| Currently, eutrophication caused by nitrogen and phosphorus becomes more and more serious. Biological nitrogen and phosphorus removal processes and technologies are the key and difficulty of study in wastewater treatment field all over the world. Cyclic Activated Sludge Technology is a preferred process due to the capability of simultaneously removing nitrogen and phosphorus, as well as simple process and flexible operation, etc. However,its application in China shows a low nitrogen and phosphorus removal efficiencies, especially for the sewage of low COD/TN(COD/TN ? 8) real domestic wastewater. Shortcut biological nitrogen removal technology is favored by many researchers due to its low energy consumption, quick reaction and small sludge production. However, hard to maintain shortcut nitrification is a limited factor for its application. Meanwhile denitrifying phosphorus removal is currently widely concerned about the new technology of sewage treatment, compared with traditional biological phosphorus removal, denitrification and phosphorus uptake system combined the process of removing nitrogen and phosphorus together, denitrifying dephosphatation process achieving dual purpose can remove nitrogen and phosphorus at the same time. It not only saves carbon source, aeration rate, but also reduces the amount of excess sludge production. How to combine CAST process with denitrifying dephosphatation and shortcut nitrification, it is significant for the actual aperation and management of sewage treatment plants.In this experiment, the actual domestic sewage(the average of COD/TN is 3.9) is treated as the object of treatment, using the improved CAST for stable operation. Utilizing temperature gradient produced by seasonal variation and controlling the suitable aeration rate to achieve shortcut biological nitrogen removal in CAST reactor, also study the effects of influent total nitrogen on the stability of shortcut nitrification of the system.Followed by domestic sewage and simulation wastewater mixed wastewater as treatment object, using the improved CAST for stable operation, and at anoxic and aerobic phase adding a certain concentration gradient of nitrite into system to the sludge acclimation, in oder to investigate the nitrite addition on the property of removing nitrogen and phosphorus in improved CAST process,and comparing the effects of anoxic phosphorus uptake capacity before and after sludge acclimation. Besides through different electron acceptors(NO3- ? NO2- ? O2)phosphorus absorption test, studying adding nitrite for the influence of sludge phosphorusuptake.By utilizing temperature gradient produced by seasonal variation and reducing aeration rate to achieve shortcut nitrification, it provides a method for CAST process in the actual wastewater treatment plant and aims at energy saving and consumption reduction. The experimental result show that shortcut nitrification is quickly achieved in CAST under the condition of the control aeration 0.5m3/h, the temperature 28±0.5? and sludge age15 days.To reduce the amount of aeration to 0.4 m3/h and maintenance shortcut nitrification at 128 cycles,it shows that in the system sludge settling property is good under mean value of nitrate accumulation rate 73.4%,up to 86.1%, the removal rate of total nitrogen69.4%,enhance 21.2% comparing with full nitrification stage. It is also found that the decrease of the total nitrogen concentration in the influent can lead to the decrease of the accumulation rate of nitrite and even the destruction of shortcut nitrification, However, once the shortcut nitrification is destructed, short term biological nitrogen removal performance can not be restored in the long term, even creating the most suitable condition by increasing the total nitrogen concentration of influent combined with regulating temperature and aeration rate. The study of phosphorous removal capacity of shortcut nitrification CAST system showed that without adding external carbon sources the average phosphorus removal rate were lower than the 12.0%, but once improve influent carbon concentration100mg/L the phosphorous removal rate was increased to 44.8%. This indicated that lack of carbon sources was the main reason to casuse the deterioration of phosphorus removal performance and increased the temperature did not improve phosphorus removal performance.To achieve nitrite denitrify dephosphatation process in CAST reactor, a certain concentration gradient of nitrite was added to the anoxic phase, at the same time phosphorus uptake test through aerobic and anoxic condition reflect acclimation phosphorus uptake ability of the system before and after sludge domestication. The main conclusions are as follows:(1)The addition of nitrite has little effect on the ammonia oxidizing bacteria(AOB)proliferation and capacity metabolism activities, and also on the nitrogen removal performance, this shows that the system still has a better denitrification capability.