Anaerobic Co-Digestion of Acid Mine Drainage, Sugarcane Vinasse and Glycerol: Effects on Sulfidogenesis and Alkalinization Capacity

Abstract

This study evaluated the anaerobic co-digestion of sugarcane vinasse and glycerol, by-products of biofuel production, for the treatment of acid mine drainage (AMD) under sulfidogenic conditions (pH 4.0–5.4). Reactor operation was divided into six phases, varying carbon sources and COD/SO4²⁻ (Chemical oxygen demand/ sulfate) ratios. In Phases I–III, vinasse and AMD were co-digested, while glycerol was introduced in Phase IV, achieving 99% sulfate removal. Sulfide existed primarily as HS⁻, with H₂S concentrations kept below inhibitory levels (<200 mg L⁻¹). Sulfate reduction led to significant alkalinity generation, with bicarbonate alkalinity remaining above 900 mg L⁻¹ in Phases III–V, raising pH from 4.6–5.4 to near-neutral (7.1–7.7). Reduced sulfate and COD removal in Phase VI were attributed to insufficient biomass adaptation to metals, lower influent pH, and acetate accumulation. Microbial analysis revealed Desulfovibrio (5.3%) as the dominant sulfate-reducing bacteria (SRB), with fermentative bacteria like Zymophilus (24.8%), Clostridium (13.0%), and Bacteroides (11.5%) playing significant roles in sulfidogenesis at moderately acidic pH levels. The co-digestion of glycerol and sugarcane vinasse has proven to be a promising approach for the treatment of sulfate-rich wastewater, offering an environmentally sustainable solution for the disposal of these by-products from biofuel production.

Keywords: Desulfovibrio, sulfate reduction, Anaerobic digestion, alkalinization, sulfate-reducing bacteria