A Study On Solid Carbon Source For Denitrification Of Low C/N Sewage

In the process of urban sewage treatment,the lack of carbon source(low C/N)in sewage will lead to the failure of denitrification process,making the effluent difficult to meet the discharge standard.In order to solve the problem of denitrification of Low C/N sewage,urban sewage treatment plants usually add carbon source in denitrification stage.Carbon source will have an important impact on denitrification process.This study is based on the characteristics of various carbon sources.In order to solve the defects of traditional solid carbon sources,several new solid carbon sources are developed around PHBV,biochar and other materials.And to explore the characteristics of materials and denitrification efficiency,and screening of dominant materials.In this paper,poly(3-hydroxybutyrate-co-3-hydroxy-valerate)(PHBV)and biochar are used as the main research materials,and three new solid carbon sources are developed:modified PHBV material,clad composite material,and hybrid composite material.Through the characterization of the structure,composition,leaching solution composition and other properties of the material,explore the basic characteristics of each material.The results show that the modification operation improves the wettability and porosity of the modified PHBV material to different degrees.The clad composite materials and hybrid composite materials exhibit rich pore structure and high specific surface area.The chemical composition test results show that the biochar in such materials has the ability to provide a carbon source for the denitrification process.In the static denitrification process,the modifier addition ratio will affect the NO3--N removal rate of modified PHBV material.Compared with the control material,there is a significant increase.Among them,the effect of the material is most significant when the amount of the modifier is 5%,and the NO3--N removal rate of the material is about 32%higher than that of the raw material.Clad composite material and hybrid composite material are used as fillers to shorten the start-up time of the reactor,and have certain load shock resistance performance.In addition,the denitrification capacity of biochar is verified,and it is finally confirmed that it has the ability to provide a carbon source for the denitrification process.Continuous denitrification results showen that the denitrification effects of the three new solid carbon sources are better than the corresponding control materials.It also includes various functional characteristics exhibit by different materials.Modifier with different dosing ratios result in different properties of the modified PHBV material,such as porosity and wettability.And thus lead to differences in NO3--N removal rates.The denitrification effect of the modified PHBV material with the modifier addition amount of 5%is the best,and the removal rate of NO3--N can reach about 98%.Clad composite material realizes the effective load of PHBV on biochar,which takes advantage of the large specific surface area of biochar and the stable denitrification performance of PHBV.At the same time,the problems of long film hanging time and slow starting speed of PHBV are improved.As a result,the coating time of the composite reactor is 36%shorter than that of the control material,and the average removal rate of NO3--N is over 95%.In addition,the change of pH can also reflect the use of materials.Hybrid composite material is a material made by mixing PHBV powder and biochar powder.At the same time,due to the existence of biochar and nano-zero valent iron(nZVI),it has the characteristics of high nitrogen removal efficiency,long effective time,good structure and strong load shock resistance.The NO3--N removal rate of the hybrid composite material reactor in the stable period can reach about 98%,which is about 5-10%higher than that of the control material,and the duration of the effect is extended by about 40%.And it shows a very good load shock resistance.The new composite materials developed in this paper are due to their own characteristics,such as the production of easily degradable soluble organic materials,high porosity(specific surface area).And many types of carbon sources.These factors make the new composite materials exhibit the characteristics of film hanging time period,high NO3--N removal rate and strong impact resistance during the denitrification process.To some extent,the inherent shortcomings of traditional solid carbon sources have been solved,laying a foundation for the future engineering use of new solid carbon sources.