Study On Environmental Impact Of Carbon Fixation And Energy Utilization By Microalgae Based On LCA Method

With the rapid development of China's economy,the continuous consumption of fossil fuels has led to a large amount of CO₂ emissions,which has caused the global warming and energy crisis to seriously affect the progress of our society and economic development.Therefore,CO₂ emission reduction and the development of renewable energy are urgently needed to change this situation.Due to its high photosynthetic efficiency,fast growth rate and high oil content,microalgae has great advantages in CO₂emission reduction and production of renewable energy.Therefore,vigorous development of the microalgae industry will have great significance for China's climate improvement and energy structure adjustment.However,the growth of microalgae is greatly affected by geographical and climatic factors,and microalgae is accompanied by energy and material inputs during growth and energy utilization,which will lead to other environmental problems.Therefore,combined with the actual geographical and climatic characteristics of China,the growth potential of microalgae in China is evaluated,and the environmental problems in the process of carbon sequestration and energy utilization of microalgae are analyzed from the perspective of life cycle.And the mitigation of the energy crisis is of great significance.In this paper,based on the growth characteristics of microalgae,a microalgae growth model based on solar radiation,temperature,relative humidity,wind speed,cloud amount and other climatic factors was constructed.Based on the meteorological data of 1981-2010 in various regions of China,the estimation of China Microalgae yield in various regions,carbon sequestration of microalgae,and production of microalgae biodiesel.The results show that,in terms of geographical distribution,due to temperature limitation,the northern part of China,the northwestern part,and the northeastern part of China are not suitable for the development of outdoor open-type runway pools for microalgae cultivation.However,in the central and southern coastal areas of China,Good light and temperature conditions are suitable for outdoor cultivation of microalgae.According to the model calculation,the theoretical growth rate of microalgae is 5.2-31.7 g/?m²?d?,and the theoretical carbon fixation of microalgae is 34.7-211.8 t/?hm²?a?.The theoretical yield of microalgae biodiesel is 3923.5-23764.9 L/?hm²?a?.In the concentrated area of microalgae cultivation,Hainan Province is currently the most suitable area for the cultivation of microalgae in outdoor open track pools due to its good geographical and climatic conditions.In order to further analyze the environmental sustainability of microalgae carbon sequestration and biodiesel production,this paper builds a system of microalgae carbon sequestration to produce biodiesel based on commercially viable outdoor runway pool microalgae culture technology and biodiesel refining technology.The life cycle assessment?LCA?was used to study the resource consumption and environmental release behavior of biodiesel produced by microalgae carbon sequestration.Adopt CML2001environmental impact assessment model and select Global Warming Potential?GWP?,Acidification Potential?AP?,Eutrophication Potential?EP?,Abiotic Depletion Potential fossil?ADP fossil?and Photochemical Oxidation Potential?POCP?,examine the environmental impact of the system,and identify key environmental issues and generated links in the system through hot spot identification and sensitivity analysis.The LCA evaluation results show that the non-renewable energy consumed by the constructed system to produce 1 t of microalgae biodiesel is hard coal with a consumption of 1.06�10³kg,followed by natural gas with a consumption of 4.19�10² m³;The pollutant is CO₂,which is 6.68�10³ kg,followed by CH₄,and the emission is 1.90�10¹ kg.Due to the environmental credit brought by the carbon fixation of microalgae,the carbon emission reduction benefit of the whole life process is 2.19 t CO₂/t microalgae biodiesel.The GWP,AP,EP,POCP,ADPfossil and total environmental impacts of the production of 1 t microalgae biodiesel are-2.19�10³ kg CO₂-Equiv,1.72�10¹ kg SO₂-Equiv,1.25 kg PO₄^3--Equiv,7.50�10^-1 kg C₂H₄-Equiv,4.82�10⁴ MJ,1.94�10^-9,among which the most important part of the total environmental impact is microalgae culture,and the most important environmental impact type is ADP fossil.The GWP,AP,EP,POCP,ADPfossil and total environmental impacts of the production of 1 t conventional petrochemical diesel were 4.48�10² kg CO₂-Equiv,7.67 kg SO₂-Equiv,4.12�10^-1 kg PO₄^3--Equiv,3.42�10^-1 kg C₂H₄-Equiv,4.98�10⁴ MJ,2.01�10^-9.Compared with traditional petrochemical diesel,the use of microalgae biodiesel to replace traditional petrochemical diesel has certain environmental improvement effects.The hotspot problem of the microalgae biodiesel life cycle is located in the microalgae cultivation stage and the microalgae harvesting stage.Reducing the amount of fertilizer used and reducing the power consumption throughout the life cycle are the main ways to reduce the environmental load of the microalgae biodiesel throughout the life cycle.