A Preliminary Study On The Cultivation Of Microalgae By Water Extract Of Silkworm Feces

Humans are confronted with environmental pollution,water scarcity,food scarcity,and resource scarcity as a result of the advancement of technology and the economy,prompting them to consider waste utilization.Because they’re the earth’s primary producers,microalgae have a high carbon sequestration capacity,a rapid reproduction rate,and don’t require a lot of arable land.Microalgae are also widely used in medicine,food,cosmetics,feed,and other industries.China is a large agricultural country that produces and exports a lot of silk.Silkworms,as silk producers,generate a significant amount of silkworm feces during the production and development process.To lower the cost of microalgae cultivation and improve the efficiency of energy recovery in the environment,this thesis converts silkworm feces into silkworm feces aqueous extract medium for microalgae cultivation.In this study,total nitrogen,total phosphorus,and COD were measured in silkworm feces aqueous extract to create a high quality medium for microalgae growth,and four algae species were used:Chlorella sorokiniana,Scenedesmus obliquus,Chlorella vulgaris,and Chlorella pyrenoidosa.Chlorella vulgaris and Chlorella pyrenoidosa were studied for their growth characteristics in silkworm feces aqueous extracts,and the target algal species were then used to increase nutrient utilization and final biological yield in silkworm feces aqueous extracts by changing their initial inoculum density.Finally,we observed nutrient utilization by phosphorus supplementation and then improved nutrient utilization by semi-continuous culture.The main findings are as follows:(1)Based on the data and image analysis provided by the box-Behnken model,we determined the maximum solubility parameters for each element per gram of silkworm feces aqueous extract,as follows: The liquid-solid ratio was 1.5 g/m L,the cooking time was 83 minutes,and the cooking temperature was 80°C.According to this process condition,nitrogen content dissolved in water per gram of silkworm feces and phosphorus content dissolved in water per gram of silkworm feces were 6.722 mg/g and 0.377 mg/g,respectively.To test the reliability of the optimal process predicted by the response surface method,the optimal conditions for each nutrient(TN,TP,NH,and COD)were a liquid-solid ratio of 15 m L/g,an 83 minute cooking period,and an 80°C boiling temperature.In water,the nitrogen content per gram of silkworm feces was measured at 6.394 mg/g,and the phosphorus content per gram of silkworm feces was measured at 0.316 mg/g.According to the response surface method,the error of the predicted solubility of nitrogen content was 4.87 %(<5 %),and the error of the final predicted value of phosphorus content was 16.3 %(> 5 %).It demonstrates that the response surface method’s maximum solubility parameters for each element per gram of silkworm feces aqueous extract are feasible,however there are some differences in phosphorus content in silkworm feces aqueous extracts.(2)As for Chlorella sorokiniana,it showed excellent growth characteristics under light,with a specific growth rate of 0.31 g/L and a p H of 8.8 after 7 days of incubation,and it was highly efficient at utilizing nutrients in silkworm feces aqueous extracts compared to other algae species.Therefore,Chlorella sorokiniana grow well in sericulture feces extracts.Our data analysis shows that Chlorella sorokiniana in sericulture feces extracts increases in nutrient utilization rate as the number of initial cells increases,and the stagnation period disappears when the density of algae is greater than 0.4 g/L.After calculation,it can be concluded that the specific growth rate of Chlorella sorokiniana is the highest at 0.4 g/L and the final final biological yield is the highest.(3)The phosphorus supplement phosphoric acid and dipotassium phosphate in this experiment were both used and absorbed by Chlorella sorokiniana as a phosphorus source.Comparatively,dipotassium phosphate as a phosphorus supplement promoted nutrient absorption by Chlorella sorokiniana in silkworm feces aqueous extract.In this case,the nitrogen to phosphorus ratio of Chlorella sorokiniana in silkworm feces aqueous extract was15:1.Chlorella sorokiniana in silkworm feces aqueous extract had a nitrogen to phosphorus ratio of 10:1 in experiments with different nitrogen and phosphorus ratios,and the nutrient utilization of Chlorella sorokiniana in silkworm feces aqueous extract was better than nonsemi-continuous culture conditions,with utilization of TN and COD ranging from 56.9 to58.32% and 67.81 to 68.8%,respectively.Additionally,Chlorella sorokiniana component analysis showed that protein content was higher in phosphorus-rich environments,while polysaccharide content was higher in phosphorus-poor environments.