Pulsed Electric Fields Assisted Lipid Extraction From Microalgae Using Low-tocxity Solvent

To cultivate lipid-rich microalgae in municipal sewage could make the sewage purified and the microalgae can be raw material to produce biodiesel. Lipid extraction was a vital link in microalgae biodiesel industry chain, but its industrialization prospect was not optimistic. The purpose of thwas study was to establish a promwasing wet route of lipids extraction, including the technologically and economically feasible ways of cell disruption and low-toxicity solvent extraction.This thesis firstly studied the influence factors of pulsed electric field in breaking cell wall of Chlorel la pyrenoidosa. Then a research was done on the factors of pulsed electric field that affected lipids extraction by single factor and multi factor optimization. The study further investigated the mechanism of pulsed electric field assisted extraction, selected a kind of solvent of low toxicity and high efficiency which can replace chloroform and methanol; finally, the study carried out the industrial feasibility analysis of the whole extraction process.The main achievements of this thesis are as follows:The optimal parameters obtained from single factor optimization and orthogonal experiment: electric field strength 20 k V/cm, flow rate 5.4 L/h, pulse repetition frequency 130 Hz, pulse width 6 μs and recycling for 3 times. Under the optimum conditions the lipid yield was 61.1% and the yield of fatty acid methyl ester was 11%, respectively improved 15.9% and 9.8% compared with the traditional method.The lipid yield and FAME yield were 63.2% and 11.9% when cultivated microalgae with simulated wastewater, respectively 61.4% and 11.4% when cultured with municipal wastewater, which shows no significant difference between the two situation. GC-MS detection proved that pulsed electric field treatment did improve the lipid extraction rate and FAME yield, but did not change the lipid profile of the extract.That PEF treatment caused dissolution of intracellular substances was one of the reasons to explain the increased rate while no lipids leaked out; through fluorescent staining and scanning electron micrographs, cell membrane integrity of C hlorella pyrenoidosa was observed destroyed under PEF treatment; pulsed electric field treatment can effectively shorten the extraction time for 4 h compared with traditional method.The solvent n-hexane/ethanol could substitute for chloroform/methanol to extract lipids. The extraction conditions: solvent ratio 3:2, liquid to solid ratio 1:1, extraction time 28 h. Combination process of pulsed electric field pretreatment and n-hexane/ethanol co-solvent had an extraction rate and yield of FAME of 54.4% and10.5%, respectively 106.7% and 91.9% of traditional method.