Study Of Choking Cavitation Technology For Disintegrating Excess Sludge

There is nearly 90% of urban sewage treatment plant in the world where biology method treats the sludge at present. The expend of dealing with the excess sludge account for from 25~40 percent of the total cost of sewage treatment plant, which greatly limits the sewage treatment rate. So it cannot satisfy the requirement of a large amount wastewater to be treated. It has become a problem solved by more and more scholars that how to reduce the amount of excess sludge. There is floc and microbial cell containing soluble organics and water. If the sludge can be effectively disintegrated, the volume of the sludge will be greatly reduced, and the efficiency of wastewater treatment can be greatly improved. So it has great practical significance.Based on orthogonal experiment, a numerical simulation on the gas-liquid two phase flow of choking cavitation device is done by using CFD software. The results of the experiment show that the factors affecting cavitation intensity from big to small in turn is flow rate Q, back pressure Pb, inlet angle γ, diameter d and length L of choking pipe. The optimal parameters for choking cavitation are Q of 2.0 m3/h, Pb of 70 kPa, γ of 35 ?, d and L of 10 mm and 50 mm.The experiment system of Choking cavitation is established to disintegrate excess sludge by changing the cavitation system of flow, back pressure and disintegrating time, and experiment research goes on, taking Sludge Setting Rate SV, Turbidity TU, Mixed Liquid Suspended Solids MLSS, Mixed Liquor Volatile Suspended Solids MLVSS, Soluble Chemical Oxygen Demand SCOD, pH, Temperature T and Disintegrating Degree DD as evaluation index. The results show that the choking cavitation technology can broken excess sludge and microbial cells, making their internal material released becoming a part of liquidoid of the excess sludge, substance in large size is broken into smaller size, which results in increasing of SCOD, turbidity increases. These prove that choking cavitationg is effective in disintegrating excess sludge. When the flow is 1.278 m3/h, the back pressure is 238.45 kPa, and cycle number N of 10, DDmax reaches 13.24%. The sludge has a small change in pH, after disintegrating, the pH is influenced slightly by the technology, which shows that choking cavitation is very useful in solving engineering problems. The trends of MLSS, MLVSS, SV are downward on the whole, which shows that materials in large size are broken into smaller size.