The acetone butanol ethanol fermentation : preliminary studies on some practical aspects : a thesis presented in partial fulfilment of the requirements for the degree of Master of Technology in Biotechnology
The dilute nature of solvents at the end of fermentation and slow overall rate of fermentation are major economic burdens on a commercial plant producing acetone, butanol, and ethanol. A preliminary feasibility costing of such a plant showed the cost of fermenters represents almost 50% of the total purchased equipment cost, and emphasised the need for improvements in the fermentation. Experiments were performed in 10-litre and 30-litre pressure vessels, a 1.5-litre vessel at atmospheric pressure, and trial runs in 100 ml bottles. Good correlations were found for the different fermentation headspace pressures (100 to 250 kPa abs.) and minimum observed pH's (pH 4.2 to pH 4.65) with final butanol yields (0.92 to 11.6 g/1); increases in both parameters correlating with increased butanol concentration. Ethanol was found to be correlated with pressure only, and acetone with neither parameter directly. Other chemical species present in the broth were also correlated with each other. It was found that a tree diagram drawn using the strongest correlations resembled closely the known metabolism of the organism in terms of the metabolic pathways, specification of active forms of the metabolites, and effect of external influences. Use of multiple linear regression in this manner was named The Factor Correlation Method, and is potentially useful for research on metabolism and similar investigation on a much broader basis. Application of this technique showed that the pressure effect was possibly due to more than a single metabolic cause, and further experiments also emphasised the complex nature of the pressure effect. The experimental work also highlighted the potential hazard of culture degeneration leading to substandard fermentation yields and eventual nonviability. Discussion on the experimental results and of the literature suggests the phenomenon is due to infection by lysogenic phage rather than spontaneous mutation, and an approximate model based on simultaneous partial differential equations parallels some observed characteristics of the phenomenon. Other topics include theoretical exercises with laboratory work on the water tolerance of methanol-petrol mixtures, the error associated with cell enumeration using a haemocytometer, and evaluation of growth and solvent production characteristics and some relevant parameters.