Physical-chemical process

Coagulation flocculation is a physical-chemical water treatment process.

The process combines the chemical action of coagulants to neutralize particle charges with the mechanical stirring provided by flocculation.

Suspended solids removal

Suspended solids are particles that are often too fine to settle. They are small in diameter and therefore difficult to remove. Clay and colloidal particles are perfect examples of suspended matter. This is because they are tiny, negatively charged particles. It also prevents the clay particles from touching each other and thus from sticking together.

Therefore, it is essential to neutralize the clay’s charge. This is what coagulation offers by adding chemical agents of opposite charge. This will help neutralize the clay particles’ charge and repulsive power. As a result, the clays will be able to stick together.

To ensure that all these suspended solids converge, we add a flocculation process that mixes the water, bringing all the particles together to form flocs.

Phosphorous removal

Phosphorus removal from wastewater can be achieved either by :

The addition of calcium, iron and aluminum salts will chemically precipitate phosphorus. Afterwards, it can be easily separated from the treated water by settling. Biological phosphorus elimination depends on the absorption of excess phosphorus.

This absorption capacity depends on the normal metabolic needs of bacteria, and is proposed as an alternative to chemical treatment. However, it requires a laboratory test phase to determine the parameters to be used for treatment.

Advantages and disadvantages

The physico-chemical water treatment technique has both advantages and disadvantages.

Advantages :

  • It reduces the time required to settle suspended solids;
  • Very effective in removing fine particles that are much more difficult to remove with other methods;
  • Supports the elimination of many protozoa, bacteria and viruses;
  • Suitable for large and medium-sized plants;
  • Provides a perfect solution to turbidity and color problems.


  • This is an expensive method that requires an experimental phase;
  • Requires precise dosage of coagulants;
  • Requires a certain level of control;
  • Coagulants require precise dosage equipment;
  • Not suitable for small installations ;

Although effective, this process only partially eliminates natural organic matter (2/3 on average). Therefore, support from additional processes, such as oxidation or even filtration, is required. This guarantees complete treatment of raw or waste water.

Designing a coagulation-flocculation reactor

Jar test

The purpose of such a test is quite simple.

It allows you to select the type of coagulant and the dose required to remove the charged particles present in the raw water.

This type of experiment simulates the interaction of a coagulant or flocculant with the characteristics of a medium.


PH also influences the quality of your coagulation. This depends on the nature of your coagulant, but also on the impurities present in your mixture. To ensure effective coagulation, it’s important to estimate not only the coagulant requirement, but also the optimum PH value.

For natural organic matter of humic and allogenic origin, an acid PH will prove more effective. For algal cells, a PH close to neutral with an acidic tendency is the most effective.

When it comes to inorganic particles, it’s best to stick to neutral PH values. When coagulating impurity mixtures, the mutual interaction between these impurities can have an impact not only on the dose of coagulant, but also on the optimum pH ranges.


As is often the case with chemical reactions, temperature will have an impact on floc formation. Thanks to jar tests, we were able to determine the effects of temperature on the :

  • formation
  • break
  • floc reformations.

A study was carried out on several coagulants at temperatures ranging from 6 to 29°C. The results for each coagulant confirmed that floc formation was slower at low temperatures. By increasing the floc shear rate, it was found that the flocs never reformed to their original size. At higher temperatures, floc reformation was found to be slower and floc size smaller.

After increased shearing, recovery is greater at lower temperatures. This implies that floc rupture is more reversible at lower temperatures.


Basically, salinity seems to have a positive impact on the flocculation process, the intensity of which depends on the substances to be flocculated and the flocculating agents. Iron is an example of a material that flocculates best in a saline solution. TSS tends to flocculate better in the presence of salt.

However, you must be careful to choose an installation that is resistant to the corrosive power of salt.

1h2o3 physico-chemical water treatment tanks

1h2o3 flocculation coagulation tanks are available in 3 standardized sizes, with volumes ranging from 4 to 12 m3. The internal volume allocation is adjustable, as is the speed of rotation for neutralization, coagulation or flocculation.

Thanks to their height, their footprint is reduced.

For an outdoor use, the tanks are covered and treated against UV rays to protect them from the sun and bad weather.

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