Feasibility study of electrodialysis as an ammonium reuse process for covering the nitrogen demand of an industrial wastewater treatment plant

Electrodialysis (ED) is a cost-effective membrane technology used is a variety of fields for desalination and concentration. This feasibility study explores the potential of ED as an NH₄-N recovery technology from anaerobic digestate liquor (ADL), and the use of the concentrate as a nitrogen source in an industrial wastewater treatment plant (WWTP). Three neighboring WWTPs were the focus of this study: Two municipal WWTPs A and B, operating anaerobic sludge stabilization, and a pulp & paper WWTP C, utilizing urea as a nitrogen source. Two-stage bench-scale experiments with the municipal ADL from WWTP A and WWTP B were conducted, and performance indicators were determined. A concentration of approximately 10 g NH₄-N/L and 15 g NH₄-N/L was obtained in stages 1 and 2, respectively. The NH₄-N removal was above 85 % in all experiment, while recovery varied between 25 and 95 %. The specific energy consumption (SEC) was on average 12.9 kWh/kg NH₄-N. Moreover, mass and energy balances in a model WWTP demonstrated that an ED side-stream treatment for NH₄-N removal coupled with microfiltration (MF) pre-treatment results in a net energy gain, also without the added benefit of the ED concentrate as a nitrogen source.