•ZVI-AC micro-electrolysis was applied to dark fermentative hydrogen production.•Hydrogen yield was enhanced up to 50.2％ with ZVI-AC micro-electrolysis.•ZVI-AC micro-electrolysis affected environmental factors and microbial community.This paper investigated the enhancement effect of zero-valent iron activated carbon (ZVI-AC) micro-electrolysis system on fermentative hydrogen production from glucose by a mixed bacterial consortium. The results showed that addition of ZVI obtained 38.2％ more hydrogen yield, and ZVI-AC micro-electrolysis could further enhance hydrogen yield (improving rate 50.2％). The ZVI-AC also got the highest hydrogen production potential and maximum hydrogen production rate (429 ± 6.1 mL and 11.50 ± 0.74 mL/h respectively). The concentration of ferrous ion, final oxidation-reduction potential and pH were measured to understand the mechanism of enhanced hydrogen production by ZVI-AC micro-electrolysis. We concluded that ZVI-AC micro-electrolysis provided a favorable environment which was proposed to be responsible for the improvement of fermentative hydrogen production. In addition, high-throughput sequencing proved that ZVI-AC micro-electrolysis could enhance diversity of microbial community and enrich Clostridium spp. for hydrogen production.

In this paper we report ammonia oxidation to nitrogen gas using microbes as biocatalyst on the anode, with polarized electrode (+600 mV vs. Ag/AgCl) as electron acceptor. In batch experiments, the maximal rate of ammonia-N oxidation by the mixed culture was ∼ 60 mg L−1 d−1, and nitrogen gas was the main products in anode compartment. Cyclic voltammetry for testing the electroactivity of the anodic biofilms revealed that an oxidation peak appeared at +600 mV (vs. Ag/AgCl), whereas the electrode without biofilms didn’t appear oxidation peak, indicating that the bioanode had good electroactivities for ammonia oxidation. Microbial community analysis of 16S rRNA genes based on high throughput sequencing indicated that the combination of the dominant genera of Nitrosomonas, Comamonas and Paracocus could be important for the electron transfer from ammonia oxidation to anode.

•CH4 content in excess of 98% was achieved from microbial electrolysis cell and anaerobic digestion coupled process.•COD removal rate was increased 3.0 times and carbon recovery was increased by 56.2%.•Reactor made of stainless steel was used for anaerobic digestion as well as the MEC cathode for H2 gas evolution.Production of upgraded biogas is required to remove as much carbon dioxide as possible. It was found that by coupling microbial electrolysis cell (MEC) and anaerobic digestion (AD) in a single-chamber, barrel-shape stainless steel reactor, compared with common anaerobic digestion (control), CH4 content in excess of 98% was achieved and CH4 yield was increased 2.3 times. Meanwhile, the COD removal rate was tripled and carbon recovery was increased by 56.2%. In this new process, unwanted CO2 was in situ converted into CH4 on anode by the dominant microbes, hydrogenotrophic electromethanogens (e.g. Methanospirillum). These microbes could utilize hydrogen gas generated at the inner surface of stainless steel reactor, which itself served as cathode of MEC through small voltage addition (1.0 V). The overall energy efficiency was 66.7%.

Heavy metal pollution, especially lead pollution in water, has been a growing concern due to the toxicity of lead to human and other beings. According to previous reports, bioelectrochemical systems (BESs) showed significant advantages in heavy metal ions removal, but have not been considered for Pb2+ removal. In this study, a novel BES with stainless steel cathode distinguished with traditional BESs was employed with mixed culture as biocatalyst for removing Pb2+ from solution. The results indicated Pb2+ could be effectively removed and hydrocerussite as the final product confirmed by X-ray diffraction was deposited on the stainless steel cathode. Furthermore, the principle of Pb2+ removal was deduced based on the experiment of the reduction of ferricyanide in the stainless steel tube-type BES. In brief, we suggested a novel low-cost approach to remove and recover Pb2+ from Pb2+-containing wastewater.

This study describes the performance of bioelectrochemical systems, based on electrochemically active mixed culture, capable of reducing CO2 to CH4 and CH3COOH via direct and/or indirect extracellular electron transfer. The metabolic pathway and end products of this mixed culture were highly dependent on the set cathode potentials. Only CH4 and H2 were produced when the cathode potentials were set in the range from −850 to −950 mV (vs. Ag/AgCl). At potentials more negative than −950 mV, CH4, H2 and CH3COOH were simultaneously produced. With a relatively large cathode surface area of 49 cm−2, CH4 and CH3COOH were produced at high rates of 129.32 mL d−1 and 94.73 mg d−1, respectively (at potential of −1150 mV). The highest current capture efficiency reached to 97% in batch potentiostatic experiments. These results presented here suggest that mixed culture show the ability to directly accept electrons from the electrode and abiotically produce H2 to convert CO2 into various organic compounds.Highlights► Bioelectrochemical systems were based on electrochemically active mixed microflora. ► Simultaneously produced CH4 and CH3COOH from CO2 in bioelectrochemical systems. ► Metabolic pathway and end products were dependent on set cathode potentials. ► CH4 and CH3COOH were produced at high rates.

