Comparison of haloacetic acid removal between biological activated carbon and nanofiltration

Abstract

Haloacetic acids are disinfection by-products generated during the chlorination process in drinking water system. Some of them are suspected human carcinogens. The U.S. Environmental Protection Agency currently limits the maximum contaminant level of sum of five haloacetic acids (HAA5) in drinking water to 60 ppb, but will soon lower to 30 ppb in the Stage two of the Disinfectants/Disinfection By-products (D/DBP) rule. In this study the removal of 60, 90 and 120 ppb HAA5 from aqueous solutions using batch scale nanofiltration (NF) using three membranes, ES 10, NTR 7410, and NTR 729 HF and ozone-biological activated carbon (BAC) methods were evaluated and compared. NF using ES 10 membrane and the ozone-BAC system are comparable in removing HAA5 at concentrations of 60 and 90 ppb (95-100% removal). Ozone-BAC, however, is more superior at the higher feed concentration of 120 ppb. The performance of the NF membrane was regulated by the operating pressure and concentration of HAA5 in feed water. Better HAA5 removal was attained at low operating pressure and low feed concentration. Unlike NF, the performance of ozone-BAC system was uninterrupted by the HAA5 comcentration. The EBCT of the BAC column was the primary controlling pareameter of the system since the pretreatment using ozonation process is considered unnecessary. Less than 20% the initial HAA5 was removed by the craction with ozone. The majority of HAA5 (80-90%) was biodegraded in the BAC column. Due to a superior performance of BAC, it is expected that BAC coumn could be used as a standalone process to control AHH5.