Study On The Nitrogen Phosphorus For Municipal Wastewater And Sludge Water Strengthening Bio-denitrification

Biological nitrogen phosphorus removal process is the dominant technology in the municipal wastewater treatment plants. Sludge water generated in the process of sludge treatment of the municipal wastewater treatment plant has the characteristics of small amount, high ammonia load and low C/N ratio, but the current sewage treatment plants directly send the sludge water back to the intake, which makes the ammonia loading of the incoming water much higher than the design value, directly affecting the denitrification effect. Through Pilot A²/O process devices and inverted A/O process test device (vice reactor) enrichment denitrifying bacteria and the experimental research of inverted A²/O process actual operation treatment effect in the No.4 Wastewater Treatment Plant of Xi'an City, the results of research show that:(1) In Pilot A²/O devices anaerobic zone, anoxic and aerobic zone hydraulic retention time was 1.9h, 3.4h and 5.1h respectively during the test and under the following conditions: temperature between 16℃ 26℃, the influent COD value between 135.5⁴79mg/L, TN value between 38.2⁷5.3mg/L, TP value between 2.75⁸. 42mg/L, NH_3-N value between 22.9⁵8.9mg/L , COD, TN, TP, NH3 -N and SS average removal rates were 84%, 60.0%, 62.2%, 96.8%, 80.1% respectively .Effluent quality meets Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant, and the system has a good impact on the pollutant load capacity;(2) The study found ammonia oxidation rate increased with the increase of sludge age, and the relationship was: Y = 0.643X+0.0124, correlation was 0.75;(3) in the A²/O system, TP removal were relevant to the hydraulic retention time of anaerobic zone and temperature, when anaerobic hydraulic retention time was 2h , phosphorus enrichment bacteria in anaerobic zone release phosphorus more fully, which can improve the phosphorus removal efficiency, so this can be used as reference in designing anaerobic zone in plant A²/O process in the future;(4) A²/O process of sludge floating in the final settling tank is mainly due to sludge bulking caused by excessive growth of filamentous bacteria and the sludge denitrification occurred at the tank bottom.. Among them, the excessive growth of filamentous bacteria is caused by low temperature in the reactor water; On the basis of certain water temperature, controlling pH value in appropriate range and DO > 2mg/L in oxygen pool can effectively prevent sludge bulking caused by excessive growth of filamentous bacteria. Denitrification occurred in the final settling tank is mainly caused by excessive nitrate entering the final settling tank. The sludge floating in the secondary sedimentation tank can be effectively inhibited by enhancing the denitrfication in anoxic tank, regulating the sludge return ratio, reducing the sludge retention time and so on, this study may be valuable for design and operation management of the similar Wastewater Treatment Plants in the future.(5) Using the activated sludge of the urban wastewater treatment plant to enrich the nitrifying bacteria, the initial ammonia concentration should be just controlled in 45.0 mg/L or so. The influent ammonia load increases with the ammonia oxidation rate increasing. When NH_3-N concentration is 400mg/L, ammonia oxidation rate is 36.48 mg/(L * h); Ammonia oxidation rate was positively associated with the influent load, the relationship was: Y=1.27X+0.74,coefficient was 0.89;(6) When sludge age is 8.5 d in A²/O process pilot plant, ammonium oxidation rate were 9.02 mg/(L?h) and 2.75 mg/(gMLSS?h), and when sludge age in inverted A/O process vice reactor) is about 13d, ammonium oxidation rate were 36.48 mg/(L?h) and 9.26 mg/(gMLSS?h); the ammonium oxidation of vice reactor is 4 times than main reactor. The main reactor ammonium oxidation rate is 14.8 mg/(L?h) from 9.02 mg/(L?h) during a month after addition;(7) Based on the monitoring of the main water quality parameters in the inverted A²/O process employed in The No.4 Wastewater Treatment Plant of Xi'an City, this paper mainly analyzed contaminant removals during over half a year operation. The results demonstrated that the total removal efficiencies of CODcr, TN, NH_3-N, TP and SS could reach to 90.5%, 65.2%, 82.0%, 54.8% and 95.8%, respectively;(8) Anaerobic zone in biological reaction pool release phosphorus effect is poor in The No.4 Wastewater Treatment Plant of Xi'an City. The main reason is that: first, anaerobic environment in anaerobic zone was not ideal, concentration of NO3--N into anaerobic zone was too high; second, design hydraulic retention time of anaerobic zone is too short, which causes releasing phosphorus inadequate, thereby affecting the phosphorus removal. Combining research results of pilot plant, design hydraulic retention time of anaerobic zone is appropriate in 2h or so, which can ensure the anaerobic release phosphorus environment to improve phosphorus removal.