Sludge Treatment by Supercritical Water Oxidation and the Optimization of Operational Conditions

Abstract

Executive summaryThe overall objective of this study was to investigate the performance of the supercritical water oxidation (SCWO) technology for the treatment of wastewater sludge, and investigate the degradation of p-tert-butylcatechol (TBC) which is a recalcitrant organic compound. The first phase of the study focused on the optimization of the thickening process that precedes SCWO, and investigated the impact of sludge temperature (10 o C -100 o C) on the optimum polymer dose and conditioning of wastewater sludge. The best results were observed at 35 o C -50 o C, where the highest filtrate volume, cake solids and settling velocity were obtained. The results showed that sludge conditioning at 35 o C -50 o C using the excess heat from the SCWO process can significantly improve treatment performance and result in savings for treatment plants. In the second phase, SCWO treatment of sludge was investigated under a range of operational conditions including sludge solids content (2-12 %), TBC concentration (0.1-1 %), reactor temperature (400-550 o C), reactor pressure (18-28 MPa), oxygen excess (n=1-8) and residence time(1-30 minutes). The results showed that the optimum initial sludge solids content was in the range of 8-10 %, and the optimum SCWO operational parameters were 550 o C, 25MPa and an oxygen excess of 5. Addition of TBC decreased the percent COD removal but still 98% COD removal with final COD values less than 50 mg/L could be achieved.These results showed that SCWO is a very effective process for sludge treatment and degradation of recalcitrant organic compounds in sludge.ii