Study On Using Ultrasonic To Intensify Denitrification And Dephosphorization Of Sewage Treatment Based On RSM Model

In China,the carbon and nitrogen ratio in urban sewage is relatively low.When using activated sludge method to treat wastewater,sewage treatment plants are often faced with the dilemma that,on the one hand,the nitrogen and phosphorus removal effect is not good due to the lack of carbon source,or more sludge to be processed due to the addition of carbon source,which increases the additional operating cost of sewage plants.On the other hand,the residual sludge produced by secondary sedimentation tank contains a large amount of organic matter,and the organic structure not only exists in the cell,but also includes some extracellular polymers.Therefore,it is of great significance to study how to convert the organic matter in the surplus sludge into carbon source which can be supplement of biological phosphorus removal and denitrification reaction,and how to use advanced technology to make sewage treatment equipment to operate more efficiently with lower energy.In view of the above research background and current situation,this paper studies the ultrasonic cracking residual sludge as the external carbon source of biological sewage treatment,in order to enhance the efficiency of nitrogen and phosphorus removal.According to the practical engineering of a sewage treatment plant in wujiang,based on the response surface box-behnken design model,the main research work and conclusions of this paper has been carried out as follows:1.This paper first introduces the technical principle of sewage treatment and the theoretical system and design basis of response surface method,and then expounds the feasibility analysis of biological sewage treatment with cracking surplus sludge used as carbon source.The single factor experiment was carried out according to the influence factors of ultrasonic cracking sludge.The BOD₅ and VFA,the designated experimental indexes,were analyzed and the three most influential indicators factors were selected as:ultrasonic energy density,action time and vibration amplitude.The box-behnken design method was used to conduct the tri-factor and tri-level laboratory trial study to establish nonlinear quadratic polynomial mathematical 3D model.According to the model,when the ultrasonic energy density was 159W/L,the operating time was 10min,and the ultrasonic amplitude was 92.46%of the designed value,the BOD₅ concentration reached the maximum 1504.7mg/L.Meanwhile,when the ultrasonic energy density was 200W/L,the action time was 8.22min,and the amplitude was 88.4%,the response value VFA concentration reached the maximum 287.255mg/L.2.According to the above research results,the optimized equipment parameters were put into wujiang sewage treatment plant for ultrasonic sludge static test and equipment preparing test.The results showed that after ultrasonic cracking the concentrations of SCOD,TN and TP in the sludge supernatant increased significantly.After 30%of the remaining sludge was treated,it was found that the sludge returned to the anoxic cell did not cause adverse effects on inverted A²O process.on the process operation,the effluent CODcr,SS,TN and NH₃-N concentrations all reach the urban sewage discharge standards,so that the sewage treatment system works well.3.A comparative experiment between the north and south reaction tanks in the sewage treatment plant was carried out.In the first experiment phase,the south reaction tank returns30%residual sludge after ultrasonic cracking,while the north one returns nothing.The results showed that the effluent concentrations in both reaction tanks all reached the urban sewage discharge standard,and the removal rate of COD,NH₃-N,TN and TP in south was higher than north,which was increased by 8%,8%,35%and 36%respectively.In the second phase,the 30%remaining sludge after treatment was adopted in the south ditch,and100%sludge without any treatment was returned in the north.The study found that the removal rate of COD,NH₃-N,TN and TP in the south was also higher than that in the north,with an increase of 5%,2%,9%and 12%.Through the two comparison experiments,it can be concluded that a large amount of organic substance cannot significantly improve denitrification and dephosphorization efficiency only by its own reflux,and the ultrasonic cracking sludge can release more high-quality carbon sources for the system reaction,improving the sewage treatment efficiency observably.4.Finally,The remaining sludge can be reduced by 20%after ultrasonic breaking.By comparing the amount of surplus sludge perduced in specific inflow,it was found that when the ultrasonic equipment was running,the average sludge yield was 0.637 kg/m³,while it remained between 0.79 kg/m³ to 0.81 kg/m³ when suspended.