Simultaneous electrochemical nutrient recovery and hydrogen generation from model wastewater using a sacrificial magnesium anode

We have demonstrated the feasibility of struvite production coupled with hydrogen generation for nutrient recovery. Electrochemical struvite was precipitated at low pH from a magnesium anode, eliminating the need for chemical additives and their associated costs. A faradaic efficiency (FE) near 30% was achieved while hydrogen was simultaneously produced with a FE near 40%. With the co-generation of two valuable products, costs for the electrochemical process are offset to help increase the feasibility of struvite production. We have also demonstrated control over the final product composition to form either an ammonia or an ammonia-free magnesium phosphate (struvite or newberyite, respectively). High temperatures decompose struvite to newberyite in the final product; however, at intermediate temperatures, competition between migration and convection dictates product composition. Under convection-dominating regimes, struvite is formed while newberyite forms under migration-dominating regimes. Identification of these parameters controlling product composition increases adaptability of the process by enabling customization of N:P ratios to serve a variety of different farming environments.