(252c) Effectiveness of Cotreatment during Fermentation on Various Feedstocks, Impact on Different Microbes, and Milling Energy Requirements

Milling during fermentation, also known as cotreatment, is being explored as an alternative to thermochemical pretreatment for increasing the accessibility of lignocellulose to biological attack. The feasibility of cotreatment hinges on achieving high carbohydrate-to-sugar conversion (also known as solubilization), the fermentative microorganism’s tolerance to milling, and the energy requirements of milling. This talk presents results on different aspects of investigating cotreatment’s feasibility; specifically, its effectiveness on different feedstocks, impact on various microorganisms, and milling energy requirements. Cotreatment in combination with CBP fermentation by Clostridium thermocellum at low solids concentrations was performed using various feedstocks: switchgrass (with and without genetic modification aimed at decreasing recalcitrance), more and less recalcitrant natural variants of Populus, and corn stover. The ability to carry out fermentation in the presence of aggressive milling is tested using the following microorganisms: Clostridium thermocellum, Thermoanaerobacterium saccharolyticum, Escherichia coli, Bacillus subtilis, and Zymomonas mobilis. As a first step towards determining energy requirements of cotreatment, substantial changes in the viscosity of corn stover slurries over the course of Clostridium thermocellum fermentation were evaluated at solids loadings representative of an industrial process. Moreover, variations of ball and disc milling have been screened for solubilization effectiveness. Ongoing work is focused on measuring the milling energy of fermented biomass; initial results will be presented on this subtopic.