Evaluation of Sedum as driver for plant microbial fuel cells in a semi-arid green roof ecosystem

A plant microbial fuel cell (PMFC) is a novel and sustainable bioelectrochemical technology that takes advantage of the organic compounds released through the plant roots (exudates) to produce power via electrochemically active bacteria. This technology has been implemented in flooded ecosystem; however, their use in arid or semiarid environments has been less explored. Thus, the use of plant adapted to conditions of less water availability could expand the application of PMFCs. In this study, seven Sedum species (succulent plants) were evaluated for their ability to generate energy under non-saturated conditions. Electrochemical results confirmed power generation by the Sedum species tested, with reactors using Sedum hybridum achieving the highest power density (92 mu Wm(-2)), followed by reactors tested with S. rupestre (15.5 mu Wm(-2)). The lowest performance was observed in systems using S. spurium (< 1 mu Wm(-2)). Total organic carbon from root exudates did not have a direct effect on PMFCs performance. Pyrosequencing analysis revealed higher abundance of bacteria in the family Micrococcaceae in anodic biofilms of S. hybridum (13.47 +/- 2.69%) reactors than in biofilms of S. rupestre (2.28 +/- 0.52%), and S. spurium (2.29 +/- 1.94%) PMFCs. Although the current magnitudes observed in our study were lower than those reported for flooded PMFCs, a positive relationship between water content of plant growth media and power outputs was observed. After irrigation, current and water gradually decrease over time with a similar rate, showing a correlation coefficient between both variables of 0.95 +/- 0.01. Moreover, it encourages further testing of PMCFs as potential indicators of soil water content in semiarid green roofs where a better water-use efficiency is needed.