SSG 2513 Introduction of Bioprocess Engineering 5.0 Bioreactor selection and optimization 5.1 Identification of various bioreactor 5.2 Sterilization in bioreactor and bioprocess unit operations
Goh Kian Mau
• References: • Bioprocess Engineering. Shuler. (9.1, 9.2, 9.3, 9.5, 15.4.1,10.4) • Bioprocess Engineering Principles. Pauline M. Doran. (P248.3 B56 1995) • Operation modes of bioreactors. (TP.248.25.B55 O63 1992) • Bioreactor Design and product yield (TP248.25 B55 B56 1992).
What is bioreactor? • The bioreactor in which biological/biochemical reaction takes place occupies a central position in the chemical process. • Synonymous for bioreactor: biochemical reactor, biological reactor, fermenter, microbial reactor. • The reactions happens inside the vessel because of the presence of either microbial fermentation or enzyme (cell-free) reactions or both.The cells or enzyme can be in suspension or immobilized form. • Bioreactors can be operated as aerobic, anaerobic, or solid state.
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The bioreactor provides the volume (height, diameter) necessary for the reaction and holds the amount of catalyst or cells required for the reaction. The energy required to over-come the activation threshold of each partial reaction is also supplied in the reactor, and the proper parameters (temperature, concentration, pressure, pH, DO, etc) are monitored and controlled.
Bioreactor Configurations • Batch Stirred Tank only 70-80% of the volume of stirred reactors is filled with liquid; this allows adequate headspace for disen-gagement (breaking off) of droplets from the exhaust gas and to accommodate any foam which may develop. If foaming is a problem, a supplementary impeller called a foam breaker maybe installed as shown above. Alternatively, antifoam agents are added to the broth; because reduces the rate of oxygen transfer. Normally mechanical foam dispersal is generally preferred.
Batch bioreactor Exhaust air (Air out)
• Before inoculation (or adding the enzymes), the batch reactor contains a certain volume of nutrient (or substrate) in suspension. • After inoculation, the process is left untouched, ie no material is added to or removed from the reactor. • However, the reactor might be aerated. • Batch reactors are often referred to as closed systems. • The term 'closed' refers to the fact that material can neither enter nor leave the reactor. (exceptional: airin and airout)
Air in
Batch bioreactor-ideal mixing • In an ideal well-mixed bioreactor, the mixing is assumed to be intense enough that the fluid is homogeneous through the reactor. • no dead zones or clumps of undissolved solid substrate floating around and there is no concentration gradients in vessel.
Fed batch bioreactor • The fed-batch reaction (FBR) is a batch reactor to which, when the nutrients approach depletion, fresh nutrients are added. In other words, the reactor is fed. It is assumed that the concentration of the nutrients added is so high that volume changes are negligible (justifying the batch part of the name).
Bubble column - no mechanical agitation. -aeration and mixing are achieved by gas sparging; this requires less energy than mechanical stirring. -height-to-diameter ratio is usually high to maximize the aeration mixing -Advantages of bubble columns include low capital cost, lack of moving parts, and satisfactory heat- and mass-transfer perfor-mance. As in stirred vessels, foaming can be a problem requiring mechanical dispersal or addition of antifoam to the medium. (Your imagination is needed, bubble and foam is different!)
Bubble column • The oxygen transfer from the air bubble and the mixing inside the bubble-column depend entirely on the behaviour of the bubbles released from the sparger. • Homogeneous flow occurs only at low gas flow rates and when bubbles leaving the sparger are evenly distributed across the column crosssection. In homogeneous flow, all bubbles rise with the same upward velocity and there is no backmixing of the gas phase. • Liquid mixing in this flow regime is also limited, arising solely from entrainment in the wakes of the bubbles. Under normal operating conditions at higher gas velocities, large chaotic circulatory flow is develop and heterogeneous flow occurs as illustrated in figure on the left.
