Ammonia recovery from high-strength scrubber effluents via pilot-scale bipolar membrane electrodialysis: Elucidating transport limitations under high current density.

Authors

Gladys Mutahi, Ian Tomassen, Jules B van Lier, Henri Spanjers

Published in

Water research. Volume 306. Pages 126519. Jul 17, 2026. Epub Jul 17, 2026.

Abstract

Bipolar membrane electrodialysis (BPMED) is a promising technology for recovering dissolved ammonia (NH₃) from concentrated wastewater streams, such as scrubber effluents. To date, most research remains laboratory-scale, while existing pilot-scale studies operate at effluent concentrations of 2 g-N/L, membrane areas below 3.5 m², and current densities under 150 A/m². In this study, a pilot-scale BPMED system with an active membrane area of 21.3 m² was operated in a sequential batch mode. Real scrubber effluents (18-22 g-N/L) were treated to simultaneously recover dissolved NH₃ and regenerate citric acid. For the first time, the influence of non-ideal phenomena including proton (H⁺) competition, NH₃ back diffusion, electro-osmotic and osmotic water fluxes on NH₃ recovery, was systematically investigated at current densities beyond typical laboratory values. At feed pH below 3, decreasing current efficiency and a sharply increasing energy consumption established an operating window for the pilot-scale BP-C system, irrespective of the applied current density. NH₃ concentrations in the base compartment increased with increasing current density, reaching 48 g-N/L at 500 A/m² and corresponding to treatment capacities of up to 1.8 kg-N/m²d. At 150 A/m², NH₃ recovery was limited by cyclic NH₄⁺ transport associated with NH₃ back diffusion, coinciding with increased electro-osmotic water flux. At higher current densities, NH₃ recovery was instead limited by electro-osmotic and osmotic water flux driven by current density and osmotic pressure gradients across the membrane. Despite comparable energy consumption (7-9 kWh/kg-N recovered) to previous pilot-scale studies, this work achieved higher NH₃ concentrations and treatment capacities while advancing mechanistic understanding of transport limitations in BPMED systems.

PMID:
42526108
Bibliographic data and abstract were imported from PubMed on 30 Jul 2026.

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