Nanqi Ren

Pyrosequencing reveals highly diverse microbial communities in microbial electrolysis cells involved in enhanced H2 production from waste activated sludge.

Renewable H(2) production from a plentiful biomass, waste activated sludge (WAS), can be achieved by fermentation, but the yields are low. The use of a microbial electrolysis cell (MEC) can increase the H(2) production yields to several times that of fermentation. We have proved that the enhancement of H(2) production was due to the ability of MECs to use a wider range of organic matter in WAS than in fermentation. To support this result strongly, we here investigated the microbial community structures of WAS and anode biofilms in WAS-fed MECs. A pyrosequencing analysis based on the bacterial 16S rRNA gene showed that dominant populations in MECs were more diverse than those in WAS (inoculum and substrate) after enrichment, and there was a clear distinction between MECs and WAS in microbial community structure. Diverse acid-producing bacteria and exoelectrogens (predominance of Geobacter) were detected in MECs but they were only rarely found in WAS. It has been reported that these acid-producing bacteria can ferment various sugars and amines with acetate, propionate, and butyrate as their major by-products. This was consistent with our chemical analyses. Detected exoelectrogens are known to use these organic acids (mainly acetate) and certain sugars to directly produce current for H(2) generation at the cathodes in the MECs. Using quantitative real-time PCR, we demonstrated that a consistent feed of alkaline-pretreated WAS containing large amounts of acetate led to a predominance of acetoclastic methanogens, while hydrogenotrophic methanogens were abundant in MECs fed both raw and alkaline-pretreated WAS. Syntrophic interactions between phylogenetically diverse microbial populations in anodophilic biofilms were found to drive the efficient cascade utilization of organic matter in WAS.

Bioconversion of lignocellulosic biomass to hydrogen: Potential and challenges.

No comprehensive review on the bioconversion of lignocellulosic biomass to hydrogen is presented. This paper provides an up-to-date review on recent research development in biotechnology-based lignocellulosic biomass-to-H(2) conversion. Bioconversion of lignocellulosic prehydrolysate, hydrolysate or cellulose to hydrogen was discussed in terms of the involved microorganisms and the bioaugmentation tactics. To achieve fully the utilization of biomass, the integrated approaches composed of coupled dark-photo fermentation and the dark fermentation and bioelectrohydrogenesis were sketched. Additionally, this review sheds light on the perspectives on the lignocellulosic biomass conversion to hydrogen, and on the scientific and technical challenges faced for the lignocelluloses bioconversion.

Polychlorinated Biphenyls in Global Air and Surface Soil: Distributions, Air−Soil Exchange, and Fractionation Effect†

Polychlorinated biphenyl (PCB) concentrations in air and soil, measured by various research groups from around the world, were compiled and analyzed. Data for air were available from most regions, particularly in Europe and Asia. The average air concentrations (pg/m(3)) for SigmaPCB at background sites were 70 (5.1-170) for Europe, 79 (49-120) for North America, 66 (18-110) for South America, 270 (9-670) for Central America, 59 (17-150) for Asia, and 15 (13-17) for Australia. Data for soils exhibited better global coverage compared to air and were available from most regions. The average soil concentrations (pg/g dry weight) for SigmaPCB at background sites were 7500 (47-97 000) for Europe, 4300 (110-25 000) for North America, 1400 (61-9 500) for South America, 580 (120-2 900) for Asia, 390 (94-620) for Africa, and 280 (140-540) for Australia. Based on available studies where coupled measurements of PCBs in air and soil were made, the equilibrium status of PCBs in the air-soil system was investigated for China, West Midlands of the UK, central and southern Europe, and along a latitudinal transect from the south of the UK to the north of Norway. Differences were observed in plots of the soil-air equilibrium status (expressed as the soil-air fugacity fraction, ff) for different PCB homologues. This was explained by varying contributions from primary and secondary emissions-spatially and temporally. The net effect after several decades of PCB emissions to air, preferential transport of lower molecular weight PCBs through primary and secondary emission, and reductions in emissions to air in recent decades is that the lower molecular weight PCBs have achieved (and in some cases exceeded) soil-air equilibrium in many parts of the world. The exception is remote and background sites that are still dominated by primary sources.

