Study On Nitrogen Removal Efficiency Of Two Types Of Biological Contact Oxidation Systems

With the development of urbanization,a large amount of urban sewage rich in nitrogen and other nutrients is discharged into the water body,resulting in eutrophication of the water body.In order to solve this problem,China’s requirements on the discharge standards of sewage treatment plant are increasingly strict,and the upgrading and reconstruction project of sewage treatment plant has become a hot spot in recent years.Biological contact oxidation process is often used in upgrading of wastewater treatment plant because of its high treatment efficiency and small covering area.Filler is the core of biological contact oxidation process,in this paper,the efficiency of the cylindrical reticular filler（filler T₁）and the cross flow honeycomb filler（filler T₂）is studied,and the effect of dissolved oxygen on nitrogen removal efficiency of the fillers is analyzed.The nitrogen removal mechanism of the reaction is studied from the perspective of microbiology by using high-throughput sequencing technology.In this paper,the influence of the layout of aerated sand plate on the flow field of the reactor is studied by numerical simulation,which provides theoretical guidance for the design and optimization of the reactor.The nitrogen removal efficiency of the two kinds of fillers was studied.It was found that under the operating conditions of DO 2-3mg/L and pH 7-8,the biofilm of the two kinds of fillers was formed after 16 days of culture.After the start-up of the reactor,the TN removal rate of T₁ was 67%-70%,and the ammonia nitrogen removal rate was 87%-88%.The TN removal rate of T₂ was 57%-63%,and the ammonia nitrogen removal rate was 86%-87%.It was found that DO of 3.5mg/l was the optimal DO condition for T₁.The TN removal rate of T₁ was 74%-76%,and the ammonia nitrogen removal rate was 93%.The results showed that the best treatment effect of T₂ was obtained when DO was 4.5mg/l.The TN removal rate was67%-69%,and ammonia nitrogen removal rate was 92%-93%.The results of high-throughput sequencing showed that there was no significant difference in nitrifying bacteria between T₁ and T₂.The proportion of Sphingobacteriales in T₁ was higher than that in T₂,but the proportion of Rhizobiales in T₂ was higher than that in T₁.Compared with the raw sludge,the proportion of Planctomycetales in T₁ and T₂ increased,and the increase range of T₁was larger.The proportion of Xanthomonadales in T₁ increased,but that in T₂decreased.The layout of aerated sand plate can affect the distribution of dissolved oxygen in the reactor,thus affecting the nitrogen removal efficiency of the reactor.In this paper,the influence of the spacing and position of aerated sand plate was investigated by numerical simulation.The results showed that the appropriate spacing could make the bubble and velocity distribution more uniform,and the appropriate turbulence intensity could promote the renewal of biofilm.With the increase of the reactor position,the residence time of air in the reactor was shortened,and the dissolved oxygen was not supplied to the lower part of the reactor.Through the comparative analysis of gas-liquid volume fraction,velocity and turbulence intensity,the optimal layout of aeration sand plate was determined as135mm spacing and 0mm position.