| Recently,the rapid development of industry has brought a lot of convenience to human activities.Also,it has brought many threats to human beings-energy crisis and environmental pollution.The amount of CO2 emitted from vehicle exhaust,industrial boilers,and flue gas gradually increases,even more,the concentration of carbon dioxide in the exhaust gas of the lime kiln is as high as 40%.With the signing of the UN Framework Convention on Climate Change,people are paying more and more attention to carbon emissions management.Microalgae can convert carbon dioxide into bio-energy through photosynthesis,alleviate the crisis of energy and greenhouse effect,have a good industrialization prospect.However,the current suspended culture has many disadvantages,such as low culture density,difficulty in biomass harvesting,and high cost,which restricts the industrial production of microalgae.In this paper,an attached microalgal culture system based on capillary effect was designed.Through the optimization of the carbon source supply scheme,ventilation scheme and cultivation parameters,the performance of the system is improved to achieve the dual goals of efficient microalgae biological carbon fixation and high-efficiency biofuel production.1)First,the absorption mechanism of inorganic carbon sources by microalgae cells in the attached system was explored.Chlamydomonas sp.JSC4 was selected in this study.In order to investigate the effect of various forms and concentrations of inorganic carbon for attached cells,the ratio of HCO3-and CO2 concentration in the culture was changed by adding NaHCO3.The experimental results showed that immobilized microalgae cells preferred to directly use CO2 in the air as the carbon source(biofilm yield is 20.25 g m-2 d-1),and adding 2 mM NaHCO3 could further promote the cellular carbohydrate content(38.70%),which was beneficial to increase the yield of biofuels such as bioethanol and butanol.2)Secondly,the mechanism of CO2 absorption by microalgae biofilms was analyzed.In this paper,5%CO2 was used as the research object.Through the combination of Computational Fluid Dynamics(CFD)simulation technology and microalgae culture experiments,a high-efficiency carbon fixation adsorption bioreactor ventilation program was obtained.The results showed that an efficient ventilation structure was selected(the air inlet was setted at the top of the reactor and the gas outlet was setted at the lower part of the reactor),and CO2 needed to be pre-wet before using.Under such conditions,the mass transfer of CO2 to microalgal biofilms was improved(31.80 g m-2 d-1).The CO2 fixation rate of the microalgal biomass was 65.70 g m-2 d-1 at the ventilation interval of 30/30(on/off)min.3)Then,in order to further improve the ability of immobilized microalgae to treat high-concentration CO2 gas,a high-concentration 40%CO2 gas was used.The experimental parameters of ventilation velocity and ventilation interval were simulated using CFD technology,and microalgae cultivation experiments were performed to verify the reliability of the simulation.The results showed that the inhibitory effect of high concentration of CO2 on microalgal cells was reduced by setting intermittent ventilation,and the productivity of microalgae biofilm was 39.37 g m'2 d-1 under a CO2 concentration range of 3-7%,the CO2 fixation was 92.14 g m'2 d'1.Immobilized microalgae can be directly used to treat high-concentration CO2 industrial waste gas by intermittent ventilation settings.4)Finally,the carbon fixation performance on different concentrations of CO2 and illumination strategy of microalgae were studied in this paper.The effects of CO2 concentration and light intensity on microalgal biomass productivity,carbon fixation,and biofuel production were studied.Under a culture condition of 5%CO2 concentration and 308 Lunol m-2 s-1 light intensity,the biofilm productivity was 66.8 g M"2 d*1,and the carbon fixation rate was 583.46 g m-2,the content of carbohydrate was 63.13%,which indicated that the algal cells was suitable for biofuel production. |
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