• Their distinguishing feature compared with the bubble column is that of liquid flow are more defined owing to the physical separation of up-flowing and down-flowing streams. • gas is sparged into a part of the vessel section called the riser. • Gas disengages at the top of the vessel leaving heavier bubble-free liquid to recirculate through the downcomer. • Liquid circulates in airlift reactors as a result of the density difference between the riser and downcomer.
Airlift bioreactor
• Packed-bed reactors are used with immobilised or particulate biocatalysts. • Medium/buffer can be fed either at the top or bottom of the column and forms a continuous liquid phase between the particles. • Damage due to particle wear is minimal in packed beds compared with stirred reactors.
Packed-bed bioreactor
• Normally the vessel is not fully packed with the bead for the expansion and movement of the bed. • When packed beds are operated in upflow mode with beads of appropriate size and density, the bed expands at liquid flow rates due to upward motion of the particles. • Because particles in fluidized beds are in constant motion, channeling and clogging of the bed are avoided and air can be introduced directly into the column.
Fluidized bed bioreactor
• Trickle-bed reactor is another variation of the packed bed. • Liquid is sprayed onto the top of packing and trickles down through the bed in small rivulets. • Air may be introduced at the base. Tricklebed -bioreactors are used widely for aerobic wastewater treatment.
Trinkle-bed bioreactor
Membrane bioreactor (MBR) • In a membrane reactor continuous processing is possible if production and separation can be incorporated in one system. • One application of the membrane bioreactor is to remove product that is formed, especially for those that can inhibit the enzyme reaction.
Sterilization in bioreactor • Most bioreactors (especially fermentation process and production of pharmaceutical products) outside of the food and beverage industry are carried out using aseptic conditions. • Most industrial bioreactors are designed for in situ steam sterilisation under pressure. The vessel should have a minimum number of internal structures, ports, nozzles, connections and other attachments to ensure that steam reaches all parts of the equipment. For effective sterilisation, all air in the vessel and pipe connections must be displaced by steam. • Think: In industry, where does the steam supply come from?
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Example of steam sterilization at the sampling port of a fermentor Sampling ports are fitted to fermenters to allow removal of broth for analysis. Initially, valves A and D are closed; valves B and C are open to maintain a steam barrier between the reactor and the outside environ-ment. Valve C is then closed, valve B partially closed and valve D partially opened to allow steam and condensate to bleed from the sampling port D. For sampling, A is opened briefly to cool the pipe and carry away any condensate that would dilute the sample; this broth is discarded. Valve B is then closed and a sample collected through D. When sampling is complete, valve A is closed and B opened for re-sterilisation of the sample line; this prevents any contaminants which entered while D was open from travelling up to the fermenter. Valve D is then closed and valve C re-opened.
Sterilization in other unit operation in bioprocess industry • • • •
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Heat sterilization Chemical sterilization (refer to handouts) Sterilization using radiation -Radiation sterilization is a good alternative for sterilizing disposable medical, laboratory and pharmaceutical products. The radiation that are commonly are ultraviolet 200-280 nm (UV), β-radiation and γ-radiation. In some industries such as the pharmaceutical, high quality of water (such as RO, milli-Q, water-forinjection (WFI)) is required. Normally, a series of filtration and ion-exchange purification steps are involved. High quality water are normally keep in water tanks before utilize, and these tanks usually are equipped with UV radiation to avoid the growth of microorganism.
Sterilization in other unit operation in bioprocess industry • -
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Sterilization by using membrane filter All microorganism including viruses have certain sizes. The microorganism can simply be removed by using membrane filter that has pore size smaller than microorganism. In some application, a series of membrane filters are used. Depth filters with bigger pore size (e.g 0.6 µm) may be used first to remove insoluble particle prior passing through membrane filters with smaller pore size (e.g 0.45 µm or 0.2 µm). (Think: Why? Check inside textbook what is the size of common microorganism).
I like membrane a lot. You must pandai pandai.
