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

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_SO) 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 in contrast to literature results. The inf_COD and inf SOi- 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. (C) 2014 Elsevier B.V. All rights reserved.