Enhanced Lipids Extraction And Efficiency From Microalgae Based On Microbial Fermentation Pretreatment And Low Toxicity Solvent

Biodiesel using microalgae as raw material has advantages of good combustion performance,environmental protection and regeneration.However,there are high energy consumption,low utilization rate,high solvent toxicity and environmental pollution exist in the cellwall-breaking and extraction process,which seriously hinders the popularization and application of biodiesel.In order to solve these problems,this study used efficient and energy-saving anaerobic microbial electro-fermentation technology to break the wall of microalgae and coupled with low-toxic organic solvents to extract lipid,which provides an important idea for low-energy and environmental lipid extraction from microalgae.The traditional organic solvents were first replaced,and then optimized through single factor test and response surface method(RSM).The screened low-toxic dual organic solvent type was petroleum ether/isopropanol,and the actual lipid relative extraction rate was 91%.Low-toxic solvents replace traditional solvents to calculate the energy consumption of each unit in the wet extraction process,reducing the total energy consumption by 27%,greatly reducing time and economic costs.Secondly,the effects of different pretreatment methods and selective fermentation on the microalgae wall-breaking and lipid extraction were investigated.The results showed that the hydrolysis rate of carbohydrate and protein was slightly slow in the early stage of fermentation of selective fermentation without physicochemical pretreatment,but the indexes were significantly improved in the late stage of fermentation.The lipid extraction rate was 84%,which was 8 times higher than that of unfermented microalgae,and the degree of fatty acid saturation was about25%.Selective fermentation without physicochemical pretreatment kept the higher heating value unchanged at 39 MJ/kg,significantly increased CN value,decreased IV value,improved the quality of biodiesel,had better combustion performance,and reduced energy consumption by 76% compared with untreated control group.During the fermentation process,we found that there are a large number of families related to the wall breaking degradation of microalgae,such as Proteobacteria,etc.,and bio hydrogenation,such as Ruminocaceae,etc.Selective fermentation without physicochemical pretreatment can lead to better hydrolysis performance and higher quality of biodiesel.Finally,in order to improve the microalgae wall breaking efficiency,the electro-fermentation technology was applied to improve the lipid extraction rate.The results showed that the electro-fermentation based on MEC greatly increased the hydrolysis rate and shortened the fermentation time by more than 2 times.The lipid extraction rate reached 90 % and the fatty saturation rate increased by 34 % after 45 h electro-fermentation,resulting in unchanged HV at 38 MJ/kg,higher CN value and lower iodine value.Under different applied voltage,the degradation rates of carbohydrate and protein were increased by 43 % and 91 % respectively at 1.0 V compared with 0.6 V after 33 h of fermentation,the lipid extraction rate of the optimal low toxic organic solvent was 78%,and the relative selective fermentation was increased by 24%.The treatment time of microalgae wall breaking was greatly shortened,and the quality of biodiesel was significantly improved.Compared with 69 h of traditional selective fermentation,the relative energy consumption of 33 h EF-MEC(1.0 V)electro-fermentation was reduced by 116%.Electro-fermentation based on t MEC echnology coupled with low toxic organic solvent is a low energy consumption and environmental protection method for microalgae lipid wet extraction,which has a certain application prospect.