Integrating divided electrolysis-microfiltration process for energy-efficient phosphorus recovery in the form of calcium phosphate

Abstract

To make up the gap of phosphorus emissions being too much as a contaminant and phosphorus being too little as a fertilizer resource, an energy-efficient electrochemically mediated precipitation-microfiltration (EMP-MF) system was rationally developed for P removal and recovery as calcium phosphate. In this system, the electrolysis cell was divided by a polytetrafluoroethylene (PTFE) membrane, allowing for the productions of acidic and alkaline effluents. The alkaline effluent was fed directly into the crystallizer for the precipitation of calcium phosphate crystals, which was well intercepted by the following Ti tubular microfilter. In this system, phosphorus recovery efficiency increased from 54 % to 90 % by elevating current density from 1 to 6 mA cm−2, accompanying the specific energy consumption increasing from 3.92 to 22.44 kWh (kgP)-1 or from 0.039 to 0.38 kWh m−3 water treated. The phosphorus recovery efficiency by ECP-MF system was promoted at high initial solution pH. The phosphorus recovery efficiency was 67 %, 85 %, and 91 %, when initial solution pH was 4.0, 8.0 and 10.0. High initial Ca2+ concentration favored the phosphorus recovery, whereas it was negatively influenced with the presence of HCO3–. In addition, the coexistence of magnesium had little effect on the recovery of phosphorus but inhibited the Ca2+ removal. Natural organic matter could enhance the phosphorus recovery, but affected the purity of the recovered product. Generally, the established ECP-MF system exhibited significant prospect in promoting the widespread applications for phosphorus recovery from the wastewater.