Microalgal biodiesel production at outdoor open and polyhouse raceway pond cultivations: A case study with Scenedesmus accuminatus using low-cost farm fertilizer medium

Abstract

The present study has successfully cultivated a promising microalga Scenedesmus accuminatus at outdoor open and polyhouse raceway ponds using low-cost farm fertilizer medium. The tested microalga was cultivated in both ambient and polyhouse conditions for summer, rainy and winter seasons. Diurnal variation in temperature (26–39 °C), humidity (57–90%), solar intensity (ambient: 44–65, polyhouse: 28–41 k lux), pH of culture suspension (6.5–10.6), and dissolved oxygen (5.5–13.1) were recorded throughout the seasons. Further, of the various culture depth and impeller speed tested, S. accuminatus was found to yield high biomass of 1.2 g L−1 and 1.11 g L−1 under ambient and polyhouse conditions, respectively at 30 cm depth with 65 rpm impeller speed. Keeping this optimal culture depth and impeller speed, the tested microalga was grown in open pond and polyhouse consecutively for two years. Under polyhouse raceway pond, the areal biomass productivity during summer, rainy and winter seasons was estimated to be 10.15, 7.83, 10.38 g m−2 day−1 respectively and correspondingly, the areal lipid productivity was estimated to be 1.05, 0.75, 1.18 g m−2 day−1 respectively. On the other hand, at ambient condition, the areal lipid productivity during summer, rainy and winter seasons was 1.19, 0.42, 1.30 g m−2 day−1 respectively. Thus, annual lipid productivity of S. accuminatus grown under ambient condition was estimated to be 3.094 ton hectare−1year-1, and 3.168 ton hectare−1year-1 under polyhouse raceway pond conditions. Notably, the estimated annual biodiesel yield 2.186 and 2.135 ton hectare−1 year−1 under polyhouse and ambient conditions respectively demonstrates Scenedesmus accuminatus is a potential choice for sustainable biodiesel production.