Bioresource Technology, Volume 157, April 2014, Pages 114-119.
Tyler Hugginsa, Heming Wanga, Joshua Kearnsa, Peter Jenkinsb,Zhiyong Jason Rena
a-Department of Civil, Environmental, and Architectural Engineering, University of Colorado, Boulder, Boulder, CO 80309, United States and
b-Department of Mechanical Engineering, University of Colorado, Denver, CO 80204, United States.
Wood-based biochars were used as microbial fuel cell electrodes to significantly reduce cost and carbon footprint. The biochar was made using forestry residue (BCc) and compressed milling residue (BCp). Side-by-side comparison show the specific area of BCp (469.9 m2 g−1) and BCc (428.6 cm2 g−1) is lower than granular activated carbon (GAC) (1247.8 m2 g−1) but higher than graphite granule (GG) (0.44 m2 g−1). Both biochars showed power outputs of 532 ± 18 mW m−2 (BCp) and 457 ± 20 mW m−2 (BCc), comparable with GAC (674 ± 10 mW m−2) and GG (566 ± 5 mW m−2). However, lower material expenses made their power output cost 17–35 US$ W−1, 90% cheaper than GAC (402 US$ W−1) or GG (392 US$ W−1). Biochar from waste also reduced the energy and carbon footprint associated with electrode manufacturing and the disposal of which could have additional agronomic benefits.
Microbial fuel cells (MFC) are bioelectrochemical systems that employ the unique ability of exoelectrogenic bacteria to convert chemical energy in wastewater directly to electricity. This technology has garnered much fascination from researchers because of its potential to aid in energy positive wastewater treatment. Although this technology has massive prospective, material costs have limited its wide spread application. Much of the material costs for MFC reactors can be attributed to the electrodes needed for biofilm formation and subsequent electricity production. Biochar, a carbon material produced from the thermoconversion of biomass, has been traditionally viewed as a soil amendment and agricultural product with carbon sequestration potential. Recently biochar has gain even more attention as a low cost adsorbent material in environmental remediation. Our research has focused on creating a conductive biochar material with the same adsorption capabilities. In this regard we can use this novel material as a dual electrode for electricity production and adsorbent for contaminate removal and recovery. As our research shows, high temperature biochar is highly conductive and performs similarly to conventional electrode materials such as activated carbon and graphite with significantly lower cost.
We currently have efforts underway to design a MFC reactors specifically around this new conductive biochar material to increase the capacity for wastewater treatment with simultaneous power production and resource recovery. Our new design has thus far proven to be compatible with the conductive biochar material and has been shown to treat wastewater to effluent quality standards (COD, nutrients, metals) while producing a satisfactory electrical current (unpublished). We have also been investigating the elution and recovery of metals and nutrients from the conductive biochar. In the end we hope to provide an alternative technology to conventional treatment systems that is energy efficient and can help to generate much needed additional revenue during the treatment process.