CO<sub>2</sub> Utilization for Water Treatment: Ion Exchange Nitrate Removal Driven by CO<sub>2</sub> without Producing Spent Brine Regenerant
Hang Dong, Hao Chen, Arup K. SenGupta
Abstract
Ion exchange (IX) is a major technology addressing groundwater nitrate violations. However, the conventional IX nitrate removal system generates environmentally harmful spent brine regenerant, the disposal of which has been increasingly banned in many regions. Meanwhile, CO2 utilization is needed in different sectors to incentivize CO2 capture for achieving carbon neutrality by the 2050s. Thus, we exemplified CO2 utilization in the water sector by investigating a CO2-driven IX system (referred to as NSR-Desal) for nitrate removal to eliminate the spent brine regenerant. The NSR-Desal system contained two IX columns including a nitrate-selective resin (NSR) and a shallow-shell weak acid cation exchange resin (SSWAC). With CO2 as the sole regenerant, NSR-Desal achieved over 70% nitrate removal from real groundwater for multiple cycles. Additionally, over 50% desalination was achieved, demonstrating the process versatility. Compared with conventional brine (12% NaCl) regeneration, CO2 regeneration decreased the spent regenerant salinity for over 50 times, which significantly reduced the chemical discharge from IX nitrate removal. CO2 utilization was estimated as 4.7 kg CO2 per m3 treated water, and partial CO2 was sequestrated as CaCO3 precipitates. We envision this study to provide insights for utilizing CO2 in the water sector for sustainable water treatment and facilitating carbon neutrality.