Two strains of Chlorella vulgaris Beijerinck isolated from two different sites in Laguna de Bay, Philippines, were studied for their resistance and ability to remove four metal ions, i.e., Cu 2+ , Cr 6+ , Pb 2+ , and Cd 2+ added separately in BG-11 growth medium. The growth of the two strains was severely inhibited at 2 mg.l −1 of Cu 2+ , 5 mg.l −1 of Cr 6+ , 8 mg.l −1 of Pb 2+ , and 10 mg.l −1 of Cd 2+ . However, the two strains exhibited different EC 50 values for the same metal ion. The WB strain had a significantly higher resistance (p<0.01) for Cd 2+ and Cr 6+ compared with the SB strain, while the SB strain had significantly higher resistance (p<0.01) for Cu 2+ compared with the WB strain. On the other hand, the two strains behaved differently in their capacity to remove the metal ions in BG-11 medium containing 1.0 mg.L −1 of the three metal ions, except for Cu 2+ , which was added at 0.1 mg.L −1 . The WB strain showed the highest removal of Cd 2+ at 70.3% of total, followed by Pb 2+ at 32%, while the SB strain exhibited the highest removal of Pb 2+ at 48.7% followed by Cd 2+ at 40.7% of the total. Both strains showed the least removal of Cr 6+ at 28% and 20.8% of the total for the WB and SB strains respectively. The percentage removal for Cu 2+ was 50.7% and 60.8% for the WB and SB strains respectively. After 12 days of incubation, both strains showed that a greater percentage of the metal ions removed were accumulated intracellularly than adsorbed at a ratio of at least 2:1. Both strains manifested the same cytological deformities, like a loss of pyrenoids at 10 mg.L −1 in all four metal ions. Discoloration and disintegration of chloroplasts were observed at 1.0 mg.L −1 in Cu 2+ and 5 mg.L −1 in Cr 6+ . The nonrelease of autospores from the mother cells was observed at 10 mg.L −1 in Cu 2+ and Cr 6+ .

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Two pilot-scale open raceway pond systems were designed and fabricated in the University of the Philippines Los Baños (UPLB) for the cultivation of Chlorella vulgaris Beijerinck to observe the biomass productivity of the alga in an open condition in the Philippines. One design was an oval track with a middle island, while the other was a multi-stage raceway pond (MSRP) consisted of several sections separated by baffles. The pond designs aimed to accommodate 1,000 L of culture. The nutrient media used was composed of urea, NPK (16-20-0), FeCl3, and Na2EDTA – a locally formulated medium that sustains the growth of the species. Paddlewheel was installed to provide mixing, which was turned on during the daytime, while aeration was continuously supplied through perforated air-distributor PVC pipes installed on the pond floor. Only natural light was utilized, and no lighting was provided during the night. The growth rate was generated by monitoring the biomass concentration in the pond through spectrophotometry at 425 nm, where optical density and biomass concentration relationship was initially established. Using the equation for first-order kinetics and taking the points from the exponential phase, the specific growth rate of Chlorella obtained from the oval raceway pond was computed to be 0.007308 h–1 with doubling time of 94.84 h. The biomass productivity rate was computed to be 308.49 g/m3-d or equivalent to 63.24 g/m2-d. On the other hand, the MSRP obtained a specific growth rate of 0.003389 h–1 with a doubling time of 204.55 h and equivalent biomass productivity of 302.19 g/m3-d or 60.44 g/m2-d. The biomass productivity obtained is comparable, even superior to other commercial open pond cultivation using C. vulgaris.