Study On Medium-aged Landfill Leachate Using Heterotrophic Denitrification-autotrophic Denitrification Combined Process

In view of aged landfill leachate,high ammonia nitrogen concentration and low C/N ratio,and the problems of the traditional biological nitrogen removal process of medium aged landfill leachate,including the need to add a large amount of organic denitrification carbon source,high alkalinity consumption and high concentration of free ammonia nitrogen to produce threshold toxicity inhibition and collapse risk effect on nitrifying bacteria and nitrifying bacteria.The new combined process of"regulatingpool-anoxicdenitrificationanddenitrification-heterotrophic denitrification-partialnitrification-anaerobicammoniaoxidationautotrophic denitrification-aerobic nitrification"was investigated for two grade biochemical treatment of medium aged landfill leachate in this paper.The effluent of the aerobic nitrification reactor was reflowed into the regulating pool,so it could have an impact on the mixture and dilution of the high ammonia nitrogen concentration wastewater in this process.At the same time,in order to achieve the purpose of heterotrophic nitrogen removal and make full use of the organic carbon source to avoid the inhibition effect on the subsequent reaction in the original water,the alkalinity of the original wastewater was offered by the heterotrophic denitrification process of anoxic denitrification.Through the process of partial nitrification anaerobic ammonia oxidation,the process of nitrogenous autotrophic nitrogen removal was achieved,and the energy and alkalinity consumption of aerobic nitrification could be reduced,and the shortage of organic denitrification carbon source in the medium aged landfill leachate was overcome.The nitrification of the combined process was improved by subsequent aerobic nitration to minimize the organic and ammonia concentration of the wastewater.The main conclusions of this study were as follows:?1?Dilution Regulation-Denitrification Heterotrophic Denitrification Startup and Research:By adjusting the reflux ratio of the nitrifying liquid in the aerobic nitrification pond,and mixing and diluting,the effect of reducing the concentration of the medium old waste leachate and the threshold of the high ammonia nitrogen concentration on the system were reduced,and the influent of the follow-up reactor was reduced.The COD_Cr,TN and NO₃^--N were 4131.86 mg/L,1398.15 mg/L and567.53 mg/L respectively.After 50 d,the reactor showed stable heterotrophic nitrification and denitrification.The final COD_Crr removal rate was finally around 67%,and the TN removal rate was about 45%.The denitrifying heterotrophic nitrogen removal process had obvious effect of alkali production,and it supplied a large amount of alkalinity requirement for subsequent reactor operation.According the test,the optimal HRT was 10 hours and the reflux ratio was 200%.The concentration of COD_Cr,TN and NO₃^--N in the effluent were 832.44 mg/L,636.74 mg/L and 39.84mg/L respectively.The removal rates of COD_Cr,TN and NO₃^--N were 74.62%,62.37%and 93.92%respectively.?2?Study on Nitridation reactor startup and influencing factors:The nitrosation reaction of the SBR reactor was started by artificial water distribution.After 21 d operation,the nitrosation was started successfully.The removal rate of NH₄⁺-N was above 94%,the effluent concentration of NO₂^--N was 45.85 mg/L,and the concentration of NO₃^--N was below 5 mg/L,and the stable NO₂^--N accumulation was achieved.According the test,the optimal operating parameters of nitrite accumulation were that DO was 1.0 mg/L,and the temperature was 28?.The influence of organic carbon source on nitrosation reaction showed that when the concentration of COD_Crr exceeded 200 mg/L,the nitrosation reaction would be inhibited obviously.The optimal operation period of SBR was that the water intake?instantaneous?-aeration 5hours-precipitation drainage was 2 hours-idle 2 hours,and the NO₂^--N/NH₄⁺-N ratio of the effluent could be stable at about 1.32,which provided a good condition for the subsequent anammox autotrophic nitrogen and nitrogen removal.?3?Study on the start-up and influencing factors of anaerobic ammonia oxidation autotrophic denitrification reactor:The concentration of NH₄⁺-N and NO₂^--N in the influent was controlled in the range of 50⁶0 mg/L,pH was about 7.4,and the temperature was 35±1?,and the reaction was started by increasing the concentration of water matrix gradually.On the 103rd day,the nitrogen removal rate of the reactor was up to 500 mg/?L·d?and the anammox autotrophic nitrogen removal reactor was successfully activated.When the average concentration of NH₄⁺-N and NO₂^--N were310.55 mg/L and 400.29 mg/L,the removal rates were 87.65%and 97.65%respectively,and the maximum denitrification load was 624.71 mg/?L·d?.The effect of organic carbon source on the inhibition of autotrophic nitrogen removal by anammox was studied.When the biodegradability of COD_Cr?glucose?was over 160mg/L,the autotrophic nitrogen and nitrogen removal reaction in the reactor was obviously inhibited.?4?Study on series operation of nitrification anammox autotrophic nitrogen removal process:Firstly,artificial water distribution is used as the influent of the series.Under the above optimum operating conditions,when the concentration of NH₄⁺-N and COD_Crr is 500 mg/L and 150 mg/L respectively,the final TN and COD_Crr removal rates are 81.09%and 63.64%,respectively.Secondly,taking the effluent of anoxic denitrification and heterotrophic nitrogen removal as the influent of the series process,the concentration of NH₄⁺-N was first controlled in 430⁵00 mg/L,then the ratio of anoxic denitrification effluent was increased,until the concentration of NH₄⁺-N was 700 mg/L,the highest removal rate of TN reached 81%,but COD_Crr removal efficiency was poor,only 45.85%.?5?Study on Influencing Factors of Aerobic Nitrification:Under the condition that the filling ratio of suspended packing is 35%,the influence of different working conditions on aerobic nitrification was studied,and the best working conditions were as follows:DO was 2.5 mg/L and HRT was 20 hours,the maximum removal rate of NH₄⁺-N was above 90.95%,the removal rate of COD_Crr was 55%,and the concentration of NH₄⁺-N and COD_Crr in the effluent were 47.81 mg/L and 370 mg/L respectively.?6?Study on Stable Operation of Heterotrophic-autotrophic Denitrification Combined Process:Adjusting the pond water with landfill leachate as the influent of stable operation of the combined process,the influent NH₄⁺-N,TN and COD_Crr concentrations were 1427.57 mg/L,1633.88 mg/L and 3131.58 mg/L respectively under optimum operating conditions,the average concentration of NH₄⁺-N in the effluent was about 23.83 mg/L,the lowest concentration was 12.88 mg/L and the removal was up to 97.91%above.The removal rate of TN was 77.44%,the effluent TN concentration was 368.48 mg/L,the COD_Crr removal rate was 79.41%,and the effluent COD_Crr concentration was 541.84 mg/L.During the operation of the combined process,there was need to add organic carbon sources and inorganic nitrification alkalinity,and the alkalinity of the effluent from the anoxic denitrification and denitrification reactor should maintain the alkalinity of the whole process.At the same time,SBR partial nitrosation reaction saved a lot of alkalinity consumption and DO consumption,which greatly reduced the operation cost of the combined process.It was concluded that the process of heterotrophic nitrogen removal and autotrophic nitrogen removal in landfill leachate has been achieved by the heterotrophic and self-combined process with partial nitrification and anaerobic ammonia oxidation.It reduced the consumption of a large number of denitrifying organic carbon sources,nitrification inorganic alkalinity and dissolved oxygen,which could greatly reduce the energy consumption of landfill leachate wastewater treatment,and provides a certain theoretical data support for the practical engineering application of the process.