Role of sulfide in regulation of the anaerobic digestion of lipids: Implications for increasing biogas production in municipal wastewater treatment plants

Anaerobic digestion (AD) of lipid-rich wastes with sewage sludge enables a utilization of the excess capacity at existing municipal anaerobic digesters for biogas production, contributing to an energy efficient wastewater treatment process and thus, a more effective use of present resources and an improved economy. However, lipids tend to degrade slowly during AD causing process disturbances, associated with accumulation of their intermediate degradation products (long chain fatty acids, LCFA) and the resulting microbial toxicity. In a laboratory trial, we observed that an increase of the sulfide level in a digester treating municipal sewage sludge resulted in a faster conversion of LCFA to biogas, by favoring growth of the LCFA-degrading microorganisms. To our knowledge, this was the first time that such a connection between sulfide level, growth of LCFA-degrading microorganisms, and LCFA turnover kinetics was reported, which provided evidences for potential regulatory role of sulfide in degradation of lipids. Thus, we hypothesized that lipids and LCFA degradation is enhanced when sulfide level is elevated in a sewage sludge digester. In this project, three working packages are proposed, which include operation of biogas reactors as well as complementary microbial and metaproteome analyses in order to investigate the role of sulfide in regulation of the AD of lipids to biogas and its effects on the dynamics and metabolic functions of microbial community.