Coagulation
In water treatment, coagulation flocculation involves the addition of polymers that clump the small, destabilized particles together into larger aggregates so that they can be more easily separated from the water. Coagulation is a chemical process that involves neutralization of …
Why is coagulation an important step in the water treatment process?
It is, however, an important primary step in the water treatment process, because coagulation removes many of the particles, such as dissolved organic carbon, that make water difficult to disinfect. Because coagulation removes some of the dissolved substances, less chlorine must be added to disinfect the water.
What are the changes in coagulation in plants?
These adjustments are a reaction to changes in the raw water entering the plant. Coagulation will be affected by changes in the water's pH, alkalinity, temperature, time, velocity and zeta potential. The effectiveness of a coagulant is generally pH dependent. Water with a color will coagulate better at low pH (4.4-6) with alum.
What are some examples of coagulants used in wastewater treatment?
A common example is chemical phosphorus removal and another, in overloaded wastewatertreatment plants, is the practice of chemically enhancing primary treatment to reduce suspended solids and organic loads from primary clarifiers. The commonly used metal coagulants fall into two general categories: those based on aluminum and those based on iron.
When are Coagulant aids used in water treatment?
In many cases, coagulant aids are not required during the normal operation of the treatment plant, but are used during emergency treatment of water which has not been adequately treated in the flocculation and sedimentation basin. A couple of coagulant aids will be considered below.
What happens right after coagulation during wastewater treatment?
Following coagulation, flocculation, a gentle mixing stage, increases the particle size from submicroscopic microfloc to visible suspended particles. The microflocs are brought into contact with each other through the process of slow mixing.
What causes coagulation in water treatment?
Coagulation is a somewhat simple chemical process that involves bringing insoluble materials together by manipulating the charges of particles, by adding iron or aluminum salts, such as aluminum sulfate or ferric sulfate, to a wastewater stream.
What happens during coagulation and flocculation?
Coagulation and flocculation are two separate processes, used in succession, to overcome the forces stabilising the suspended particles. While coagulation neutralises the charges on the particles, flocculation enables them to bind together, making them bigger, so that they can be more easily separated from the liquid.
How does coagulation filtration work?
A coagulant (typically either iron or aluminum salts with polymeric materials) is added and mixed with the influent water. The larger particles formed by coagulation are then removed from the water by filtration (typically sand, anthracite coal, or a combination of the two).
What happens during coagulation?
Coagulation is the chemical water treatment process used to remove solids from water, by manipulating electrostatic charges of particles suspended in water. This process introduces small, highly charged molecules into water to destabilize the charges on particles, colloids, or oily materials in suspension.
What are the coagulation process?
Coagulation, also known as clotting, is the process by which blood changes from a liquid to a gel, forming a blood clot. It potentially results in hemostasis, the cessation of blood loss from a damaged vessel, followed by repair.
What is coagulation or flocculation?
Coagulation is the destabilization of colloidal particles brought about by the addition of a chemical reagent called as coagulant. Flocculation is the agglomeration of destabilized particles into microfloc and after into bulky floccules which can be settled called floc.
Why is coagulation and flocculation important for water treatment?
Coagulation and flocculation are both critical processes to separate and remove suspended solids in water and wastewater treatment. These processes improve the clarity of the water to reduce turbidity.
What kind of process is coagulation filtration?
precipitative processCoagulation/filtration is a precipitative process. The most widely used coagulants for water treatment are aluminum and ferric salts, which hydrolyze to form aluminum and iron hydroxide particulates, respectively.
What is used in coagulation in water treatment?
Aluminum sulfate (alum) is the most common coagulant used for water purification. Other chemicals, such as ferric sulfate or sodium aluminate, may also be used. Coagulation is usually accomplished in two stages: rapid mixing and slow mixing.
What is the function of coagulation in water treatment quizlet?
The purpose of coagulation and flocculation is to remove particulate impurities and color from the water being treated.
Why is coagulation important?
Blood clotting, or coagulation, is an important process that prevents excessive bleeding when a blood vessel is injured. Platelets (a type of blood cell) and proteins in your plasma (the liquid part of blood) work together to stop the bleeding by forming a clot over the injury.
Overview
In water treatment, coagulation and flocculation involve the addition of compounds that promote the clumping of fine floc into larger floc so that they can be more easily separated from the water. Coagulation is a chemical process that involves neutralization of charge whereas flocculation is a physical process and does not involve neutralization of charge. The coagulation-flocculation pr…
Factors
Coagulation is affected by the type of coagulant used, its dose and mass; pH and initial turbidity of the water that is being treated; and properties of the pollutants present. The effectiveness of the coagulation process is also affected by pretreatments like oxidation.
Mechanism
In a colloidal suspension, particles will settle very slowly or not at all because the colloidal particles carry surface electrical charges that mutually repel each other. This surface charge is most commonly evaluated in terms of zeta potential, the electrical potential at the slipping plane. To induce coagulation, a coagulant (typically a metallic salt) with the opposite charge is added to the water to overcome the repulsive charge and "destabilize" the suspension. For example, the c…
Determining coagulant dose
The dose of the coagulant to be used can be determined via the jar test. The jar test involves exposing same volume samples of the water to be treated to different doses of the coagulant and then simultaneously mixing the samples at a constant rapid mixing time. The microfloc formed after coagulation further undergoes flocculation and is allowed to settle. Then the turbidity of the sampl…
Limitations
Coagulation itself results in the formation of floc but flocculation is required to help the floc further aggregate and settle. The coagulation-flocculation process itself removes only about 60%-70% of Natural Organic Matter (NOM) and thus, other processes like oxidation, filtration and sedimentation are necessary for complete raw water or wastewater treatment. Coagulant aids (polymers that bridge the colloids together) are also often used to increase the efficiency of the …
See also
• Electrocoagulation
• Industrial wastewater treatment
• Industrial water treatment