Studies On Biodiesel Production By Microalgae Cultivation With Molasses Waste Water And Walnut Shell

Biodiesel is a clean,contamination-free,and renewable energy.Given its advantages,biodiesel has received widespread attention worldwide.However,its high production cost,which reached 75%of the total cost,has restricted its development.Therefore,choosing suitable and low-cost raw materials has become a hot research topic.Microalgae,the most widely distributed single-cell or group microorganisms on Earth,can effectively utilize sunlight for photosynthesis that converts solar energy into biomass energy.Biodiesel production with microalgae as raw material has many advantages.Exogenous phytohormones can reduce the cost of biodiesel production from microalgae.Melatonin widely exists in many plants as a plant hormone;it promotes plant growth and delays plant senescence by regulating photosynthesis,cell cycle,DNA replication,metabolism,and lipid synthesis.In the present study,Monoraphidium sp.FXY-10 and Monoraphidium sp.QLZ-3 were used to establish a low-cost culture method and synthesize microalga lipid efficiently.The effects of molasses wastewater on the growth and lipid accumulation of microalgae were studied.Additionally,the key genes of microalga lipid synthesis in industrial wastewater were elucidated.The algal growth cycle decreased in photo-bioreactor,which provided a theoretical basis and practical significance for reducing the cost of lipid production and expanding the industrialization of cultivation.The results are as follows:?1?Molasses wastewater was used to prepare the microalga medium with exogenous MgSO₄·7H₂O.The maximum biomass and lipid content was obtained in800?mol L^-1 Mg²⁺conditions.Total nitrogen?TN?,total phosphorus?TP?,and COD from molasses wastewater were effectively removed by using microalgae.In addition,Mg²⁺enhanced Ca²⁺,Fe3+,and Cu²⁺absorption in molasses wastewater.The results showed that appropriate Mg²⁺concentration could promote microalgal growth and lipid accumulation in molasses wastewater.Meanwhile,Mg²⁺could decrease the concentration of relevant metal ions,TN,TP,and COD value in molasses wastewater by using microalgae.?2?However,the mechanism of melatonin regulation of microalgal growth and lipid synthesis in wastewater has rarely been reported.In this experiment,melatonin promoted microalgal growth and lipid accumulation in molasses wastewater with Mg²⁺.The lipid content of microalgae reached 68.69%,and the maximum biomass was 1.22g L^-1.Additionally,protein content in algal cells decreased,but the carbohydrate content increased.COD,TN,and TP in molasses wastewater were removed.In addition,the activities of acetyl coenzyme A carboxylase?ACCase?and malic enzyme?ME?were upregulated under exogenous melatonin,but the activity of phosphoenolpyruvate carboxylase?PEPC?was downregulated.The results showed that melatonin promoted algal growth and lipid accumulation by regulating the activity of key enzymes.Our findings provided a new theoretical basis for improved lipid production and decreased culture cost of microalgae.?3?Large-scale microalga cultivation will be conducted in the future.The photo-bioreactor of microalga cultivation provides a theoretical basis for algal industrialized cultivation.The biomass and lipid content of microalgae were effectively improved in the photo-bioreactor with WSE under 12%CO₂ conditions.The absorption rates of nitrogen and phosphorus in WSE were utilized.At the same time,the increased chlorophyll content and upregulated rbcL gene expression levels promoted CO2fixation on the single needle algae Monoraphidium sp.QLZ-3.Under the condition of12%CO₂,microalgae promoted polyphenol absorption in WSE.Polyphenols are antioxidants that may regulate the antioxidant system to upregulate accD and kas gene expression levels for lipid accumulation in algal cells.