Nano-selenium/protein is a kind of lower toxic supplement to human. Many microorganisms can reduce selenite/selenate to intracellular or extracellular selenium nanoparticles. This study examined the influence of dissolved oxygen on the expulsion of extracellular selenium/protein produced in Saccharomyces cerevisiae. More of the added selenite was reduced to extracellular selenium nanoparticles by yeast cells only under oxygen-limited condition than under aerobic or anaerobic condition. For the first time, we evidenced that selenium/protein nanoparticles synthesized in vivo were transported out of the cells by vesicle-like structures under microaerophilic environment. The characterizations of the extracellular spherical selenium/protein nanoparticles were also examined by SEM, TEM, EDX and FTIR.

A stable microbial consortium, separated from a refinery wastewater sample, was able to utilize carbazole as the sole source of carbon, nitrogen, and energy, and liberated ammonia from excess nitrogen. Two bacterial strains (NCY and NCW) were isolated from the microbial consortium using a nutrient agar plate. Based on the 16S rDNA sequence analysis, the two bacteria were identified as Chryseobacterium sp. NCY and Achromobacter sp. NCW, respectively. No intermediates of carbazole degradation were detected by high-performance liquid chromatography. The substrate specificity assay showed that the consortium could utilize compounds similar to carbazole, such as phenanthrene, naphthalene, and imidazole. Neither the pure strain NCY nor NCW could degrade carbazole after domestication for several times. It was suggested that the two bacteria formed a microbial consortium capable of metabolizing carbazole.

•The MFC with acetate as electrons donor increased the removal rate of CAP.•The CAP degradation was optimized using Box-Behnken model.•Antibacterial activity of CAP was eliminated after treatment by MFC.•The electrogenic bacteria enriched in MFC under the closed-circuit mode.The performance of a microbial fuel cell (MFC) in terms of degradation of chloramphenicol (CAP) was investigated. Approximately 84% of 50 mg/L CAP was degraded within 12 h in the MFC. A significant interaction of pH, temperature, and initial CAP concentration was found on removal of CAP, and a maximum degradation rate of 96.53% could theoretically be achieved at 31.48 °C, a pH of 7.12, and an initial CAP concentration of 106.37 mg/L. Moreover, CAP was further degraded through a ring-cleavage pathway. The antibacterial activity of CAP towards Escherichia coli ATCC 25922 and Shewanella oneidensis MR-1 was largely eliminated by MFC treatment. High-throughput sequencing analysis indicated that Azonexus, Comamonas, Nitrososphaera, Chryseobacterium, Azoarcus, Rhodococcus, and Dysgonomonas were the predominant genera in the MFC anode biofilm. In conclusion, the MFC shows potential for the treatment of antibiotic residue-containing wastewater due to its high rates of CAP removal and energy recovery.

The anaerobic digestion (AD) and microbial electrolysis cell (MEC) coupled system has been proved to be a promising process for biomethane production. In this paper, it was found that by co-cultivating Geobacter with Methanosarcina in an AD–MEC coupled system, methane yield was further increased by 24.1%, achieving to 360.2 mL/g-COD, which was comparable to the theoretical methane yield of an anaerobic digester. With the presence of Geobacter, the maximum chemical oxygen demand (COD) removal rate (216.8 mg COD/(L·hr)) and current density (304.3 A/m3) were both increased by 1.3 and 1.8 fold compared to the previous study without Geobacter, resulting in overall energy efficiency reaching up to 74.6%. Community analysis demonstrated that Geobacter and Methanosarcina could coexist together in the biofilm, and the electrochemical activities of both were confirmed by cyclic voltammetry. Our study observed that the carbon dioxide content in total gas generated from the AD reactor with Geobacter was only half of that generated from the same reactor without Geobacter, suggesting that Methanosarcina may obtain the electron transferred from Geobacter for the reduction of carbon dioxide to methane. Taken together, Geobacter not only can improve the performance of the MEC system, but also can enhance methane production.Download high-res image (87KB)Download full-size image