| Recently,due to the increasing depletion of oil resources,environmental protection,especially the urgency of CO2 emission reduction and other factors,the research and development of bioenergy has been paid more attention.Biodiesel is one of the important products of bioenergy and sustainable supply of its raw materials is the key issues which restricts the development.Microalgae become one of the most promising material to produce biodiesel since its advantages of rapid growth,high oil content,strong environmental adaptability,"not competing with terrestrial crops,not competing with arable land".The development of technology of microalgae biodiesel production has become one of the most active field of bioenergy in recent years worldwide.At present,although the technical route of biodiesel production from microalgae cultivation has been achieved in the laboratory,microalgae biodiesel production in commercial scale has been hindered by the high cost and lack of research in the process of mass cultivation of microaglae and biodiesel production.Microalgae production efficiency is low due to the low concentration of microalgae culture in the photobioreactors and serious biomass loss caused by biological contamination.In addition,low production of microalgae also limits its development and application in health care products,pharmaceuticals,cosmetics,agricultural chemicals,feed and other industries.This paper mainly studies the effects of pipeline modification on the output of the tubular photobioreactor and the effects of biological contamination control on the reduction of biomass during cultivation.Moreover,the effects of microalgae crude oil and biomass on the yield of biodiesel using enzymatic conversion were studied.The main results were as follows:1.By CFD simulation,the effects of inner spiral rib on the fluid in the pipeline were studied and the effects of rib parameters on swirl number were analyzed.(1)Compared with ordinary pipeline,the presence of spiral rib can significantly improve the fluid swirl number.Within certain range of rib number,the more rib,the more fluid swirl number is and 8 ribs had the maximum swirl number,which increased 2.5 folds compared to 1 rib pipe.(2)Within the same number of spiral ribs,smaller pitch generated larger fluid swirl number.Compared with 1000 mm pitch,fluid swirl number was increased by 1.3 folds in 500 mm pitch pipe.2.The effects of the modified tubular photobioreactor on the cultivation of Scenedesmus were studied indoor using pilot scale(1300 L)tubular photobioreactor under 24 h artificial light source.The growth rate and biomass concentration of microalgae in modified tubular photobioreactor were obviously higher than conotrol which were consistent with the CFD simulation results.The growth rate and cell density in pipes which modified with 8 ribs and 500 mm pitch were 0.055 d-1 and 3.2 g·L-1,respectively,which were both increased by 45% compared to the control.3.Combined with morphological and molecular ecology technology(DGGE),the composition and population of the biological contaminants in Chlorella culture from open ponds were studied.There were 19 kinds of biological contaminants or operational taxonomic units,including two species of fungi,six species of flagellates,three species of amoebas,two cercozoas,and three species of ciliates,one rotifer and two large insects.Among the contaminants,Poterioochromonas malhanensis was found to be the main harmful contamination since only within two days,the cell number of Chlorella reduced 8 times while the cell number of P.malhanensis increased 15 times.In addition,through one year morphological observation of Scenedesmus culture in outdoor tubular photobioreactor,13 kinds of contaminations were found including one rotifer,three species of amoebas,six species of ciliates and three species of flagellates.Besides rotifer,Leptophrys sp.was also found to be a harmful contamination to Scenedesmus culture since 1.98 fold of biomass loss was caused by this amoeba within three days.4.Ultrasonication was applied to prevent and control the contamination during microalgae cultivation.(1)The lethal effects of ultrasound on P.malhanensis and a rotifer were studied.The mortality of P.malhanensis and rotifer raised with the increase of sonication dose and became saturated gradually.The maximum mortality rate is 88.6% and 96.4%,respectively.(2)The effects of sonication on the growth of Chlorella and Scenedesmus were also studied.There was no inhibition on microalgae growth no matter which growth phase the algae were in under 20 J·mL-1 of sonication dose.There was also no significant effect on lipid content.In the contrary,3 J·mL-1 of sonication dose can even promote the growth of Scenedesmus from lag phase and the cell concentration was increased by 18.8% compared with control after 10 days of cultivation.(3)P.malhanensis control in Chlorella cultivation was studied using ultrasonication.It was found that P.malhanensis was effectively eliminated by sonication during the cultivation.In addition,10 kinds of contaminations found in cultivation was removed or inactivated by sonication including Colpodella sp.,Saccharomyces sp.,Brachionus calyciflorus,Bradysia sp.,Spumella spp.,Platycotis sp.,Orchitophryidae and two species of fungi,which reduced 52.6% of the total contamination group in Chlorella culture.(4)Since Leptophrys sp.is not sensitive to ultrasound,the lethal effect of pH on Leptophrys sp.was studied.It was found that the number of Leptophrys sp.reduced 9 folds after adjusting pH to 6 by CO2 and maintain for 4 h while the growth of Scenedesmus had not been affected.5.Enzymatic esterification of microalgae crude oil into biodiesel was established and the effects of reaction system and reaction conditions on conversion rate were studied.(1)1:1 was the best oil to t-butanol ratio for the reaction system which could produce more biodiesel.(2)The conversion rate increased with the oil methanol molar ratio increasing to 1:12 and there was no significant different of conversion rate between 1:12 and 1:24.(3)There was no significant effect of temperature on the conversion rate in the range of 25-55 oC.(4)After 4 h of reaction under optimum conditions in 25 oC,the maximum conversion rate reached 99.1%.The conversion rate still could reach 95% if reduced oil methanol mole ratio to 1:3 after 12 h reaction.(5)The conversion rate of different oil substrates ranged from 75% to 99% after 4 h reaction under optimum conditions,indicating that the system could adapt to a variety of substrates.(6)After 165 h of pretreatment in the reaction system,enzyme N435 still kept more than 90% of the activity,indicating that the system reduced the inactivation effect of methanol on enzyme and the enzyme was suitable for repeated use in the established reaction system.6.In situ enzymatic conversion of microalgae biomass into biodiesel was established and the effects of reaction system and reaction conditions on biodiesel yield from dry microalgae biomass were studied.(1)In order to find the optimal co-solvent ratio,different dry Nannochloropsis oceanica IMET1 biomass to t-butanol weight ratio was tested and the yield increased significantly as the biomass to t-butanol ratio changed from 1:1 to 1:2.Further increase in the t-butanol input led to a decrease in yield possibly due to dilution effects.Dry N.oceanica biomass to methanol weight ratio was also tested and 2:1 was found to be the optimal ratio.(2)The optimal reaction temperature was determined and the yield increased from 99.3% at 25 oC to 106.8% at 45 oC due to higher extraction efficiency.(3)Under optimal reaction conditions,which was the biomass to t-butanol and methanol ratio of 2:4:1 at 25 oC,the yield reached up to 99.2% after 8 h of reaction and the maximum yield increased to 107.7% after 12 h of reaction,which was higher than the yield from crude oil indicating that in situ reaction had advantages in biomass utilization.(4)After 55 days of pretreatment in the reaction system,enzyme N435 still kept more than 95% of the activity,indicating that the enzyme was suitable for repeated use in the established in situ reaction system.Moreover,the effects of reaction system and reaction conditions on biodiesel yield from wet N.oceanica biomass were studied.Under optimal reaction conditions,which was the wet biomass to t-butanol and methanol ratio of 1:1:2 at 45 oC,the yield could reach 81.5% after 16 h of reaction.The enzyme stability in the system was also tested.The presence of water seriously affected the stability of the enzyme N435 and the enzyme activity dropped to 57.8% after 4 days pretreatment in the established system together with water. |
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