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Open Pond Systems
Open pond systems are the most common system of algae cultivation, already used commercially in the United States to produce nutritional products and treat wastewater. In recent years many companies have begun focusing on this growth model for biofuels and chemicals. In fact, open ponds were the focus of the Department of Energy’s Aquatic Species Program in the 1980s and 1990s.
Open pond systems use shallow (typically one-foot deep) ponds, from about one acre to several acres in size, in which the algae are exposed to natural solar radiation (sunlight) which they convert into biomass. Typically the ponds are called raceway ponds because their shape resembles a race track. They often use paddle wheels or other water moving devices to keep the algae circulating.
The harvesting method is often a two stage process based on the particular properties of the algae and requirements of the process. A fraction of the pond water is generally harvested every day, and the algal biomass within the water is concentrated. The biomass is then processed further, for example to extract the oil for to conversion into biodiesel, jet fuel, or some other oil-based product. The residues, or even the entire biomass, can also be dried and used for animal feeds.
Open pond systems for the production of biofuels are already under development. For example, Sapphire Energy is developing a commercial-scale open pond production facility in southern New Mexico and is aiming to produce millions of gallons of fuel annually by 2017.
UCSD’s Dr. Mitchell gives a lesson in algae 101
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