Effect And Mechanism Of Nitrogen And Phosphorus Removal In Black And Odorous Water By The Symbiosis System Of Oedogonium Brevicingulatum And Activated Sludge

With the acceleration of urbanization in my country,black and odorous water has become one of the urgent environmental problems affecting the urban water resources environment.In order to achieve the goal of efficient and green restoration of black and odorous water,ecosystems have been often used to remove nitrogen and phosphorus in black and odorous water in actual governance.The biological treatment method based on algal-bacteria symbiosis technology has the advantages of high denitrification and phosphorus removal efficiency,low energy consumption,and no secondary pollution,and is an effective method for treating black and odorous water.The application of algal-bacteria symbiosis technology to the treatment of black and odorous water is not only related to the process parameters in the operation of the system,but also affected by the water quality conditions.In this paper,we selected a dominant denitrification and phosphorus removal algae species-Oedogonium brevicingulatum,which was screened in an urban sewage treatment plant in the early stage,and investigated its denitrification and phosphorus removal effect on simulated black and odorous water and under the condition of external carbon source.Removal of nitrogen and phosphorus in urban sewage.Taking the denitrification and phosphorus removal efficiency as the main evaluation index,the process conditions were optimized for the O.brevicingulatum-activated sludge symbiosis system.The effects of dissolved oxygen,p H and water temperature on the denitrification and phosphorus removal of the algal-bacterial symbiotic system were further evaluated.Scanning electron microscopy（SEM）was used to observe the morphology of sediment microorganisms,algae and algal cells,and 16S r DNA high-throughput sequencing was used to analyze the microbial community changes in the process of nitrogen and phosphorus removal in the algal-bacteria symbiotic system.The main conclusions of this paper were as follows:（1）After a 7-day experimental period,the removal rates by O.brevicingulatum of NH₄⁺-N,TP and COD_Crin simulated black and odorous water were 54.1%,57.5%and 25.7%,respectively.The NH₄⁺-N concentration was lower than the mild black odor standard,and the TP concentration reached the surface V class water standard.After adding the carbon source Na HCO₃,the O.brevicingulatum had the effect of NH₄⁺-N,TP and COD_Crin the simulated urban sewage after a 12 h experimental period.The removal rates were 100%,91.2%and 100%,respectively.The Monod kinetic equation was used to calculate and fit,and it was confirmed that Na HCO₃promoted the growth of O.brevicingulatum,thereby improving its nitrogen and phosphorus removal efficiency.（2）Optimize the process parameters of the algal-bacteria symbiosis system constructed by O.brevicingulatum and activated sludge.When the algal-bacteria dry weight ratio was 3:1,the biomass was 0.6 g/L,and the aeration volume was 0.4 L/min,the removal effect of NH₄⁺-N,TP and COD_Crin the simulated black and odorous water was the best;under the optimal process conditions,O.brevicingulatum-activated sludge symbiosis system was continuously operated to treat the simulated black and odorous water for 15 days,During the period of 5-13days,the concentration of NH₄⁺-N in effluent was lower than the standard concentration of mild black odor,the concentration of TP was lower than the concentration standard of surface V class water,and the concentration of effluent COD_Crwas always lower than the standard concentration of surface class III water during operation;Nitrogen,phosphorus and organic matter contents in the sediment after treatment by the algae-bacteria symbiotic system decreased,and the sediment also changed from black to yellow-brown at first,showing an aerobic state.（3）To investigate the effect of the O.brevicingulatum-activated sludge symbiosis system under different water quality conditions,the nitrogen and phosphorus removal efficiency was investigated.During the 48-h experiment period,the dissolved oxygen concentration was 2.0 mg/L in the experiment.The removal rate of NH₄⁺-N,TP and COD_Crincreased by 18.9%,25.0%and 27.5%respectively compared with the 0.4 mg/L experimental group.The range is 6.5-7.5;if the water temperature is too high or too low,it will have an inhibitory effect on the activity of the O.brevicingulatum-activated sludge symbiosis system,thereby affecting the denitrification and phosphorus removal efficiency.When the temperature is 25°C,it is beneficial to the algae and the life activities of the symbiotic system.The algal-bacterial symbiosis system was used to treat the actual black and odorous water samples.The average effluent concentrations of NH₄⁺-N,TP and COD_Crwere 6.81,0.34 and 15.4 mg/L,the concentration of NH₄⁺-N reaches the standard of not black and odorous,the TP reaches the V standard for surface water,and the COD_Crmeets the standard III for surface water.（4）Sampling the sediments of the 5 sampling points of the black and odorous water,and measuring the NH₄⁺-N,TN,TP and organic matter content of all the sediment samples.Through calculation,it is concluded that the left main canal bottom sediment is slightly polluted;The release flux was higher under the condition than that under the standing condition,the overlying water was more turbid,and the SS was higher,indicating that the river channel was more prone to black odor at suitable temperature after rain;the O.brevicingulatum and bacteria micelles were observed by scanning electron microscope.Tightly intertwined to form algal-bacterial symbionts with good nitrogen and phosphorus removal performance;at the phylum level,Proteobacteria,Firmicutes and Green The relative abundances of Chloroflexi increased,and they were mainly involved in the denitrification and phosphorus removal process with O.brevicingulatum,and formed a mutually beneficial symbiotic relationship;at the genus level,Flavobacterium,The relative abundances of Arcobacter,Comamonas,Longilinea and Brevundimonas all increased,determined by It can be seen that the nitrogen and phosphorus removal of black and odorous water is achieved by the cooperation between different bacterial groups,various functional microorganisms and algae in the algal-bacterial symbiotic system.