EVALUATING OZONE DOSE FOR AOC REMOVAL IN 2-STEP GAC FILTERS

Upgrading an existing post-ozonation plant with two-step granular acti vated carbon (GAC) filtration for assimilable organic carbon (AOC) rem oval was studied. The effects of ozone dose on AOC formation and its r emoval in the subsequent two-step GAC filtration was studied using che mically pretreated 2 to 14 degrees C humic lake water. Two parallel pi lot-plant trains with different ozone doses (0 to 1.2 mgO(3)/mgTOC) an d a short-term ozonation study were performed. The optimum ozone dose for maximum AOC formation was 0.4-0.5 mgO(3)/mgTOC. The AOC-P17 of ozo nated water was three-fold higher and AOC-NOX over ten-fold higher tha n in non-ozonated water, while the following biofiltration (first step ) removed 51% and 72% of AOC-P17 and AOC-NOX, respectively. The adsorb er (second step) contributed to less than 10% of the overall AOC reduc tion. It appeared that biofiltration is a feasible method in upgrading water treatment plants for AOC removal even when treating cold humic waters, while the subsequent adsorber seems to have less significance for AOC removal. (C) 1998 IAWQ. Published by Elsevier Science Ltd.