M92
Switchgrass solubilization by mixed methanogenic enrichments with comparison to pure cultures of Clostridium thermocellum
Monday, April 25, 2016
Key Ballroom, 2nd fl (Hilton Baltimore)
X. Liang*, X. Shao, E. Holwerda, L. Tian and L.R. Lynd, Dartmouth College, Hanover, NH, USA; T. Richard, The Pennsylvania State University, State College, PA, USA; J. Regan, The Pennsylvania State University, University Park, PA, USA; D.M. Klingeman, J.M. Whitham and S.D. Brown, Oak Ridge National Laboratory, Oak Ridge, TN, USA
Microbially-mediated fermentation of lignocellulose is a promising approach for biofuel production. Diverse, mixed microbial enrichment cultures provide an indication of the achievable extent of biomass solubilization. Yet there has been limited fundamentally-oriented study of grass fermentation under the conditions anticipated for a high-rate, industrial process, including very high solids concentration, short residence times and high temperature. Motivated by this perspective, we have initiated study of thermophilic grass fermentation using mixed culture anaerobic enrichments
.Triplicate semi-continuous, anaerobic digesters were operated at 55oC and allowed to come to steady-state at residence times (RT) of 20 days, 10 days and 5 days. The initial substrate concentration was 30 g/L mid-season switchgrass and this feed rate was maintained by regular replacement of 1/10 of reactor contents to achieve the nominal residence times. Total carbohydrate solubilization at RT = 20, 10, and 5 days was 69.4%, 62.8%, and 55.2% respectively.
We have encountered two surprises in our work thus far:
1) Whereas we expected a shift from methanogenesis to acidogenesis as the RT decreased to 5 days, almost all electron flux was to methane under all conditions tested with mixed enrichments.
2) Whereas we expected mixed enrichments to achieve higher solubilization than pure cultures of C. thermocellum, in fact solubilization with C. thermocellum was consistently higher.
Perspectives on possible explanations for these observations will be offered, aided by characterization of microbial populations using 16S rDNA analysis.
