Bioelectricity production from a phytoplankton, Chlorella vulgaris, and a macrophyte, Ulva lactuca was examined in single chamber microbial fuel cells (MFCs). MFCs were fed with the two algae (as powders), obtaining differences in energy recovery, degradation efficiency and power densities. C. vulgaris produced more energy generation per substrate mass (2.5k Wh/kg), but U. lactua was degraded more completely over a batch cycle (73 +/- 1%, COD). Maximum power densities obtained using other single cycle or multiple cycle methods were 0.98 W/m(2) (277 W/m(3)) using C. vulgaris, and 0.76 W/m(2) (215 W/m(3)) using U. lactuca. Polarization curves obtained using a common method of linear sweep voltammetry, (LSV) overestimated maximum power densities at a scan rate of 1 mV/s. At 0.1 mV/s, however, the LSV polarization data was in better agreement with single and multiple-cycle polarization curves. The fingerprints of microbial communities developed in reactors had only 11% similarity to inocula and clustered according to the type of bioprocessed used. These results demonstrated that electricity production in MFCs. Biotechnol, Bioeng. 2009,103: 1068-1076. (C) 2009 Wiley Periodicals, Inc.