Fermentative production of 1,3-propanediol from glycerol by Clostridium butyricum up to a scale of 2m3

Summary The conversion of glycerol to 1,3-propanediol (PD) by Clostridium butyricum DSM 5431 was studied in anaerobic culture. Growth and product formation were optimal at pH = 7.0 and T = 35° C, while aeration rate and stirrer speed were found to have no significant influence. As increasing amounts of initial glycerol led to inhibition of growth, cultivations were done in fed-batch operation. Comparative cultivations were carried out in an air-lift (ALR) and a stirred-tank reactor (STR) having equal working volumes (V _L = 30 l) and no difference in product formation was found. The process was scaled up to reactor sizes of 1.2 m³ (ALR) and 2.0 m³ (STR). The same results were obtained irrespective of reactor volume as well as reactor type (STR/ALR). PD concentrations of approximately 50–58 g·l^–1 and overall productivities of 2.3–2.9 g·l^–1 ·h^–1 could be reached. Offprint requests to: W.-D. Deckwer     

Model Predictive Temperature Control for Calorimetric Measurements in Baker’s Yeast Fermentations

We intended to establish a system for calorimetric measurements on a pilot scale. The on‐line calculation of model equations of the heat balance around the reactor is supposed to be simple at a constant fermentation temperature. To obtain higher accuracy in temperature control, a model predictive control (MPC) system is developed. MPC with the accuracy of 0.1 °C is much more precise than the classical single loop temperature control (SLC) with 1 °C. Calorimetry has a very high dynamic behavior compared with other on‐line determined parameters also representing metabolic activity. In a purely oxidative fed‐batch fermentation of baker’s yeast the accuracy of calorimetry is verified. The combustion enthalpy of glucose, calculated using on‐line data of microbial heat production and substrate consumption, corresponds very well with the data in the literature. It is now possible to determine the fraction of substrate uptake, utilized for energy (factor k) and biosynthesis (factor a) metabolisms on‐line.     

Ambruticin S production in amino acid rich media

Summary The antimycoticum ambruticin was produced by cultivating the myxobacterium Sorangium cellulosum in shake flasks and stirred tank reactors with 10- and 30-1 working volumes. During growth and product formation amino acid concentrations in the complex media were measured by HPLC. In the logarithmic growth phase free aspartate and glutamate were assimilated without product formation. After consumption of aspartate and glutamate, growth was limited and ambruticin production set in. The effects of biological parameters such as age, amount of inoculum, pretreatment of cells before inoculation and time of precultivation were also investigated.Offprint requests to: W.-D. Deckwer     

Ambruticin S production in air-lift and stirred-tank bioreactors

Summary Using the method of equi-inocular synchronized comparative fermentation (EISCF) the cultivation of Sorangium cellulosum So ce 10 and production of the polyketide antibiotic ambruticin S was compared in stirred-tank and air-lift reactors of different geometry. This method requires that inocula originate from the same pre-culture and cultivation parameters are synchronized to similar values. Similar ambruticin yields were obtained from both reactor systems provided that the concentration of dissolved oxygen (DO) was maintained above a certain value (ca. 40%). For cultivation of S. cellulosum it is the DO level rather than the oxygen transfer rate which presents the proper criterion for scale-up and comparative reactor studies. Offprint requests to: W.-D. Deckwer     

Some Experiments and Conclusions about the Influence of Pure H2 Gason the Anaerobic Degradation of Propionate by Mixed Cultures

Reaction enthalpy for propionate degradationΔG₀ is only negative when the partial pressure ofhydrogen pH₂ is less than 10^—4 bar. This means that for pH₂ more than 10^—4 bar, a total anaerobic degradation of propionate is impossible for thermodynamic reasons. Therefore, with increasing pH₂, the anaerobic degradation rate of propionate via acetate is inhibited. There are two ways to investigate the inhibitory effect of pH₂: to keep the concentration of hydrogen consuming bacteria low or to increase the mass transfer by feeding the hydrogen at higher flow rates. The author used an extended fixed bed reactor filled with polyurethane particles as a carrier for the bacteria, aerated with pure H₂ gas. The results, compared with the literature by using model equations in order to standardize the data, correspond well: The addition of pure H₂ gas has no observable effects on propionate degradation.In the fixed bed reactor with immobilized bacteria, it was not possible to reach an inhibitory concentration of H₂ and high process stability could be maintained.