New Utilization Technology: Producing Compound Amino Acids from Sewage Sludge by Acid Hydrolysis

In this study, a new and effective utilization technology for waste activated sludge (WAS) has been employed to produce compound amino acids. The process was achieved by two-step hydrochloric acid (HCl) hydrolysis of sewage sludge (SS). Firstly, the SS was hydrolyzed for proteins by HCl under high temperature and pressure in self-made hydrolysis reactor. And the effects of the hydrolytic temperature, time and pH on the extraction ratio of proteins were investigated in detail. The results show that the best extraction efficiency of proteins is obtained at a pH 0.5, T=121 degrees C and a reaction time of, 5 h, under which condition, the protein extraction ratio is the highest of 78.5% (38.2% of initial dry WAS weight), and the DS weight reduces about 45.4%. Then the sludge proteins were hydrolyzed for compound amino acids by HCl and the compound amino acids produced were extracted by ion-exchange resin method. Major technological parameters such as the HCl loading, hydrolytic time and temperature on the hydrolysis efficiency were investigated in detail. And the optimum condition for protein hydrolysis was as follows: T=110-120 degrees C, hydrolytic time=10 h, hydrochloric acid (mL) /dry WAS (g) ratio is 8:1. Under this condition, the amino acids yield were 10.7-12.2 [(g amino acids) / (100 g WAS)] and the extraction ratio of amino acid was high to 80.9%. This novel utilization technology of WAS is environmentally friendly and economically feasible, which can provide an abundant resource of amino acids.