yield is often limited by the occurrence of methanogenesis. To reduce methane production, an air treatment process was applied as a cost-effective approach, however, the reported method of using air or oxygen sparging may cause an energy loss because of residual dissolved oxygen in the MEC solution. In this study, an air-exposed biofilm was applied to improve H2 production in single-chamber MECs. Twelve reactors with 0.8 V applied voltage were operated in four batch conditions (three replicates for each): (a) the biofilm was aerated for 10 minutes before the medium was refilled (air speed: 0.8–1 L min−1); (b) the biofilm was air-exposed for 10 minutes before the medium was refilled; (c) a fresh medium was used to immediately refill after the reacted medium was discharged; (d) nitrogen gas was sparged for 10 minutes after the fresh medium was refilled (as a control treatment). It was found that the H2 yield increased by ∼60% after biofilm aeration under condition (a), and the hydrogen production rate was up to 1.3 mL per mL per reactor d, while little methane was detected. In contrast, under conditions (c) and (d), the maximum production rate of methane was 0.1 mL CH4 per mL reactor per d, while the production rate of hydrogen decreased to 0.8 mL per mL reactor per d. This work indicated that a short-term aeration treatment could substantially affect energy recovery and methanogen communities located in biofilms.

Biofuel from lignocellulosic materials is a promising type of fuel because it does not compete with food supplies and has a sustainable production process. However, the primary obstacle for producing biofuels from lignocellulose is the low-energy productivity of microorganisms. In this research, thermophilic bacterial strain DD32, which effectively converts lignocellulose to hydrogen, was isolated and characterized. This strain was identified as Thermoanaerobacterium thermosaccharolyticum according to 16S rRNA sequence homology. The maximum H2 production yield reached 12.08 mmol H2 g−1 Avicel, which is equivalent to 2.17 mol H2 mol−1 glucose, at the optimal condition of 55 °C and pH 7.5 with 5.0 g L−1 Avicel. To our knowledge, this result represents the highest H2 yield from cellulose for thermophilic bacterial monocultures reported so far. Moreover, the hydrogen productivity of strain DD32 from raw (non-pretreated) lignocellulosic biomass is also tested. Results show that the highest hydrogen yield and lignocelluloses degradation rate reached 6.38 mmol H2 g−1 and 44.29% from corn stalk after 72 h of incubation. This yield was almost 2–3 times that of other thermophilic strains. These results suggested that newly isolate T. thermosaccharolyticum DD32 could serve as an effective microbial catalyst for lignocellulosic hydrogen production.

Recent research has highlighted the existence of some bacteria that are capable of performing heterotrophic nitrification and have a phenomenal ability to denitrify their nitrification products under aerobic conditions. A high-salinity-tolerant strain ADN-42 was isolated from Hymeniacidon perleve and found to display high heterotrophic ammonium removal capability. This strain was identified as Pseudomonas sp. via 16S rRNA gene sequence analysis. Gene cloning and sequencing analysis indicated that the bacterial genome contains N2O reductase function (nosZ) gene. NH3-N removal rate of ADN-42 was very high. And the highest removal rate was 6.52 mg/L · h in the presence of 40 g/L NaCl. Under the condition of pure oxygen (DO >8 mg/L), NH3-N removal efficiency was 56.9 %. Moreover, 38.4 % of oxygen remained in the upper gas space during 72 h without greenhouse gas N2O production. Keeping continuous and low level of dissolved oxygen (DO <3 mg/L) was helpful for better denitrification performance. All these results indicated that the strain has heterotrophic nitrification and aerobic denitrification abilities, which guarantee future application in wastewater treatment.

