Ozonation of Municipal Secondary Effluent; Removal of Hazardous Micropollutants and Related Changes of Organic Matter Composition

The major part of the regulated priority substances and family of compounds defined in the European Water Framework Directive and some other organic micropollutants were tracked in a municipal biotreated secondary effluent. Micropollutants detected in the effluent were subjected to different ozone doses related to different oxidation extents. Ozone confirmed its efficiency in terms of micropollutant reduction when applied to a municipal biotreated effluent. Accordingly, it achieved reductions exceeding 70% for 91% of the pollutants detected at high ozone dose. Organic matter transformation was also investigated by both controlling evolution of surrogates including chemical oxygen demand, dissolved organic carbon, UV254 absorbance, etc. - and the fate dissolved organic fractions by means of size exclusion chromatography followed by organic carbon detection. At ozone dose lower than the initial ozone demand of the effluent, ozone first attacked the hydrophobic aromatic compounds. At ozone dose higher than 50 mg/L, ozone probably solubilized suspended particles and principally oxidized high molecular weight molecules (> 1,000 Da) to convert them into more hydrophilic compounds. Therefore, most reactions of ozone with the micropollutants take place in competition with fast reactions of ozone with the hydrophobic fraction of the dissolved organic matter.