Review of Free\nAmino Acids in Source Water (River,\nLake, and Reservoir): Occurrence, Composition, Molar Yields, Formation\nPotential, and Contribution to N‑DBPs

Although free amino acids (FAAs) are known as an important\nprecursor\nof nitrogenous disinfection byproducts (N-DBPs), their levels and\ncomposition in source water as well as their contributions to drinking\nwater N-DBPs are not clear. This review provides a summary of occurrence\nand compositions of FAAs in different water sources as well as their\nmolar yields and contributions to N-DBPs formation. Moreover, the\nimpacts of advanced oxidation processes (AOPs) on N-DBPs formation\nare also summarized. The average concentrations of FAAs in rivers,\nlakes, and reservoirs were 439, 402, and 370 nM (about 56.2, 51.5,\nand 47.4 μg/L), in which cysteine, ornithine, alanine, glutamic\nacid, and serine were dominant among individual FAAs, with an average\nlevel of 25.6, 8.6, 6.2, 6.0, and 5.3 μg/L, respectively. During\nthe chlorination process, the molar yields of FAA for dichloroacetonitrile\n(DCAN), trichloroacetonitrile (TCAN), dichloroacetamide (DCAM), and\ntrichloronitromethane (TCNM) were not detectable (ND)-7.1, ND-3.55,\nND-0.93, and ND-1.99 μmol/mmol, respectively, contributing 7.0%,\n11.9%, 0.3%, and 10.3%, on average, to drinking water N-DBPs. During\nchloramination, the molar yields of FAA fall within ND-5.55, ND-3.55,\n0.4-176, and ND-1.52 μmol/mmol, constituting on average 5.3%,\n18.4%, 0.8%, and 3.0% of DBPs’ formation in drinking water.\nThe information provided may help enrich the knowledge of FAAs and\ngain insights toward the importance of FAAs in forming N-DBPs.