Electricity generation in microbial fuel cells using neutral red as an electronophore

Neutral red (NR) was utilized as an electron mediator in microbial fuel cel ls consuming glucose to study both its efficiency during electricity genera tion and its role in altering anaerobic growth and metabolism of Escherichi a coli and Actinobacillus succinogenes. A study of chemical fuel cells in w hich NADH, NR, and ferricyanide were the electron donor, the electronophore , and the electron acceptor, respectively, showed that electrical current p roduced from NADH was proportional to the concentration of NADH, fourfold m ore current was produced from NADH in chemical fuel cells when NR was the e lectron mediator than when thionin was the electron mediator. Ln microbial fuel cells in which E. coli resting cells were used the amount of current p roduced from glucose when NR was the electron mediator (3.5 mA) was 10-fold more than the amount produced when thionin was the electron mediator (0.4 mA). The amount of electrical energy generated (expressed in joules per mol e of substrate) and the amount of current produced from glucose (expressed in milliamperes) in NR-mediated microbial fuel cells containing either E. c oli or succinogenes were about 10- and 2-fold greater, respectively, when r esting cells were used than when growing cells were used. Cell growth was i nhibited substantially when these microbial fuel cells were making current, and more oxidized end products were formed under these conditions. When se c-age sludge (i.e,, a mixed culture of anaerobic bacteria) was used in the fuel cell, stable (for 120 h) and equivalent levels of current were obtaine d with glucose, as observed in the pure-culture experiments. These results suggest that NR is better than other electron mediators used in microbial f uel cells and that sludge production can be decreased while electricity is produced in fuel cells, Our results are discussed in relation to factors th at may improve the relatively low electrical efficiencies (1.2 kJ/mol) obta ined with microbial fuel cells.