Plasma-assisted pretreatment (PAP) of lignocellulosic biomass has been shown to be an efficient method to decompose lignin and consequently facilitate microbial access to cellulose and hemicellulose. In the present study, PAP was tested for its suitability to enhance bioconversion of wheat straw to methane. In thermophilic batch experiments, methane yields of up to 366？mL/g volatile solids (VSs) were achieved, accounting for a yield increase of 45%. Common lignin-derived inhibitors like 5-hydroxymethylfurfural (5-HMF) and furfural were not detected after PAP, but toxicity test resulted in lower methane yields at higher substrate concentrations, indicating the presence of other unidentified inhibitors. However, in a continuous lab-scale biogas reactor experiment, stable codigestion of cattle manure with 20% PAP wheat straw was demonstrated, while no signs of adverse effects on the anaerobic digestion process were observed. After the introduction of the pretreated wheat straw to the reactor, volatile fatty acid concentrations remained low and stable, while gas production increased. In co-digestion, the PAP wheat straw was converted at an average yield of 343？mL CH4/gVS. 1. Introduction Anaerobic digestion (AD) is a widely applied method of managing agricultural byproducts such as animal manure and crop residues with multiple benefits. Treating organic material in biogas plants can produce renewable energy in the form of biogas, reduce land-use related environmental impacts, and improve the fertilizer quality of manure. These benefits have increased the interest in biogas technology worldwide. At present, the economic benefits of AD of agricultural residues are, however, limited because manure has a low energy density and many fibrous residues are only poorly degraded. This results in a low biogas yield which is a barrier to the expansion of biogas technology for energy production purposes. However, manure and crop residues hold the potential for a more efficient conversion to biogas as a considerable fraction of the organic material remains undigested in currently applied biogas processes. The main reason for the low yields lies in the structure of the biomass. Crop residues and fibers contained in manure mainly consist of lignocellulose, which is poorly degraded in biogas reactors as lignin is not degradable under anaerobic conditions and prevents microbial access to cellulose and hemicelluloses [1, 2]. Hence, removing lignin can facilitate anaerobic degradation of the fibers and thereby increase the biogas yield of manure and crop residues
References
[1]
B. B. Ress, P. P. Calvert, C. A. Pettigrew, and M. A. Barlaz, “Testing anaerobic biodegradability of polymers in a laboratory-scale simulated landfill,” Environmental Science and Technology, vol. 32, no. 6, pp. 821–827, 1998.
[2]
S. I. Mussatto, M. Fernandes, A. M. F. Milagres, and I. C. Roberto, “Effect of hemicellulose and lignin on enzymatic hydrolysis of cellulose from brewer's spent grain,” Enzyme and Microbial Technology, vol. 43, no. 2, pp. 124–129, 2008.
[3]
P. Alvira, E. Tomás-Pejó, M. Ballesteros, and M. J. Negro, “Pretreatment technologies for an efficient bioethanol production process based on enzymatic hydrolysis: a review,” Bioresource Technology, vol. 101, no. 13, pp. 4851–4861, 2010.
[4]
F. Talebnia, D. Karakashev, and I. Angelidaki, “Production of bioethanol from wheat straw: an overview on pretreatment, hydrolysis and fermentation,” Bioresource Technology, vol. 101, no. 13, pp. 4744–4753, 2010.
[5]
H. Hartmann, I. Angelidaki, and B. K. Ahring, “Increase of anaerobic degradation of particulate organic matter in full- scale biogas plants by mechanical maceration,” Water Science and Technology, vol. 41, no. 3, pp. 145–153, 2000.
[6]
I. Angelidaki and B. K. Ahring, “Methods for increasing the biogas potential from the recalcitrant organic matter contained in manure,” Water Science and Technology, vol. 41, no. 3, pp. 189–194, 2000.
[7]
Z. Mladenovska, H. Hartmann, T. Kvist, M. Sales-Cruz, R. Gani, and B. K. Ahring, “Thermal pretreatment of the solid fraction of manure: impact on the biogas reactor performance and microbial community,” Water Science and Technology, vol. 53, no. 8, pp. 59–67, 2006.
[8]
M. Hjorth, K. Gr？nitz, A. P. S. Adamsen, and H. B. M？ller, “Extrusion as a pretreatment to increase biogas production,” Bioresource Technology, vol. 102, pp. 4989–4994, 2011.
[9]
G. Lissens, A. B. Thomsen, L. De Baere, W. Verstraete, and B. K. Ahring, “Thermal wet oxidation improves anaerobic biodegradability of raw and digested biowaste,” Environmental Science and Technology, vol. 38, no. 12, pp. 3418–3424, 2004.
[10]
P. F. Vidal and J. Molinier, “Ozonolysis of lignin—improvement of in vitro digestibility of poplar sawdust,” Biomass, vol. 16, no. 1, pp. 1–17, 1988.
[11]
K. Kratzl, P. Claus, and G. Reichel, “Reactions of lignin and lignin model compounds with ozone,” Tappi, vol. 59, no. 11, pp. 86–87, 1976.
