Research On Optimizing Operation For Urban Wastewater Treatment Plant Based On WEST Software

Strict discharge standards and requirements of energy saving and consumption reduction call for higher requirements for the operation of wastewater treatment plants?WWTP?.Taking Jingjiang municipal WWTP as study object,the actual operation condition and problems of improved A²/O process and the Orbal oxidation ditch process in this WWTP are investigated and analyzed.The mathematical models of the two processes are constructed by using WEST software,and then the research on the optimal operation of the two processes are carried out based on these models.The optimized operation plan of the improved A²/O process is put forward and implemented actually,and effectively improves the removal efficiency of pollutants.The plan also reduces the energy consumption of operation.The main conclusions are as follows:?1?The average influent water volume of the improved A²/O process is 7735 m³/d,and the average removal rates of COD,TN,TP and NH₄⁺-N are 88.29%,50.11%,72.08%and 94.78%respectively.The effluent concentration of NH₄⁺-N fluctuates greatly at low temperature in winter and the effluent concentration of TN exceeds the standard separately.The average influent water volume of Orbal oxidation ditch process is 7593 m³/d,removal rate of COD is higher than 86%,TN and TP removal rates are 59.24%and 71.1%,respectively.In summer and autumn,NH₄⁺-N removal rate is higher than 95%,and in winter,sometimes NH₄⁺-N effluent concentration exceeds 5 mg/L.?2?The removal of COD is completed through microbial degradation and adsorption,aerobic bacterial respiration and nitrogen and phosphorus removal process in the improved A²/O process.NH₄⁺-N is removed by nitrification in aerobic zone.The removal of TN occurs in anoxic zone and pre-anoxic zone plays more than 20%of the nitrogen removal function.The low nitrogen removal efficiency is due to excessive aeration in aerobic zone destroying the anaerobic and anoxic environment and low-carbon influent limiting denitrification.The removal of P mainly depends on chemical phosphorus removal because the DO concentration in aerobic zone is too high,sludge discharge mass is low and sludge activity is low.The removal of COD in Orbal oxidation ditch process mainly takes place in anaerobic tank.NH₄⁺-N is removed by nitrification reaction in middle ditch and inner ditch.TN is mainly removed by denitrification reaction in anaerobic tank and outer ditch.Low carbon influent and excessive aeration in outer ditch affect the removal efficiency of TN,and the effluent concentration of NO₃^--N is high.More than 50%of TP is removed by chemical addition in the Orbal oxidation ditch process actually.?3?The models of improved A²/O and Orbal oxidation ditch processes in four different seasons and months are constructed by WEST software.The simulation errors are within acceptable ranges through influent component determination,parameter sensitivity analysis and parameter adjustment.The optimization conditions of the improved A²/O process determined by simulation are as follows:DO is controlled within 1³mg/L,sludge discharge mass is100m³/d,internal reflux ratio is 1 and external reflux ratio 0.8 in spring,summer and autumn;DO is controlled within 2³mg/L,sludge discharge mass is 75 m³/d,internal reflux ratio is 1and external reflux ratio is 0.7 in winter;the dosage of liquid PAC?Polyaluminium chloride?decreased to 0.07 kg/m³.The optimum parameters of Orbal oxidation ditch process are as follows:internal reflux ratio is cancelled,external reflux ratio is 0.8,sludge discharge mass is90 m³/d in spring;internal reflux ratio is 0,external reflux ratio is 0.8,sludge discharge mass is100 m³/d in summer and autumn;internal reflux ratio is 0 external reflux ratio is 1,sludge discharge mass is 90 m³/d in winter;the dosage of liquid PAC is 0.07 kg/m³ in spring,summer and autumn and 0.09 kg/m³ in winter.?4?The actual effect of the optimized program applied in the improved A²/O process is that the average removal rate of COD is 88.08%.The average removal rate of NH₄⁺-N is 89.99%,6.10%higher than before,and the average removal rate of TN is 55.01%,5.61%higher than before.The average removal rate of TP is 74.82%,which is 2.12%higher than before optimization.The implementation of the optimized plan has reduced the nitrification reaction,enhanced the denitrification effect and realized simultaneous nitrification and denitrification in aerobic zone.Nearly 50%of TP is removed by biological phosphorus removal because of the increase of phosphorus uptake in aerobic zone and the denitrifying phosphorus occurring in the anoxic zone.The average energy consumption is 7.87%lower than that of the same period before optimization,and the average daily use of poly aluminum chloride was 12.3%lower than that before the implementation of the plan.The results above show that WEST software can be used to simulate and optimize the operation of wastewater treatment process,and can provide technical support for the stable operation,energy saving and consumption reduction of wastewater treatment process.