Physico-chemical treatment applications
The applications of physico-chemical treatment are very numerous in water treatment and among them we have :
Milk clotting
Here’s a 3-step guide to how milk is coagulated to form cheese.
There are three main steps in the cheese-making process:
- First, it is important to use enzymes to split the casein.
- To proceed with the following step, which involves the aggregation of micelles by flocculation, it is essential to have catalyzed 80% of the casein.
- Flocculation is also at work during the milk renneting phase. This step is the physical process of aggregating casein particles to form a gel.
- After shedding its water-soluble tail, casein can no longer keep the particles apart. The micelles come into contact with each other to form chains and clusters that continue to grow, forming a three-dimensional network that traps the water inside. So we will obtain a jelly.
- Finally, in the third phase of enzymatic coagulation, the networks continue to form, causing the gel to firm up. When this gel is sufficiently firm, the cheese is then cut.
Coagulation in chemistry.
Chemical coagulation can take many forms, and is very different from those used in water management.
Flocculation of suspended solids
Suspended solids flocculation is often used to eliminate turbidity. This turbidity hinders the effectiveness of disinfection treatments. Therefore, coupled with coagulation and applied as the final step, flocculation increases the size of flocs by the addition of polymer. Its flocs can then be separated from the treated water by decantation or flotation.
Flocculation of soil and clay.
Clays impart specific properties to the soils in which they are present, which are attributed to:
- their very small size.
- the sheet-like structure.
- the negative charge they carry (electron-negative colloids).
Together with soil water and other colloids (humic acids in particular), they form complex colloidal solutions that flocculate when the surface charges of the particles are neutralised by cations. This phenomenon is reversible, so the particles return to their dispersed state when the cations are eliminated through rinsing.
The flocculation of clay-humic complexes causes the agglomeration of other fine soil constituents (silts, sands). The observation of soil clods, whether they are porous and aerated, resistant to mechanical pressures, rain without disintegrating, or quite the opposite (hard-packed soil), provides information about the degree of flocculation. In simplified terms, the degree of flocculation is more significant when it involves large-sized cations with a substantial charge deficiency.
The cations Al+++, Fe+++, Ca++, Mn++, Mg++, Fe++ enable stronger flocculation than ions K+, Na+… the ‘worst’ being the H+ ion, which additionally imparts a more acidic reaction to soils as its concentration increases. Mineral exchanges between plants and soil (in other words, soil fertility) depend to a large extent on the flocculation quality of clay-humus complexes.
FAQ
What is a Jar test and why is it essential in physicochemical treatment?
The Jar test is a laboratory method for simulating the coagulation-flocculation process under controlled conditions. It is used to identify the type and optimal dose of reagents (coagulants, flocculants) to be used according to the quality of the water to be treated. Thanks to this test, the performance of the treatment is improved while reducing the costs and environmental impacts related to the overconsumption of chemicals.
Can wastewater be reused after physico-chemical treatment?
Yes, in many industrial sectors, physicochemically treated wastewater can be reused for non-potable uses: cooling equipment, washing equipment, or even certain manufacturing processes. This approach, called REUT (reuse of treated wastewater), significantly reduces drinking water consumption and meets the challenges of water sobriety.
What types of industries use physico-chemical treatment?
Physico-chemical treatment is widely used in industries such as automotive, agri-food, textiles and surface treatment. Each sector uses it for specific reasons: removal of heavy metals, fats, dyes or organic compounds that are difficult to degrade biologically.
How is the sludge from physico-chemical treatment managed?
The sludge generated must be stabilized to prevent fermentation and reduce its volume. This stabilization can be biological (anaerobic digestion), chemical (addition of lime), or thermal (drying). Once stabilised, the sludge can be recycled: agricultural spreading, composting, anaerobic digestion or incineration with energy recovery.
What are the new technologies associated with physico-chemical treatment?
Emerging technologies include membrane filtration (ultrafiltration, nanofiltration) for finer separation of pollutants, advanced oxidation processes (ozone, hydrogen peroxide) to degrade resistant organic compounds, and ion exchange to remove certain metals. These solutions are increasingly being integrated into conventional treatment chains to optimize water quality.
