金属铁对水中微量污染物的去除特性及机理研究

发布时间：2019-01-04 06:51

【摘要】：饮用水水体或水源中存在一类高氧化态且毒性较强的微量污染物,它们难以被现有的常规处理或深度处理工艺去除,零价铁还原是潜在去除技术之一。本文研究了金属铁对四氯化碳(CCl4)、卤乙酸(HAA9)与溴酸盐(Br O3-)三类微量污染物的去除特性、影响因素与反应机理,为相关污染物的去除提供理论依据及解决方案。填充柱实验表明,在空床接触时间(EBCT)为2.5-10 min,反应温度为5-35oC范围内,金属铁对一氯乙酸(MCAA)的去除率为16.4-81.3%;对CCl4、HAA8和BrO3-的去除率基本接近100%。CCl4、MCAA与二氯乙酸(DCAA)去除过程中卤素质量不守恒,推测是溶解氧(DO)的存在导致金属铁对污染物的去除机制发生改变。摇瓶实验表明,当温度为25oC,反应时间为2 h时,随着DO浓度从0增加到12 mg/L,金属铁对BrO3-的去除效果不断下降;对CCl4、MCAA、DCAA与三氯乙酸(TCAA)的去除效果先上升后下降,最佳的DO浓度分别为1.27、1.52、1.52与0.75 mg/L。CCl4、MCAA、DCAA、TCAA与BrO3-的去除率分别为12.1-45.8%、1.25-27.5%、22.4-68.1%、26.0-80.5%与52.5-100%;伪一级反应速率常数分别为0.08-0.29、0.0002-0.16、0.12-0.53、0.18-0.73与0.41-3.91 h-1。金属铁去除污染物的步骤包括迁移、扩散、吸附与还原过程。金属铁颗粒表面的腐蚀产物从外到内依次为纤铁矿、绿铁锈、磁铁矿与氧化亚铁,污染物经非导电层(纤铁矿)扩散到导电层内,随后被还原。金属铁去除CCl4与MCAA的限速步骤为还原过程;去除DCAA与TCAA的限速步骤在DO浓度低于2.59 mg/L时为还原过程,较高时为扩散过程;去除Br O3-的限速步骤为传质过程。当污染物氧化能力大于氧时,DO的存在对污染物的去除产生抑制作用;反之,在一个较低的DO区间(0-2 mg/L)内可强化污染物的去除效果。基于金属铁去除污染物的机理,本文提出针对不同微量污染物的金属铁及其组合去除工艺。金属铁填充柱(EBCT为10 min)对Br O3-的去除率基本接近100%;吹脱与金属铁组合工艺(气水比为2、曝气时间为10 min、EBCT为2.5 min)对CCl4的去除率达98%;金属铁与生物活性炭组合工艺(EBCT分别为2.5与10 min)对HAA9的去除率达99%。
[Abstract]:There are a class of highly oxidized and highly toxic trace pollutants in drinking water or water source which are difficult to be removed by conventional or advanced treatment processes. Zero valent iron reduction is one of the potential removal techniques. In this paper, the removal characteristics, influencing factors and reaction mechanism of three kinds of trace pollutants of carbon tetrachloride (CCl4), haloacetic acid (HAA9) and bromate (Br O 3-) by metal iron were studied, which provided theoretical basis and solution for the removal of related pollutants. The packed column experiment showed that the removal rate of (MCAA) by metal iron was 16.4-81.3 when the empty bed contact time (EBCT) was 2.5-10 min, and the reaction temperature was 5-35oC. The removal rate of CCl4,HAA8 and BrO3- is close to 100%. The mass of halogen is not conserved during the removal of CCl4MCAA and dichloroacetic acid (DCAA). It is inferred that the existence of dissolved oxygen (DO) leads to the change of the removal mechanism of pollutants by iron metal. The results of shaking flask test showed that when the temperature was 25oC and the reaction time was 2 h, the removal efficiency of BrO3- was decreased with the increase of DO concentration from 0 to 12 mg/L,. The removal efficiency of CCl4,MCAA,DCAA and trichloroacetate (TCAA) increased first and then decreased. The best DO concentration was 1.27o1.52 mg/L.CCl4,MCAA,DCAA,TCAA and 0.75 mg/L.CCl4,MCAA,DCAA,TCAA and BrO3- removal efficiency were 12.1-45.8, respectively. 1.25-27.5: 22.4-68.1% 26.0-80.5% and 52.5-100%; The pseudo-first-order reaction rate constants are 0.08-0.29, 0.0002-0.16, 0.12-0.53, 0.18-0.73 and 0.41-3.91 h-1, respectively. Removal of contaminants by metal iron involves migration, diffusion, adsorption and reduction. The corrosion products on the surface of metallic iron particles are followed by fiberite, green rust, magnetite and ferrous oxide, and the contaminants are diffused through the non-conductive layer (pyrite) into the conductive layer, and then reduced. The limiting step of removing CCl4 and MCAA is reduction process, the limiting step of removing DCAA and TCAA is reduction process when the concentration of DO is lower than 2.59 mg/L, and the limiting step of removing Br O _ 3- is mass transfer process when the concentration of DO is lower than 2.59 mg/L. When the oxidation capacity of pollutants is greater than that of oxygen, the presence of DO can inhibit the removal of pollutants, whereas in a lower DO range (0-2 mg/L), the removal efficiency of pollutants can be enhanced. Based on the mechanism of removal of pollutants by metal iron, the removal process of metal iron and its combination for different trace pollutants is proposed in this paper. The removal rate of Br O _ 3- by metal iron filled column (EBCT = 10 min) was close to 100, and the removal rate of CCl4 by blowing off with metal iron (air-water ratio was 2, aeration time was 10 min,EBCT, 2.5 min) was 98%. The removal rate of HAA9 by the combined process of metal iron and biological activated carbon (EBCT = 2. 5 and 10 min) was 99%.
【学位授予单位】：清华大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TU991.2

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