The promise of generating electricity from the oxidation of organic substances using metal reducing bacteria is drawing attention as an alternate form of bio technology with positive environmental implications In this study we examined various experimental factors to obtain the maximum power output in a dual chamber mediator less microbial fuel cell (MFC) using Geobacter sulfurreducens and acetate as an electron donor in a semi continuous mode The G sulfurreducens culture conditions were optimized in a nutrient buffer containing 20 mM of acetate and 50 mM of fumarate at pH 6 8 and 30 degrees C For use in the MFC system electrodes were made with carbon paper (area 11 5 cm(2)) and spaced 1 5 cm apart Once the MFC was inoculated with the pre cultured G sulfurreducens in the anode chamber and while air was continuously sparged to the cathode chamber, the cells produced electricity stably over 60 days with the regular addition of 20 mM acetate generating the maximum power density of 7 mW/m(2) with a 5000 Omega load The current output was significantly increased by 1 6 times after 20 days of incubation under the same experimental conditions when the carbon paper anode was coated with carbon nanotubes (C) 2010 Professor T Nejat Veziroglu Published by Elsevier Ltd All rights reserved