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WATER FILTRATION BY COAGULATION METHOD

The removal of destabilized and agglomerated particles in the filter bed includes two interconnected processes, particle transport and particle attachment to filter grains, smaller filter grauns,smaller filter velocity, increase of water temperature and increase of particle size (only for particles>l µ m) improve particle transport and consequently filtration efficiency. Minimum transport and filtration efficiency can be expected for particles of approximate 1p m. efficient attachment of agglomerates to the filter grains can be achieved only when the colloidal matter destabilized. In direct filtration, impurities as turbidity and color will be removed after destabilization by coagulation.This coagulation reaction takes place within a few seconds during rapid mixing. At this point the formed particles are very smaller. In Line direct filtration the setting and flocculation step are eliminated and the destabilized water is transported directly to a filter. Consequently flocculation, takes place in the bed filter. The rate of agglomeration of small destabilized particles to visible flocks is dependent principally upon the number of effective collision of particles. In contrast in conventional treatment 5 to 45 minutes may be needed for complete agglomeration of all particles. At this point enough collisions have occurred so that the flock particles have grown to a size that will settle rapidly. Fe (III) has fewer tendencies to form polynuclear species compared with A(III). The positive ions(polymers) absorb at the surface of negatively charged colloidal matter which results in a reduction of their negative potential. Therefore, it can be seen that pH plays very important role in stability of different iron hydrolysis products.