The selection of coagulant determines the quality of the wastewater

“Selecting the right coagulant is important in order to ensure that the wastewater that is discharged from your company or wastewater plant is of an acceptable quality.”

The chemical precipitation process

Coagulation is a chemical process involving charge neutralistion, which causes the colloidal particles to accumulate in microflocs.

Coagulants are used as the first part of the precipitation process. They react with dissolved and suspended substances and form these microflocs. With the use of polymers, the microflocs can be gathered into large flocs, which can be separated from the water phase and dewatered.

Coagulants are divided into two main groups: organic and inorganic coagulants. Special mixtures of inorganic and organic coagulants are gaining more and more ground, as in some applications they produce a better result than standard coagulants do individually.

Inorganic coagulants

Inorganic coagulants, mostly metal salts, are used in large amounts to treat wastewater. The most commonly used products are probably ferric chloride and polyaluminium chloride (PAC), but sodium aluminate (NaAIO2) is also widely used.
Norlex Chemicals manufactures its own PAC and sodium aluminate, which is produced at the Norlex Group’s plant in Kalundborg, Nordisk Aluminat.

Organic coagulants

Organic coagulants include products that can be based on amines, polyDADMAC or tannins.

Amines and polyDADMAC are the most commonly used. They are widely used in the industry and potable water treatment, where inorganic coagulants do not produce the same result.

Tannin-based products have a more limited use but are an attractive alternative due to their green profile. Today, they are used in the fishing industry in particular.

Special blends

Special blends of organic and inorganic coagulants are gaining more and more ground as higher demands are placed on the treatment of water and wastewater. These mixtures often generate a much better result than the coagulants do separately.

Most mixtures are based on PAC and amines, but products containing iron chloride (either iron (II) or iron (III)) and magnesium also have applications where they generate a noticeable effect.

Applications include:

Norlex’s special precipitation chemicals

Wastewater may contain substances that are not captured during the normal precipitation process with coagulants. For example, the content of heavy metals may be too high. For this purpose, special precipitation products are used that form insoluble complexes with these substances, which precipitate as small particles. These are caught in the flocculation process and bound into the sludge.