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饮用水安全是一个很严重的全球性问题,关系到人类的健康。随着水污染的严重和人类的增加,大量的污染物在水源中被检测出[1-2]。传统的水处理工艺(混凝、沉淀和过滤)对微污染物的去除不是很有效,除非添加其他处理工艺[3-5]。预氧化工艺能够有效去除微污染物,在饮用水处理厂中被广泛采用[6-7]。
在水处理过程中,常用的预氧化剂有高锰酸钾(KMnO4)和过氧化氢(H2O2)[8-10]。由于KMnO4和H2O2具有各种缺点,限制了它们在饮用水处理过程中的使用。例如,KMnO4能够引起浊度和颜色的增加[11-12]。由于需要严格的酸性条件、自由基的产率及利用率低以及H2O2不够稳定等原因,所以限制了芬顿氧化的使用[13-14]。相比KMnO4和H2O2,单过硫酸盐(PMS)具有无色、稳定、溶解性高等特性[15-16],因此,PMS也能够被应用在预氧化过程中。
氯离子(Cl−)是天然水体中广泛存在的卤素离子[17]。PMS不仅能够氧化降解有机物,同时也能氧化Cl−为有效氯(HOCl/OCl−)[18]。HOCl/OCl−会和有机物发生化学反应生成消毒副产物(DBPs)[19-20]。DBPs具有致畸、致癌和致突变的特性[21-23]。长期饮用含有DBPs的饮用水,会使癌症的患病概率显著上升。如何减少PMS预氧化体系中DBPs的生成值得研究。
氨基酸(AAs)广泛的存在于天然水体中,在天然水体中的浓度约为50—1000 µg·L−1,占总溶解性有机氮和溶解性有机碳的比例约为35%和2.6%,同时也是DBPs的重要前体物[24-25]。酪氨酸(Tyr)作为一种天然AA,广泛存在于多肽、蛋白质和藻类中[26]。此外,PMS已经成功的应用在部分小水厂和泳池的消毒过程中。因此,Tyr被选定为DBPs的前体物,研究PMS预氧化体系中DBPs的生成特性。
本论文以Tyr和实际水样为研究对象,研究PMS预氧化体系中,预氧化时间、PMS浓度、Cl−浓度、pH对DBPs生成以及毒性的影响,为DBPs的合理控制提供理论依据。
单过硫酸盐预氧化体系中消毒副产物的生成特性
Disinfection byproduct formation during peroxymonosulfate pre-oxidation process
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摘要: 单过硫酸盐(PMS)作为预氧化剂,在预氧化过程中能够去除微污染物。但是PMS也能够氧化氯离子(Cl-)为有效氯(HOCl/OCl-)。HOCl/OCl-会和有机物发生反应生成消毒副产物(DBPs)。DBPs具有致畸、致癌和致突变的特性。然而,有关PMS预氧化过程中DBPs生成特性的研究相对较少。本文考察了预氧化时间、PMS浓度、Cl-浓度和pH对DBPs浓度和细胞毒性(CTI)的影响。研究结果表明,随着预氧化时间以及Cl-浓度的增加,DBPs浓度和CTI增加。随着PMS浓度的增加,三氯甲烷、水合三氯乙醛、二氯乙酰胺和三氯乙酰胺的浓度增加,但是二氯乙腈、三氯乙腈的浓度和CTI先增加后降低。随着pH的增加,DBPs浓度和CTI降低。综合而言,在PMS预氧化过程中,在满足预氧化效果的同时,应缩短预氧化时间,降低原水中Cl-浓度,同时提高pH,来降低DBPs浓度和毒性。Abstract: Peroxymonosulfate (PMS) is used as the pre-oxidant, which can remove effectively micropollutants during pre-oxidation process. However, PMS can also convert chloride (Cl-) to reactive chlorine (HOCl/OCl-). HOCl/OCl- can react with organic matter and then generate disinfection byproducts (DBPs). DBPs have teratogenic, carcinogenic and mutagenic properties. Few studies investigated the formation of DBPs during the PMS pre-oxidation process. This study investigated effects of pre-oxidation time, PMS concentration, Cl- concentration and pH on the formation of DBPs and cytotoxicity index (CTI). Results showed that DBPs concentrations and CTI increased as pre-oxidation time and Cl- concentration increased. The concentrations of trichloromethane, trichloroacetaldehy, dichloroacetamide and trichloroacetamide increased as the PMS concentration increased, while the concentrations of dichloroacetonitrile and trichloroacetonitrile, and CTI first increased and then decreased. DBPs concentrations and CTI decreased as the pH increased. In general, under the condition of ensuring requirement of pre-oxidation, the pre-oxidation time should be reduced to reduce DBPs concentrations and toxicity during PMS pre-oxidation process. Furthermore, Cl- concentration in water should be reduced and pH should increase during PMS pre-oxidation process.
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Key words:
- peroxymonosulfate /
- pre-oxidation /
- disinfection byproduct /
- tyrosine /
- chloride
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表 1 DBPs的细胞毒性
Table 1. The cytotoxicity of DBPs
DBP种类 Type of DBP TCM TCAL DCAN TCAN DCAM TCAM 细胞毒性LC50x/(mol·L−1) 104 860 175 6250 521 488 -
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