H: Questions Flashcards
In a lab scale fermentor, what is the function of the condenser? Briefly, how does it work?
The condenser is the air-out tube and works by condensing water vapour from the culture onto a cold surface (it has a water jacket surrounding the air-out tube through which cold water is continually circulated). It prevents condensation affecting the air-out filter.
In a lab scale fermentor, what is the function of the cold finger? Briefly, how does it work?
The cold finger is a heat exchange coil that works in conjunction with a heating element and a temperature probe to control temperature within a fermentor. It is an enclosed tube inserted into the culture through which cold water is circulated.
What is the aspect ratio (AR) in fermentor design? What is the typical value of the AR for a stirred tank fermentor?
The height-to-diameter ratio of a fermentor.
It is typically 2:1 to 6:1.
What is meant by the working volume of a fermentor?
The maximum volume of growth medium that can be placed in a fermentor and still allow for adequate aeration, mixing and (if relevant) fed-batch additions (all of which increase the medium volume).
Define the volumetric productivity of biotechnology process?
The amount of product produced per unit volume of fermentor per unit time (including ‘down-time’).
What does the acronym SIP refer to in industrial media sterilisation/bioreactor technology?
‘Full’ Sterilisation In Place’ heats up the liquid in a reactor (media or water) to generate the steam necessary for steam sterilisation (achieved via heating jackets, coils, electrical heat fingers or direct steam injection). This is the most common method.
What does the acronym ‘CIP’ refer to in fermentor technology?
‘Cleaning in place’: cleaning of bioreactor between fermentation runs. The reactor needs to be equipped with CIP supply and return lines and spraying nozzles. The cleaning solutions are prepared in a ‘CIP’ kitchen. Spraying nozzles are sited in the fermentor to cover all the surfaces with a cleaning solution. Spray velocities of 1.5 to 2.5 m/s are required.
Name two factors involved in foam formation in a fermentor and two methods by which it may be reduced?
Causes are the media being rich in proteins, production of detergent-like molecules by cells, and high agitation. Methods of reduction include modifying the media, using a foam separator, breaking bubbles by shear force, using ultrasonic disruption, using a condenser, or having adequate head space.
What is the relevance of maintaining positive pressure in fermentor/fermentation vessels?
A positive pressure helps in maintaining sterility by preventing the entry of aerial contaminants.
In a lab scale fermentor, what is the function of O-rings? Briefly, how do they work?
O-rings are a type of gasket that work by compression, providing an aseptic seal against fermentor insertions such as probes. On compression by a screw assembly, they tighten around the insertion and prevent any movement
What key control elements are necessary to maintain a constant pH within a laboratory scale bioreactor?
pH probe, pump for addition of acid or alkali, buffer in medium.
What key control elements are necessary to maintain a constant temperature within a bench-scale bioreactor?
Temperature probe (to measure temperature), temperature heating element (to heat up broth to required temperature), cold-finger heat exchanger (to dissipate metabolic heat during active culture growth).
Provide the specification of the metal used in the construction of large-scale bioreactors. Briefly, why is such a specification necessary?
High-quality stainless austenitic steel (US grade 316L: 18% Cr; 10% Ni; 2.5% Mb).
It needs to be shatter/chip/crack-proof and resistant to corrosion (chloride environment) with minimal leachate.
The bioreactor represents a harsh environment for steel. Identify the main elements of stainless steel and provide two accelerants for rust which are present in microbial media?
The main elements of stainless steel are Fe, Cr, Ni and Mb. Examples of rust accelerants are oxygen, water, and salts.
