| Most of wastewater treatment plants in China faced up with many problems, such aslow processing capacity, low operation load which was lower than design load, highoperation cost, high energy consumption and low operation control level. It wasimportant to build a mathematical model which can reflect the actual operationsimulation of the sewage plant and to resolve these problems on wastewater treatmentplants with the established model. But, there was no standard method for determing thewastewater characteristic parameters, building the sewage plant process model. Altough amacro fitting evaluation standard was put forward in GMP, in practical applications, adetailed evaluation standard fitting was needed to establish to specific situation. So,finding a method to determine the wastewater characteristic parameters, to build thesewage plant process model and to build the fitting evaluation standarad was crucial forbuilding a sewage process model which can reflect the actual operation simulation of thesewage plant.On the basis of previous research, according to the operation of the urban WWTP inWuzhong district of Suzhou. ASM2was used to simulate the operation of the oxidationditch process in the sewage plant with the BioWin software, and the average waterquality monitoring data on July2011to September2011in the summer and the data onOctober9,2011-2011to October12, for three consecutive days of24h dynamic datamathematical simulations were done for the operation of the sewage plant. The modelcan reflect the real operation status of the plant fairy. Using the established sewage plantprocess model for sewage plant were analyzed, the diagnosis, and provides theimprovement sugguestion for sewage plant.Five process models of the wastewater treatment were put forward with measuredDO change tendency along the oxidation ditch, the empirical formula, the partitionmethod which was proposed by the GPS-X software and set up corresponding model ofthe plant process. From effluent and sludge distribution, five process models wereanalyzed and compared, the result showed that the different partition of the oxidationditch basically have no effect on the simulation result and the most reasonable processmodel of the wastewater treatment plant was chosen at last.The history data was checked by the material balance method and the materialbalance showed that the two stages of the datas were accurate. The emission of theexcess sludge and the amount of the return activated sludge were checked by the material balance of phosphorus. The emission of the excess sludge was653m3/d, and the amountof the returned activated sludge was8396m3/d.The inflow water and the effluent water of the sewage plant were determined by thetest method. The component ratio value of the easily dissolving organic matterbiodergradation was0.270, the component ratio value of the degradation of solubleorganic matter was0.098. According to the reference and combine the urban WWTP inWuzhong district of Suzhou, the component ratio value of the slowly biodegradationmatrix was0.220, the component ratio value of the inert particulate organic matter was0.412.According to the fitting evaluation standard which was proposed by the GoodModeling Practice, and combined with the research purpose of the topic, the fittingevaluation criterion of the model was established.The average absolute error of the nitrogen index (ammonia nitrogen, nitrate nitrogen,total nitrogen) is less than1mg/L, the average absolute error of the phosphorus index(phosphate phosphorus, total phosphorus) was less than0.5mg/L, the average absoluteerror of the total suspended solid was less than5mg/L, the average relative error of themixed liquid suspended solid was less than10%.The steady-state simulation of the model was carried out with the historical data ofthe wastewater treatment plant, by comparing the simulated results and the measuredresults of the effluent(ammonia, TN, TP, SS) and the sludge distribution of system(MLSS of oxidation ditch, Return activated sludge). The results shows that using thedetermined wastewater characteristic parameters and adjusting the denitrifying bacteriamaximum specific growth rate to0.700, the rest of the kinetic parameters andchemometrics coefficients using the default parameter values, the sewage plantsimulation results and the measured results was fitting well. The average relative error ofthe returned sludge was1.19%, the average relative error of the mixed liquid suspendedsolid of the oxidation ditch was2.07%, the absolute error of ammonia was0.02mg/L, theabsolute error of the total nitrogen was0.52mg/L, the absolute error of the totalphosphorus was0.06mg/L, and the average absolute error of the suspended solid was1.6mg/L.Dynamic simulation of the model was carried out with the measured influent data,by comparing the simulated results and the measured results of the effluent (ammonia,TN, TP, SS) and the sludge distribution of system (MLSS of oxidation ditch, Returnactivated sludge). Using the calibration model and adjusting the denitrifying bacteria maximum specific growth rate to1.200, the sewage plant simulation results and themeasured results was fitting well. The average absolute error of effluent ammonianitrogen was less than1mg/L, the average absolute error of effluent nitrate nitrogen wasless than1mg/L, and the average absolute error of the effluent TN concentration was lessthan1mg/L. The average abslute error of the nitrate nitrogen and total nitrogen was closeto1mg/L. The reason why the simulated results of the nitrate nitrogen and the totalnitrogen did not fit the measured results was that the dissolved oxygen concentration waslow in the oxidation ditch and the mixed liquid went into the second settling tank mightcause the denitrification, however, when we build the process model we assumed that thesecond tank was an ideal tank. The average absolute error of effluent TP was less than0.5mg/L, the mean absolute error of effluent SS was less than5mg/L, the averagerelative error of the biochemical pond sludge concentration was less than10%, and theaverage relative error of sludge concentration less than10%. It was proved that themodel can reflect the actual operation simulation of the wastewater treatment plant.At last, the operation of the urban WWTP in Wuzhong district of Suzhou wasanalysed, evaluated and diagnosed by the use of the sewage plant process model. Severalimprovement suggestions were put forward in view of the phosphorus removal efficiencywas not high. In order to improve the anaerobic condition, we divided the anaerobic intoseveral districts and connected series. To create conditions for indirect gain more volatileorganic compounds, we could increase the volume to extend the hydraulic retention timeof anaerobic zone. |
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