Research On The System Performance Of Step-feed Modified A/O Process

With the development of the society,the sewage treatment of high ammonia nitrogen and low carbon nitrogen ratio more and more get the attention of people.The step-feed Modified A/O process was used to treat the sewage of high ammonia nitrogen and low C/N,investigating the difference of flow distribution ratio,volume ratio and HRT on system of organic matter removal,nitrification and denitrification and the influence of the total phosphorus removal,and the water quality changes in each reaction tank was analyzed.The conclusions are as follows:First,the removal efficiency of organic matter and Ammonia nitrogen had little difference under different flow distribution ratio,reaching to being above 90% and95% respectively,and the average effluent concentration of COD and Ammonia nitrogen were below in 50mg/L and 5mg/L respectively.The removal efficiency of total nitrogen and total phosphorus were affected by the flow distribution ratio significantly.The removal efficiency of total nitrogen and total phosphorus improved obviously with the inflow proportion of anaerobic and first oxygen increasing,and when he flow distribution ratio was 1:1:2:2 and 1:2:2:1,the removal efficiency of total nitrogen and total phosphorus were 63.08%,81.76% and 72.03%,89.49%respectively.Second,the water quality changes in each reaction tank was analyzed when the flow distribution ratio was 1:2:2:1,showing that the concentration of organic matter was lower because of because of dilution,assimilation and denitrification after entering system,creating favorable conditions for the nitration.Ammonia nitrogen could be nitrified completely,and the effluent concentration of Ammonia nitrogen was below in 5mg/L.The effluent concentration of nitrate was more and more with the denitrification being incomplete because of the limit of carbon source.The most of phosphorus was accumulated in first aerobic after PAO release excessive phosphorus in anaerobic,and the concentration of total phosphorus was lower inanoxic tank than in aerobic tank,indicating that phosphorus was removed in anoxic by DPB.Third,the removal efficiency of organic matter and Ammonia nitrogen had little difference under different volume ratio,reaching to being above 85% and 90%respectively.The removal efficiency of total nitrogen and total phosphorus were affected by the volume ratio significantly.With the increase of advanced anoxic/anaerobic volume ratio,denitrification get enough reaction time in the advanced anoxic,leding to the increase of removal efficiency of total nitrogen from74.28% to 78.46%,but leding to the decrease of removal efficiency of total phosphorus from 93.63% to 88.73%.With the increase of anoxic/aerobic volume ratio,the time of organic matter in aerobic tank reduced,but more carbon source could be used effectively,weakening the accumulating phosphorus absorption effect and the removal efficiency of total phosphorus.Forth,the removal of total nitrogen was reduced mainly by the way of denitrification,and the increase of anoxic volume was benefit to the improvement of removal efficiency of total nitrogen.The removal of total phosphorus was reduced mainly by the way of releasing phosphorus and accumulating phosphorus effect in anaerobic and aerobic tank respectively,and the removal of total phosphorus in anoxic tank accounted for only a small fraction of the removal of total phosphorus in aerobic tank,and the key factors of the removal of total phosphorus was anaerobic volume.Fifth,the influence of HRT changes on the removal of organic matter and total phosphorus was little.With the HRT being increased from 8h to 12 h,the time of organic matter by microbial used became to be longer,and anaerobic-releasing phosphorus and aerobic-accumulating phosphorus effect became to be better,leding to the average effluent concentration of COD and total phosphorus being lower.The nitrification and denitrification effect is greatly influenced by HRT.With the HRT being increased from 8h to 10 h,the nitrification and denitrification effect increased significantly,the removal efficiency of Ammonia nitrogen and total nitrogen increased from 92.57%,72.20% to 92.57%,72.20% respectively.With the systemHRT continue to be longer,the improvement of removal efficiency of Ammonia nitrogen and total nitrogen was only about 1%.In conclusion,the increase of system HRT could improve the effect of sewage treatment,but the increase of HRT will increase infrastructure investment and operation cost,leding to the increase of sewage treatment cost,so the HRT of system must be economic and reasonable.