Impact of chemical oxidation on biological treatment of a primary municipal wastewater. 1. Effects on COD and biodegradability

Municipal wastewaters taken from a primary sedimentation tank were subjected to different chemical oxidation processes (ozonation or UV radiation alone or combined with hydrogen peroxide) to observe the evolution of COD and BOD/COD ratios. Ozonation of wastewater led to different increases of COD level reduction depending on pH and carbonate-bicarbonate ion concentrations. Direct photolysis or hydrogen peroxide alone were found to be inappropriate technologies. On the other hand, advanced chemical oxidation, that is, oxidation with ozone or UV radiation combined with hydrogen peroxide, increased COD level reduction only when wastewater was previously decarbonated. Thus, elimination of carbonate-bicarbonate ions, increase of pH and addition of hydrogen peroxide (10(-3) M) yield increases COD level reduction rates. Finally, preozonation also allows improvement of wastewater biodegradability.