V7

open

open

open

closed

Fig. 7.2S. Containment sampling unit for Chapter 2 (Werner, 1992).

Fig. 7.2S. Containment sampling unit for Chapter 2 (Werner, 1992).

At Containment levels 2 and B3/4, probes are fitted with triple 'O'-ring seals (Hambleton et al., 1991). Although double 'O'-ring seals with steam tracing have been described they are not normally considered to be feasible (Leaver and Hambleton, 1992). The use of pre-inserted back-up probes is recommended as a means for dealing with probe failure rather than using a retractable electrode housing during a fermentation cycle because of the danger of leakage of broth (Hambleton et al., 1991).

Foam control

In any fermentation it is important to minimize foaming. When foaming becomes excessive, there is a danger that filters become wet resulting in contamina tion. There is also the possibility that siphoning will develop, leading to the loss of all or part of the contents of the fermenter. Methods for foam control are considered in Chapter 8 and antifoams are discussed in Chapter 4. In certain circumstances antifoams may cause problems with aeration or downstream processing. Foam breakers which break down foam by an impact mechanism created by some type of rotating mechanism inside the fermenter are manufactured by Bioengineering AG (Switzerland), Chemap AG (Switzerland), Electrolux (Sweden), Frings (Germany) and New Brunswick Scientific Ltd (U.S.A.). Mechanical foam breakers used in Acetators for vinegar production are described later in this chapter. Domnick Hunter (U.K.) manufacture the 'Turbosep', in which foam is directed over stationary turbine blades in a separator and the liquid fraction is returned to the fermenter.

Aseptic Sampling Fermenter WernerSteam Traced Aseptic Valve

Fk;. 7.26. Resterilizable harvest-sampling valve for Level 2 containment (New Brunswick, Hatfield, England). This spool-type valve is connected to the bottom of the fermenter vessel in the closed position (a), pressurized steam circulates throughout the entire valve body and through the product condensate line (B) via a steam inlet line (A). Aseptic withdrawal of samples is achieved with the valve in the open position (b). To prevent possible contamination when the plunger is raised, steam is circulated to the lower valve area. Action of the plunger is controlled by an air cyclinder.

Steam in

Quick connect fitting

Removable cap

Steam in

Quick connect fitting

Steam Sterilizable Feed Ports Fermentor

Removable cap

Steam out

Fig. 7.27. Steam sterilizable liquid-feed port (Beck et al., 1987).

Steam out

Fig. 7.27. Steam sterilizable liquid-feed port (Beck et al., 1987).

At Containment level 1 or B2, the exhaust air system should shut down automatically if the foam control system fails (Werner, 1992).

Monitoring and control of various parameters

These factors are considered in detail in Chapter 8.

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