Essay On Coagulation

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Coagulation Introduction Coagulation and flocculation processes are essential in a number of diverse disciplines including biochemistry, rubber manufacturing and in water and wastewater treatment (Bratby, 2006). These processes are typically used in destabilizing, agglomerating and subsequent removal of particles. Coagulation is a physico-chemical process which neutralizes the colloidal particles in water by a chemical called coagulant. The neutralization forces the colloidal particles to join together to form small aggregates called flocs which are easily filtered from the water. The widely used coagulants in water treatment are metal salts including aluminium sulphate , aluminium chloride , polyaluminium chloride , ferric sulphate and ferric chloride (Saunders and Saunders, 1991). The primary mechanisms by which coagulant can remove both organic and inorganic contaminants from water include colloid destabilization, precipitation and co-precipitation (Langelier and Ludwig, 1949; Randtke, 1988; Saunders and Saunders, 1991). Mer and Healy(1963) deplored the indiscriminate use of the terms coagulation and flocculation which is found…show more content…
However, the ions , , and are not directly involved in the coagulation process. The actual coagulant species involved in the coagulation are formed after the coagulant chemicals are added to water (Jiang and Graham, 1996). Since aluminium and iron are hydrolyzing metal ions, their addition to water lead to the formation of numerous mononuclear and polynuclear species as well as solid precipitates (Saunders and Saunders, 1991; Jiang, 2001). The existence of various charged mononuclear and polynuclear species is a function of the prevailing conditions, i.e., pH, Eh and the concentration of the parent species and can be predicted using thermodynamic calculations e.g., Eh-pH

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