A pilot plant study in four parallel filter runs was performed in order to determine the effect of ozonation and two-step granular activated carbon (GAC) filtration on the removal of disinfection by-product (DBP) precursors. The results showed that ozonation significantly decreased the adsorbable organic halogens (AOX) (35%), simulated distribution system (SDS) AOX (37%) and SDS trihalomethanes (THM) (76%) from chemically treated and sand-filtered lake water, but did not decrease either short-term or the long-term chlorine demand. Biofiltration with exhausted GAC had a minor importance in the precursor removal (0-20%). The performance of adsorptive GAC filtration was strongly dependent on the age of the GAC filter bed, which was also seen as a strong correlation between the natural organic matter (NOM) measurements and DBP formation potential. Disinfection with chloramine produced lower THM, AOX, mutagenicity and MX (Z-3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone) levels compared to chlorine disinfection.

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