Wastewater Treatment Services

Wastewater Treatment – Definition of Flocculation

Flocculation refers to the precipitation of suspended solids from water by gravity. This definition is both simple and accurate.

Wastewater Treatment  – Definition of Coagulation

Coagulation refers to the elimination of the electrical charges of repulsion surrounding particles in suspension. This definition does not mean that suspended solids have been precipitated. That refers to the above definition of flocculation. It can only occur once the suspended solids have been coagulated.

It is not uncommon in water treatment polymers that solids in suspension require a coagulant first in order to eliminate the charges of repulsion so that the solids can then be traded next with a flocculant. It is only then that the flocculant can perform its job of bringing together the small masses of suspended solids such that the weight of those masses overcomes gravity.

So the reader can now see that water treatment polymers can react in two different but related fashions to clarify water streams and to dewater sludges and slurries. As we discuss the types of coagulant sin types of flocculants and their functions we will base our comments on the above definitions. Please also see our technical paper entitled “Water Treatment Dictionary” in the product data section in our website.

Wastewater Treatment – Types of Coagulants

In the section discussing water treatment polymers we will describe the types of coagulant’s used in various processes. Coagulant’s are positively charged species which allow suspended solids to precipitate with or without the aid of a flocculant. Primary coagulation’s are described as metal salts of iron or aluminum. Common names for such primary coagulants are ferric chloride and alum, also known as, aluminum sulfate. These primary coagulates are commonly used in potable water treatment, the mining industry and other applications. There are many applications in which a primary coagulant, the inorganic coagulates, will function effectively without additional reagents. Primary coagulant’s are normally furnished as high density solutions because the dilution of powdered or granular coagulant is quite difficult.

There is another category of coagulants which can be referred to as coagulant aids. This group of water treatment polymers consists of organic coagulants which are not minerals as are the primary coagulants. This group consists primarily of dadmac and epi coagulants. The dadmac designation refers to poly diallyl dimethyl quaternary ammonium chloride compounds. The epi designation refers to epichlorohydrin/alkylamine compounds. There are some applications which require the use of both a primary coagulant and anticoagulant aid in order to achieve the desired level of solids’ precipitation and supernatant clarity. Supernatant is another water treatment polymer term for clarified water. In a small number of water treatment polymer applications it can be required that a coagulant is followed by a flocculant in order to achieve the desired water quality results. This is often referred to as a dual polymer or the “Coagulation and Bridger Approach.” This is a common treatment modality when colloidal suspensions of solids are present and may have been formed by a the function of surfactants or other emulsification agents which are part of the industrial process. In the product data section of our website this approach is discussed in more detail. Organic coagulates are furnished as concentrated solutions because of the manufacturing process. The exception is the dadmac product which is available in both granular and bead forms. Extremely high volume consumers such as mines usually prefer the granular or bead form.

There is a subset in water treatment polymers consisting of both primary coagulants and coagulant aids which are blended together. The combination of the two types of coagulant’s can produce a special synergistic activity which promotes better results than applying only one type of coagulant. Jar tests are the best way to determine if the Coagulation and Bridger Approach or a coagulant blend will be the most effective treatment modality for a specific application.