Bioethanol Production from Green Alga Chlorella Vulgaris Under Different Concentrations of Nitrogen

Ethanol fuel or ethyl alcohol is an alternative to gasoline; it can be used as additive to gasoline, and also as a feed chemical in the transesterification process for biodiesel. A number of bio feed stocks are currently being experimented for biofuel production; algae have emerged as one of the most promising sources for biofuel production. The locally isolated microalga chlorella vulgaris was used in the current study to test their ability to production bioethanol through stimulated in different nitrogen concentration treatments (0, 4, 8, 12 g/l), and effect of nitrogen concentrations on the content of primary products (carbohydrate and protein), also the yield of bioethanol. The growth curves of C. vulgaris were different among the treatments. The stationary phase was identified as day 5, 9, 12 and 14 in treatments 0, 4, 8 and 12 g/l nitrogen respectively. The growth rate (K) increased from 0.14 to 0.20 for the treatments 8 g/l and 0 g/l respectively. The shortest doubling time (G) was 1.4 days in treatments 0 g/l while the longest was 3.0 days in 12 g/l. The carbohydrate content for C. vulgaris increased from 17.35% at 8g/l (control) to 24.60% at 4g/l treatment and 32.75% at 0g/l treatment of dry weight. While, the carbohydrate content decreased from 17.35% at control to 14.11% at 12g/l treatment. The protein content was decreased sharply when nitrogen concentrations decrease. It is recorded 51.17% at 8g/l (control), 33.60% at 4g/l treatment and 15.07% at 0g/l treatment. While, it is increased in treatment 12g/l in contrast with control treatment. The highest bioethanol yields of 27.08% and 24.09% were obtained in treatments 0g/l and 4g/l respectively compare with control which gave 17.34% ethanol. While, the lower bioethanol yields was recorded in treatment 12g/l which gave 14.87% in contrast with control. The highest carbohydrate content and bioethanol yield were obtained under nitrogen starvation, but the protein content recorded the lowest content under nitrogen starvation.