•We studied biofilm community and MEC performance in a bioelectrochemical system.•Five reactors were analyzed on different levels of H2, CO2, and CH4 production.•The high H2 producing reactor had the lowest abundance of hydrogenases.•The high H2 producing reactor had a higher amount of cytochrome genes.Microbial electrolysis cells (MECs) use exoelectrogenic microorganisms to convert organic matter into H2, although yields can vary significantly with environmental conditions, likely due to variations in microbial communities. This study was undertaken to better understand how microbial communities affect reactor function. Using wastewater as inoculum, 15 MEC reactors were operated for >50 days and subsequently five reactors were selected for further analysis. Solution (26 mL) was collected every 3–4 days for DNA extraction. DNA was hybridized to GeoChip, a comprehensive functional gene array, to examine differences in the reactor microbial communities. A large variety of microbial functional genes were observed in all reactors. Performances ranged from poor (0.1 ± 0.1 mL) to high (12.2 ± 1.0 mL) H2 production, with a maximum yield of 5.01 ± 0.43 mol H2/molglucose. The best performance was associated with higher cytochrome c genes, considerably higher exoelectrogenic bacteria (such as Shewanella, Geobacter), less methanogens and less hydrogen-utilizing bacteria. The results confirmed the possibility to obtain an effective community for hydrogen production using wastewater as inoculum. Not like fermentation, hydrogen production was significantly controlled by electron transporting process in MECs. GeoChip findings suggested that biofilm formation can be highly stochastic and that presence of dissimilatory metal-reducing bacteria and antagonistic methanogens is critical for efficient hydrogen production in MEC reactors.

•Combined strategy of chemical pretreatment and MEC was applied for WAS utilization.•Four kinds of chemical pretreatments were tested to enhance VFAs accumulation in WAS.•Cascade utilization was proved in combined strategy which affected H2 production.•SDS get high acetic and propanoic accumulation for best H2 yield in combine strategy.Cascade conversion methods are required to treat waste sludge (WAS) targeting at abundant biomass embedded in its cells and extracellular polymer. Two limiting factors have to overcome to obtain efficient conversion: (i) low release of soluble organics in raw WAS; (ii) limited conversion rate from organics to energy. Combined strategy of effective chemical pretreatment and microbial electrolysis was tested. Four kinds of chemicals (SDS, NaOH, peracetic-acid and β-cyclodextrin) were chosen to enhance volatile fatty acids (VFAs) production and following effects on hydrogen production and energy recovery by microbial electrolysis was further studied. The highest VFAs concentration was accumulated to 4712.69 mgCOD/L by β-CD within 3 days, which was increased to 4 times of unpretreated WAS. Other three chemicals respectively achieved ∼2.5-fold increase by SDS and PAA, and ∼2-fold increase by NaOH. However, the highest hydrogen yield was 8.5 mgH2/gVSS with energy efficiency of 138% ± 8% by SDS pretreatment. The pretreatment substantially affects VFAs components, reflected on cascade changing of current and hydrogen production rate. The cascade conversion indicated that accumulation of acetate and propionate in SDS pretreatment benefited the most hydrogen production in combined strategy.

Chlorinated nitroaromatic antibiotic chloramphenicol (CAP) is a priority pollutant in wastewaters. A fed-batch bioelectrochemical system (BES) with biocathode with applied voltage of 0.5 V (served as extracellular electron donor) and glucose as intracellular electron donor was applied to reduce CAP to amine product (AMCl2). The biocathode BES converted 87.1 ± 4.2% of 32 mg/L CAP in 4 h, and the removal efficiency reached 96.0 ± 0.9% within 24 h. Conversely, the removal efficiency of CAP in BES with an abiotic cathode was only 73.0 ± 3.2% after 24 h. When the biocathode was disconnected (no electrochemical reaction but in the presence of microbial activities), the CAP removal rate was dropped to 62.0% of that with biocathode BES. Acetylation of one hydroxyl of CAP was noted exclusive in the biocatalyzed process, while toxic intermediates, hydroxylamino (HOAM), and nitroso (NO), from CAP reduction were observed only in the abiotic cathode BES. Electrochemical hydrodechlorination and dehalogenase were responsible for dechlorination of AMCl2 to AMCl in abiotic and microbial cathode BES, respectively. The cyclic voltammetry (CV) highlighted higher peak currents and lower overpotentials for CAP reduction at the biocathode compared with abiotic cathode. With the biocathode BES, antibacterial activity of CAP was completely removed and nitro group reduction combined with dechlorination reaction enhanced detoxication efficiency of CAP. The CAP cathodic transformation pathway was proposed based on intermediates analysis. Bacterial community analysis indicated that the dominate bacteria on the biocathode were belonging to α, β, and γ-Proteobacteria. The biocathode BES could serve as a potential treatment process for CAP-containing wastewater.

