owned by Earthrise Nutritionals (www.earthrise.com), is used to produce cyanobacterial biomass for food.
In raceways, any cooling is achieved only by evaporation. Temperature fluctuates within a diurnal cycle and seasonally. Evaporative water loss can be significant. Because of significant losses to atmosphere, raceways use carbon dioxide much less efficiently than photobioreactors. Productivity is affected by contamination with unwanted algae and microorganisms that feed on algae. The biomass concentration remains low because raceways are poorly mixed and cannot sustain an optically dark zone. Raceway ponds and other open culture systems for producing microalgae are further discussed by Terry and Raymond (1985). Production of microalgal biomass for making biodiesel
has been extensively evaluated in raceway ponds in studies sponsored by the United States Department of Energy (Sheehan et al., 1998). Raceways are perceived to be less expensive than photobioreactors, because they cost less to build and operate. Although raceways are low-cost, they have a low biomass productivity compared with photobioreactors.