In the water and wastewater treatment industry—from large municipal treatment plants to industrial facilities—there’s a recurring problem: How to capture the tiny, invisible suspended particles in water and produce crystal-clear, contaminant-free water. The solution lies in a critical process called coagulation and flocculation , and at the heart of this modern process are powerful chemicals called electrolyte polymers.
This article comprehensively investigates this process and describes the role of electrophilic polymers as the most effective means in the formation of separable heavy aggregates.
Main problems: settled particles and suspended particles
Solid particles suspended in water, such as dirt, organic matter, bacteria, and industrial exhaust fumes, repel each other due to their negative surface charge. This electrostatic repulsion prevents them from sticking together and allows them to remain suspended in the water for extended periods. These particles are so small (colloidal) that they are difficult to separate using simple sedimentation methods. This is where the processes of coagulation and agglomeration come into play.
The difference between coagulation and aggregation
Although these two terms are often used synonymously, they represent different phases of the same process:
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Coagulation: This is the first phase. In this phase, a coagulant is added to the water. This substance, usually positively charged (such as alum or a cationic polyelectrolyte), neutralizes the negative surface charge of the particles. Once the repulsive forces are removed, the particles become unstable and can move closer together.
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Coagulation: The second step after coagulation is the addition of another substance, called a coagulant . Electrolytic polymers are most effective in this phase. These long-chain polymers act as molecular bridges , connecting small, unstable particles. The coating of the particles forms large, strong, and heavy aggregates, called coagulants . These coagulants are large and heavy enough to be easily separated from the water by sedimentation or flotation.
Electroactive polymers: The unsung heroes of the process
Electroactive polymers are synthetic or natural , water-soluble polymers whose chains contain charged functional groups. This charge makes them so effective.
Depending on the charge, electroactive polymers can be classified as follows:
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Cationic polyelectrolytes: carry a positive charge. These electrolytes are ideal for neutralizing negatively charged particles and are the most common type of electrolyte. They act as coagulants (charge neutralizers) and complexing agents (charge gap fillers). They are particularly widely used in the treatment of municipal and industrial wastewater with high organic content.
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Anionic electrolyte polymers: These polymers carry a negative charge. These polymers are typically used when suspended solids are positively charged, or with mineral coagulants such as alum, which form positively charged complexes. They are primarily used as coagulants.
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Nonionic electrolyte polymers: They are uncharged. Their mechanism of action is primarily based on the formation of physical bonds and surface adsorption. They are effective when the surface charge of the particles is insignificant or when pH changes negatively affect the properties of charged materials.
Compared to conventional coagulants such as alum, the use of electrolytic polymers offers the following advantages:
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More effective: They form larger, stronger and faster blood clots.
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Lower consumption: The required dosage of electropolymer is significantly lower than that of metal coagulants (usually in the ppm range).
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Less sludge: Because fewer chemicals are added, the amount of sludge generated is significantly reduced, reducing disposal and management costs.
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Settling rate: Heavy solids settle faster, allowing for smaller settling tanks and lower initial investment.
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Flexibility: By selecting the appropriate type and molecular weight, they can be optimized for different types of water and wastewater.
Electrolytic polymers are used in numerous industries.
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Drinking water treatment: removal of turbidity, colorants and organic substances.
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Municipal wastewater treatment: Separation of activated sludge in post-coagulation tanks.
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Mining and processing industries: thickening and drying of residues.
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Food industry: Used to separate suspended solids in industrial wastewater.
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Papermaking: water circulation and fiber retention.
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Oil and gas drilling: Used to control viscosity and particle separation of drilling mud.
Key points to improve the use of electropolymers
For the effective use of electrolytic polymers, the following must be considered:
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Cup test: Before the final decision is made , a cup test is conducted to determine the exact type of polyelectrolyte, the optimal dosage, and the injection site. This test simulates realistic conditions on a small scale.
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Preparation of stock solution: Electrolytic polymers must be properly prepared using special equipment (e.g., granulators) to avoid the formation of fisheye defects and maximize efficiency.
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Injection point and mixing: The intensity and duration of mixing are crucial factors. Fast mixing promotes even distribution of the coagulant, while slow mixing promotes its growth without disintegration.
Finally
Coagulation and flocculation are two fundamental physical processes in water and wastewater treatment, without which high quality standards cannot be achieved. Electroactive polymers with intelligent properties play a key role. By neutralizing charges and forming bridges between particles, these polymers transform small, unwanted particles into more manageable flocs. Selecting the right material and optimizing its use not only ensures the quality of the final product but also enables significant reductions in operating costs, energy consumption, and sludge management. Therefore, a comprehensive understanding of this process and the factors influencing it is crucial for every water and environmental engineer and specialist.