Energy And Environmental Impact Analysis Of Water Treatment Integrated Microalgae Biodiesel Life Cycle System

Biodiesel produced by microalgae is considered to be the most potential biofuel because of the high photosynthetic efficiency,short growth cycle,high oil yield and quality,small ground area demand and good adaptability of algae.However,the traditional dry processes with freshwater culture for producing microalgae biodiesel need supplement of nitrogen and phosphorus fertilizers.At the same time,they consume considerable freshwater and energy,which make significant contribution to environmental impact and,especially,the initial fossil fuel consumption.Therefore,the combined wastewater culture and pyrolysis esterification process,as an alternative for cultivation and process route are becoming attractive.It is thus particularly important to make analysis on the energy consumption and environmental impact of the life cycle system of such a process to ensure the sustainability of microalgae biodiesel produced.The main purpose of this study is to establish an approach to evaluate the sustainability of the wastewater treatment integrated microalgae biodiesel production process from the perspective of energy consumption and environmental impact based on the concept of life cycle analysis.In this paper,the system boundary from microalgae cultivation to biodiesel production and the corresponding mathematical models of energy consumption and environmental impact assessment were established for four kinds of microalgae biodiesel production processes,i.e.traditional process fresh water cultivation route,traditional process wastewater cultivation route,pyrolysis esterification fresh water cultivation route and pyrolysis esterification wastewater cultivation route,have been established.Based on the principle of life cycle analysis,the inventory analysis of each stage of the four technical routes is summarized.The direct energy consumption and initial fossil fuel consumption of each technical route were calculated by using the energy consumption evaluation model,and the main factors affecting the energy consumption were identified.As a result,the sustainability of the wastewater treatment integrated microalgae biodiesel was explained through the comparison and analysis,and at the same time,a life cycle assessment approach for wastewater treatment integrated microalgae was also established.The results showed that the energy ratio and energy efficiency ratio of the four technical routes were all greater than 1,and the initial fossil energy consumption for the production process of pyrolysis esterification wastewater cultivation route was reduced because the initial fossil energy consumption in the waste water culture of microalgae was lower than that in the fresh water culture,which led also to the reduction of fertilizer input in the production process.Based on the principle of life cycle analysis,the environmental impact assessment of four technical routes was carried out,and the environmental impact index and total environmental impact index of each environmental type were obtained.The results showed that the environmental impact of the production process of microalgae diesel oil with integration of the wastewater treatment was the lowest,and that of the traditional process with fresh water culture was the greatest.The analysis also shows that the input of fertilizer contributed significantly to the environmental impact.Among the six types of environmental impact,photochemical smog contributed the most to the total environmental index.Wastewater culture and pyrolysis esterification process was shown to be conducive to reducing environmental emissions and can be used as an alternative technology route for microalgae biodiesel production.