Valorization of fat balls and primary scum from wastewater treatment: a promising renewable lipid feedstock for biodiesel production

We investigated the potential of waste materials from wastewater treatment plants (WWTPs) to serve as an alternative lipid feedstock for biodiesel production. The average lipid recoveries from fat balls (46.4%) and primary scum (49.5–54.5%) were higher than the lipid recovery of primary sludge (15.8–16.4%). The yield of biodiesel produced from the extracted lipids ranged from 5.7 to 20.1%. There were considerable site- and season-dependent variations in the characteristics of the lipid waste materials. Radiocarbon analysis indicated the presence of fossil-derived carbon (26.0–42.0%) in the biodiesel obtained from wastewater lipids. Finally, we estimated the potential for biodiesel production from WWTP-derived lipids; about 9,053.0 metric tons of biodiesel per year could be produced from fat balls and primary scum in Japan, potentially satisfying 32% of Japan's current biodiesel demand. The results indicate that lipid-rich materials from WWTPs represent a valuable alternative feedstock for biodiesel production.