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

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.

[Occurrence and Prediction Model of Disinfection By-Products in Tap Water].

Disinfection by-products (DBPs) are defined as important parameters that can deteriorate drinking water quality. The investigation was performed at a laboratory located on a campus in H City of the Zhejiang province. The purpose of the work was to obtain knowledge on the occurrence of DBPs in tap water and boiled water taken from the same pipe, to establish a statistical model to predict DBPs information in tap water based on physicochemical parameters, and to evaluate carcinogenic and non-carcinogenic risks caused by DBPs on a predictional level. The results showed three categories of trihalomethanes (THMs), haloacetonnitrile (HANs), and haloacetic acids (HAAs), including 10 species of disinfection by-products detected in drinking water. The detection rate of target DBPs in tap water was 100% and the concentrations varied in the ranges of 10.12-28.39, 0.98-5.19, and 2.65-7.83 µg·L-1, respectively. In boiled water, bromochloracetonitrile (BCAN) was not detected; the detection rates of tribromomethane(TBM), trichloroacetonitrile (TCAN), and dibromoacetonitrile (DBAN) were 46.43%, 82.14%, and 92.86%, respectively, while the detection rate for other DBPs was 100%. The concentrations of THMs, HANs, and HAAs were in the ranges of 0.60-12.58, 0.02-0.52, and 2.42-5.86 µg·L-1, respectively. After heating, the concentrations of THMs and HANs decreased by 84.22% and 91.45%, respectively. No obvious decrease was found for HAAs. The pH value and specific ultraviolet absorbance (SUVA) had positive correlation with DBPs, whereas residual chlorine and ammonia nitrogen had negative correlation with DBPs. Based on the correlation between the physicochemical parameters and DBPs, a multiple linear regression prediction model of THMs was established, with deviation less than 10.00%, which can be used for the prediction of THMs in tap water. Based on the EPA recommended health risk assessment model, the carcinogenic and non-carcinogenic risks of chlorine disinfection by-products through oral intake were calculated. It was found that the carcinogenic risks caused by the disinfection by-products in the tap and boiled water were (17.24-84.63)×10-6 and (25.49-258.82)×10-7, respectively, and the non-carcinogenic risks were (4.17-50.32)×10-2 and (6.52-107.74)×10-3, respectively. The carcinogenic risk caused mainly by THMs and bromodicloromethane (BDCM) contributed the highest cancer risk in tap water, while for boiled water, trichloromethane (TCM) was found to contribute the highest cancer and non-carcinogenic risk. In boiled water, the reduction of THMs was up to 94.38%, and the cancer risk was reduced by 79.00%.