The characteristics of hydrogen production from individual and mixed volatile fatty acids (VFAs) were compared among three photosynthetic bacterial strains, Rhodopseudomonas sp., Rhodopseudomonas palustirs W004 and Rubrivivax sp. Rhodopseudomonas sp. and R. palustirs W004 could convert both butyrate and acetate into hydrogen. Rubrivivax sp. could assimilate butyrate and acetate, but could not produce hydrogen from them when individual VFA was used as substrate. The highest hydrogen amount (2191.7 mL/L culture), COD reduction efficiency (85.3%) and H(2) yield (468.3 mL H(2)/g COD) were achieved by Rhodopseudomonas sp. with butyrate as carbon source. All the three strains could produce hydrogen from mixed VFAs. Rhodopseudomonas sp. and R. palustirs W004 could digest the substrates completely. Hydrogen production from mixed VFAs by Rubrivivax sp. lasted for 3.7 days and only 38.8% of COD was reduced, for high pH value of the culture harmed hydrogen production. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.