Fermentor Operation

Cellulase manufacturers adopt specific procedures for storing and propagating cultures to obtain reproducible fermentations. The cellulase-producing fungi are typically stored frozen at -80°C or freeze-dried. To prepare the inoculum (seed) mixture, an aliquot is taken and grown in consecutive liquid cultures of increasing volume. The volume of the last step, the seed fermentor, is typically 1-10% of the main fermentor volume. 

The growth medium includes defined salts, complex nutrients, surfactants, and inducer. The salts are the typical fermentation salts, including potassium phosphate, ammonium nitrate, ammonium sulfate, calcium chloride, and magnesium sulfate [33]. The complex nutrients are most often 5 to 25 g L of corn steep liquor but can also include yeast extract. The surfactants are added to control or suppress foam formation. The surfactants used include commercial antifoams as well as soybean oil or palm oil. The inducers are proprietary to each manufacturer but will contain an inexpensive mixture of soluble and/or insoluble sugars. Some inducers used include milk whey, which contains lactose Solka floe cellulose or, sugar or paper mill waste streams. 

The temperature and pH of the fermentor is monitored and controlled throughout the fermentation. For Trichoderma, the conditions are 28-30 °C, pH 4-5. For the other fungi, the temperatures and pH are higher, typically 37 °C, pH 6.2-7. 

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In case the Monod equation holds for the rates of cell growth in the exponential growth, with decelerating and stationary phases in a uniformly mixed fermentor operated batchwise, a combination of Equations 4.2 and 4.6 gives... 

Instrumentation for measuring and controlling the temperature, pressure, flow rates, and fluid compositions, including oxygen partial pressure, is necessary for fermentor operation. (Details of instrumentation and control for fermentation are provided in Chapter 13.)... 

At the start of the batch fermentor operation, the broth must be heated to the fermentation temperature, which is usually in the range of 30-37 °C, by passing steam or warm water through the coil or the outer jacket. 

Nienow, A.W. Gas dispersion performance in fermentor operation. Chem. Eng. Progr. 1990, 61-71. 

The relationship between Kj A and fermentor operating variables was given by Cooper et al. [41] ... 

Consider a fermentor, operated at constant volume, in vhich a single, rate-limiting substrate promotes biomass growth and product formation. Under the assumption of instant yield, one can derive the following material balances that describe the concentrations in the fermentor (Henson and Seborg, 1991) ... 

This section will review recent reports of attempts to produce PHA. Emphasis will be put on processes using R. eutropha or A. latus, and the survey will be limited to literature on PHA production in bioreactor only. While flask experiments are the necessary first stages in the development of new production strategies (e.g., the use of inexpensive substrates and sources of growth factors, as recently reported in [229] and [230], respectively) and therefore of high interest, the potential of a novel system can be truly assessed only once it has been scaled up to fermentor operation, in which culture conditions at least approach those of industrial fermentations. The other area of research with a possible future impact on large-scale production of PHAs, the use of transgenic plants, will be briefly discussed. 

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