| The standard of wastewater discharge was controlled more strictly with the severe eutrophication question getting worse and worse which makes the the nitrogen and phosphorus removal technology aiming for eutrophication control be the study focus in the wastewater treatment area. It's difficult to further improve the removal efficiency of A/O process because of its high sludge reflux ratio(R) ,uneven organic load and low utilization of Volume.Aiming at this questions, we design a process flow called step-feed A/O biological nitrogen removal process, and carried some experiments in the laboratory to validate the feasibility of this process flow in removing the nitrogen in the wastewater.By means of contrast, we finally decided that the flow distribution ratio ,the HRT(Hydraulic Retention Time) in the anoxic tank(HRT anoxic tank) and sludge reflux ratio(R) were the main influential parameters in the step-feed A/O biological nitrogen removal process and carried out the comparative experiments for every single parameter respectively. The experiment validates that: (1) when influent flow rate distribution ratios=1:1, distribution of Organic load is more uniform,so the use of carbon is much better. (2)With the extension of HRT anoxic tank Removal of nitrogen is better. (3)Removal of nitrogen increase little when sludge reflux ratio(R) ranges from 200% to 300%. Carbon is the major factor of incomplete of denitrification,at the same time , dissolved oxygen of anoxic tank is high when sludge reflux ratio(R) is bigger. Dissolved oxygen consumed part of carbon in wastewater,and also inhibited the activity of denitrifying bacteria.So,Under the condition that the flow was 50 liters per hour, and the other parameters were: HRT(for the aerobic tank) equaled 6.0 hours,HRT(for the second sedimentation) equaled 1.2 hours, and ratio of sludge reflux is 100%, the outcomes of the experiments showed that, The results show that process will reach the best removal effect when influent flow rate distribution ratios=2:1, HRT anoxic tank=3h and R=200%: The average removal rate of the TN,NH4+-N and COD were respectively 74.42%,98.24% and 87.94%,when the influent concentration of TN,NH4+-N and COD were respectively 295mg/L,42.52mg/L and 44.63mg/L, and the concentrations of these three targets in the outflow were 30 mg/L,0.09 mg/L and 17.64 mg/L, among which the concentrations of the NH4+-N and COD were much better than the standards(5mg/L and 50mg/L) provided by the first level standard A of"the pollutant discharge standards of the urban wastewater treatment plant"(GB 18918-2002). and the concentration of the TN in the outflow also achieve the first level standard B.Studying the performance of the traditional nitrogen removal under the optimum parameters without steep-feed,the result shows that :The average removal rate of the TN,NH4+-N and COD were respectively 74.42%,98.24% and 87.94%,when the influent concentration of TN,NH4+-N and COD were respectively 295mg/L,42.52mg/L and 44.63mg/L, and the concentrations of these three targets in the outflow were 30 mg/L,0.09 mg/L and 17.64 mg/L.Removal of NH4+-N and COD was close but Removal of TN of step-feed A/O biological nitrogen removal process is better.Sequencing batch reactor by a small pilot test to investigate mechanism of efficient denitrification of step-feed A/O biological nitrogen removal process .Analysis shows: Denitrification rate and percentage denitrification rate of step-feed A/O biological nitrogen removal process is 0.51 times and 0.62times of that of traditional A/O process respectively in 0~0.5h. Denitrification rate and percentage denitrification rate of step-feed A/O biological nitrogen removal process is 3.75 times and 7.9times of that of traditional A/O process respectively in 0.5~1.0h. denitrification rate and percentage denitrification rate of step-feed A/O biological nitrogen removal process is 11.67 times of that of traditional A/O process in 1.0~2.0h.balanced load organic plays a greater role in step-feed A/O biological nitrogen removal process. Load of sludge is lower in local area, and Microorganism make full use of endogenous carbon for denitrification, so nitrogen removal will be more efficient.
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