Study On The Influnce Of Light And Gas Flow Rate On Microalgae Of CO₂-Fixation Cultivation In High Density

With rapid development of the global economy and social advancement, thedemand of fossil fuel has been increasingly growing, which had brought about theincrease of CO₂concentration in the air. Consequently, a series of environmentalproblems has appeared which seriously affected production and life of human beings.So, controlling the CO₂emission is of great significance. CO₂-fixation by microalgaephotosynthesis is a economical and effective technique. We must culture the microalgaein high density whicn can fix CO₂in high concentration in order that we can use thistechnique widely in practical production. So we should optimizate cultivationconditions of microalge. For that reason, this paper studyed the mathematical model oflight intensity attenuation in culture solution and optimizated the conditions of light andgas flow rate in the culture of Chlorella sp. strain XⅠ and strain XⅡ.1. Taking daylight lamp as light source, setting the initial light intensity,determined the changement of light intensity with depth of culture solution underdifferent cell concentration. Through analysising the data we got results as follows. Thelight intensity will decrease under exponential law with depth of solution increasing inthe culture solution of strain XⅠ and strain XⅡ when cell concentration is constant.But the light intensity decrease more slowly with the increase of cell concetration andlenth of optical path in the culture solution of strain XⅡthan that in the culture solutionof strain XⅠ.2. L representing lenth of optical path, absorbency OD representing cellconcentration, E0representing initial light intensity and E representing the light intensityunder certain lenth of optical path, through regressive analysis of light intensityattenuation data, the equation of light intensity attenuation about strain XⅠ and strainXⅡ was obtained.ln（E0/E）=（0.4280OD－0.0035）L+1.0344OD－0.0399ln（E0/E）=（0.2746OD－0.0315）L+1.0855OD－0.4430The equation fitted to the data well through examination. According to the equation, wecan adjust light intensity with culture process so that the cell will receive sufficientlight. 3. The comparative test between variable lighting and constant lighting underdaylight lamp showed: For strain XⅠ, variable lighting was better for its growth thanconstant lighting in the tapered bottle, the flat plate reactor and the column typereactor, so variable lighting should be used. For strain XⅡ, variable lighting didn’tmake it grow better in the tapered bottle and the flat plate reactor so constant lightingshould be used, and variable lighting was better than constant lighting in the columntype reactor so we should choose variable lighting. Increasing light intensity graduallyaccording to culture time will abate light intensity attenuation in culture solution of highcell concentration. So the cell will receive sufficient light, which promote themicroalgae cultivation in high density.4. The comparative test between three LED monochromatic lighting and daylightlighting showed that LED blue light was best for cultivation of strain XⅠ and strainXⅡ. The experiment results also indicated that it could improve utilization ratio ofspectrum, enhance photosynthesis and promote the growth of microalgae to use LEDmonochromatic light corresponding to absorption peak wavelength of microalgae. AndLED light has energy saving property and low light intensity attenuation, which make itmuch better than daylight lamp.5. The experiment of optimizing gas flow rate condition under daylight lampshowed: Optimum constant gas flow rates of strain XⅠ were1.6L/min in the flat platereactor and1.8L/min in the column type reactor. Optimum constant gas flow rates ofstrain XⅡ were1.2L/min in the flat plate reactor and1.4L/min in the column typereactor. The control mode of gas flow rate should be constant flow rate when strain XⅠand strain XⅡ are cultured in the flat plate reactor. The control mode of gas flow rateshould be variable flow rate when strain XⅠ and strain XⅡ are cultured in the columntype reactor. It can promote the growth of microalgae to improve the gas flow rateappropriatly with cell concentration increasing in the culture process and high cellconcentration will be reached.