Mitigation of Magnesium Electrode Fouling by Polarity Reversal Electrocoagulation for Struvite Production from Source-Separated Urine

Abstract

Electrochemical struvite precipitation is proposed to be an effective technology for phosphate recovery to tackle the problem of depleting, finite phosphate rocks and eutrophication. However, the corrosion of magnesium ions from the anode is hindered due to the formation of passivation layer that limits the technological scale-up. The study investigates the behavior of magnesium ion, corrosion and formation of passivation layer using electrochemical techniques of chronopotentiometry, cyclic voltammetry and potentio-dynamic polarization. Further, polarity reversal technique was explored to inhibit the formation of fouling layer on the magnesium electrode. The polarity reversal time varied from 0-10 min to observe the change in the process parameters that ultimately influence phosphate recovery and struvite yield from source-separated urine. Polarity reversal electrocoagulation (PR-EC) increases the phosphate recovery by 1.40x and reduces the energy demand by 0.66x as compared to direct current electrocoagulation (DC-EC). The precipitate produced were analysed using Fourier transformed infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscope (SEM) and Energy dispersive X-ray spectroscopy (EDX) confirmed the formation of pure struvite crystals. The decrease of phosphate recovery in the sequence batch experimental runs was non-significant for PREC, confirming its efficiency over DC-EC due to the uniform corrosion of the magnesium