| Autotrophic denitrification is an innovation of wastewater biological denitrification technology,it through the ammonia oxidizing bacteria(AOB)converting the waste water in ammonia to nitrite,then through anaerobic ammonia oxidation(Anammox)will ammonia and nitrite is converted into nitrogen.It compared with the traditional nitrification/denitrification process,oxygen demand is reduced by 2 times,don't need additional carbon source.nitrogen removal per unit produced by the consumption of excess sludge and basicity of about 10 times less.operation cost greatly reduced.Activated sludge model(ASMs)focuses on the basic principle of wastewater biological treatment process,and its dynamic simulation of substrate degradation and microbial growth and so on various parameters.the mathematical relationship between the quantitative description,has been successfully applied to guide the design of the sewage treatment system.simulation and control operation.But ASMs there are a large number of assumptions and simplified,if not considering the generation of soluble microbial products(SMP)and consumption of the sewage treatment system in microbial populations and denitrification performance.lack of system in the influence of pH value on the impact of change on the chemical reaction process description,etc.System this paper studies the granular sludge system autotrophic denitrification process of mathematical simulation.explores the SMP production,and consumption as well as the system of pH value on the system performance and the impact of microbial population structure.The main research contents and research results are as follows:(1)Established a contains the AOB.Anammox.nitte oxidizing bacteria(NOB)and heterotrophic bacteria(HB)four microbial populations of autotrophic denitrification granular sludge system model.simulation assessment of the formation of SMP and consumption process.By comparing in considering the SMP and does not consider the SMP in both cases,the granular sludge system of ammonia nitrogen and total nitrogen removal ability,concentration of liquid phase in the substrates and microbial population changes over time,matrix in a granular sludge,and microbial populations of one dimensional space changes,to assess the SMP affect ASMs simulate granular sludge system.Results show that the consideration of SMP system,the microbial utilization of nutrients part used to translate into UAP and EPS,accordingly inhibit the growth of the NOB,lowered the Anammox sensitivity to the dissolved oxygen inhibition,thus make the system have higher ratio of Anammox,beneficial to remove the nitrogen in the system by autotrophic denitrification process.Therefore,compared with no account of the SMP,considering the SMP autotrophic denitrification granular sludge ASMs simulation system has a higher total nitrogen removal rate.(2)By changing a series of key operational parameters,the performance of the self-feeding denitrifying granular sludge system and the difference of microbial population structure in different simulated scenarios were investigated.Results show that when the ammonia nitrogen in the water load is less than 300 g m-3 d-1,the system of the dissolved oxygen concentration must be strictly controlled between 0.25-1.20 mg O2,L-1,in order to achieve higher total nitrogen removal rate in wastewater(>90%).When the particle size of granular sludge is less than 0.75 mm,the system can achieve higher ammonia nitrogen and total nitrogen removal rate,while larger particles are not conducive to the removal of ammonia nitrogen and total nitrogen.When the hydraulic retention time is less than 0.15 d.total nitrogen removal efficiency of dissolved oxygen concentration is quite sensitive to the small changes will significantly change the dissolved oxygen concentration in the microbial community structure under steady state,and fiuther affect the total nitrogen removal efficiency.A series of biochemical processes were established to describe the changes of pH in the system and its effect on the system performance and microbial population.It was found that the ratio of the growth rate of AOB and Anammox was basically normal distribution with the change of pH value,and the maximum growth rate was reached at 7.4 and 7.6 respectively.However,the growth rate of NOB showed the S-type distribution with the change of pH value,and the pH value below 6.5 completely inhibited NOB activity,but the high pH value(greater than 7.5)did not inhibit the growth of NOB.By comparing the total nitrogen removal rate and ammonia nitrogen removal rate under different pH conditions,it can be found that the ammonia nitrogen removal rate reaches the peak value at the pH value of 7.5.which corresponds to the optimal pH value(7.4)of AOB.However,the total nitrogen removal rate reached the highest pH value at 7,which is because the activity of AOB and Anammox can remain at a high level under this pH condition,while the growth ofNOB can be better inhibited. |
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