Impact of resin loading on ion exchange equilibrium for removal of organic matter and inorganic ions

Ion Exchange (IEX) applications for drinking water can be limited due to high volumes of brine, brine waste and treated water corrosivity. Reusing the resin by operating at reduced regeneration frequency can overcome this. However, assessing changes on the resin loading over reuse cycles is complex because multiple presaturant ions participate in the exchange and existing models only account for the exchange with one presaturant ion. This study developed a theoretical multicomponent model for the determination of IEX equilibria when the resin loading increases due to reuse. The model suggested that both electrostatic interactions and admicelle formation were the separation mechanisms. The model revealed that under reduced regeneration frequencies, brine use and waste generation can be reduced by more than 90%, where the bicarbonate-form resin offered the potential for lower corrosivity. However, changes in resin loading after 5 reuse cycles showed that the risk of corrosion increased. For the tested source water, reusing the bicarbonate-form resin every 5 cycles would achieve the most sustainable option with 41% NOM removal and 79% brine and waste reduction. Under these conditions, almost 100% of exchange capacity is recovered after regeneration.

Fate and removal of trace pollutants from an anion exchange spent brine during the recovery process of natural organic matter and salts

The results of this sampling campaign on pilot scale processes aim to evaluate the occurrence and behavior of trace organic micro-pollutants and metal elements during anion exchange treatment of surface water and the subsequent treatment of generated spent brine with two types of electrodialysis membrane pairs. This knowledge is relevant to assess the quality and reusability of secondary products created during brine treatment; specifically the excess of sodium chloride to be recycled onsite and the natural organic matter, mostly consisting of humic substances, which find multiple applications in the agricultural industry. This study highlights that (1) the attachment mechanism of organic micro-pollutants to anion exchange resin occurs through electrostatic interaction and the subsequent transfer through ion exchange membranes is restricted by size exclusion; and (2) the complexation of trace metals compounds with the natural organic matter partly explains their removal by anion exchange. Complexes remain stable during treatment of the brine with electrodialysis.