Protein extraction from excess sludge by barium hydroxide hydrolysis process

Abstract

Protein could be extracted effectively from excess sludge by barium hydroxide (Ba(OH)2) hydrolysis process. During the extraction process, insoluble protein in sludge was turned into soluble protein, and part of the soluble protein were hydrolyzed into peptide, amino acids, water, carbon dioxide and ammonium. To obtain the maximum concentration of soluble protein, the effects of barium hydroxide, temperature and time on the hydrolysis degree of the sludge protein and protein concentration were investigated. Under optimal conditions of 0.2 M Ba(OH)2, 110 ℃ of the reaction temperature, and 4 h of hydrolysis time, the degree of sludge protein hydrolysis and the protein concentration was 79.10% and 1106.11 mg/L, respectively. Through building a SPSS multiple nonlinear regression model, the optimal protein concentration was calculated. Barium ions were converted into barium sulfate precipitates by adding an equal amount of sulfuric acid in the hydrolysate. Then the precipitates were washed with 0.1 M NaOH to obtain pure barium sulfate and protein solution. Protein was separated and obtained from sludge hydrolysate by centrifugation and filtration, which could be used as a wood binder or foaming agent.