| Microalgae is a high quality biodiesel feedstock,it has the advantages of high photosynthetic efficiency and high oil content,short culture period and less land occupation compared to the traditional oil crops.At present,the main system for microalgae cultivation is suspension culture.However,high cost of harvesting and low biomass productivity of suspension culture limit its use.While the microalgae biofilm culture system effectively overcomes the above problems.Therefore,in this study a novel biofilm cultivation system was developed,in which a membrane material separated gas phase from liquid phase,thus,the gas disturbance to biomass growth was avoided,and the adsorption capacity and biomass density of microalgae were improved.In this thesis,the effects of gas flow rate,carbon dioxide concentration and light intensity were investigated at aim to optimizing the operation conditions of this cultivation system.The effect of different gas velocity on the growth and metabolism of microalgae biofilm was studied.The results show that the biomass,chlorophyll a and chlorophyll b of microalgae increased first and then decreased with the increase of gas velocity.The highest biomass of 28.4 g/m2 was obtained at the gas velocity of 40 ml/min,the content of chlorophyll a and chlorophyll b reached the maximum value of 13.91 mg/g and 9.15 mg/g at the velocity of 60 ml/min.Also,the content of starch in algae cells was first decreased and then increased with gas velocity increase.Carotenoids,Protein and oil content change slightly,accounting for 0.00178-0.0028%,25.89-29.82% and 12.96-15.8% of the cell dry weight,respectively.The CO2 removal efficiency showed the highest value(62.4%)at the velocity of 20 ml/min.The effect of CO2 concentration on the growth and metabolism of microalgae biofilm was investigated,and it is found that the biomass,protein and lipid content of microalgae biofilm increased first and then decreased,and reached the maximum at 3% CO2 condition.The highest biomass yield of the mature algal biofilm was 29.02 g/m2,the content of protein and oil was highest,accounting for 27.85% and 15.8%,respectively.When the concentration of CO2 in the reactor was more than 1%,the content of chlorophyll a(22.11-24.56 mg/g)was higher than that of air group.Chlorophyll b content increased with the CO2 concentration,and the highest content was 16.25 mg/g at 10% CO2 concentration.The content of carotenoids kept relatively constant.The starch content decreased first and then increased with the increase of CO2 concentration.The lowest starch content(20.49%)was obtained at 3% CO2.In addition,the CO2 removal efficiency showed the highest value(52.5%)at the CO2 concentration of 3%.The effect of light intensity on the growth and metabolism of microalgae biofilm was investigated,and it is found that the biomass,carotenoids and lipid content of microalgae biofilm increased with the light intensity and reached the maximum at at light intensity of 230 ?mol·m-2·s-1.The highest biomass,the carotenoids content and the lipid content was 38.52 g/m2,3.6 mg/g and 31%,respectively.The content of chlorophyll a and chlorophyll b and starch content of microalgae increased first and then decreased with the increase of light intensity.The contents of chlorophyll a and chlorophyll b were up to the maximal value of 24.81 mg/g and 15.08 mg/g at the light intensity of 20 ?mol·m-2·s-1.The maximal content of starch was 39% at the light intensity of 30 ?mol·m-2·s-1.In addition,the content of protein changed slightly.The main fatty acids were C16:0,C16:1,C18:0,C18:1,C18:2 and C18:3,which comprising 30% saturated fatty acid and 60% unsaturated fatty acid.The experimental results show that the reasonable carbon source supplementation and illumination were essential for growth and oil production of microalgae,thus carbon and light energy should be reasonable use in the culture process of algae. |
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