Kim Jaeshin, Benjamin M M Mark M
Department of Civil and Environmental Engineering, University of Washington, PO Box 352700 Seattle, WA 98195-2700, USA.
Water Res. 2004 Apr;38(8):2053-62. doi: 10.1016/j.watres.2004.01.012.
Arsenate and nitrate can be removed quantitatively from drinking water by anion exchange. However, if the raw water contains substantial concentrations of sulfate or nitrate, the resin becomes exhausted quickly, and the requirements for regenerant (brine) can make the process unattractive. Previously, we described a modified ion exchange operating procedure for arsenic removal from solutions containing sulfate that could overcome this problem. This paper extends that work to solutions containing nitrate, and presents a mathematical model for the process. The selectivity coefficient for sulfate over nitrate of a strong base anion exchange resin increased dramatically with increasing ionic strength, partially counteracting the decrease in SO(4)/NO(3) separation factor predicted from mass action considerations. The value of this selectivity coefficient in different solutions can be used in conjunction with mass balances and solid/liquid equilibrium considerations to explore the brine requirement when the modified treatment process is applied to influent waters with various compositions. The modeling results indicate that, for relatively low influent nitrate concentrations, the volume of water treated per unit volume of brine used can be increased greatly by using the modified ion exchange process. At higher influent nitrate concentrations, the modified process remains advantageous, but is less so. The use of separate brine solutions to regenerate the upstream and downstream columns magnifies the benefits of the modified process significantly. If the sulfate in the brine is precipitated as CaSO(4)(s) rather than BaSO(4)(s), the brine usage rate increases by only 30-40%, even though the former solid is orders of magnitude more soluble than the latter.
通过阴离子交换可从饮用水中定量去除砷酸盐和硝酸盐。然而，如果原水中含有大量的硫酸盐或硝酸盐，树脂会很快耗尽，并且再生剂（盐水）的需求会使该工艺缺乏吸引力。此前，我们描述了一种用于从含硫酸盐溶液中去除砷的改良离子交换操作程序，该程序可克服这一问题。本文将该工作扩展至含硝酸盐的溶液，并给出了该过程的数学模型。强碱阴离子交换树脂对硫酸盐相对于硝酸盐的选择性系数随离子强度的增加而急剧增大，部分抵消了根据质量作用原理预测的SO(4)/NO(3)分离因子的降低。该选择性系数在不同溶液中的值可与质量平衡及固/液平衡考虑因素相结合，以探讨将改良处理工艺应用于各种成分的进水时的盐水需求。建模结果表明，对于相对较低的进水硝酸盐浓度，通过使用改良离子交换工艺，每单位体积盐水处理的水量可大幅增加。在较高的进水硝酸盐浓度下，改良工艺仍然具有优势，但优势较小。使用单独的盐水溶液再生上游和下游柱可显著放大改良工艺的益处。如果盐水中的硫酸盐沉淀为CaSO(4)(s)而非BaSO(4)(s)，即使前者固体的溶解度比后者高几个数量级，盐水使用率仅增加30 - 40%。
