| Nearly90%sewage water is treated by Activated Sludge Process throughout the world nowadays. It is a notable shortcoming of this process that a lot of sewage activated sludge would be produed. It will take a large amount of inventment and operating cost, about20～60%of the total plant, which has become the heavy burden of a sewage water treatment plant. As a result of the increasing of population and the perfection of municipal works, the production of sewage sludge will increase in our country. So to treat the sewage sludge efficiently, cut down the production of sludge, secure the regular operation of the sewage water treatment plant, and turn waste sludge into resource will be an important subject in the future.Most oganic matter of extra slude was in the microbal cells, the cell wall was a kind of semirigid structure, which could protect the cell. It is of great difficult to degradate the cell wall so it would take longer residence time. A great deal of reseach on shortening residence time was performed by means of destroying the cell walls, making the cells’ including come out into the water. Hydraudynamic cavitation method was carried out to destroy the cell wall and temper the sludge by its high temperature(200-300℃), high pressure, strong shock-wave, microjet with high speed, and other extreme conditions.As the complex component of sludge with kinds of animalcules, it is of great difficult to mensurate the disintegration rate of sludge cells quantificationally. In order to overcome the interference caused by the different kinds of sludge cells and other impurities, the density of SCOD(Soluted Chemical Oxygen Demand), protein and DNA(Deoxyribonucleic acid) int the sample sludge were measured. As the process of disintegration of sludge by hydraudynamic cavition was a complex and changeable process, it is difficult to reseach base on the theory, therefore, physical model was designed, and series of experiments were performed, according to the experimental results the relationship between design parameters of the cavitator and the cell disintegration rate was studied, furthermore, the mathematical equations were given and the sensortivity of the parameters were analyzed, then the efficiency and practicability of hydrodynamic cavitition method was discussed, through analysis and exploration the inherent law, some technical and theoretic surport was improved. The cavition effect could make the materials in the cells dissove out into the aqueous phase, the chararictics of the sludge change, the solid amout decrease, which would improve the degradation velocity, increase the biological gas production, influence the drying performance of the sludge, and the new zero release process might come intobeing, concomitanly. The air-entrapping polling plate cavitition device was used to disintegrate the extra sludge from a municipal sewage plant, and some basic theoretical problems were researched, which involved, the digestion mechanism under the hydrodynamic condition, in other words, the relationship between the parameters of the cavition device and the digestion effection of the extra sludge, the drying performance changement contrast with under the ultrasonic cavitation condition, the changement of aerobic digestion vilocity of the disintegration exstra sludge and the new technology of extra sludge treatment exsploraiton.According to the orthogonal experiment, the cavition paramenters such as the aerobic ratio, cavitation number, and the cavition time would do have some effect on the dissolution rate. The cavitation number would have the great effect, the aerobic ratio would have smaller one. The cavitation time was longer the more inclution of the sludge cells would be dissolved out. As the cavitation process would use up great deal of energy, the longer cavitaiton time the more energy would be taken. The energy consumption and other infllunce facters were considered, and the best operational parameters were figured out. On the condition that the cavitation number was1.8, the aerobic ratio was1.4%, the energy consumption of the hydrodynamic cavitation device was539W/kg. If the cavitation process took30minutes, it would use954MJ’s energy, which of ultrasonic cavitation would be1792MJ,46.8%of the energy would be saved, and in the early15minute, the dissolution rate of hydrodynamic cavitation would be higher (0.06%/s).The sedimentation and filtration performance of extra sludge after cavitation treatment would be bad to a certain extent. The main reason might be that the cells’ wall were destroyed by the cavitaiton effect and the fragments and the internal matter came into liquid phase, which influenced the sedimentation and filtration performance of extra sludge.The aerobic digestion experiment illuminated that the extra sludge after cavitation treatment would be digested easier and with higher digestion velocity. If the sludge sample had been cavitaiton treated, on the20th. day, the remove rate of TS was52.9%and that of SCOD was56.8%. If the sludge sample had not been cavitation treated, on the twentieth day, the remove rate of TS was only35.6%, and that of SCOD was38.3%. The experimental researchment illuminated that the cavitation process disintegrated the sludge cells effectively, which made the internal substance come out of the sludge cells, at the same time, the protein, polysacchorride and other large molecules were disintegrated, which accelerated the aerobic digestion process. Althrough the cavitation effect would bring backward sedimentation and filtration performance, in the later stages (after15days) the sedimentation and filtration performance of cavitaiton sludge sample would be better than that of without cavitation treatment. Therefore, the conclusions could be drawn that the cavitation treatment could accelerate the aerobic digestion process, and bring the digestion sludge with better sedimentation and filtration performance.The Free Gas Core Mode(FGCM) was put forward in the paper, which could explain that the primeval gas cores were the origin of the cavitation process, nevertheless, the latest cavitaiton strength did not be influenced by the number of the primeval gas cores. The FGCM theory illuminated that the hot point effect while extinction of the gas cores would produce new gas cores. Base on the analysis, it was explained that how the cavitation effect disintegrated the extra sludge cells from microcomic angle. According to the dimensional method, viscosity coefficient and surface tension coefficient were considered in the cavitaiton parameter. Base on the analysis and experimental investigation, mathematical modeling work was done, and the relationship among disintegration result and cavitation number, viscosity coefficient and surface tension coefficient. Conclusion could be drawn that, smaller cavitaiton number, the more free gas core would stay in the effect zone, therefore, the cavitation effect would be stronger. If the water’s viscosity is high, the disintegration effect will be backward obviously. While the viscosity goes up by10percent, the digestion rate was decreased by6.93percent, which illuminated that farely high tempreture, smaller viscosity and surface tension coefficients would being better cavitation effect with lesser energy consumption.A new cavitation device was design and made in the lab, the useful volume of the it was8.24×10-5m3, therefore the sludge sample was treated cirdularly. It would not be economically if this kind of device used on a large scale, further experiment investigation should be performed, such as enlarge the useful volume of the cavitation device, several devices be used in seriers or in paralled connection. Therefore, it would be nececary to research on the scale effect and the plus energy consumption of seriers and parallel connection. The FGCM was put forward, base on which, it was explained that the cavitaiton intensity is up to the cavitaiton number, and have nothing go do with the amount of original gas cores. But the theory of that free gas core produce by that the heat effect and low pressure effect of cavitation still have no experimental support because lack of observation method. The mathematic model considered a sludge cells as spheres with equal diameter, obviously, it was different from the act. According to the model research, it could be explained that sludge cell disintegration by cavitation rom microcosmic angle. The mathematicl model analysed the connection of the disintegration effect and the parameters of the cavitation system, but the mensurabel result had some error. Actually, the cavitation process has the characteristic of randomized procedure, the further theory research should be done by adhibiting the mathematical theory of randomzed procedure. |
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