背景:甘油,作为副产品,主要来自许多作物转化为生物柴油,乙醇,和脂肪酯。其生物转化为1,3-丙二醇(1,3-PDO)是一种环境友好的方法。连续发酵比补料分批发酵和分批发酵有许多显著的优点,如高产品浓度,易于进料操作,长期高生产率,无需频繁的种子培养,和能源密集型灭菌。然而,通常很难收获高浓度的产品。
结果:在这项研究中,首先设计了一个三阶段连续发酵,用丁酸梭菌从粗甘油生产1,3-PDO,其中第一阶段发酵负责提供处于强劲生长状态的优秀细胞,第二阶段重点是促进1,3-PDO生产,第三阶段旨在进一步提高1,3-PDO浓度并尽可能降低残留甘油浓度。通过三阶段连续发酵,产生80.05g/L的1,3-PDO作为最大浓度,同时保持5.87g/L的残留甘油,产量为0.48g/g,生产率为3.67g/(L·h)。根据第一阶段的14组实验数据,建立了一个动力学模型来描述1,3-PDO浓度之间的复杂关系,基材,生物量,还有丁酸盐.随后,该动力学模型用于优化和预测第一阶段发酵中11.26g/(L·h)的最高1,3-PDO生产率,甘油进料浓度和稀释率分别为92g/L和0.341h-1。此外,为了在没有第三阶段发酵的情况下实现目标1,3-PDO产量为80g/L,第二个发酵罐与第一个发酵罐的预测最小体积比为11.9。基于动力学的两阶段连续发酵与预测结果得到了很好的实验验证。
结论:报道了一种新的三阶段连续发酵和动力学模型。然后基于动力学模型的优化,开发了一种更简单的两阶段连续发酵。这种基于动力学的两阶段连续发酵的开发可以实现1,3-PDO的高水平生产。同时,应用动力学优化多阶段连续发酵为其他生化产品生产提供了参考。
BACKGROUND: Glycerol, as a by-product, mainly derives from the conversion of many crops to biodiesel, ethanol, and fatty ester. Its bioconversion to 1,3-propanediol (1,3-PDO) is an environmentally friendly method. Continuous fermentation has many striking merits over fed-batch and batch fermentation, such as high product concentration with easy feeding operation, long-term high productivity without frequent seed culture, and energy-intensive sterilization. However, it is usually difficult to harvest high product concentrations.
RESULTS: In this study, a three-stage continuous fermentation was firstly designed to produce 1,3-PDO from crude glycerol by Clostridium butyricum, in which the first stage fermentation was responsible for providing the excellent cells in a robust growth state, the second stage focused on promoting 1,3-PDO production, and the third stage aimed to further boost the 1,3-PDO concentration and reduce the residual glycerol concentration as much as possible. Through the three-stage continuous fermentation, 80.05 g/L 1,3-PDO as the maximum concentration was produced while maintaining residual glycerol of 5.87 g/L, achieving a yield of 0.48 g/g and a productivity of 3.67 g/(L·h). Based on the 14 sets of experimental data from the first stage, a kinetic model was developed to describe the intricate relationships among the concentrations of 1,3-PDO, substrate, biomass, and butyrate. Subsequently, this kinetic model was used to optimize and predict the highest 1,3-PDO productivity of 11.26 g/(L·h) in the first stage fermentation, while the glycerol feeding concentration and dilution rate were determined to be 92 g/L and 0.341 h-1, separately. Additionally, to achieve a target 1,3-PDO production of 80 g/L without the third stage fermentation, the predicted minimum volume ratio of the second fermenter to the first one was 11.9. The kinetics-based two-stage continuous fermentation was experimentally verified well with the predicted results.
CONCLUSIONS: A novel three-stage continuous fermentation and a kinetic model were reported. Then a simpler two-stage continuous fermentation was developed based on the optimization of the kinetic model. This kinetics-based development of two-stage continuous fermentation could achieve high-level production of 1,3-PDO. Meanwhile, it provides a reference for other bio-chemicals production by applying kinetics to optimize multi-stage continuous fermentation.