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

Abstract

Abstract 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 (SO 4 2− ) pulses were applied at different SO 4 2− /COD ratios to obtain dynamical responses. The results showed an increase in H 2 S gas of up to 33%, when influent COD (inf_COD) and influent SO 4 2− (inf_SO 4 2− ) increased at a SO 4 2− /COD ratio of 0.05. A decrease of inf_COD together with an increase of inf_SO 4 2− caused propionic acid degradation (up to 90%), suggesting strong contribution of propionate degrading sulfate reducing bacteria at SO 4 2− /COD ratios ⩽0.10, in contrast to literature results. The inf_COD and inf_SO 4 2− fluctuations at a SO 4 2− /COD ratio of 0.10 caused inhibition by H 2 S aq, [H 2 S] free and propionic acid to sulfate reducing bacteria (SRBs), methanogens or both. At a SO 4 2− /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 SO 4 2− /COD ratio (0.05 or 0.10) accumulated as effluent COD rather than as COD_CH 4gas , showing deterioration of the anaerobic digestion, while the sulfur was displaced to the gas phase at a SO 4 2− /COD ratio of 0.05 or to the liquid phase at SO 4 2− /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.