Effects of typical nitrogenous compounds on trihalomethanes formation and chlorine demand during drinking water chlorination

Glycine(Gly),cysteine(Cys),aspartic acid(Asp),leucine(Leu),lysine(Lys),and methyl amine(MA) were chosen as typical nitrogenous compounds,and the effects of them on trihalomethanes (THMs) formation and chlorine demand were performed on filtrated water. Results show that the nitrogenous compounds enhance THMs formation,and the increased levels are controlled by characteristics and the concentration of nitrogenous compounds. The increase in THMs formation follows the order of Asp(126 μg/L)>Cys(119 μg/L)>MA(106 μg/L)>Lys(97 μg/L)≈Gly(96 μg/L)>Leu(80 μg/L)(while nitrogenous compounds=1.0 mg/L,and background THMs=60 μg/L). The increase in chlorine demand is approximately proportionate to the content of nitrogenous compounds,which illustrates that the increase is mainly caused by the reaction of nitrogenous compounds with chlorine. And the increase in chlorine demand follows the order of Cys(27.8 mg/L)>Asp(22.6 mg/L)=Gly(22.6 mg/L)>Lys(21.6 mg/L)>MA(14.1 mg/L)>Leu(11.8 mg/L) (while nitrogenous compounds=1.0 mg/L,and background chorine demand=1.8 mg/L). The mechanisms of nitrogenous compounds enhancing THMs formation are summ the increase of chlorine demand raising THMs formation in reaction of NOM with chlorine,and the THMs formation in chlorination of nitrogenous compounds themselves.

Modeling and verifying chlorine decay and chloroacetic acid formation in drinking water chlorination

This study presents a phenomenological model that can be used by the water professionals to quantify chlorine decay and disinfection byproduct(DBP)formation in water.The kinetic model was developed by introducing the concept of limiting chlorine demand and extending an established reactive species approach.The limiting chlorine demand,which quantifies chlorine reactive natural organic matter(NOM)on an equivalent basis,was mathematically defined by the relation between ultimate chlorine residue and initial chlorine dose.It was found experimentally that NOM in water has limiting chlorine demand that increases with chlorine dose once the ultimate residue is established.These results indicated that the complex NOM has a unique ability to adjust chemically to the change in redox condition caused by the free chlorine.It is attributed mainly to the redundant functional groups that persist in heterogeneous NOM molecules.The results also demonstrated that the effect of chlorine dose on the rate of chlorine decay can be quantitatively interpreted with the limiting chlorine demand.The kinetic model developed was validated for chlorine decay and chloroacetic acid formation in finished drinking water.