Performance of the Acid-Gas Anaerobic Digestion Process for Minimization of Siloxane and Hydrogen Sulfide in the Biogas

During anaerobic sludge digestion, organosilicon compounds volatilize, enter the gas recovery stream, and are oxidized to microcrystalline silicon dioxide causing significant damage to energy infrastructure. This research investigated the effect of acid-gas anaerobic digestion on the behavior of the volatilization of these organosilicon compounds, particularly octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5). A bench scale acid reactor was operated at varying solids retention times and temperatures in order to quantify the effects in the downstream gas reactor, which was operated at a constant mesophilic conditions. Results indicated that the tested acid reactor conditions did not cause a change in behavior of the D4 and D5 siloxane volatilization in the gas reactor. However, it was observed that hydrogen sulfide gas was decreased in the gas reactor when an acid reactor was utilized. Cumulative volatile solids reduction and gas reactor methane yield data did not indicate an enhancement due to utilization of acid-gas digestion.