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Photosynthesis and Bio-fuels
In the normal process of direct photosynthesis, plants and algae absorb light, water and carbon dioxide and then use chlorophyll to convert them into the fuel they use to survive. This fuel is called ATP; one of its ingredients is a ribose sugar. Algae can be used to produce bio-fuels such as bio-diesels, potentially at a yield of between 5,000 and 10,000 gallons per acre. By comparison, soy can produce only about 50 gallons per acre, so in theory algae could be an excellent source for bio-fuels. However, the costs of growing algae through direct photosynthesis can be prohibitive.
Costs of Direct Photosynthesis
Because algae can be grown in any water source exposed to light, it might seem that the production of bio-fuel from algae should be extremely inexpensive. However, less than a third of the weight of an algae cell is oil, and the remainder is protein and carbohydrates that have to be removed to extract the oil. Algae can be genetically engineered to produce a larger percentage of oil but at the cost of growing more slowly. Algae can be grown in any body of water, but it is difficult to keep other species from driving out the less-robust genetically-engineered algae used for bio-fuel. The algae can be grown in bio-reactors instead, but then there are costs associated with maintaining the bio-reactors and drying them out. Because of all these factors, algae-produced bio-fuel can cost as much as $32.81 per gallon.
Indirect Photosynthesis
Indirect photosynthesis is a process for getting around the costs associated with using direct photosynthesis to produce algae for bio-fuels. The process works by exposing a biomass feed mixture composed of ingredients, such as wood waste, starches and sugars, to light and carbon dioxide, then feeding the sugar-rich mixture to algae in a fermentation procedure. The algae are placed into kettles with the sugar mixture and locked away from light, so they don't engage in photosynthesis directly. Instead, they feed on the sugars as the mixture ferments. When the process is complete, the oil can be squeezed from the algae.
Solazyme
One company using the indirect photosynthesis process is Solazyme. Direct photosynthesis is used only for a few of Solazyme's higher-end products. For the company's bio-diesel, the indirect photosynthesis fermentation process is used instead. Although Solazyme claimed in 2009 that it could produce an affordable fuel within 36 months, the company was operating at a loss at the time of its initial public offering in 2011. It is still unclear whether or not indirect photosynthesis will produce an affordable bio-fuel.