Effets de l'ozonation et de la filtration biologique sur la demande en chlore et sur les précurseurs de trihalométhanes et des composés organo-halogénés totaux
The effects of biological treatment (ozonation followed by biological activated carbon filtration (BAC)) on chlorine demand and on formation of trihalomethanes (THM) and total organic halides compounds (TOH) were studied at the Sainte-Rose water treatment facility, Laval. The plant influent is a surface water with a dissolved organic carbon of 6–7 mg/L. Results showed that ozonation marginally reduced (0–6%) short term chlorine demand but that BAC filtration reduced it by 40–55%. Ozonation versus BAC filtration was found to effect THM and TOH formation differently from the removal of the chlorine demand. THM (4-h contact with chlorine) and TOH formations were reduced by 48–60% and 39%, respectively, via ozonation. With BAC filtration, THM and TOH formations were reduced by 20–34% and 16%, respectively, with respect to the ozonated influent. For all essays, an initial significant decrease in residual chlorine was followed by an increase in TOH and subsequently in THM. The initial chlorine doses used for measuring the chlorine demand were found to have an effect on the final results. An increase in the initial chlorine dose resulted in a higher chlorine demand as well as in higher THM and TOH formations. The effect was found to be more profound at chlorine doses less than 3 mg Cl2/mg total organic carbon. Key words: chlorine demand, chlorination by-products, trihalomethane, total organic halides, ozonation, filtration, biological activated carbon.