Optimization Of Microalgae Biodiesel Extraction Based On Microbial Electro-Fermentation Pretreatment

Third-generation biodiesel made from microalgae is currently a high-quality fuel to alleviate energy pressure and greenhouse effect.Yet,there are some drawbacks in the preparation of biodiesel from microalga,such as high energy consumption,low lipid extraction rate and poor biodiesel quality.In this study,parameters of microalgae biodiesel extraction from microbial electro-fermentation pretreatment were optimized,the biodiesel quality was evaluated comprehensively,and the economic analysis of the whole process was carried out to lay the foundation for the expanded production.Firstly,this study was conducted to investigate the power production performance and wastewater treatment of microbial fuel cell（MFC）with static start-up and continuous flow start-up to pave the way for microbial electrolytic cell（MEC）fermentation of microalgae.The COD removal rate,power density and internal resistance of MFC at static start-up were89.6%,141.8 m W/m³ and 248.9Ω,and 84.7 Wh/m³ energy is recovered.On this basis,the reactor was operated steadily with continuous flow start-up by gradually increasing the load,and the final COD removal rate was 81.6%,with a power density of 115.6 m W/m³,and 109.6Wh/m³ energy was recovered during the start-up process.Secondly,to avoid unnecessary energy input during the electro-fermentation pretreatment of microalgae by MEC,the optimal applied voltage for continuous flow MEC was investigated.The results showed that the substrate degradation rate increased as the applied voltage increased,and 0.8 V was the optimum applied voltage for microalgae electro-fermentation.Under this condition,the highest lipid extraction rate（85%）was achieved and the biodiesel quality was improved with the help of biohydrogenation of microorganisms,which reached the fatty acid saturation of 71.7%and the C16:0 percentage of 54.7%,and all its indexes met the national biodiesel standards;It was also confirmed that not the higher applied voltage was better,which was mainly related to the Aeromonadaceae and Pseudomonadaceae involved in the metabolism of lipids.Finally,on the base of 0.8 V applied voltage,the influence of hydraulic residence time（HRT）on the lipid extraction of microalgae electro-fermentation pretreatment was explored.The results of the pilot test showed that 42 h was the optimal HRT,when the lipid extraction rate was 70.8%and the biodiesel quality was the best with an overall score of 7.5 and a relative energy consumption of 3.42 MJ/g biodiesel.After calculations,if this research method and test results are extended to the actual biodiesel production project,it can reduce 11.4 t CO₂ per ton of biodiesel production,which proves that the technology is feasible and promising.The method of microbial electro-fermentation pretreatment of microalgae for biodiesel preparation studied in this paper provides a theoretical basis for the expanded production of microalgal biodiesel.