There are two operations involved in the coagulation process. Mixing is the process wherein a dissolved coagulant material is rapidly dispersed with violent agitation throughout the water being treated. Flocculation involves the continuous agitation of wastewater at much slower velocities to allow for the agglomeration of very small particles into well defined flocs that settle readily. The most widely used coagulants for wastewater treatment are aluminum and iron salts. Waters high in organic matter are best treated with aluminum sulfate.
Ferric compounds are useful in removing odor problems.
Aluminum sulfate and ferric chloride are the coagulants of choice for the chemical coagulation of phosphorus from wastewater. In many cases, coagulant aids are also added to the mixing tanks to adjust the pH of the solution to optimize coagulation. Coagulant aids include activated silica, polyelectrolyte compounds, and clay. Biological Nitrification and Denitrification a. Nitrification does not remove the nitrogen but only changes its form.