丙氨酸在紫外/氯工艺中生成挥发性DBPs的潜能

Formation Potentials of Volatile Disinfection Byproducts from Alanine during UV/Chlorine Process

采用紫外/氯(UV/chlorine)组合工艺对原水中代表性氨基酸-丙氨酸(Ala)进行处理,并对该过程中产生的挥发性消毒副产物(三卤甲烷和卤乙腈)进行测定和分析.研究了不同投氯量、pH、紫外照射时间、溴离子和氨氮浓度对消毒副产物(DBPs)生成潜能的影响.结果表明,丙氨酸经紫外/氯工艺处理后会产生三氯甲烷(TCM)和二氯乙腈(DCAN)两种消毒副产物,且TCM、DCAN的质量浓度在处理15 min时达到最高的20.37μg/L和34.17μg/L,在较低的[Ala]/[Cl2]、较长的紫外照射时间以及中性的pH条件下有利于减少TCM和DCAN的产生,本试验得出的最佳工况为[Ala]/[Cl2]=1∶2,紫外照射2 h,溶液pH=7.此外,水中存在的溴离子使得UV/chlorine消毒后产生了溴氯乙腈(BCAN),增加了消毒副产物的种类和毒性;而氨氮的存在则会减少相应的消毒副产物的产生.还对不同工艺进行了对比,单独紫外照射时没有产生消毒副产物,单独使用氯时TCM产率小于UV/chlorine的产率,但DCAN的产率大于UV/chlorine的产率.最后,提出了UV/chlorine处理丙氨酸生成消毒副产物的可能途径:先是进攻丙氨酸氮原子上的氢,接着是脱羧基和脱氨基作用,生成乙醛和乙腈,再经过一系列取代和水解反应生成二氯乙腈和三氯甲烷.以上试验结果可以为紫外/氯组合工艺的应用和推广提供理论依据.

UV/chlorine process was employed to treat polluted water containing alanine(Ala),and the volatile disinfection byproducts(trihalomethanes and haloacetonitriles)generated during the process were determined and analyzed.The effects of chlorine dosage,pH,UV radiation time,concentrations of bromide and ammonia ions on the formation potential of disinfection byproducts(DBPs)were investigated.The results showed that trichloromethane(TCM)and dichloroacetonitrile(DCAN)were produced after UV/chlorine process,and the concentrations of TCM and DCAN reached the highest values of20.37μg/L and34.17μg/L at15min,respectively.Lower[Ala]/[Cl2]molar ratio,longer UV radiation time,and neutral pH can reduce the production of TCM and DCAN,and the optimum conditions in this experiment were as follows:[Ala]/[Cl2]=1∶2,UV irradiation for2h,and pH=7.Besides,the presence of bromide ions can form bromochloroacetonitrile(BCAN)during UV/chlorine process,which increased the types and toxicity of DBPs,while the existence of ammonia produced fewer DBPs when compared with the ammonia-free solution.Different processes were also compared,UV irradiation alone did not produce DBPs,and the yield of TCM for chlorine alone was lower than that of UV/chlorine,but the yield of DCAN was greater than that of UV/chlorine.Finally,a possible pathway for UV/chlorine treatment of alanine to generate DBPs was proposed below:first,the hydrogen on the nitrogen atom of alanine was attacked,followed by decarboxylation and deamination to produce acetaldehyde and acetonitrile,and finally a series of substitution and hydrolysis reactions to produce dichloroacetonitrile and trichloromethane were performed.The aforementioned results can provide a theoretical basis for the application and popularization of UV/chlorine process.