Initial Investigations of a Shallow-Layer Algal Production System

A system for the intensive cultivation of the marine diatom Phaeodactylum tricornutum is described and evaluated. Unique features of the system include: (a) the incorporation of solar heat collection device which transmits only photosynthetically active radiation (PAR) to the growing culture; (b) the formulation of a new seawater enrichment medium that promotes physiological responses not previously observed in culture; and (c) the use of a foam fractionation device which separates microalgae, from the culture media, adds CO₂-enriched air, and/or simultaneously recirculates the growing culture in shallow layers through an interconnecting series of hemicylindrical channels. The outdoor system demonstrated that very high ash-free dry weight yields of Phaeodactylum tricornutum are produced, a result of high photosynthetic efficiency. Actual yield over an eight-day period was equivalent to 39.57 ash-free dry tons/acre-year. Observed photosynthetic efficiency, based on photosynthetically active radiation incident upon the external surface of the system, is 13.1 percent, nearly three times the limit previously considered economically practical. The data indicate that greater yields may be expected using this system at locations receiveing higher insolation. A conservative projection is that 80 ash-free dry tons/acre-year will be realized in land regions receiveing 3 × 10¹⁰ Btu/acre-year total solar radiation. It is concluded that this system clearly warrants further investigation to determine its capacity to produce large and economical quantities of algal biomass for use as potential petroleum-fuel substitutes. The development of a comprehensive and systematic bio-engineering program is recommended to upgrade and evaluate the system to its full potential.