Effect of Fat, Oil, and Grease (FOG) on Digested Sludge Dewaterability

Clean Water Services investigated the impact that co-digestion with Fat, Oil and Grease (FOG) has on the dewaterability of digested sludge. During a 4-month evaluation, more FOG was fed to one of the two anaerobic digesters at the Durham AWWTF while fed thickened primary and secondary sludge evenly. The digester feed, FOG stream and digested sludge were characterized by measuring parameters such as proteins, lipids and carbohydrates, orthophosphate, and cations concentrations. Dewaterability was assessed through analysis conducted by Dr. Matthew Higgins at Bucknell University. The results indicated that FOG addition had no negative impact on the digested sludge dewaterability. The polymer demand was more affected by the thickened primary and secondary sludge VS loads than FOG loading and cake solids percentage seem to improve with higher FOG VS load proportion. The presence of charged compounds in the digestate such as phosphate and cations impacted some of the dewatering characteristics.