| Biological nitrogen removal of sewage is affected by a variety of environmental factors,including DO concentration,carbon source type,C/N ratio,pH,temperature,etc.The new biological nitrogen removal process can efficiently remove ammonia nitrogen from water and reduce the amount of carbon sources,but it has higher requirements on the environment and may produce more nitrous oxide(N2O)during operation.Therefore,conventional biological nitrogen removal technology is mostly used in practice.For sewage plants,factors such as the type of carbon source and pH are affected by the lifestyle of residents and the nature of the wastewater produced by industrial enterprises,the cost of controlling the operating temperature is relatively large.DO concentration can be regulated by changing the aeration rate,and C/N ratio can be realized by changing the amount of carbon source added.The study on the influence of different factors on biological nitrogen removal efficiency is helpful to control these factors rationally and improve the efficiency of nitrogen removal.At the same time,the mathematical model can better dynamically reflect the influence of such factors on the removal of nitrogen-containing compounds,microbial growth and decay and N2O production in the process of biological nitrogen removal,which is convenient to timely adjust the influencing factors to improve the efficiency of biological nitrogen removal and reduce the production of N2O in the process.Based on the ASM3 model,the kinetic model of nitrification and denitrification processes were constructed respectively.The nitrification stage model covered hydroxylamine(NH2OH)oxidation(also known as the nitrification of autotrophic ammoxidation bacteria(AOB))and AOB denitrification process.The denitrification stage model covered heterotrophic bacteria(HD)denitrification process.Therefore,the model constructed can not only describe the changes of nitrogen-containing compounds(nitrate nitrogen(NH4+),nitrite nitrogen(NO2-),nitrate nitrogen(NO3-)),chemical oxygen demand(COD)and microorganisms(AOB,HD,nitrite oxidizing bacteria(NOB))over time,but also include N2O and intermediate products(NH2OH,NO,NOH)and so on over time.The reaction equation,rate equation and parameter definition of nitrification and denitrification processes are described in detail.The nitrification process includes 13 reaction processes,including HD aerobic growth and aerobic endogenous respiration process,aerobic storage of COD process,intracellular storage substances of heterotrophs(XSTO)aerobic respiration process,AOB and NOB aerobic endogenous respiration process,NOH chemical decomposition process,4-step nitrification and 2-step AOB denitrification process.The denitrification process consists of four reaction processes,namely the reduction process of NO3-,NO2-,NO and N2O.After the construction of the model matrix is completed,parameter sensitivity analysis was carried out on all kinetic parameters in the process of nitrification and denitrification,and the influence degree of each parameter on each component in the process of nitrification and denitrification was analyzed,and the parameters with greater influence on each component were obtained.Several groups of experimental data and literature data were used to calibrate and verify the nitrification and denitrification processes,which successfully verified the accuracy of model simulation and the correctness of matrix construction.The simulation value of the model and the correlation between the literature and the actual measurement value R2 are all≥0.7,and the model has a good prediction effect for each component.The model calibration and verification are successful,and the parameter calibration is completed.The effects of different DO concentrations on NH4+ degradation rate,nitrification rate and nitrification time were studied by using the model after successful calibration and sequencing batch experiment.The effects of different C/N on the total nitrogen(TN)removal rate,COD removal rate,denitrification rate,etc.The effect of the sequence of nitrogen source and carbon source on TN removal rate and COD reduction in simultaneous nitrification and denitrification in the same container;Predict the N2O production under different DO conditions,N2O production under different C/N conditions,and the influence of the combined action of DO and C/N on the N2O production;Effect of the order of adding nitrogen source and carbon source on the production of N2O in simultaneous nitrification and denitrification process.The experimental operation conditions were optimized to explore the appropriate DO concentration,C/N ratio and adding sequence to improve the efficiency of biological nitrogen removal,shorten the reaction time and reduce the production of N2O,in order to provide reference for the biological nitrogen removal process under the same process operating conditions. |
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