Study On Nitrogen And Phosphorus Removal By Functional Fillers In A Integrated AO Reactor

Rapid urbanization development has increased the discharge of polluted water containing nitrogen and phosphorus.High concentrations of nitrogen and phosphorus can cause eutrophication of water bodies,thus putting the health of the water environment at risk.Among various wastewater treatments,biofilm process is widely used because of its high treatment efficiency,simple operation and low cost.As the core of the biofilm process,the physical structure and chemical stability of the filler affects the speed and ease of film attachment.Compared with traditional fillers,artificial rock wool（ARW）is rich in mineral elements and has a larger specific surface area,which is more conducive to the growth of microorganisms.Manganese oxide（MnO_x）has high redox capacity and catalytic activity in biochemical systems.The electrical conductivity of carbon fiber powder（CFP）accelerates extracellular electron transfer in biochemical systems.Based on this,two modified biopackers,MnO_x@ARW and CFP@ARW,were firstly prepared in this study,and an integrated AO reactor was constructed using them.To investigate the effects of different C/N,HRT and DO concentrations on the effectiveness of nitrogen removal and phosphorus removal in each reactor,and to determine the optimal operating conditions of each reactor.On this basis,the reactor with the best effect of nitrogen and phosphorus removal was modified so as to further improve its nitrogen and phosphorus removal effect.Further,high-throughput sequencing was used to study the microbial community structure in different systems of each reactor separately and to explain the mechanism of action of the associated microorganisms.The main findings are as follows:（1）Methanol diffusion method is an effective method for the modification of ARW by MnO_x.Four MnO_x modification methods,namely,impregnation,Mn Cl₂ redox,methanol diffusion and KMnO₄ redox,were selected to modify ARW.It was confirmed by mass,SEM and EDS analysis that the modified ARW surface was loaded with MnO_x and the ARW-MnO₂methanol diffused fiber surface was loaded with the most MnO_x particles.Meanwhile,the ARW-MnO₂ methanol diffusion system was the most effective for nitrogen removal and phosphorus removal compared to the other three MnO_x modification methods.Its stabilized removal rates of COD,NH₄⁺-N,NO₃^--N and TN were increased by 7.51%,17.02%,2.15%and 11.19%,respectively,compared with the original ARW system.（2）The integrated AO reactor filled with MnO_x@ARW has a good effect of nitrogen removal and phosphorus removal.When the influent COD,NH₄⁺-N,NO₃^--N and PO₄^3-concentrations were 275 mg/L,20.7 mg/L,35.5 mg/L and 3 mg/L,respectively,the C/N was4.89,the HRT was 12 h and the DO concentration of the aerobic system was 3.7 mg/L,the best results of nitrogen removal and phosphorus removal were achieved in the R1,R2 and R3 reactors.At this time,the average effluent concentrations of COD,NH₄⁺-N,TN and PO₄^3-from each reactor reached the primary A standard in GB18918-2002"Discharge Standards for Pollutants from Urban Wastewater Treatment Plants".Then the comparison revealed that the R2 reactor filled with MnO_x@ARW was better than the R1 and R3 reactors in terms of nitrogen and phosphorus removal.（3）The best aerobic system of R2 reactor for nitrogen and phosphorus removal was modified into a trickling filter system（R4 reactor）,and its nitrogen and phosphorus removal effect was further improved.Among them,the average removal rates of COD,NH₄⁺-N,NO₃^--N,TN and PO₄^3-were increased by 7.47%,4.61%,0.67%,3.49%and 1.11%,respectively,for the R4 reactor compared with the R2 reactor at the optimal operating conditions.（4）High-throughput sequencing of the microbial community structure in the different systems of each reactor revealed significant differences in the structure of the microbial communities in the different systems.Specifically analyzed at the phylum,order and genus levels,each system has its own dominant phylum,dominant order and dominant genus,and it is the differences in these bacterial groups that lead to differences in the effectiveness of nitrogen and phosphorus removal in each reactor.Compared to the R2 reactor,the aerobic system of the R4reactor had a higher percentage of Proteobacteria and Nitrospirae at the phylum level;At the class level,the percentages of Gammaproteobacteria,Alphaproteobacteria and Nitrospira were elevated;At the genus level,the proportion of both Nitrospira and Tolumonas increased and new dominant genera such as Hydrogenophaga were added.Under the condition that the microbial community structure of the anaerobic system of the R4 reactor was the same as that of the R2reactor,the nitrogen and phosphorus removal effect of the R4 reactor was further improved.