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Combined Electrodialysis and Peptide-Directed Struvite Recovery System

Recovery of N and P as struvite (MgNH4PO4 6H2O) has gained interest in recent years as both a flow assurance measure and as a sustainable P source for fertilizer. Electrochemically precipitated struvite offers advantages compared to conventional precipitation methods by reducing the need for expensive additives and has the potential for coupling with renewable energy sources. However, high energy inputs to overcome the solution resistance of most wastewaters limit the feasibility of the technology. In this work, a coupled electrodialysis-struvite recovery system is presented to concentrate the wastewater (producing a separate desalinated stream) while producing struvite in a single unit operation. Furthermore, a common dental peptide was explored as a method to control and increase growth of struvite crystals at neutral pH. Cysteine-capped peptide was attached to a gold mesh substrate in a range of loadings (5-27ug/cm2). Chronoamperometry was conducted by first placing the peptide-loaded mesh in the struvite reactor filled with synthetic wastewater at pH 7.1 and then applying a range of potentials (0.5-0.99V) to the magnesium anode. White precipitates were observed and characterized as struvite by XRD. Struvite crystal morphology was investigated by SEM. We report that a peptide loading of 19 ug/cm2 led to a nearly 14% increase in struvite precipitated compared to bare Au with no peptide attached. Furthermore, longer, dendritic struvite crystals formed in the presence of peptide compared to orthorhombic crystals which formed without peptide. These results indicate that the peptide alters local supersaturation, leading to an increase in directional crystal growth. By demonstrating the utility of peptides for increasing struvite precipitation at neutral pH, our findings improve the viability of electrochemical struvite precipitation for a wider range of wastewater compositions and highlights how peptides can modulate crystal growth.