Cheese whey wastewater diluted to 10 g lactose/L was initially subjected to dark-fermentation by Enterobacter aerogenes MTCC 2822, and the VFAs-rich spent medium (acetic acid 1900 mg/L, butyric acid 537 mg/L, and traces of propionic acid) was subjected to photo-fermentation through enrichment by Ni2+ (0-8 mu mol/L), Fe2+ (0-100 [mu mo]a) or me(0-15 mmol/L) in batch mode by Rhodopseudomonas BHU 01 strain. The maximum cumulative H-2 production (144 ml) and yield (58 mmol) was obtained at 4 gmol Ni2+/L. Likewise, Fe2 (60 p.moVL) resulted in maximum cumulative H2 production (139 ml) and yield (56 mmol). Nevertheless, 6 mmol of me did not significantly affect H2 production (110 ml) or yield (44 mmol); the latter value in close proximity with the control (37 mmol). The concomitant reduction in COD was maximum (15.61%) for 4 irtmol Ne+/L, followed by 15.33% for 60 jimol Fe2'11. and the least for 6 mmol mem (14.5%). The observations suggest the role of Fe2+ and Ni2 ' in regulation of nitrogenase and hydrogenase, while that of me+ mainly in the biosynthesis of photopigment bacteriochlorophyll (Bchl). Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.