Cellulosic Substrates and Challenges Ahead

Authors: Qureshi, Nasib

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 6/11/2015
Publication Date: 7/24/2015
Citation: Qureshi, N. 2015. Cellulosic Substrates and Challenges Ahead [abstract].

Interpretive Summary:

Technical Abstract: The cost of production of butanol (acetone-butanol-ethanol; or ABE) is determined by feedstock prices, fermentation, recovery, by-product credits and the waste water treatment. Along these lines, we have an intensive research program on the use of various agricultural substrates, fermentation strategies, product recovery, process integration, and process economics. Feedstock price is of paramount importance and for this reason, it is necessary to use feedstocks that are economical. Such substrates include agricultural residues. Their prices range from $24-72 ton-1 as opposed to current corn price of $142.5 ton-1. Use of cellulosic substrates present challenges due to compositional differences and recalcitrance to conversion. These characteristics require use of additional processing steps such as pretreatment that can result in the generation of fermentation inhibitors. This coupled with differences in sugar compositions impact fermentation, varying the titer of products obtained. For this process, we have used a number of feedstocks including wheat straw, corn stover, barley straw, switchgrass, and sweet sorghum bagasse (SSB). Fermentation of wheat straw hydrolyzate was successful without any detoxification thus producing approximately 28.2 gL-1 ABE, while other feedstock hydrolyzates required detoxification prior to fermentation. Untreated barley straw hydrolyzate only resulted in the production of 7.1 gL-1 total ABE while corn strover hydrolyzate resulted in no cell growth and fermentation. However, upon detoxification by overliming, barley straw, and corn stover hydrolyzates resulted in the production of 26.6 and 26.3 gL-1 total ABE, respectively, using Clostridium beijerinckii P260 (provided by Prof. David Jones, University of Otago, Dunedin, New Zealand). Overliming of hydrolyzates will add to the overall cost of ABE production. In order to combat the uncertainty of hydrolyzates in any butanol producing company, it is essential that research and development be carried out, in parallel, so that sudden change of feedstock does not hamper ABE production strategies. Additionally, mild pretreatment techniques should be applied when treating these residues in order to minimize inhibitor formation and reduce detoxification costs.