Effects of competitive cations and dissolved organic matter on ammonium exchange and up-concentration properties of ion exchangers from domestic wastewater under multicycle exchange - regeneration operation

This study aimed to investigate the impact of competitive cations and dissolved organic matter (DOM) on ammonium exchange and up-concentration properties of ion exchangers for domestic wastewater treatment during the multicycle exchange - regeneration operations. Three ion exchangers, including zeolite, strong acid cation resin and 4A molecular sieve (MS), all showed good NH₄⁺ separation and up-concentration properties in 30 exchange - regeneration cycles. The exchange capacities of zeolite, resin, and MS decreased by 8.2 %, 10.4 %, and 4.8 % in the presence of Ca²⁺ and Mg²⁺, while DOM only impaired the exchange ability of zeolite. The up-concentration factors of zeolite, resin, and MS were 5.1, 11.5, and 5.0, respectively. Isothermal tests and breakthrough curves confirmed that long-term salt regeneration slightly reduced the exchange capacity, and the presence of competitive cations and DOM shortened the breakthrough time. Elemental mass balance further demonstrated that Ca²⁺ and Mg²⁺ were easily trapped by ion exchangers and could be released into the regeneration solution, which should be precipitated to avoid accumulation for long-term cyclic operation. Morphological analysis indicated that the presence of Ca²⁺ and Mg²⁺ would cause the resin to crack. Overall, for domestic wastewater treatment, the resin exhibited the highest NH₄⁺ capture ability and up-concentration properties with low resistance to Ca²⁺ and Mg²⁺ contamination, while silicate exchangers with a regular and compact structure had higher durability but lower up-concentration properties.