The enhanced lipid productivity of Chlorella minutissima and Chlorella pyrenoidosa by carbon coupling nitrogen manipulation for biodiesel production

Biodiesel production from microalgae has been researched extensively and attempted to commercialize on a large scale, but there are major hurdles in the production process like harvesting and low lipid content, which should be studied to enhance the process and make it economical. Present study aimed to improve the lipid productivity of Chlorella minutissima and Chlorella pyrenoidosa by modifying the carbon and nitrogen content of the medium. Both organisms were grown in BG11 medium for the first 6 days and thereafter grown in a modified BG11 medium completely deprived of nitrogen for 2 to 10 days. Nitrogen deprivation increased the lipid productivity of Chlorella minutissima to 20% and that of Chlorella pyrenoidosa to 17.6% by day 6. This was further coupled with carbon addition in the form of citric acid (5 g/L), sodium acetate (5 g/L), sodium carbonate (5 g/L), and sodium potassium tartarate (5 g/L), which increased the total lipid productivity of Chlorella minutissima up to 24% and that of Chlorella pyrenoidosa up to 23%. The highest lipid productivity of up to 24% for Chlorella minutissima and up to 23% for Chlorella pyrenoidosa was observed with nitrogen deprivation coupled with sodium acetate. Acidic transesterification revealed the presence of fatty acid methyl esters, majority of which consisted of hexadecanoic acid methyl ester and octadecanoic acid methyl ester. Maximum of 3% fatty acid methyl esters for Chlorella minutissima and 4% for Chlorella pyrenoidosa were obtained under nitrogen deprivation and sodium acetate as a carbon source. Thus, nitrogen deprivation coupled with sodium acetate as an increased carbon source in BG11 medium helps to increase the lipid productivity of Chlorella minutissima and Chlorella pyrenoidosa, and produces long-chain fatty acid methyl esters of C17 and C19 along with C21, C25, and C29.