The treatment of landfill leachate obtained from municipal solid waste(MSW) by using a lab-scale sequencing batch reactor(SBR) was studied.The aim of achieving and stabilizing partial nitrification and denitrification and the characteristics of advanced nitrogen removal were investigated.The experimental results showed that for 95 days running,stable partial nitrification with nitrite accumulation rate above 92.5% was achieved and maintained successfully.The stable biological nitrogen removal via partial nitrification and denitrification was realized and the average removal efficiency of NH+4-N and TN were above 97.2% and 91.7%,respectively.The DO,ORP and pH could be used as the process control parameters for SBR reactor,because the characteristic points on the profiles indicated exactly the nitrification and denitrification end point.The nitrite oxidizing bacteria(NOB) was more sensitive than ammonia oxidizing bacteria(AOB) to the free ammonia(FA) and free nitrite acid(FNA),so the activity of NOB was inhibited by the synergetic effect of highly concentrated FA and FNA in the SBR nitrification.Furthermore,the key factor of achieving and stabilizing partial nitrification and denitrification for a long time was optimization of nitrifying microbial population by the assistance of process control,which was proved by FISH analysis.
A system consisting of a two-stage up-flow anaerobic sludge blanket (UASB), an anoxic/aerobic (A/O) reactor and a sequencing batch reactor (SBR), was used to treat landfill leachate. During operation, denitrification and methanogenesis took place simultaneously in the first stage UASB, and the effluent chemical oxygen demand (COD) was further removed in the second stage UASB. Then the denitrification of nitrite and nitrate in the returned sludge by using the residual COD was accomplished in the A/O reactor, and ammonia was removed via nitrite in it. Last but not least, the residual ammonia was removed in SBR as well as nitrite and nitrate which were produced by nitrification. The results over 120 d (60 d for phase I and 60 d for phase II) were as follows: when the total nitrogen (TN) concentration of influent leachate was about 2500 mg/L and the ammonia nitrogen concentration was about 2000 mg/L, the shortcut nitrification with 85%-90% nitrite accumulation was achieved stably in the A/O reactor. The TN and ammonia nitrogen removal efficiencies of the system were 98% and 97%, respectively. The residual ammonia, nitrite and nitrate produced during nitrification in the A/O reactor could be washed out almost completely in SBR. The TN and ammonia nitrogen concentrations of final effluent were about 39 mg/L and 12 mg/L, respectively.
WU Lina, PENG Chengyao, ZHANG Shujun, PENG Yongzhen Key Laboratory of Beijing for Water Quality Science and Water Environment Recovery Engineering, Beijing University of Technology, Beijing 100124, China.
