III. B.2.a. Hawaii ARPS Project Initiation, 1980-1981

As mentioned earlier, the concept for the ARPS project derived from the Raymond (1981) patent. The project was initiated in early 1980s, with construction of a single, 48-m2 raceway system completed in early 1981 (Laws 1981). During this first year, chemostat experiments using two strains of P. tricornutum were carried out. The tests revealed large differences in protein and lipid productivity between the strains. This laboratory work also investigated cell harvesting by “foam fractionation” in which the foam formed by the aeration of the cultures via air lift mixing was collected and found to contain some 10-40 times the cell concentration of the liquid. However, the harvesting efficiency was not reported.

One difficulty noted in the laboratory experiments was the low cell densities achieved, compared with the original reports by Raymond for the ARPS system. Researchers tried to increase cell density by increasing the pond depth to 0.6 m, rather than 0.1 m as proposed by Raymond (1979). This resulted in other problems (low cell density, shading-see below), and the depth was again reduced to 30 cm. The laboratory experiments were extrapolated to predict an outdoor productivity of almost 130 mt/ha/yr, at least for the best P. tricornutum strain, similar to the Raymond prediction. However, this extrapolation was based on the invalid assumption that such laboratory growth rates can be used to predict outdoor productivities.

The initial work also studied the effect of CuSO4 filters, concluding that although any productivity increases would be minor, installation of CuSO4 filters is advisable in the APRS, “as it would help manage overheating of the culture and store a potentially valuable by-product, heat.” Finally, the “flashing light” effect was investigated. The time constants (1 s light: 1 s dark), and low light intensities used were quite different from the classic flashing light effect of Kok (1953), which uses approx. 1-5 psec high intensity light flashes, followed by about five times longer dark periods. Only small, “not particularly encouraging”, productivity increases were noted. Still, a 70% increase in productivity was predicted, though the basis for this was not stated.

Laws (1981) also reported on initial results with the 48-m2, 0.6-m deep, airlift-mixed flume system. Cell densities were much lower than predicted, likely because of the great depth of the culture, which was later reduced. The report concluded that, assuming $30,000/ha/yr production cost, a biomass production of 180 mt/ha/yr AFDW would allow oil production (with protein byproducts) competitive with fossil fuel. However, this productivity figure was extrapolated from the indoor chemostat work, and increased by one-third, as “effects of modulated blue light on the system will allow the extra production to be achieved,” so the reliability of this prediction is questionable.