Rhodopseudomonas palustris purple bacteria fed Arthrospira maxima cyanobacteria: demonstration of application in microbial fuel cells

Abstract

Micro MFC devices support parallel, low cost and reproducible analysis for high-throughput screening and sensitivity analyses of biological and electrochemical performance parameters respectively. In this study a micro MFC (μMFC) device was developed, fabricated and operated to enable screening of the purple non-sulphur bacterium Rhodopseudomonas palustris (R. palustris, NCIMB1174 culture collection) using acetate and two renewable substrates, Arthrospira maxima (A. maxima) and glycerol. The use of A. maxima as a carbon source for the metabolism and growth of R. palustris as well as a substrate to generate power within an MFC provided positive results. R. palustris, with its wide range of metabolic modes, directly consumed solid substrate A. maxima with a biomass concentration increase of 0.041 ± 0.004 g DW/L over the growth cycle. Along with the batch phase flat plate μMFC (μMFC) a fed batch flat plate MFC (FBFP-MFC) and a continuous flat plate MFC (CFP-MFC) were used to evaluate the exoelectrogenic activity of R. palustris during this investigation. The μMFC system showed that power generation was independent of R. palustris growth phase and concentration. Further studies using flat plate-MFC systems concluded that current and power generation were not limited by substrate concentration or anolyte conductivity. Moreover, the use of A. maxima as a MFC feedstock resulted in the highest volumetric power among the three substrates investigated (10.4 mW m⁻³). The potential applications for cultivating R. palustris purple bacteria using A. maxima cyanobacteria as the primary carbon source are of great interest and offer a new approach to future energy systems.