Isolation And Screening Of Two Microalgal Species For N,P Removal And Biomass Production

Objective:This study was designed to isolate and screen native microalgal species from different fresh water habitats in Lanzhou,to discover potential species for wastewater treatment and biofuel generation.Methods:Microalgal species were isolated from the artificial lakes of Five Springs Park and Yan Tan Park in Lanzhou city,and identified by morphololation and molecular markers.Microalgae isolated were cultured in BBM medium the growth was measured by spectrophotometer with the optical density（OD）at 680nm and the specific growth rates were calculated.Nutrient removal including total nitrogen（TN）and total phosphorus（TP）was studied during the cultivation of isolated microalgae.TN and TP were analyzed by water-quality auto-analyzer.After cultivation,whole biomass composition（including fatty acid,carbon and protein）was analyzed.The properties of the biodiesel including cetane number,cold filter plugging point,iodine value,saponification value,kinematic viscosity and oil stability index were calculated based on the Fatty acids methyl esters（FAMEs）profile.The proximate analyses including moisture,volatile,and ash content of microalgae were analyzed through furnace.Ultimate analyses provided elemental composition（%）of carbon（C）,hydrogen（H）,nitrogen（N）,sulfur（S）,and oxygen（O）in microalgal biomass using Elementar.The freeze-dried microalgal biomass（1.5 mg）was analyzed to study the functional groups through Fourier-transform infrared（FT-IR）spectroscopy.While 5 mg biomass was used for thermogravimetric analysis（TGA）.Results:（1）Two microalgal strains were isolated from the artificial lakes of Five Springs Park and Yan Tan Park,were indentified as Tetradesmus dimorphus GEEL-04and Desmodesmus asymmetricus GEEL-05 by molecular markers,respectively.T.dimorphus GEEL-04 showed higher growth(1.46 OD_680nm)compared with D.asymmetricus GEEL-05(1.16 OD_680nm),while,both showed a similar specific growth rate of 0.149 day^-1 and 0.148 day^-1.The p H of the medium increased from 6.8（initial medium p H）to 9.65±0.16 and 9.17±0.23 on 28^th day of T.dimorphus GEEL-04 and D.asymmetricus GEEL-05 culture,respectively.（2）T.dimorphus GEEL-04 removed 99.6%TN and 99.5%TP,D.asymmetricus GEEL-05 showed 99.0%and 98.3%TN and TP removal,respectively,after 28 days of cultivation.（3）The elemental composition of T.dimorphus GEEL-04 biomass had C（50.13%）,H（7.56%）,N（6.09%）,S（0.59%）,and O（35.63%）.In contrast,D.asymmetricus GEEL-05 biomass possessed C（43.01%）,H（6.79%）,N（6.90%）,S（0.42%）,and O（42.87%）.（4）T.dimorphus GEEL-04 and D.asymmetricus GEEL-05 accumulated higher protein content of 40.02 and 45.10%,followed by 31.91 and 24.64%carbohydrate,and15.41 and 24.16%lipid,respectively.The major fatty acids profile of T.dimorphus GEEL-04 and D.asymmetricus GEEL-05 were palmitic acid,stearic acid,oleic acid,and linoleic acid accounting for 25.22–27.15%,12.34–15.49%,6.15–6.39%,and28.36–34.59%,respectively.The fatty acid composition of both microalgal strains showed high palmitic acid and linoleic acid corresponding to high quality biodiesel.（5）Estimated biodiesel properties generated from T.dimorphus GEEL-04exhibited good qualities falling under international standard.Estimated biodiesel properties except CFPP based on FAME profile of D.asymmetricus GEEL-05 were in accordance to international standards i.e.,EN 14214,ASTM 6751-03 and GB/T 20828.（6）The FT-IR spectra absorbance revealed different function groups indicating the presences of proteins,lipids,and carbohydrates in microalgal biomass.Thermogravimetric analysis also indicated≥80%volatile content in both isolates.Conclusions:（1）Two microalgal strains were isolated from the artificial lakes of Five Springs Park and Yan Tan Park,were indentified as Tetradesmus dimorphus GEEL-04 and Desmodesmus asymmetricus GEEL-05 by molecular markers,respectively.（2）T.dimorphus GEEL-04 and D.asymmetricus GEEL-05 could be potential candidates for N,P removal base on high growth kinetics,removal efficiency.（3）T.dimorphus GEEL-04 has high content of Highly Unsaturated Fatty Acid and estimated biodiesel properties exhibited good qualities.D.asymmetricus GEEL-05 has high amount of lipid and estimated biodiesel properties except CFPP exhibited good qualities.Both strains of microalgae have higher value of bioenergy.T.dimorphus GEEL-04 and D.asymmetricus GEEL-05 could be suitable in coupling of biomass/biodiesel production with nutrients removal（N,P）.