The Study Of Enhanced Carbohydrate Production Efficiency Of Chlorella Sorokiniana By Sulfur Starvation Culture

Microalgae are the third generation bioenergy raw materials after starch and lignocellulosic materials.It has the characteristics of simple culture,high photosynthetic efficiency,fast growth,high biomass yield,and strong environmental adaptability,which has attracted widely attention in recent years,and are considered to have the potential to partially take place the fossil fuels in large scale.Microalgae efficiently fixes carbon dioxide through photosynthesis.It can not only accumulate lipids for biodiesel production,but also can accumulate a large amount carbohydrates.Hydrolysis the carbohydrates and its conversion into biofuels such as bio-ethanol or butanol by microbial fermentation has a great significance for utilization of microalgae biomass.Nutrient limitation can regulate the carbon metabolism pathway of microalgae,and it is one of the important methods to improve the carbohydrate content in microalgae biomass.However,nutrient limitation often affects the growth of microalgae and decrease the final biomass yield.Therefore,it is very important to find the balance point of the carbohydrate content and biomass yield of microalgae under nutrient limitation conditions to improve the biomass energy production of microalgae.In this study,Chlorella sorokiniana UTEX1230 was used as the research material.The effects of sulfur deprivation,sulfur free and sulfur starvation on the growth,biomass production capacity and carbohydrate content of C.sorokiniana UTEX1230 under different cultivation modes(bacteria-free and semi-open mode)were investigated.At the same time,low concentration acid solution was used to hydrolyze Chlorella biomass,and the effects of key factors of hydrolysis reaction on the hydrolysis efficiency were analyzed.Finally,the production capacity of fermentable sugars from C.sorokiniana UTEX1230 and the efficiency of each treatment method were compared statistically.The experimental results showed that the limitation of sulfur affected the growth and biomass accumulation of Chlorella.The growth was more rapid in the semi-open culture mode.The sulfur deprivation increased the carbohydrate content of Chlorella to 25.6%(w/w),the carbohydrate content increased to 62.5%after sulfur free treatment,and sulfur starvation increased the carbohydrate content to 29.9%.Low concentration sulfuric acid hydrolyzed Chlorella biomass to glucose effectively.The conditions of dilute acid treatment was calculated as combined severity(CS),and the CS values was positively correlated with the glucose yields.When the CS value was greater than 1.0,the glucose yield reached more than 40%.Comprehensive data analysis showed that although sulfur deprivation could increase the carbohydrate content of Chlorella,the process of medium replacement was complex and time consuming;sulfur free cultivation could obtain the highest carbohydrate content,and the treatment time was the shortest,but the total yield was slightly lower than sulfur starvation.The sulfur starvation with the initial sulfur concentration of 25%could not only ensure the carbohydrate content,but also resulted in a good biomass yield.The total glucose sugar yield obtained by sulfur starvation was high and the treatment was also convenient,thus it has practical application value.This study provided an experimental basis for improving the carbohydrate yield of microalgae by means of nutrient stress,and provided theoretical basis and research ideas for sugars and biofuels production from microalgae.