Effects of temperature and time on oil extraction from some Nigerian indigenous fresh water microalgae species

Abstract

This study determined the effects of temperature and time on oil extraction from indigenous freshwater microalgae– Dictyosphaerium, Chlorella, Desmodesmus and Cosmarium species, cultured in fifteen 2-litre column photobioreactors (PBR) (three per specie).  Growth and specific growth rates for the mixotrophic>autotrophic cultivation of the species. Oil was extracted from the dried microalgae species at temperatures ranging from 40 to 120 °C at 20 ^oC intervals and times ranging from 30 to 210 minutes at 30 minutes’ intervals, by accelerated solvent extraction method. Extraction temperature, time and type of microalgae species had significant effect (p < 0.05) on oil yield (temperature > time > type of species).  As extraction temperature and time increased, Desmodesmus armatus gave the optimum oil yield (72.6% at 92.5 ^oC), whereas, Cosmarium spp. produced the least (45.5% at 91.7 ^oC). Optimal oil yield and temperatures of Desmodesmus subspicatus, Chlorella lewinii and Dictyosphaerium spp. were  68.2% and 92.5 ^oC; 72.3% and 91.9 ^oC; and 66.7% and 92.5 ^oC respectively. The optimization result showed that oil extraction from microalgae should be conducted at about 80 ^oC and at the first 30 minutes of heating for oil extraction. These findings reduce extraction wastages of time, cost, energy, resources and chemicals.