Screeing Of Lipid-rich Energy Microalgae And Study On Its Nitrogen And Phosphorus Removal Properties In Donestic Sewage

The hot topic of energy crisis and environmental problems is attracting increasing concern worldwide. So there are increasingly urgent requirements for renewable energy. Microalgae possess numerous competitive superiorities such as rapid growth rate, high lipid content, less land required for cultivation and so on. Thus, microalgae have been widely studied in biodiesel production since the start of the 21st century. Biodiesel is a biodegradable, renewable, non-toxic and carbon neutral energy source. So, biofuel are considered to be the high potential substitutes for fossil fuels in the future. While, there are two bottleneck problems that impede the large-scale commercial production. They are low yield and high cost respectively. Promising solutions to overcome these bottlenecks are to screen microalgae with high lipid content and lower the cost. Researchers put forward using wastewater as medium to cultivate microalgae in order to couple biodiesel production with wastewater treatment simultaneously. This application can realize the transformation of the sewage treatment system to the production system, with both environmental and economic benefits.This study screened and purified microalgae from actual bodies of water in Jinan Shandong province, four purified strains were obtained at last via identification and examination. Secondly, With the purpose of combing of wastewater treatment and biofuel production, using four microalgae newly isolated as candidates to evaluate their growth, nutrient removal efficiency and lipid accumulation properties in synthetic sewage. At last, With the purpose of cutting down the cultivation cost in conjunction with wastewater treatment, Scenedesmus sp. SDEC-13 which was proved has higher nutrient removal efficiency and better lipid accumulation properties in the synthetic sewage was chosen as candidate to be cultivated in campus sewage and the sewage was recycled until it can be discharged on standard. In addition, biomass application such as biodiesel and protein production in campus sewage was also evaluated. The main conclusions in this paper are as follows:(1) By the isolation and purification procedures, four pure unialgal strains were finally obtained. Transmission electron microscopy images indicated that much lipid and starch was found in the chloroplast and cytoplasm of the four candidate algae strains, proving that these algae have the potential to produce carbohydrate and biofuels. Using molecular biology identification we named these four microalgae as Chlorella sp. (SDEC-10), Chlorella sp. (SDEC-11), Scenedesmus sp. (SDEC-12) and Scenedesmus sp. (SDEC-13) respectively. In addition, the four algae strains have been preserved in Freshwater Algae Culture Collection at the Institute of Hydrobiology (FACHB-Collection). The serial numbers of them are FACHB-1765, FACHB-1767, FACHB-1766, FACHB-1768 respectively. Scenedesmus sp. SDEC-12 and Scenedesmus sp. SDEC-13 have been also preserved in China Center for Type Culture Collection (CCTCC, Wuhan), the numbers are CCTCC NO:M 2014497 and CCTCC NO:M 2014498 respectively.(2) All the four strains could adapt to the synthetic sewage quickly and obtained higher biomass than in BG-11 medium. Meanwhile they could produce as much as 25% lipid which was also higher than that obtained in BG-11 medium. They exhibited relatively high nutrient removal efficiencies in synthetic sewage. The total phosphorus removal efficiency of the four strains was nearly 100%, but in the case of total nitrogen and ammonium the removal efficiency was relatively low.(3) Among the four strains, Scenedesmus SDEC-13 performed best both in nutrient removal and in biofuel production. With regard to nutrient removal, Scenedesmus SDEC-13 had the maximum ammonium removal efficiency (65%). According to lipid properties, Scenedesmus SDEC-13 is most suitable for biodiesel production on account of having the highest lipid productivity, nearly equal percentage of saturated fatty acids (SFAs) and unsaturated fatty acids (UFAs) and higher amounts of monounsaturated fatty acids (MUFAs). On the whole, Scenedesmus SDEC-13 is the optimum candidate among the four algae strains.(4) Campus sewage used was filtered by gauze only without consuming pretreatment to cultivate the newly isolated microalgae Scenedesmus SDEC-13. Campus sewage could be utilized twice in procession to cultivate Scenedesmus SDEC-13. Nutrients was efficiently removed with the phosphorus and nitrogen removal efficiency nearly 100% and more than 70% respectively in twice use of campus sewage. Ammonium was consumed rapidly within five days in 1st use. There was no significant difference in the lipid and protein content but distinct difference in their respective productivity which is ascribed to the lower biomass productivity caused by limited nutrients in 2nd use. SDEC-13 performed better biodiesel quality compared with BG-11 medium and produced high quality protein when cultivated in campus sewage. Finally, the campus sewage after twice use reached the corresponding discharge standard.