| With the continuous improvement of sewage discharge standards,China’s sewage treatment plants are facing severe technical challenges.Anddue to the shortage of land and excessive investment,it is difficult to construct new sewage treatment plants.The efficiency of TN and TP removal in sewage treatment plants adopted traditional secondary treatment process is limited,the effluent quality isableto meet the“Class A”standard ofthe“Urban Sewage Treatment Plant Pollutant Discharge Standard(GB18918-2002)”,but can’t reach the“Special Discharge Limits”of“Urban Sewage Treatment Plant Pollutant Discharge Standard(draft)”(special discharge limits’indicators:COD≤30 mg/L,NH3-N≤1.5mg/L,TN≤10mg/L,and TP≤0.3mg/L).Meanwhile,the traditional secondary treatment process also has problemofmass biological sludge production,andthe residual sludge treatment and disposal is difficult and costly.Therefore,it is of great practical significance to study a secondary treatment process that can meet higher discharge standards and achieve sludge reduction.In this paper,a pilot plant of the activated sludge and fixed filler coupling process wasestablished based on the hydraulic retention time(HRT)consistent with the traditional secondary treatment process.Under the promise of no major modification to the traditional process,the established pilot plant was able to improve the effluent quality and reduce the amount of excess sludge at the same time.In order to improve effluent quality and reduce excess sludge at a low cost,the following measures were adopted in this study:1.Increase the internal return flow ratio and the intensity of anoxic stirring,and install fixed biofilm in the anoxic zone to enhance denitrification capacity;2.Maintain the anoxic HRT of the original process to reduce reconstruction cost;3.Install Fixed biofilmin the aerobic zone to enable simultaneous nitrification and denitrification,and meanwhile,reduce excesss ludge yield by means of micro-animals sludge predation.Basedon the Box-Behnken curved surface design,the influence of 4 factors(including aerobic DO value,internal reflux ratio,sludge concentration and intensity of anoxic stirring)and their interaction to the effluent quality was discussed,and a regression model and theoverall effluent quality were taken into account at the same time to search the optimal operation parameters for energy saving purpose.The results showed that the effect of aerobic DO value and sludge concentration were more significant than that of internal reflux ratio and anoxicstirring intensity on effluent quality,and there was a significant interaction between aerobic DO value and sludge concentration.When operating thepilotplant at optimum conditions(aerobic DO of 3.9 mg/L,reflux ratio of 150%,sludge concentration of 4900 mg/L,stirring intensity of 170 w/t),the DO value of 3.9 mg/L was able to improve the effect of COD and NH3-N removal,and thetransformation of ammonia to nitrate enriched the material basis for denitrification.By increasing the reflux ratio,more nitrogen-containing mixture could be reflux to the anoxic zone,which provides the material basis for denitrification process and increases the denitrification capacity.Increasing the sludge concentration could be helpful for the removal of organic matters.Increasing the stirring intensity made the anoxic zone mix evenly and made full use of the denitrifying HRT.According to the response surface results,the process operating conditions were adjusted,the COD concentration of the effluent was 28mg/L,the NH3-N concentration was 0.47mg/L,and the TN concentration was 8mg/L,all of which could meet the special discharge limit requirements of the“Urban Sewage Treatment Plant Pollutant Discharge Standard(draft)”.The results show that the push-flow coupling process unit has a better treatment effect on conventional,low temperature,low concentration and high concentration domestic sewage.(1).For conventional sewage,the mean COD inlet water was 202mg/L,the mean COD effluent water was 15.39mg/L,the mean NH3-N inlet water was 17.45mg/L,the mean NH3-N effluent water was 0.19mg/L,the mean TN inlet water was 21.83mg/L,the mean TN effluent water was 7.63mg/L,the mean TP inlet water was 1.94mg/L,the mean TP effluent water was0.18mg/L.(2)Low temperature sewage,the mean COD inlet water was 146.63mg/L,the mean COD effluent water was 20.51mg/L,the mean NH3-N inlet water was 16.92mg/L,the mean NH3-N effluent water was 0.43mg/L,the mean TN inlet water was 22.06mg/L,the mean TN effluent water was 7.93mg/L,the mean TP inlet water was 2.35mg/L,the mean TP effluent water was 0.27mg/L.(3)For low concentration sewage,the mean COD inlet water was108.07mg/L,the mean COD effluent water was 12.53mg/L,the mean NH3-N inlet water was16.99mg/L,the mean NH3-N effluent water was 0.25mg/L,the mean TN inlet water was20.79mg/L,the mean TN effluent water was 7.85mg/L,the mean TP inlet water was1.77mg/L,the mean TP effluent water was 0.23mg/L.(4)In high concentration sewage,the mean COD inlet water was 220.09mg/L,the mean COD effluent water was 15.55mg/L,the mean NH3-N inlet water was 26.54mg/L,the mean NH3-N effluent water was 0.32mg/L,the mean TN inlet water was 32.41mg/L,the mean TN effluent water was 7.25mg/L,the mean TP inlet water was 1.73mg/L,the mean TP effluent water was 0.3mg/L.The push-flow coupling process unit can treat all kinds of sewage,and the effluent all of which could meet the special discharge limit requirements of the“Urban Sewage Treatment Plant Pollutant Discharge Standard(draft)”.Through the statistics calculation of excess sludge production in Plug-flow coupling process,results wereasfollows:by processing every 10000 tons of sewage,theplug-flow coupling process produced 4.05 tons of excess sludge,lower than 5.1 tons(80%moisture content)of the sewage treatment plant,the sludge reduction effect is about 20.6%;the suspended sludge and packing carrier microscopy results showed that there is a variety of kinds of protozoan and metazoan in the plug-flow coupling process pilot plant,its crafted environment could promote the enrichment of metazoan.The metazoan predation of sludge could improve the activity of sludge,which could be beneficial to form a more stable ecological system in the sewage treatment process.Under the condition of the same effluent quality,modify the A~2O process to plug-flow coupling process has no structural modification and does not need to shut down production,and the cost of upgrading and reconstruction is significantly lower than that of modification to MBBR process.In terms of operation,the power consumption per ton of push-flow coupling process was about 0.6kwh/t,and the power consumption per ton of MBBR process was about0.74kwh/t.Therefore,the overall operation cost of the push-flow coupling process is lower than that of the MBBR process.In this paper,the pilot experiment and application of the push-flow coupling process treating actual domestic sewage were studied.And the aim of this study was to provide a feasible direction and scientific basis for the subsequent process operation adjustment of municipal wastewater treatment plant. |
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