Sustainable removal of ammonia via a coupled ion exchange and electrolysis system

Anaerobic digestion (AD) sludge dewatering liquor is associated with a persistent problem of the total ammonia nitrogen (TAN) removal. We investigated a coupled system consisting of ion exchange and electrolysis. TAN was recovered using a Prussian blue analog (PBA)-immobilized adsorbent and removed by electrolysis along with hydrogen gas production. Batch tests revealed that PBA exclusively adsorbed TAN and was recovered by ion exchange, despite the application of actual wastewater. Langmuir and Temkin models showed good fits with the experimental data (R² > 0.99). In continuous column tests, >87.6 % TAN was consistently recovered without a decrease in the adsorption capacity for 12 cycles. TAN recovered in the regenerant was removed within 270 min to <30 mg-N/L, and the oxidation rate lasted without any notable change. Although NO₃^- and K⁺ concentrations increased continuously to >1 M, the electro-oxidation rate was stable. Investigation of the PBA surface demonstrated that no accumulation of competing ions occurred, and ion exchange was effectively performed. The capital and operational expenditures were determined as 4.109 and 3.191 M$, respectively. This suggested that the proposed system is comparable to the various TAN removal processes. The proposed system is a promising technology for recovering TAN and producing hydrogen gas.