Considerations for the use of Flocculants and Coagulants - PUB4008

Flocculants and Coagulants are commonly used in the treatment of water and wastewater to help bind suspended sediment and fines. These are commonly available and economically achievable methods to reduce suspended sediment and comply with environmental regulations; however, no product is without potential concerns, particularly the potential for impacts to aquatic ecosystems.

The process of using Coagulation and Flocculation

Coagulation is the process of binding suspended or fine solids not otherwise settleable using an additive with an ionic charge opposite to the suspended solid of concern. A coagulation additive, also known as a coagulant, is a chemical compound used in water and wastewater treatment which neutralizes the particulate’s ionic charge and allows the suspended solids to bind together, creating a particle called microfloc.

Flocculation follows coagulation in this method of water and wastewater treatment. The process of flocculation involves binding the microfloc produced during or after the coagulation process. This typically involves gentle agitation and mixing of the treated water allowing the microflocs to interact and bond together with each other, and/or an additive. A flocculation additive, also known as a flocculant, is a water-soluble agent with long polymers that help bind fine suspended solids. Once bound, a larger visible particle called floc, is produced.

Depending on the specific product, some coagulants necessitate the addition of a flocculant for proper use and vice versa. To determine the appropriate use for a given flocculation or coagulation product, users must refer to manufacturer’s recommendations.

Separating Floc from Water

As floc particles develop, the mass of the floc particle also increases and allows it to naturally settle out of the water column. In the event this does not occur consult the manufacturer’s recommendations for recommended actions. Many manufacturers will accept water samples to help determine the appropriate compounds to facilitate the needed reaction. If this is available, it is highly recommended as it may prevent the unintentional release of flocculant or coagulant contaminated water.

Once floc has settled out of the water column, the water should be removed or decanted in a manner that maintains the floc’s separation from the water being removed. This can be done with decanting methods such as but not limited to floating pumps, valves and weirs.

In some cases, flocculated material can be dredged from the bottom of the mixing area through mechanical or hydraulic methods and set aside for proper disposal. Ultimately the appropriate method of separation will vary depending on site conditions, industry type, equipment availability, and material being treated.

Department Allowed Flocculants 

While the department does not endorse or recommend any particular chemicals, the coagulants and flocculants, commonly used in industries, that have been reviewed are listed below. These coagulants and flocculants are only allowed when used per manufacturers specifications and in accordance with permit conditions.

Flocculants Not Allowed by the Department 

The following flocculants are not allowed for use under a Missouri State Operating Permit. 
Emulsion Based Flocculants with petroleum distillates are not allowed at this time due to potential to negatively impact aquatic life.