Photobioreactor

• 2.1 Converted laboratory fermenter
• 2.2 tubular photobioreactors
• 2.3 Tannenbaum photobioreactor
• 2.4 plate photobioreactors
• 2.5 films photobioreactors

Photobioreactor generally

A bioreactor is a plant for the production of micro-organisms outside of their natural and artificial within a technical environment. The prefix "photo" describes the property of the bioreactor for the cultivation of phototrophic, that is light for its own energy -using organisms to serve. These organisms use the process of photosynthesis, to build their own biomass from light and CO2. These organisms include plants, mosses, macroalgae, microalgae, cyanobacteria and purple bacteria. The core objective of a photobioreactor is the controlled provision of a habitat that offers the optimum conditions for the respective organism. This allows a photobioreactor significantly higher growth rates and purities, as would be the case in a natural or nature- like environment. Basically, biomass can be produced from waste water and nährsalzhaltigen kohlenstoffdioxidhaltigen exhaust gases in photobioreactors.

Open versus closed systems

The first approach to the controlled breeding of phototrophic organisms were and are open ponds or pools, also known as open ponds or raceway ponds. It is the culture suspension, the liquid that contains all the necessary nutrients for the respective organism and CO2, promoted in a circle and lit on the open surface directly from the sun. This design is the easiest way to breed phototrophic organisms, but achieved because of the up to 30 cm deep pool and the resulting low average light entry only small area-based growth rates. In addition, the cost of pumping energy is relatively high, as much water must be pumped with low product concentration.

In areas of the world where many people live, land is expensive; elsewhere, water is a scarce resource, which is discharged and released to the atmosphere in an open design. For these reasons, attempts have been made since the 1950s to develop closed systems in which the phototrophic organisms are grown to higher biomass densities and thus less water needs to be pumped. In addition, it comes with a closed design to any system-related water losses and the risk of contamination by agricultural water birds or dust entry is minimized.

Photobioreactor types

All modern photobioreactors in common is that the development is a balancing act between small layer thickness, optimum use of natural light, low pumping effort, low investment and microbial purity. This has led to multiple approaches, of which only a few systems were able to maintain currently on the market.

Converted laboratory fermenter

The simplest approach consists in the conversion of classic glass fermenters as they come in the biotechnology laboratory scale for use in many cases. An example of this is the Moss - reactor in which a maladjusted glass vessel from the outside is supplied with light. About the existing lid holes, the process values ​​are monitored and made ​​of gas exchange. This type is quite common to find on a laboratory scale, made ​​the leap to production scale because of the limit container size failed.

Tubular photobioreactors

A principle that has made the leap into the production scale, constructed from pipes systems. In this case, glass or plastic pipes constructed in horizontal or vertical orientation and powered by a central unit with pump, sensors and nutrients or CO2. Systems based on this principle have been established world of laboratory sizes up to production scale and are for example for the production of the carotenoid astaxanthin from the green alga Haematococcus pluvialis or the manufacture of food supplements from the green alga Chlorella vulgaris used. Benefits of the systems are of high purity and good productivity in the system. Production can take place at a high level of quality and high dry matter contents at the end of the production enable energy- efficient processing. The relatively high price of equipment has a negative impact on a wide use of biomass thus produced. Economically viable concepts found only in high- price products in food supplements and cosmetics.

The advantage of the tubular reactors is used in addition to the large-scale production of biomass in small scale. In a combination of the above glass container with a thin coil can also be a laboratory scale relevant amount of biomass produce the regulated via a complex control unit grows under highly controlled conditions.

Tannenbaum photobioreactor

An alternative approach describes the development of a photobioreactor similar to the construction of a pine tree due to its truncated conical geometry and the attached helically, transparent double circuit mimics and their properties. The reactor system is modular and can thus be scaled in the out -door use on agricultural standards. The choice of location is not critical because of the closed design as with other tube photobioreactors; therefore can be used in principle, not agricultural land. A special material is intended to minimize in this reactor, the Biobelagbildung in the cultivation of micro-algae, and thus reaching a high final concentration of biomass. A contamination- free operation would be achieved with high plant availability in combination with turbulence and the design as a closed system.

Plate photobioreactors

Another approach to development is the construction of plastic or glass plates. Here, differently shaped plates are arranged such that between them a thin layer of culture suspension of the organisms is a good light source. In addition, by here compared to tubular reactors simpler design, the use of low-cost plastic is possible. Were implemented, meanwhile, meandering flow-through or fumigated bottom plates that have convinced even with good productivity. Unresolved challenges exist about the durability of the material or in the formation of Immobililsierungen. The large-scale use is further hampered by the limited scalability of the systems.

Currently goes to the IBA in Hamburg from April 2013 with a house built into the facade glass plates as photobioreactors in operation.

Films photobioreactors

In the course of price reduction of photobioreactors, various systems have been designed from films. Favorable PVC or PE films are suspended so that you a culture suspension can be captured and held. Priced put these technologies standards, but it is the reactors are unsustainable disposable. It must also be reckoned with increased investment needs through necessary support systems.

Perspectives of the photobioreactor development

In the course of discussion on the CO2 sequestration using microalgae or their use as a biofuel source a great development pressure is created on the manufacturers of photobioreactors. None of the aforementioned systems is to produce up today capable of phototrophic biomass grown at a price level that can compete with fossil oil. New developments are for example in the direction of drip method, in which ultra-thin layers should lead with the use of exhaust gas and waste water to maximum growth. Worldwide research is also very hard on genetically modified microalgae. Whether rising oil prices will lead to a breakthrough remains to be seen.