| The use of municipal wastewater to cultivate microalgae is conducive to reducing biodiesel production cost and realizing resource utilization of municipal wastewater,which has broad application prospects.Microalgae breeding and cultivation are the primary and key links in microalgae biodiesel industry chain.However,the scarcity of high quality algae species,the contradiction between the growth of microalgae and the accumulation of lipid are the main problems.In order to improve the lipid yield of microalgae in municipal wastewater,the thesis primarily obtained Scenedesmus obliquus SC-W with excellent lipid production performance and good adaptability to municipal wastewater.Based on its characteristics,the effective ways to promote the lipid production of S.obliquus culticated in municipal wastewater were studied and the application in the expanded culture system of the plate photobioreactor under promoting conditions was investigated.Finally,the mechanism of promoting conditions to promote lipid production of S.obliquus was studied.The high-efficiency microalgae was screened by comparing the lipid production and tolerance to municipal wastewater of different microalgae species.The results showed that S.obliquus(SC-W)had higher lipid productivity,better municipal wastewater tolerance.Raw municipal watewater filtered by coarse filter without any sterilization could be directly used for its cultivation,which was conducive to large-scale cultivation of microalgae.A strategy of promoting lipid production by adding nutrients,plant growth regulators and bacteria to the municipal wastewater was proposed.Through orthogonal test the optimal conditions to promote lipid production of S.obliquus was Fe SO4 1.5 mg/L,IAA 7.5 mg/L,TRIA 5 mg/L,EM 0.01.Under the optimal condition,the lipid productivity of S.obliquus could reach 82.8 mg/L/d,increased by 116% compared to the control group(32.3 mg/L/d).And the increase of the content of monounsaturated fatty acids was beneficial to the improvement of the quality of the biodiesel.Lipid production of S.obliquus in the expanded culture system of the plate photobioreactor under the promotion conditions was investigated.The promotion conditions effectively promoted lipid production of S.obliquus,the biomass and lipid yield of S.obliquus were 131.5 and 34.0 mg/L/d,respectively,113%,93% higher than the control group.During the four cycles of batch culture of S.obliquus under promotion conditions,the biomass and lipid production were 0.52-0.56 and 0.14-0.16 g/L.Nitrogen and phosphorus in municipal wastewater were mainly absorbed by S.obliquus.With the expansion of culture scale and technological progress,the preparation of biodiesel from S.obliquus with municipal wastewater as the medium had a good application prospect in energy consumption.Microscopic observation and element content analysis were carried out on plant growth regulator IAA,EM bacteria treatment groups and the control group.The results showed that IAA and EM bacteria could mainly increase the biomass productivity through promoting microalgal cell division and increasing cell number per unit time.Moreover,the treated group was more deficient of nitrogen than that of the control group,which was conducive to the synthesis of lipid.The lipid yield of microalgae was determined by the biomass yield and the lipid co ntent.When using municipal wastewater to cultivate S.obliquus,IAA and EM bacteria balanced the biomass yield and lipid content in the same system,promoted the substantial increase of biomass yield with not significantly affecting the lipid content,and finally achieved a substantial increase of lipid yield.The metabolic regulation mechanism of plant growth regulator IAA on lipid productivity of S.obliquus was studied using metabolomics techniques.Analysis of the main metabolic pathway and metabolic network found that through upregulation or downregulation of different metabolites,the activity of the TCA cycle and the purine metabolism pathway was enhanced,thus providing more energy and genetic material for the growth and division of S.obliquus.The addition of EM bacteria in culture systerm could increase the bacteria diversity and be beneficial to the system stability.Also,it could effectively regulate the bacteria structure in municipal wastewater.Adding EM bacteria increased the abundance of bacteria associated with organics and nitrogen degradation,which was helpful to provide more carbon sources for the growth of S.obliquus and form a state of nitrogen deficiency,thus improving biomass production and lipid accumulation of S.obliquus.At the same time,the proportion of bacteria with flocculation and lysis to microalgae decreased,which provided a favorable environment for the growth of S.obliquus. |
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