| Facing increasingly strict sewage discharge limits,adding external carbon sources is a measure that low-carbon sources sewage plants have to take to achieve TN compliance.At present,in order to improve the denitrification effect of sewage plants,most of them adopt the fully nitrification operation mode with higher DO control.This operation mode exacerbates the contradiction of low carbon sources in low-carbon wastewater treatment plants.Through operation optimization,improving the denitrification capacity of the wastewater’s own carbon source has positive significance for reducing the amount of external carbon source added.A large number of engineering practices have shown that adding denitrification filters at the end of the sewage treatment plant can improve the denitrification effect.However,the addition of low-molecular-weight carbon source organic compounds has an increased COD concentration in the effluent,and the transportation and storage risks of low-molecular-weight carbon sources pose risks.In this case,the solid carbon source denitrification filter has gradually become a new research hotspot.Existing research shows that the artificial solid carbon source has good denitrification effect,but it is expensive;natural solid carbon source is cheap,but the nitrogen removal rate is slow.Therefore,in view of the nature of natural solid carbon source materials,studying the method of increasing the denitrification rate has positive significance for the application of natural solid carbon source materials.The thesis was based on the technical upgrading of TN in a low carbon source wastewater treatment plant in Chongqing.Based on the optimization of the operation,the research focused on the natural nitrogen removal technology of corn cob.In order to ensure the controllable boundary of the low-carbon source wastewater treatment plant operation optimization study,a new low-carbon source wastewater treatment plant design parameter in Chongqing was used as a reference.A pilot plant with a daily processing scale of A~2/O oxidation ditch of 48 m~3 was newly built.Based on the operating parameters of the sewage plant,the operation optimization research of the pilot plant was carried out.On the basis of optimized operation,a low-cost corn cob natural solid carbon source was filled in the anoxic tank of the A~2/O process,and the nitrogen removal of the corn cob solid carbon source A~2/O oxidation ditch in the anoxic tank under different operating conditions was studied.Performance,denitrification kinetics of anoxic ponds,microbial community characteristics.The following research conclusions were obtained:(1)Based on the operating parameters of a low-carbon source sewage plant in Chongqing,the DO at the end of the aerobic tank was controlled to 2.3 mg/L,and the operation was optimized based on the adjustable operating parameters(HRT,R)of the sewage plant.The research results showed that:the high proportion of ammonia nitrogen in the total nitrogen of the effluent of the short HRT system limited the further improvement of the nitrogen removal efficiency;the high R will induced the destruction of the hypoxic environment in the hypoxic pool,which was not conducive to denitrification.Based on the comprehensive treatment effect and energy consumption,it was recommended that HRT should be controlled to 8 h,the R should be less than 200%when treating low-carbon source wastewater,and the TN concentration effluent ranged from 14.81 to 17.69 mg/L.The average TN removal rate was 66%.(2)The surface characteristics of the solid carbon source of corn cob were studied by scanning electron microscope technology,and the dissolution and release characteristics of the carbon source of corn cob were studied by immersion experiments.The results showed that the surface of corn cob was rough,after the use of microorganisms,a large number of loose and dense holes increased the capacity for microorganisms to attach.The C/N ratio of corncob leaching solution was greater than134,which will not increase the nitrogen load of the system;the initial hydrolysis speed of corncob after film hanging was reduced,which reduced the initial loading of the system and facilitated the rapid startup of the system after loading.The daily COD leaching amount reached 0.048 mg/(L·g).(3)The denitrification effect of corn cob solid carbon source A~2/O system under different operating conditions was studied.The research results showed that based on the optimization experiment of operating parameters,the nitrogen removal efficiency of the low-carbon source wastewater treatment system increased with the increase of the R after filling the corn cob.When R=200%,the effluent TN could be guaranteed to be less than 15 mg/L;when R=300%,the effluent TN could be guaranteed to be less than 8 mg/L.The short-oxygen tank with short HRT and high-dissolved oxygen system had a buffering capacity for the high-dissolved oxygen that flows back,and maintained a stable denitrification efficiency during short HRT.When R≥200%,it could ensure that the dissolved oxygen in the anoxic tank was maintained at 0.23mg/L.The effluent TN was less than 11 mg/L.The denitrification efficiency of the low-temperature system in winter increased with the extension of HRT.When HRT≥10 h,it could ensure that the ammonia nitrogen effluent was less than 3 mg/L,and the total nitrogen effluent was less than 12 mg/L.The effluent COD concentration of the corn cob solid carbon source A~2/O system in the anoxic pond under different working conditions was less than 25 mg/L,and there was no risk of exceeding the standard.(4)The denitrification kinetics and microbial community characteristics of the hypoxic pond were studied.The results showed that the denitrification rate of corn cob using biofilm for denitrification was faster,and the denitrification rate of corn cob was 0.71 mg/(g·h).The biofilm was enriched with denitrifying bacteria such as Unclassified＿f＿Methylophilaceae,Hyphomicrobium,and Terrimonas.Suspended sludge bacteria were mainly fermenting bacteria common in sewage plants such as Unclassified＿f＿Anaerolineaceae.There were also many fungal microorganisms capable of degrading cellulose in the anoxic tank system,such as unclassified＿p＿Rozellomycota,Trichosporon,Candida,Penicillium and so on.They worked together to complete denitrification with corn cob or other carbon sources. |
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