Ferguson Megan A, Hering Janet G
Department of Environmental Science and Engineering, California Institute of Technology,1200 E. California Boulevard, Pasadena, California 91125, USA.
Environ Sci Technol. 2006 Jul 1;40(13):4261-7. doi: 10.1021/es0524853.
Compliance with the U.S. drinking water standard for arsenic (As) of 10 microg L(-1) is required in January 2006. This will necessitate implementation of treatment technologies for As removal by thousands of water suppliers. Although a variety of such technologies is available, most require preoxidation of As(III) to As(V) for efficient performance. Previous batch studies with illuminated TiO2 slurries have demonstrated that TiO2-photocatalyzed AS(III) oxidation occurs rapidly. This study examined reaction efficiency in a flow-through, fixed-bed reactor that provides a better model for treatment in practice. Glass beads were coated with mixed P25/sol gel TiO2 and employed in an upflow reactor irradiated from above. The reactor residence time, influent As(III) concentration, number of TiO2 coatings on the beads, solution matrix, and light source were varied to characterize this reaction and determine its feasibility for water treatment. Repeated usage of the same beads in multiple experiments or extended use was found to affect effluent As(V) concentrations but not the steady-state effluent As(III) concentration, which suggests that As(III) oxidation at the TiO2 surface undergoes dynamic sorption equilibration. Catalyst poisoning was not observed either from As(V) or from competitively adsorbing anions, although the higher steady-state effluent As(III) concentrations in synthetic groundwater compared to 5 mM NaNO3 indicated that competitive sorbates in the matrix partially hinder the reaction. A reactive transport model with rate constants proportional to incident light at each bead layer fit the experimental data well despite simplifying assumptions. TiO2-photocatalyzed oxidation of As(III) was also effective under natural sunlight. Limitations to the efficiency of As(III) oxidation in the fixed-bed reactor were attributable to constraints of the reactor geometry, which could be overcome by improved design. The fixed-bed TiO2 reactor offers an environmentally benign method for As(III) oxidation.
2006年1月起要求饮用水中砷（As）含量符合美国10微克/升的标准。这将使数千家供水商必须采用去除砷的处理技术。尽管有多种此类技术可供使用，但大多数技术都需要将As(III)预氧化为As(V)才能高效运行。先前关于光照TiO2悬浮液的批次研究表明，TiO2光催化氧化As(III)的过程迅速。本研究在流通式固定床反应器中考察了反应效率，该反应器能更好地模拟实际处理过程。玻璃珠涂覆有混合的P25/溶胶凝胶TiO2，并用于从上方照射的上流反应器中。改变反应器停留时间、进水As(III)浓度、珠子上TiO2涂层的数量、溶液基质和光源，以表征该反应并确定其用于水处理的可行性。发现在多个实验中重复使用相同的珠子或延长使用时间会影响出水As(V)浓度，但不会影响稳态出水As(III)浓度，这表明TiO2表面的As(III)氧化经历了动态吸附平衡。未观察到As(V)或竞争性吸附阴离子导致的催化剂中毒现象，尽管与5 mM NaNO3相比，合成地下水中较高的稳态出水As(III)浓度表明基质中的竞争性吸附质会部分阻碍反应。尽管有简化假设，但一个速率常数与每个珠子层的入射光成正比关系的反应传输模型很好地拟合了实验数据。TiO2光催化氧化As(III)在自然阳光下也很有效。固定床反应器中As(III)氧化效率的限制归因于反应器几何形状的限制，这可以通过改进设计来克服。固定床TiO2反应器为As(III)氧化提供了一种环境友好的方法。
