Enhanced boron removal by electricity generation in a microbial fuel cell

Abstract

Boron needs to be removed during desalination, because excessive boron in the product water for irrigation can deteriorate plant growth. In this study, a microbial fuel cell (MFC) equipped with anion exchange membrane (AEM) was proposed and investigated to remove boron via two successive steps: boric acid is ionized to borate ions in the presence of high pH as a result of cathode reaction, and borate ions are transported across AEM driven by electricity generation. Two scenarios were examined, the MFC as a pretreatment process and the MFC as a post-treatment step in connection with conventional desalination. In the pretreatment mode, the MFC achieved 40–50% boron removal and the high pH condition could benefit downstream desalination or other methods for further boron removal. In the post-treatment mode, the MFC removed 80–90% of boron and decreased the boron concentration from 20 to 2 mg L⁻¹ or from 5 to 1 mg L⁻¹ , which meets the irrigation water requirement. The removal rate in this MFC was much higher than that of a previously reported microbial desalination cell coupled with Donnan Dialysis system. Those results have demonstrated the potential of using MFCs for boron removal with benefits of conductivity reduction and electricity generation.