Treatment of dyehouse waste-water by supercritical water oxidation: a case study

Abstract

BACKGROUND: Supercritical water oxidation (SCWO) of dyehouse waste-water containing several organic pollutants has been studied. The removal of these organic components with unknown proportions is considered in terms of total organic carbon concentration (TOC), with an initial value of 856.9 mg L-1. Oxidation reactions were performed using diluted hydrogen peroxide. The reaction conditions ranged between temperatures of 400-600 degrees C and residence times of 8-16 s under 25 MPa of pressure. RESULTS: TOC removal efficiencies using SCWO and hydrothermal decomposition were between 92.0 and 100% and 6.6 and 93.8%, respectively. An overall reaction rate, which consists of hydrothermal decomposition and the oxidation reaction, was determined for the hydrothermal decomposition of the waste-water with an activation energy of 104.12 (+/- 2.6) kJ mol(-1) and a pre-exponential factor of 1.59(+/- 0.5) x 10(5) s(-1). The oxidation reaction rate orders for the TOC and the oxidant were 1.169 (+/- 0.3) and 0.075 (+/- 0.04) with activation energies of 18.194 (+/- 1.09) kJ mol(-1), and pre-exponential factor of 5.181 (+/- 1.3) L-0.244 mmol(-0.244) s(-1) at the 95% confidence level. CONCLUSION: Results demonstrate that the SCWO process decreased TOC content by up to 100% in residence times between 8 and 165 under various reaction conditions. The treatment efficiency increased remarkably with increasing temperature and the presence of excess oxygen in the reaction medium. Color of the waste-water was removed completely at temperatures of 450 degrees C and above. (C) 2010 Society of Chemical Industry