Study On Sludge Reduction By Vortex Cavitation Combined With Ozonation

Most of our sewage treatment plants in China use the activated sludge process,which leads to the treatment and disposal of excessive excess sludge has become a difficulty in the water treatment industry.The sludge reduction technology reduces the output of sludge from the source,which has significant economic and environmental benefits.In this paper,a process of sludge reduction by vortex cavitation and ozone oxidation was proposed.The test device is designed and its core component were analyzed by numerical simulation.By comparing experiments,the sludge reduction effects of vortex cavitation combined with ozone oxidation,individual vortex cavitation and traditional aeration plate ozone oxidation were compared.The influencing factors of vortex cavitation combined with ozone oxidation sludge reduction were explored,and the optimal process parameters were determined.Under the optimal technological conditions,the sludge characteristic change and cell dissolving process of sludge reduction by vortex cavitation combined with ozone oxidation was further explored,and the mechanism of vortex cavitation combined with ozone oxidation sludge reduction was briefly analyzed.The main conclusions are as follows:(1)The CFD(Computational Fluid Dynamics)technology was used to simulate the internal pressure distribution and cavitation effect of the vortex cavitator under the conditions of air flow rate of 1 L/min,sludge pipeline pressure of 0.4 MPa and sludge flow rate of 14 L/min.The results show that the vortex can be generated after the fluid enters the vortex cavitator.The center of the vortex is near the central axis of the vortex cavitator,and the pressure at the center of the vortex decreases.There is a region near the central axis of the vortex cavitator that meets the cavitation conditions,and cavitation can occur.(2)Compared with the sludge reduction effect and carbon source release effect under the three modes of vortex cavitation combined with ozone oxidation,single vortex cavitation and traditional aeration plate ozone oxidation,it was found that the sludge reduction effect and carbon source release effect under the mode of vortex cavitation combined with ozone oxidation was the best,and the reaction time was the shortest,the sludge treatment efficiency was the highest.After 60 minutes of reaction,the MLSS removal rate reached 93.6%,and after 45 minutes,the sludge removal rate reached 93.6%.Moreover,the MLVSS/MLSS of sludge decreased significantly under the synergistic effect of vortex cavitation and ozonation,and the removal effect of organics in sludge solid phase increased significantly.At the same time,under the condition of vortex cavitation and ozone oxidation,the rate of sludge cell dissolution was high,the effect of cell dissolution was good,and the release effect of carbon source was obviously better than the other two methods.At 45 min,the SCOD in the supernatant of sludge increased from 43.64 mg/l to 565.9 mg/l,which was 12.97 times of the initial concentration,and the DDCOD reached 11.82%.(3)The influencing factors of sludge reduction effect were investigated in terms of sludge concentration,initial p H of sludge,and ozone dosage.It is found that too high sludge concentration affects sludge reduction effect,and too low sludge concentration will increase cost.Under the condition of meeting sludge reduction requirements,the sludge concentration should be increased as much as possible,and the reasonable sludge concentration is 4 g/L.The optimal initial p H of sludge is 9.When the initial p H of sludge is adjusted to 9,the removal rate of MLSS and MLVSS of sludge is improved,and the release effect of carbon source of sludge is better.The optimal ozone dosage of the sludge reduction technology by vortex cavitation and ozonation is in the range of 10-20 mg O3/g SS.When the sludge concentration is 4 g/L and the initial sludge p H is 9,the optimal ozone dosage is 15 mg O3/g SS.(4)Under the best reaction conditions,the characteristics change and cytolysis process of sludge treated by vortex cavitation and ozonation were studied.Observation through a biological microscope revealed that after treatment of vortex cavitation and ozone oxidation,the sludge flocs changed from large and dense to small and dispersed,and a large amount of sludge cell intracellular content was dissolved.The sludge settling performance was improved and the carbon source release effect was good.The SCOD increased from 47.62 mg/L to 360.5 mg/L,which was 7.57 times of the initial concentration.The biochemical properties of the supernatant were improved significantly,and the B/C increased from 0.18 to 0.31.The concentration of total nitrogen,total phosphorus,polysaccharides and protein in the sludge supernatant increased to a certain extent,TN increased from 2.83 mg/L to 33.27 mg/L,which was 11.76 times of the initial concentration;TP increased from 5.2 mg/L to 13.14 mg/L,2.53 times of the initial concentration;polysaccharide increased from 7 mg/L to 37 mg/L,5.29 times the initial concentration;protein concentration increased from 3.06 mg/L to 8.41 mg/L,2.75 times of the initial concentration.(5)The changes of DOM(dissolved organic matter)in the liquid phase of sludge before and after the treatment of vortex cavitation and ozonation were further explored by three-dimensional fluorescence spectrum.It was found that the aromatic protein II and soluble microbial metabolites in the DOM of the supernatant increased significantly after the treatment of vortex cavitation and ozonation,and a large number of humic acids appeared at the same time,which indicated that a large amount of organic substances in the cell were dissolved out.However,the decrease of aromatic protein I and fulvic acid in the supernatant indicates that these two kinds of substances are easy to be oxidized and decomposed into small molecules without fluorescence characteristics under the synergistic effect of vortex cavitation and ozone.