Development of a single phase nitrate feeding strategy for enhanced lipid productivity from green microalgae for biodiesel production

Biomass productivity and cellular lipid content are two major components that influence the ultimate lipid productivity from algal biomass. In this report, a nitrate feeding strategy was developed taking three green microalgae, Scenedesmus obliquus, Chlorella vulgaris, and C. minutissima, to achieve higher lipid productivity under single phase cultivation. Four different strategies, i.e. nitrate-sufficient, nitrate-deficient, biphasic nitrate-deficient and low-dose sequential nitrate feeding, were examined. The biphasic nitrate-deficient approach depicted the maximum lipid productivity. To bring this biphasic approach to a single phase, sequential limited nitrate feeding strategy was examined. This showed nitrate supplementation with a 1/100th dose of standard N 11 medium at an interval of 3 days resulted in a significant rise in lipid productivity. The biodiesel samples also demonstrated the predominance of saturated and monounsaturated fatty acid methyl esters. This study, therefore, suggests that with appropriate standardization, the usual biphasic approach can be brought down to a single phase, thereby reducing the overall cost of microalgal biomass production for biodiesel purpose. Moreover, this strategy is user-friendly, and would reduce the nitrate requirements for large-scale cultivation, thus, would result in cost-effective and eco-friendly biodiesel production from microalgae. (c) 2016 American Institute of Chemical Engineers Environ Prog, 36: 222-231, 2017