Cationic polymers are critical coagulant aids at drinking water plants, but the same polymers are simultaneously N-nitrosodimethylamine (NDMA) precursors upon chloramine exposure. We hypothesized the low-molecular fraction, which represents a small mass residual in polyDADMAC cationic polymer, reacts with chloramines, may not be well removed during coagulation, and is thus responsible for forming parts-per-trillion (ppt) concentrations of NDMA in finished water. To identify strategies capable of reducing post-coagulation residual polymer associated with NDMA formation, this study fractionated polyDADMAC by molecular weight, characterized reactivity of each fraction, and quantified precursor contributions to NDMA formation potential during bench-scale test and NDMA concentration due to formation during treatment during pilot tests. Diaultrafiltration of the cationic polymer produced a low molecular weight fraction (<10 kDa) and a purified polyDADMAC (>10 kDa). Native organic matter in bench- and pilot- tests contributed 19–38% of NDMA formed throughout treatment, while polymers were responsible for 62–81% of NDMA formed. The <10 kDa fraction of polyDADMAC was more reactive (450–540 ng NDMA per mg DOC) and formed >10× NDMA than non-purified polyDADMAC in jar tests. Purified polyDADMAC, with <10 kDa fraction removed, formed 54% less NDMA during pilot tests (and 63% less during jar tests) than non-purified polyDADMAC. There was no adverse effect on coagulation or subsequent filter performance by using purified polyDADMAC, but significantly (p < 0.05) less NDMA formed in filtered water when using diaultrafiltered cationic polymer. Thus, removing the low molecular weight impurities (<10 kDa) by polymer suppliers would lead to an equally-effective coagulant-aid that substantially lowers NDMA formation during drinking water treatment.

中文翻译：

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纯化和去除低分子量级分的聚DADMAC可减少水处理过程中N-亚硝基二甲胺的形成

阳离子聚合物是饮用水厂的关键助凝剂，但相同的聚合物同时是N氯胺暴露后的亚硝基二甲胺（NDMA）前体。我们假设低分子部分代表着聚DADMAC阳离子聚合物中的少量质量残留物，与氯胺反应，在凝结过程中可能无法很好地去除，从而导致最终的NDMA达到百万分之几（ppt）的浓度。水。为了确定能够减少与NDMA形成相关的凝结后残留聚合物的策略，本研究通过分子量，表征每个馏分的反应性以及在实验室规模测试过程中量化前体对NDMA形成潜力的定量贡献以及由于形成过程中形成的NDMA浓度对聚DADMAC进行了分级。中试期间的治疗。阳离子聚合物的超滤产生低分子量级分（<10 kDa）和纯化的polyDADMAC（> 10 kDa）。在整个试验过程中，天然有机物占NDMA形成的NDMA的19-38％，而聚合物占NDMA形成的62-81％。在广口瓶测试中，与未纯化的polyDADMAC相比，polyDADMAC的<10 kDa部分具有更高的反应性（每mg DOC 450-540 ng NDMA），形成的NDMA大于10倍。与未纯化的polyDADMAC相比，去除了<10 kDa分数的纯化的polyDADMAC形成的NDMA少了54％（在广口瓶测试中减少了63％）。通过使用纯化的polyDADMAC，对凝结或随后的过滤性能没有不利影响，但显着（在广口瓶测试中，与未纯化的polyDADMAC相比，polyDADMAC的10 kDa组分的反应性更高（每mg DOC 450-540 ng NDMA），形成的NDMA大于10倍。与未纯化的polyDADMAC相比，去除了<10 kDa分数的纯化的polyDADMAC形成的NDMA少了54％（在广口瓶测试中减少了63％）。通过使用纯化的polyDADMAC，对凝结或随后的过滤性能没有不利影响，但显着（在广口瓶测试中，与未纯化的polyDADMAC相比，polyDADMAC的10 kDa组分的反应性更高（每mg DOC 450-540 ng NDMA），形成的NDMA大于10倍。与未纯化的polyDADMAC相比，去除了<10 kDa分数的纯化的polyDADMAC形成的NDMA少了54％（在广口瓶测试中减少了63％）。通过使用纯化的polyDADMAC，对凝结或随后的过滤性能没有不利影响，但显着（p <0.05）使用diaultrafiltered阳离子聚合物时，在过滤水中形成的NDMA少。因此，通过聚合物供应商去除低分子量杂质（<10 kDa）将导致同等有效的助凝剂，大大降低饮用水处理过程中NDMA的形成。