Algal biomass as fuel for stacked-MFCs for profitable, sustainable and carbon neutral bioenergy generation

BACKGROUND: This work compares the performance of three stacked microbial fuel cells constructed with different number of single-MFC (MFC₁ with two stacked-MFCs, MFC₂ with ten stacked-MFCs and MFC₃ with twenty stacked-MFCs), and operated under the same conditions for one month. RESULTS: According to results, algae suspensions can be used as fuel for MFC-stacks, although current efficiencies obtained are low. In comparing the effect of number of cells stacked on the performance of the stacks, it was found that the higher the number of cells stacked, the higher the energy harvested from algae. However, because of the very efficient consumption of COD in the first MFC of the stacks (not only by electrogenic but also by non-electrogenic microorganisms) and the sequential circulation of the fuel through the different cells of the stack, in all cases the systems ran out of fuel and this was reflected in lower production of electricity, compared with that expected taking into account the number of cells stacked. Results obtained from the polarization curves and the cathodic oxygen consumption also support this explanation. CONCLUSIONS: Results demonstrate that algal biomass is a suitable fuel for energy generation using MFC technology and provides microorganisms not only of a carbon source but also with the required nutrients. However, the low coulombic efficiencies obtained in the three stacks indicate that feeding algae to MFC also promotes the formation of an important amount of non-electrogenic microorganisms that compete successfully with bioelectrogenic microorganisms for the substrate provided.