摘要
搅拌式生物反应器是生物反应器的重要一种,搅拌系统是搅拌式生物反应器的核心装置。在好氧的发酵生产过程中,细胞需要分子态的氧作为呼吸链电子传递系统末端的电子受体,最终与氢离子结合成水并释放出大量能量,供细胞维持生长和合成反应使用。抗生素发酵多数是需氧发酵,氧的传递与摄取和抗生素合成有十分密切的关系。发酵液中氧扩散速率是限制很多抗生素发酵呼吸过程的因素。因此,如何改善溶氧已成为好氧发酵过程控制的重要课题。
本文在30L全自动发酵罐中,通过改变搅拌浆不同组合型式以及通气量和搅拌转速等操作条件,研究水溶液和高粘度CMC溶液的溶解氧性能,找出了容量传递系数Kla比较高的几种搅拌型式。实验结果表面:水溶液和高粘度CMC溶液的Kla随搅拌转速的增加比随通气量的增加升幅较大;相同操作条件下,在低粘度范围(1-100cp)比在高粘度范围(100-200cp)内粘度的增加对Kla的影响更为显著;在水溶液中,双层园盘涡轮平直叶、底层园盘涡轮半圆管叶+上层园盘涡轮平直叶、底层园盘涡轮半圆管叶+上层园盘涡轮箭叶搅拌浆组合的溶解氧性能总体优于底层园盘涡轮平直叶+上层园盘涡轮45°斜直叶和底层园盘涡轮平直叶+上层园盘涡轮弯叶搅拌浆组合,其中尤以双层园盘涡轮平直叶搅拌浆在各种操作条件下的溶解氧性能最稳定;在高粘度CMC溶液中,底层园盘涡轮半圆管叶+上层园盘涡轮箭叶搅拌浆组合整体优于底层园盘涡轮平直叶+上层园盘涡轮45°斜直叶。
通过抗生素发酵罐设计放大实例以及对现有抗生素生产发酵罐搅拌系统改进,即洛伐他汀1m~3中试罐由2层园盘涡轮箭叶改为2层园盘涡轮平直叶、放大设计头孢菌素120m~3发酵罐时采用底层园盘涡轮半圆管叶+上面3层轴向流搅拌器(原36m~3发酵罐为3层园盘涡轮平直叶搅拌器)、大观霉素大生产42m~3发酵罐的搅拌系统由3层园盘涡轮平直叶优化为底层园盘涡轮平直叶+上面一层轴向流搅拌器时,跟踪各相应生产品种洛伐他汀、头孢菌素和大观霉素的发酵单位、发酵液溶解氧、菌丝体浓度、发酵液总糖浓度的变化,实验数据表明:改进搅拌系统后的发酵罐(包括放大设计的发酵罐)的溶解氧整体优于改进前;改进后的发酵单位,洛伐他汀增加40%,大观霉素和头孢菌素也略有增加,并且改进后
Stirred-tank bioreactor is one of the most important bioreactors. The agitation system is a key component in the stirred-tank bioreactor. In aerobic fermentation processes, cells in the culture medium need oxygen, which acts as the electronic acceptor of electron transfer system in the respiratory chain. Oxygen interacts with hydrogen ion to form water, releasing a large amount of energy, which is required by the cells for their maintenance and the synthetic reactions. Most of the fermentation processes for antibiotic production are aerobic, and the antibiotic synthesis is greatly affected by the transport and uptake rates of oxygen. The diffusion rate of oxygen in the fermentation is a limiting factor for many antibiotic fermentation processes. Therefore, enhancing oxygen transfer is very critical for the aerobic fermentation.In this study, by using a 30 L automatic fermentor, the performance of the oxygen transfer in aqueous media and high viscous CMC solution were investigated by changing the process parameters such as the combinations of different kinds of agitators, the aeration rate and the agitation speed. Several manners of agitation that improved volumetric oxygen transfer coefficient (Kla) were identified. The results indicated that Kla values in aqueous media and high viscous CMC solution increased with both agitation speed and aeration rate, but agitation speed is more effective than aeration rate;Kla decreased with the increase of viscosity and it decreased more serious in higher viscosity (100-200 cp) than in lower viscosity (1-100 cp). In water, the combination of two layers of disc turbine impellers with flat blades, disc turbine with half tube blade as bottom impeller and disc turbine with flat blade as upper impeller, disc turbine with half tube blade as bottom impeller and disc turbine with arrow blade as upper impeller resulted in high oxygen transfer rate than the
combinations of disc turbine with flat blade as bottom impeller and disc turbine with 45° oblique blade as upper impeller, disc turbine with flat blade as bottom impeller and disc turbine with curved blade as upper impeller. Among all the tested conditions, the combination of two layers of disc turbine impellers with flat blade had the most stable result for control of dissolved oxygen level;However, in high viscous CMC solution, the combination of disc turbine with half tube blade as bottom impeller and disc turbine with arrow blade as upper impeller was better than disc turbine with flat blade as bottom impeller and disc turbine with 45° oblique blade as upper impeller .Several agitation systems were re-designed for current antibiotic manufacturing and the fermentation tanks with the new agitation systems were scaled up. For example, two layers of disc turbine impellers with arrow blade in 1 m3 fermentation tank in the pilot scale for manufacturing Lovastatin was replaced by two layers of disc turbine impellers with flat blade;when the fermentation tank for Cephalothin was scaled up to 120 m3, disc turbine with half tube blade as bottom impeller and three layers axial flow impellers as upper agitators were used to replace the previous three layers disc turbine with flat blade impellers in previous 36m3 fermentor. Also disc turbine with flat blade as bottom impeller and one layer axial flow impeller as the upper agitator was used in a 42 m3fermentor for production of Spectinomycin to replace the formerly used three layers disc turbine with flat blade impellers. For all the fermentations of Lovastatin-, Cephalothin and Spectinomycin with the re-designed agitation systems, the time course of the antibiotic unit, the level of dissolved oxygen, "the concentrations of the cell and the sugar were monitored. The experimental results demonstrated that the level of the dissolved oxygen in the fermentation tanks with the re-designed agitation systems was improved significantly. The fermentation unit using the new system for
production of Lovastatin was increased up to 40% compared with the previous one. The new agitation systems also improved the fermentation units to some extent for Spectinomycin and Cephalothin, respectively. In addition, the power consumption for agitation reduced about 10. 53 Kw using the new agitation system for Spectinomycin fermentation. Experimental results also showed that the multiple disc turbine agitators were better for the small-sized fermentation tanks. However, for the big-sized tanks, it is better to use disc turbine agitator for bottom mixing and axial flow impeller for upper mixing. This combination of agitators takes advantages of both radial flow impeller for good dispersion and axial flow impeller for desirable circulation, which provides an excellent environment for aerobic fermentation. Finally, the production of Spectinomycin in a 42 m 3 fermentor using the improved agitation systems could increase economic benefit of 415￡,15 thousand Yuan per year compared with that using the old one. Therefore, the improvement in the agitation systems makes a significant contribution to the manufacture of antibiotic.
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