Integrated hydrogen production process from cellulose by combining dark fermentation, microbial fuel cells, and a microbial electrolysis cell

Hydrogen gas production from cellulose was investigated using an integrated hydrogen production process consisting of a dark fermentation reactor and microbial fuel cells (MFCs) as power sources for a microbial electrolysis cell (MEC). Two MFCs (each 25 mL) connected in series to an MEC (72 mL) produced a maximum of 0.43 V using fermentation effluent as a feed, achieving a hydrogen production rate from the MEC of 0.48 m(3) H(2)/m(3)/d (based on the MEC volume), and a yield of 33.2 mmol H(2)/g COD removed in the MEC. The overall hydrogen production for the integrated system (fermentation, MFC and MEC) was increased by 41% compared with fermentation alone to 14.3 mmol H(2)/g cellulose, with a total hydrogen production rate of 0.24 m(3) H(2)/m(3)/d and an overall energy recovery efficiency of 23% (based on cellulose removed) without the need for any external electrical energy input.

Occurrence and Profiles of Phthalates in Foodstuffs from China and Their Implications for Human Exposure

Phthalate esters are used in a wide variety of consumer products, and human exposure to this class of compounds is widespread. Nevertheless, studies on dietary exposure of humans to phthalates are limited. In this study, nine phthalate esters were analyzed in eight categories of foodstuffs (n = 78) collected from Harbin and Shanghai, China, in 2011. Dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP), diisobutyl phthalate (DIBP), benzyl butyl phthalate (BzBP), and diethylhexyl phthalate (DEHP) were frequently detected in food samples. DEHP was the major compound found in most of the food samples, with concentrations that ranged from below the limit of quantification (LOQ) to 762 ng/g wet weight (wt). The concentrations of phthalates in food samples from China were comparable to concentrations reported for several other countries, but the profiles were different; DMP was found more frequently in Chinese foods than in foods from other countries. The estimated daily dietary intake of phthalates (EDIdiet) was calculated based on the concentrations measured and the daily ingestion rates of food items. The EDIdiet values for DMP, DEP, DIBP, DBP, BzBP, and DEHP (based on mean concentrations) were 0.092, 0.051, 0.505, 0.703, 0.022, and 1.60 μg/kg-bw/d, respectively, for Chinese adults. The EDIdiet values calculated for phthalates were below the reference doses suggested by the United States Environmental Protection Agency (EPA). Comparison of total daily intakes, reported previously based on a biomonitoring study, with the current dietary intake estimates suggests that diet is the main source of DEHP exposure in China. Nevertheless, diet accounted for only <10% of the total exposure to DMP, DEP, DBP, and DIBP, which suggested the existence of other sources of exposure to these phthalates.

Optimization of culture conditions for hydrogen production by Ethanoligenens harbinense B49 using response surface methodology

The design of an optimum and cost-efficient medium for high-level production of hydrogen by Ethanoligenens harbinense B49 was attempted by using response surface methodology (RSM). Based on the Plackett-Burman design, Fe(2+) and Mg(2+) were selected as the most critical nutrient salts. Subsequently, the optimum combination of the selected factors and the sole carbon source glucose were investigated by the Box-Behnken design. Results showed that the maximum hydrogen yield of 2.21 mol/mol glucose was predicted when the concentrations of glucose, Fe(2+) and Mg(2+) were 14.57 g/L, 177.28 mg/L and 691.98 mg/L, respectively. The results were further verified by triplicate experiments. The batch reactors were operated under an optimized condition of the respective glucose, Fe(2+) and Mg(2+) concentration of 14.5 g/L, 180 mg/L and 690 mg/L, the initial pH of 6.0 and experimental temperature of 35+/-1(o)C. Without further pH adjustment, the maximum hydrogen yield of 2.20 mol/mol glucose was obtained based on the optimized medium with further verified the practicability of this optimum strategy.

