| Under the dual background of energy crisis and environmental pollution,microalgae biodiesel has become a research hotspot.The use of municipal wastewater to culture microalgae to produce biodiesel can not only produce new energy,but also realize the recycling of wastewater.Microalgae harvesting and oil extraction during the preparation of microalgae biodiesel is the most energyconsuming step,making the cost of microalgae biodiesel high and difficult to achieve industrial application.Based on this background,this paper applied the daphnia feeding to the harvesting process of microalgae,and extracted the daphnia oil.The production of microalgae lipid biodiesel was converted into the production of daphnia lipid biodiesel.The purpose was to obtain a microalga harvesting and oil extraction process with low cost and high efficiency and industrial application prospects.In this paper,a high-quality daphnia was screened,and the factors affecting the feeding of microalgae by daphnia were studied.The single-factor optimization of the one-step oil extraction method and two-step oil extraction method of the daphnia was carried out,and the mechanism of the extraction of microalgae and oil extraction by the daphnia was discussed.The design of the ladder harvesting device and the outdoor expansion experiment were carried out,and the technical and economic feasibility analysis of the whole process was carried out.Through the study of the factors affecting the feeding of microalgae by highquality daphnia,the optimal parameters for the feeding of microalgae by daphnia were as follows: temperature was 25 °C;light intensity 0 lux;the dosage of daphnia was 150 ind·?100 m L algae solution?-1;the feeding time was 0.5 h.The optimization parameters of the one-step oil extraction method of the daphnia were as follows: the solvent dosage was 10 m L·?100 ind daphnia?-1,and the extraction time was 5 h.At that time,the lipid conversion rate was 71.4%?feeding time was 0.5 h?,and 52.5%?feeding time was 1 h?.The optimization parameters of the two-step oil extraction method of the daphnia were: the liquid to material ratio was 2:3?m L sample: m L solvent?,and the extraction time was 3 h.The lipid conversion rate under this condition was 35.0%.According to the composition analysis and FTIR analysis of the extract,it was found that after the daphnia ingested the microalgae,most of the proteins and polysaccharides in the microalgae were used by the daphnia for their own metabolism.Analysis of fatty acid composition found that daphnia biodiesel was better than Chlorella pyrenoidosa biodiesel oil;1 g dry weight Chlorella pyrenoidosa was extracted by traditional chloroform methanol method,one step oil extraction method of the daphnia and two-step oil extraction method of the daphnia.As a result,the amount of FAME obtained by the one-step method was the largest.The optimized parameters of the ladder harvesting device were: the level of the device was 7 grades,the residence time of each algae solution was 1 h,the dosage of the daphnia was 300 ind·?100 m L algae solution?-1,and the feeding time of the daphnia was 0.5 h.Under the above conditions,the outdoor expansion experiment showed that the chlorella harvest efficiency reached 98.5%,and the daphnia oil extraction effect was 0.0034 g·?100 ind daphnia?-1,and the oil conversion rate reached 72.0%.Through technical and economic feasibility analysis,the process of harvesting microalgae and oil extraction by daphnia was low energy consumption,high efficiency and application prospect. |
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