School of Environment, MOE Key Laboratory of Water and Sediment Sciences/State Key Lab of Water Environment Simulation, Beijing Normal University, Beijing, 100875, China.
Department of Civil and Environmental Engineering, Colorado State University, Fort Collins, CO, 80523, United States.
Water Res. 2020 Apr 15;173:115571. doi: 10.1016/j.watres.2020.115571. Epub 2020 Jan 31.
This study demonstrated the presence of a critical equivalent ratio of the competing anion (i.e., sulfate and bicarbonate) to chloride ion in recycled brine to achieve highly-selective nitrate removal from nitrate-rich groundwater in the standard-anion exchange resin (AER) (i.e., with trimethylamine functional groups) column process. With increasing bicarbonate (or sulfate):chloride equivalent ratio in brine used to circularly activate/regenerate the standard-AER column, considerable bicarbonate (sulfate) removal and dumping were observed. The critical bicarbonate (sulfate):chloride equivalent ratio of 2:5 (8:1) in brine effectively achieved zero net bicarbonate (sulfate) removal (<5%) from feedwater during long-term exhaustion-regeneration cyclic operation. The feed rate (6-18 BV/h) played a key role in determining the critical sulfate:chloride equivalent ratio in brine, while the feed sulfate concentration (145-345 mg/L) slightly changed the critical sulfate:chloride equivalent ratio. The use of optimized ternary brine (with a sulfate:chloride:bicarbonate equivalent ratio of 42:5:2) stably achieved long-term highly-selective nitrate removal from groundwater in the standard-AER column process with brine electrochemical treatment. The possible mechanism for nitrate selectivity included the modification of the sulfate: and bicarbonate:chloride equivalent ratios in the standard-AER column by the optimized brine in circular activation/regeneration mode; this changed the column elution and breakthrough curves, inhibited the competition of sulfate and bicarbonate for ion exchange sites during exhaustion according to the separation factor, and finally achieved selective nitrate removal from feedwater.
本研究表明，在标准阴离子交换树脂（AER）（即具有三甲胺官能团）柱工艺中，从富硝酸盐地下水中高度选择性地去除硝酸盐，循环再生盐水中竞争阴离子（即硫酸盐和碳酸氢盐）与氯离子的关键当量比是存在的。随着循环激活/再生标准-AER 柱所用盐水中碳酸氢盐（或硫酸盐）与氯离子当量比的增加，观察到相当大的碳酸氢盐（硫酸盐）去除和倾倒。盐水中碳酸氢盐（硫酸盐）与氯离子的关键当量比为 2:5（8:1），可在长期耗尽-再生循环运行中有效地实现从给水中去除净碳酸氢盐（硫酸盐）<5%。进料速率（6-18 BV/h）在确定盐水中关键硫酸盐：氯离子当量比方面起着关键作用，而进料中硫酸盐浓度（145-345mg/L）略微改变了关键硫酸盐：氯离子当量比。优化的三元盐水（硫酸盐：氯离子：碳酸氢盐当量比为 42:5:2）的使用通过盐水电化学处理在标准-AER 柱工艺中稳定地实现了从地下水中长期高度选择性地去除硝酸盐。硝酸盐选择性的可能机制包括优化盐水在循环激活/再生模式下对标准-AER 柱中硫酸盐和碳酸氢盐：氯离子当量比的修改；这改变了柱洗脱和突破曲线，根据分离因子抑制了硫酸盐和碳酸氢盐在耗尽过程中对离子交换位点的竞争，最终实现了从给水中选择性去除硝酸盐。
