Surface water sources, groundwater as well as wastewater contain a lot of sediment particles, dissolved solids, and colloidal particles with diverse sizes and masses. By mechanical treatment methods, it is only possible to remove residue particles larger than 1mm in size, but with residue particles and solids below 1mm in size, it is necessary to apply the physicochemical coagulation method. – flocculation takes place in flocculation tank – flocculation for removal.
What is coagulation – flocculation?
Colloidal particles and solids suspended in water are often very small in size and have a negative charge. Therefore, they are not able to settle on their own. They tend to repel each other due to the same charge, causing chaotic repulsive motion in the solution. Colloidal particles are composed of two layers. The innermost layer is the nucleus which has a negative charge while the outer shell has a positive charge. The potential difference between the surface layer of colloidal particles and the solution is called Zeta electromotive potential. The more negative the zeta potential, the more stable the colloidal particles.
Colloidal particle structure and Zeta electrokinetic potential
Coagulation is the process of adding oppositely charged ions (positive charge) to neutralize the charge of colloidal particles in water, increasing the zeta potential, breaking the stability of the particles. , prevents the chaotic movement of ions in water.
Flocculation is the process of linking together flocs after flocculation under the influence of stirring at a small speed to increase the size and volume of the flocs so that the flocs The residue can easily settle.
Simulate the flocculation – flocculation process
Structure and operation of acacia flocculant tank
Image of coagulation – flocculation work
The mixing tank is where coagulants such as aluminum alum, iron alum, PAC, etc. are mixed with water and flocculation aids can be added to promote the flocculation process faster. When coagulant is added to water, the reaction will occur quickly, so in the flocculation tank, a stirrer will be installed to create a turbulent flow in the water so that the coagulant and water can come into complete contact with each other.
Factors affecting the flocculation process that we need to consider are:
- Effect of pH
- Water temperature
- Type and concentration of coagulant and flocculation aid
- Stirring speed
The reaction tank is where the coagulation process, also known as flocculation, takes place under the influence of a stirrer at a lower speed than in the mixing tank so that small flocs bond together to form large flocs that can spontaneously dissolve. can settle.
Factors affecting the flocculation process that we need to pay attention to:
- Stirring speed
Image of a wastewater treatment system with a coagulation – flocculation system
What wastewater treatment systems are flocculation tanks used in?
For wastewater containing a lot of suspended solids, high color, chemicals, etc., in the treatment technology line, it is necessary to add flocculation and flocculation process before sedimentation to remove all suspended residue and then the process. biological treatment.
Some wastewater requires a flocculation system during the treatment process, such as:
- Textile wastewater
- Plating wastewater
- Laundry wastewater
- Printing ink waste water
- Supply water treatment
- Groundwater treatment
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