Chemical pre-treatment involves the separation of oil emulsions, surfactants, suspended solids and dissolved metals from a water or wastewater stream, achieved by the dosing of appropriate chemicals.
Suspended solids (solids that cannot be dissolved in water) in a water or wastewater stream can be removed from the water by chemical pre-treatment in the form of coagulation and flocculation.
- Coagulation and flocculation – Coagulation involves the dosing of a coagulant followed by rapid mixing of the coagulant with the water to destabilise the particles. As suspended particles have a natural electric charge, the addition of a coagulant destabilises the charges, so that the particles attract each other to form larger solids which are then able to settle more easily in a clarifier. Coagulation is followed by flocculation which involves the slow mixing of the flocculant with water. This promotes particle collisions and leads to the agglomeration of particles which can settle easier
- pH correction – Acids or bases are dosed into water or wastewater streams thereby adjusting the pH to satisfy certain water quality requirements. For example, municipalities require specific pH values for the discharge of wastewater into the municipal sewer systems
- Precipitation of metals – chemicals are added to precipitate valuable metals, for example, if nickel is present in solution, by adding lime, nickel hydroxide is formed which precipitates out of the solution and nickel can then be recovered as a metal
Resource Recovery Benefits
Pre-treatment to reverse osmosis (to precipitate the removal of undesirable compounds and impurities to prevent membrane fouling)
Compliance with regulatory standards
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