Evaluation of microalga for biodiesel using lipid and fatty acid as a marker – A central composite design approach

•Present study compared green alga and cyanobacteria for high growth and lipid.•CCD reveals that the variables day 20 and pH 9 were significant for ample lipid.•Nitrogen deprived Chlorella cells at 27 °C shown high lipid and desired fatty acids.•FTIR and GC analysis of biodiesel conformed lipid conversion and revealed its suitability for fuel.

Present study used central composite design (CCD) to evaluate algal strains for biodiesel by optimizing their harvesting time and pH. As a preliminary step, green alga Chlorella vulgaris MCRC A0001 and two cyanobacteria Chroococcus turgidus MCRC A0002 and Spirulina platensis MCRC A0005 have been explored for growth in terms of cell number, protein, chlorophyll-a, dry weight and pH from every 5th day till 25th day of growth. Furthermore, no hitherto report on CCD approach to inspect the impact of harvesting period and pH on algal lipid content. As evident from CCD, seemly candidate C. vulgaris MCRC A0001 exhibited high lipid content of 0.22 g dry weight−1 on day 20 compared to other strains. Under nitrogen stimulus, C. vulgaris MCRC A0001 grown under 0 g nitrogen/L and 27 °C showed 1.39 gL−1 biomass which marginally equal to control, and a significant increase in total lipid about 26% which is 4% high over control forum. It is noteworthy that, high biomass coupled with high lipid content was observed in nitrogen deprived and limited cells of C. vulgaris MCRC A0001. Additionally, robust methyl ester yield at 0.69 g g−1 was observed in 1:9 ratio of lipid-methanol and 3% NaOH, and ester yield was confirmed by FTIR spectra and gas chromatogram. Besides, gas chromatographic analysis revealed an increase in C16:0–29.61%, C18:1–25.33%, C18:2–11.3% which are prerequisite for biodiesel production. Further, biodiesel was critically analyzed for Degree of unsaturation (DU-77.32) and Long chain saturation factor (LCSF-2.96) which accords the European standard.