The Phosphorus Metabolism Mechanism And Phosphorus Crystal Induction Efficiency Of High-efficiency Yeast For Phosphorus Removal

With the continuous advancement of industrialization,agricultural modernization and urbanization,water eutrophication has become one of the prominent water pollution problems in the world.The occurrence of water eutrophication is closely related to the excessive phosphorus concentration in water,and phosphorus is also a non-renewable resource.Therefore,removing phosphorus from wastewater and recycling it has become an effective way to solve the eutrophication of water body and ensure the sustainable development of phosphorus resources.Yeast,as a kind of single-celled fungi,has the characteristics of osmotic pressure resistance,acid resistance,high temperature resistance and high metabolic efficiency,strong adaptability and wide distribution,and is one of the important biological factors in the geochemical cycle.It has also been used in the treatment of phosphorus containing wastewater.The residual sludge produced in the process of dephosphorization by yeast is rich in protein,various amino acids and phosphates,etc.,which can realize the recovery and utilization of biological resources,and has gradually become a research hotspot.However,at present,the study on biological phosphorus removal by yeast is still in the initial stage,and the mechanism of phosphorus removal by yeast is still unclear.In this study,a highly efficient dephosphorization yeast strain BZ was selected from the anoxic/aerobic alternate biofilm system by our previous research group as the research object,and its dephosphorization mechanism and its phosphate metabolism induced enhanced dephosphorization efficiency of magnesium ammonium phosphate（MAP）crystallization were investigated.The strain was identified as Trichosporon asahii,named Trichosporon asahii BZ（hereinafter referred to as BZ）after physiological and biochemical characteristics study and molecular biological identification.The phosphorus removal efficiency and mechanism of simulated municipal wastewater were investigated.Under the optimal culture conditions,the variation trend of total phosphorus in supernatant,extracellular polymer,cell membrane and cell body of strain BZ in the process of phosphorus removal and the contribution rate of phosphorus removal were investigated,and the transfer path of phosphate removal by strain BZ in synthetic wastewater was obtained:At the initial stage of inoculation of yeast BZ into synthetic wastewater,phosphate was first absorbed into cells and stored in extracellular polymers（EPS）.In the late stage,nutrients are deficient,and intracellular phosphorous substances are decomposed to release energy for cell metabolism.Meanwhile,total phosphorus is released into EPS and supernatant.Among them,the contribution rate of EPS to total phosphorus removal was about 20-30%,that of intracellular total phosphorus removal was about 60-70%,and that of cell membrane was about 5-10%.The storage form of phosphorus was obtained by ³¹P NMR scanning of strain EPS and cell body:The forms of phosphorus in EPS were mainly positive phosphorus,phosphoric mono ester,phosphoric diester and polyphosphorus,accounting for 24.55%,39.41%,30.63%and 5.41%,respectively.The forms of phosphorus in bacteria were mainly positive phosphorus,phosphoric mono ester,phosphoric diester,pyrophosphate and polyphosphorus.The intracellular energy storage substances were polyhydroxy fatty acid ester（PHA）and glycogen in the process of phosphorus removal,which showed a trend of first increasing and then decreasing.According to the test results,the phosphorus metabolism model of yeast BZ was speculated as follows:When the strain inoculation to the synthetic wastewater,EPS wrapped in the surface of the bacteria,use its adsorption capacity,adsorption of phosphate in water,part of phosphate combined with EPS polysaccharide in phosphate monoester and diester phosphate phosphorus esters such as organic matter,when in a state of poor phosphorus,cells feel the external environment changes,the release of acid phosphatase and phosphate transporters to EPS and cell membrane,Decomposition phosphate esters,release energy by consuming intracellular energy storage substances such as PHA,synthesize glycogen and absorb into the cell by the reverse concentration gradient of external phosphate in an active transport way,and form intracellular phosphorus storage substances such as pyrophosphate and polyphosphate.Combining yeast and MAP crystallization phosphorus,phosphorus biological-build coupling process,with A²O craft Yan Yang Chi rich phosphorus that for target wastewater supernatant fluid,forming a yeast BZ phosphorus metabolism induced reinforced magnesium ammonium phosphate crystallization phosphorus removal system,explore the yeast inoculation quantity,inoculation time,p H adjustment and Mg²⁺dosing time of process system technology,Key influencing factors such as p H value,reaction time,aging time,stirring intensity,N/P ratio and Mg/P ratio were explored to determine the optimal technical parameters:The inoculation amount of yeast was 5%（v/v）,the incubation time was 8 h,magnesium salt was added at 2 h,the initial phosphorus concentration was 60 mg/L,P:N:Mg=1:2:2,p H=10.0,the stirring intensity was 300 r/min,the reaction time was 30 min,and the aging time was 30 min.The response surface test was designed and optimized to obtain the regression equation Y=96.90+0.6121A+0.0066B+0.0256C-0.4602AB-0.4484AC-0.0263BC-1.34A²-0.0835B²-0.4635C²,and the model P<0.01.Under this condition,the fitting model is highly significant,and the fitting degree R² is 0.9787.By fitting the crystallization reaction kinetics test,the process of enhancing MAP crystallization induced by yeast phosphorus metabolism to treat phosphate in the supernatant of A2O anaerobic pool is more consistent with the tertiary reaction kinetics,that is,1/2[reactant concentration PO₄^3--P]shows linear relationship with time approximately.The reaction model was obtained as y=（1/（2（0.0312t+0.4595）））^1/2,R²=0.9586,and the reaction rate constant was 0.2609.The analysis of the crystallization process and products showed that the surface of yeast formed a dense point-like distribution at the initial crystallization stage,which was tightly wrapped on the surface of yeast,and it was speculated that the yeast was wrapped in magnesium ammonium phosphate crystal.The diameter of the mixture of yeast and crystal is more than 5μm.The volume of the mixture increases gradually with the process of the reaction,and finally the larger crystal is formed.The crystallization products are mainly magnesium ammonium phosphate crystals,and a small amount of magnesium hydroxide crystals are crystal by-products.In this study,Trichosporon asahii was used as the research object to investigate the phosphate metabolism characteristics of the strain in typical wastewater,the role of EPS and cell body in phosphorus removal,and the expression of yeast PHO mechanism,so as to form a yeast phosphorus metabolism model.On this basis,the process system of phosphorus metabolism induced by yeast and enhanced crystallization of magnesium ammonium phosphate was constructed to provide a theoretical basis for the extensive application of yeast in phosphorus removal process.