Aeration On Membrane Fouling Controlling And Its Mechanism In Flat-sheet Membrane Bioreactors

Membrane fouling and high aeration cost have become main restrictions forwidespread application of membrane bioreactors. This paper studied effects andmechanism of aeration process for membrane fouling control. We investigated effectsof membrane clearance on membrane fouling and explained the reasons with bubbleparameters. The orifice diameter of tubular aerator was optimized and theperformance between the tubular aerator and disc microporous aerator was comparedto select the most suitable aeration devices for membrane fouling control. A newMBR of dual aeration mode was designed and studied. Air flow rate both in the aeraof microorganism aeration and membrane aeration was optimized in the aspects ofenergy cost and membrane fouling.The paper studied the influences of clearance between membranes (4.0,8.0and12.0mm, respectively) on the membrane fouling process. A simulated membranebioreactor was constructed to study the bubble formation, shapes and rising betweenmembrane clearances using clean water as permeate. The results indicated that whenthe membrane clearance was4.0mm, membrane fouling rate was the smallest.Observation of the bubble formation and movement through image pickup in thesimulated membrane bioreactor and image analysis revealed that when the clearanceof the membranes was4.0mm, the bubble deforms through distortion to the largestextent and emerges as cap shape, providing the largest scouring surface of themembranes. The uprising velocity of bubble is significantly reduced due to the―walleffects‖.For the bubbling devices with different orifice diameter, the one with1.0mmorifice diameter efficiently reduced the membrane fouling rate, simultaneouslyproviding higher concentration dissolved oxygen for the aeration MBR. The tubularaerator with1.0mm orifice diameter was better in reducing membrane fouling thanthe disc microporous aerator. The tubular aerator with1.0mm orifice diameter wasthe desired aerator, for it can efficiently control membrane fouling as well as anexcellent aerator for providing oxygen.The dual aeration mode MBR was designed and assembled. Aeration with tinybubbles was applied for microorganism aeration, and big bubbles for membraneaeration. The microorganism aeration area was well aerated and the activated sludgehad high activity. And in the membrane aeration area, the increasing of air intensity had obvious effects on sludge particle distribution and EPS content, thereforerelatively low air intensity was preferred. The suggested air intensity ofmicroorganism aeration area and membrane aeration area was40L/h and60L/hrespectively. The dual aeration mode MBR had advantages such as low energy costand low membrane fouling rate, so it deserved to be widely applied in the industry ofwastewater treatment.