Electricity Production from Steam-Exploded Corn Stover Biomass Yi Zuo, ² Pin-Ching Maness, ‡ and Bruce E. Logan* ,² Department of CiVil and EnVironmental Engineering, Penn State UniVersity, UniVersity Park, PennsylVania 16802, and National Renewable Energy Laboratory, Golden, Colorado 80401 ReceiVed January 23, 2006. ReVised Manuscript ReceiVed April 24, 2006 Electricity generation using microbial fuel cells (MFCs) was examined from corn stover waste biomass using samples prepared through either neutral or acid steam-exploded hydrolysis processes that convert the hemicellulose to soluble sugars. Maximum power densities in fed-batch tests using an air-cathode MFC were 371 ( 13 mW/m 2 and 367 ( 13 mW/m 2 for the neutral and acid hydrolysates (1000 mg-COD/L, 250 Ω). Power output exhibited saturation kinetics with respect to fuel concentration, with predicted maximum power densities of P max ) 475 mW/m 2 and half-saturation constants of K s ) 347 mg/L (neutral) and P max ) 422 mW/m 2 and K s ) 170 mg/L (acid). Coulombic efficiencies (CEs) were comparable to that found using carbohydrates in this type of MFC, with values ranging from 20 to 30% for both hydrolysates. All sugars (monomeric or oligomeric) were completely utilized, with overall biochemical oxygen demand (BOD) removal efficiencies of 93 ( 2% (neutral) and 94 ( 1% (acid). Power output could be increased by using a cathode containing a diffusion layer, resulting in maximum power densities of 810 ( 3 mW/m 2 (neutral) and 861 ( 37 mW/m 2 (acid). Power was further increased by increasing solution conductivity to 20 mS/cm, resulting in 933 mW/m 2 (neutral) and 971 mW/m 2 (acid) for the two hydrolysates. Additional increases in solution conductivity lowered the anode potential and did not increase power. These results demonstrate the potential for a new method of renewable energy production based on conversion of biomass to electricity using MFCs. Introduction Corn stover is currently the largest waste biomass resource in the United States, consisting of more than one-third of the total solid waste produced, including municipal solid waste. 1 An estimated 250 million dry tons of corn stover is produced annually. 2 Only a small amount of corn stover is reused as animal feed or bedding, with >90% left unused in fields. 1 Corn stover typically contains 70% cellulose and hemicellulose and 15-20% lignin. 3 The hemicellulose components can be con- verted to monomeric and oligomeric sugars by a steam- explosion process, forming a sugar-enriched liquid hydrolysate fraction. Ethanol can be recovered from the steam-exploded biomass liquid, but <47% of carbohydrates can be converted to ethanol. 4 Hydrogen can be produced from the liquefied hemicellulose at an overall utilization efficiency of 87-94% of the glucan and xylan, respectively, 5 but most of the chemical oxygen demand (COD) remains as fermentation end products consisting primarily of acetic and butyric acids. 6 Microbial fuel cells (MFCs) represent a new method for energy production and organic matter degradation. Electro- chemically active bacteria oxidize organic matter at the anode surface, releasing electrons and protons. Those electrons are transferred from the anode to the cathode through an external circuit, while the protons move to the cathode directly through solution. At the cathode, oxygen or other chemicals such as ferricyanide accept the electrons. MFCs can be used to generate electricity from various carbohydrates, including low-molecular sugars such as glucose, 7-9 and complex carbohydrates and carbohydrate-containing wastewaters such as sucrose, starch, molasses, and wastewater from food (cereal) processing plants. 10-13 The energy conversion based on Coulombic ef- ficiency (CE), or the percent of electrons recovered from the * Corresponding author. Phone: (814) 863-7908. Fax: (814) 863-7304. E-mail: blogan@psu.edu. ² Penn State University. ‡ National Renewable Energy Laboratory. (1) Glassner, D. A.; Hettenhaus, J. R.; Schechinger, T. M. Corn stover potential: Recasting the corn sweetener industry. In PerspectiVes on new crops and new uses; Janick, J., Ed.; ASHS Press: Alexandria, VA, 1999; pp 74-82. (2) Atchison, J. E.; Hettenhaus, J. R. InnoVatiVe methods for corn stoVer collecting, handling, storing and transporting; NREL/SR-510-33893; National Renewable Energy Laboratory: Golden, CO, 2004. (3) Glassner, D. A.; Hettenhaus, J. R.; Schechinger, T. M. Corn stover collection project. Proceedings of Bioenergy ’98: Expanding Bioenergy Partnerships; Madison, WI, 1998; pp 1100-1110. (4) Lynd, L. R. Overview and evaluation of fuel ethanol from cellulosic biomass. Annu. ReV. Energy EnViron. 1996, 21, 403-465. (5) Datar, R.; Huang, J.; Maness, P. C.; Mohagheghi, A.; Czernik, S.; Chornet, E. Hydrogen production from the fermentation of corn stover biomass pretreated with a steam explosion process. Intl. J. Hydrogen Energy 2005, manuscript submitted for publication. (6) Logan, B. E. Biologically extracting energy from wastewater: Biohydrogen production and microbial fuel cells. EnViron. Sci. Technol. 2004, 38, 160A-167A. (7) Liu, H.; Logan, B. E. Electricity generation using an air-cathode single chamber microbial fuel cell in the presence and absence of a proton exchange membrane. EnViron. Sci. Technol. 2004, 38, 4040-4046. (8) Rabaey, K.; Lissens, G.; Siciliano, S. D.; Verstraete, W. A microbial fuel cell capable of converting glucose to electricity at high rate and efficiency. Biotechnol. Lett. 2003, 25, 1531-1535. (9) Chaudhuri, S. K.; Lovley, D. R. Electricity generation by direct oxidation of glucose in mediatorless microbial fuel cells. Nat. Biotechnol. 2003, 21, 1229-1232. (10) He, Z.; Minteer, S. D.; Angenent, L. T. Electricity generation from artificial wastewater using an upflow microbial fuel cell. EnViron. Sci. Technol. 2005, 39, 5262-5267. (11) Min, B.; Logan B. E. Continuous electricity generation from domestic wastewater and organic substrates in a flat plate microbial fuel cell. EnViron. Sci. Technol. 2004, 38, 5809-5814. (12) Niessen, J.; Schroder, U.; Scholz, F. Exploiting complex carbohy- drates for microbial electricity generationsabacteria fuel cell operating on starch. Electrochem. Commun. 2004, 6, 955-958. 1716 Energy & Fuels 2006, 20, 1716-1721 10.1021/ef060033l CCC: $33.50 © 2006 American Chemical Society Published on Web 05/28/2006