Yong Yuan

Scalable microbial fuel cell (MFC) stack for continuous real wastewater treatment.

A tubular air-cathode microbial fuel cell (MFC) stack with high scalability and low material cost was constructed and the ability of simultaneous real wastewater treatment and bioelectricity generation was investigated under continuous flow mode. At the two organic loading rates (ORLs) tested (1.2 and 4.9kg COD/m(3)d), five non-Pt MFCs connected in series and parallel circuit modes treating swine wastewater can enable an increase of the voltage and the current. The parallel stack retained high power output and the series connection underwent energy loss due to the substrate cross-conduction effect. With continuous electricity production, the parallel stack achieved 83.8% of COD removal and 90.8% of NH(4)(+)-N removal at 1.2kg COD/m(3)d, and 77.1% COD removal and 80.7% NH(4)(+)-N removal at 4.9kg COD/m(3)d. The MFC stack system in this study was demonstrated to be able to treat real wastewater with the added benefit of harvesting electricity energy.

Enhanced performance of air-cathode two-chamber microbial fuel cells with high-pH anode and low-pH cathode

In the course of microbial fuel cell (MFC) operation, the acidification of the anode and the alkalization of the cathode inevitably occur, resulting in reduction of the overall performance. In an attempt to reverse the membrane pH gradient, a tubular air-cathode two-chamber MFC was developed that allowed pH adjustment in both compartments. With an anodic pH of 10.0 and a cathodic pH of 2.0, the tubular MFC provided an open circuit voltage of 1.04V and a maximum power density of 29.9W/m(3), which were respectively 1.5 and 3.8 times higher than those obtained in the same MFC working at neutral pH. Particularly, the suppression of methanogenesis at high alkaline anode (pH 10.0) contributed to a significant enhancement in coulombic efficiency. The MFC maintained 74% of its performance after 15 days of operation in continuous-flow mode. The appropriate pH adjustment strategy in both compartments ensures a promising improvement in MFC performance.

Long-term evaluation of a 10-liter serpentine-type microbial fuel cell stack treating brewery wastewater

A 10-liter serpentine-type microbial fuel cell (MFC) stack was constructed by extending 40 tubular air-cathode MFC units in a 3-D alignment pattern. When operated in series and fed with brewery wastewater, the stack produced an open circuit voltage of 23.0V and a maximum power density of 4.1W/m(3) (at 0.7A/m(3)). During long-term performance (180days), electrochemical tests were conducted to explore the reasons for deterioration in performance of the stack system. Cyclic voltammetric measurements suggested that the cathodes, not the anodes, were responsible for the decrease in performance over time. After the cathode surface was rinsed with water, the power density produced by the stack system fully recovered instantaneously, due to the decrease in cathode alkalization and increase in humidity of the cathode side. This study provided an optimal configuration of a MFC stack for MFC scale-up towards large-scale applications.

Electrocatalytic activity of anodic biofilm responses to pH changes in microbial fuel cells.

This study investigates the effects of anodic pH on electricity generation in microbial fuel cells (MFCs) and the intrinsic reasons behind them. In a two-chamber MFC, the maximum power density is 1170 ± 58 mW m(-2) at pH 9.0, which is 29% and 89% higher than those working at pH 7.0 and 5.0, respectively. Electrochemical measurements reveal that pH affects the electron transfer kinetics of anodic biofilms. The apparent electron transfer rate constant (k(app)) and exchange current density (i(0)) are greater whereas the charge transfer resistance (R(ct)) is smaller at pH 9.0 than at other conditions. Scanning electron microscopy verifies that alkaline conditions benefit biofilm formation in MFCs. These results demonstrate that electrochemical interactions between bacteria and electrodes in MFCs are greatly enhanced under alkaline conditions, which can be one of the important reasons for the improved MFC output.

Bioelectricity generation by a Gram-positive Corynebacterium sp. strain MFC03 under alkaline condition in microbial fuel cells

This work studied an alkalophilic Gram-positive bacterium, Corynebacterium sp. strain MFC03, for its ability to produce electricity in the absence of an exogenous mediator under alkaline pH in microbial fuel cells (MFCs). The experimental results demonstrated that the strain MFC03 was capable of utilizing organic acids, sugars and alcohols as electron donors to generate electricity under above desired conditions. At an optimal pH of 9.0, the glucose-fed MFC achieved a maximum power density of 7.3 mW/m(2) and a Coulombic efficiency (CE) of 5.9%. In the presence of 0.1mM anthroquinone-2,6-disulfonate (AQDS), the maximum power density was enhanced to 41.8 mW/m(2) and CE was increased to 18.4%. The cyclic voltammetry measurements revealed that the electron transfer mechanism in the strain MFC03-based MFC was mainly via the excreted redox compounds in the medium solution.

