Experimental Research on Protein Extraction from Excess Activated Sludge by Papain Hydrolysis

The excess activated sludge from the Shanghai Qingpu sewage treatment plant was hydrolyzed by papain hydrolysis to extract protein. The results showed that the conditions of optimal papain hydrolysis process are described as follows: enzyme/substrate 6%, pH 6.5, the ratio of liquid to solid 4:1, hydrolysis time 5.5h and hydrolysis temperature 55 °C. On this basis, the contents of heavy metals and some kinds of amino acid from the extracts, while security and nutrition were taken into consideration, were determined. The results showed that the contents of heavy metals were lower, living up to the Health Standard for Animal Feed (China), and some kinds of amino acid were essential for animal growth in the extracts. So it was possible to take the extracts as animal feed additives.