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Common Challenges of Bioreactors
Bioreactors are containers with a life supporting environment within them, used to carry out biochemical reactions using living organisms or chemical derived from living organisms. Algal bioreactors are those based on photosynthesis utilizing green algae for various purposes such as biomass production, CO2 fixation, etc. It has attracted much of world’s attention due its capability of producing bio diesel and bio ethanol.

In the current scenario, where fuel prices are going up fast, bio diesel and bio ethanol are inviting more use as additives to fossil fuel or even as itself. These demand mass production of both the mentioned bio fuels. Here arise the challenges faced in setting up and maintenance of bioreactors. Right from the maintenance of the bioreactor environment which includes irradiance levels, CO2 concentration, pH, salinity, nutrient levels, O2 concentrations etc., to unresolved issues affecting the overall efficiency of the bioreactor. Efficiency is crucial for any bioreactor. Any critical change in the internal environment of a bioreactor will end up in its reduced efficiency.

Challenges related to a bioreactor start right from its construction and setting up. A location for it needs to be chosen wisely. In the construction and setting up of bioreactors, geographical factors play a vital role. Moisture of the selected area seems to be a challenging task, taking into account, the levels of optimum moisture needed. For example, the average moisture levels in northwest countries are much higher than the required optimum moisture levels of an algal bioreactor, whereas in dry desert zones it is way too low than the required. Any faults during the operational procedures hence may lead to serious drops in the efficiency of the bioreactor, or even total loss of the whole contents of the system in extreme cases. Problems related to sterilization could be pointed out here, in the case of complete loss of the bioreactor contents. Around 3-5% of bioreactors set up every year are being failures due to the problem of sterilization. Hence, an aseptic operation is strictly required for a bioreactor. Single use bioreactors gained much attraction from the fact that it skips dangers of sterilization problems. Single use bioreactors are made up of disposable bags rather than from glass or steel as in conventional bioreactors. The disposable bags used are sterilized, minimizing further sterilization requirements. Also when at a risk of breach of sterilization standards massive loss can be prevented. Single use bioreactors are said to heavily cut down costs of setting up a bioreactor. Cost of setting up a bioreactor is challenge faced while constructing one. Until now, the costs of mass production bioreactors meant for large scale production of those like bio fuels, are not at all as low as to extract all the positives of a bioreactor. Single use bioreactors may cut down the cost of setting up by around 60%, as its components are only disposable bags consisting of three layers. But maximum capacities of these single use bioreactors are only around 1000 liters, or up to highest of 2000 liters, which can’t be used when much higher capacities are needed. Also, the single use bioreactors show its disadvantage in the achievable oxygen transfer rate, which sets the advantage of costs upside down, and limiting the single use bioreactors to the pharmaceutical field mostly.

When the bioreactor is ready to start working, crucial challenges comes up. Most important aspect that needs to be taken care is the control of the biochemical reaction environment, which is the key factor that aids in the maximum productivity. Temperature is another major factor just like the moisture. Hence, for this purpose the heat load should be calculated, equating heat production rate, reactor liquid volume, specific growth rate, biomass concentration, and yield coefficient. Then heat transfer methods can be employed accordingly. Heat transfer can be done externally or internally. For large reactors internal methods should be used because only internal methods can soak up heat in larger quantities compared to external methods. While smaller reactors require only external cooling jackets and external cooling coils, which have got the advantage of being free from cleaning problems. Internal heat transfer methods are difficult to clean, and they are easily fouled by the cell growth on the surface. Another challenge to overcome is the gas transfer, which can be accomplished through agitation. Agitation can be caused by mechanical stirring or can be air driven agitation. Mechanical agitation is possible only for small reactors, viscous liquids or those with low heat reactions. Bioreactors and those with high reaction heat can depend only on air driven agitations. In the ongoing maintenance of a bioreactor the foam that accumulates at the top needs to be removed. Mechanical foam breakers or chemical anti foam agents are used to remove the foam and prevent foam formation respectively. In the case of aerobic bioreactors, providing adequate aeration is task that needs proper attention, otherwise seriously causing steep decline in productivity and efficiency of the bioreactor. Anaerobic bioreactors are devoid of this problem as its efficiency does not depend upon aeration. By obtaining the accurate leachate data, most of the key challenges in the internal environment control of a bioreactor can be accomplished. Also, when air inputs are given for aeration purposes in an aerobic bioreactor or for the agitation purposes for heavy mass and high reaction heat bioreactors, dry air inputs needed to be given. Then evaporation needs to be taken care of with appropriate methods.

Material used for the construction of the bioreactors is critical area of attention. Only material which is completely anti corrosive and could be used for construction is glass. But it can only be used for construction of small bioreactors. Larger bioreactors need metal itself for the construction purposes. On long term use of bioreactors, the main problem encountered is the corrosion of the metal area of the bioreactor. The metal parts will be in a hostile environment due to the varying pH levels and salinity of the contents in the bioreactor. The metal surfaces need to be coated with anti corrosive substances, for the prevention of damage caused by corrosion. For this purpose mostly iron mica containing anti corrosion solutions are used.

The all these issues need to be resolved to set up and run a bioreactor at its perfection. And, the extra researches in overcoming them are worth the effort because of the numerable applications of bioreactor, including those we are having now, and those we are looking to the future.
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