Comparison of protein extraction methods from excess activated sludge

Abstract

In this study, we used chemical methods (acid-thermal (AT) and alkaline-thermal (AKT)), enzymatic methods (single enzyme (SE) and composite enzyme (CE)) and assisted enzymatic methods (ultrasonic assisted enzyme (USE) and thermal assisted enzyme (TE)) to extract proteins from excess activated sludge. The advantages and applicability of each method were compared and analyzed in terms of their protein extraction rate (R_P), energy consumption, material consumption and cost, protein hydrolysates and sludge dewatering performance. The results showed that the R_P of the chemical methods were more than 75%, which were much higher than those of the enzymatic methods. Moreover, the R_P of SE was significantly strengthened by physical means (ultrasonic or thermal), and the average R_P was increased by more than 39% compared with that of enzymatic methods. The energy consumption analysis showed that chemical methods consumed significantly more energy than the enzymatic methods. Further analysis of enzymatic methods and assisted enzymatic methods revealed that although the energy consumption of USE was similar to that of SE, its enzyme consumption and cost were lower. In addition, the proteins extracted by USE had a high content of amino acids, which was suitable for the preparation of animal feed. The proteins extracted by AKT had a high content of polypeptides, which was beneficial to the preparation of a protein foaming agent. Furthermore, the sludge dewatering performance after hydrolyzation by the six hydrolysis methods was significantly improved, which was beneficial to the separation of proteins.

Keywords: Excess activated sludge; Protein extraction; Protein hydrolysis; Specific resistance of sludge.