Aqueous nitrate removal by D417 resin: thermodynamic, kinetic and response surface methodology studies

A critical review of various adsorbents for selective removal of nitrate from water: Structure, performance and mechanism

Nitrate is ubiquitous pollutant due to its high water solubility, usually contributing to eutrophication, and posing a threat to aquatic ecosystem and human health. Adsorption approach has been widely used for nitrate removal because of the simplicity, easy operation, and low cost. Adsorbent plays a key role in the adsorptive removal of nitrate. The adsorption performance and adsorption mechanism are determined by the structural feature of adsorbent that is dependent on the preparation method. In this review, various types of adsorbents for nitrate removal were systematically summarized, their preparation, characterization, and adsorption performance were evaluated; the factors influencing the nitrate adsorption performance were discussed; the adsorption isotherm models, kinetic models and thermodynamic parameters were examined; and the possible adsorption mechanisms responsible for nitrate adsorption were categorized; the possible correlation of adsorbent structure to adsorption performance and adsorption mechanism were explained; the potential applications of adsorbents were discussed; finally, the strategies for improving adsorption capacity and selectivity towards nitrate, the challenges and future perspectives for developing novel adsorbent were also proposed. This review will deepen the understanding of nitrate removal by adsorption process and help the development of high-performance adsorbents for selective nitrate removal from water and wastewater.

Implication of Non-electrostatic Contribution to Deionization in Flow-Electrode CDI: Case Study of Nitrate Removal From Contaminated Source Waters

While flow-electrode capacitive deionization (FCDI) operated in short-circuited closed cycle (SCC) mode appears to hold promise for removal of salt from brackish source waters, there has been limited investigation on the removal of other water constituents such as nitrate, fluoride or bromide in combination with salt removal. Of particular concern is the effectiveness of FCDI when ions, such as nitrate, are recognized to non-electrostatically adsorb strongly to activated carbon particles thereby potentially rendering it difficult to regenerate these particles. In this study, SCC FCDI was used to desalt source waters containing nitrate at different concentrations. Results indicate that nitrate can be removed from source waters using FCDI to concentrations <1 mg NO₃-N L^-1 though a lower quality target such as 10 mg L^-1 would be more cost-effective, particularly where the influent nitrate concentration is high (50 mg NO₃-N L^-1). Although studies of the fate of nitrate in the FCDI system show that physico-chemical adsorption of nitrate to the carbon initially plays a vital role in nitrate removal, the ongoing process of nitrate removal is not significantly affected by this phenomenon with this lack of effect most likely due to the continued formation of electrical double layers enabling capacitive nitrate removal. In contrast to conventional CDI systems, constant voltage mode is shown to be more favorable in maintaining stable effluent quality in SCC FCDI because the decrease in electrical potential that occurs in constant current operation leads to a reduction in the extent of salt removal from the brackish source waters. Through periodic replacement of the electrolyte at a water recovery of 91.4%, we show that the FCDI system can achieve a continuous desalting performance with the effluent NO₃-N concentration below 1 mg NO₃-N L^-1 at low energy consumption (~0.5 kWh m^-3) but high productivity.