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Concept
Photobioreactor
Summary
A photobioreactor (PBR) refers to any cultivation system designed for growing photoautotrophic organisms using artificial light sources or solar light to facilitate photosynthesis. PBRs are typically used to cultivate microalgae, cyanobacteria, and some mosses. PBRs can be open systems, such as raceway ponds, which rely upon natural sources of light and carbon dioxide. Closed PBRs are flexible systems that can be controlled to the physiological requirements of the cultured organism, resulting in optimal growth rates and purity levels. PBRs are typically used for the cultivation of bioactive compounds for biofuels, pharmaceuticals, and other industrial uses.
The 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 PBRs. 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.
The construction of closed PBRs avoids system-related water losses and minimises contamination. Though closed systems have better productivity compared to open systems due to the advantages mentioned, they still need to be improved to make them suitable for production of low price commodities as cell density remains low due to several limiting factors. 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. However, light attenuation and increased carbon dioxide requirements with growth are the two most inevitable changes in phototrophic cultures that severely limits productivity of photobioreactors.
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Algae fuel
Algae fuel, algal biofuel, or algal oil is an alternative to liquid fossil fuels that uses algae as its source of energy-rich oils. Also, algae fuels are an alternative to commonly known biofuel sources, such as corn and sugarcane. When made from seaweed (macroalgae) it can be known as seaweed fuel or seaweed oil. In December 2022, ExxonMobil, the last large oil company to invest in algae biofuels, ended its research funding. In 1942 Harder and Von Witsch were the first to propose that microalgae be grown as a source of lipids for food or fuel.
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A bioreactor refers to any manufactured device or system that supports a biologically active environment. In one case, a bioreactor is a vessel in which a chemical process is carried out which involves organisms or biochemically active substances derived from such organisms. This process can either be aerobic or anaerobic. These bioreactors are commonly cylindrical, ranging in size from litres to cubic metres, and are often made of stainless steel. It may also refer to a device or system designed to grow cells or tissues in the context of cell culture.