- Biochemical engineering
Biochemical engineering is a branch of
chemical engineeringor biological engineeringthat mainly deals with the design and construction of unit processes that involve biological organisms or molecules. Biochemical engineering is often taught as a supplementary option to chemical engineering or biological engineering due to the similarities in both the background subject curriculum and problem-solving techniques used by both professions. Its applications are used in the food, feed, pharmaceutical, biotechnology, and water treatment industries.
A bioreactor may refer to any device or system that supports a biologically active environment. [GoldBookRef|title=bioreactor|url=http://goldbook.iupac.org/B00662.html] In one case, a bioreactor is a vessel in which is carried out a chemical process which involves
organisms or biochemically active substances derived from such organisms. This process can either be aerobicor anaerobic. These bioreactors are commonly cylindrical, ranging in size from liters to cubic meters, and are often made of stainless steel.
A bioreactor may also refer to a device or system meant to grow cells or tissues in the context of
cell culture. These devices are being developed for use in tissue engineering.
On the basis of mode of operation, a bioreactor may be classified as batch, fed batch or continuous (e.g.
Continuous stirred-tank reactor model). An example of a continuous bioreactor is the chemostat.
Organisms growing in bioreactors may be suspended or immobilized. The simplest, where cells are immobilized, is a
Petri dishwith agar gel. Large scale immobilized cell bioreactors are:
Bioreactor design is a relatively complex engineering task. Under optimum conditions, the microorganisms or cells are able to perform their desired function with 100 percent rate of success. The bioreactor's environmental conditions like gas (i.e., air,
oxygen, nitrogen, carbon dioxide) flow rates, temperature, pHand dissolved oxygen levels, and agitation speed/circulation rate need to be closely monitored and controlled.
Most industrial bioreactor manufacturers use vessels,
sensors and a control systemnetworked together.
Fouling" can harm the overall sterility and efficiency of the bioreactor, especially the heat exchangers. To avoid it, the bioreactor must be easily cleaned and as smooth as possible (therefore the round shape).
heat exchangeris needed to maintain the bioprocess at a constant temperature. Biological fermentation is a major source of heat, therefore in most cases bioreactors need refrigeration. They can be refrigerated with an external jacket or, for very large vessels, with internal coils.
In an aerobic process, optimal oxygen transfer is perhaps the most difficult task to accomplish.
Oxygenis poorly soluble in water--even less in fermentation broths--and is relatively scarce in air(20.8%). Oxygen transfer is usually helped by agitation, which is also needed to mix nutrients and to keep the fermentation homogeneous. There are, however, limits to the speed of agitation, due both to high power consumption (which is proportional to the cube of the speed of the electric motor) and to the damage to organisms caused by excessive tip speed (3.14*dia of the impeller in mm * notation of the Speed/60(hr)] causing shear stress.
Industrial bioreactors usually employ
bacteriaor other simple organisms that can withstand the forces of agitation. They are also simple to sustain, requiring only simple nutrient solutions, and can grow at astounding rates.
A photobioreactor (PBR) is a
bioreactorwhich incorporates some type of light source. Virtually any translucent containercould be called a PBR, however the term is more commonly used to define a closed system, as opposed to an open tankor pond.
Bioreactors are also designed to treat
sewageand wastewater. In the most efficient of these systems there is a supply of free-flowing, chemically inert media that acts as a receptacle for the bacteria that breaks down the raw sewage. Examples of these bioreactors often have separate, sequential tanks and a mechanical separator or cyclone to speed the division of water and biosolids. Aerators supply oxygen to the sewage and media further accelerating breakdown. In the process, the liquids Biochemical Oxygen Demand BODis reduced sufficiently to render the contaminated water fit for reuse. The biosolids can be collected for further processing or dried and used as fertilizer. An extremely simple version of a sewage bioreactor is a septic tank whereby the sewage is left in situ, with or without additional media to house bacteria. In this instance, the biosludge itself is the primary host (activated sludge) for the bacteria. Septic systems are best suited where there is sufficient landmass and the system is not subject to flooding or overly saturated ground and where time and efficiency is not of an essence.
In bioreactors where 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. Higher organisms also need more complex growth medium.
NASA tissue cloning bioreactor
NASAhas developed a new type of bioreactor that artificially grows tissue in cell cultures. NASA's tissue bioreactor can grow heart tissue, skeletal tissue, ligaments, cancer tissue for study, and other types of tissue. [http://science.nasa.gov/NEWHOME/headlines/msad05oct99_1.htm]
For more information on artificial tissue culture, see
Biological hydrogen production (Algae)
Biofuel from algae
* [http://inventgeek.com/Projects/photo-bio-reactor/overview.aspx Photo-bioreactor] .
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