Novel technology of amino acids preparation and recovery from excess sludge

Thermal alkaline method can effectively extract protein from excess sludge. During the extraction process, insoluble proteins in sludge were turned into soluble proteins, and partly soluble proteins were hydrolyzed into peptides, amino acids and by-products: water, carbon dioxide and ammonium. The optimum conditions were as follows: 0.1 M NaOH, the temperature of 70 °C, reaction time of 5 h. Then the soluble proteins were hydrolyzed into amino acids with hydrochloric acid furtherly. The optimal process parameters of hydrochloric acid hydrolysis were as follows: the hydrolysis temperature of 110 °C, heating time of 12 h, and acid to supernatant ratio of 0.8. The results show that proteins of 46.33% were extracted from the excess sludge and the amino acids yield was 75.49%, namely approximately 9 g per 100 g of dry sludge under the optimum hydrolysis conditions. The contents of amino acids in hydrolysate were determined by automatic amino acid analyzer and the functional groups of hydrolysate were characterized by Fourier transform infrared (FTIR) spectrum. There were 17 kinds of amino acids in the hydrolysate，which can be used as deodorants, food additives, preservatives and corrosion inhibitors.