The Efficiency And Metabolism Of Yeasts Candida Rugosa BL3 For Phosphorous Removal

The eutrophication of lakes in China has become increasingly serious and caused more frequent cyanobacterial blooms.The excessive discharge of phosphorus is a major contributor to this phenomenon.At the same time,the continuous development and utilization of phosphorus resources will lead to a serious shortage crisis because phosphorus is a non-renewable resource.Therefore,the treatment and reuse of phosphorus?P?in wastewater are key challenging issues that our planet have to face nowadays.Yeast,a common unicellular fungus in biological phosphorus removal system,has some advantages compared with phosphate accumulating organisms?PAOs?,such as its large size,fast growth,good sludge flocculation and sedimentation performance.Due to the yeast accounts for a smaller proportion of activated sludge and its research is not mature,but the application of yeast should not be ignored.In this study,the Candida rugosa BL3,which was selected from the anoxic/oxic?A/O?alternate biofilm system,was used as the experimental strain to study the efficiency and mechanism for phosphorous removal.The strain was identified as Candida rugosa and named as Candida rugosa BL3?hereafter,Strain BL3?.Strain BL3are phenotypically characterized by colonies of milky white coloring,with wet appearance,flat and waxy surface,sticky and easy to pick up,and microscopically by the presence of round ascospore without throwing spore,pseudophyphae and true hyphae.The generation time?RT?is 2.53 h.In this paper,the biomass and phosphorus removal performance of Stain BL3 were compared at different inoculation amount,temperature,pH value,dissolved oxygen content,carbon source,the ratio of carbon and phosphorus?C/P?and the ratio of nitrogen and phosphorus?N/P?.The results showed that the optimum inoculum amount was 5%,the optimum growth and phosphorus removal conditions were:temperature:25-35?,pH:5-7,aerobic condition,the mixed carbon source of glucose and sodium acetate,C/P was 40,and N/P was 3.The dynamic changes of phosphate concentration in supernatant,cell,extracellular polymeric substance?EPS?and membrane of BL3 were studied.It was found that most of the phosphorus in the liquid phase was absorbed by EPS secreted by the cells and a small part of that was absorbed and utilized by the cells in the early stage of culture;in the later stage of culture,the phosphorus stored in EPS began to transfer to the cells.When the phosphorus concentration in the supernatant no longer changes,the contribution rate of EPS was 60-70%,that of bacteria was 10-20%,and that of cell membrane was 5-10%.The results of Scanning Electron Microscopy?SEM?showed that the bacteria were full of vitality before dephosphorization.After dephosphorization,the cells became smaller and fuzzy.According to Energy Dispersive Spectroscopy?EDS?spectrum analysis,the cell surface was mainly composed of C,N and O elements.The percentage of P peak atom before dephosphorization is only 0.28%,but after dephosphorization,the percentage of P peak atom increased to 3.16%,indicating that the phosphorus element in the culture medium was transferred to the cell surface or cell interior.Three kinds of intracellular polymers,poly-hydroxyalkanoate?PHA?,glycogen and polyphosphate?Poly-P?,and two kinds of extracellular carbon sources,sodium acetate and glucose,were studied by beaker test.The storage morphology of intracellular phosphorus was detected by ³¹P nuclear magnetic resonance?NMR?technology.The energy storage substance in strain BL3 was PHA and glycogen,and the phosphorus storage substance was Poly-P.About 10%is orthophosphate,15%is phosphate monoester,55%is phosphate diester and 20%is polyphosphate.The dephosphorization process of yeast BL3 was as follows:firstly,strain BL3 used sodium acetate to synthesize PHA and glucose to synthesize glycogen;secondly,strain BL3used the synthesized PHA and glycogen as the energy substance to absorb the free inorganic phosphate particles from the outside and synthesize poly-P,to maintain its own metabolic needs.By studying the main components and dynamic variation process of EPS secreted by BL3 in the process of dephosphorization,this experimentanalyzed the response of acid phosphatase?APs?in the process of dephosphorization,and detected the form of phosphorus storage in EPS,and preliminarily obtained the phosphate metabolism model in EPS.It is found that the main components of EPS are protein and polysaccharide,the ratio was about 7:3.There was a direct positive correlation between the activity of acid phosphatase secreted by BL3 and the phosphorus removal rate.At different initial phosphorus concentrations,the secretion of acid phosphatase is different:when the external phosphorus content was lower than the required phosphorus consumption for the growth of strain BL3,a large amount of acid phosphatase will be secreted by strain BL3;when the external phosphorus content met the required phosphorus consumption for cell growth,the secretion of acid phosphatase will be reduced appropriately.³¹P Nuclear Magnetic Resonance?NMR?spectra showed that in EPS,orthophosphate accounted for about 40%,polyphosphate for about43%,and the others mainly existed in the form of phosphate monoester and phosphate diester,accounting for 10%and 7%,respectively.The absorption of P in the environment by BL3 was regulated by the mechanism of PHO:the cells sensed the concentration of external P,and released the corresponding acid phosphatase and phosphate transporter.The acid phosphatase transformed the organic phosphorus in EPS into the easily absorbed inorganic phosphate ion,and the free inorganic phosphate ion was transported to the cell by the phosphate transporter secreted by the cells.In this paper,Candida rugosa BL3 was selected as the research object to explore its phosphorus removal in simulated municipal wastewater,phosphorus removal efficiency under different environmental conditions,phosphate metabolism pathway of cell and the role of EPS in the process of phosphorus removal.The phosphorus removal mechanism of BL3 was clarified,which provided a theoretical basis for exploring new phosphorus removal microorganisms.