Enriched activated sludge that can effectively convert crude glycerol into bio-hydrogen was selected by an eco-biotechnological approach, in very strict conditions, using biodiesel-derived glycerol as the only carbon source. The thus obtained functional consortium was characterized by the genera Klebsiella, Escherichia/Shigella and Cupriavidus. During enrichment, the dominant metabolic end-product shifted from a 1,3 propanediol to ethanol, with a concomitant increase of the hydrogen yield from 0.18 ± 0.003 to 0.66 ± 0.06 mol/mol and an almost five-fold increase of the hydrogen production. Glycerol degradation efficiency showed an increase of around 50%. In optimized and upscaled conditions it was possible to obtain a hydrogen production rate of 2960 mL H2/L/day ± 185 at a near stoichiometric yield (of 0.90 mol/mol ± 0.01), with a carbon recovery of almost 90%, both in sterile and non-sterile conditions. Glycerol was almost totally degraded (degradation efficiency of 97.42% ± 0.98), independently of the glycerol type used.Highlights► Possibility to select bacteria directly on the crude glycerol. ► Efficient biological conversion of crude glycerol from biodiesel stream. ► High H2 yield and production, both on pure and crude glycerol. ► High yields also in non-sterile conditions. ► Importance of metabolic cooperation mechanisms (syntrophism and/or cross-feeding).

•Double-frequency synchronous, alkali and anaerobic fermentation increased SFL accumulation.•H2, CO2 and CH4 production of MEC with different extra voltages (0.6–1.2 V) have been analyzed.•We evaluated energy efficiency and coulombic efficiency of MEC with different extra voltages.•The utilizing rule of complex substances in SFL was HAc > HPr > nHBu > nHVa > TC > protein.•The optimum extra applying voltage of MEC is found to be 0.8 V.Waste activated sludge (WAS), which is rich in organic substances, provides an energy resource. To recover hydrogen from the organic wastes, microbial electrolysis cell may be used as an efficient device. Since different extra applied voltages have significant effects on the efficiency of microbial electrolysis cell, this paper explores different extra applied voltages (0.6 V–1.2 V) affecting the utilization of sludge fermentation liquid (SFL) that is treated with synchronous double-frequency (28 + 40 kHz) and alkali coupling 72-bacth mesothermal anaerobic fermentation (35 °C). It is found that 0.8 V was the optimum extra applied voltage. With this voltage, the highest energy recovery efficiency will be 169 ± 1% and the peak of soluble chemical oxygen demand (SCOD) removal efficiency can be found at 51.4 ± 0.6%; Coulombic efficiency is 98.9 ± 1.0%. The order of complex matter consumption is found to be HAc > HPr > nHBu > nHVa > total carbohydrates > protein. The processing methods of synchronous double-frequency, alkaline, coupling with anaerobic fermentation are feasible for microbial electrolysis cell to transform large amount of waste activated sludge into energy.

The short-chain fatty acids (SCFAs) accumulated in waste activated sludge (WAS) fermentation was adopted as an alternative extra carbon source for biohydrogen production in microbial electrolysis cells (MECs). WAS was pretreated by bi-frequency ultrasonic and the highest SCFAs were accumulated at 3rd day. Three groups of tests were conducted in single chamber MECs for H2 production under different SCOD concentrations. SCOD removals were up to 60% at diluted influent, but reduced to 50% at original concentration. Highest H2 yield was 1.2 mL H2/mg COD at 2-fold dilution with 155% energy efficiency. Results showed that >90% of acetate and ∼90% of propionate were effectively converted to hydrogen, and next were n-butyrate and n-valerate (at dilutions), but <20% of iso-butyrate and iso-valerate were converted. The overall biohydrogen recovery in this study was 120 ml H2/g VSS/d. This work shows a possibility of cascade utilization of WAS fermentation liquid and H2 generation in MEC.Highlights► We studied bio-H2 production in MECs feeding with waste activated sludge. ► Hydrolysis and acidification were improved by bi-frequency ultrasonic pretreatment. ► Acetate and butyrate in fermentation liquid were most converted to hydrogen in MECs. ► Energy efficiency using sludge for H2 was much higher than that without pretreatment.

