Achieving low-cost, highly selective nitrate removal with standard anion exchange resin by tuning recycled brine composition. (15th April 2020)

• Record Type: Journal Article
• Authors: Duan, Shoupeng; Tong, Tiezheng; Zheng, Shaokui; Zhang, Xueyu; Li, Shida
• Is Part Of: Water research. Volume 173(2020)
• Publication Date: 2020-04-15
• Subjects: Nitrate -- Selective ion exchange -- Groundwater -- Brine reuse -- Resin activation; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2020.115571
• Languages: English
• ISSNs: 0043-1354

Abstract

Abstract: 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. Graphical abstract: Image 1 Highlights: It achieved highly-selective nitrate removal by standard anion exchange resins (AERs). Circular activation mode modified anionic column elution and breakthrough curves. Critical anionic equivalent ratio in brine finally inhibited ion exchange during exhaustion. Sulfate in brine and feedwater had no significant effect on nitrate removal by standard AER. It shares an identical nitrate-selective removal mechanism as nitrate-selective AERs.