Assessing the effectiveness of ozonation followed by GAC filtration in removing bromate and assimilable organic carbon.

Bromate (BrO3-) and assimilable organic carbon (AOC) removal by activated carbon after ozonation is a subject of concern, since BrO3- and AOC are commonly found in the ozonation of bromide-containing and organic-rich waters. In batch ozonation experiment of this study, the major ozonation by-products were bromate, bromform, aldehydes, and AOC, and the levels of these by-products is affected by operational parameters of ozonation. Results from rapid small-scale column tests (RSSCT) indicated that the granular activated carbon (GAC) capacity for BrO3- removal was dependent on the GAC type and empty bed contact time (EBCT). The GAC with a high number of basic groups and higher pH(pzc) values showed an increased BrO3- removal capacity. On the other hand, BrO3- removal was improved by increasing EBCT. In the GAC pilot plant, a GAC column (operating with 15 min EBCT) preloads for 12 months achieved a BrO3-, and AOC removal range from 7-96% and 41-85%, respectively. And the BrO3- amount removed was found to be proportional to the influent BrO3- concentration. However, the capacity of GAC for bromate adsorption apparently decreased with prolonged operational time (after 3 months). This may be a result of the bacterial biomass adsorbed on the GAC surface hindering BrO3- reduction by GAC either by blocking pores or adsorbing at the activated sites for BrO3- reduction.