Bioreactors

bioreactors assignment

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ASEEM BBAS



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Bioreactors
A bioreactor is any manufactured or engineered device or system that supports a biologically
active environment. In one case, a bioreactor is a vessel in which a chemical process is carried
out which involves organisms or biochemically active substances derived from such organisms.
.A device or system meant to grow cells or tissues in the context of cell culture may also be
referred to bioreactors. These devices are being developed for use in tissue
engineering or biochemical engineering.
Structure:
Bioreactor design is a relatively complex engineering task, which is studied in the discipline
of biochemical engineering. Under optimum conditions, the microorganisms or cells are able to
perform their desired function with limited production of impurities. The environmental
conditions inside the bioreactor, such as temperature, nutrient concentrations, pH, and dissolved
gases (especially oxygen for aerobic fermentations) all affect the growth and productivity of the
organisms. The temperature of the fermentation medium is maintained by a cooling jacket, coils,
or both. Particularly exothermic fermentations may require the use of external heat exchangers.
Nutrients may be continuously added to the fermenter, as in a fed-batch system, or may be
charged into the reactor at the beginning of fermentation. The pH of the medium is measured and
adjusted with small amounts of acid or base, depending upon the fermentation. For aerobic (and
some anaerobic) fermentations, reactant gases (especially oxygen) must be added to the
fermentation. Since oxygen is relatively insoluble in water (the basis of nearly all fermentation
media), air (or purified oxygen) must be added continuously. The action of the rising bubbles
helps mix the fermentation medium and also "strips" out waste gases, such as carbon dioxide. In
practice, bioreactors are often pressurized; this increases the solubility of oxygen in water. In an
aerobic process, optimal oxygen transfer is sometimes the rate limiting step. Oxygen is poorly
soluble in water—even less in warm fermentation broths—and is relatively scarce
in air (20.95%). Oxygen transfer is usually helped by agitation, which is also needed to mix
nutrients and to keep the fermentation homogeneous. Gas dispersing agitators are used to break
up air bubbles and circulate them throughout the vessel.
These bioreactors are commonly cylindrical, ranging in size from litres to cubic metres, and are
often made of stainless steel.
Application:

It can be applied to basically all types of biocatalysis including enzymes, cellular organelles, and
animal and plant cells.
In plant propagation
© Nutrient uptake and growth rate is increased because the surface of the cultures is
always in contact with medium

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© Handling of cultures, such as inoculation and harvest, is easy. It also reduces the
number of culture vessels and the area of culture space, which further reduces the
overall cost of the production.
© Large number of plantlets which are free from physiological disorder can easily be
produced in one batch in the bioreactor.
© Forced aeration is performed which improves the growth rate and final biomass.

Types of Bioreactors
Photobioreactor
A photobioreactor (PBR) is a bioreactor which incorporates some type of light source. Virtually
any translucent container could be called a PBR; however the term is more commonly used to
define a closed system, as opposed to an open tank or pond. Photobioreactors are used to grow
small phototrophic organisms such as cyanobacteria, algae, or moss plants. These organisms use
light through photosynthesis as their energy source and do not require sugars or lipids as energy
source. Consequently, risk of contamination with other organisms like bacteria or fungi is lower
in photobioreactors when compared to bioreactors for heterotroph organisms.
Sewage treatment
Bioreactors are also designed to treat sewage and wastewater. In the most efficient of these
systems, there is a supply of a free-flowing, chemically inert medium which acts as a receptacle
for the bacteria that break down the raw sewage. Examples of these bioreactors often have
separate, sequential tanks and a mechanical separator or cyclone to speed the separation of water
and biosolids. Septic systems are best suited where there is sufficient landmass, and the system is

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not subject to flooding or overly saturated ground, and where time and efficiency are not
prioritized.

Up and Down agitation bioreactor

Unique up and down agitation in the bioreactor.
Up and down agitators are useful to avoid shear stress to the cells. These are done by instead of a
traditional propeller agitator, which requires an expensive motor and magnetic coupling. Vertical
up and down motion is achieved by a motor together with an inexpensive membrane perfectly
assure sterility and produce an efficient mixing without formation of a vortex (no baffles
needed).
NASA tissue cloning bioreactor
In bioreactors in which the goal is to grow cells or tissues for experimental or therapeutic
purposes, the design is significantly different from industrial bioreactors. Many cells and tissues,
especially mammalian ones, must have a surface or other structural support in order to grow, and
agitated environments are often destructive to these cell types and tissues.
NASA has developed a new type of bioreactor that artificially grows tissue in cell cultures.
Air driven bioreactors
A bubble column bioreactor (Figure 36.2.Ba) is a reactor, in the shape of a column, in which the
reaction medium is kept mixed and aerated by the introduction of air at the bottom (IUPAC,
1997). The major advantages of bubble column bioreactors are the low capital costs,
uncomplicated mechanical configurations and less operational costs due to low energy
requirements.
Mechanically agitated bioreactors
The various plant bioreactors designs are proposed by various authors depending upon the plant
species used. The most common and popular bioreactor is the stirred tank bioreactor.
Horizontal vessels or rotary drum reactors have significantly higher surface area to volume ratio
than other reactor types. Therefore, mass transfer is achieved with comparably less power
consumption. However, the drawback is their comparatively high energy consumption in large
scale operations.

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REFERENCES
 www.epa.gov/solidwaste/nohaz/municipal/landfill/bioreactor.htm
 http://nptel.ac.in/cources/102103016/36
 http://em.wikipedia.org/wiki/bioreactor