| Increasing industrial wastewater,domestic sewage and food wastewater poses a great challenge to the protection of the water ecosystem.Traditional wastewater treatment processes often have many defects such as expensive engineering costs.Fortunately,compared with traditional physicochemical methods,microalgae treatment not only avoid secondary pollution,it also purified the wastewater and obtain microalgae biomass to extract biodiesel.Although there are more than fifty thousand species of microalgae currently and several thousand species have been preserved in the algal species bank,only a few hundred species have been studied for their chemical composition.Therefore,the resources of microalgae species for utility are still limited.At present,the resource utilization of microalgae in China is in initial stage,so it is particularly valuable to isolate,identify and screen microalgae with specific function.Extreme environment is the best condition for obtaining excellent algae species.In this study,eight species of microalgae were isolated,purified and identified from Zhangye area of Hexi Corridor,China.Screened microalgae contain following merits:high lipid production,excellent nutrient removal efficiency and valuable byproducts acquisition.The main conclusion of this study are as follows:（1）In this study,microalgae in the soil and water environment of the Hexi Corridor were cultured using solid medium.And then microalgae were isolated and examined by microscopy until pure strains were obtained.The isolated strains were initially identified as green algae,and the phylogenetic trees of eight microalgae were constructed according to 18S r RNA gene sequence analysis.Eight species of microalgae named Scenedesmus sp.HXY1、Scenedesmus sp.HXY2、Desmodesmus sp.HXY3、Scenedesmus sp.HXY4、Scenedesmus sp.HXY5、Scenedesmus sp.HXY6、Desmodesmus sp.HXY7 and Desmodesmus sp.HXY8,respectively.Eight species of microalgae were cultured in BG-11 for 12 days.The lipid content of the eight algae ranged from11.1%to 19.7%.Among them,Desmodesmus sp.HXY8 had the highest lipid content and fatty acid percentage of C16-C18 of 19.7%and 92.5%,respectively.And it had the hightest pigment content of 103.87 mg g-1.Therefore,Desmodesmus sp.HXY8 was selected as the optimal lipid-producing algae species to obtain biodiesel while continuing to extract pigments to reduce the cost of biodiesel production.（2）The concentrations of TOC,TP and TN in the simulated wastewater were 878 mg L-1,13.67 mg L-1 and 52.34 mg L-1,respectively.Simulated wastewater treatment with microalgae could achieve good nutrient removal efficiency.Among them,Scenedesmus sp.HXY2 had the best nutrient removal efficiency after 8 day,with the removal efficiency of 96.07%,96.62%,94.52%and 99.09%for TOC,TDN,TDP and NH3-N,respectively.Moreover,Scenedesmus sp.HXY2 had the highest lipid content and unsaturated fatty acid content of 15.56%and 60.07%,respectively.Therefore,Scenedesmus sp.HXY2 was selected as the optimal nutrient removal efficiency algae species and was expected to obtain high quality biodiesel,which greatly reduces the cost of treating wastewater.（3）The concentrations of COD,TDN and TDP in potato wastewater were 1504.00 mg L-1,127.89 mg L-1 and 11.11 mg L-1,respectively.Potato wastewater treatment with microalgae could purify wastewater.Eight species of microalgae were the most effective in removing COD,with the removal efficiency ranging from 88.36%to 92.77%.Among them,Scenedesmus sp.HXY5had good purification effect on potato wastewater,with removal efficiencies of 92.53%,58.76%and 32.26%for COD,TDN and TDP,respectively.The pigment content of Scenedesmus sp.HXY5(7.0 mg g-1)was lower than that of Scenedesmus sp.HXY4(15.3 mg g-1),but higher pigment yields were obtained due to the highest microalgal biomass content of Scenedesmus sp.HXY5.Therefore,in this study,Scenedesmus sp.HXY5 was selected as the optimal algal species to purify potato wastewater and to obtain high value pigments. |
