Removal and recovery of phosphorus from low-strength wastewaters by flow-electrode capacitive deionization

Phosphorus (P) concentrations as low as 10 mg/L P can lead to eutrophication in natural waters. Meanwhile, phosphorus is an important and non-renewable resource for humans, animals and plants. This study investigated the removal and recovery of phosphorus from low-strength wastewaters by flow-electrode capacitive deionization (FCDI) to realize the sustainable utilization of phosphorus. Effects of different operating parameters on the performance of FCDI for phosphorus removal were systematically studied, including applied voltage, flow rate and flow direction of feed water, initial phosphorus concentration, carbon black content and initial pH value. Results showed that the applied voltage and initial pH value had great influence on the phosphorus removal efficiency. The removal efficiency of phosphorus reached about 97% when the operating parameters were optimized. The FCDI system possessed good removal performance of phosphorus after six consecutive cycling tests. In addition, the low concentration of feed phosphorus solution (100 mg/L P) could be effectively concentrated by 16 times after 11 h of operation through the enrichment experiment, leading to a final concentration of 16.8 mg/L P in feed solution and 1567 mg/L P in the aqueous phase of flow electrodes. To conclude, these results revealed that FCDI system is effective in phosphorus removal and recovery, and has great application prospects in treatment of phosphorous wastewaters.