Bioelectrochemical acidolysis of magnesia to induce struvite crystallization for recovering phosphorus from aqueous...

A novel struvite crystallization method induced by bioelectrochemical acidolysis of magnesia (MgO) was investigated to recover phosphorus (P) from aqueous solution using a dual-chamber microbial electrolysis cell (DMEC). Magnesium ion (Mg²⁺) in the anolyte was firstly confirmed to automatically migrate from the anode chamber to the cathode chamber, and then react with ammonium (NH₄⁺) and phosphate (PO₄^3-) in the catholyte to form struvite. Recovery efficiency of 17.8%-60.2% was obtained with the various N/P ratios in the catholyte. When MgO (low solubility under alkali conditions) was added into the anolyte, the bioelectrochemical acidolysis of MgO naturally took place and the released Mg²⁺ induced struvite crystallization in the cathode chamber for P recovery likewise. Besides, there was a strong linear positive correlation between the recovery efficiency and the MgO dosage (R² = 0.935), applied voltage (R² = 0.969) and N/P ratio (R² = 0.905). Increasing the applied voltage was found to enhance the P recovery via promoting the MgO acidolysis and the released Mg²⁺ migration, while increasing the N/P ratio in the catholyte enhanced the P recovery via promoting the struvite crystallization. Moreover, the electrochemical performance of the system was promoted due to more stable anolyte pH and lower pH gradient between the two chambers. Current density was promoted by 10%, while the COD removal efficiency was improved from 78.2% to 91.8% in the anode chamber.