Optimization Of Process Conditions For Flocculating Scendesmus Obliquus By Biological Method And The Flocculation Mechanism Research

As an important marine resource rich in vitamins,minerals and high quality single cell protein（SCP）,active polysaccharides and polyunsaturated fatty acid active ingredients,microalgae have good applications in food,medicine,energy and environmental protection,but the high cost of cell harvesting has become an important limiting factor for its application.Current methods of microalgae harvesting are mainly physical or chemical,which have the disadvantages of high energy consumption,high cost,low efficiency and introduction of chemical pollution.Biological method of harvesting has become a hotspot for microalgae harvesting research in recent years due to the advantages of low energy consumption,environmental protection and not affecting the application of microalgae biomass at a later stage.The aim of this thesis is to investigate a bioflocculation method using fungi for flocculation of Scendesmus obliquus.Based on the screening of flocculating strains,the optimized bioflocculation conditions were obtained by investigating the effects of flocculation p H,temperature,rotational speed and algae on the flocculation effect of P.aeruginosa,and then the mechanism of fungal flocculation was explored from the perspectives of adsorption kinetics,cell surface charged properties and extracellular polymer composition analysis.The research of the paper will be of great importance to develop an economical and efficient,green and safe method for harvesting microalgae and promote the industrial application of microalgal biomass.The main research results are as follows.（1）Screening and optimization of culture conditions for flocculating fungal strains of Scendesmus obliquus.In order to select the fungal strains with good flocculation effect on Scendesmus obliquus,the flocculation effect of one fungal strain and five common edible fungi isolated from alcoholic wastewater culture of Scendesmus obliquus was investigated by using the flocculation rate as the index,and the results showed that both the isolated fungal strain and edible fungi could be used as auxiliary fungi for flocculation of Scendesmus obliquus.In order to investigate the suitable culture conditions of the fungus,the dry weight and specific surface area were used as the indexes to optimize the culture conditions of the fungus,and the suitable carbon source was glucose or sucrose,the nitrogen source was yeast paste,and the p H was 7.（2）Optimization of process conditions for biological flocculation.The results showed that the optimum process conditions for flocculation of Phomopsis sp.were p H 9,28℃,160 r/min,and the addition of 5.5 g（wet weight）of mycelium spheres,and the flocculation rate reached 84.33%under these conditions;the process conditions for flocculation of Pleurotus eryngii were p H 3,flocculation temperature of 26℃,rotation speed of 180 r/min,and the initial flocculation rate was 85.67%at p H 3,26℃,180r/min and initial concentration of OD₀=0.6.The removal rate of TP,TN and COD reached97.37%,55.41%and 42.79%,respectively.The flocculation rate of Pleurotus eryngii in wastewater reached 59.68%.（3）Study on the mechanism of flocculation of Scendesmus obliquus by biological method.The results showed that the adsorption of the algae by the mycelial spheres of Pleurotus eryngii was mainly chemisorption.The results of 3D-EEM showed that the extracellular polymers that played a major role in flocculation were proteins,polysaccharides and humic acids;FITR showed that the functional groups that played a major role in flocculation were O-H,N-H,C=O,and P-O.