Derivates variation of phenylalanine as a model disinfection by-product precursor during long term chlorination and chloramination

Abstract

Dissolved nitrogenous organic matter in water can contain precursors of disinfection by-products (DBPs), especially nitrogenous DBPs (N-DBPs). Amino acids are ubiquitous as dissolved nitrogenous organic matter in source water and can pass through drinking water treatment processes to react with disinfectants in finished water and in the distribution system. Phenylalanine (Phe) was selected as a model amino acid precursor to investigate its derived DBPs and their variations during a chlorination regime that simulated water distribution with residue chlorine. The 7-day DBPs formation potential (DBPsFP) test with chlorine revealed chlorination by-products of phenylalanine including trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs), and halonitromethanes (HNMs), but not trichloronitromethane (TCNM) which was a significant N-DBP detected during the first 48 h of chlorine contact. The formation of most carbonaceous DBPs (C-DBPs) increased with chlorination time; however N-DBPs and non-chlorinated byproducts of phenylacetonitrile and phenylacetaldehyde reached their highest concentration after 2 h of reaction, and then gradually decreased until below detection after 7 days. The chlorination influencing factors indicated that light enhanced the peak yield of DBPs; the pH value showed different influences associated with corresponding DBPs; and the presence of bromide ions (Br−) generated a variety of bromine-containing DBPs. The DBPsFP test with chloramine reduced C-DBPs generation to about 1/3 of the level observed for chlorine disinfection and caused an increase in dichloroacetonitrile. Surveillance of DBPs during drinking water distribution to consumers should consider the varying contact times with disinfectants to accurately profile the types and concentrations of C-DBPs and N-DBPs present in drinking water.