|Ezeji, Thaddeus - U OF I|
|Blaschek, Hans - U OF I|
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: April 23, 2004
Publication Date: April 1, 2004
Citation: Ezeji, T., Qureshi, N., Blaschek, H. 2004. Recent advances in acetone butanol ethanol (ABE) fermentation [abstract]. World Congress on Industrial Biotechnology and Bioprocessing. Paper No. 37. Technical Abstract: The Acetone Butanol Ethanol (ABE) fermentation process is of interest for chemical/fuel production from renewable resources. Butanol is a chemical which has excellent fuel characteristics. It has a higher octane value than ethanol, more miscible with gasoline and diesel, and has a lower vapor pressure. Butanol has research and motor octane numbers of 113 and 94 compared to 111 and 92 for ethanol. It is currently used as a feedstock chemical in the plastic industry and as a food grade extractant in the food and flavor industry. Unfortunately, economical production of butanol via fermentation is hampered by end product inhibition, uneconomical product recovery, and the use of dilute glucose or starch solutions, thereby resulting in large process stream volumes. Usually, maximum total ABE concentration of 20 g/L when using Clostridium acetobutylicum or C. beijerinckii is achieved. The low ABE concentration negatively impacts the economics of fermentation derived butanol relative to petrochemical-derived butanol. However, substrate cost is still the most influential factor affecting the price of butanol. Use of degermed corn as feed for ABE bioconversion process employing C. beijerinckii BA101 and recovery by gas stripping may have added economic advantage over the use of glucose. In this article, we report on ABE fermentation characteristics of degermed corn when using C. beijerinckii BA101 in a continuous fermentation process, and integrated ABE fermentation and recovery system employing gas stripping technology. C. beijerinckii BA101 ferments corn mash efficiently to produce ABE under appropriate nutritional and environmental conditions. Corn (yellow dent variety) contains 61% starch, 3.8% corn oil, 8.0% protein, 11.2% fiber, and 16.0% moisture. Since the corn oil and fiber content of the corn are not needed in ABE fermentation, they can be removed, and these will allow for byproduct credit. Corn is cleaned, tempered, and channeled into the degerminator. The germs containing corn oil are removed for oil extraction, and the degermed corn is ground and sieved into appropriate particle size. The meal is then mixed with water and thermo-stable alpha-amylase, and cooked at 100 degree C for 5 min to liquefy (liquefaction) the starch. The mash is cooled, and the secondary enzyme (glucoamylase) is added to convert the liquefied starch to glucose (saccharification). Continuous fermentation was used for the bioconversion of the saccharified degermed corn to ABE. The saccharified degermed corn solution and glucose (as control) were supplemented with P2 medium nutrients in order to support good growth and ABE production by C. beijerinckii BA101. The bioreactor was fed at a dilution rate of 0.03 h**-1 and saccharified degermed corn solution/feed volume (4 L) was replaced every 72-84 h. The continuous reactor fed with saccharified degermed corn solution produced approximately 14.0 g L**-1 total ABE (max.) as compared with 12.0 g L**-1 total ABE (max.) from the control. Maximum productivity recorded with saccharified degermed corn and glucose solutions were 0.42 and 0.36 g L**-1h**-1, respectively. The residual glucose concentrations of the effluents were 20.1 and 29.1 gL**-1, respectively. Interestingly, decreasing the P2 nutrient supplements of the saccharified degermed corn solution in half did not result in a decrease in ABE productivity. It is concluded that C. beijerinckii BA101 utilized the nutrients in the degermed corn to compensate for the reduction in the P2 medium supplements. It is anticipated that reduction by half in P2 medium supplements would significantly reduce the butanol price. Due to low final ABE concentration, high effluent streams, potential for substrate and nutrient waste associated with continuous ABE fermentation systems, we developed a highly efficient laboratory-scale integrated ABE fermentation and recovery system employing gas stripping technology. The simultaneous fermentation and product recovery approach appears to have solved most of the early problems associated with the AB fermentation such as product inhibition, poor reactor productivity, and high volume process streams encountered in the traditional AB batch fermentation process. Gases (CO2 & H2) produced during the fermentation are used for the stripping process and recycled. The ABE vapors are condensed and removed. It should be noted that during gas stripping, acids and substrates are not removed from the fermentation broth. Elimination of butanol inhibition resulted in an elevated cell concentration, a high substrate utilization rate, together with the complete utilization of substrate and acids. The productivities (using glucose as substrate) of the integrated batch, fed-batch, and continuous processes employing gas stripping was improved up to two, four, and three fold, respectively, when compared to the batch process. The productivity of the traditional ABE batch bioreactors ranges from 0.1-0.3 g/L.h and requires larger fermentors, which produce larger effluent volumes. The potential of inexpensive agricultural raw materials can be realized when this new technology is applied to the bioconversion processes for ABE production. We are currently testing this new technology using degermed corn as substrate. Preliminary results are very encouraging and will be presented at the meeting.