Chlorination disinfection of drinking water effectively prevents waterborne diseases, but results in unintended disinfection byproducts (DBPs) from the reactions between organic materials in water and disinfectants. As alanine (Ala), phenylalanine (Phe) and tyrosine (Tyr) exist in much source water, the chlorination characteristic of the three amino acids (AA) and the formation pathways for chloroform (CF) during chlorination of model Tyr were studied. Chlorine demand and CF yield of the important intermediate product 2,4,6-trichlorophenol (2,4,6-TCP) were also examined. The results indicated that chlorine demand and CF yield of Tyr were much higher than those of Ala and Phe based on the same chlorination conditions, which indicated that Tyr was an important precursor of CF. Based on the analysis of GC/MS and calculation of frontier electron densities (FED2), the formation pathway of CF during chlorination of Tyr was proposed as Tyr→ 4-monochlorophenol (4-MCP) → 2,4-dichlorophenol (2,4-DCP) → 2,4,6-TCP → CF. The yields of CF and 2,4,6-TCP could be reduced by switching chlorination to chloramination. However, the disinfection performance of chloramination is inferior to chlorination. The removal of precursor (Tyr, etc) before disinfection may be a more promising method to reduce the generation of CF.

Key words: drinking water, dissolved organic nitrogen, tyrosine, disinfection by-product, chloroform, formation mechanism