Electrochemically Controlled Crystallization Using Selective Bipolar Membrane Electrodialysis
Year: 2026
Type: preprint
Abstract: Nitrogen and phosphorus nutrient recovery from wastewater represents a critical frontier for circular fertilizer manufacturing and effective water treatment. Conventional chemical precipitation remains hindered by the need for expensive reagent consumables. Here, we examine an integrated, chemical-free electrochemical mixer (ECM) system that leverages selective bipolar membrane electrodialysis (SBED) to achieve precise struvite (MgNH4PO4 · 6H2O) crystallization. We furthermore demonstrate how control over current density (1–5 mA cm−2), specific charge loading (20–40 C m−3), and hydraulic retention time (τ = 2.3–6.9 s) enhances downstream crystallization yield, purity, and morphology. Shortening retention promotes boundary-layer convection, reducing in-cell scaling energy penalty (∆E) by 86% and total stack energy consumption by 22%. Operating within an optimized pH window (7.7 < pH < 9.0) governs crystal morphology and allows for 91% yield of highly pure struvite (> 97%), bypassing competitive newberyite crystallization. We unify the ECM transport kinetics and crystallization thermodynamics into a single dimensionless descriptor—the crystallization index—which establishes a linear correlation to predict the product yield based on upstream transport dynamics. Steady specific energy consumption of 9.38 ± 0.9 kWh kg−1 − struvite through autonomous in-situ acid flushing confirms system stability with minimal scaling. Finally, techno-economic analysis evaluates the levelized cost of struvite produced as $996 t−1, which is a reduction in operating expenditures by a maximum of 89% compared to commercial phosphorus recovery installations. Ultimately, the ECM eliminates crystallization chemical dependencies and reduces membrane scaling bottlenecks, establishing a highly tunable and efficient separations reactor with precise control of crystal products.
Source: ChemRxiv
Institution: Georgia Institute of Technology
Language: English
Subfield: Waste Management and Disposal
Field: Environmental Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7220423800