Study On Treatment Of Decentralized Sewage By A New Type Of Pneumatic Mixed Purification Tank

Purification tank is an integrated treatment device used to treat dispersed sewage.It is regarded as an important measure to replace septic tank and improve rural water resources environment.However,although the treatment efficiency of purification tank has been improved compared with septic tank,there are still many problems,such as unstable ammonia nitrogen concentration in effluent,and the total nitrogen concentration can not meet the discharge standards.Due to the limitations of type selection,operation and maintenance,energy consumption and other factors,mechanical stirring impellers are often not installed in small-scale purification tanks.Therefore,the dead zone and short flow problems caused by structural corner and sludge accumulation in purification tanks are important factors restricting the improvement of pollutant removal efficiency.In this paper,a new type of pneumatic mixing purification tank is designed,which mainly includes circular sleeve structure,intermittent pneumatic mixing of anoxic tank and three-stage aerobic tank,etc.It can effectively solve the above problems.This paper mainly explores the effects of aeration rate,nitrate reflux ratio and aerodynamic mixing frequency on the flow characteristics of the water in the purification tank and the removal efficiency of COD,ammonia nitrogen and total nitrogen in sewage.The specific experimental contents and results are as follows:The dead zone and short flow of the new type of pneumatic mixing purification tank were investigated by flow tracer experiment.The results showed that increasing aeration volume of the aerobic tank was beneficial to improving the volume utilization ratio of the aerobic tank,and a certain frequency of pneumatic mixing was beneficial to improving the volume utilization ratio of the anoxic tank.Simulated sewage treatment experiment explored the optimal aeration rate of three-stage aerobic tank,the optimal nitrate reflux ratio and the optimal aerodynamic mixing frequency of anoxic tank.The results showed that the optimal aeration rate of aerobic tank was 1.4 L/min,the total nitrogen removal rate of simultaneous nitrification and denitrification could reach 59%when the dissolved oxygen concentration of the first aerobic tank was 1.5 mg/L;Under the condition of 150%reflux ratio,the optimal pneumatic mixing frequency is 8 times per hour,and the total nitrogen removal rate is increased by 3.94%.At this time,ammonia nitrogen,COD,and total nitrogen can all meet the first A standard of urban sewage discharge.The actual domestic sewage treatment experiment tested the actual treatment effect of the new pneumatic mixing purification tank and explored the low temperature resistance.The results showed that the optimal pneumatic mixing frequency was 4 times/hour at 200%reflux ratio,the removal rate of ammonia nitrogen was increased by 7.6%,the removal rate of total nitrogen was increased by 17.47%.COD,ammonia nitrogen and total nitrogen steadily met the first-class A discharge standard of urban sewage;The effluent index can reach the first class B standard of urban sewage under the condition of low temperature 12-15?.This study effectively improved the treatment capacity of ammonia nitrogen and total nitrogen in small-scale purification tank,and provided experimental basis for the optimal design of purification tank.