Sustainability Evaluation Of Microalgae Biodiesel Life Cycle Process Based On Emergy Analysis Theory

Microalgae biodiesel has attracted wide attentions as a prospective thirdgeneration biofuel and the technological feasibility of microalgal biodiesel production has been reported.However,the energy-intensive consumption sub-processes involved in the production pathway perhaps result to deteritoration on sustainability,thus,the sustainale assessment of the entire process is essential to be evaluated via Life Cycle Assessment.Meanwhile,nutrient supply in microalgae growth nay affects the global chemical fertilizer supply chain of economic crop cultivatoin.Therefore,technical advances are necessary to improve the utilization efficiency of nutrients to promote the microalgae biodiesel production.At present,there are mainly two approaches to solve the problem which is named as nutrient-recycle method as well as by-product protein method respectively.In this study,energy and carbon balance model is established based on the life cyle method to assess sustainability of conventional microalgae biodiesel life cycle process(Case 1),the nutrient-cycle method integrated microalgae biodiesel process(Case 2),and the byproduct protein method involved microalgae biodiesel process(Case 3).The results show that the energy balance ratio(EBR)and carbon balance ratio(CBR)of the above three processes are all larger than 1,which means positive energy balance and carbon balance results.However,the prior energy balance or the carbon balance analysis concentrates on single perspective while cannot make assessment of the microalgal biofuel process from a higer perspective comphrensively.Therefore,this study implemented the emergy analysis method to assess the sustainability of the three processes in a more balanced perspective.Emergy analysis inherits the idea of life cycle analysis,where emergy is proposed as a common creteria to assess the integrated mass,energy and information flow in and out ecosystem and social ecomical systems.In emergy analysis,energies and substances from different resources are in the same comparion standard.It is more comprehensive than other systematic analysis methods.The emergy analysis results show that the sustainable development index(ESI)of Case1 is 0.048;the ESI of Case 2 is 0.302;the ESI of Case 3 is 0.276.Compared with Case1 and Case 3,Case 2 has better potential for sustainable development.Based on the sensitivity analysis of Case 2,the results show that using normal nitrogen nutrition patterns,natural-growth microalgae biomass as raw material,electricity generated by clean energy,and human labor in regions with lower UEV can effectively improve the sustainability of the microalgae biodiesel life cycle process.This study also compared the life cycle process of microalgae biodiesel with microalgae bioethanol,soybean biodiesel,rapeseed biodiesel,sunflower biodiesel,palm tree biodiesel and jatropha biodiesel.Emergy analysis results show that the microalgae biodiesel life cycle process performs superiority in sustainability assessment than other biofuel life cycle processes.