Optimization of the degradation of sewage sludge by wet air oxidation. Study of the reaction mechanism on a cellulose model compound

Abstract

The aim of this work is to optimize the degradation yield of an activated sludge and to study the reaction mechanism on a cellulose model compound. This optimization is performed with a Simplex design with four parameters: reaction temperature (280- 350 °C), injected air pressure (40-60 MPa), reaction time (10-45 minutes) and COD concentration (0.5-5 g L -1). The better yield obtained on TOC concentration is 82 5% at 330 °C. Over this temperature, the yield substantially decreases. The use of cellulose a s a model compound for activated sludge confirms optimization results and leads to the identification of by-products and free rad ical species participating in the reaction. Two major organic compounds have been detected: 4-oxo pentanoic acid and 3-oxo butanoic acid, and three types of radicals: HO°, CO 2° -and °CH(OH)CH3.