Design of Experiments (DoE) was applied to improve the ability of enriched activity sludge to efficiently convert crude glycerol from biodiesel industry into hydrogen and ethanol, using a very simple synthetic medium. Based on Plackett–Burman screening design, glycerol concentration, temperature and initial pH were identified as significant variables. Box–Behnken design and Response Surface Method (RSM) were then used for optimization. The maximum hydrogen yield of 0.96 mol H2/mol glycerol was estimated at the temperature of 37.0 °C, initial pH of 7.9 and glycerol concentration of 15.0 g/L. Maximum hydrogen production rate of 2191 mL/L/d was estimated at the temperature of 37.3 °C, initial pH of 8.0 and glycerol concentration of 15.2 g/L. Finally maximum ethanol production of 7.92 g/L was estimated at an initial pH of 8.0 and glycerol concentration of 15.0 g/L (temperature had no significant effect). These results show that it is possible to obtain both, high yield and production of hydrogen and ethanol together, using a very simple synthetic medium, without trace element- and vitamin solution, tryptone or yeast extract.Highlights► Highly efficient biological conversion of crude glycerol from biodiesel stream. ► Maximum yield and production, both of hydrogen and ethanol at the same time. ► Statistical optimization of mixed consortium thanks to stability of enriched sludge. ► Results obtained without use of yeast extract, triptone, vitamin and mineral solution.

A sediment microbial fuel cell (SMFC) with three dimensional floating biocathode (FBC) was developed for the electricity generation and biodegradation of sediment organic matter in order to avoid negative effect of dissolved oxygen (DO) depletion in aqueous environments on cathode performance and search cost-effective cathode materials. The biocathode was made from graphite granules with microbial attachment to replace platinum (Pt)-coated carbon paper cathode in a laboratory-scale SMFC (3 L in volume) filled with river sediment (organic content 49±4 g·kg−1 dry weight). After start-up of 10 days, the maximum power density of 1.00W·m−3 (based on anode volume) was achieved. The biocathode was better than carbon paper cathode catalyzed by Pt. The attached biofilm on cathode enhanced power generation significantly. The FBC enhanced SMFC performance further in the presence aeration. The SMFC was continuously operated for an over 120-day period. Power generation peaked within 24 days, declined gradually and stabilized at a level of 1/6 peak power output. At the end, the sediment organic matter content near the anode was removed by 29% and the total electricity generated was equal to 0.251 g of chemical oxygen demand (COD) removed.

With the aim of enhanced degradation of azo dye alizarin yellow R (AY) and further removal of the low-strength recalcitrant matter (LsRM) of the secondary effluent as much as possible, our research focused on the combination of aerobic bio-contact oxidation (ABO) with iron/carbon microelectrolysis (ICME) process.The combined ABO (with effective volume of 2.4 l) and ICME (with effectively volume of 0.4 l) process were studied with relatively short hydraulic retention time (HRT) of 4 or 6 h.At the HRT of 6 h with the reflux ratio of 1 and 2, the AY degradation efficiency in the final effluent was >96.5%, and the total organic carbon (TOC) removal efficiency were 69.86% and 79.44%, respectively. At the HRT of 4 h and the reflux ratio of 2, TOC removal efficiency and AY degradation efficiency were 73.94% and 94.89%, respectively. The ICME process obviously enhanced the total AY removal and the generated micromolecule acids and aldehydes then that wastewater backflow to the ABO where they were further biodegraded.The present research might provide the potential options for the advanced treatment azo dyes wastewater with short HRT and acceptable running costs.

