The Study Of Influencing Factors On Lipid Accumulation And Carbon Fixation Of Chlorella Vulgaris

As the suitable feedstock for biodiesel production, microalgae can grow extremelyrapidly and are rich in oils. At the same time, there are many enormous andenvironmental benefits in the Micro-algae carbon fixation technology. Many researchersin the word focus on the application of microalgae fixed CO₂from flu-gas, wastewatertreatment and lipid products. This thesis has used single factor experiment method toinvestigate various environmental factors, on the growth of algae in BG11and realwastewater, including cultivation modes, CO₂injection, turbulence, lighting conditionand nutrients. This study also set up a continuous flow experiment to investigate lipidproducts coupled with wastewater treatment and flu gas emission.Firstly, the carbon fixation and lipid product lows of Chlorella vulgaris which wasstudied under different cultivation mode. Chlorella vulgaris exhibited the highestgrowth ratesunder mixotrophic and heterotrophic condition. The lipid production rate ofChlorella vulgaris under heterotrophic and mixotrophic condition were0.9times and1.6times more than that under phototrophic condition. CO₂fixed rate was0.63timesunder phototrophic condition than that under mixotrophic condition. COD removeal ratewas higher than90%under heterotrophic condition but just80%under mixotrophiccondition.Secondly, the carbon fixation and lipid products lows of Chlorella vulgaris wasstudied under different aeration conditions.1) The addition of CO₂in systemsignificantly increased the cell density and decreased lipid products. As the CO₂concentration increased CO₂fixation and COD removal rate was decreased. When CO₂concentration was5%, CO₂fixed rate were the biggest. COD in effluent was higher than65mg/L when CO₂was added.2) As the aeration rate was increased the cell density wasincreased and CO₂fixed rate was decreased, but lipid contents and has a reduction afteran amplify. When aeration rate was0.1L/min, Chlorella vulgaris has the slowest growth,the biggest CO₂average fixed rate and the smallest COD removal rate, which were0.32g/L,29.32%and57%. Chlorella vulgaris has a high lipid products when aerationbetween0.2L/min and0.6L/min.Thirdly, the carbon fixation and lipid products laws of Chlorella vulgaris wasstudied under different lighting conditions.1)8000lx was the most suitable lightintensity for Chlorella vulgaris growth, lipid accumulation and CO₂fixed. Underdifferent light intensity, COD removal rate could reach65%.2) With the increase of thetime of light, growth speeded and of Chlorella vulgaris. Lipid content was between11%and14%. When light time was16h, CO₂average fixed rate and COD removal rate werethe biggest, which were19.5%and86%, and COD of effluent was under50mg/L.Lastly, the carbon fixation and lipid products laws of Chlorella vulgaris was studied under different nutrient conditions.1) Algae cell density, lipid content and lipidproduction rate were the highest when cultivated in50%wastewater with50%tap-water, which were0.31g/L,16.02%and49.20mg/L. When cultivated in25%wastewater with75%tap-water, CO₂average fixed rate was the highest, which was15.44%. COD removal rate changed little.2) The addition of phosphorus in systemextend the logarithmic period. When TN/TP was6:1, algae cell density, lipidcontent,lipid production rate and CO₂average fixed rate were the biggest. With thereduction of proportion of nitrogen and phosphorus, COD removal rate was increased.3)Supplementary glucose could increase algae cell density and lipid content, but decreaseCO₂fixed rate. When COD/TN was230:1, lipid content was the highest, which was15.89%, and lipid production rate was180.35mg/L.The carbon fixation and lipid products laws of Chlorella vulgaris was studiedunder different pretreatment methods by using continuous flow. Chlorella growth andoil accumulation were well, but carbon fixed rate and wastewater treatment were poorwhen medium was sterilized. After the stage of operation, algae dry weight was1.23g/L,and lipid production rate was295.7mg/L when medium was sterilized, and the othergroup were1.08g/L and257.8mg/L. The effluent of system which was not sterilizedcould meet the first grade A standards of Discharge standard of pollutants formunicipal wastewater treatment plant. Chlorella vulgaris could accumulate lipidcultivated in wastewater which was not sterilized, and also could fix CO₂andwastewater treatment.