Treatment of municipal sewage fats by wet oxidation

Wet air oxidation (WAO) was investigated in order to improve the biodegrada bility of domestic sewage fats, and the kinetics of the connected reactions were studied. Concentrated fatty solutions (200 g/l), obtained by saponifi cation, were treated by WAO at 50 bar and temperatures ranging from 160 to 240 degrees C in a 11 laboratory-scale reactor. The continuous injection in the reactional medium of a stream of air ensured a non-limitative absorpti on of oxygen. The degradation of the bioresistant fraction of the organic m atters was assessed by an analysis of the extracted hexane matters (EHM). T ime curves of the concentrations of fatty acids revealed the role played by the saturated fatty fraction on the limitation of the kinetics of the remo val of all the EHM. The saturated fatty acids turned out to be the least re active, with apparent activation energies greater than those for the unsatu rated fatty acids (50 kJ/mol versus 25-35 kJ/mol). In addition, according t o the mechanisms described in the literature, the oxidation products of sat urated compounds are less biodegradable than those of unsaturated ones. Thu s, to obtain a significant degradation of the saturated fraction in a limit ated time period, a temperature of over 200 degrees C must be used. Followi ng 1 h of oxidation at 240 degrees C, the overall treatment (saponification and oxidation) leads to the achievement of a five-factor reduction of both chemical and bioresistant oxygen demands.