Nitrobenzene (NB) is a toxic compound that is often found as a pollutant in the environment. The present removal strategies suffer from high cost or slow conversion rate. Here, we investigated the conversion of NB to aniline (AN), a less toxic endproduct that can easily be mineralized, using a fed-batch bioelectrochemical system with microbially catalyzed cathode. When a voltage of 0.5 V was applied in the presence of glucose, 88.2 ± 0.60% of the supplied NB (0.5 mM) was transformed to AN within 24 h, which was 10.25 and 2.90 times higher than an abiotic cathode and open circuit controlled experiment, respectively. AN was the only product detected during bioelectrochemical reduction of NB (maximum efficiency 98.70 ± 0.87%), whereas in abiotic conditions nitrosobenzene was observed as intermediate of NB reduction to AN (decreased efficiency to 73.75 ± 3.2%). When glucose was replaced by NaHCO3, the rate of NB degradation decreased about 10%, selective transformation of NB to AN was still achieved (98.93 ± 0.77%). Upon autoclaving the cathode electrode, nitrosobenzene was formed as an intermediate, leading to a decreased AN formation efficiency of 71.6%. Cyclic voltammetry highlighted higher peak currents as well as decreased overpotentials for NB reduction at the biocathode. 16S rRNA based analysis of the biofilm on the cathode indicated that the cathode was dominated by an Enterococcus species closely related to Enterococcus aquimarinus.

Strain isolation using conventional roll tube/plating technique is time consuming and is able to culture in vitro only a small fraction of existing microbes in a natural microflora. This paper proposed a simple and rapid method to select the as-simple-as-possible biological consortium by serially diluting the original mixed culture. The diluted which remains, while the one diluted in serial loses the target function, is defined as the functional consortium of the original mixed culture. Since the microbial structure and the reaction pathway incorporated with the functional consortium is much simpler than its original mother liquor, detailed analysis on the strain interaction is possible without the risk of losing key functional strains as often caused from conventional isolation method. The rumen liquor that can degrade cellulose and produce hydrogen is used as a demonstration example. A “rumen cellulose-degrading bacterial consortium” (RCBC) was identified using the proposed enrichment strategy.

In order to optimize operations of microbial electrolysis cell (MEC) for hydrogen production, microbial anode potential (MAP) was analyzed as a function of factors in biofilm anode system, including pH, substrate and applied voltage. The results in “H” shape reactor showed that MAP reflected the information when any factor became limiting for hydrogen production. Commonly, hydrogen generation started around anode potential of −250 mV to −300 mV. While, higher current density and higher hydrogen rate were obtained when MAP went down to −400 mV or even lower in this study. Biofilm anode could work normally between pH 6.5 and 7.0, while the lowest anode potential appeared around 6.8–7.0. However, when pH was lower 6.0 or substrate concentration was less than 50 mg L−1 in anode chamber, MAP went up to −300 mV or above, leading to hydrogen reduction. Applied voltage did not affect MAP much during the process of hydrogen production. Anode potential analysis also showed that planktonic bacteria in suspended solution presented positive effects on biofilm anode system and they contributed to enhance electron transfer by reducing internal resistance and lowering minimum voltage needed for hydrogen production to some extent.

With limited external applied voltage, the microbial electrolysis cell (MEC) could produce hydrogen by exoelectrogenic microorganisms. The present study revealed that a cubiod-shaped chamber effectively reduces the distance between electrodes and thereby reduces the internal resistance of the entire cell. With 0.6 V of applied voltage, the cuboid MEC had a columbic efficiency of 33.7%, much higher than that achieved in the H-shaped MEC test (ca. 15%) of comparable size. Filling the anode chamber with granular activated carbon further enhanced the columbic efficiency to 45%. The corresponding hydrogen conversion rate could reach 35%.

Methane production occurs during hydrogen gas generation in microbial electrolysis cells (MECs), particularly when single chamber systems are used which do not keep gases, generated at the cathode, separate from the anode. Few studies have examined the factors contributing to methane gas generation or the main pathway in MECs. It is shown here that methane generation is primarily associated with current generation and hydrogenotrophic methanogenesis and not substrate (acetate). Little methane gas was generated in the initial reaction time (<12 h) in a fed batch MEC when acetate concentrations were high. Most methane was produced at the end of a batch cycle when hydrogen and carbon dioxide gases were present at the greatest concentrations. Increasing the cycle time from 24 to 72 h resulted in complete consumption of hydrogen gas in the headspace (applied voltage of 0.7 V) with methane production. High applied voltages reduced methane production. Little methane (<4%) accumulated in the gas phase at an applied voltage of 0.6–0.9 V over a typical 24 h cycle. However, when the applied voltage was decreased to 0.4 V, there was a greater production of methane than hydrogen gas due to low current densities and long cycle times. The lack of significant hydrogen production from acetate was also supported by Coulombic efficiencies that were all around 90%, indicating electron flow was not altered by changes in methane production. These results demonstrate that methane production in single chamber MECs is primarily associated with current generation and hydrogen gas production, and not acetoclastic methanogenesis. Methane generation will therefore be difficult to control in mixed culture MECs that produce high concentrations of hydrogen gas. By keeping cycle times short, and using higher applied voltages (≥0.6 V), it is possible to reduce methane gas concentrations (<4%) but not eliminate methanogenesis in MECs.

