Experimental Study On Short-cut Nitrification And Denitrification Biological Nitrogen Removal Process Of Landfill Leachate

Landfill leachate was a kind of wastewater with complex composition and high concentration of pollutants.The characteristics of leachate included high concentration of organic matter,high ammonia nitrogen,poor biodegradability,various refractory organic matter,high salinity,heavy metal ions and unstable water quality.The complex component increased difficult to deal with leachate.The single physical and chemical methods could realize the effective removal of ammonia nitrogen.But the methods have some defects,such as harsh process conditions and higher equipment requires.The leachate could not meet the treatment conditions of traditional biological nitrogen removal method.It also could not achieve long-term stability of leachate treatment.Therefore,how to effectively remove ammonia nitrogen from landfill leachate had been the focus in the field of landfill leachate treatment.In this study,the leachate from Fenghuang county solid waste landfill in Xiangxi state was choosed as the research object.In the light of the high ammonia nitrogen concentration of landfill leachate,a feasibility study of short cut nitrification treatment of landfill leachate by using aerobic(O)-Fenton(F)-anoxic/aerobic(A/O)process was carried out.The treatment process consisted of three parts.Each part of the operation conditions were as follows: 1)aerobic activated sludge process,in order to achieve accumulation of nitrite nitrogen(NO2--N)under aerobic conditions;2)Fenton process,this operation was mainly for improving the biodegradability of leachate and providing effective carbon source for the subsequent biological treatment;3)A/O process,aimed to realize denitrification under anoxic condition and further removal of organic matter under aerobic condition.In this study,the original leachate was used as the research object,the removal efficiency of nitrogen in leachate by multistage treatment system was investigated,and microbial diversity in the system was analysised.The significance of this study was to provide a scientific reference for the shortcut nitrification treatment of high ammonia nitrogen content in leachate.The main research results are as follows:1.O treatment stage.This stage used batch sludge acclimation method.The activated sludge from municipal wastewater treatment plant was gradually adapted to the high ammonia nitrogen load in the leachate by gradually increasing the concentration of free ammonia(FA=6.7-68.5mg/L).The acclimation temperature was maintained at 25±0.1?,and the pH value was 7.5-8.0.After 15 days of acclimatization,the system entered a stable stage.The influent ammonia concentration was 417.95-674.61mg/L,temperature was 31±1?,pH value was 8.0±0.3,the effluent nitrite accumulation rate(NAR)was above 80%,and the NO2--N concentration was up to 761.93 mg/L.Therefore,the system was successful achieved the short-cut nitrification.2.F treatment stage.As the effluent B/C ratio of O stage was 0.02 to 0.04,it could not meet the requirement of carbon source for denitrification.In order to improve the B/C ratio,FeSO4·7H2O and H2O2 were chosen as the Fenton reagents,and their optimal dosage ratio was determined to be 1:3 by lab-scale experiment.The most suitable amount of FeSO4·7H2O and H2O2 in F stage were 16 mL and 48 g respectively,which was determined through the same times magnification experiment.And the p H value in this process needs to be adjusted to 3.2±0.2.After treatment,the effluent B/C increased to 0.1-0.2,and the total biodegradation capacity was 5 times higher than that of the original O treatment.3.A/O process: A/O process was consisted of anoxic denitrification part and further aerobic oxidation part.The microorganisms in the system were acclimated by the method of continuous culture and domestication.After a week of acclimatization,the system was achieved stable operation.When the anoxic denitrification process was controlled by DO lower than 0.5mg/L,the pH value is 7.5-7.8,the temperature is 31±1?.After a week of acclimatization,the system achieved stable operation.In anoxic denitrification process,DO concentration was lower than 0.5mg/L,pH value was 7.5-7.8,and temperature was 31±1?.In aerobic process,DO concentration was 2.0mg/L,pH value was 7.0-7.5.The concentration of NO2--N in effluent was very low,its removal rate was 95%,NO3--N concentration was maintained at about 60mg/L.4.The microorganisms in the reactors were analyzed by 16 S rDNA method.The dominant species were obtained in different reactors were different.However,Proteobacteria,Bacteroidetes and Chloroflexi were the main categories in the whole system.The Nitrospirae content was low in the O stage,which belongs to NOB and is beneficial to the accumulation of NO2--N in the system.The genus level analysis showed that a large number of Nitrosomonas and a relatively small number of Nitrospirales exsited in the O stage,which belongs to AOB and NOB respectively.The amount of AOB was 11 times of NOB.The system was achieved stable treatment of ammonia in leachate during the long term operation.The system was achieved removal of NH4+-N and TN,with NH4+-N?80%,TN?75% respectively.The AOB was dominant in the shortcut nitrification system.The high efficiency of nitrite accumulation was achieved.However,the system was vulnerable to environmental factors during the operation.The results showed that the ammonia nitrogen in effluent was increased and the removal rate of total nitrogen was decreased.This study verified the feasibility of O-F-A/O process for the treatment of landfill leachate by shortcut nitrification denitrification.By adjusting the operating parameters to the best,the process could realize stable shortcut nitrification denitrification and it was achieved deep denitrification treatment of landfill leachate.