COMPLETE TREATMENT OF OLIVE MILL WASTEWATERS BY A WET AIR OXIDATION PROCESS COUPLED WITH A BIOLOGICAL STEP

The wet air oxidation (WAO) process catalysed by hydrogen peroxide coupled with bioxidation for the treatment of olive mill wastewaters (OMW) was investigated. OMW cannot be conveniently treated by biological processes as they contain important amounts of phenol-like compounds, toxic and recalcitrant to biodegradation. Oxidation was conducted according to the 'hydrogen peroxide promoted wet air oxidation'' process between 180 and 200-degrees-C. It consists of injecting continuously hydrogen peroxide at a low dosage (10% on a COD basis) into a WAO reactor in order to promote the radical reactions and then lowering the temperature and pressure constraints. WAO treatment allows a complete decolouration of the solution, a 77% chemical oxygen demand (COD) reduction; the remaining COD is mainly low molecular weight carboxylic acids (chiefly acetic) easy for a biological post-treatment. Compared to the various processes reported in the literature, this two step process offers a good opportunity for OMW depollution.