Effects of process conditions on simultaneous removal and recovery of boron from boron-laden wastewater using improved bipolar membrane electrodialysis (BMED)

Abstract

The anthropogenic emission of boron to the environment has posed a serious risk to human and animal health due to its non-biodegradability and the resulting accumulation in the body. Bipolar membrane electrodialysis (BMED) has been proven to be an economical and effective process to remove and recover boron from wastewater. In this work, we verified multiple process parameters to evaluate the efficiency of boron removal and recovery using intermittent and continuous BMED modes. Higher initial boron concentrations appeared to reduce the boron processing rate, but this reduction may be ameliorated by increasing current density. Similarly, higher initial pH was observed to retard the removal rate of boron with increasing mass transfer rate. When solution pH was controlled from 9.5 to 10.5 and the current density was 6.36 A/m2 under maximum allowable voltage of 12 V, boron removal and recovery efficiencies were 98.6% and 86.5%, respectively. During the pH-control process, current variation pattern indicated that current density was associated with initial boron concentrations in salt apartment. When the current variation pattern was applied to a five-cycle sequential feed-batch BMED process, it accurately reflected the timing of complete boron removal and recovery on a batch fill-and-draw process. The overall boron removal and recovery efficiencies were 98.53% and 81.2%, respectively, with an energy consumption of 31.5 Wh/g. Under these conditions, the final boron concentrations in effluent were less than 10 mg/L, as required by the Taiwan Environmental Protection Administration (EPA). Overall, BMED is a cost-effective treatment process for boron-containing wastewater. The proposed process indicator reflecting sequential BMED process progression based on process information will further elucidate the automatic process control in industrial applications.