饮用水含氮与含碳消毒副产物的生成潜能及其毒性

消毒副产物生成潜能测试常用于表征水中消毒副产物的前体物含量.不同于三氯甲烷等含碳消毒副产物，二卤代乙腈（DHANs）与二卤代乙酰胺（DHAcAms）等含氮消毒副产物在氯消毒的余氯存在下易分解，并且在氯胺消毒过程中可由氯胺提供氮源生成，因此常用于含碳消毒副产物的生成潜能测试方法（如Krasner提出的测试法）可能无法有效揭示DHANs与DHAcAms的前体物水平.本研究以三氯甲烷和氯醛两种含碳消毒副产物为对比，考察DHANs与DHAcAms在饮用水氯消毒与氯胺消毒过程中不同投氯量与反应时间下的生成量，识别最大生成量对应的消毒条件，以便更好地评估水样中DHANs与DHAcAms的前体物浓度.同时，对消毒过程中生成的这些挥发性消毒副产物进行毒性评价.结果显示，两个水样氯消毒的DHANs与DHAcAms生成量分别为6.19~40.08、1.34~15.75 nmol·mg^-1（mg^-1以TOC计）；氯胺消毒的DHANs与DHAcAms生成量分别为2.63~21.46、18.43~49.99 nmol·mg^-1.Krasner测试法条件下的DHANs与DHAcAms生成量均最低.在投氯量为TOC+8×NH₃-N、反应时间为24 h的氯消毒条件下，氯胺投加量20×TOC、反应时间为3 d的氯胺消毒条件下，两个水样具有最高水平的DHANs与DHAcAms生成量，并且消毒副产物毒性也高于Krasner法测试条件下的毒性水平.因此，氯消毒采用投氯量TOC+8×NH₃-N、反应时间24 h，氯胺消毒采用投加量20×TOC、反应时间3 d的生成潜能测试条件可能更好地揭示水中DHANs和DHAcAms的前体物浓度水平.

Formation potential and estimated toxicity of nitrogenous and carbonaceous disinfection byproducts in drinking water

The disinfection by-product (DBP) formation potential test is commonly used to evaluate the precursor concentrations of disinfection by-products in drinking water. Different from carbonaceous DBPs such as trichloromethane, nitrogenous DBPs such as dihaloacetonitriles (DHANs) and dihaloacetamides (DHAcAms) decompose rapidly in the presence of residual chlorine during chlorination, and can be produced using nitrogen in chloramines during chloramination. Therefore, the commonly used potential test methods for carbonaceous DBPs (such as the test method proposed by Krasner) may not effectively assess the precursor concentrations of DHANs and DHAcAms. This study investigated the concentrations and toxicities of the volatile DBPs, including DHANs, DHAcAms, trichloromethane and chloral hydrate, formed during chlorination and chloramination of drinking water at different disinfectant doses and contact times, and identified the disinfection conditions at which the maximum DHAN and DHAcAm yields were obtained. The identified conditions therefore could be used to assess the precursor concentrations of DHANs and DHAcAms. The yields of DHANs and DHAcAms were 6.19~40.08 and 1.34~15.75 nmol·mg^-1 TOC, respectively, during chlorination of two water samples and were 2.63~21.46 and 18.43~49.99 nmol·mg^-1TOC, respectively, during chloramiantion. The yields of DHANs and DHAcAms were the lowest under the conditions of the formation potential test method proposed by Krasner. The yields of DHANs and DHAcAms were highest at chlorine dose of TOC+8×NH₃-N after 24 h of reaction time during chlorination, and at monochloramine dose of 20×TOC after 3 d of reaction time during chloramination. The estimated toxicity of the DBPs formed under these two conditions were higher than that under the conditions of Krasner test method. Therefore, using the chlorination with a dose of TOC+8×NH₃-N and a reaction time of 24 h, and the chloramination condition of a dose of 20×TOC and a reaction time of 3 d might preferably reveal the precursor concentrations of DHANs and DHAcAms in drinking water.