Influence of secondary effluent quality on micropollutants removal at full-scale ozonation tertiary treatment
Influence de la qualité des eaux secondaires sur l'élimination des micropolluants par ozonation
Résumé
Dissemination of chemical substances in the environment is becoming a major issue and wastewater effluents are one the main point sources. The goal of the present work was to determine the performances on micropollutants removal of a recently developed process consisting in ozone contactor followed by a post-denitrification submerged biofilter and the impact of the secondary effluent quality (especially organic matter and nitrite concentration). A full-scale tertiary ozonation unit (600 m3/h) built at Sophia-Antipolis WWTP was operated under various ozone doses and secondary effluent chemical composition. The groups of micropollutants monitored include pharmaceuticals, hormones and pesticides (domestic uses) with different reactivity toward ozone. Main results show that ozone transfer of 0.4 gO3/gDOC, achieved high removal of micropollutants with high reactivity toward ozone (carbamazepine, diclofenac for example) when transfer of 0.7 gO3/gDOC was required to achieve 70% removal of micropollutants with the lowest reactivity toward ozone. Nitrite presence in secondary effluent at concentration up to 0.7 mg NO2-N/L was demonstrated to have an influence on removal of micropollutants with lowest reactivity toward ozonation when it has no influence on micropollutants with the highest reactivity.