Capacitive deionization (CDI) for removal of phosphate from aqueous solution

Abstract

In this investigation, a commercial capacitive deionization (CDI) unit is utilized to treat phosphate wastewater. CDI deionization studies were performed to evaluate the effects of various experimental parameters, including initial pH, flow rate, and initial concentration on the removal of phosphate. The optimal pH value was around 5–6. The CDI removal efficiencies obviously decreased as the flow rate (1.6–8.0 L/min) or the initial phosphate concentration (50–300 mg P/L) increased. The highest removal of phosphate and reduction in conductivity were 86.5 and 81.5% obtained at a flow rate of 4.8 L/min, and an initial phosphate concentration of 50 mg P/L, and the lowest were approximately 77.4 and 73.1% obtained at an initial phosphate concentration of 300 mg P/L. A three-stage treatment yielded a reduction in conductivity and a removal of phosphate up to 98 and 93%, obtained at a phosphate concentration of 300 mg P/L. A pseudo-first-order rate model was adopted to describe the kinetics of electrosorption, and the k value was found to be about 0.88 min−1 at an initial phosphate concentration of 300 mg P/L. The energy consumption clearly increased with an increase in the initial phosphate concentration and decreased with an increasing in the flow rate. The optimal operating condition was a flow rate of 4.8 L/min for per unit of phosphorus removed, and the energy consumption for the treatment of wastewater was 7.01 kWh/kg P (removed) (or 1.65 kWh/m3). The advantages of the CDI process are low cost and the lack of need for any chemical to be used. CDI is a suitable technology for removing phosphate from wastewater.