Submitted to: Biomass and Bioenergy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 28, 2009
Publication Date: February 1, 2010
Citation: Qureshi, N., Saha, B.C., Dien, B., Hector, R.E., Cotta, M.A. 2010. Production of Butanol (a Biofuel) from Agricultural Residues: Part I - Use of Barley Straw Hydrolysate. Biomass and Bioenergy. 34(4):559-565. Interpretive Summary: This research is a breakthrough on conversion of barley straw to ethanol. This is important because butanol is a superior biofuel to ethanol: It can be used effectively for transportation, packs more energy than ethanol on weight basis, and can be produced using microbial cultures from glucose or corn. Unfortunately, the high cost of these substrates (glucose or corn) makes butanol’s production cost inefficient. The price of barley straw has been $26/ton as opposed to corn which was over $133-230/ton during recent months. For this reason economically available substrates such as barley straw should be used. In these studies, barley straw was hydrolyzed to simple sugars using dilute acid pretreatment and enzymatic hydrolysis. It is essential to hydrolyze agricultural biomass to sugars using enzymes before conversion to butanol as butanol producing cultures do not hydrolyze these substrates to sugars. This research will benefit US farmers who grow corn and the US transportation industry.
Technical Abstract: Fermentation of dilute sulfuric acid barley straw hydrolyzate (BSH; undiluted/untreated) by Clostridium beijerinckii P260 resulted in the production of 7.09 gL**-1 ABE (acetone butanol ethanol; AB or ABE), an ABE yield of 0.33, and productivity of 0.10 gL**-1h**-1. This level of ABE is much less than that observed in a control experiment (21.06 gL**-1) where glucose (initial concentration 60 gL**-1) was used as a substrate. In the control experiment, an ABE yield of 0.41 and productivity of 0.31 gL**-1h**-1 were observed. This comparison suggested that BSH is toxic to the culture. Low productivity of barley straw hydrolyzates was most likely due to the presence of fermentation inhibitors present. To reduce this potential toxicity effect, BSH was treated with lime followed by fermentation. The treated BSH resulted in a successful fermentation and ABE concentration of 26.64 gL**-1. This was superior to both glucose and untreated BSH (initial sugar 60 gL**-1) fermentations. In this fermentation, an ABE yield of 0.43 and productivity of 0.39 gL**-1h**-1 (390% of untreated/undiluted BSH) was obtained. It should be noted that using lime treated BSH, a specific productivity of 0.55 h**-1 was obtained as compared to 0.12 h**-1 in the control fermentation suggesting that more carbon was directed to product formation.