Ozonation treatment of urban primary and biotreated wastewaters: Impacts and modeling

Most of the published studies concerning water and wastewater ozonation for subsequent reutilization or discharge are focused on applying ozone as an advanced treatment process downstream a biological secondary treatment. Ozonation usually shows good performances in improving water quality as shown when monitoring aggregate parameters during ozone treatments. Nevertheless, additional studies related to ozone application on pre-biological treatment stages should be considered for a better understanding of its effects on water quality as well as on the existing process performances. Therefore, the present study investigates the impact of ozone on the organic matter from municipal waste water effluents with the aim to highlight potential benefits depending on the ozone application point. Special focus was made on ozone transfer and kinetics. To do so, aggregate parameters as Chemical Oxygen Demand (COD), Biological Oxygen Demand (BOD), turbidity and absorbance at 254 nm (UV254) were selected to characterize the effluent quality before and after treatment. These parameters provided useful information regarding the extent of oxidation, the changes in aromaticity and in biodegradability of the effluent organic matter (OM). Ozone application to primary effluents displayed a positive impact on aggregate parameters, improving effluent quality. For both type of effluents, the ozone consumption can be classically described by two characteristics which are the immediate ozone demand and the subsequent constant of first order decay. Their evaluation pointed out the major influence of global organic matter parameters.