Phosphate Recovery from Excess Sludge by Conventional Electrodialysis (CED) and Electrodialysis with Bipolar Membranes (EDBM)

Phosphate recovery from excess sludge by electrodialysis was investigated on the basis of a reformation of enhanced biological phosphorus removal (EBPR) technology. Electrodialysis operations containing conventional electrodialysis (CED), electrodialysis with bipolar membrane (EDBM), and integration of CED and EDBM were used for phosphate recovery. Phosphate was recovered as a concentrated phosphate solution and phosphoric acid by CED and EDBM, respectively. Both batch and continuous operation models were adopted. Nearly all of the phosphate in the solution could be recovered under batch operation of CED, and the recovery ratio could reach 95.8% under continuous operation. In the integration of electrodialysis, EDBM could realize the in situ conversion of the concentrated phosphate into phosphorus acid effectively, as another recovery form. A net production of phosphorus acid about 0.075 mol/L could be obtained under an operating current of 50 mA/cm(2) for EDBM, and the energy consumption was 29.3 kWh/(kg H3PO4) with a current efficiency about 75%.