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SOLIDS DEWATERINC 219

possess long chains that trap and enmesh small COAGULATION
floe particles to form larger floe particles.
Nonionic and anionic polymers are classed as The process of chemically neutralizing the nega-
flocculants depending on their molecular weight. tive charge on colloidal matter in waste waters to
Coagulants, by principle, must possess low mo- form small floe particles is called "coagulation."
lecular weight and cationic charge. Table 13-1 lists Most colloidal suspended matter in water carries
the characteristics of polyelectrolytes used in wa- a negative charge by nature. It can consist of
ter and waste water treatment applications. emulsified oil particles, solid particles, dirt, metal
Current water treatment polymers are available fines, or biological particles. These particles will
in three physical forms: powder, aqueous solution, not settle until this charge is neutralized. Water
and emulsion. The powders are the most common treatment polymers that carry a positive charge
and oldest form for flocculants. Powdered products and low molecular weight (coagulants) can be added
must be dissolved in water to approximately 2% to the water to neutralize the colloidal charges.
or less before they can be applied. Inorganic chemical salts such as aluminum sul-
Solution polymers have become quite common. fate, ferric sulfate, ferric chloride, and calcium
These polymers need only to be diluted before ap- chloride, among others, have historically been
plying them. Many flocculant polymers are cur- used as coagulants. The major disadvantages to
rently available in solution form, containing 2% to these inorganic coagulants are (1) large volumes
10% active polymer. These polymers are much of resultant sludge, (2) the sludge is stable and dif-
easier to handle and apply than the older, pow- ficult to further treat, (3) inorganics require nar-
dered forms. Coagulant polymers are always sold row pH ranges for activation, and (4) solids are
in liquid form. added to the water that later must be removed.
The newest product form for flocculants is the Polymer coagulants provide excellent coagula-
emulsion. This polymer is in the form of small tion without the drawbacks of inorganic coagu-
droplets suspended in a hydrocarbon and surfac- lants. The major advantages include (1) minimal
tant carrier. Emulsion polymers must first be ac- dosage requirements, (2) the sludge volume is
tivated, or inverted, in water before they can be minimized, (3) they work over wide pH ranges,
applied. These require a special polymer makeup and (4) a minimum amount of solids are required
and feeding system. to be added to the water. Coagulation is usually

TABLE 13-1. Characteristics of Water Treatment Polymers
Class Charge Molecular Weight Form

1. Cationic Coagulants 5,000 to 200,000 Liquid solutions
Polyamines
Polyquaternaries
Poly DADM
DMA-EPI
2. Cationic Flocculants + 1,000,000 or more Powders, solutions, or emulsions
Copolymers of:
Acrylamide and Methacrylate
Acrylamide and DADM
Mannich Polymers
3. Anionic Flocculants 1,000,000 or more Powders, solutions, or emulsions
Polyacrylates
Copolymers
Acrylamide and Acrylate
4. Nonionic Flocculants 0 1,000,000 or more Powders, solutions, or emulsions
Polyacrylamides
Notes: DADM = Diallydimethyl Ammonium Chloride
DMA = Dimethylamine
EPI = Epichlorohydrin