Nitrate adsorption and desorption during biological ion exchange

Ion exchange (IEX) is an effective NO₃^– removal technology and research has shown promise for bioregeneration of NO₃^– laden IEX resins, creating an ideal technology for decentralized systems by removing the need for chemical regeneration that results in brine wastes. This work aimed to advance the applicability of biological ion exchange (BIEX) by evaluating the effect of secondary IEX between organic acids, natural organic matter (NOM), and buffer solutions commonly present in BIEX systems and NO₃^–, which is often displaced from the resin by these compounds. Organic acids had separation factors ranging from 0 (little to no adsorption affinity) to 2.8 (40–50% of NO₃^– displaced from the resin), with higher molecular weight molecules yielding higher separation factors. Separation factors for NOM ranged from 0 to 2.1, with higher carbohydrate compositions identified as a major influence for higher separation factors. Batch denitrification experiments were conducted using sludge and woody mulch as sources of bacteria, and charge balances revealed that secondary IEX with inorganic ions and organic compounds facilitated NO₃^– displacement from the resins followed by aqueous phase denitrification.