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Abstract The aim of this study is to isolate microalgae strains with high lipid productivity from natural water area, and to optimize the fermentation conditions which is the basis for industrial production of biodiesel. Seventeen microalgaes were isolated and cultivated from a variety of fresh habitats, then identified according to their morphological characteristics. A comparison study was made among 11 species based on biomass, lipid content and lipid productivity. Three strains Scenedesmus ovalternus, Chlorella pyrenoidosa and Chlamydomonas reinhardii with highest biomass and lipid content were selected to study the optimal growth conditions including light, pH, temperature, carbon, nitrogen, and combinations of different levels of carbon and nitrogen sources. Our data suggested the three microalgaes grow faster and at the same time had higher lipid productivity when cultured with adding glucose in the dark. The optimal temperature for the three microalgaes was 28℃. The optimal pH for S. ovalternus and C. pyrenoidosa was 7.0, and for C. reinhardii was 9.0. Glucose and urea were the optimal carbon source and nitrogen source for the three algaes, respectively. Considering microalgal lipid productivity, the best carbon and nitrogen sources combinations for S. ovalternus were 30 g/L glucose and 2.1 g/L urea; for C. pyrenoidosa were 40 g/L glucose and 2.1 g/L urea; and for C. reinhardii were: 30 g/L glucose and 1.2 g/L urea. C. reinhardii and C. pyrenoidosa were tested for fermentation in 5-liter fermenter. Compared with the fermentation using shake flask, fermentation time reduced from 7 d to 5 d and cell density of C. reinhardii and C. pyrenoidosa achieved were 61.2 (OD540 nm) in 118 h and 59.86 (OD540 nm) after 5 days. Beside the two microalgae biomass of dry weight increased from 11.2 g/L and 8.8 g/L to 26.58 g/L and 20.19 g/L, respectively; lipid content from 20.3%and 17.2% to 23.2% and 20.1%, respectively; and lipid productivity from 0.3248 g/L/d and 0.2162 g/L/d to 1.2333 g/L/d and 0.8112 g/L/d, respectively. According to the results, through the optimization of fermentation conditions, the lipid productivity of microalgaes Y7, Y9, isolated and screened from natural waters, can reach 1.2333 g/L/d and 0.8112 g/L/d, which are expected to apply in the industrialization for biodiesel production.
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Received: 11 December 2009
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