An external magnetic field moderating Cr(VI) stress for simultaneous enhanced acetate production and Cr(VI) removal in microbial electrosynthesis system

Abstract

A stressful heavy metal circumstance disfavors production of acetate from bicarbonate reduction in the biocathode of microbial electrosynthesis system (MES) with simultaneous function of heavy metal removal/recovery. It is of great interest to explore effective approaches to moderate the heavy metal stress with achievement of simultaneous enhanced acetate production and heavy metal removal in MES. Herein, a magnetic field strength of 100 mT was successfully employed to moderate Cr(VI) stress, achieving simultaneous production of acetate at a rate of 1.48 ± 0.01 mg/L/h and Cr(VI) removal at a rate of 1.67–2.42 mg/L/h in the Serratia marcescens Q1 catalyzed cathode of MES under periodical addition of bicarbonate and Cr(VI), 1.35-fold (acetate production) and 1.34–1.46 times (Cr(VI) removal) of those in the controls in the absence of magnetic field. This simultaneous efficient acetate production and Cr(VI) removal was regulated by the magnetic field and the stressful Cr(VI), which induced the S. marcescens to physiologically release additive amounts of extracellular polymeric substances with a compositional diversity and containing the electrochemically active c-type cytochromes to facilitate extracellular electron transfer. This study confirmed the importance of magnetic field in developing the S. marcescens catalytic activity for moderating Cr(VI) stress, and thus provided a feasible approach for simultaneous efficient acetate production and Cr(VI) removal/recovery in MES, from waters contaminated with Cr(VI).