Semi-continuous anaerobic co-digestion of thickened waste activated sludge and fat, oil and grease

Co-digestion of thickened waste activated sludge (TWAS) and fat, oil and grease (FOG) was conducted semi-continuously under mesophilic conditions. The results showed that daily methane yield at the steady state was 598 L/kg VSadded when TWAS and FOG (64% of total VS) were co-digested, which was 137% higher than that obtained from digestion of TWAS alone. The biogas composition was stabilized at a CH4 and CO2 content of 66.8% and 29.5%, respectively. Micronutrients added to co-digestion did not improve the biogas production and digestion stabilization. With a higher addition of FOG (74% of total VS), the digester initially failed but was slowly self-recovered; however, the methane yield was only about 50% of a healthy reactor with the same organic loading rate.

► Co-digestion of thickened waste activated sludge (TWAS) with fat, oil and grease (FOG).
► Co-digestion of TWAS and FOG at 64% VS increased biogas production by 137%.
► FOG addition ratio at 74% of total VS caused inhibition of the anaerobic digestion process.
► Micronutrients addition did not significantly improve the biogas production and digestion stabilization.