Recent research showed that the recovery of ammonia from simulated ammonium citrate scrubber effluent via bipolar membrane electrodialysis (BPMED) is less energy-intensive than from ammonium sulfate solutions. Nonetheless, the application of citric acid as scrubbing agent is limited by its high costs. This study aimed to improve BPMED performance for ammonium recovery using ammonium salts mixtures (ammonium sulfate and ammonium citrate) as feed solutions. Unlike previous studies that focused mainly on single-salt systems, it investigated how this combination affects ammonium recovery efficiency, current efficiency, energy consumption, ammonia diffusion, H⁺ and OH⁻ leakage to the diluate compartment, and anions transport across anion exchange membranes (AEMs) during BPMED. The ammonium recovery efficiency was higher for pure ammonium citrate (45.2 %) and mixture solutions (32.0–45.9 %) than for pure ammonium sulfate (26.8 %). Higher efficiency resulted from reduced competition between protons and ammonium across the cation exchange membrane (CEM). Feed with a higher ammonium citrate proportion increased buffer capacity, preventing protons leakage from the acid to the diluate compartment. This resulted in higher ammonium current efficiency for pure ammonium citrate (34.8 %) and mixture solutions (24.9–35.7 %) than for pure ammonium sulfate (20.4 %). The energy consumption was lower for pure ammonium citrate (14.1 kWh/kg-N recovered) and mixture solutions (13.0–17.4 kWh/kg-N recovered), than for pure ammonium sulfate (22.3 kWh/kg-N recovered). Ammonia diffusion from the base to the acid compartment reduced current efficiency by 19–23 % and accounted for 30–40 % of the total ammonium transported from the feed. This study demonstrated the effective use of ammonium citrate as one of the salts in the mixture to achieve high ammonium recovery efficiency with reduced energy consumption.

Simulated ammonium sulfate scrubber effluent was treated using bipolar membrane electrodialysis (BPMED) to recover sulfuric acid for reuse in the scrubber, and ammonium hydroxide as a product, without using any chemicals. The effect of pH and temperature of the feed solution on the energy consumption of the BPMED and the purity of the recovered acid and base were investigated in batch experiments. Experiments were conducted during a 3-hour period using a scrubber effluent with the following characteristics: 50 g/L ammonium sulfate, pH ranging from 1 to 5 and temperature ranging from 20 °C to 30 °C. The energy consumption at pH 5 was lower than that at pH 1, i.e., 6.9 MJ/kg SO₄^2- and 7.7 MJ/kg SO₄^2-, respectively. The purity of the acid recovered from the feed solution with a pH of 5 was 36 %, whereas the feed with a pH of 1 resulted in an acid purity of 72 %. These values corresponded to a mass of ammonia diffusion of 6.9 g and 2.3 g, respectively. The purity of the base recovered from the feed with a pH of 5 was 84 %, whereas this was 69 % for the feed with a pH of 1. Higher temperature of the feed solution, i.e., 30 °C compared to 20 °C, resulted in a lower energy consumption: 7.1 MJ/kg SO₄^2- compared to 9.5 MJ/kg SO₄²⁻, respectively. The temperature had a very limited effect on the acid and base purities, with values ranging from 80 % to 82 % for the acid, and from 33 % to 36 % for the base. Our study demonstrated the effective application of BPMED for the treatment of simulated acidic scrubber effluent, with simultaneous recovery of ammonia and sulfuric acid.