Photocatalytic ozonation of winery wastewaters

The combination of UV-A/vis radiation and ozone, in the presence of titanium dioxide, has been investigated as a potential destructive technology for the treatment of winery wastewaters. The contribution of the adsorption stage, single ozonation, photolytic ozonation, and photocatalysis has previously been assessed. Adsorption onto the TiO2 surface accounts for a 15-20% removal of the initial chemical oxygen demand (COD). The rest of the subsystems attain COD conversion values in the range of 37-43%. The photocatalytic ozonation of the effluent, under the operating conditions investigated, increases the COD depletion to a value close to 80%. The working pH was studied in the range of 3-11, the optimum value being located in the acidic region (pH 3). A saturation-like behavior is experienced when the amount of TiO2 used is varied in the interval of 0-3 g L-1. Contrary to the use of ozone alone, the system UV-A/vis/O-3/TiO2 leads to the total mineralization of the COD removed. A proposed pseudoempirical model suggested the existence of a synergistic effect when radiation, ozone, and titanium dioxide are combined.