| Excessive nitrogen in the water environment and eutrophication have caused global environmental problems.The main denitrification process in existing actual projects is still carried out using the traditional denitrification process.The biggest problem of the traditional denitrification process is the lack of denitrification carbon source.Many scholars have studied a large number of external carbon sources,but they have focused on the carbon release and nitrogen removal performance of carbon sources,and less research has been done on the mechanism of carbon release and the dynamic balance of nitrogen removal.Therefore,the research focus of this thesis is on the carbon release mechanism and nitrogen removal dynamic balance of porous carbon release fillers,and at the same time provide theoretical support for practical engineering applications of walnut shell-zeolite porous carbon release fillers.In this dissertation,the long-term carbon release mechanism of walnut shell-zeolite porous filler for static carbon release was firstly studied,and its carbon release components were analyzed by three-dimensional fluorescence spectroscopy.At the same time,two-stage nitrification and denitrification BAF was started,and different HRT and The optimal operating conditions of C/N,revealing the mechanism of walnut shell-zeolite porous carbon release filler for denitrification through the microbial community structure of nitrification and denitrification.Finally,the composition of the filler was changed during the test,and the amount of denitrified carbon dynamic balance and costing.Through a series of experimental studies,the following results were obtained:(1)Through the static carbon release test,the maximum carbon release of walnut shell and walnut shell-zeolite porous filler were 11.311 mg/g and 3.066 mg/g,respectively.Carbon release is divided into three phases:rapid release,slow release and stable release.The carbon release process conforms to the first-order conforms,second-order kinetics and the Ritger-Peppas kinetic equation.The mechanism of carbon release during the rapid release phase is mainly coexistence of diffusion and corrosion;during the slow release phase,it is mainly caused by the diffusion of FICK.It can be known from the three-dimensional fluorescence spectrum that the carbon source components released within 2-6 days are mainly tryptophan proteins that are easily degradable and fulvic acid-like substances that are difficult to degrade.(2)Under different operating conditions and the results of response surface method optimization,it can be known that the best operating conditions are 9.67 h for the first-stage O-BAF HRT,C/N is 7.5;the second-stage A-BAF HRT is 11.01 h,C/N is 7.48.Under the best operating conditions,the removal rates of primary O-BAF for NH3-N,COD,and TN are 100%,94.35%,and 48.59%,the removal of A-BAF for NO3-N and TN are 83.70%and 81.23%.The P-values of the first-order O-BAF and second-order A-BAF in the analysis of variance in the response surface are both less than 0.01,which are extremely significant,indicating that the model has high accuracy and precision,and the predicted value of first-order is obtained.The removal rates of NH3-N,COD and TN were 100%,98.83%,and 51.80%;the removal rates of secondary NO3-N and TN were 81.78%and 82.84%.The maximum difference between the test value and the predicted value is 4.48%,which indicates that the models established by the test can accurately simulate this test.(3)Analysis results of microbial community structure:According to Biolog results,the utilization rate of first-class O-BAF for three types of carbon sources such as sugars,lipids and amino acids is high,and the utilization rate of sugars reaches 100%at the highest;Secondary A-BAF has higher utilization of lipids and amino acids,and especially prefers the use of lipids.According to the results of high-throughput sequencing,the characteristic functional microorganisms in O-BAF and A-BAF are mainly Thiothrix,Enterobacter,Enteroacter,norank-f-Saprospiraceae,Nitrospira and autotrophic denitrifying bacteria Silanimonas,Thauera,Denitratisoma,Hydrogenophaga.(4)The research on carbon balance and filler change characteristics shows that the main consumption of carbon source is denitrification and need 319.34 mg/d,and the main dissolution method is microbial action,and the dissolution amount is 309.928 mg/d.The treatment of 1 mg of NO3-N requires 3.38 mg of carbon source,which is 3.92 mg of walnut shell.With the use of fillers,a large number of pore structures appeared on the inner and outer surfaces of the fillers.The main functional groups on the surface did not shift,and the main characteristic absorption peaks became weak.(5)The actual domestic sewage treatment operation results show that:in the stable operation stage,the total nitrogen in the influent is 5.93?38.02 mg/L,and the average total nitrogen concentration in the effluent is 8.74 mg/L,which is lower than the "Emission Standard of Pollutants for Urban Wastewater Treatment Plants" The total nitrogen effluent standard 15 mg/L of Grade A.The walnut shell-zeolite porous carbon-releasing filler can be used as BAF filler to achieve efficient nitrogen removal performance.This paper reveals the carbon release mechanism of walnut shell-zeolite porous filler,the dynamic carbon balance and nitrogen removal mechanism in BAF,which provides a carbon source for the denitrification and nitrogen removal process,improves the nitrogen removal efficiency,and saves the cost of nitrogen removal.It provides data support and theoretical basis for the practical engineering application of carbon release fillers. |
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