Research On The Growth And Oil Synthesis Of Microalgae Cultured In Rice Straw Hydrolysate

One of the bottlnecks in the industrial application of microalgae is its high cost of cultivation.Straw is regarded as a kind of cheap culture raw material because of its structural characteristics,but the relevant research is still rarely reported.The main limiting factor is that the enzymes used in the hydrolysis of straw are not very active and expensive.Therefore,in this study,the cellulase produced by Aspergillus niger and Trichoderma viride was compounded to obtain a compound enzyme with strong ability to degrade straw,and the hydrolysate obtained by hydrolyzing straw was used to cultivate microalgae for growth and oil synthesis.In order to reduce the cost of microalgae cultivation.The main research results of the paper are as follows:First,the laboratory screened a strain of Aspergillus niger having cellulase-producing ability from activated sludge in a sewage treatment plant.As the enzyme production conditions are greatly affected by the environment and nutritional factors,so as improve the ability of Aspergillus niger enzyme production efficiency.In this study,single factor experiments were used to optimize the carbon source,nitrogen source,temperature,pH,inoculum size,and culture time for enzyme production.After optimized,the enzyme production capacity of Aspergillus niger was significantly improved.The optimal enzyme production conditions were: bran as a carbon source,urea as a nitrogen source,pH 5,temperature 30°C,inoculum size 6%,culture time Under the condition of 5 days,in this condition,the filter paper activity,CMC enzyme activity,and ?-glycosidase activity reached 4.65 U/m L,19.43 U/m L,and 65.41 U/m L,respectively.Compared with 3.22 U/m L,13.51 U/m L,and 49.78 U/m L before optimization,their enzyme activities increased by 44%,43%,and 31%,respectively.Secondly,according to the characteristic that cellulase produced by Trichoderma viride and Aspergillus niger can complement each other,the cellulase produced by the two strains is compounded.The study found that the compounding ratio,plus metal ions and concentration are the key factors affecting the activity of the compound enzyme.At a compounding ratio of 1:1,it reached a maximum?4.78 U/m L?in filter paper enzyme activity representing total cellulase activity.The data shows that compared with the five metal ions of Fe³⁺,Na⁺,Mg²⁺,Zn²⁺ and Ca²⁺,when the added metal ions have a K⁺ concentration of 0.1 mmol/L,they have a significant enhancement effect on the enzyme activity of the compound enzyme.Using microcrystalline fiber as substrate,the efficacy of compound enzyme and monomer enzyme treatment was investigated.It was found that the use of compound enzyme treatment of microcrystalline cellulose can reach a sugar content of up to 220 mg/g,Aspergillus niger monomer enzyme up to 175 mg/g,and Trichoderma viride monomerase up to 86 mg/g.It shows that the effect of compound enzyme on the actual treatment of cellulosic substances is much higher than that of Aspergillus niger monomerase and Trichoderma virideFinally,the straw was treated by the traditional pretreatment method.After pretreatment,it was found that there is high lignin removal rate and high cellulose retention rate under the alkali pretreatment conditions.Scanning electron microscopy?SEM?and infrared spectroscopy?FTIR?were used to observe the changes in morphology and chemical structure of the straw which before and after treatment.Orthogonal design experiments were used to determine the optimum conditions for the enzymolysis reaction: 48 h,pH4.8,enzyme concentration 30 U/g,and substrate concentration 40 g/L.Under these conditions,the hydrolyzate contained 5.9 g/L glucose and 3.0 g/L xylose.The total sugar content of the hydrolyzate was 61.97% of the sugar yield of the relevant commercial enzyme under the same conditions.The relevant conditions for optimizing the use of cellulose hydrolysate as a carbon source for microalgae were optimized.After optimization,biomass and oil content were increased by 29% and 33%,respectively.The microalgae cultured with the hydrolysate as a carbon source were compared with those cultured with other carbon sources.It was found that the biomass and oil production of microalgae cultured using the hydrolysate as a carbon source was significantly higher than that of xylose and components.Although there is still a gap between the efficiency of microalgae cultured with glucose,But the use of cellulose hydrolysate to cultivate microalgae is undoubtedly more competitive.