In the mid-1980s an algal mass culture project for biodiesel production was supported by the ASP in Israel (Arad 1984, 1985, 1986), as a cooperative project among the following groups:

1. Israel Oceanographic and Limnological Research Institute, with Dr. Ben-Amotz, who investigated lipid production at the laboratory and micropond scale;

2. Ben-Gurion University of the Negev, with Professor A. Richmond as Principal Investigator, investigating algal mass cultures with outdoor ponds, essentially of the HRP design.

3. Technion University, with Professor Gedaliah Shelef in charge of developing suitable microalgae harvesting technology.

During the first 2 years of the project Ben-Amotz (1984, 1985) screened laboratory cultures of unicellular algae isolated in Israel and elsewhere. Of a score of strains tested, Nanochloropsis salina and B. braunii were the highest lipid producers, with lipid content as high as 50% in semi­continuous nitrate-limited cultures. Other strains had lipid contents <20%. Lipid composition and chemical characteristics (e. g., hydrocarbon contents) were also determined for many cultures. Nannochloropsis sp., P. tricornutum and C. gracilis were studied in more detail in 0.5- Liter, pH-controlled chemostats for effects of temperature, light intensities, nutrients (Fe and nitrate), salinity and other parameters. The author concluded that “nitrogen limitation does not induce the production and accumulation of lipids,” but the “algae attain a low protein-carbohydrate ratio.” Previous reports in the literature describing lipid accumulation in algae induced by N limitation were attributed to trace element limitations. Actually, the data is typical of chemostat results, in which growth rate imposed by culture dilution do not allow lipid induction as is observed in batch or semi-continous cultures.

During the final year of this project, Ben-Amotz (1986), optimized the growth of two cultures, C. gracilis and Nannochloris atomus in laboratory chemostats and in 0.35-m2 outdoor “microponds.” The ponds were mixed by air sparging, which would reduce pO2 levels. Maximal productivities of 40 g/m2/d were obtained with C. gracilis during June-August, and highest photosynthetic efficiency (9.5% PAR) was achieved in the fall (when productivity was 27.3 g/m2/d, AFDW). During the winter, productivity decreased by about half, but lipid contents in the N-sufficient algal cells increased almost as much, reproducing the low-temperature effect on lipid content seen in the laboratory cultures. Attempts were also made to increase lipid production by Si limitation, but this was unsuccessful due to rapid contamination with green algae.

The work by Professor Richmond and colleagues (1984; Boussiba et al. 1985, 1986), started with laboratory growth and lipid content experiments with more than a dozen algal strains. Outdoor cultivation was carried out for 2 years with small (2.5-m2, 12-cm deep) paddle wheel-mixed high rate ponds. Among other factors, the effects of culture density on productivity and lipid content

were studied, with the expected result that maximal productivity depended on the culture density (actually, on the areal concentration), but that this does not have major effects on lipid content. At the optimal density of 350 mg/L (45 g/m2), productivity in the summer was 24.5 g/m2/d and lipid content about 16% for N. salina, and somewhat higher (28.1 g/m2/d and 22 %) for Isochrysis galbana (both SERI Culture Collection strains). However, experiments with varying pond depths but constant areal biomass densities resulted in productivity differences of up to twofold, contrary to theory and expectations. Other factors (pO2, etc.) likely accounted for this. However, mixing speed had no significant effect on productivity. The authors stated: “These data reflect the complexity of the process of optimizing outdoor biomass production….”

Professor Shelef (1984a, b; Shelef et al. 1985) carried out experimental and engineering studies of algal harvesting. The major effort was on the use of chemical flocculants for affecting algal sedimentation. Much of the work focused on I. galbana, grown, as above, on seawater of various concentrations. As expected, the higher the ionic strength (salinity), the greater amounts of chemical flocculants (alum, ferric chloride, chitosan) were required to induce algal flocculation. Autoflocculation, achieved by interrupting the CO2 supply, was also very effective. Other processes investigated were sand bed filtration, microstrainers (a 21 pm polyester weave allowed some 80%-90 % harvest efficiency), dissolved air flotation (after chemical flocculation, the method of choice for most commercial installations), and again, chemical “enforced” flocculation (recycling some of the precipitate to reduce flocculant needs). An economic analysis suggested various “allowable” flocculant costs for assumed biomass values. Overall, however, chemical flocculants are too expensive for biodiesel production.

During the final year of this project, a 100-m2 pond was operated with I. galbana for 1 month (Arad 1986). In batch culture it took 12 days for the culture to enter stationary phase, and a productivity of 23.6 g/m2/d was measured for about 2 weeks after starting dilutions. The culture was harvested with FeCl3 and alum using a dissolved air flotation unit from Technion. The flocculated algae had rather low lipid contents, compared to centrifuged algae. In conclusion, the Israeli project provided another dimension to the ASP effort, generally supporting the conclusions and results obtained by the U. S. work.