Haloacetic acid removal by granular activated carbon

Haloacetic acids (HAAs) are disinfection by-products (DBPs) in drinking water and are regulated under the Stage 1 Disinfectants and Disinfection Byproducts Rules (D/DBP) by the United States Environmental Protection Agency (USEPA). The most popular methods for DBP control included enhanced coagulation/softening processes. Granular activated carbon (GAC) adsorption is also widely used for the removal of HAA precursors. Several studies revealed that HAAs could be removed by biologically active carbon (BAC). The purpose of this study is to explore the processes of HAA removal by activated carbon adsorption and biodegradation in drinking water systems. The adsorption capacities of GAC were determined by adsorption isotherms and revealed that the adsorption process plays only a minor role in HAA removal. Several bioactivity inhibition factors were applied to BAC columns and the reduction in bioactivities verified that biodegradation is the major avenue of HAA removal. Chloride released from HAAs incubated with BAC indicated that a complete dehalogenation took place with corresponding depletion of the HAA compounds. This further confirms that the major means for HAA removal in BAC column involved biological dehalogenation and biodegradation. The BAC biofilm community structure was also explored. From the ribosomal intergenic spacer region analysis, biofilm diversity was greater at the beginning of the GAC filter operation. With biofilm development, HAA removal commenced. When the bacterial community stabilized, HAA removal efficiency achieved steady state. This research will provide water professionals with a better understanding of the process of HAA removal by GAC in water treatment and assist water systems in complying with D/DBP rules.