(2) NO2-was added to the system and the sludge was domesticated in long term, which is beneficial to screen out denitrification phosphorus accumulation bacteria using NO3-& NO2- as electron acceptor, yet the addition of NO2- inhibit poly phosphorus bacteria in aerobic stage.(3)NO2- inhibit a part of microorganisms growth resulted in a decrease of theVI concentration of sludge, which lead to poor phosphorus removal and the effluent COD below standard.At aerobic stage, a certain concentration gradient of nitrite(5mg/L, 10mg/L, 15 mg/L,20mg/L) was added to the system in long term. The results show that NH4+ and COD most was removed under different operating conditions, this proves that the concentration of NO2- has trifling impact on ammonia oxidizing bacteria(AOB) proliferation and capacity metabolism activities. When the addition of NO2--N at aerobic stage was 5 mg/L, 10 mg/L,15 mg/L in CAST reactor, the performance of nitrogen and phosphorus removal was deteriorated at the initial stage of each working condition. After a period of acclimation, the system can be recovered and has a good performance of nitrogen and phosphorus removal.When the addition of NO2--N was 20 mg/L, the nitrogen and phosphorus removal performance of the system has deteriorated, and there is no sign of recovery, which proves that critical value of PAOs aerobic phosphorus uptake inhibition is 20mg/L. Yet the PAOs activity was also inhibited, which may be explained that the existence of NO2- inhibited the respiration of PAOs. When the addition of NO2--N was 5mg/L, 10mg/L in CAST reactor,the phosphorus release and phosphorus uptake capacity of sludge was not inhibited, and phosphorus release rate and phosphorus uptake rate and total nitrogen removal rate were higher than before, and there is a loss of nitrite in the aerobic phase. This indicated that under aerobic condition PAOs can also use NO2- as electron acceptor to absorb phosphorus.When the addition of NO2--N was 15mg/L, the amount of phosphorus release began to decrease under anaerobic condition of sludge. Meanwhile the anoxic phosphorus uptake of PAOs was suppressed within the system. It also remained shrinks when the addition of NO2--N was 20mg/L, the aerobic phosphorus uptake capacity of PAOs was inhibited.Phosphorus uptake small pilot studies have shown that when adding NO2--N into CAST reactor at aerobic stage and achieving long term domestication, the capacity of sludge denitrification and phosphorus uptake using NO2- as electron acceptor was constantly improved. It was also found that at initial CAST process operation sodium acetate as the sole carbon source is easy to cause sludge bulking. The addition of NO2- at aerobic stage inhibit the growth of filamentous bacteria, causing the fall of sludge SVI and a rise of sludge settling property. However, the presence of NO2- resulted in a decrease of the concentration of the sludge, because a amount of microorganism were killed or cell proliferation was lower than sewage sludge quantity.After aerobic acclimation, a certain concentration gradient of NO2--N(20mg/L, 10mg/L,5mg/L) was added at anoxic stage. The results show that the domestication of sludge at aerobic anoxic stage has a bad effect on nitrogen and phosphorus removal at each initial condition. With the decreasing concentration of NO2--N, the recovery time is longer, but eventually it has a good performance of nitrogen and phosphorus removal in CAST reactor,which means the system enhance anti impact ability after adding NO2- at anoxic phase.Moreover the sludge has a good performance of phosphorus uptake in anoxic condition.It was found through the mean curve fitting of the ratio between the amount of phosphorus uptake and nitrite dosage under the condition of the stable operation stage, with the decrease of nitrite dosage, the ratio of anoxic phosphorus uptake and nitrite dosage increased at first and then decreased, which indicated that the efficiency of sewage sludge utilization increased and then decreased. It was also found that under the condition of the stable stage specific phosphorus uptake rate increased gradually with the decrease of dosage of nitrite in phosphorus uptake rate curve fitting of a typical aerobic cycle, then proved that the addition of nitrite inhibited the phosphorus uptake by phosphorus accumulating bacteria at aerobic stage. NO3- ratio of phosphorus uptake was similar to NO2- ratio of phosphorus uptake according to the trend of phosphorus uptake rate in the curve, both of which increased first and then decreased, which showed that the sludge anoxic phosphorus uptake capacity increased first and then decreased. However the NO3- ratio of phosphorus uptake rate standard deviation range is larger than that of NO2-, which showed that the effect of nitrite dosage decreased on PAOs by using NO3- to carry out denitrification and phosphorus uptake was greater than that of PAOs by using NO2-. |
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