Flow pattern and load ratio optimisation in electroconcentration cell for simultaneous nutrients and hydrogen recovery from digestate

Anaerobic digestate, although contributing only 1 to 3% of total wastewater volume, accounts for more than 25% of the nitrogen load in treatment plants. Electroconcentration (EC) has emerged as a promising approach for nitrogen recovery. However, its performance is strongly dependent on load ratio and the flow pattern used during operation. This investigation evaluates the combined influence of load ratio and flow pattern by evaluating three flow configurations: intermixed anode to cathode flow (ICF), anode to cathode flow without intermixing (ACF), and cathode to anode flow without intermixing (CAF), each operated at load ratios of 1, 1.22, and 1.5. Among all tested conditions, the CAF configuration at a load ratio of 1.5 achieved the highest ammonium nitrogen recovery (71.2 ± 1.60%) with the lowest energy consumption, while also enabling the simultaneous recovery of 0.63 m 3 of H₂ per m 3 of digestate treated per day. These results demonstrate that the selection of both load ratio and flow pattern plays a critical role in optimising nutrient and hydrogen recovery in EC systems. • Electroconcentration (EC) enables nutrient and hydrogen recovery from reject water. • Investigated the crucial role of optimising flow pattern and load ratio (L N ). • Cathode-to-anode flow at L N of 1.5 yields 73.3% NH 4 + -N recovery and 0.63 m 3 H 2 /m 3 ·d. • The NH 4 + -N shows highest transport efficiency among competing cations. • Energy-efficient integration of EC in treatment plants.