Microbial conversion of lignocellulose to hydrogen is a fascinating way to provide a renewable energy source. A mesophilic bacterium strain G1 that had high cellulose degradation and hydrogen production activity (2.38 mmol H2 g−1 cellulose) was isolated from rumen fluid and identified as the Enterococcus gallinarum. Hydrogen production from cellulose by using sequential co-cultures of a cellulosic-hydrolysis bacterium G1 and Ethanoigenens harbinense B49 was investigated. With an initial Avicel concentration of 5 g l−l, the sequential co-culture with G1 and strain Ethanoigenens harbinense B49 produced H2 yield approximately 2.97 mmol H2 g−1 cellulose for the co-culture system.

Ammonia-oxidizing archaea (AOA) and bacteria (AOB) are widely distributed in the natural environment and play crucial roles in the nitrification process and the removal of nitrogen (N). Although planktonic microbial community plays an important role in river biogeochemical cycles, few studies have attempted to address the characteristics of AOA and AOB in the water column of river ecosystems. This study examined the community structures, distributions and abundance of planktonic AOA and AOB in the Dongjiang River and their responses to the changes in environmental parameters through quantitative polymerase chain reaction, cloning, and sequencing of ammonia mono-oxygenase (amoA). The abundance ratio of AOB to AOA varied from 0.07 to 9.4 along the river and was positively correlated with the concentration of ammonium. Significantly positive correlations were observed between the abundance of AOB and potential nitrification rates, which suggested that the contribution of AOB to nitrification was greater than that of AOA in the river. Phylogenetic analyses showed that AOA communities could be divided into three branches of Thaumarchaeota: Group 1.1a, Group 1.1a associated and Group 1.1b, with most sequences belonging to Group 1.1a. All AOB sequences fell within Nitrosomonas and Nitrosospira species, and the majority of sequences were affiliated with the latter. Multivariate statistical analyses indicated that the community distributions of AOA and AOB were significantly correlated with the concentrations of nitrate and total suspended solids, respectively. These findings fundamentally improved our understanding of the role of planktonic AOA and AOB in nitrogen cycling and their responses to changes in environmental factors in the river ecosystem.

Microbial Fuel Cells (MFCs) are a promising technology for treating wastewater in a sustainable manner. In potential applications, low temperatures substantially reduce MFC performance. To better understand the effect of temperature and particularly how bioanodes respond to changes in temperature, we investigated the current generation of mixed-culture and pure-culture MFCs at two low temperatures, 10°C and 5°C. The results implied that the mixed-culture MFC sustainably performed better than the pure-culture (Shewanella) MFC at 10°C, but the electrogenic activity of anodic bacteria was substantially reduced at the lower temperature of 5°C. At 10°C, the maximum output voltage generated with the mixed-culture was 540–560 mV, which was 10%–15% higher than that of Shewanella MFCs. The maximum power density reached 465.3 ± 5.8 mW/m2 for the mixed-culture at 10°C, while only 68.7 ± 3.7 mW/m2 was achieved with the pure-culture. It was shown that the anodic biofilm of the mixed-culture MFC had a lower overpotential and resistance than the pure-culture MFC. Phylogenetic analysis disclosed the prevalence of Geobacter and Pseudomonas rather than Shewanella in the mixed-culture anodic biofilm, which mitigated the increase of resistance or overpotential at low temperatures.Download high-res image (299KB)Download full-size image

