Study Of Nitrogen And Phosphorus Removal Of A~2/O And Its Deformation Processes

While inversed A2/O process had solved the systemic problems that existed in nitrogenand phosphorus removal process, which had good nutrient removal efficiency, but the mainproblems to be resolved, such as: PAO and denitrifying bacteria existed in the anaerobic zonewould compete for carbon, distribution ratio of influent and so on. The subject wasestablished based on these issues, and we designed a new nutrient removal process, namedparallel A2/O process. We built a ASM2D model for parallel A2/O process, using the model ofthe process succeed in achieving a steady-state simulation and getting the optimum operatingconditions of the process, at the same time, the comparative study of its nitrogen andphosphorus removal efficiency had been done. When the influent concentration of COD,NH4+-N,TN and TP was380mg/L,34mg/L,45mg/L and4.2mg/L, by testing and simulating,we got the following conclusions:⑴The experiment showed that, the removal efficiency of COD of each process behavedas multi-point water A2/O process> parallel A2/O process> Johannesburg process (JHBprocess)> A2/O process> inverted A2/O process, the removal rates respectively were96.8%,95.1%,94.4%,93.5%and93.0%, the COD effluent concentration was maintained at50mg/Lor less. COD removal efficiency of anaerobic tank and anoxic tank in parallel A2/O processwas63.0%and18.2%, COD removal efficiency of anaerobic tank and anoxic tank in inversedA2/O process was44.7%and55.3%, most of the COD in multi-point water A2/O process andA2/O process was removed in the anaerobic tank, removal rate reached up to74.4%and86.1%, COD in JHB process was mainly removed in pre-anoxic tank, removal rate reachedup to88.0%.⑵The experiment showed that, the nitrite effluent concentration of each process waslower than0.5mg/L, the nitrate effluent concentration was between2.0~5.5mg/L. Due to thestructure of the reactor, denitrification only occurred in anoxic tank in inversed A2/O process;denitrification rates in anoxic tank and anaerobic tank of parallel A2/O process, multi-pointwater A2/O process and A2/O process respectively were49.1%and50.9%,42.2%and57.8%, 39.8%and60.2%, denitrification rates in pre-anoxic tank, anaerobic tank and anoxic tank ofJHB process were55.6%,1.0%and43.4%.⑶The experiment showed that, the removal efficiency of TP of each process behaved asparallel A2/O process> A2/O process> multi-point water A2/O process> inversed A2/Oprocess> JHB process, the removal rates respectively were96.5%,94.0%,89.3%,86.5%and79.3%. Phosphorus release phenomenon in anaerobic tank was most significant in parallelA2/O process, the amount of phosphorus release reached up to198.9mg/d, followed by theA2/O process, the worst is JHB process; the phosphorus release phenomenon also appeared inanoxic tank in inversed A2/O process, parallel A2/O process and JHB process, and theinversed A2/O process was the best; aerobic tank in parallel A2/O process had the bestphosphorus removal effect, followed by the inversed A2/O process and JHB process.⑷In this experiment, denitrifying phosphorus phenomenon only happened in the anoxictank of A2/O process and multi-point water A2/O process, the ratios of the amount ofphosphorus in anoxic tank accounted for the amount of phosphorus release in anaerobic tankwere0.03%and20.2%, for the inversed A2/O process and parallel A2/O process weren’texperience anaerobic-anoxic process, so that this phenomenon did not occur.⑸The experiment showed that, the removal efficiency of NH4+-N of each processbehaved as inversed A2/O process> multi-point water A2/O process> A2/O process> JHBprocess> parallel A2/O process, the removal rates respectively were99.2%,99.1%,98.4%,98.2%and97.3%, NH4+-N effluent concentration in parallel A2/O process was higher,reached up to1mg/L, the other process was0.8mg/L or less. The amount of nitrification inaerobic tank of each process was no different, nitrification behaved as inversed A2/O process>multi-point water A2/O process> parallel A2/O process> A2/O process> JHB process,nitrification rate respectively was64.6%,58.9%,51.5%,47.9%and37.4%, showing inversedA2/O process had the best nitrification effect.⑹The experiment showed that, the removal efficiency of TN of each process behaved asmulti-point water A2/O process> JHB process> inversed A2/O process> A2/O process>parallel A2/O process, removal rates respectively were90.2%,87.6%,86.8%,85.0%and83.8%, TN effluent concentration maintained at5mg/L or so.⑺According to the optimization and simulation of the parallel A2/O process, we got the conclusion that when the sludge reflux ratio R=1, the reflux ratio RI=2.5, influent flowdistribution ratio of anaerobic tank and anoxic tank was ě:ě=2:1, volume ratio of anaerobictank, anoxic tank and aerobic tank was V1: V2: V3=1:2:4, the SRT=20d, the process couldachieve the best operating results. Under these operation conditions, the removal rates ofCOD, NH4+-N, TN and TP were94.5%,98.0%,87.7%and95.2%.