| Along with the accelerated process of urbanization, the construction of sewage treatmentplant has made great progress. The biological treatment is the main method for sewagetreatment. However, large amount of excess sludge is generated in such process. Thetreatment and disposal of sludge is a pressing problem to be solved. Sludge aerobic digestionis a promising way for our country, which can make the sludge achieve stabilization andreduction. But high running costs restrict the application of sludge aerobic digestion. Manyresearchs proved that the ultrasonic pretreatment was a favorable way to enhance theefficiencies of sludge hydrolysis and aerobic sludge digestion. But the ultrasonic treatmentalso has the problem of high energy consumption. In this way, the low-cost magnetic methodis combined with ultrasonic treatment to improve the sludge aerobic digestion efficiency.There are three parts in this paper. The effects of magnetic field strength, ultrasonicenergy density and treatment time on sludge disintegration were investigated firstly. This partof the experiment was aimed to prove the promotive effect of the magnetic field on ultrasonictreatment for sludge. In the second part, sludge aerobic digestion experiment was performed.The sludge aerobic digestion was comparatively studied with combined magnetic field-ultrasound pretreatment and ultrasound-only pretreatment. Furthermore, the optimalproportion of the sludge pretreatment was determined by studying the effect of differentinoculation amounts of excess sludge on aerobic digestion in the third part.The results of the study on the sludge treated with combined ultrasonic-magnetic methodshowed that (1) the combined ultrasonic-magnetic pretreatment was more effective for sludgedisintegration than the ultrasonic pretreatment. The SCOD dissolution rate of the sludge bycombined treatment increased with the increase of the magnetic strength. The SCOD value ofthe sludge treated by combined method was1240mg/L higher than that of sludge treated byultrasonic method when the ultraconic energy density, the treatment time and the magneticfield intensity were0.5W/mL,5min and1620Gs respectively. Magnetic field did notincrease energy consumption of the sludge pretreatment.(2) The SCOD dissolution rate ofthe sludge which was treated by combined method was41.6%when the treatment time was5min, the ultraconic energy density was1.4W/mL and the magnetic field strength was840Gs. This is higher than the SCOD dissolution rate (40.6%) of the sludge which was treated byultrasounic process under the same treatment time and the ultraconic energy density of2.5W/mL. The combination of magnetic field with ultrasound could effectively reduce theenergy consumption of sludge treatment.(3) The promoting function of the magnetic field onsludge ultrasonic treatment was obvious when the treat time was shorter than5min.Compared with ultrasonic treatment, the sludge SCOD value of combined treatment wasincreased33.0%when the treatment time was2min, the ultrasonic energy density was0.5W/mL and the magnetic field strength was840Gs.The aerobic digestion experiment results showd that the MLSS and MLVSS forcombined pretreatment (0.5W/mL、5min、840Gs) sludge decreased42.7%and51.1%,respectively. The combination pretreatment of ultrasonic and magnetic field was moreconducive to aerobic sludge digestion. Its reduction and stabilization efficiences wereremarkable.The effect of inoculation amount on aerobic digestion indicated that the inoculationamount of60%was the best choice for sludge aerobic digestion. The stability time of theaerobic digestion under those conditions was2d shorten than controlled group (when thepretreatment parameters were: the ultrasonic energy density0.5W/mL, the treatment time10min and the magnetic field strength1300Gs). |
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