Characterization of the sulfate reduction process in the anaerobic digestion of a very high strength and sulfate rich vinasse

• Sulfate reduction of a very high strength and sulfate rich vinasse was characterized.
• Close mass balances indicated that the data were suitable for dynamic modeling.
• Variations in biogas quality (by H2Sgas) were highest at a SO42−/COD ratio of 0.05.
• H2Saq and [H2S]free inhibited methanogens and SRBs at SO42−/COD ratios ⩾0.10.
• Propionate uptake at SO42−/COD ratios ⩽0.10 suggested strong contribution of pSRB.

This article characterizes the sulfate reduction process in the anaerobic digestion of a very high strength and sulfate rich vinasse, where chemical oxygen demand (COD) and sulfate (SO42−) pulses were applied at different SO42−/COD ratios to obtain dynamical responses. The results showed an increase in H2Sgas of up to 33%, when influent COD (inf_COD) and influent SO42− (inf_SO42−) increased at a SO42−/COD ratio of 0.05. A decrease of inf_COD together with an increase of inf_SO42− caused propionic acid degradation (up to 90%), suggesting strong contribution of propionate degrading sulfate reducing bacteria at SO42−/COD ratios ⩽0.10, in contrast to literature results. The inf_COD and inf_SO42− fluctuations at a SO42−/COD ratio of 0.10 caused inhibition by H2Saq, [H2S]free and propionic acid to sulfate reducing bacteria (SRBs), methanogens or both. At a SO42−/COD ratio of 0.20 this inhibition became severe for methanogens and SRBs, leading to reactor failure. Mass balance calculations showed COD and sulfur recoveries from 90% to 98% in most cases. Increments of inf_COD within a constant SO42−/COD ratio (0.05 or 0.10) accumulated as effluent COD rather than as COD_CH4gas, showing deterioration of the anaerobic digestion, while the sulfur was displaced to the gas phase at a SO42−/COD ratio of 0.05 or to the liquid phase at SO42−/COD ratios ⩾0.10. Based on the closed mass balances results, the data presented here are considered reliable for calibrating mathematical models, when sulfate reduction in the anaerobic digestion of a very high strength and sulfate rich vinasse is of primary interest.