Hydrogen production with effluent from an ethanol–H2-coproducing fermentation reactor using a single-chamber microbial electrolysis cell

Hydrogen can be produced by bacterial fermentation of sugars, but substrate conversion to hydrogen is incomplete. Using a single-chamber microbial electrolysis cell (MEC), we show that additional hydrogen can be produced from the effluent of an ethanol-type dark-fermentation reactor. An overall hydrogen recovery of 83+/-4% was obtained using a buffered effluent (pH 6.7-7.0), with a hydrogen production rate of 1.41+/-0.08 m(3) H(2)/m(3) reactor/d, at an applied voltage of E(ap)=0.6 V. When the MEC was combined with the fermentation system, the overall hydrogen recovery was 96%, with a production rate of 2.11 m(3) H(2)/m(3)/d, corresponding to an electrical energy efficiency of 287%. High cathodic hydrogen recoveries (70+/-5% to 94+/-4%) were obtained at applied voltages of 0.5-0.8 V due to shorter cycle times, and repression of methanogen growth through exposure of the cathode to air after each cycle. Addition of a buffer to the fermentation effluent was critical to MEC performance as there was little hydrogen production using unbuffered effluent (0.0372 m(3) H(2)/m(3)/d at E(ap)=0.6 V, pH 4.5-4.6). These results demonstrate that hydrogen yields from fermentation can be substantially increased by using MECs.

Efficient electricity generation from sewage sludge usingbiocathode microbial fuel cell

Microbial fuel cells (MFCs) with abiotic cathodes require expensive catalyst (such as Pt) or catholyte (such as hexacynoferrate) to facilitate oxidation reactions. This study incorporated biocathodes into a three-chamber MFC to yield electricity from sewage sludge at maximum power output of 13.2 ± 1.7 W/m(3) during polarization, much higher than those previously reported. After 15 d operation, the total chemical oxygen demand (TCOD) removal and coulombic efficiency (CE) of cell reached 40.8 ± 9.0% and 19.4 ± 4.3%, respectively. The anolyte comprised principally acetate and propionate (minor) as metabolites. The use of biocathodes produced an internal resistance of 36-46 Ω, lower than those reported in literature works, hence yielding higher maximum power density from MFC. The massively parallel sequencing technology, 454 pyrosequencing technique, was adopted to probe microbial community on anode biofilm, with dominant phyla belonging to Proteobacteria (45% of total bacteria), Bacteroidetes (19%), Uncultured bacteria (9%), Actinobacteria (7%), Firmicutes (7%), Chloroflex (7%). At genera level, Rhodoferax, Ferruginibacter, Propionibacterium, Rhodopseudomonas, Ferribacterium, Clostridium, Chlorobaculum, Rhodobacter, Bradyrhizobium were the abundant taxa (relative abundances>2.0%).

Accelerated Reduction of Chlorinated Nitroaromatic Antibiotic Chloramphenicol by Biocathode

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.

Sequestration of CO2 discharged from anode by algal cathode in microbial carbon capture cells (MCCs).

Due to increased discharge of CO(2) is incurring problems, CO(2) sequestration technologies require substantial development. By introducing anodic off gas into an algae grown cathode (Chlorella vulgaris), new microbial carbon capture cells (MCCs) were constructed and demonstrated here to be an effective technology for CO(2) emission reduction with simultaneous voltage output without aeration (610+/-50 mV, 1000 Omega). Maximum power densities increased from 4.1 to 5.6 W/m(3) when the optical density (OD) of cathodic algae suspension increased from 0.21 to 0.85 (658 nm). Compared to a stable voltage of 706+/-21 mV (1000 Omega) obtained with cathodic dissolved oxygen (DO) of 6.6+/-1.0 mg/L in MCC, voltage outputs decreased from 654 to 189 mV over 70 h in the control reactor (no algae) accompanied with a decrease in DO from 7.6 to 0.9 mg/L, indicating that cathode electron acceptor was oxygen. Gas analysis showed that all the CO(2) generated from anode was completely eliminated by catholyte, and the soluble inorganic carbon was further converted into algal biomass. These results showed the possibility of a new method for simultaneous carbon fixing, power generation and biodiesel production during wastewater treatment without aeration.