Physical-chemical process

Coagulation flocculation is a physico-chemical treatment process of water.

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 cause all these suspended solids to meet, a flocculation phase is added, which, by stirring the water, will cause all the particles to meet and thus form flocs.

Phosphorous removal

Phosphorus removal from wastewater can be achieved by:

The addition of calcium, iron and aluminum salts will chemically precipitate phosphorus. It can then easily be 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 advantages but also 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.

Disadvantages:

  • 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. In this way, raw or waste water is guaranteed complete treatment.

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 needed 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

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 mixtures of impurities, the mutual interaction between these impurities can have an impact on the coagulant dose, but also on the optimal pH ranges.

Temperature

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.

Salinity

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.

The physico-chemical water treatment tanks of 1h2o3

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

Thanks to their height, their footprint is reduced.

For outdoor installation, the tanks are covered and anti-UV treated to protect them from the sun and bad weather.

Discover our coagulators and flocculators
Coagulation Flocculation CFE range for outdoor use

FAQ

Why carry out laboratory tests before sizing a physico-chemical treatment?

Laboratory tests, such as Jar-tests, make it possible to simulate the real conditions of the physico-chemical treatment in order to select the most effective reagents (coagulants, flocculants) and to determine their optimal dosages. This not only improves treatment efficiency, but also minimizes operating costs and prevents unnecessary overdoses. These tests are essential to adapt the solution to the specific characteristics of the water to be treated.

Automation allows critical treatment parameters (pH, flow rate, reagent dosing, etc.) to be regulated in real time, ensuring consistent performance even when pollutant load changes. It also facilitates data traceability, preventive maintenance and the reduction of human error, while ensuring long-term energy and reagent savings.

Yes, physico-chemical treatment is often used upstream or in addition to biological treatment. By reducing the initial pollutant load (suspended solids, metals, phosphorus, etc.), it lightens the work of micro-organisms in biological basins and stabilises the overall yield. This synergy is particularly useful for industrial or highly loaded effluents.

Chemical treatment is based solely on chemical reactions (neutralization, oxidation, precipitation). Physico-chemical treatment combines the action of chemicals and physical processes (settling, flotation, filtration) to transform contaminants into separable particles. It is more versatile and often more effective for complex or industrial waters.

Chemical precipitation is used to remove dissolved ions that are otherwise difficult to filter. This includes phosphorus (in the form of phosphate), water hardness (calcium and magnesium), heavy metals (zinc, copper, iron), sulfates, and fluorides. By adding suitable reagents, these elements form insoluble compounds that are then extracted by settling or flotation.

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