[12]
N. Schultz-Jensen, Z. Kádár, A. B. Thomsen, H. Bindslev, and F. Leipold, “Plasma-assisted pretreatment of wheat straw for ethanol production,” Applied Biochemistry and Biotechnology, vol. 165, pp. 1010–1023, 2011.
[13]
N. Schultz-Jensen, F. Leipold, H. Bindslev, and A. B. Thomsen, “Plasma-assisted pretreatment of wheat straw,” Applied Biochemistry and Biotechnology, vol. 163, no. 4, pp. 558–572, 2011.
[14]
F. Leipold, A. Fateev, Y. Kusano, B. Stenum, and H. Bindslev, “Reduction of NO in the exhaust gas by reaction with N radicals,” Fuel, vol. 85, no. 10-11, pp. 1383–1388, 2006.
[15]
F. Leipold, N. Schultz-Jensen, Y. Kusano, H. Bindslev, and T. Jacobsen, “Decontamination of objects in a sealed container by means of atmospheric pressure plasmas,” Food Control, vol. 22, no. 8, pp. 1296–1301, 2011.
[16]
M. Laroussi and F. Leipold, “Evaluation of the roles of reactive species, heat, and UV radiation in the inactivation of bacterial cells by air plasmas at atmospheric pressure,” International Journal of Mass Spectrometry, vol. 233, no. 1–3, pp. 81–86, 2004.
[17]
B. M. Penetrante, J. N. Bardsley, and M. C. Hsiao, “Kinetic analysis of non-thermal plasmas used for pollution control,” Japanese Journal of Applied Physics, vol. 36, no. 7, pp. 5007–5017, 1997.
[18]
F. Leipold, Y. Kusano, F. Hansen, and T. Jacobsen, “Decontamination of a rotating cutting tool during operation by means of atmospheric pressure plasmas,” Food Control, vol. 21, no. 8, pp. 1194–1198, 2010.
[19]
A. E. Greenberg, L. S. Clesceri, and A. D. Eaton, Standard Methods For the Examination of Water and Wastewater, American Public Health Association, 18th edition, 1992.
[20]
I. Angelidaki, L. Ellegaard, and B. K. Ahring, “Compact automated displacement gas metering system for measurement of low gas rates from laboratory fermentors,” Biotechnology and Bioengineering, vol. 39, no. 3, pp. 351–353, 1992.
[21]
E. Varga, A. S. Schmidt, K. Réczey, and A. B. Thomsen, “Pretreatment of corn stover using wet oxidation to enhance enzymatic digestibility,” Applied Biochemistry and Biotechnology A, vol. 104, no. 1, pp. 37–50, 2003.
[22]
F. B. Castro, P. M. Hotten, E. R. Orskov, and M. Rebeller, “Inhibition of rumen microbes by compounds formed in the steam treatment of wheat straw,” Bioresource Technology, vol. 50, no. 1, pp. 25–30, 1994.
[23]
W. S. Borneman, D. E. Akin, and W. P. VanEseltine, “Effect of phenolic monomers on ruminal bacteria,” Applied and Environmental Microbiology, vol. 52, no. 6, pp. 1331–1339, 1986.
[24]
E. Ximenes, Y. Kim, N. Mosier, B. Dien, and M. Ladisch, “Deactivation of cellulases by phenols,” Enzyme and Microbial Technology, vol. 48, no. 1, pp. 54–60, 2011.
[25]
J. E. Hernandez and R. G. J. Edyvean, “Inhibition of biogas production and biodegradability by substituted phenolic compounds in anaerobic sludge,” Journal of Hazardous Materials, vol. 160, no. 1, pp. 20–28, 2008.
[26]
M. Torry-Smith, P. Sommer, and B. K. Ahring, “Purification of bioethanol effluent in an UASB reactor system with simultaneous biogas formation,” Biotechnology and Bioengineering, vol. 84, no. 1, pp. 7–12, 2003.
[27]
E. Bruni, A. P. Jensen, and I. Angelidaki, “Steam treatment of digested biofibers for increasing biogas production,” Bioresource Technology, vol. 101, no. 19, pp. 7668–7671, 2010.
[28]
A. G. Hashimoto, “Effect of inoculum/substrate ratio on methane yield and production rate from straw,” Biological Wastes, vol. 28, no. 4, pp. 247–255, 1989.
[29]
K. Boe, D. J. Batstone, J. P. Steyer, and I. Angelidaki, “State indicators for monitoring the anaerobic digestion process,” Water Research, vol. 44, no. 20, pp. 5973–5980, 2010.
[30]
H. B. Nielsen, H. Uellendahl, and B. K. Ahring, “Regulation and optimization of the biogas process: propionate as a key parameter,” Biomass and Bioenergy, vol. 31, no. 11-12, pp. 820–830, 2007.
[31]
J. E. Holladay, J. F. White, J. J. Bozell, and D. Johnson, “Top value-added chemicals from biomass; volume II-results of screening for potential candidates from biorefinery lignin,” Tech. Rep. PNNL-16983, 2007.
