HAAs are a group of organic disinfection by-products (DBPs) regulated under the Stage 1 Disinfectants and Disinfection By-Products Rule. Enhanced coagulation/softening for precursor removal and alternative disinfectants are common means for controlling HAAs and other DBPs in finished water. Several studies have suggested that BAC could be used for the effective removal of HAAs. However, the mechanism of HAA removal in GAC filters is not clear. In addition, the design and operation parameters of GAC filters are largely undefined. The objectives of the proposed research were (1) to study the mechanisms of haloacetic acid (HAA) removal using granular activated carbon (GAC) filtration, (2) to evaluate the effects of water temperature and empty bed contact time (EBCT) on HAA removal in biologically active carbon (BAC) columns, and (3) to explore techniques to accelerate bioactivity development in GAC filters.