Microbial fuel cells with Photosynthetic-Cathodic chamber in vertical cascade for integrated Bioelectricity, biodiesel feedstock production and wastewater treatment.

This study aimed to develop efficient microbial fuel cells (MFCs) for integrated bioelectricity, biodiesel feedstock production and wastewater treatment. Among wastewaters tested, MFC fed with anaerobic digester effluent from rubber industry gave the maximum power density (55.43 ± 1.08 W/m3) and simultaneously removed COD, nitrogen and phosphorus (by 72.4 ± 0.9%, 40.5 ± 0.8% and 24.4 ± 1.5%, respectively). 16S rRNA gene analysis revealed that dominant microbial communities were: Firmicutes (43.68%), Bacteroidetes (25.41%) and Chloroflexi (15.02%), which mostly contributed to bioelectricity generation. After optimizing organic loading rate, photosynthetic oleaginous microalgae were applied in cathodic chamber in order to increase oxygen availability, secondarily treat anodic chamber effluent and produce lipids as biodiesel feedstocks. Four MFCs with photosynthetic-cathodic chamber connected in vertical cascade could improve power density up to 116.9 ± 15.5 W/m3, sequentially treat wastewater, and also produce microalgal biomass (465 ± 10 g/m3) with high lipid content (38.17 ± 0.01%). These strategies may greatly contribute to sustainable development of integrated bioenergy generation and environment.

Enhancing Electricity Generation Using a Laccase-Based Microbial Fuel Cell with Yeast Galactomyces reessii on the Cathode.

The fungi associated with termites secrete enzymes such as laccase (multi-copper oxidase) that can degrade extracellular wood matrix. Laccase uses molecular oxygen as an electron acceptor to catalyze the degradation of organic compounds. Owing to its ability to transfer electrons from the cathodic electrode to molecular oxygen, laccase has the potential to be a biocatalyst on the surface of the cathodic electrode of a microbial fuel cell (MFC). In this study, a two-chamber MFC using the laccase-producing fungus Galactomyces reessii was investigated. The fungus cultured on coconut coir was placed in the cathode chamber, while an anaerobic microbial community was maintained in the anode chamber fed by industrial rubber wastewater and supplemented by sulfate and a pH buffer. The laccase-based biocathode MFC (lbMFC) produced the maximum open circuit voltage of 250 mV, output voltage of 145 mV (with a 1,000 Ω resistor), power density of 59 mW/m2, and current density of 278 mA/m2, and a 70% increase in half-cell potential. This study demonstrated the capability of laccase-producing yeast Galactomyces reessii as a biocatalyst on the cathode of the two-chamber lbMFC.

Development of a UBFC biocatalyst fuel cell to generate power and treat industrial wastewaters.

Agro-industry wastewaters normally contain high levels of organic matter and require suitable treatment before discharge. The use of Microbial fuel cells, a novel wastewater treatment, can provide advantages over existing treatment methods. In this study, an up-flow bio-filter circuit (UBFC) for treating wastewaters without chemical treatment or nutrient supplement, was developed to solve a clogging problem. The optimal conditions included an organic loading rate of 30.0 g COD/L-d, hydraulic retention time of 1.04 day, pH level of 5.6-6.5 and aeration at 2.0 L/min. External resistance of the circuit was tested. COD removal levels of 8.08, 20.1 and 26.67 g COD/L-d were obtained, while fed with sea food, biodiesel and palm oil mill wastewater, respectively. These rates are higher than for conventional technologies. The carbon fiber brush immobilized base increased the performance of the new UBFC by 17.54% over that obtained in a previous study, while the cost was slightly decreased about 4.48%.

Upflow bio-filter circuit (UBFC): biocatalyst microbial fuel cell (MFC) configuration and application to biodiesel wastewater treatment.

A biodiesel wastewater treatment technology was investigated for neutral alkalinity and COD removal by microbial fuel cell. An upflow bio-filter circuit (UBFC), a kind of biocatalyst MFC was renovated and reinvented. The developed system was combined with a pre-fermented (PF) and an influent adjusted (IA) procedure. The optimal conditions were operated with an organic loading rate (OLR) of 30.0 g COD/L-day, hydraulic retention time (HRT) of 1.04 day, maintained at pH level 6.5-7.5 and aerated at 2.0 L/min. An external resistance of circuit was set at 10 kΩ. The purposed process could improve the quality of the raw wastewater and obtained high efficiency of COD removal of 15.0 g COD/L-day. Moreover, the cost of UBFC system was only US$1775.7/m3 and the total power consumption was 0.152 kW/kg treated COD. The overall advantages of this invention are suitable for biodiesel wastewater treatment.

Effect of nitrate on the performance of single chamber air cathode microbial fuel cells.

The effect of nitrate on the performance of a single chamber air cathode MFC system and the denitrification activity in the system were investigated. The maximum voltage output was not affected by 8.0mM nitrate in the medium solution at higher external resistance (270-1000Omega), but affected at lower resistance (150Omega) possibly due to the low organic carbon availability. The Coulombic efficiency was greatly affected by the nitrate concentration possibly due to the competition between the electricity generation and denitrification processes. Over 84-90% of nitrate (0.8-8.0mM) was removed from the single chamber MFCs in less than 8h in the first batch. After 4-month operation, over 85% of nitrate (8.0mM) was removed in 1h after the MFC was continuously fed with a medium solution containing nitrate. Only a small amount of nitrite (<0.01mM) was detected during the denitrification process. The similar denitrification activity observed at different external resistances (1000 and 270Omega) and open circuit mode indicates that the denitrification was not significantly affected by the electricity generation process. No electricity was generated when the MFC fed with 8.0mM nitrate was moved to a glove box (no oxygen), indicating that the bacteria on the cathode did not involve in accepting electrons from the circuit to reduce the nitrate. Denaturing Gradient Gel Electrophoresis (DGGE) profiles demonstrate a similar bacterial community composition on the electrodes and in the solution but with different dominant species.