Ion-exchange regeneration efficiency and life cycle environmental impacts

The regeneration efficiency, cost, life cycle impacts, and disposal implications of ion exchange (IX) regeneration using NaCl, NaHCO₃, KCl, and KHCO₃ salts were compared. In regeneration jar tests, chloride regeneration efficiency was higher for polystyrene anion exchange resin, while bicarbonate regeneration efficiency was higher for polyacrylic anion exchange resin. Potassium regeneration efficiency was higher than sodium regeneration efficiency for all cation exchange resins tested. NaHCO₃ and KCl are approximately 5 to 10 times more expensive than NaCl, and NaHCO₃ and KCl generally had higher environmental impacts than NaCl depending on the impact category. However, there are potential benefits of NaHCO₃ and KCl over NaCl in terms of disposal that may offset the higher costs and life cycle impacts. NaHCO₃ regenerant could offset costs used to address high corrosion potential in distribution systems and household plumbing, chronically acidified receiving waters, and wastewater nitrification limited by low alkalinity. KCl regenerant could offset costs for agricultural potassium inputs at a lower required dilution than NaCl based on impacts to hydraulic conductivity and plant nutrient requirements. KHCO ₃ is not recommended as an IX regenerant due to its cost, which is ∼25 times higher than NaCl, high environmental impacts, and no further benefits over NaHCO₃ or KCl in terms of disposal.