Open ponds

Open ponds, specifically mixed raceway ponds are much cheaper to build and operate, can be scaled up to several hectares for individual ponds and are the method of choice for commercial microalgae production.

However, such open ponds also suffer from various limitations, including more rapid (than closed systems) biological invasions by other algae, algae grazers, fungi and amoeba, etc., and temperature limitations in colder or hot humid climates.

The hydraulics (e.g. dispersion and mass transfer coefficients) of large ponds are also uncertain. Nevertheless, about 98% of commercial algae biomass production is currently with open ponds, even for high value nutritional products, which sell for prices over a hundred- and even a thousand-fold higher that allowable for biofuels.