M.M. Ghangrekar

Performance of microbial fuel cell subjected to variation in pH, temperature, external load and substrate concentration.

During field application, the microbial fuel cell (MFC) will be exposed to variations in operating parameters. Hence, the performance of MFC, exposed to variation in temperature, pH, external resistance and influent chemical oxygen demand (COD), was investigated in the terms of coulombic efficiency (CE) and COD removal efficiency, while treating a synthetic wastewater. The performance was analyzed under two temperature ranges such as 20-35 degrees C and 8-22 degrees C. Operation under higher temperature range favored higher COD removal efficiency of 90% and lower current (0.7 mA) and CE (1.5%). At lower temperature range, although the COD removal efficiency of MFC decreased (59%), it gave higher current (1.4 mA) and CE (5%). The highest current was generated at pH of 6.5 in the anodic chamber with CE of 4%. Higher pH difference between anodic and cathodic electrolyte favored higher current and voltage. Within the range of COD tested (100-600 mg/l), linear correlation was observed between the current and substrate removed.

Rice mill wastewater treatment in microbial fuel cells fabricated using proton exchange membrane and earthen pot at different pH

Performance of microbial fuel cells (MFCs), fabricated using an earthen pot (MFC-1) and a proton exchange membrane (MFC-2), was evaluated while treating rice mill wastewater at feed pH of 8.0, 7.0 and 6.0. A third MFC (MFC-3), fabricated using a proton exchange membrane (PEM), was operated as control without pH adjustment of the acidic raw wastewater. Maximum chemical oxygen demand (COD) removal efficiencies of 96.5% and 92.6% were obtained in MFC-1 and MFC-2, respectively, at feed pH of 8.0. MFC-3 showed maximum COD removal of 87%. The lignin removal was 84%, 79%, and 77% and the phenol removal was 81%, 77%, and 76% in MFC-1, MFC-2, and MFC-3, respectively. Maximum sustainable volumetric power was obtained at feed pH of 8.0, and it was 2.3 W/m(3) and 0.53 W/m(3), with 100 ohm external resistance, in MFC-1 and MFC-2, respectively. The power was lower at lower feed pH. MFC-3 generated lowest volumetric power (0.27 W/m(3)) as compared to MFC-1 and MFC-2. More effective treatment of rice mill wastewater and higher energy recovery was demonstrated by earthen pot MFC as compared to MFC incorporated with PEM.

Performance evaluation of low cost microbial fuel cell fabricated using earthen pot with biotic and abiotic cathode.

An attempt has been made to produce low cost MFC from the commercially available earthen pots in India, without involving any costly membrane. This MFC gave a maximum power output of 16.8 W/m(3) at a Coulombic efficiency (CE) of 31.3% with graphite plate cathode. With stainless steel mesh cathode and KMnO(4) as cathodic electrolyte the power production and CE of 70.48 W/m(3) and 64.5%, respectively, was obtained. The performance of this earthen pot MFC was evaluated with biotic and abiotic cathode. Although, biofilm formation on the cathode is observed to be helpful in enhancing power out put, the thicker biofilm on the cathode showed reduction in power. This MFC demonstrated competitive performance as compared to MFC incorporated with membrane. This low cost MFC, with total production cost of less than 1.0

Experience with UASB reactor start-up under different operating conditions

, as per Indian market, demonstrated its utility as a wastewater treatment and onsite power generation device.

PERFORMANCE OF MICROBIAL FUEL CELL IN RESPONSE TO CHANGE IN SLUDGE LOADING RATE AT DIFFERENT ANODIC FEED PH

Four laboratory upflow anaerobic sludge blanket (UASB) reactors were operated at different operating parameters viz ., hydraulic retention time (HRT), upflow velocity, organic concentration, and Ca2+ concentration in the wastewater. These operating parameters gave different values of organic loading rates (OLRs) and sludge loading rates (SLRs). The reactor performance during start-up was evaluated at different values of the above listed parameters. Also, the effects of these parameters on the granule characteristics were investigated. It was observed that COD removal efficiency at steady state was profoundly influenced by SLR. The reactor started with SLR of 0.6 kgCOD/ kg VSS.d could result in about 50% COD removal at steady state. The reactor performance could not improve even after three months of operation. Up to 0.3 kgCOD/ kgVSS.d the reactor performance was good with more than 90% COD removal at steady state. The OLD and SLR also determine time required for the reactor to achieve steady state. Different operating conditions also have the bearing on the strength of the granules cultivated. The methanogenic activity measured on acetate for each reactor was observed between 0.259 and 0.909 kg CH4 COD/ kgVSS.d. The sludge production in all the reactors was between 0.087 and 0.13 kgVSS/ kgCODin. The mathematical model was developed in order to predict sludge production.

Application of electro-active biofilms

Performance of two dual chambered mediator-less microbial fuel cells (MFCs) was evaluated at different sludge loading rate (SLR) and feed pH. Optimum performance in terms of organic matter removal and power production was obtained at the SLR of 0.75 kg COD kg VSS(-1) d(-1). Maximum power density of 158 mW/m(2) and 600 mW/m(2) was obtained in MFC-1 (feed pH 6.0) and MFC-2 (feed pH 8.0), respectively. Internal resistance of the cell decreased with increase in SLR. When operated only with biofilm on anode, the maximum power density was 109.5 mW/m(2) in MFC-1 and 459 mW/m(2) in MFC-2, which was, respectively, 30% and 23.5% less than the value obtained in MFC-1 and MFC-2 at SLR of 0.75 kg COD kg VSS(-1) d(-1). Maximum volumetric power of 15.51 W/m(3) and 36.72 W/m(3) was obtained in MFC-1 and MFC-2, respectively, when permanganate was added as catholyte. Higher feed pH (8.0) favoured higher power production.

