Studies On Process Optimization About Industrial Cultivation And Harvest Of Egracilis

Euglena gracilis is a kind of mixotrophic（heterotrophic,photoautotrophic）microalga,which has the characteristics of fast growth,comprehensive nutrition,rich in active substances（paramylon,vitamin E）and so on.It makes a wide range of potential applications in food additives,drugs,health care products and has attracted more and more attentions from many scholars in the world.However,there are still numerous problems in promoting industrial cultivation of E.gracilis,such as low biomass,high harvesting cost,and high volume of water consumption.In order to promote and stabilize the industrial culture of E.gracilis,this study tried to optimize the three keys of the culture of Euglena,such as the culture,harvesting method and medium reuse,to obtain a low-cost industrial culture process of E.gracilis.The main contents and results of this paper are summarized as follows:（1）The coupling culture technology of high-density heterotrophic fermentation and photoautotrophic to recover green was established.The data of cultivation status of this process were compared with photoautotrophic conditions.The maximum biomass of strain in heterotrophic culture in the fermentation tank was 21.5g/L,which was 10.75 times the maximum biomass of E.gracilis.Meanwhile,the content of paramylon in heterotrophic and photoautotrophic conditions was up to 13.7g/L and0.7g/L respectively.After the transfer of heterotrophic cells to photoautotrophic status for re-greening for 72 hours,the chlorophyll content in the cells reached 33ug/ml,which recovered to more than 90%of the chlorophyll content in the pure photoautotrophic culture,and the biomass increased by 50%compared with that in the pure photoautotrophic culture.The coupling culture model of heterotrophic and autotrophic has the advantages of both high biomass and active substances and reduces the costs of seed production to a certain extent.（2）E.gracilis were harvested based on the method of regulating pH of the medium.Na OH and HCl solutions were used to adjust the pH of microalgal cells and culture medium at different concentrations.When the pH was higher than 10.0,cells completely broke down and the intracellular inclusions were suspended into the liquid.When the pH was 8.5,the flocculation efficiency of microalgal cells reached more than 90%.Therefore,when the pH of the weak base was 8.5,the harvesting efficiency of microalgal cells was the highest.Further study of the mechanism revealed that the medium contained a large amount of PO₄^3-,Mg²⁺and a small amount of Ca²⁺,among which Ca²⁺was the main factor for flocculation.Under the condition of a weak base with pH 8.5,calcium phosphate precipitation with a positive charge would be formed,and then it would be neutralized with negatively charged microalgal cells to result in flocculation and precipitation.The flocculation efficiency of microalgal cells in pilot culture reached 82.4%,2.5 times that of the control（32.9%）.Besides,the yield of algal paramylon was significantly higher than that of the control group,with a maximum yield of 0.6 g/L,2.4 times that of the control group.At the same time,the chloroplast content was basically maintained.Compared with the traditional centrifuge harvesting method,this method is simple to operate and low cost.（3）Evaluation of reuse of E.gracilis culture medium treated with activated carbon.The results showed that the recovered medium cold be circulated for at most twice,and had adverse effects on the growth indexes（dry weight,chlorophyll,etc.）of E.gracilis afterwards.However,the cultural waste solution after the adsorption of activated carbon can significantly reduce the inhibition of the growth of E.gracilis,so that the growth of E.gracilis in the treated medium can reach the level of fresh culture medium.Three dimensional fluorescence activation-emission matrix（FEEM）analysis revealed the presence of many similar humic acids in the recovered media,which may be the main reason why the recovered media could not be reused for many times.The culture medium treated with activated carbon can significantly reduce the concentration of these inhibitors,increase the cycle times of culture,and reduce tailwater discharge.Through process the heterotrophic-photoautotrophic coupling dilution of the recovered medium harvesting microalgal cells by pH flocculation,we could greatly reduce the culture cost.These studies will lay a good foundation for the industrial culture of Euglena.