photobioreactor

thumb|Moss bioreactor|Moss photobioreactor to cultivate [[mosses like Physcomitrella patens at the laboratory scale]] A photobioreactor (PBR) refers to any cultivation system designed for growing photoautotrophic organisms using artificial light sources or solar light to facilitate photosynthesis. Photobioreactors are typically used to cultivate microalgae, cyanobacteria, and some mosses. Photobioreactors can be open systems, such as raceway ponds, which rely upon natural sources of light and carbon dioxide. Closed photobioreactors are flexible systems that can be controlled to the physiological requirements of the cultured organism, resulting in optimal growth rates and purity levels. Photobioreactors are typically used for the cultivation of bioactive compounds for biofuels, pharmaceuticals, and other industrial uses.

==Open systems== thumb|Open raceway pondThe first approach for the controlled production of phototrophic organisms was a natural open pond or artificial raceway pond. Therein, the culture suspension, which contains all necessary nutrients and carbon dioxide, is pumped around in a cycle, being directly illuminated from sunlight via the liquid's surface. Raceway ponds are still commonly used in industry due to their low operational cost in comparison to closed photobioreactors. However, they offer an insufficient control of reaction conditions due to their reliance on environmental light supply and carbon dioxide, as well as possible contamination from other microorganisms. Using open technologies also result in losses of water due to evaporation into the atmosphere.