Particle behavior in air agitation submerged membrane filtration

Small water treatment plants and slow sand filtration plants can hardly meet strict water quality standards. As a possible solution, an air agitation submerged membrane system was studied. The system produced suitable water at high flux with an acceptable suction pressure of 0.2–0.3 k f/cm 2. The study focused on investigating particle behavior in the air agitation submerged membrane system to understand more about the filtration and fouling by particles. It was found that the particles in the air agitation submerged system behaved differently from the cross-flow system although the rising air bubbles made a water stream on the membrane surface. Small particles in the submerged system seemed to move on the membrane surface more easily when compared to those in the cross-flow system. Although particles larger than 15 μm accumulated on the membrane surface, most all large particles were easily removed from the surface during the backwash whereas the small particles, especially those less than 2 μm, tended to remain on the membrane surface. The particles in the agitated water system collided and agglomerated together to form bigger flocs. It was postulated that agitating water in a preceding tank might keep the membrane from clogging by small particles.