Coupling coagulation using tannin-based product with electrodialysis reversal to water treatment: A case study

Membrane technologies are being applied to obtain water suitable for human and industrial uses. This paper addresses a case study about the electrodialysis reversal (EDR) process installed in a municipal water treatment plant, in order to obtain desalted water. The EDR was applied as a tertiary treatment, after the conventional treatment that uses a tannin-based product as coagulant. EDR performance was evaluated in terms of ions removal and of the system electrical behavior. In 54 days of operation, effects of fouling caused by residual tannin-compounds on the ion-exchange membranes were observed. Fouling affected the EDR performance increasing the electrical resistance and membranes potential and reducing the ions transport. On the other hand, the membranes cleaning operation was able to reestablish the EDR system performance, indicating that the interactions tannin-membrane are not permanent. EDR produced high-quality water achieving conductivities lower than 40 μS cm−1 by removing up to 60% for cations and 70% for anions.