Phosphate Pre-Concentrate from Wastewater for Phosphate Recovery by Selectrodialysis

Abstract

Selectrodialysis can be used to pre-concentrate the phosphate before crystallization. The process can provide a promising and sustainable renewable source of phosphate. The three major factors that led to an increase in phosphate concentration in the product of selectrodialysis are (i) an increase in current density, (ii) initial pH of the product, and (iii) initial feed concentration of phosphate. As a result, phosphate concentration in the product can reach 16 mM with a purity of 44%, current efficiency to transport phosphate and chloride for a standard anion exchange membrane and for a monovalent selective anion exchange membrane are 26.6% and 63% respectively. Those competing ion such as nitrate, bicarbonate and sulphate in wastewater create a decrease in the phosphate pre-concentrating efficiency by selectrodialysis. An inhibition of these ions to the phosphate concentrating process was found to occur initially and disappeared as the system keeps operating. The phosphate concentrating efficiency in the product was significantly reduced from 188% to 78% after 210 minutes, but after 300 minutes, this value could be recovered to 161%. It is concluded from the result that selectrodialysis is technically feasible method to recover nutrients from waste streams. The cost of wastewater treatment, preventing water pollution and yielding valuable and sustainable resources can ultimately be reduced.