A Study On Culturing Oil-producing Chlorella With Sludge Dewatering Liquid And CO₂

Nowadays,our world is experiencing the challenges of scarce resources and energyshortages, therefore the application of microalgae in production of biodiesel has been of greatconcern in the research of new energy field.However, the conventional methods of cultivatingmicroalgae require large amounts of nitrogen and phosphorus inorganic salts,which lead to thehigh production costs. The sludge dewatering liquid contains a high concentration of nitrogenand phosphorus and the conventional biological treatment process usually needs to refluxdewatering and then mixed with the raw water which will increase the processing load anddecrease the pollutant removal efficiency. The global warming is becoming worse and worse,therefore the study of carbon dioxide fixation technology has become one of the world’s hotspots in the field of global climate change. Aiming at above existing problems, this study intendsto develop chlorella by using sludge dewatering liquid and CO₂,in order to reduce theoil-producing microalgae’s production costs effectively and realize the recycling use of wastewater and CO₂.In this study, Chlorella pyrenoidosa （C.pyrenoidosa） was used as a training object,constant light incubator and the homemade airlift photo bioreactor were used as incubators, andthe chlorella’s nutrient solution was sludge dewatering liquid which was taken from a municipalwastewater treatment plant in Guangzhou. The chlorella growth situation under the condition ofstatic and dynamic state was studied. The feasibility of using sludge dewatering liquid as amatrix of cultivating chlorella was discussed. The effects of temperature, light intensity,inoculum density on the growth of chlorella were studied, the nitrogen and phosphorusabsorption and utilization was analyzed in the experiment.Then investigated light intensity,inoculum density, CO₂concentration on oil yield of chlorella,found out the optimumconditions for producing oil,and the oil composition was analyzed.The main researchachievements are as following:（1） Chlorella gets the laegest biomass and oil productivity when the volume ratio ofslugde liquor and traditional medium was4:6; slightly larger than the individual situation of thetraditional medium,the biomass was0.778g/L,the oil productivity is14.588mg·L^-1·d^-1; It iscompletely feasible to using the sludge dehydration liquor and traditional medium in a volume ratio of4:6as a mixture mediun to cultivate microalgae.（2） It showed that light intensity, spectrum, initial pH had significant influence on theremoval rate of ammonia nitrogen and soluble phosphate by chlorella and the initial inoculationconcentration, CO₂concentration did not have a significant role on that. The maximumutilization of nitrate nitrogen and ammonia nitrogen by chlorella were99.80%and98.86%, thehighest removal rate of solubility phosphate was61.63%.（3）The optimal cultivation conditions of high lipid production were that: room temperatureof about25℃, the volume ratio of sludge dehydration liquor and traditional medium of4:6, theration of light and darkness of10h:14h, the total supplying gas flux of1000ml/min, theintensity of light of3350lux, the inoculum density （OD665nm）of0.100, the initial pH of6.02,blue spectrum, the CO₂concentration of5%and the highest lipid production efficiency couldattain40.061mg·L^-1·d^-1.（4） The results of fatty acids compositions analysis by GC/MS demonstrated that the kindsof fatty acids were abundant, but mainly of C₁₄、C₁₅and C₁₆fatty acid. The main saturatedfatty acid was C_14：0with40.74%of total lipid; the percent of unsaturated fatty acid was about16.4%including about14.99%of C_16：1.