Anoxic Phosphorus Uptake Performance Strengthening Technology In Muct Process

Sewage discharge standard is rising with eutrophication gradually becoming a prominent problem. Sewage disposal technology must remove not only organics but also nitrogen and phosphorus. Nitrogen and phosphorus removal aiming at eutrophication control is a hot problem in the sewage disposal. Denitrifying phosphorus removal has been a new and noticeable biological technology in recent years. It can save oxygen consumption, and reduce original carbon, excess sludge and effective volume of reactors. Hence it plays an important role in increasing the nitrogen and phosphorus removal feasibility of domestic sewage, especially domestic sewage with low C/N ratio.In order to promote the research development and practical application of MUCT process, especially to exert full advantage of domestic sewage with low C/N ratio, the relation between recirculation ratio and anoxic phosphorus uptake were investigated by using simulative domestic sewage in this project. The concentration of NO3--N in the second anoxic zone was settled as a parameter strengthening the anoxic phosphorus uptake capability and optimizing the process, and the relation between the concentration of NO3--N in the second anoxic zone and C/N ratio of influent was also studied. Typical variation rule of DO, pH and ORP in each stage was investigated for the first time. The feasibility of ORP settling as a parameter strengthening the anoxic phosphorus uptake capability and optimizing the process was discussed. The effects of both the anaerobic zones and the second anoxic zone running as a succession of CSTRs on the anaerobic phosphorus release and the anoxic phosphorus uptake were studied respectively. Optimal number of CSTRs in series was determined.Most COD was change into PHA by PAO in anaerobic zones in MUCT process, and the transformation ratio is affected by mixed-liquor return ratio (γ). The anaerobic phosphorus release was influenced byγ. The anaerobic phosphorus release reached the highest level of 6.89g/d whenγwas 1.5. Phosphorus uptake occurred in the second anoxic zone and aerobic zones in MUCT process. The anoxic phosphorus uptake was closely related to reflux ratio of nitrification (α). The anaerobic phosphorus uptake mass fraction reached the maximum of 0.44 whenα was 4. The difference between anoxic phosphorus uptake and aerobic phosphorus uptake was 6.8% after calculation. Additional carbon source could be saved when anoxic phosphorus uptake was strengthened. Whenαwas 3 andγwas 1.5, the maximum of carbon source saving was 24.29%.NO3--N concentration in the second anoxic zone, which was influence by the C/N ratio of influent, could be settled as controls parameter of anoxic phosphorus uptake performance in MUCT process. When C/N ratio were 5, 5.45, 6, 6.67, 7.5, 8.57, 10 and 12, the optimal NO3--N concentration in the second anoxic zone (SNO3) were 2.75, 2.5, 2.25, 2, 1.75, 1.5, 1.25 and 1, respectively, with the anoxic phosphorus uptake mass fraction of 0.467, 0.455, 0.44, 0.410, 0.365, 0.300, 0.210 and 0.100, respectively.There was a linear correlation between ORP and the concentration of NO3--N in the second anoxic zone. Hence ORP, which was also influence by the C/N ratio of influent, could be settled as controls parameter of anoxic phosphorus uptake performance instead of NO3--N concentration in MUCT process. When C/N ratio were 5, 5.45, 6, 6.67, 7.5, 8.57, 10 and 12, the optimal ORP were -71, -83, -90, -94, -101, -113, -117, -124mV, respectively.The more CSTRs in series of the anaerobic zones was, the more the anaerobic phosphorus released, thus the anaerobic phosphorus uptake mass fraction was also increasing in MUCT process. The results showed that COD removal and consumption speed, TP release and phosphorus release speed were increased obviously when the number of CSTRs in series increased from 1 to 2 under the same total HRT. The recommended number of CSTRs in series of the anaerobic zones was 2 under the conditions of this experiment. The more CSTRs in series of the second anoxic zone was, the lower TP concentration in effluent of the second anoxic zone was, thus the anoxic phosphorus uptake mass fraction was also increasing evidently. The recommended number of CSTRs in series of the second anoxic zone was 2 under the conditions of this experiment.The mass balance computing results of NH4+-N and NO3--N proved a distinct Simultaneous Nitrification and Denitrification (SND) phenomenon in MUCT process, which played an important role in practical application of MUCT process.