Electrodialytic treatment of boron-containing wastewater

The electrodialytic removal of boron-containing wastewater (industrial landfill leachate), containing 63.5-76.5 mg/L of B, was examined in laboratory. An ED unit, equipped with AMX and CMX Neosepta (Tokuyama Co.) membranes and 0.19 mm membrane-to-membrane distance, was applied. Leachate was treated in two steps. In the first, slightly pre-acidified leachate was partially desalinated to remove ca 80% of total salinity. In the second one, under alkaline conditions (pH = 9-10), up to 97% of boron was removed. It was found, that high initial diluate pH value doesn't enable reliable boron flux through the membrane that may be explained by high mobility and relatively high content of hydroxide ions. Thus, OH ions are primarily transported from the depleted diffusion layer through membrane. The dosage of sodium hydroxide solution to the diluate stream was then necessary to maintain required pH level. The boron current efficiency reached 25% and boron flux across membrane 150 μg/cm² h. The estimated total cost of leachate treatment in proposed two-stage electrodialysis found was equal to $1.27/m³.