The quantitative relationship between sulfate reducing bacteria (SRB) and hydrogen (H(2)) production from sulfate (SO(4)(2-)) and ferrous [Fe(II)] enriched wastewater was investigated. Both Fe(II) (0-11,600 mg/L) and SO(4)(2-) (0-20,000 mg/L) improved the H(2) production efficiency from wastewater. The H(2) yields were increased up to 1.9 mol H(2)/mol glucose in 580-1750 mg Fe(II)/L and 1000-3000 mg SO(4)(2-)/L enriched wastewater at pH 5.8-6.2. Quantitative Fluorescence In Situ Hybridization (FISH) analyses revealed that the specific sulfate reducing activities (SSRA) were increased from 0.08 and 0.06 to 0.16 and 0.21 g TS/g SRB h in response to variations in sulfate concentration from 300-20,000 mg/L at pH 5.8 and 6.2, respectively. H(2) production was not influenced by low SSRA (<= 0.1 g TS/g SRB h), which was independent of pH variation. The results demonstrated that the SSRA and Fe(II) concentration can significantly influence on the biological H(2) production from SO(4)(2-) and Fe(II) containing wastewater. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.