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Wastewater Treatment
Technology Tutorial
Coagulants
and Flocculants
Coagulants and flocculants are chemicals used
to precipitate insoluble substances. The purpose of
coagulation and flocculation is to cause small pollutant
particles such as metals to aggregate and form large
enough flocs so that they can be separated from the
wastewater through sedimentation.
There are three main types of coagulants that
are used to overcome the repulsive forces of particles,
thus causing them to aggregate. Electrolytes, organic
polymers, and synthetic polyelectrolites are added to
wastewater and then flocculation tanks mix the water
to promote flocs and subsequent physical separation.
Rate of flocculation is dependent upon many factors including
concentration of particles, particle contact, and range
of particle sizes. Coagulation targets dissolved ions
such as metal and radionuclides. Some difficulties with
this technology include the frequent need to adjust pH
levels, the creation of toxic sludge that must be eventually
mitigated, and the difficulty that results in trying to
address the chemical nature of multiple compounds. This
technology has been used consistently in the electronics
and electroplating industry as well as for applications
in groundwater treatment.
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