Biochar as a substitute for graphite in microbial electrochemical technologies

Abstract

Biochar has emerged as an attractive electrode material due to its biocompatibility, low cost and reduced environmental impact. The temperature at which biochar is produced greatly affects its physicochemical properties and its environmental performance. Despite that, only biochar obtained at relatively high temperatures (800 to 1000 °C) has been applied in microbial electrochemical technologies (METs) so far. In this work, the physicochemical and electrical properties of biochar electrodes obtained at several temperatures (500 °C to 1000 °C) are explored and compared to those of graphite which is the most commonly used electrode material in METs. Besides, the associated carbon emissions and energy input of the production process at each temperature are estimated and compared to those of graphite. Results indicate that low-temperature (600 °C) biochar electrodes generate about half of the electric current obtained with high-temperature biochar or graphite electrodes. Furthermore, carbon emissions and energetic inputs for the production of low-temperature biochar are much lower than those of graphite production, with the 600 °C electrodes having a net positive carbon footprint and also a lower production cost. Nevertheless, further research is needed to optimize biochar conductivity and mechanical performance in order to allow its integration into large scale METs.