We are developing a process to produce biohydrogen from palm oil mill effluent. Part of this process will involve photohydrogen production from volatile fatty acids under low light conditions. We sought to isolate suitable bacteria for this purpose from Songkhla Lake in Southern Thailand. Enrichment for phototrophic bacteria from 34 samples was conducted providing acetate as a major carbon source and applying culturing conditions of anaerobic-low light (3000 lux) at 30 degrees C. Among the independent isolates from these enrichments 19 evolved hydrogen with productivities between 4 and 326 ml l(-1) d(-1). Isolate TN1 was the most efficient producer at a rate of 1.85 mol H(2) mol acetate(-1) with a light conversion efficiency of 1.07%. The maximum hydrogen production rate for TN1 was determined to be 43 ml l(-1) h(-1). Environmentally desirable features of photohydrogen production by TN1 included the absence of pH change in the cultures and no detectable residual CO(2). (C) 2009 Published by Elsevier Ltd on behalf of international Association for Hydrogen Energy.