Effect Of Buffer Solution On Butanol Fermentation By Clostridium Acetobutylicum

Recently, global concerns on sustainable supply of crude oil and environmental issues associated with the over-consumption of petroleum-based products, particularly transportation fuels, have revitalized biofuels production. Among these alternatives, bio-butanol as an advanced biofuel has attracted worldwide attention. However, the major problems associated with ABE fermentation include selection of low-cost feedstocks, multiple end-products and by-products, poor stress tolerance, low butanol production, productivity and yield, and high cost of butanol recovery, which seriously hinder the scale-up bio-butanol industrial production. Thus, there is a necessity for developing an efficient bioprocess engineering strategy for addressing these challenges.In the past decades, intensive studies have been carried out on the efficiency of ABE fermentation, which has been demonstrated to inevitably depend on not only environmental pH and acids (butyrate) re-assimilation but also the essential availability of nutrients such as metal ions in media. Therefore, in this study, a novel buffer system including MnCO3, CaCO3 and butyrate was further developed via Response Surface Optimization. As a consequence, the environmental pH level could be regulated to some extent by the buffering effect of MnC03 and CaCO3, coupled with supplementation of micronutrient metal ions and butyrate, which were of great importance to butanol biosynthesis.In this study, several experiments were first performed for single-factor testing, whereas MnC03, CaCO3 and butyrate were thus chosen as buffering alternatives in ABE fermentation (in 250mL screw-capped bottles containing 100mL fermentation medium) using sugar mixture (glucose/fructose=1:4) as carbon sources simulating the hydrolysate of Jerusalem artichoke tubers via Response Surface Optimization method. The Response Surface Optimization results showed that the optimized level of MnC03, CaCO3 and butyrate was 0.41,8.09 and 5.20 g/L, respectively, with a theoretical butanol production of 10.89 g/L. Finally, the ABE fermentation (in 250mL screw-capped bottles containing 100mL fermentation medium) under this optimized condition gave an actual butanol production of 10.87 g/L.Batch ABE fermentation (in a regular stirred fermentor with a working volume of 1.1 L) using sugar mixture (glucose/fructose=1:4) as carbon sources simulating the hydrolysate of Jerusalem artichoke tubers was further conducted to investigate the fermentation kinetics associated with environmental pH, sugar utilization, cell growth, acids re-assimilation and ABE biosynthesis under the optimized buffering condition above. The experimental results showed that butanol production of 10.52 g/L was achieved with an increase of 135.87% compared to that of 4.46 g/L in the control, and butanol productivity/yield of 0.15 g/L/h and 0.25 g/g were obtained along with enhanced acids re-assimilation and sugar utilization. It should be noted that the environmental pH was also dramatically influenced under the optimized condition.Finally, this optimized buffering system was successfully applied in batch ABE fermentation using the hydrolysate of Jerusalem artichoke tubers. Especially, butanol/ABE production of 11.21 and 16.55 g/L were achieved with increases of 96.00% and 92.90% compared to those of 4.46 and 10.52 g/L, respectively in the control. Furthermore, butanol productivity/yield of 0.12 g/L/h and 0.20 g/g were increased by 71.40% and 53.80% compared to those of 0.07 g/L/h and 0.13 g/g in the control, indicating this optimized buffering system was efficient bioprocess engineering strategy for low-cost ABE fermentation.