Effect of pulsed electric field pretreatment on primary sludge for enhanced bioavailability and energy capture

Primary sludge (PS) is a renewable and sustainable energy source, but pretreatment often is required to accelerate hydrolysis of organic solids. Pulsed electric field (PEF) treatment has been proven effective for waste activated sludge (WAS), but its impact on PS is not known. We evaluated the impacts of PEF pretreatment of PS on energy recovery by methanogenesis and fermentation to volatile fatty acids (VFAs). PEF treatment achieved successful microbial inactivation of PS and it modestly enhanced conversion of PS chemical oxygen demand to methane (by ∼8%) and to VFAs by fermentation (by ∼7%) by increasing hydrolysis rates. Thus, the impact of PEF treatment was small for PS alone, compared to the much more significant increases in methane conversion from WAS or WAS+PS. This difference points to the value of optimizing ratios of PS:WAS for PEF treatment, whether the goal is methanogenesis or fermentation to VFAs.