硝酸根对颗粒状铁降解三氯乙烯的影响(英文)

Effects of nitrate on trichloroethylene degradation (TCE) by granular iron

为研究硝酸根对颗粒状铁降解三氯乙烯的影响,进行了柱实验和相应的反应铁腐蚀电位测定。在硝酸根离子存在条件下,铁的腐蚀电位相应升高,系统条件也因之发生变化,导致钝性的铁氧化物在铁表面生成。因而,三氯乙烯和硝酸根离子降解速率明显减小, 并且降解速率减小的程度与硝酸根离子的浓度成比例。当污染液流过反应柱时,硝酸根离子与铁反应, 被还原为氨根离子。该反应造成硝酸根离子的浓度梯度,使钝化区在柱中上移,从而影响了三氯乙烯的降解曲线。与三氯乙烯单独与铁反应相比,当含4 7 mg/L硝酸根的三氯乙烯溶液流经反应柱170 孔隙体积后,降解50% 三氯乙烯所需的时间(t50) 从小于4 h增加到大于10 h;而当三氯乙烯溶液中加入100 mg/L硝酸根离子,仅17 孔隙体积溶液流经反应柱后,三氯乙烯降解t50就已大于14 h。研究结果表明,由于硝酸根离子对铁的腐蚀电位和铁表面氧化膜的不利作用,在处理靶污染物为高浓度硝酸根离子和三氯乙烯共同污染的地下水时,铁渗透反应隔栅不是最佳选择。如果靶污染物中硝酸根离子浓度比较低,则在设计铁隔栅时应考虑到硝酸根离子造成的不利因素,相应增加铁墙的厚度,从而确保三氯乙烯的降解效果。

In this study, column experiments, including measurements of corrosion potential, were conducted to determine the effects of nitrate on trichloroethylene (TCE) degradation by granular iron. The presence of nitrate resulted in a positive shift in corrosion potentials, and thus shifted the conditions to favour the formation of a passive oxide film at the iron surface. Consequently, significant decreases in TCE and nitrate degradation rates were observed. The extent of the decline in iron reactivity was proportional to the nitrate concentration. The reduction in nitrate to ammonia in the columns resulted in a migrating zone of passivity and thus migration of the TCE profiles. For a nitrate concentration of 4.7 mg/L, TCE degradation t_(50) (time needed to degrade half of the initial concentration) increased from less than 4 h in the presence of TCE alone to more than 10 h after 170 PV (pore volume) of nitrate addition; at a nitrate concentration of 100 mg/L, t_(50) of TCE increased to more than 14 h after only 17 PV. The findings of this study suggest that iron PRBs may not be a suitable choice for in situ remediation of groundwater containing high levels of nitrate as a co-contaminant with chlorinated organics, owing to its adverse effects on iron corrosion potentials and surface film formation. At low nitrate levels, the effect of nitrate should be taken into account in iron PRB design. A thicker wall may be needed to ensure satisfactory TCE removal.