| At present,with the promulgation of the action plan of prevent and control water pollution,at the same time the increasingly strict requirements of sewage nitrogen discharge standards,sewage treatment plants are generally faced with upgrading.Secondary biochemical effluent is basically low carbon nitrogen ratio wastewater,and the nitrogen removal effect is poor due to the lack of carbon sources for denitrification,which is difficult to meet the nitrogen discharge requirements.Therefore,the additional carbon source is needed for deep denitrification treatment.The traditional liquid carbon source has disadvantages such as high pharmaceutical cost,easy to cause secondary pollution,and the need for adding equipment and instruments.To solve the problem,the study prepared three new solid carbon release materials with slow carbon release function as microbial carriers of denitrification biological filter(DNBF)and provide electron donor for the denitrification process,so as to strengthen the denitrification effect of denitrification biological filter.In this study,corn kernels and potato residue were used as raw materials for carbon release.Corn kernels solid slow-release carbon source PECP was prepared by polyvinyl alcohol(PVA)embedding method,potato residue solid slow-release carbon source SCPR was prepared by silica gel cross-linking method,and potato residue solid slow-release carbon source CWPR was prepared by cement encapsulation method.Secondly,the preparation conditions of three kinds of solid slow-release carbon sources were optimized,and the related properties of the optimized solid carbon sources were explored.Secondly,after the successful start-up of DNBF membrane,solid slow-release carbon source filler was added and mixed with ceramsite.The influence of slow-release carbon source material on the denitrification effect of DNBF was explored under different working conditions.Once again,after the successful hanging membrane started-up of DNBF,solid slow-release carbon source was added and mixed with ceramsite.The influence of solid carbon source on the denitrification effect of DNBF was investigated under different working conditions.The denitrification kinetics of DNBF was established and the balance between supply and demand of organic matter was studied.Finally,three kinds of solid carbon sources are compared and analyzed.Finally,three kinds of solid carbon sources were compared and analyzed.PECP was prepared by PVA embedding method,the carbon release performance test showed that the carbon release maximum was 296.11 mg/(g·L).The carbon release process satisfied the second-order kinetics.The single factor test of the effects of different PVA and corn kernels content on PECP carbon release performance showed that when PVA content was 6%,the carbon release maximum was 292.76 mg/(g·L),and the minimum transfer coefficient K was 30.37.When corn kernel content was 12%,the carbon release maximum was 329.59 mg/(g·L),and the minimum transfer coefficient K was 29.47 when corn kernel content was 8%.Used the transfer coefficient K as the response value,the optimal preparation conditions of PECP by response surface methodology were as follows:PVA content was 6.657%,corn kernel content was 7.781%,Sodium alginate content was 0.484%,mixing temperature was 80.24 ?.After optimization,the organic matter release of PECP material increased,the carbon release rate slowed down,and the compressive strength was increased.The static denitrification test showed that the NO3--N removal rate reached 75.02%when the PECP dosage was 20 g/L.The single factor test of SCPR compressive strength of potato residue sustained-release carbon source prepared by silica gel cross-linking method showed that the compressive strength first increased and then decreased with the increased of NH4Cl concentration,and first increased and then decreased with the increase of dilute H2SO4 concentration.Orthogonal test showed that the order of influencing the compressive strength of SCPR material was the concentration of NH4Cl>the quality of potato residue>the concentration of dilute H2SO4.The optimal conditions for SCPR material preparation were as follows:NH4Cl concentration was 25%,dilute H2SO4 concentration was 60%,and the mass of potato residue was 5 g.The optimized compressive strength was 9.03?9.55 MPa,the carbon release maximum was 129.87 mg/(g·L),and the mass transfer coefficient K was 14.51.Static denitrification test showed that NO3--N removal rate was 75.11%,the effluent NO3--N concentration was 13.46 mg/L,when SCPR dosage was 40 g/L.The single factor tests on the compressive strength of CPR prepared by cement encapsulation showed that the compressive strength first increased and then decreased with the increase of potato residue particle size,potato residue content and cement solid-to-water ratio.Used the compressive strength as the response value,the preparation conditions of CWPR were optimized by response surface methodology.After optimization,the optimal conditions were as follows:potato residue particle size was 3.50 mm,potato residue content was 13.90 g and cement solid-to-water ratio was 60.93%.The optimized compressive strength was 12.25?14.32 MPa,the carbon release maximum was 116.55 mg/(g·L),and transfer coefficient K was 14.30.The static denitrification test showed that the NO3--N removal rate was 67.27%,the effluent concentration was 16.46 mg/L when the CWPR dosage was 40 g/L.The surface of the ceramsite was covered by gray-and-black biofilm 42 d after the film-hanging start-up of the denitrification biological filter.The removal rates of COD and NO3--N both reached more than 50%,and the film-hanging start-up was basically completed.Under the action of solid slow-release carbon source PECP,DNBF has a better denitrification effect when the inlet load was 0.1 m3·/(m2·h),the ratio of cermet to solid slow-release carbon source PECP was 12:1,influent NO3--N concentration was 47.49?52.75 mg/L,the removal rates of NO3--N,NO2--N and TN were 71.76%,91.70%and 71.32%respectively,effluent concentration was 13.84 mg/L,0.04mg/L and 14.20mg/L,and the average effluent COD concentration was 48.23 mg/L.Under the effect of the solid slow-release carbon source SCPR,DNBF has a better denitrification effect when the hydraulic load was 0.1m3·/(m2·h),the ratio of cermet and SCPR filler was 6:1,and the influent NO3--N concentration was 50.09mg/L.The removal rates of NO3--N,NO2--N and TN were 74.95%,84.78%and 73.46%,respectively,and the average effluent COD concentration was 44.17 mg/L.The removal effect of DNBF pollutants under the action of two kinds of solid slow-release carbon source all met the requirements of Level A standard of Pollutant Discharge Standard for Urban Wastewater Treatment Plant(GB18918-2016);The changes of the amount of biofilm and denitrifying bacteria in the upper part of DNBF were consistent with the changes of denitrification efficiency.The denitrification kinetics of DNBF under the action of PECP and SCPR showed that the denitrification rate has a good correlation with COD concentration.The organic matter release experiments of PECP and SCPR in clean water and anaerobic sludge showed that the organic matter was mainly released under the action of microorganisms,and the biological release rate was 89.74%and 86.50%,respectively.The denitrification test showed that the effective utilization rate of carbon source was 97.22%and 96.91%,respectively.The organic matter release rate of PECP and SCPR materials was mainly affected by the denitrification rate of DNBF.Three kinds of slow-release carbon source material compressive strength meet the strength requirement of filter material in water treatment,in the water can keep certain structure form,the expansion deformation degree is small.With a certain porosity,organic matter in the solid carbon source can be released smoothly.The results of electron microscopy showed that the surface of the material was rough and porous,the structure was loose,and it is easy to be attached by microorganisms.The comprehensive cost of solid carbon source required by PECP,SCPR and CWPR for degrade per unit mass nitrate nitrogen was 13.46 yuan/(kg N),10.60 yuan/(kg N)and 8.81 yuan/(kg N),respectively.Compared with liquid carbon source reagent cost,three kinds of slow-release solid carbon source material price is low,and there is no need for pharmaceutical feeding equipment and automatic control system,the risk of secondary pollution to water quality is low,so they have good application prospect. |
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