Characterization of the curing process from high-solids anaerobic digestion

A laboratory-scale study was completed to simulate aerobic curing of solid-phase residue (digestate) from an anaerobic reactor fed a mixture of food and landscape wastes. The degree of organic stabilization was determined through routine analysis of oxygen uptake rates, percent O2, temperature, volatile solids, and Solvita Maturity Index; measurements of ammonia and volatile fatty acid (VFA) concentrations served as indicators of phytotoxicity. Results suggest that stabilization of organics and elimination of phytotoxic compounds from anaerobic digestate preceded significant reduction of each volatile sulfur compound (VSC) detected (hydrogen sulfide, methanethiol, and dimethyl sulfide). Within 10–15 days of curing, stabilization of organics was achieved and phytotoxic compounds were eliminated, whereas reduction of VSCs to low levels required 15–20 days of curing. Based on these results, incomplete curing and anaerobic microenvironments within a curing facility may increase odor potential via formation of VSCs, whereas sufficiently cured digestate will resist VSC formation, despite the onset of anaerobic conditions.