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

The aim of this work is to optimize the degradation yield of an activated s ludge and to study the reaction mechanism on a cellulose model compound. Th is optimization is performed with a Simplex design with four parameters: re action temperature (280-350 degreesC), injected air pressure (40-60 MPa), r eaction time (10-45 minutes) and COD concentration (0.5-5 g L-1). The bette r yield obtained on TOC concentration is 82 5% at 330 degreesC. Over this t emperature, the yield substantially decreases. The use of cellulose as a mo del compound for activated sludge confirms optimization results and leads t o the identification of by-products and free radical species participating in the reaction. Two major organic compounds have been detected: 4-oxo pent anoic acid and 3-oxo butanoic acid, and three types of radicals: HO degrees , CO(2)degrees (-) and degrees CH(OH)CH3.