Investigation And Discussion On Ultrasonic Cleaning Online In The Membrane Bioreactor

According to the problems in the study of membrane pollution for ultrasonic cleaning in the MBR, a scheme was proposed in this dissertation. In the scheme, online ultrasonic cleaning was used for hollow fiber membrane in the MBR. The ultrasonic effect on sludge characteristics was studied by a series of continuous tests. The results can be used as a reference for online cleaning parameters selection; the optimum ultrasonic test parameters, the best operating conditions, and proper radiative position of ultrasound were sought to obtain the best cleaning effect.The sludge concentration decreased gradually with prolongation of the ultrasonic action time. Ultrasound has no obvious effect on MLSS, while MLVSS changes greatly. The proper ultrasonic action time can improve the sludge settling property. However, if the ultrasound sustainingly act for long time, the intracellular material will enter into the water, which make the sludge supernatant turbid. The filtration performance of the sludge deteriorated when the ultrasonic action time was prolonged.The increasing of dissolution rate of SCOD in the sludge with the increasing of ultrasonic action time is different at different time regions. As the ultrasonic action time increases, the sludge activity first increases and then decreases. The concentration of SMP in the sludge increases with the increase of ultrasonic action time, but the chang law of EPS concentration is just the opposite. The change law of polysaccharide content in SMP or EPS as the increase of ultrasonic action time has good correlation with that of SMP or EPS content. The sludge structure was destroyed heavily with 15 minutes ultrasonic effect, the intracellular material entered into the water.The optimum time of ultrasonic cleaning is 10 minutes. There is no significant effect on cleaning result after 10 minutes. The closer distance between membrane and ultrasound source, the better cleaning effect. But when the distance is too small, the structure of membrane is prone to be destroyed in the cleaning process. The best distance between membrane and ultrasound source is 5cm in this experiment. The flux recovery rate of the membrane improves as the ultrasonic power increases. The optimal ultrasonic power is 352W in this dissertation.The cleaning effect using ultrasound alone is not ideal. However, the mode combined aeration with ultrasound can improve the cleaning effect significantly. At the best aeration intensity of 0.6 m3/(m2·h), the flux recovery rate can reach to 74.24 percent with 10min synergetic cleaning. Double-plate radiating correspondedly can improve the cleaning effect, double-plate radiating face to face is the most effective pattern.