Anaerobic digestion of lipid-rich waste

Abstract

Lipids present in waste and wastewater, also referred as fat, oil, and grease (FOG), can be efficiently converted to methane. This fact constitutes an opportunity for conserving the high energy content of waste lipids, thus facilitating its storage and future use as fuel, electricity, and heat. In anaerobic bioreactors, long-chain fatty acids (LCFAs) are released during hydrolysis of FOG. LCFAs tend to form stable emulsions, adhere to all available surfaces, and adsorb on the microbial cell walls leading to foam formation, sludge flotation, and washout, as well as temporary inhibition of microbes. These problems can be prevented if a correct balance between LCFA accumulation and biodegradation is assured, by sequential feeding and degradation steps. Appropriate reactor operation is the key strategy to prevent the excessive accumulation of LCFA and to stimulate microbial acclimation, especially during the start-up phase. After successful acclimation, a continuously feeding operation is possible, provided that there is proper process control through an adequate monitoring protocol. In addition to adequate operation, a suitable reactor design is recommended. Among other technologies, the inverted anaerobic sludge blanket (IASB) was recently developed for the direct treatment of FOG-containing wastewater. This chapter reports a protocol with a detailed operation and monitoring strategy for achieving effective methane production from FOG-containing waste and wastewater and presents a brief description of the basic concepts behind the development of the reactor.