Study On Nitrogen Removal And Soluble Microbial Products Of The Denitrification Biological Filter

Denitrification Biological Filter（DNBF）is a common process in the wastewater treatment biofilm method.It has the advantages of large hydraulic load,low investment cost,high effluent quality,easy film formation,and high treatment efficiency.Denitrification has been widely used and has been a hot spot in the field of advanced treatment of urban sewage.It is often accompanied by the growth,reproduction,metabolism,and cell decay of microorganisms in the biochemical reaction process of wastewater nitrogen removal treatment.In these processes,a large amount of soluble microbial products（SMP）are produced,which are produced by microorganisms.The organic substances released from metabolism and endogenous respiration to the outside world not only reduce the effectiveness of wastewater treatment,but also affect the quality of effluent water and limit the reuse of wastewater.Determining the main components of SMP has very important research significance for understanding the effects of wastewater products in different operating stages and the composition of different carbon sources on SMP.Therefore,this paper explores the denitrification effect of different growth stages in the denitrification biological filter with different carbon sources,studies the formation characteristics,content composition and other physical and chemical properties of SMP before and after the film is formed,and uses this as a basis to study the corresponding subsequent treatment methods in order to obtain a more efficient denitrification process.The aim is to quantitatively control the yield of SMP and improve the availability of SMP,combined with process regulation and bioaugmentation technology,to reduce the impact of SMP on effluent water quality and deep denitrification,and to explore the influence of SMP on the adsorption behavior of heavy metal ions,which provides important practical guidance for the advanced treatment of secondary wastewater from sewage treatment plants.The main research contents and results are as follows:（1）Exploring the denitrification effect of the denitrification biological filter using sodium acetate（D₁）,methanol（D₂）,and glucose（D₃）as carbon sources,it can be concluded that the denitrification effect of three DNBFs with different carbon sources can achieve more than 90%.The accumulation rate of nitrite nitrogen in the three filters was compared as D₁<D₂<D₃,and the COD removal rate of the filter with sodium acetate as the carbon source was significantly lower than that with methanol and glucose as the carbon source.The total SMP content of DNBF effluent from different carbon sources is D₁>D₃>D₂.The proportions of the main components in the effluent SMP of the three filters are also different.Among them,the protein in SMP is the main component,and the content accounts for the total SMP.The content is 50±2%,followed by polysaccharides and humus,which account for 15±2%and 15±2%respectively.（2）The effects of the denitrification biological filters with different carbon sources are also different along the way.The content of nitrite nitrogen in the effluent of the three filters gradually decreases from the height of the filter to the bottom.At sampling port No.1,the nitrite nitrogen content of D₁effluent is significantly higher than that of D₂and D₃.The relationship between the nitrite nitrogen content of the three DNBFs is D₁>D₃>D₂.Starting from the No.2 sampling port,the accumulation of nitrite nitrogen in the three reactors tended to be flat,and the content tended to 0 mg/L.At sampling port No.1,the nitrate nitrogen content of D₁was significantly greater than that of D₂and D₃reactors.Starting from sampling port No.2,the nitrate nitrogen content of the three filters all tended to 0 mg/L,of which D₂effluent nitrate nitrogen The content is almost 0 mg/L starting from the No.1sampling port,which has reached the requirement for denitrification of the effluent.The content and composition of SMP in the effluent water from denitrification biofilters with different carbon sources are slightly different,mainly showing a trend of increasing first and then gradually decreasing and tending to stabilize,but the overall range of changes is not large,indicating that the metabolic activities of microorganisms has reached its peak in the middle and top stage of the filter.In general,the denitrification effect of the denitrification biological filter has reached the required effluent effect at about 30 cm～50 cm.（3）In this paper,SMP in the effluent of the DNBFs with various carbon sources are used to study the chelating behaviors of Cu²⁺by SMP under different temperatures,and p H values.The experiment results are fit well with the Langmuir,Freundlich,and Temkin adsorption isotherm models.When the temperature is 35°C and p H is 5,the chelating capacity of Cu²⁺by the SMP of the DNBF with sodium acetate as the carbon source is better than that under other conditions.The maximum adsorption capacity for Cu²⁺by SMP is 0.574g/g.SEM,FT-IR and 3D-EEM analyses reveal that the morphological characteristics of SMP have changed significantly after chelating heavy metals.The chelation of SMP and metal ions mainly depends on the functional groups,such as-COOH,-NH₂,and-OH which are rich in protein,polysaccharide,and humus.