Protein extraction from excess sludge by alkali-thermal hydrolysis

The protein in excess sludge can be extracted effectively by the alkali-thermal method, and the extracted protein can be used as a foaming agent and in other industrial raw materials to realize its resource utilization. In this paper, the factors influencing sludge protein extraction by the alkali-thermal method were optimized based on the protein extraction rate and the polypeptide content, which determine the foaming performance of the extracted protein. The results showed that the optimal conditions were a pH of 12, a temperature of 120 °C, a reaction time of 4 h, and a sludge moisture content of 92%. Under these optimized conditions, the extraction rate of protein and the concentration of polypeptides were 88.3% and 6599 mg/L, respectively. Additionally, the foaming performance of the extracted protein solution was tested, and the foamability and foam stability were close to 450% and 88.8%, respectively. Therefore, the sludge protein extracted by the alkali-thermal method can meet the relevant standards of foam extinguishing agents and concrete foaming agents in China. In addition, the dewatering performance of the hydrolyzed sludge was improved by 93.1%, which provided favorable conditions for the subsequent separation of the protein solution.