Recovery of potassium from landfill leachate concentrates using a combination of cation-exchange membrane electrolysis and magnesium potassium phosphate crystallization

Abstract

Simultaneous removal of high levels of organic pollutants and recovery of nutrients from concentrates generated from the nanofiltration (NF) or reverse osmosis membrane separation process is a significant environmental challenge. In this study, a combined cation-exchange membrane electrolysis (CEME)/magnesium potassium phosphate crystallization process for the recycling of NF concentrates generated from treating landfill leachate was developed. These NF concentrates contained high levels of organics, ammoniacal-nitrogen, chloride as well as valuable potassium ions. The removal of these pollutants and feasibility of potassium recovery were evaluated. This study demonstrated that the proposed combined process can effectively remove 82%, 99%, 34%, 99% of organic matter, ammoniacal-nitrogen, total nitrogen, and chloride ions, respectively, while simultaneously allowing recovery of chloride and potassium ions from NF concentrates as beneficial products (gaseous chlorine and valuable magnesium potassium phosphate precipitates, a buffered fertilizer, respectively) and collection of a further electrolysis by-product (hydrogen). The recovered gaseous chlorine was reused on site as a decolorizing agent for synthetic dye containing wastewater and complete decolorization was achieved. The results indicate that recycling of NF concentrate via the CEME electrolysis/magnesium potassium phosphate crystallization process is feasible.