| With the development of environmental protection of China and the state attaches great importance to water pollution control and governance, the discharge standard of sewage treatment has been improved in many cities. In the action plan for prevention and control of water pollution promulgated by the state council in 2015, strengthen urban life pollution control on the overall requirements of taking full control of pollutant discharge, according to the newest urbanization state plan requirement, all across the country, in 2020,the county and city sewage treatment should be reached 85%, 95% respectively. Therefore, to speed up urban sewage treatment facilities construction and renovation and adjust measures for local conditions of the existing urban sewage treatment facilities are still the important tasks.Most of the wastewater treatment plants in China use simultaneous phosphorus and nitrogen removal process(A2O).Facing the problem of total nitrogen excessive and unstable emissions.The main reason is the insufficient organic carbon source of the urban sewage treatment plant water and C/N is lower than 4.Canceling PST has become a important measurement to improve measures of organic carbon source in order to reduce the concentration of secondary effluent TN. However, it leads to the granularity of inorganic and organic matter into the aeration tank, causing excess production of surplus sludge and aeration over consumption. On the other hand,it makes the changes of denitrification carbon source structure changes and impact on denitrification rate. In a certain volume of anoxic tank(that is,a certain hydraulic retention time) can be used as a effective denitrification carbon source CODSS effectiveness is not clear.Accurate prediction and in-depth analysis of the urban sewage water quality distribution characteristics and pollutant load is the affiliated process of parameters determine of the urban sewage treatment facilities, and auxiliary equipment operation characteristics and to ensure that the necessary conditions for stable effluent treatment goal. Denitrification rate of urban sewage treatment works is the important factor of the design of anoxic zone and anoxic selection tank.Research Contents:(1) On the basis of water quantity and water quality of research,test two sewage treatment plants in J city in nearly three years. By using mathematical statistics to systematically analysis J city sewage quantity change rule; analysis of main pollutant(COD, BOD5, SS, TP, NH3-N and TN) concentration variation characteristics and probability distribution; analysis of biodegradability of urban sewage and proportion relation between the organic matter, nitrogen, phosphorus, etc.(2)By using dynamic precipitation test apparatus,investigate apparatus under different conditions of precipitation time removal efficiency of COD and SS and precipitate out of the water changes the structure of carbon source component.(3)With the effluent from grit chamber and PST,investigate PST removal efficiency of main pollutants,Compare the changes in the structure of carbon source components for the two.(4) with batch denitrification reactor, investigate the removal rules of COD and NO3-N in the process of denitrification for the effluent from grit chamber and PST;with kinetics to study the difference of the both denitrification characteristics.Conclusions:(1)Water inflow in the first sewage treatment works in J city is(20100±1800)m3/d average three years;variation coefficient is 9.04%..water inflow in the second sewage treatment works in J city is(95900±13300)m3/d average three years; variation coefficient is 13.91%.Sewage quantity is relatively stable, conforms to the sewage treatment plant water features.(2)The trend of BOD5 、COD、SS and TP in the influents were in accordance with positively skewed distribution;the trend of NH3-N and TN in the influents were in accordance with negatively skewed distribution.(3)COD average from 1972 samples is 361.52mg/L, the median is 336mg/L, The probability distribution of relative higher concentration range from 282 mg/L ~468mg/L;cumulative probability is 69%. When cumulative probability is 95%.,COD is 620mg/L.BOD5 average from 2032 samples is 140.95mg/L, the median is 130mg/L, The probability distribution of relative higher concentration range from 100 mg/L~175mg/L;cumulative probability is 72%. When cumulative probability is 95%., BOD5 is 265mg/L.SS average from 2034 samples is 190.96mg/L, the median is 182mg/L, The probability distribution of relative higher concentration range from 108mg/L~225mg/L;cumulative probability is 70%. When cumulative probability is 95%., SS is 350mg/L.NH3-N average from 2003 samples is 50.75mg/L, the median is 51.24mg/L, The probability distribution of relative higher concentration range from 34 mg/L ~69mg/L;cumulative probability is 83%. When cumulative probability is 95%.,NH3-N is 78mg/L.TN average from 2043 samples is 56.95mg/L, the median is 57.66mg/L, The probability distribution of relative higher concentration range from 39mg/L ~80mg/L;cumulative probability is 85%. When cumulative probability is 95%.,TN is 84mg/L.TP average from 2043 samples is 5.85mg/L, the median is 5.61mg/L, The probability distribution of relative higher concentration range from 3.9 mg/L ~7.2mg/L;cumulative probability is 76%. When cumulative probability is 95%., TP is 9.3mg/L.(4)BOD5/COD average from 1983 samples is 0.41, the median is 0.39.the probability distribution of BOD5/COD ratios between 0.2 and 0.4 is 62.9%; between 0.4 and 0.6 is 25.2%;indicating an adequate biodegradation ability of the influents. BOD5/TN average from 1999 samples is 2.58, the median is 2.39.The probability distribution of BOD5/TN ratios between 1 and 3.3 is 89.7%;less than 10.0% of the values are above 4,which could not meet the demands for denitrification.(5) The effluent from grit chamber contains relative much CODSS,average CODSS/COD is 50.41%;average VSS/SS is 42.58%;PST with 2h precipitation time, the removal rate of COD and CODSS are 25.2%、43.4% respectively;the removal rate of SS 、 VSS and ISS are 41.6 % 、 10.1 % and 61.8 %respectively.Precipitation time at around 45 min have the biggest impact of carbon source component structure.At this time,it can quickly remove ISS and retain most of VSS.(6) According to denitrification test results,Trend of denitrification can be divided into 3 stages(rapid decline;decelerate decline;slow decline).Under the condition of insufficient carbon source(<3), the denitrification process is in first-order kinetics reaction.(7)After cancelling the PST, the removal rate of NO3--N can be increased by 18.5%,CODss have the positive impact on adding external carbon source.(8) When effluent of grit chamber as the carbon source, denitrification rate are7.93 mg NO3--N/(g VSS·h),3.61 mg NO3--N/(g VSS·h)and1.95 mg NO3--N/(g VS S·h) relatively.When effluent of PST as the carbon source,denitrification rate are 8.07 mg NO3--N /(g VSS·h)、4.19 mg NO3--N /(g VSS·h)、1.98 mg NO3--N /(g VSS·h) relatively.(9)Denitrification with effluent of PST for 290 min,the removal rate of NO3--N is 57%, average denitrification rate is 4.85 mg NO3--N /(g VSS·h);for 350 min,the removal rate of NO3--N is 76%, average denitrification rate is 3.53 mg NO3--N /(g VSS·h).(10)Denitrification with effluent of grit chamber for 370 min,the removal rate of NO3--N is 70%,average denitrification rate is 4.39 mg NO3--N /(g VSS·h),for 530 min,the removal rate of NO3--N is 83%, average denitrification rate is 3.66 mg NO3--N /(g VSS·h). |
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