| Reduction of carbon dioxide(CO2)emission and its resource utilization have become a major issue to be solved urgently in the global industry and agriculture production.Biological carbon fixation based on photosynthesis is a key factor in the realization of carbon cycle in nature.Compared with crops,microalgae,as a unicellular and autotrophic organism,has a number of characters such as fast-growing and high carbon sequestration efficiency.Currently,they are being applied to fix CO2 form coal based flue gas for co-production of high value-added biomass products.However,high levels of CO2,NOx and SO2 in the flue gas always cause excessive acidification of the culture medium,leading to severe inhibition of microalgae growth.Therefore,Microalgae applied to fix CO2 in flue gas must have the strong ability to tolerate high acid and CO2.in the present study,we established the optimized test system of the simulated flue gas to evaluate the acid resistance and CO2 level of several commonly-used economic microalgae,aiming to identify the excellent microalgae strains that could be used to fix flue gas CO2.Meanwhile,the main factors affecting the acid resistance of microalgae was examined,followed by developing a simple and effective method to improve the acid resistance of microalgae based on resistance domestication.The main results were described as the followings:1.Analysis of absorption kinetics of simulated flue gas showed that the pH in medium solution would sharply decrease to pH 3 within two days,when treated by the simulated aeration condition(C02:15%;SO2:150 ppm;NO:300 ppm;nitrogen balance).Whereafter,the pH in medium solution was stabilized at 2.5-3.2.An industrial microalgae strain was obtained,which displayed strong resistance to acid and high level of CO2.The treatments with 10%CO2,20%CO2 and different initial pH in the medium were conducted to evaluate the tolerance to high acid and CO2 for a number of economic microalgae,including Chlorella,Scenedesmus obliquus,Haematococcus pluvialis,Phaeodactylum tricornutum Nannochloropsis oceanica,and Chlamydomonas reinhardtii.The strain of Scenedesmus obliquus showed the fastest growth rate the strongest tolerance to acid and the high concentration of CO2,indicating that this strain can be used as agood industrial microalgal strain for fixing CO2 from flue gas.In addition,the optimized test system of simulated flue gas was established using the Scenedesmus obliquus as a test strain.This system is used to investigate the stress tolerance,growth and production features of microalgae.3.The present study was conducted to establish a simple and effective method of microalgae domestication for enhancing the microalgae resistance against acid stress and their initial growth rate when inoculated into low-pH medium.The initial growth rate of the Scenedesmus is 0.253 g/d/L by the acid-domesticated and the UV-treated,which significantly higher than by acid domestication at pH 4.5(0.132 g/d/L)and 5-min induction at low-dose of UV radiation(0.092 g/d/L)in low-pH environment.The more remarkable effects were achieved by combining such acid domestication and UV induction.The domesticated seed algae could grow normally in the acidic environment of pH 3,whereas the non-domesticated microalgae growth was seriously inhibited.The initial growth rate of the domesticated seed algae was 6.6 times higher than that of the non-domesticated microalgae in low-pH environment.The results showed that acid domestication and UV induction could significantly improve Scenedesmus tolerance against low-pH environment.4.Adding gibberellin accelerates the growth of Scenedesmus and ablity of acid resistance under acidification culture medium,In the initial pH 3.0 medium conditions,Scenedesmus was the fastest growing algal strain and showed the strongest acid resistance ability.The growth of Scenedesmus was enhanced from 5?25 mg/L of gibberellin.The 10 mg/L is the best.Under the initial pH 2.5 medium conditions(equivalent pH at the time of flue gas passages),the Scenedesmus continued to grow after the 4-6 days adaptation and reached the highest biomass 0.45 g/L(DW)at 10 day.It was found that the Scenedesmus became white and death in control(0 mg/L of gibberellin)This study based on optimization of simulated flue gas test system.Identification and acquisition of fine green algal strains which can be used to fix CO2 of flue gas,and establishment of resistant acclimation and gibberellin control techniques for improving the acid resistance of microalgae.From the source,it provides new knowledge and new strategy for microalgae direct immobilization and transformation of flue gas CO2 process system for the cultivation and construction of acid tolerant and high concentration CO2 microalgae.It is helpful for the development of high value utilization industry of biological carbon sequestration and CO2 resource utilization. |
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