Abstract
In anion selectrodialysis (aSED) multivalent anions are entrapped in the so called “product stream” between a standard anion exchange membrane (SA membrane) and a monovalent anion selective membrane (MVA membrane). This study was carried out on nitrified and ultra-filtrated effluent of an upflow anaerobic sludge blanket reactor (UASB) of a potato processor. The selectivity for phosphate of various membranes that could act as SA membranes was tested on lab scale. From the calculated selectivities and current efficiencies for phosphate transport two membranes, the Fujifilm Type 1 membrane and the PC-Acid 100 OT membrane from PCA are good candidates to replace the previously used PC-SA membrane from PCA. Lowering the pH had a negative effect on the mobility of the phosphate ions and it is proposed that it is the HPO42- ion that migrates through the SA membrane. Increasing the voltage resulted in a better phosphate mobility through the PC-Acid 100 OT membrane. Also, on pilot scale the PC-Acid 100 OT membrane performed much better than the PC-SA membrane: the current efficiency for phosphate transport was higher whereas the current efficiency for DIC transport was lower with the PC-Acid 100 OT membrane than with the PC-SA membrane. The PC ACID 100 OT is recommended as standard anion exchange membrane in pilot and full scale stacks for recovery of phosphate by aSED.
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