Malic acid production using a biological electrodialysis with bipolar membrane

Malic acid is a valuable organic acid and important acidulant in food and pharmaceutical industries and can be produced using electrodialysis with bipolar membrane (EDBM). The aim of this study was to investigate the possibility of malic acid production using a system integrating EDBM and biochemical process, i.e., the microbial electrodialysis and chemical-production cell (MEDCC). With an applied voltage of 1.0 V, the MEDCC successfully conversed 0.3 M malate into 0.23 M malic acid, which was about four times as that produced in the EDBM (0.06 M). The maximum current density in the MEDCC was five times higher than that in the EDBM (10 vs. 1.9 A/m2). The specific electric consumption for the malic acid production in the MEDCC was 0.34 kWh/kg, which was only 10-30% of that in the reported EDBMs. In the MEDCC, the energy from the anode biodegradation provided about 50% of the total energy demand (0.68 kWh/kg) during the malic acid production. Our results show that the MEDCC should be a promising method for organic acid production with advantages of lower electrical consumption and diverse substrates utilized by exoelectrogens.