Simultaneous Recovery of Potassium, Chloride and Removal of COD from Landfill Leachate Concentrates Using a Combination of Cation-Exchange Membrane Electrolysis

Nanofiltration (NF) and reverse osmosis (RO) filtration system are widely used in landfill sites as polishing step for advanced treatment of landfill leachates. The membrane systems always generate large amount  of  concentrates containing high level of refractory organic compounds, potassium, chloride and other inorganics, which hardly be treated via conventional biological process. Thus, a proper disposal of these concentrates from or RO systems is critically important.The advanced oxidation processes (e.g, electrochemical oxidation, Fenton oxidation and ozone oxidation) are generally used in treatment of the concentrates. However, the potential resource such as K⁺and chloride in concentrates are not efficiently recycled but discharged to environment. In present study, we explore innovative and environmentally sustainable treatment processes, a combined cation-exchange membrane electrolysis (CEME)/magnesium potassium phosphate (MPP) crystallization process, for treating NF concentrate, which include (a) contaminant removal: organic pollutant and ammoniacal-nitrogen removal; (b) recycling and onsite reuse of chloride ions in the form of gaseous chlorine; (c) separation and beneficial recovery of potassium from NF concentrates.

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. And the recovered gaseous chlorine was reused on site as a decolorizing agent for synthetic dye (RhB) containing wastewater and complete decolorization was also achieved. The potassium ions were recovered  via magnesium potassium phosphate crystallization . Additionly, about 53% of the potassium (from 2762 mg/L to 1389 mg/L) was removed via formation of magnesium potassium phosphate(MgKPO₄·6H₂O) precipitate.

A combination of membrane electrolysis process is demonstrated to be an effective method for the convenient recycling of NF concentrates generated from a landfill plant. This combined process achieves effective removal of organic pollutants in the concentrates and complete removal of NH₃-N via an active chlorine-mediated reaction. The combined process also simultaneously enables highly efficient recycling of chloride and potassium ions from NF concentrates as beneficial products (gaseous chlorine and MgKPO₄·6H₂O buffered fertilizer, respectively). Additionally, we have demonstrated that the recovered gaseous chlorine could be reused on site as a decolorizing agent for treating colored wastewater (i.e., RhB solution), and that complete decolorization could be achieved. The results indicates that recycling of NF concentrate via the combination  process is feasible.