•Proteome in total cell extract of C27 was observed under micro-aeration condition.•Micro-aeration increases abundance of 73 protein spots and decreases that of 23 spots.•C27 has efficient enzyme system to conduct DSR reactions under micro-aerobic condition.•Micro-aeration increases cell growth and enhance cell defensive system of strain C27.Pseudomonas sp. C27 is a facultative autotrophic bacterium (FAB) that can effectively conduct mixotrophic and heterotrophic denitrifying sulfide removal (DSR) reactions under anaerobic condition using organic matters and sulfide as electron donors. Micro-aeration was proposed to enhance DSR reaction by FAB; however, there is no experimental proof on the effects of micro-aeration on capacity of denitrifying sulfide removal of FAB on proteomic levels. The proteome in total C27 cell extracts was observed by two-dimensional gel electrophoresis. Differentially expressed protein spots and specifically expressed protein spots were identified by MALDI TOF/TOF MS. We identified 55 microaerobic-responsive protein spots, representing 55 unique proteins. Hierarchical clustering analysis revealed that 75% of the proteins were up-regulated, and 5% of the proteins were specifically expressed under micro-aerobic conditions. These enzymes were mainly involved in membrane transport, protein folding and metabolism. The noted expression changes of the microaerobic-responsive proteins suggests that C27 strain has a highly efficient enzyme system to conduct DSR reactions under micro-aerobic condition. Additionally, micro-aeration can increase the rates of protein synthesis and cell growth, and enhance cell defensive system of the strain.

•SCFAs yield was enhanced by co-digesting waste activated sludge and corn stover.•Corn stover proportion in feedstock determined the acidification product spectrum.•Corn stover addition improved the hydrolysis and acidification of particulate organics.•Optimal feedstock proportion was 65%WAS:35%CS from carbon balance and cost estimation.Volatile fatty acids (VFAs) are the most suitable and biodegradable carbon substrates for many bioprocesses. This study explored a new approach to improve the VFAs production from anaerobic co-digesting waste activated sludge (WAS) with corn straw (CS). The effect of feedstock proportion on the acidification efficiency was investigated. The maximum VFAs yield (corresponding fermentation time) was substantially increased 69% (96 h), 45% (72 h), 13% (120 h) and 12% (120 h) with 50%, 35%, 25% and 20% CS proportion of feedstock, respectively. HAc (acetic acid) was consistently the most abundant, followed by HPr (propionic acid) and n-HBu (butyric acid) in the co-digesting tests. The increase of CS in feedstock led to more production of HAc and HPr. Moreover, the consumption of protein and carbohydrate were also improved remarkably from 2955 and 249 mg COD/L (individual WAS fermentation) to 6575 and 815 mg COD/L (50%WAS:50%CS co-digestion) from 120 onward, respectively. The highest contribution of CS to additional VFAs production was1113 mg VFAs (as COD)/g CS/L in the 65%WAS:35%CS co-digesting test. Our study indicated a valuable method to improve VFAs production from anaerobic co-digesting WAS and CS.

This paper is concerned with predicting the chemical oxygen demand, the common criterion of the outlet water in most wastewater treatment plants. A fuzzy modeling approach is proposed which can efficiently eliminate the complex nonlinear terms existing in Activated Sludge Model No. 1 (ASM1). First, the structure of fuzzy rules in the approach is identified based on ASM1. Further, by combining the well-known fuzzy c-means cluster algorithm and the method of least squares, the fuzzy space of input variables required in the approach is partitioned and the consequent parameters are identified using the data in Benchmark Simulation Model No. 1, which can be replaced by the data in a real wastewater treatment plant. The effectiveness of the proposed approach is illustrated by comparing the predicted values of chemical oxygen demand and the experimental measurements obtained from the Benchmark Simulation Model No. 1.

