Effect Of SRT On Denitrifying Phosphorus Removal System With Side-stream Phosphorus Removal

Based on comprehensive reviewing the theoretical and technical of biological nitrogen and phosphorus removal, analyzing the characteristics such as good nitrogen and phosphorus removal effect, low sludge yields and long sludge age of the denitrifying phosphorus removal system with side-stream phosphorus removal (A2N-P-SBR) researched previously, the thesis considers that the sludge age control of the denitrifying phosphorus removal system with side-stream phosphorus removal is different from the traditional biological phosphorus removal system because of the change of phosphorus removal method. So the effect of SRT on denitrifying phosphorus removal system is studied by using method of sludge age control. The variation trend of energy of each biological phosphorus removal period of the system with different sludge age is measured by microcalorimetric. From the perspective of energy and material change, conversion and cyclic process of carbon of the biological nitrogen and phosphorus removal system is tracking measured. Based on analyzing the carbon sources utilization, inner reasons of the low oxygen demand, sludge yield and good nitrogen and phosphorus removal efficiency of the denitrifying phosphorus removal system with side-stream phosphorus removal are revealed. The experiment results show that:①The longer the sludge age is, the lower the effluent COD concentration is in the denitrifying phosphorus removal system with side-stream phosphorus removal (A2N-P-SBR). There is a little changes of the effluent total phosphorus concentration of the system with different SRT. The removal rate of the TN is all above 93%, and the sludge age values of biological phosphorus and nitrogen removal system can be determined merely by biological nitrogen removal system. Effluent concentration of ammonia nitrogen and total nitrogen decrease rapidly at first and then change to be steady. With the SRT increase, microorganisms stranded in the denitrifying phosphorus removal SBR increase, the average sludge concentration is higher. And the sludge volume index (SVI) increase, settling property enhance, p content in sludge increase. When the SRT is 32d and 64d, effect of anaerobic phosphorus release and anoxic denitrification of SBR in A2N-P-SBR is best. When the SRT is less than 32d, COD uptake increases with sludge age increases of SBR. When the SRT is greater than 32d, COD absorption decreases with the sludge age increases. The effluent concentration of each pollutant, nitrogen and phosphorus removal rate at all stages of SBR and the sludge settling properties are comprehensively analyzed. They results show that there is a good treatment effects when SRT is greater than 32d. The treatment effect is best when the Sludge age is 32d; the emission amount of sludge is least and pollutant removal effect is good when the sludge age is 160d.②After the phosphorus removal of anaerobic stages in nitrogen and phosphorus removal SBR, if there is a long anoxic stage before aerobic stage, the system can provide a good living environment for DPB and contribute much to the effect of aerobic phosphorus uptake. Phosphorus uptake and nitrogen release of anoxic stage can be completed in 50min. It shows that the reaction time of anoxic stage definitely can be shortened. Whether the short anoxic stage affects the activity and the dominant position of DPB still needs further experiment. When the reaction time of nitrifying SBR is 5h after the reaction cycle is Shortened, the optimum dissolved oxygen in the reactor can be controlled between 1.0mg / L ~ 1.5mg / L. Under the optimum conditions, ammonia can be completely oxidized and consume less energy, and can prevent microbes from entering into endogenous phase.③The longer the SRT is, the lower the sludge yield coefficient (Ys) is in the nitrogen and phosphorus removal SBR. When the sludge age is greater than 32d, the Ys of denitrifying phosphorus removal system is under 0.2. It is far below the value (0.4 to 0.5) of traditional biological nutrient removal system. The result indicates that denitrifying phosphorus removal system with side-stream phosphorus removal has a low sludge removal yield.④When the acetic acid is as a carbon source in denitrifying phosphorus removal system, the molar heat production is twice than the heat produced from traditional biological phosphorus removal system. The heat released from the aerobic phase is far greater than the anaerobic phase in traditional biological phosphorus removal system. The analysis of the total heat release shows that attenuation coefficient (Kd) of the traditional biological phosphorus removal system is 0.02. The time needed for the anaerobic exothermic peak is shortened when the SRT gets longer in denitrifying phosphorus removal system. There is a good linear relationship between SRT and the heat value (K(ΔGR)).The longer the sludge age the higher the K(ΔGR). Less energy is used for the synthesis of cellular material with sludge age. Cell proliferation is restrained, and sludge yield coefficient is low. When the SRT is a common 20d, the heat release is 104.59kJ/mol e-. The change of heat release and the apparent sludge yield coefficient is quite similar, and they are closely related. The practical heat release is greater than the theoretical heat release in denitrifying phosphorus removal system. The result indicates that when the energy stored in the anaerobic stage is utilized completely in the anoxic stage, the microorganism will continue to use other carbon sources such as dead cells or the carbon source to denitrify and release heat. As a consequence the redox reaction is finished completely, there is no more energy used for bacterial reproduction in the system. That is the basic reason of low sludge yield of the denitrifying phosphorus removal system.The results of the study reveal the influence mode of different sludge age on the denitrifying phosphorus removal system with side-stream phosphorus removal, and provide the reference of bioenergetics and thermodynamics for the denitrifying phosphorus removal technology.This research was sponsored by the National Natural Science Foundation of China (50278101) and Grand science and technology special project in National Water Pollution Control and Management of China(2009ZX07315).