100Water temperature: Cold water temperatures can cause two factors which add to the difficulty of
the coagulation process. As water temperatures approach freezing, almost all chemical reactions
occur more slowly. It can be more difficult therefore to evenly disperse the coagulants into the
water. As a result, the coagulant process becomes less efficient, and higher coagulant dosages
are generally used to compensate for these effects. In addition, floc settling characteristics become
poor due to the higher density of the water during near freezing temperatures.
Mixing Effects: Poor or inadequate mixing results in an uneven dispersion of the coagulant.
Unfortunately, many older plants were designed with mixing facilities which generally do not
accomplish mixing in the most efficient manner. As a result, it becomes necessary to use higher
than necessary dosages of coagulant to achieve an optimum level of efficiency in the process. The
effects of low turbidity and cold water temperatures can tend to aggravate the lack of adequate
mixing facilities in some plants.
Effect of the coagulant: The choice of the proper coagulant for the given conditions is of critical
importance in maintaining an efficient coagulation scheme under widely varying conditions. The
chemicals most commonly used in the coagulation process are Aluminum Sulfate, Ferric Chloride,
Ferric Sulfate, and Cationic Polymers.