The effect of anode degradation on energy demand and production efficiency of electrochemically precipitated struvite

Abstract: The electrochemical recovery of phosphorus (P) from wastewater in the form of struvite (MgNH₄PO₄⋅6H₂O) has been shown as a viable replacement for industrial phosphate-based fertilizers. Electrochemical struvite precipitation is dependent upon the oxidation of a magnesium (Mg) anode, and the corrosion process creates a dynamically changing anode surface with likely impacts on reactor performance. In this work, a scaled-up electrochemical reactor (16 L) was designed to study reactor performance over time as anode degradation caused changes to struvite production and energy demand. A concentrated synthetic wastewater was used and electrochemical precipitation was monitored from batch to batch across six separate batch reactor experiments. Generally, the scaled-up electrochemical reactor improved struvite recovery (40–54%) over our previously reported lab-scale reactor (38%); however, the production exponentially decreased with the number of batch experiments from ~ 320 to ~ 210 g/batch, while the consumed energy exponentially increased from 0.9 to 1.6 kWh/batch due to severe degradation of the Mg anode. FTIR, XRD, SEM, XPS, and chemical analyses confirmed a total production of ~ 1.6 kg of high-quality struvite with an energy input of 4.6 kwh kg⁻¹. Graphic abstract: [Figure not available: see fulltext.]