Valorization-driven conversion of ammonium in digested sludge filtrate into hydrogen via ion exchange and electrolysis

• A novel method for the removal of ammonia and produce hydrogen gas is proposed. • Study on ammonia adsorption mechanism and ammonia recovery efficacy were carried out • Economic viability of the proposed system is investigated. • Enables contaminant to utilize as an energy source. The treatment of total ammonia nitrogen present in digested sludge filtrate is challenging in food waste valorization owing to the high concentrations and non-biodegradability. This study proposed an integrated approach coupling ion exchange using copper hexacyanoferrate and electro-oxidation to recover and convert ammonia nitrogen into hydrogen. Batch adsorption experiments demonstrated a maximum adsorption capacity of 60.04 mg-N/g, consistent with pseudo-second-order kinetics and the Langmuir isotherm model. In addition, fixed-bed column tests demonstrated stable ammonium recovery over five adsorption–desorption cycles, achieving an average recovery efficiency of 85%. The desorption step produced regenerants containing >2,200 mg-N/L, enabling efficient electrolysis. Meanwhile, electro-oxidation of the concentrated regenerant proceeded following pseudo-first-order kinetics, but the low current efficiency (26.2%) and high specific energy consumption (92.9 kWh/kg-N) limited its performance owing to the lack of optimization of the electrolytic cell. The levelized cost of hydrogen analysis, based on scaled-up operation (1,000 m 3 /d), yielded 16.46 EUR/kg-H 2 , dominated by electricity costs. When considering avoided ammonia nitrogen removal expenses, the levelized cost of hydrogen decreased to 5.95 EUR/kg-H 2 , though it remained above the benchmarks for commercial water electrolysis. However, the levelized cost of hydrogen could be reduced to the benchmarks through improving energy efficiency of 15% for the electrolyzer. These findings highlight the technical feasibility of coupling ion exchange with electrolysis for ammonia nitrogen valorization, while emphasizing the need for electrode and membrane optimization to improve energy efficiency and economic competitiveness. The proposed system contributes to sustainable circular resource management by transforming nitrogen-rich waste into renewable hydrogen fuel.