Coagulation in wastewater

The Oxford Dictionary definition of the term coagulation is "the action or process of a liquid, especially blood, changing to a solid or semi-solid state" and this is not dissimilar to its use in wastewater treatment.

Industrial effluent or wastewater may contain materials - including oil, grease, metals or toxic materials -  that can be dissolved or suspended in the water. Therefore, by using the process of coagulation in wastewater treatment solid waste can be brought together into a more solid state so it can be more easily removed.

How does coagulation work?

Finely distributed solids (colloids) suspended in effluents are stabilised by negative electric charges on their surfaces. This causes them to repel each other, causing them to remain unsettled, preventing them from colliding and forming into larger masses.

Adding a coagulant to the water produces positive charges, overcoming the repelling charge of the colloids, thus neutralising the force that keeps them apart. In wastewater treatment the coagulant is mixed thoroughly using industrial mixers to ensure it is well dispersed throughout the liquid. Once the coagulation process is complete the suspended particles become attracted to each other, causing them to cling together and form floc.

What coagulants are available?

There are a number of effective chemical coagulants that are available to treat industrial effluent or wastewater:

  • Aluminium Sulphate (Alum)
  • Poly Aluminium Chloride (PAC)
  • Ferrous Sulphate
  • Sodium Aluminate
  • Silicon Derivatives
  • Lime
  • Synthetic Organic Polymers

Currently, the most widely used chemical coagulants for wastewater treatment are Alum and PAC. When these chemical agents are mixed with water they form positively charged aluminium hydroxide floc which gathers the negatively charged clay, silt, bacteria and organic matters, causing them to settle down.

Belmar Technologies is a proven provider for both individual process equipment and a total solutions integrator for the water, industrial effluent and environmental control industries. We also supply a wide range of chemicals and wastewater treatment additives.  For more information, or to discuss industrial effluent treatment methods for your industry, please feel free to get in touch either by email to or by calling  +44 (0) 1327 586 008.