Modeling the Conversion and Fate of Sulfur Containing Compounds in Mesophilic Anaerobic Digestion

Three types of batch tests were conducted in support of modeling the conversion and fate of sulfur-containing compounds in mesophilic anaerobic digestion. The important role of methanogens in volatile organic sulfur compounds (VOSCs) degradation was confirmed by comparing their behaviour in incubations that were conducted with and without methanogeninhibitor (sodium 2-bromoethanesulfonic, BES). Degradation rates of VOSCs were estimated from the results of batch tests in which VOSCs were dosed. In these tests it was found that acetate, which was added as a potentially competing carbon source with the VOSCs, had no effect on VOSC degradation. Incubations of methionine with methanogen-inhibition were performed to estimate the rates of formation of VOSCs from this sulfur-containing amino acid. Through collective analysis of the results of the batch tests, the conversion processes of VSCs during anaerobic digestion have been framed. Zero order kinetics have been found to describe the conversion processes and rate constants have been developed. Furthermore, the relationship between the releases of ammonia-N and VSC-S during mesophilic anaerobic digestion was explored. Simultaneous release of ammonia-N and VSC-S was observed when the simple substrate, methionine, was used. However, ammonia did not represent the release of VSC-S when raw sludge was used as the digestion substrate.