Study On Cultivation Of Chlorella Sorokiniana By Cocoon Cooking Wastewater In Photobioreactor

Microalgae are photosynthetic microorganisms with high carbon fixation efficiency,fast growth rate,and short growth cycle.Because it can synthesize various bioactive substances with unique functions,it has been widely used in medicine,cosmetics,bait,biofuel,environmental monitoring,and other fields.To reduce the cost of microalgae cultivation,it has been demonstrated that algae cultivation coupled with wastewater treatment is an ideal scenario for sustainable production of algae-based biofuels and bio-based chemicals,since large quantities of freshwater and nutrients required for algae growth could be saved and the associated life cycle burdens could be reduced significantly.Previous studies showed that cocoon cooking wastewater was suitable wastewater for Chlorella sorokiniana,and the final biomass of Chlorella sorokiniana reached 0.49 g/L.Based on the previous research results,to further improve the microalgae biomass accumulation and nutrient removal efficiency,firstly,a set of 300 m L bubbling bioreactor,coupled with cocoon cooking wastewater to cultivate microalgae in the reactor,and optimize the environmental factors（initial cell density,aeration rate,light intensity,photoperiodicity）for culturing microalgae;then,to reduce the cost of the reactor and verify the applicability of the optimal conditions for cultivating microalgae,a 3 L simple photobioreactor was developed and modified to expand the suspension culture of Chlorella sorokiniana,so as to use the reactor to couple cocoon cooking wastewater Large-scale cultivation of microalgae to provide data support.Finally,to improve the harvest efficiency of industrial microalgae,alum and Fe Cl₃ with low price and wide sources were selected as flocculants to carry out single factor experiment and response surface optimization experiment to determine the optimal harvest conditions.The main research results are as follows:（1）A maximum algal biomass,specific growth rate,and biomass productivity of 3.96g/L,0.663 d^-1,and 516.11 g/L/d,respectively,were achieved when Chlorella sorokiniana was cultivated in the bioreactor with an initial cell density of 0.8 g/L,an aeration rate of3.34 L air/L culture/min,light intensity of 150μmol m^-2 s^-1 and photoperiodicity of 16L:8D.Meanwhile,removal efficiencies of ammonium,total nitrogen,total phosphorus,and chemical oxygen demand reached 93.12%,80.79%,93.08%,and 69.08%,respectively,which were significantly higher than that obtained in our previous studies.（2）With the change of microalgae culture conditions（initial cell density,aeration rate,light intensity,and photoperiodicity）,the chemical composition of microalgae cells will also change.The results showed that the protein content,lipid content,carbohydrate content and pigment content of Chlorella sorokiniana were 57.91%,24.56%,15.83%and 1.12%,respectively.（3）The 3 L simple bioreactor coupled with cocoon cooking wastewater to culture C.sorokiniana has certain feasibility and operability.The optimized four cultivation parameters（initial cell density,aeration rate,light intensity,and photoperiodicity）were also suitable for the cultivation of Chlorella sorokiniana with cocoon cooking wastewater in a simple bioreactor,and the final algae biomass was 3.43 g/L.Chlorella sorokiniana was cultured by coupling cocoon cooking wastewater in a simple bioreactor,which was also beneficial to Chlorella sorokiniana to absorb and utilize nutrients in wastewater and improve the utilization rate.After cultivation,the removal rates of NH₄⁺-N,TN,TP,and COD in CCW by Chlorella sorokiniana were 92.61%,78.50%,97.31%,and 66.88%,respectively.（4）Chlorella sorokiniana was cultured in a simple bioreactor coupled with cocoon cooking wastewater.By the end of algae cultivation,the contents of protein,carbohydrate,lipid,and pigment were 53.25%,14.25%,27.95%and 2.66%respectively,which were basically the same as those of Chlorella sorokiniana cultured in 300 m L bioreactor for 7days.（5）When the concentration of alum,flocculation time and initial OD value of Chlorella sorokiniana was 0.8～1.2 g/L,10～30 min,and 0.4～1.2 respectively,the alum flocculation is used to harvest the Chlorella sorokiniana higher efficiency.Factors such as alum concentration,flocculation time,and initial OD value of Chlorella sorokiniana have significant effects on the flocculation efficiency of Chlorella sorokiniana.The effect of these three factors is in the order:alum concentration>initial OD value>flocculation time.Also,the response surface method was used to determine the optimal process conditions for Chlorella sorokiniana flocculent with alum:alum concentration of 1.2 g/L,initial OD value of 0.8,flocculation time of 30 min.under these conditions,the flocculation efficiency of Chlorella sorokiniana flocculent reached 98.49%.（6）With Fe Cl₃ as the flocculant,when the concentration of Fe Cl₃,the flocculation time,and the initial OD value of Chlorella sorokiniana were 0.4～0.8 g/L,30～60 min,and 0.8～1.6,respectively,Fe Cl3 was used to flocculate and harvest Chlorella sorokiniana higher efficiency.The order of the factors affecting Fe Cl₃ flocculation and harvesting of Chlorella sorokiniana was the initial OD value of Chlorella sorokiniana>Fe Cl3 concentration>flocculation time.The optimal process conditions for the use of Fe Cl₃ to flocculate and harvest Chlorella sorokiniana were:the initial OD value of Chlorella sorokiniana was 1.60,the concentration of Fe Cl₃ was 0.6 g/L,and the flocculation time of 38 minutes,under thses process conditions,the flocculation efficiency of Chlorella sorokiniana reached 98.57%.