| With the rapid growth of China’s economy and the continuous improvement of people’s living standards,the total annual sewage discharge is huge.Sewage treatment plant in the process of sewage treatment will produce a large number of sludge,sludge treatment costs are an important expense of the daily operation of sewage treatment plant.In this paper,taking the A~2/O process as an example of the poor effect ofdenitrogen removal and phosphorus removal caused by insufficient carbon source in treating municipal sewage,this paper puts forward that the air-blanking effect on reflux sludge is formed by Laval nozzle to form a strong shear force,promote the destruction of sludge structure and release carbon-containing organisms,improve the carbon content of water bodies,and achieve carbon source replenishment and sludge reduction.Based on the analysis of Lavar injection theory and air-clearing theory,the force characteristics of sludge particles in Laval nozzle are obtained.When the sludge particles enter the expansion section of the Laval nozzle,they disintegate due to the continuous impact of shear force caused by the emptying effect,releasing carbon-containing organic matter from the sludge particles.In this paper,the flow characteristics of sludge particles in each section of Laval nozzle are analyzed,and the gas content and air area area of Laval nozzle expansion segment are used as the evaluation index of sludge cracking effect,and the best structural parameters are determined.Based on the theoretical analysis,the paper establishes the Laval jet flow model,uses Fluent to perform numerical simulation of the Laval nozzle flow field,and studies the internal velocity flow field,vapor content and the change law of the area of the hollowing area when the Laval nozzle inlet pressure,shrinkage angle and throat diameter are variables.The results show that the emptying of the expansion section of the Laval nozzle meets the conditions for the emptying,the increase of inlet pressure can not only increase the vapor content of the expansion section of the Laval nozzle,but also increase the air area of the expansion section,the increase of the diameter of the throat will reduce the vapor content of the expansion section of the Laval nozzle,and the increase of shrinkage angle will increase the vapor conten t of the expansion section of the Laval nozzle.Finally,it is concluded that the structure parameters of Laval nozzle are optimal when the shrink angle is 60 degrees and the diameter of the throat is 5mm.In this paper,a test device for laval sludge cracking was set up,and it was found that after 60minutes of treatment of water-containing sludge,the median particle size of sludge particles decreased from the initial s.67.62μm to 12.13μm,the content of SCOD on water-containing sludge increased 63 times,the total nitrogen content increased 4times,the total phosphorus increased 1 times,and ammonia nitrogen increased 11.9times.The particle size change of sludge particles shows that the cracking behavior occurs when the sludge particles pass through the expansion section of laval nozzle,an d the change of the indicators reflects that the sludge particles release the various organic matter contained in themselves and dissolve in the water when they are cracked,and the increase in the carbon content in the upper liquid after cracking indicate s that the sludge can be used as asupplementary carbon source after the A~2/Oprocess sludge reflux section.The introduction of Laval nozzle into the A~2/Oprocess sludge reflux segment can not only increase the carbon source and increase the nitrogen and pho sphorus removal rate in the process,but also reduce the sludgeyield of the A~2/Oprocess at the source,which plays an important role inimproving theefficiency of A~2/Oprocess sewage treatment。... |
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