Proteins Recovery from Hydrothermally Treated, Diluted, and Centrifuged Sewage Sludge Samples

Abstract

Direct application of sewage sludge (SS) as a fertilizer is a major concern owing to the presence of pathogens and organic pollutants. Hydrothermal pretreatment of the sludge is considered an effective method for the solubilization of particulate matter and proteins recovery. In the present study, diluted SS (solids ∼1.2%) and centrifuged sewage sludge (CSS; solids ∼8%) were subjected to thermal hydrolysis (TH) at temperatures varying from 160°C to 220°C for 3 h. Amongst various macromolecules, the concentration of proteins was found to be highest in the treated sludge. From the solubilized sludge obtained after TH at optimum conditions (i.e., 160°C and 1 h), proteins were recovered using two precipitation methods (i.e., ammonium sulfate and pH adjustment). Ammonium sulfate precipitation method resulted in 85%–90% of proteins recovery with high selectivity. However, its recovery as well as selectivity (with respect to humic acid and carbohydrates) were significantly reduced for the liquid fraction obtained after TH treatment of CSS.