New fragmented electro-active biofilm (FAB) reactor to increase anode surface area and performance of microbial fuel cell

Abstract

Microbial fuel cell (MFC) technology is a promising sustainable future energy source with a renewable and abundant substrate. MFC critical drawbacks are anode surface area limitations and electrochemical loss. Recent studies recommend thick anode biofilm growth due to the synergetic effect between microbial communities. Engineering the anode surface area is the prospect of MFC. In this study, a microbial electrode jacket dish (MEJ-dish) was invented, first time to the authors’ knowledge, to support MFC anode biofilm growth. The MFC reactor with MEJ-dish was hypothesized to develop a variable biofilm thickens. This reactor is called a fragmented electro-active biofilm-microbial fuel cell (FAB-MFC). It was optimized for pH and MEJ-dish types and tested at a bench-scale. Fragmented (thick and thin) anode biofilms were observed in FAB-MFC but not in MFC. During the first five days and pH 7.5, maximum voltage (0.87 V) was recorded in MFC than FAB-MFC; however, when the age of the reactor increases, all the FAB-MFC gains momentum. It depends on the MEJ-dish type that determines the junction nature between the anode and MEJ-dish. At alkaline pH 8.5, the FAB-MFC generates a lower voltage relative to MFC. On the contrary, the COD removal was improved regardless of pH variation (6.5–8.5) and MEJ-dish type. The bench-scale studies support the optimization findings. Overall, the FAB improves the Coulombic efficiency by 7.4–9.6 % relative to MFC. It might be recommendable to use both FAB and non-FAB in a single MFC reactor to address the contradictory effect of increasing COD removal associated with the lower voltage at higher pH. This study showed the overall voltage generated was significantly higher in FAB-MFC than MFC within limited pH (6.5–7.5); relatively, COD removal was enhanced within a broader pH range (6.5–8.5). It supports the conclusion that FAB anode biofilms were vital for COD removal, and there might be a mutualism even though not participated in voltage generation. FAB could provide a new flexible technique to manage the anode surface area and biofilm thickness by adjusting the MEJ-dish size. Future studies may need to consider the number, size, and conductor MEJ-dish per electrode.