Submitted to: Biomass and Bioenergy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 3, 2008
Publication Date: November 1, 2008
Citation: Qureshi, N., Saha, B.C., Hector, R.E., Cotta, M.A. 2008. Removal of Fermentation Inhibitors from Alkaline Peroxide Pretreated and Enzymatically Hydrolyzed Wheat Straw: Production of Butanol from Hydrolysate Using Clostridium beijerinckii in Batch Reactors. Biomass and Bioenergy. 32(12):1353-1358. Interpretive Summary: Butanol is a superior fuel to ethanol and can be produced from corn or agricultural residues such as corn stover, corn fiber, or wheat straw. In these studies, we investigated the use of wheat straw for this fermentation. In order to be able to produce butanol from wheat straw, this substrate was pretreated using alkaline peroxide and hydrolyzed using enzymes. Pretreatment and hydrolysis of wheat straw are essential for fermentation as butanol producing cultures cannot hydrolyze agricultural residues to simple sugars. Unfortunately, alkaline peroxide pretreatment resulted in the production of inhibitory salts that inhibited fermentation. The salts were removed from the sugar solution using membranes (electrodialysis) followed by fermentation. Medium from which salts were removed was successfully fermented to butanol. As a result of salt removal, reactor productivity was improved by 83%. Production of butanol from wheat straw and/or agricultural residues would benefit farmers and the United States public.
Technical Abstract: In these studies, alkaline peroxide pretreatment of wheat straw was investigated. Pretreated wheat straw was hydrolyzed using celluloytic and xylanolytic enzymes, and the hydrolysate was used to produce butanol using Clostridium beijerinckii P260. The culture produced less than 2.59 gL**-1 acetone butanol ethanol (ABE) from alkaline peroxide wheat straw hydrolysate (APWSH) that had not been treated to reduce salt concentration (a neutralization product). However, fermentation was successful after inhibitors (salts) were removed from the hydrolysate by electrodialysis. A control glucose fermentation resulted in the production of 21.37 gL**-1 ABE, while salt removed APWSH resulted in the production of 22.17 gL**-1 ABE. In the two fermentations, reactor productivities were 0.30 and 0.55 gL**-1h**-1, respectively. A comparison of use of different substrates (corn fiber, wheat straw) and different pretreatment techniques (dilute sulfuric acid, alkaline peroxide) suggests that generation of inhibitors is substrate and pretreatment specific.