Phosphate pre-concentration from municipal wastewater by selectrodialysis: Effect of competing components

The effect of competing ions in wastewater on the phosphate pre-concentrating efficiency by selectrodialysis was demonstrated in this study. Nitrate, bicarbonate and sulphate are three ions frequently present in wastewater. An inhibition of these ions to the phosphate concentrating efficiency was found to occur initially, but if the system runs for a longer time, the effect disappears. In the presence of nitrate, bicarbonate and sulphate, the phosphate concentrating efficiency in the product was significantly reduced from 188% to 78% after 210 min, but this could be recovered to 161% after 300 min. In addition, when operating selectrodialysis with synthetic municipal wastewater, phosphate was concentrated in the product with a twofold concentration compared to the initial concentration in the wastewater. Scaling on the cation exchange membrane and monovalent selective anion exchange membranes was observed during the selectrodialysis process when carrying out the experiment with synthetic municipal wastewater, but the membranes were almost completely recovered after a simple acid cleaning with 0.1 M HCl solution for 1 h. The present study indicates that selectrodialysis successfully concentrates phosphate from wastewater in the product stream, which makes a subsequent crystallization process viable to recover phosphate from wastewater.