Comprehensive evaluation of sewage sludge dewatering performance with supercritical CO2: Parameters optimization, mechanism, feasibility assessment

Dewatering is a prerequisite and crucial link for efficient disposal of sewage sludge (SS). Conventional mechanical dewatering has the disadvantage of adding a large amount of chemicals which results in secondary pollution and negative effects on energy recovery from SS. In this study, the performance of SS dewatering with supercritical CO2 (scCO2) was evaluated comprehensively, and the effects of operation parameters, mechanism and feasibility for commercialization were explored. The result showed that 26.29 wt.% of the maximum water removal from the SS was obtained with the optimal scCO2 treatment conditions (20 MPa, 60 degrees C and 90 min), and the treated SS had a higher heating value (HHV) of 20.58 MJ/kg. The scCO2 released bound water by disintegrating extracellular polymeric substances (EPS) and cell, and displaced water in sludge. Hence, the water removed by scCO2 treatment far exceeded the solubility of water in scCO2. Moreover, economic and environmental analysis showed that the removal cost of 1 t water from the SS was $65.81 by scCO2, and 196.66 kg CO2eq was eliminated with cleaner power supply, which showed superior commercialization potential. This study provides comprehensive understanding and in-depth insight into a novel and efficient sludge dewatering technology.