Effect of selected herbicides on growth and hydrocarbon content of Botryococcus braunii (Race B)

The algae Botryococcus braunii, one of the potential renewable resources for production of liquid hydrocarbons, was used for testing the effect of selected herbicides on algal growth and hydrocarbon content. Twenty-two herbicides representing 14 modes of action were assayed. Accelerated solvent extraction (ASE) was used to extract hydrocarbon from algae and the results showed that ASE was an efficient method for algal hydrocarbon extraction at 50°C extraction temperature, 10.3MPa of pressure and 1 static cycle using n-hexane as extraction solvent. The photosystem II inhibitor diuron was the most toxic herbicide for algal growth, but hydrocarbon content increased from 34.9 to 42.4% of dry biomass in the presence of a 0.1mg/L concentration of diuron. The photosystem I inhibitor diquat was inhibitory to growth of B. braunii, but hydrocarbon content increased to 43.3% of dry biomass when treated with 5mg/L diquat. S-metalochlor, a mitosis inhibitor, reduced both algal growth and hydrocarbon content. Hydrocarbon content decreased to 16.4, 14.0 and 5.5% of dry biomass, respectively when treated with 0.1, 1, and 5mg/L S-metalochlor. The carotenoid biosynthesis inhibitor fluridone did not affect algal growth at 0.1mg/L, but decreased hydrocarbon content from 34.9 to 13.2%. The fatty acid and lipid biosynthesis inhibitor thiobencarb had no effect on algal growth or hydrocarbon content at 0.1mg/L, but it inhibited algal growth and decreased hydrocarbon content from 34.9 to 7.8% at 1mg/L. The oxidative phosphorylation uncoupler dinoterb at 0.1mg/L reduced algal biomass by 52.8% and decreased hydrocarbon content from 34.9 to 30.0%. The use of B. braunii as a source of fuel will undoubtedly require the use of an outdoor open pond system. These results will be useful for improving algal oil production while developing management systems to control invasive algal species in outdoor open pond systems ultimately keeping the oil producing algae pure.