Study On The Preparation And Denitrification Effect Of New Composite Carbon Source Substrate

Excessive nitrogen in rivers is one of the main causes of eutrophication.Although the sewage discharge standards in China are becoming more and more strict,due to the low concentration of carbon source material in the secondary treatment of sewage,it is impossible to ensure the complete denitrification process,resulting in high nitrate concentration in the effluent,making it difficult to effectively control the total nitrogen,resulting in eutrophication of water bodies.In this paper,polyvinyl alcohol(PVA),sodium alginate(SA),polycaprolactone(PCL)and corncob were used to prepare a new composite carbon source substrate,which was used as an electron donor in the denitrification process and the growth carrier of microorganisms.The substrates were modified by adding ferrous sulfate(CSF-1),ferrous chloride(CSF-2),aeration foaming(CSA),foaming agent foaming(CSH)and surfactant foaming(CSK),respectively.The differences in physical properties,static carbon release performance,static nitrogen removal performance and dynamic nitrogen removal performance between the modified matrix and the unmodified matrix(CS)were studied.The effects of modified substrate on microbial community structure and biodiversity in the reactor were analyzed,and the denitrification process was explored,which laid a theoretical and practical foundation for the removal of nitrate pollution in water.The specific research results are as follows:(1)The physical properties and static carbon release and nitrogen removal properties of the new composite carbon source substrate were studied.It was found that the density of each modified substrates and the unmodified substrate was about 1g/cm~3,and the compressive strength was greater than 230 N/cm~2.There were a large number of porous structures on the surface of CSA,CSK and CSH substrates,and the surface of CS,CSF-1 and CSF-2 substrates was smooth.The final cumulative carbon release amount of each substrates in clear water was CSH>CSK>CSA>CS>CSF-2>CSF-1,and the maximum saturated concentration C_mand mass transfer coefficient K were smaller than those of corncob,achieving the effect of slow release of carbon source material.In the static nitrogen removal study,the complete removal time of nitrate nitrogen in CSA,CSK and CSH was roughly the same,and was greater than that in CS,CSF-1 and CSF-2.(2)The dynamic denitrification performance of the new composite carbon source substrate under different nitrate nitrogen loadings and hydraulic loadings was studied,and it was found that there was no significant difference in the nitrogen removal efficiency of each reactor under low and medium nitrate nitrogen loadings.In the high concentration stage,CSA substrate reactor had the best removal efficiency for nitrate nitrogen,total nitrogen and ammonia nitrogen,with the removal rates of94%,88%and 72%,respectively.At different hydraulic loading stages,with the increase of hydraulic loading,the nitrogen removal efficiency of each reactor decreased.Compared with other reactors,CSA substrate reactor had the best nitrogen treatment effect.The total nitrogen and nitrate nitrogen removal rates were 76%and77%at medium loading stage,and 24%at high loading stage.Based on the physical properties,static carbon release and nitrogen removal properties,and nitrogen treatment effects under different nitrate nitrogen loads and hydraulic loads,CSA substrate had good treatment effects at different stages,and aeration treatment was the best improvement method in the production process.(3)The differences of microbial species diversity and community structure in the lower,middle and upper substrates of CSA substrate reactor and CSK substrate reactor with better treatment effect were studied,and it was found that the microbial community structure in the CSA substrate reactor was quite different,and the dominant genera in the lower,middle and upper substrates of the reactor were Chlorobium,unclassified＿Planctomycetaceae and Azotobacter,respectively.The dominant bacteria in the lower part of CSK substrate reactor were Chlorobium,and the dominant bacteria in the middle and upper parts were Methyloversatilis.Microbial diversity analysis showed that the microbial structure of the upper,middle and lower parts of the CSA substrate reactor was significantly different,and the microbial structure of the upper,middle and lower parts of the CSK substrate reactor was slightly different.(4)According to the kinetic simulation results of the substrate in the reactor and the change of water quality along the reactor,it was found that the CSA and CSK substrate reactors were dominated by the traditional biological denitrification process,and there might be short-cut nitrification and denitrification process and anaerobic ammonia oxidation process.The carbon source utilization of CSA and CSK substrates was analyzed and compared with similar products at home and abroad.The results showed that CSA and CSK substrates had good denitrification performance.In some deep denitrification processes,CSA and CSK substrates could replace traditional liquid carbon sources as carbon sources for wastewater treatment.