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 andreduced environmental impact. The temperature at which biochar is produced greatly affects itsphysicochemical properties and its environmental performance. Despite that, only biochar obtainedat relatively high temperatures (800 to 1000 °C) has been applied in microbial electrochemicaltechnologies (METs) so far. In this work, the physicochemical and electrical properties of biocharelectrodes obtained at several temperatures (500 °C to 1000 °C) are explored and compared tothose of graphite which is the most commonly used electrode material in METs. Besides, theassociated carbon emissions and energy input of the production process at each temperature areestimated 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-temperaturebiochar or graphite electrodes. Furthermore, carbon emissions and energetic inputs for theproduction of low-temperature biochar are much lower than those of graphite production, with the600 °C electrodes having a net positive carbon footprint and also a lower production cost.Nevertheless, further research is needed to optimize biochar conductivity and mechanicalperformance in order to allow its integration into large scale METs.