西北地区复合污染地下水氨氮-铁锰催化氧化去除机理研究

The distribution of ground water resource in china is not balanced, the north part of the country which takes two thirds of the land, shares only one third of total resource, and the 65% of drinking water supply in this region depends on groundwater. However, the groundwater resource in northern china has been declined and polluted in recent years. According to newly reports, the numbers of wells in which ones water is safe for drinking in China take only 5% of all wells checked. Ammonia, manganese and iron are the most common pollutants of groundwater in China. So it is necessary to improve the technology in groundwater treatment to ensure the drinking water safety of the country. The process should be efficiency and available to removal the ammonia, iron and manganese in short process. So the research on mechanism of removal of ammonia as well as the manganese and iron in sands filter is necessary and urgent..Aims at the removal of ammonia with high concentration in groundwater by high efficiency and short process unit, started from the research on filter material surface catalytic activity and process mechanism, the treatment of groundwater resource with composite pollution in northwest area was studied. By studying the structure, compositions and chemical states of active filter material as well as the adsorption mechanism and adsorptive position of the reactants in the catalytic reactions, the formation mechanism of the active filter film could be understood. The mechanism and the kinetics of the catalytic oxidation of ammonia, manganese and iron as well as the chemical and physical combined actions and affections caused by other pollutions on removal of ammonia were studied by isotopic tracer method, chemical characterization of filter material and pilot scale experiments. In that case, the kinetic model of co-removal of ammonia, manganese and iron in groundwater by auto oxidation-filter process could be established, the scientific references and guidance were provided for design and operation of ammonia, manganese and iron co-treatment units. The over grown activity film on the sands' surface increases the filtration resistance, causes the reduction of water production rate of the filter bed and the worse outlet water quality.The physical and chemcal methods are studied to reduce the thickness of the catalytic activity filter film.

以高负荷氨氮污染为特征的复合污染地下水短流程高效处理为目标，以滤料表面活性滤膜催化氧化氨氮的特性研究为切入点，以西北地区城市复合污染地下水处理为研究对象，针对氨氮、铁、锰非稳态接触催化氧化去除过程，重点开展活性滤膜物理结构、化学组成与元素形态、滤料表面污染物附着机理、吸附活性位及其对氨氮催化氧化特性作用等方面的研究，从微观角度探明活性滤膜形成机理。利用同位素示踪法确定反应过程中各元素形态变化及相际迁移机理，结合对滤料表面性质进行的微观化学表征与现场中试系统处理数据，考察氨氮在石英砂滤层中物理及化学催化协同作用下的转化机理，以及水中铁锰与其他水质指标对氨氮去除效果的作用与影响，研究过程反应动力学。在此基础上，建立地下水自然氧化条件下过滤过程中协同去除水中铁、锰、氨氮的反应动力学模型，为高效去除复合污染地下水中铁、锰、氨氮的短流程过滤单元设计与运行提供科学依据与理论指导。

利用高锰酸钾持续氧化原水中锰离子和亚铁离子，可在石英砂滤料表面快速形成一层锰氧化物的“活性氧化膜”，这层氧化膜对于氨氮和锰具有同步高效的去除作用。优化确定了滤料表面的挂膜条件和工艺参数。利用现场中试系统，对催化氧化过滤系统进行了持续、系统的紫外、臭氧和过氧化氢协同灭活研究，在完全灭活条件下，该系统对水中氨氮和锰的去除率保持在90%以上，充分证明了氧化膜的化学催化氧化作用是去除水中氨氮和锰的主导作用。该成果改变了国内外广泛认可的氨氮去除的生物氧化主导作用，提出了一种水中氨氮去除的新的技术和工艺。通过SEM、XRF和XPS等表征方法初步提出氨氮和锰的催化氧化机理：氧化膜与O2反应生成具有强氧化性的中间产物 •O，中间产物 •O在氨氮反应的电子转移中同时作为氧化剂和还原剂；吸附态的[≡Mn-OH]和Mn2+在氧化膜界面上发生催化氧化反应，生成复杂的氧化物，其中仅少量氧化物转化为氧化膜，两个反应均有H+生成。水温（高于6.6 ℃）、pH（8.5~6.5）的变化及常见阴阳离子（Na+、K+和Cl-）对氨氮去除影响不大，高浓度的Mg2+和Ca2+对氨氮的去除影响较大。现有研究中生物条件下氨氮的最大去除负荷约为1.5~6 g/(m3h)，远低于本研究中氧化膜对于氨氮的最大去除负荷（22.2 g/(m3h)）。对于氨氮和锰的去除，氧化膜的活性具有高效且持久的稳定性（超过一年）。为解决进水中有铁锰存在时导致滤池反冲洗周期明显降低的问题，对长期运行表面氧化膜过度增长的滤料进行化学脱膜实验，优化确定了脱膜的工艺条件，脱膜后保证氧化膜活性基本不变，同时又有效恢复反冲洗周期（从39.1 h增加到61.6 h）。