Effect of Activated Carbon Replacement Ratio in Drinking Water Treatment Plant Activated Carbon Filters on the Removal of Disinfection By-Product Precursors and Pesticide-Related Emerging Contaminants
Activated carbon (AC) filters in drinking water treatment plants (DWTPs) experience significant adsorption performance decline over extended operation, yet complete media replacement is a major cost. To evaluate cost-effective strategies, pilot-scale column experiments with five AC replacement ratios (0%, 30%, 50%, 70%, and 100%) were conducted to assess removal of disinfection by-product (DBP) precursors and pesticide-related emerging contaminants. For dissolved organic matter (DOM), all fractions except low molecular weight compounds (LMWC) achieved >85% of the removal obtained with full replacement when 70% new AC was used, with UV254 removal reaching 70%. LMWC, due to small molecular size and low adsorption energy, required higher replacement ratios or full replacement for substantial removal. For DBPs, removal of trihalomethanes (THMs) and haloacetic acids (HAAs) was insensitive to replacement ratio, while haloacetaldehydes (HALs) removal improved markedly with increasing ratio, indicating structural selectivity. For pesticide-related contaminants, all except triazoles achieved >95% removal at 70% replacement; triazoles, due to high water solubility, high polarity, and low octanol-water partition coefficient, achieved only ~60% removal. Overall, replacing 70% of AC restored treatment performance to >80% of that with full replacement, ensuring effluent quality while saving ~30% of new carbon cost. Molecular structure, polarity, and pore size matching are key determinants of removal efficiency; optimizing replacement ratio balances water quality and economic benefits.