| According to the problems that water sewage treatment plants in some cities and towns are in low carbon-nitrogen ratio, lack of carbon source for denitrification, low effective utilization of carbon source and non-ideal condition of nitrogen removal effect, aiming at the goal to develop the urban sewage efficient nitrogen removal technology, Step Feed Multi-stage Biofilm Reactor is developed. Through the study on the Nitrogen Removal Efficiency by the number of Step-feed point, volume distribution and flow distribution, and so on, Step Feed mode of Multi-stage Biofilm Reactor is established which increased the utilization of carbon sources. On this basis, A systematic study is made on the impact of simultaneous nitrification and denitrification in Multi-stage Biofilm Reactor such as dissolved oxygen (DO), load, ALK and temperature ,then the key parameters in systematic efficient nitrogen removal is obtained. At the same time, dynamic model of simultaneous nitrification and denitrification in step feed multi-stage biofilm reactor is established, and use the Java software for programming simulation. Applied the model of computer simulation, and according to the different water treatment and water quality objectives ,the model can identify reactor series, step-feed flow ratio and distribution of key design parameters of the simulation which provides a powerful tool for scientific designing optimization of the reactor . Major conclusions of the study are as follows:①The screening test of packing in the reactors indicates that:under the same test conditions, the total nitrogen removal rate of reactor used suspended packing and semi-soft combined packing are respectively 70% and 69.4%, while it has no significant effect on nitrogen removal, and semi-soft combined packing which has a better anti-blocking performance is suggested in the engineering.②The study of Step-feed indicates that: the number of Step-feed point, volume distribution and flow distribution have significant impact on the performance of nitrogen removal efficiency of the reactor. Under the condition of water temperature at 25℃, dissolved oxygen of 5mg/L, the biofilm density of the reactor of 30 percent, organic load of 1.2kgCOD/m3.d, nitrogen load of 0.22kgTN/m3.d, using section 1, 3, 6 Step-feed with 2:2:1 flow rate distribution can treat COD, NH4+-N and TN from 205mg/L,32.5mg/L and 36.8mg/L to 38mg/L, 1.5mg/Land 11.1mg/L respectively, with the removal rate respectively 80%, 95.3% and 69.2%, which achieved the A in first grade discharge standard of"Discharge standard of pollutants for municipal wastewater treatment plant"(GB18918-2002).③The study of influencing factors of nitrogen removal efficiency indicates that: DO, load, temperature and alkalinity of the reactor affected the performance of nitrogen removal efficiency significantly, when the temperature is between 15℃and 20℃, the load increases from 0.5kgCOD/m3.d and 0.14kgTN/m3.d to 1.5kgCOD/m3.d 0.38kgTN/m3.d, nitrification rate and denitrification rate increased from 4.7gN/m3.h and 3.9gN/m3.h to 11.8gN/m3.h and 8.8gN/m3.h respectively. The process of simultaneous nitrification and denitrification decrease nitrification rate and denitrification rate of the system, when the water temperature is up 15℃, temperature has little influence on nitrogen removal efficiency in simultaneous nitrification and denitrification process; when the water temperature is below 15℃, nitrification rate is affected by the temperature notably; while the temperature declines from 15℃to 5℃, nitrification rate decreases from 10.8gN/m3.h to 6.2gN/m3.h, declined about 43 percent, and denitrification rate decreases from 7.3gN/m3.h to 4.4gN/m3.h, declined about 40 percent.④On this basis, dynamic model of simultaneous nitrification and denitrification in step feed multi-stage biofilm reactor is established.⑤The study on the simultaneous nitrification and denitrification model of computer simulation indicates that: in order to make the municipal sewage (COD,NH4+-N and TN is respectively 300mg/L,50mg/L and 60mg/L) reach the A in first grade discharge standard of"Discharge standard of pollutants for municipal wastewater treatment plant"(GB18918-2002), for optimum reaction series the step feed multi-stage biofilm reactor should be 8 series, and the water flow at all levels allocated to the respective percentages is 35%, 15%, 10%, 15% , 10%, 10%, 10% and 0%, and HRT≥7h. The results of the study provides a scientific basis for the Engineering application of step feed multi-stage biofilm reactor and a new way for urban sewage treatment. It has an important practical value and practical significance.
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