| The step-feed A/O process was widely concerned and acknowledged due to its unique advantages.The main innovations of this experiment was to combine the step-feed A/O process with A2/O process,instilling a mixture of the circulatory system for each segment of the A/O process,and come up with the step-feed cyclic A/O process.It can have a better effect than sewage treatment by absorbing the advantages of A/O and A2/O.Experiments were conducted towards artificial wastewater,with the COD concentration of 211-459 mg/L,ammonia concentration of 54-85 mg/L,total nitrogen concentration of 57-88 mg/L,pH ranging from 7 to 8.This paper mainly focused on the influence of mixed reflux and HRT on the system performance and rate(including the rate of OUR?AUR and NUR)and the mean concludes as follows:(1)This paper studied the impact of mixture reflux on system performance under the ratio of 0,100%and 200%.Results show that the reflux ratio has little effect on system's COD and ammonia nitrogen removal.The water is more stable and satisfies A standards with a relatively high removal rate.Comparatively,if reflux is increased from 0 to 100%,the system for total nitrogen removal is obvious;but if it is increased from 100%to 200%,the removal effect is not intuitive and even decrease slightly.experiments show that the higher the reflux ratio does not mean a better performance,and it has a proper range.(2)The step-feed cyclic A/O process can improve TN removal rate from more than 60%to more than 80%,and COD?NH4+-N?TN can all satisfy standards under the conditions of NH4+-N 75 mg/L and C/N ratio 4.5.So the step-feed cyclic A/O process has a unique advantage in the treatment of low C/N ratio wastewater.(3)This paper analyzed the changes in water quality with the reflux ratio of 100%and discovered that if every level of aerobic zone increased,each level of aeration aerobic zone should be gradually reduced in order to maintain the activity of activated sludge and reduce energy consumption.pH value is comparatively stable without too much fluctuations despite some slight decrease.Anoxic water entered from different sub-district levels,which can make organic matter ratio reduce greatly by dilute of mixture,microbial metabolism and denitrification.It can create favorable conditions for the nitration reaction and make the effluent COD meet the A standard so that the system can have a high removal rate of COD.The low ratio of C/N of wastewater restricts the effect of denitrification for lack of carbon resource so that nitrate has accumulated.Sludge concentration in the system gradually decreased due to the dilution of water,forming a concentration gradient,but the average sludge concentration increased than traditional activated sludge.(4)This paper studied the effects that HRT has on system performance with the hydraulic retention time of 8h,10h and 12h,finding that HRT has little influence on COD removal with a high removal rate and water floods stably and satisfies A standard.NH4+-N and TN removal rate improved a lot when HRT increased from 8h to 10h,however,when it comes to 12h,the effect was not so obvious.Overall,the removal effect was better and less costly with the HRT at 10h.(5)The system has a strong load to sustain flooding.During the experiment,although the influent COD,NH4+-N and TN fluctuated heavily,the water quality was relatively stable,indicating that the system has a strong impact load and stable treatment effects.(6)Batch reactor was used to measure rates of OUR?AUR and NUR of the activated sludge in the step-feed A/O process,the rate of OUR is 36.02mgDO/(gMLSS·h),the rate of AUR is 5.74mg NH4+-N/(gMLSS-h),the rate of NUR is 3.86mgNO3--N/(gMLSS·h).Results show that the rate of OUR and AUR is higher,but the rate of NUR is lower,in order to improve the rate of NUR,it can be achieved by appropriately increasing the amount of easily biodegradable organics in sewage;the rate of AUR and NUR can be used to design the aerobic zone and anoxic zone of the step-feed A/O process. |
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