Bioelectricity generation and microcystins removal in a blue-green algae powered microbial fuel cell.

Bioelectricity production from blue-green algae was examined in a single chamber tubular microbial fuel cell (MFC). The blue-green algae powered MFC produced a maximum power density of 11 4 mW/m(2) at a current density of 0.55 mA/m(2). Coupled with the bioenergy generation, high removal efficiencies of chemical oxygen demand (COD) and nitrogen were also achieved in MFCs. Over 78.9% of total chemical oxygen demand (TCOD), 80.0% of soluble chemical oxygen demand (SCOD), 91.0% of total nitrogen (total-N) and 96.8% ammonium-nitrogen (NH(3)-N) were removed under closed circuit conditions in 12 days, which were much more effective than those under open circuit and anaerobic reactor conditions. Most importantly, the MFC showed great ability to remove microcystins released from blue-green algae. Over 90.7% of MC-RR and 91.1% of MC-LR were removed under closed circuit conditions (500Ω). This study showed that the MFC could provide a potential means for electricity production from blue-green algae coupling algae toxins removal.

Nitrogen-doped carbon sheets derived from chitin as non-metal bifunctional electrocatalysts for oxygen reduction and evolution

Affordable, efficient electrocatalysts for oxygen reduction reactions (ORR) and oxygen evolution reactions (OER) are critical for various energy technologies. Herein, we report that an activated carbon sheet (ACS) derived from chitin is an efficient non-metal bifunctional electrocatalyst for both ORR and OER. In alkaline media, the as-prepared ACS exhibited remarkable electrocatalytic activity for the oxygen reduction reaction, which was significantly superior to an unactivated carbon sheet (CS) and comparable to the commercial Pt/C catalyst with excellent durability and resistance to the crossover effect. Meanwhile, the same ACS also presents high catalytic activity towards OER, with a small overpotential of ∼1.64 ± 0.02 V versus RHE. The excellent electrocatalytic properties of the ACS originated from the combined effect of optimal nitrogen doping, high surface area, and porous architecture. This work demonstrates that the ACS is a promising material candidate with high-performance in electrocatalytic applications in energy technologies.

Coupling of anodic biooxidation and cathodic bioelectro-Fenton for enhanced swine wastewater treatment.

A novel bioelectrochemical reactor with anodic biooxidation coupled to cathodic bioelectro-Fenton was developed for the enhanced treatment of highly concentrated organic wastewater. Using swine wastewater as a model, the anode-cathode coupled system was demonstrated to be both efficient and energy-saving. Without any external energy supply to the system, BOD(5), COD, NH(3)-N and TOC in the wastewater could be greatly reduced at both 1.1g COD L(-1)d(-1) and 4.6g COD L(-1)d(-1) of OLR, with the overall removal rates ranging from 62.2% to 95.7%. Simultaneously, electricity was generated at around 3-8 Wm(-3) of maximum output power density. Based on electron balance calculation, 60-65% of all the electrons produced from anodic biooxidation were consumed in the cathodic bioelectro-Fenton process. This coupled system has a potential for enhanced treatment of high strength wastewater and provides a new way for efficient utilization of the electron generated from biooxidation of organic matters.

Development of Enterobacter aerogenes fuel cells: From in situ biohydrogen oxidization to direct electroactive biofilm

This study described an Enterobacter aerogenes-catalyzed microbial fuel cell (MFC) with a carbon-based anode that exhibited a maximum power density of 2.51 W/m(3) in the absence of artificial electron mediators. The MFC was started up rapidly, within hours, and the current generation in the early stage was demonstrated to result from in situ oxidation of biohydrogen produced by E. aerogenes during glucose fermentation. Over periodic replacement of substrate, both planktonic biomass in the culture liquid and hydrogen productivity decreased, while increased power density and coulombic efficiency and decreased internal resistance were unexpectedly observed. Using scanning electron microscopy and cyclic voltammetry, it was found that the enhanced MFC performance was associated with the development of electroactive biofilm on the anodic surface, proposed to involve an acclimation and selection process of E. aerogenes cells under electrochemical tension. The significant advantage of rapid start-up and the ability to develop an electroactive biofilm identifies E. aerogenes as a suitable biocatalyst for MFC applications.