Effect of fed-batch vs. continuous mode of operation on microbial fuel cell performance treating biorefinery wastewater

Abstract

Bioelectrochemical systems have been shown to treat low-value biorefinery streams while recovering energy, however, low current densities and anode conversion efficiencies (ACE) limit their application. A bioanode was developed via enrichment of electroactive biofilm under fed-batch and continuous feeding conditions using corn stover-derived waste stream. The continuously-fed MFC exhibited a current density of 5.8±0.06A/m2 and an ACE of 39%±4. The fed-batch MFC achieved a similar current density and an ACE of 19.2%, however, its performance dropped after 36days of operation to 1.1A/m2 and 0.5%, respectively. In comparison, the ACE of the continuously-fed MFC remained stable achieving an ACE of 30%±3 after 48days of operation. An MFC treating a biorefinery stream post fuel separation achieved a current density of 10.7±0.1A/m2 and an ACE of 57%±9 at an organic loading of 12.5g COD/L-day. Characterization of the microbial communities indicate higher abundance of Firmicutes and Proteobacteria and lower abundance of Bacteriodetes and a higher level of Geobacter spp. (1.4% vs. 0.2%) in continuously-fed MFC vs. fed-batch MFC. The results demonstrate that limiting substrate to the equivalent maximum current that the anode can generate, maintains MFC performance over a long term for high strength wastewaters, such as those generated in the biorefinery.