The Study Of Nitrogen Disinfection By-Products HNMs Formation Characteristic

Currently, the existence of disinfection by-products(DBPs)is an important hidden danger that can not be ignored in drinking water safety domain. So far more than 700 DBPs have been detected, among which halonitromethanes (HNMs) in drinking water has been a public concern due to its potential high toxicity to human health. However, the formation rule of HNMs still remains unclear. The main objectives of this article was to 1) develop the models to evaluate the HNMs formation upon chlorination/chloramination of source water from Tai Lake and Qiantang River,2)investigate the factors(such as property/origin of organic matter, pH, reaction time, temperature, ect) that influence the contribution of nitrite to HNMs formation. The conclusions showed as following:1) the total formation of HNMs (T-HNMs) during chlorination and chloramination of Tai Lake and Qiantang River could be described using the following models: (1)T-HNMC12= (10)5.367 (DON)6.645 (Br-)0.737 (DOC)-5.537 (Cl2)0.333 (t)0.165 (R2=0.974, p< 0.01, n=33), and (2) T-HNMNH2Cl= (10)-2.481 (NH2Cl)0.451(NO2-)-0.382 (Br-)0.630 (t)0.640 (Temp)0.581(R2=0.961, p< 0.05, n=33), respectively. The key factors that influenced the T-HNM yields during chlorination were dissolved organic nitrogen (DON), bromide and dissolved organic carbon(DOC). However, the nitrite, bromide concentrations and the reaction time mainly affected the T-HNM yields during chloramination. Further analysis indicated that the bromine incorporation factors (BIFs) for trihalogenated HNMs generally decreased as the chlorine/chloramine dose, temperature and reaction time decreased and increased as the bromide concentration increased.2) During chlorination, whether for allochthonous organic matter(OM) (falling leaves (FLOM) and green leaves (GLOM) of phonex tree) or autochthonous OM (intracellular organic matter (IOM) made from the Microcystis aeruginosa), the addition of nitrite significantly enhanced the HNMs yields, and the extent of HNMs enhancement derived from nitrite addition was most obviously reflected in FLOM, followed by GLOM, and the least was IOM. Moreover, the rise in HNMs yields due to the nitrite addition all showed an increasing trend with pH, yet kept stable as the reaction time prolonged from 1d to 7d or the temperature increased from 20 to 30℃. During chloramination, the extent of HNMs enhancement derived from nitrite addition was ranked as allochthonous OM (FLOM and GLOM)> autochthonous OM (bovine serum albumin BSA). But the pH, temperature and reaction time showed no obvious trend for the contribution of nitrite to HNMs formation.3) The article focuses on none nitrogen organic matter such as phenol, p-cresol, m-cresol, o-cresol, phenylcarbinol, benzaldehyde, methanal, ethanal, n-propanal, methanol, ethanol, n-propanol, isopropanol, formic acid, acetic acid, propionic acid, lactic acid, and acetone to explore the role of nitrite in trichloronitromethane (TCNM) formation during chlorination and chloramination. Results are as follows:①During chlorination, the addition of nitrite significantly promoted the TCNM yields for phenols. Highest TCNM formation was observed in o-cresol at 9.95 μg/L. However, no/trace TCNM was detected for all aliphatic compounds during chlorination with nitrite. The further chlorination tests for o-cresol with nitrite showed that the yields of TCNM increased with reaction time, pH and temperature.②During chloramination, the addition of nitrite did not significantly promoted the TCNM yields for all of organic matter. So it can be speculated that chloramine rather than nitrate participate in the formation of TCNM. Among the benzene compounds, P-cresol produced the largest amount of TCNM (17μg/L), while for the compounds without benzene, propanal produced the largest amount of TCNM (about 6.88 μg/L). For p-cresol, TCNM yields showed linear increase with reaction time and temperature yet reached maximum at pH 7. And the TCNM yields for n-propanal was high under fllowing conditions:reaction time for 3 d, at pH 7, temperature for 10℃. Overall, TCNM formation was higher in chloramination than in chlorination regardless of adding nitrite. In the end, according to the results, the hypothesized pathways of TCNM formation were proposed during chlorination and chloramination.