Effect of chemically modified Vulcan XC-72R on the performance of air-breathing cathode in a single-chamber microbial fuel cell

The concept of an electro-active biofilm (EAB) has recently emerged from a few studies that discovered that certain bacteria which form biofilms on conductive materials can achieve a direct electrochemical connection with the electrode surface using it as electron exchanger, without the aid of mediators. This electro-catalytic property of biofilms has been clearly related to the presence of some specific strains that are able to exchange electrons with solid substrata (eg Geobacter sulfurreducens and Rhodoferax ferrireducens). EABs can be obtained principally from natural sites such as soils or seawater and freshwater sediments or from samples collected from a wide range of different microbially rich environments (sewage sludge, activated sludge, or industrial and domestic effluents). The capability of some microorganisms to connect their metabolisms directly in an external electrical power supply is very exciting and extensive research is in progress on exploring the possibilities of EABs applications. Indeed, the best known application is probably the microbial fuel cell technology that is capable of turning biomass into electrical energy. Nevertheless, EABs coated onto electrodes have recently become popular in other fields like bioremediation, biosynthesis processes, biosensor design, and biohydrogen production.

Graphene supported α-MnO2 nanotubes as a cathode catalyst for improved power generation and wastewater treatment in single-chambered microbial fuel cells

The catalytic activity of modified carbon powder (Vulcan XC-72R) for oxygen reduction reaction (ORR) in an air-breathing cathode of a microbial fuel cell (MFC) has been investigated. Chemical modification was carried out by using various chemicals, namely 5% nitric acid, 0.2N phosphoric acid, 0.2N potassium hydroxide and 10% hydrogen peroxide. Electrochemical study was performed for ORR of these modified carbon materials in the buffer solution pH range of 6-7.5 in the anodic compartment. Although, these treatments influenced the surface properties of the carbon material, as evident from the SEM-EDX analysis, treatment with H(2)PO(4), KOH, and H(2)O(2) did not show significant activity during the electrochemical test. The HNO(3) treated Vulcan demonstrated significant ORR activity and when used in the single-chamber MFC cathode, current densities (1115mA/m(2), at 5.6mV) greater than those for a Pt-supported un-treated carbon cathode were achieved. However, the power density for the latter was higher. Such chemically modified carbon material can be a cheaper alternative for expensive platinum catalyst used in MFC cathode construction.

Improving performance of microbial fuel cell with ultrasonication pre-treatment of mixed anaerobic inoculum sludge.

Microbial fuel cells (MFC) are a promising system to simultaneously accomplish the goal of energy production and wastewater treatment. In the MFC, the cathode plays an important role in achieving high power density and thereby improving the cell performance. In the cathode, an allotrope of carbon [activated carbon, graphite, multi-walled carbon nanotubes (MWCNTs)] is commonly used as a support material for catalysts, such as Pt. Here we show the improved performance of single-chambered MFC (sMFC) using hydrothermally synthesized α-manganese dioxide nanotubes (MnO2-NTs) as the catalyst and graphene as the support in the cathode. With a fixed MnO2-NTs loading, a maximum volumetric power density of 4.68 W m−3 was achieved from the sMFC with MnO2-NTs/graphene, which is higher than that of MnO2-NTs/MWCNTs (3.94 W m−3) and MnO2-NTs/Vulcan XC (2.2 W m−3) composite cathodes, but marginally lower than that of the benchmark Pt/C cathode (5.67 W m−3). The MnO2-NTs/graphene composite also showed a higher oxygen reduction reaction (ORR) activity than the MnO2-NTs/MWCNTs and MnO2-NTs/Vulcan XC composites implying that the former is a better catalyst than the later two. This study demonstrates the high ORR activity and high power generation ability of the cost-effective MnO2-NTs/graphene composite and makes it a potential cathode material for the replacement of expensive Pt in constructing large-scale MFC for wastewater treatment and bioelectricity production.

Comparison of oxygen and hypochlorite as cathodic electron acceptor in microbial fuel cells.

Effect of low-frequency ultrasound pre-treatment to inoculum on performance of microbial fuel cell (MFC) was evaluated. Mixed anaerobic sludge was pre-treated with ultrasonication duration of 2.5, 5, 7.5, and 15 min, and the performance of MFC using this inoculum was compared with the MFC inoculated without any pre-treatment to the sludge. The effect of combined pre-treatment, using ultrasonication and heating of the inoculum, on performance of the MFC was also evaluated. Maximum power density during polarization in a MFC inoculated with ultrasonication pre-treatment to the sludge for 5 min (40 kHz, 120 W) was 2.5 times higher than that obtained without any pre-treatment to the inoculum sludge. Substrate removal was higher in the MFC with ultrasonicated inoculum, than inoculum without any pre-treatment and combined pre-treated with ultrasonication and heating. These results evidently demonstrated the advantages of ultrasonication pre-treatment to the inoculum for enhancing power and organic matter removal of the MFC.