GeoChip (II) and single strand conformation polymorphism (SSCP) were used to characterize anode microbial communities of a microbial electrolysis cell (MEC). Biofilm communities, enriched in a two-chamber MEC (R1, 0.6 V applied) having a coulombic efficiency (CE) of 35 ± 4% and a hydrogen yield (YH2) of 31 ± 3%, were used as the inoculum for a new reactor (R2). After three months R2 achieved stable performance with CE = 38 ± 4% and YH2=31±7%. Few changes in the predominant populations were observed from R1 to R2. Unlike sludge inoculation process in R1 in the beginning, little further elimination was aroused by community competitions in anode biofilm reformation in R2. Functional genes detection of biofilm indicated that cytochrome genes enriched soon in new reactor R2, and four genera (Desulfovibrio, Rhodopseudomonas, Shewanella and Geobacter) were likely to contribute to exoelectrogenic activity. This work also implied that symbiosis of microbial communities (exoelectrogens and others) contribute to system performance and stability.Highlights► We studied anodic microbial community changes in a bioelectrochemcial system. ► New reactor were inoculated by biofilm communities and started up soon on performance. ► Exoelectrogens did not overwhelm other communities during biofilm reformation. ► A part of other functional communities potentially contributed to electron transport. ► Coulombic efficiency slightly increased and explained by increased cytochrome genes.

•The variations of influent loading altered S0 recovery rate and bacterial structure.•The optimized loads of acetate, nitrate and sulfide were 0.95, 0.79, and 0.34 kg d−1 m−3, respectively.•The highest S0 recovery rate was 77.9% when Thauera and Sulfurimonas were predominant.•Insufficient loading caused a low S0 yield and sulfide oxidation activity.•Excess nutrient loading caused the over-oxidation of S0 to sulfate.To characterize the impact of influent loading on elemental sulfur (S0) recovery during the denitrifying and sulfide oxidation process, three identical, lab-scale UASB reactors (30 cm in length) were established in parallel under different influent acetate/nitrate/sulfide loadings, and the reactor performance and functional community structure were investigated. The highest S0 recovery was achieved at 77.9% when the acetate/nitrate/sulfide loading was set to 1.9/1.6/0.7 kg d−1 m−3. Under this condition, the genera Thauera, Sulfurimonas, and Azoarcus were predominant at 0–30, 0–10 and 20–30 cm, respectively; meanwhile, the sqr gene was highly expressed at 0–30 cm. However, as the influent loading was halved and doubled, S0 recovery was decreased to 27.9% and 45.1%, respectively. As the loading was halved, the bacterial distribution became heterogeneous, and certain autotrophic sulfide oxidation genera, such as Thiobacillus, dominated, especially at 20–30 cm. As the loading doubled, the bacterial distribution was relatively homogeneous with Thauera and Azoarcus being predominant, and the nirK and sox genes were highly expressed. The study verified the importance of influent loading to regulate S0 recovery, which could be achieved as Thauera and Sulfurimonas dominated. An influent loading that was too low or too high gave rise to insufficient oxidation or over-oxidation of the sulfide and low S0 recovery performance.Download high-res image (219KB)Download full-size image

•Proteomic analysis was made on Pseudomonas sp. C27 under DSR environment.•Key enzymes for nitrogen metabolism for C27 were identified.•Key enzymes for carbon metabolism for C27 were identified.•Key enzymes for sulfide metabolism for C27 were identified.•Sulfide stress up-regulated key enzymes of C27 for DSR reactions.Pseudomonas sp. C27 is a facultative autotrophic bacterium that can effectively conduct mixotrophic and heterotrophic denitrification reactions using organic matters and sulfide as electron donors. There is no experimental confirmation on proteomic levels the pure C27 strain can have the capability to simultaneous removal of sulfide, nitrate and organic carbon from waters. The proteome in total C27 cell extracts was observed by two-dimensional gel electrophoresis. The 160 mg/L sulfide up-regulated or specifically expressed succinate dehydrogenase, iron–sulfur protein, oxidoreductase, serine hydroxymethyltransferase, and iron superoxide dismutase for sulfide metabolism, 2-oxoglutarate dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase, NAD+-dependent aldehyde dehydrogenase, malate dehydrogenase and succinate dehydrogenase for carbon metabolism, and nitrous-oxide reductase and respiratory nitrate reductase for nitrogen metabolism. The study confirmed that the C27 strain has an effective enzyme system to conduct denitrifying sulfide removal reactions. Also, sulfide stress can enhance energy consumption rate and rates of nitrate reduction and sulfide oxidation by C27. Conversely, sulfide stress repressed the sulfate-reducing power of C27, evidenced by down-regulation or specific un-expression of sulfate ABC transporter, periplasmic sulfate-binding protein in the (C + N + S) sample.Download full-size image