The Cultivation And Lipids Characteristics Of Scenedesmus Dimorphus In Photobioreactor

In recent years, the worldwide energy shortage and environmental problems become increasingly serious, and looking for a renewable alternative energy is imminent. Some microalgae could use inorganic or organic carbon for the accumulation of biomass as a raw material of the biodiesel production. The process has been considered a viable technology because of sustainability and environmental friendliness. This research investigated the growth and lipids characteristics of Scenedesmus dimorphus under different CO₂ concentrations, the conditions of autotrophic and mixotrophic mode using the nitrogen sufficient and nitrogen deficient two period's cultivation method, the condition provided by secondary effluent, in a 2L bubbling column photobioreactor. Furthermore, the energy evaluation and conditions improvement when continuously cultured using secondary effluent was study in a 100L photobioreactor. Main results of this dissertation were shown as follows:(1) S.dimorphus could grow at 10%-20% CO₂ and the highest biomass was observed under 10% CO₂ concentration. The maximum biomass concentration, CO₂ biofixation rate and lipids content were 1.950 g/L, 0.224 g/L and 35.90 %, respectively. The dominant fatty acids of the microalgae were C16–C18 under different CO₂ levels. 10% CO₂ concentration was favorable for the accumulation of total fatty acids and polyunsaturated fatty acids. The lipids content of S.dimorphus at stationary phase was higher than that at logarithmic phase under the same CO₂ level. Consequently, S. dimorphus was a potential microalgal for both CO₂ mitigation from the ?ue gases and biodiesel production.(2) S.dimorphus grew well in mixotrophic mode. Under the condition of BG11+5.4 g/L Glu, S.dimorphus got the maximum biomass concentration and lipids content with the value of 4.5g/L and 29.62%, respectively, which were 2.57 times and 1.51 times of those in autotrophic culture. Both in autotrophic and mixotrophic mode, the biomass concentration and lipids content in the nitrogen sufficient period were higher than those in nitrogen deficient period. The dominant fatty acids were still C16–C18. So the mixotrophic mode and two period's cultivation method could improve the growth and lipids accumulation of S.dimorphus. Under the mixotrophic mode, the concentration of glucose increased from 1.2 g/L to 5.4 g/L, the biomass concentration improved 1.25 times, and the utilization of glucose were more than 80%. Both indicated that the S.dimorphus had great potential in using glucose for biomass production and appropriate improvement of glucose concentration could accelerate the growth of microalgae S.dimorphus.(3) When cultured in secondary effluent, the maximum biomass concentration of S.dimorphus was 244 mg/L and 174 mg/L with batch and continuous operation, respectively. Besides, in batch cultivation, the lipids content was 26.06% and the main fatty acids were C16-C18. The nitrogen and phosphorus level in the discharge water reached the national level A emission standard. All the results evidenced that S. dimorphus was feasible in the technology coupled the advanced treatment of wastewater and microalgal biomass production.(4) When cultured by continuous operation, UV-sterilization or addition of nutrients could improve the maximum microalgal biomass concentration, and the promoting effect was more obvious when adding nutrients. When combining both the treatments, the promotion of biomass accumulation is the best. The energy evaluation when continuously cultured in secondary effluent was done and the NER was 1.76×10^-4. The cost should be reduced by using sunlight as light source or adding a biorefinery strategy, the resulting NER would be even higher simultaneously.