Sewage sludge and fat rich materials co-digestion - Performance and energy potential

Abstract

Abstract The aim of this study was to estimate the energy potential of sewage sludge co-digestion with grease trap waste. The semi-continuous process was carried out at lab scale bioreactors under mesophilic conditions where, in contrast to the literature data, the reactor was operated at a significantly shorter hydraulic retention time (10 days). The concentration of grease trap waste was increased up to 54% in the feedstock on a volatile solids content basis. Although, significant variations in the organic loading rate were observed, the biogas production and methane yield increased with a larger addition of fat-rich waste. Despite the fact that the concentration of long chain fatty acids obtained in the present study significantly exceeded the accepted level inhibiting the fermentation process, it had no negative impact on process performance. The calculated energy balance showed that the addition of grease trap waste will provide an increased production of biogas. As shown the energy balance, as the ratio of biogas-derived energy to energy consumed, after co-substrate introduction of the co-substrate improved by about 30%. Furthermore, implementation of the co-digestion process at the wastewater treatment plant may lead to an increased recovery degree of wastewater treatment plant energy consumption via electric energy supplied by methane combustion, even up to 100% in comparison to anaerobic digestion of sewage sludge alone.