These are the bioreactors specialized for the fermentation that can be carried out either by exposing to sunlight or artificial illumination. Since artificial illumination is expensive, only the out of door photobioreactors are preferred. Certain important compounds are produced by employing photobioreactor Ex, B-carotena asthaxanthin.
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'Types of Photobioreactor'
The different type of photobioreactors are shown in fig. they are made up of glass or more commonly transparent plastic. The array of tubes or flat panels constitute light receiving systems (solar receivers). The culture can be circulated through pump or airlift pumps. It is essential that the cell are in continues circulation without forming sediments further adequate penetration of sunlight should be maintain. The tube should also be could to prevent rise in temperature. Photobioreactors are usually operated in a continuous mode at temperature in the range of 25-45 C. microalgae and cyanobacteria are normally used. The organisms grow during day light while the products are produce during nights.
Types Of Photobioreactor:
Photobioreactors are differentiated into two types:
- Open system
- Close system
Open system:- The first approach for the controlled production of phototrophic organisms was and still is a natural open pond or artificial raceway pond. There in, the culture suspension, which contain all necessary nutrients and carbon dioxide, is pumped around in a cycle, being directly illuminated from sun light via the liquid surface. This construction principle is the simplest way of production for phototrophic organism. But due to their death (upto 0.3m) and the related reduced average light supply, open systems only reach limited a real productivity rates.
In addition the consumption of energy is relatively high, as high amount of water containing low product concentration have to be processed. Open space is expensive in area with dense population, while water is rare in others. Using open technologies causes high losses of water due to the evaporation into the atmosphere.
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Closed system:- Since the 1950” s several approaches have been conducted to develop closed systems, which theoretically provide higher cell densities of phototrophic organisms and therefore the lower demand of water to be pumped than open systems. The addition, closed concentration avoids system- related water losses and the risk of contamination through landing water birds or dust is minimized. All modern photobioreactors have tried to balance between a thin layer of culture suspension, optimized light application, low pumping energy consumption, capital expenditure and microbial purity. Many different systems have been tested, but only a few approaches were able to perform at an industrial scale. Examples of the closed system photobioreactor which are redesigned laboratory fermenters, tubular photobioreactor, Christmas tree photobioreactor and horizontal photobioreactor.
