Physical-chemical treatment

For water pre-treatment

What is physico-chemical treatment?

Whether producing drinking water or treating wastewater, a crucial step in the treatment process is removing particles. These particles have different sizes. They are divided into 4 categories:
  • dissolved(< 0,08 μm),
  • colloidal(0,08 – 1 µm),
  • supracolloidal(> 1 – 100 µm)
  • settleable(> 100 µm).
The type of treatment and its effectiveness depend on the size of the particles present in the water to be treated. Coarse particles are easy to remove using a lamella clarifier, for example. Finer particles settle poorly, but a drum filter can easily trap them. However, colloidal and dissolved particles cannot be properly treated by mechanical processes. In this case, we use physico-chemical treatments! By adding chemicals (known as coagulants and flocculants), we can create the right physical conditions for them to agglomerate and be removed. Physico-chemical treatment is a combination of two stages known as coagulation-flocculation. This is a classic method for separating suspended solids in treatment plants. Physico-chemical treatment is generally combined with settling processes or filtration. After a pH correction stage called “neutralization”, the water undergoes coagulation and then flocculation, where the particles agglomerate to form “flocs”. Finally, a physical separation stage separates the flocs from the treated water. We can describe the steps involved in this process as follows:
  • Neutralization: pH correction to achieve optimum coagulant efficiency (value indicated on product data sheet).
  • Coagulation: quick mixing of a coagulant with the property of neutralizing the negative charges of particles contained in water.
  • Flocculation:By slowly mixing another chemical called flocculant for several tens of minutes, flocs form and aggregate.
  • Separation: This is the physical separation of solids (by settling, flotation or filtration), which settle easily thanks to their increased volume and density!
The word clarifloculation refers to all these steps combined

What is physico-chemical treatment used for?

This type of treatment is used in many cases for many applications:
  • Accelerate particle settling speed (Hazen speed) to reduce the size of structures and save floor space
  • Remove fine, colloidal and dissolved particles
Physico-chemical treatment is highly effective in eliminating suspended solids (SS). This process also removes some phosphorus, BOD5, COD, TOC (drinking water) and heavy metals. Treatment performance depends on a number of aspects and the physico-chemical properties of the effluent. Therefore, laboratory tests, called jar tests, must be carried out to determine
  • the most suitable chemical products
  • optimal chemical doses
  • optimal contact time.

Some examples of packages involving physico-chemical treatment:

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