紫外辐射对腐殖酸分子结构及其混凝过程的影响规律研究

发布时间：2018-05-14 15:41

本文选题：混凝 + 饮用水　；参考：《西安建筑科技大学》2013年硕士论文

【摘要】：腐殖酸（HA）广泛存在于各类水体中，其在饮用水中的存在不利于其他有机物的去除，而且它是消毒副产物的前驱物，因此，腐殖酸的去除受到越来越多的关注。传统的混凝-沉淀-过滤水处理工艺对腐殖酸等有机物的去除效果并不理想，而紫外光照除了能将水中的有机物直接矿化外，还能够促进后续混凝过程的进行。本课题研究了紫外光照射后腐殖酸分子结构的变化特征，考察了水质条件对紫外照射前后腐殖酸混凝性能的影响规律，并对紫外预处理对腐殖酸混凝的促进作用机理进行了探讨，得出如下实验结论：紫外光照射对腐殖酸溶液的pH值和TOC浓度均有一定的影响。碱性条件下，紫外照射后腐殖酸溶液pH显著降低，气相色谱数据表明，紫外光照射后溶液中生成了部分小分子酸；酸性条件下，紫外照射后腐殖酸溶液pH略微升高，，分析认为这与腐殖酸酸性基团的生成速率及矿化速率有关，当pH=7时，紫外照射后腐殖酸溶液的TOC下降率约为10%。此外，紫外辐射作用对腐殖酸分子结构也存在影响。pH=8和pH=10的两种腐殖酸溶液的E4/E6值随着辐射时间的增加而减小；紫外辐射后腐殖酸溶液的三维荧光强度减弱，且红外光谱图中的一些官能团也发生了改变。水质条件对紫外照射前后腐殖酸的混凝性能具有一定的影响。改变溶液的pH值，不经紫外预处理的腐殖酸溶液最佳混凝效果出现在pH=5时，经过紫外预处理的腐殖酸溶液最佳混凝效果出现在pH=6时；当pH大于5.5时，紫外预处理对腐殖酸混凝具有促进作用，这种促进在pH=7时达到最大，pH=7时不经紫外预处理的PHA（上海巨枫腐殖酸）混凝出水残余量为7.592mg/L，而经过紫外预处理后PHA混凝出水残余量降低到1.935mg/L。研究发现，浊度和阳离子（Ca2+、Mg2+）会对聚合氯化铝（PACl）混凝腐殖酸水样起促进作用，但Ca2+、Mg2+的存在会抑制紫外预处理对腐殖酸混凝的促进作用；碱度对紫外照射前后腐殖酸的混凝影响较小，当碱度从5mg/L增加到100mg/L时，紫外预处理前后的腐殖酸溶液去除率降低值基本相同（约为15%）；腐殖酸分子结构也会影响其混凝效果，分子尺寸较大且亲水基团少的腐殖酸分子更易于被混凝去除。在常规水处理pH值范围内，紫外辐射作用可以有效地促进腐殖酸的混凝。对于PHA来说，当pH=6.0-8.0时，腐殖酸溶液经紫外预处理后的混凝出水中PHA残余量为1.5-3.0mg/L，明显低于未经预处理出水残余量（5-8mg/L），这可能与PHA的吸附聚集有关。对比不同pH值条件下紫外辐射前后腐殖酸的Zeta电位变化情况发现，相同条件下紫外照射后PHA的Zeta电位降低，双电层被压缩，这更易于胶体脱稳聚集；原子力显微镜（AFM）成像图谱也表明，紫外辐射后PHA的聚集体厚度和粒径均小于光照前的，且对紫外照射前后腐殖酸分子量分级后发现，经紫外辐射后大于100kDa的PHA分子含量增加。
[Abstract]:Humic acid (HA) is widely used in various kinds of water bodies, and its presence in drinking water is not conducive to the removal of other organic compounds, and it is the precursor of disinfection by-products. Therefore, the removal of humic acid has attracted more and more attention. The traditional coagulation-precipitation-filtration water treatment process is not ideal for the removal of organic compounds such as humic acid, but UV irradiation can not only directly mineralize the organic matter in the water, but also promote the subsequent coagulation process. In this paper, the changes of humic acid molecular structure after ultraviolet irradiation were studied, and the influence of water quality on the coagulation properties of humic acid before and after ultraviolet irradiation was investigated. The promoting mechanism of UV pretreatment on the coagulation of humic acid was discussed, and the experimental results were as follows: UV irradiation has a certain effect on the pH value and TOC concentration of humic acid solution. In alkaline condition, the pH of humic acid solution decreased significantly after ultraviolet irradiation. The gas chromatographic data showed that some small molecular acids were formed in the solution after ultraviolet irradiation, and the pH of humic acid solution increased slightly after ultraviolet irradiation in acid condition. It is considered that this is related to the formation rate and mineralization rate of acid group of humic acid. When pH = 7, the TOC decrease rate of humic acid solution is about 10 after ultraviolet irradiation. In addition, the effects of ultraviolet radiation on the molecular structure of humic acid were also observed. The E4/E6 value of humic acid solution decreased with the increase of radiation time, and the fluorescence intensity of humic acid solution decreased with the increase of irradiation time. And some functional groups in the infrared spectra have also changed. The coagulation properties of humic acid before and after UV irradiation were influenced by water quality conditions. The best coagulation effect of humic acid solution without UV pretreatment is at pH = 5, the best coagulation effect of humic acid solution after UV pretreatment is at pH = 6, and when pH is greater than 5.5, the best coagulation effect of humic acid solution without UV pretreatment appears at pH = 5. Ultraviolet pretreatment can promote the coagulation of humic acid. When pH = 7, the maximum pH = 7 was reached, and the residual amount of PHA (Shanghai giant maple humic acid) coagulation effluent without UV pretreatment was 7.592 mg / L, while that of PHA coagulation effluent decreased to 1.935 mg / L after UV pretreatment. It was found that turbidity and cationic Ca ~ (2 +) _ (2) mg _ (2) could promote the coagulation humic acid water sample, but the presence of Ca2 _ (2) mg _ (2) inhibited the effect of UV pretreatment on the coagulation of humic acid. The alkalinity had little effect on the coagulation of humic acid before and after ultraviolet irradiation. When the alkalinity increased from 5mg/L to 100mg/L, the decreasing value of the removal rate of humic acid solution before and after UV pretreatment was basically the same (about 15%); the molecular structure of humic acid also affected the coagulation effect of humic acid. Humic acid molecules with larger molecular size and less hydrophilic groups are more easily removed by coagulation. In the range of pH value of conventional water treatment, ultraviolet radiation can effectively promote the coagulation of humic acid. For PHA, the residual amount of PHA in coagulation water after UV pretreatment is 1.5-3.0 mg / L when pH=6.0-8.0 is used, which is obviously lower than that of unpre-treated effluent (5-8 mg / L), which may be related to the adsorption and aggregation of PHA. Comparing the changes of Zeta potential of humic acid before and after ultraviolet irradiation under different pH conditions, it was found that the Zeta potential of PHA decreased and the double electric layer was compressed under the same conditions, which was more easy for colloidal destability and aggregation. Atomic force microscopy (AFM) images also showed that the aggregate thickness and particle size of PHA after UV irradiation were smaller than those before and after UV irradiation. After the molecular weight classification of humic acid before and after UV irradiation, it was found that the content of PHA molecule after UV irradiation was higher than that of 100kDa.
【学位授予单位】：西安建筑科技大学
【学位级别】：硕士
【学位授予年份】：2013
【分类号】：TU991.2

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