Coagulation alum floe

Water purification and recycling is now a major industry.The method of treatment depends on the source of the water, the use envisaged and the volume required. Luckily the human body is very tolerant to changes in the composition of drinking water, and in many communities this may contain 0.5 gl or more of dissolved solids (Table 14.7). Prior treatment may consist of coagulation (by addition of alum or chlorinated FeS04 to produce floes of Al(OH)3 or Fe(OH)3), filtration, softening (removal of... 

Add coagulant usually alum in the sweep floe concentration of 20 to 50 mg/L adjust pH to 6 to... 

We did not expect that the removal of dioxin from well and runoff water by alum coagulation and flocculation would be effective, as there is little or no suspended organic phase to act as a carrier for dioxin. This problem was solved by adding a high molecular weight polymer that would be adsorbed to and carried down with the floe. Partition of dioxin into the polymer is so favored that parts per million levels of polymer should remove most of the dioxin. The results of jar tests to find the optimum level of polymer, at a fixed 100 ppm level of aluminum are given in Table III. 

The charge on the suspended solids is often sufficiently negative to yield a stable dispersion that settles slowly and is difficult to filter. In this case, the key to effective colloid removal by sedimentation is reduction of the zeta potential to zero or near-zero. Once the charge is reduced or eliminated, electrostatic repulsive forces are minimized. The gentle agitation of the flocculation basin then causes numerous colloid collisions, first with formation of microflocs and then with visible floe particles, which can easily be settled or filtered. Coagulants such as alum, ferric chloride or cationic polymers all function primarily as charge reducers [4,41,42]. 

Coagulants are often added in conjunction with lime to increase the settling rate of calcium carbonate and magnesium hydroxide. Most of these coagulants are acidic in nature and react with the alkalinity of the water. Commonly used coagulants include aluminium sulphate (alum), sodium aluminate, ferric sulphate and ferrous sulphate (Table 6.8). Alum reacts with natural alkalinity in water to form aluminium hydroxide floe (Equations 2.5—2.8) [14]. About 1 ppmofalumdecreaseswater alkahnity by 0.5 ppm and produces 0.44 ppm of CO2 ... 

Coagulant A chemical (e.g. alum ofiron salts) used to form a floe used in the clarification ofturbid or coloured water, and as an aid in removing colloids. See also Zeta potential. 

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