Enhancement of Lipids Content in Chlorella sp. Under Phosphorus Limitation and Heavy Metal Addition for Biodiesel Production

Microalgae are photosynthetic microorganisms that could be used as potential microbial cell factories by directly converting CO2 into valuable bioproducts and biofuels. This study aims to improve the production of biofuel from the isolated green alga Chlorella sp., in terms of an increase in its lipid content and its conversion to fatty acid methyl esters (FAMEs) when the cells are grown under the influence of phosphorus (P) limitation and heavy metal addition. The results show that the highest content of lipids, at 68.9%, was achieved within one day under 0% P with a 17 µM cobalt addition. Moreover, supplementation with a low Pb concentration increased cell growth even under P limitation, but under this condition, its lipid content was decreased after seven days of growth. The lipids of Chlorella sp. were transesterified to produce FAMEs. The overall biodiesel properties of the obtained FAMEs were of acceptable quality according to the standards (ASTM and EN). Additionally, the energy conversion from light energy to lipids was shown to be in the range of 10–16% conversion efficiency within seven days. Hence, the physiological modification of Chlorella sp. culture by phosphorus limitation coupled with the addition of a low concentration of heavy metals enabled the improvement of lipid content, with the subsequent transesterification resulting in the production of biodiesel with acceptable quality.