There are four main mechanisms for coagulation: double layer compression, adsorption and charge neutralization, sweep flocculation, and inter-particle bridging. Sweep flocculation is the primary mechanism used for drinking water treatment and will be the focus of this lesson. Sweep flocculation occurs with the addition of iron or aluminum, usually added as ferric sulfate or aluminum sulfate, which can easily dissolve into the water. Iron and aluminum form many different cationic species in the pH range of less than 7 or 8, which help destabilize the natural particles by compressing and or eliminating the negative surface charge on the particles. Many other salts and materials can add cations into the water, but what is unique about iron and aluminum is that when they are added at a high enough concentration they will begin to precipitate in the form of iron hydroxide, FeOH(s), and aluminum hydroxide, AlOH(s). It is the formation of these precipitates that instigate the sweep flocculation. The hydroxide solids not only help to eliminate the negative charges on the particles, but form a fluffy and sticky layer around the particles, effectively destabilizing them.
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Why is coagulation an important step in the water treatment process?
Mar 04, 2017 · Coagulation Mechanism. The colloidal particles carry electrical charges; normally negative charge. So the opposite charges coagulant is added to the water to overcome the repulsive charge and “destabilize” the suspension. Usually a metallic salt like alum is added as a coagulant to create positively charged ions.
What chemicals are used in the coagulation process?
Oct 15, 2021 · Coagulation treatment is usually carried out before sedimentation and filtration. During the process, a coagulant is added to water, and its positive charge neutralizes the negative charge of suspended contaminants. Neutralization causes suspended particles to bind together (hence the term). In clumps known as “flocs”, these particles sink ...
What is the process of coagulation of water in an alkaline medium?
Coagulation plays a vital role in the wastewater treatment process, allowing for solids removal and dewatering, water clarification, lime softening, and sludge thickening. With the help of other specialized chemicals and mechanical filtration methods, coagulants help companies maintain a consistent and reliable source of clean water to support their industrial processes.
How is coagulation carried by coagulants?
So treatment involving coagulation and flocculation is typical of surface water. ... Coagulants due to their positive charge attract negatively charged particles in the water. Coagulation is a unit process of addition of coagulant chemicals to water and rapid mixing so as to neutralize the electrical charges of the colloidal particles in the ...
What are the four mechanisms of coagulation?
What kind of process is coagulation filtration?
What is the coagulation process?
What is coagulation in the water cycle?
What is used in coagulation in water treatment?
What is coagulation and flocculation in the water treatment process?
How does sedimentation work in water treatment?
What are the 5 steps of water treatment?
What are the 4 steps of water treatment?
- Coagulation and Flocculation. ...
- Sedimentation. ...
- Filtration. ...
- Disinfection.
Why is coagulation important in water treatment?
What is the purpose of coagulation water treatment?
The purpose of coagulation water treatment process is to removes the colloidal particles from water. The water may contain suspended matter, small or large solid particles. Sedimentation and filtration processes can removes most of the solid particles but the small particles that are remains in colloidal suspension cannot removes.
What is the process of coagulation?
The process of consolidation of colloidal particles by neutralizing the charges with a coagulant, so that they can remove from the treated water by sedimentation or filtration is called coagulation. It is a vital part for drinking water and wastewater treatment.
Why is alum added to water?
Usually a metallic salt like alum is added as a coagulant to create positively charged ions. Normally 5-10% solution of coagulant is used.
What are the factors that affect the coagulation of water?
The process of coagulation of water depends on various factors like pH of the medium, temperature of water, coagulant feed concentration, coagulant dosage, type of coagulant, mass and initial turbidity. Moreover it is also depends on pre-treatment and type of pollutants present.
What is the name of the chemical that neutralizes the negative charges on colloidal particles?
This chemical is known as coagulant. The positive charges of the coagulant neutralize the negative charges on the colloidal particles. As a result the particles are able to coagulate into coarse formations which are easily removable. The process of consolidation of colloidal particles by neutralizing the charges with a coagulant, ...
What is the purpose of a positive charge of a coagulant?
The positive charges of the coagulant neutralize the negative charges on the colloidal particles. As a result the particles are able to coagulate into coarse formations which are easily removable. The process of consolidation of colloidal particles by neutralizing the charges with a coagulant, so that they can remove from ...
What is a coagulant?
Coagulants. Coagulants are the chemicals that are used to removes tiny particles in water. We used different types of coagulants in coagulation water treatment process. Generally, we can categories the common type of coagulant into two groups, aluminium base and iron base.
What is a Coagulant for Water Treatment?
Ferric sulfate, aluminum sulfate, or ferric chloride, classed as aluminum or iron salts, are common coagulants for water treatment.
How Does Coagulation Treatment Work?
Coagulation treatment is usually carried out before sedimentation and filtration. During the process, a coagulant is added to water, and its positive charge neutralizes the negative charge of suspended contaminants.
What Is Removed During Coagulation?
Coagulation is most effective at removing suspended solids and natural organic matter like gravel, sand, algae, clay, iron, protozoa, and even bacteria. Many of these contaminants can give water an unpleasant taste when present in large quantities, and can also give water a brown or orange color.
What Are the Most Common Types of Coagulants?
The most commonly used chemical for coagulation is aluminum sulfate. Ferric sulfate, ferric chloride, or sodium aluminate are also popular types of coagulants.
How to Choose a Coagulant for Water Treatment
The type of coagulant used by your local water treatment facility will usually depend on availability and affordability. With aluminium sulfate being available, affordable and highly effective, it is the preferred choice for public water treatment around the world.
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What Coagulants Are Used In Water Treatment?
In order to use coagulation in your water treatment, you have to apply coagulants to chemically initiate the process. These specialty chemicals should be formulated to meet your specific water quality application based on a particle analysis of your dissolved/suspended solids.
Organic Coagulants
Organic coagulants are best used for solid-liquid separation. They are also good options to use when trying to reduce sludge generation. Being organic in nature, these coagulants offer the added benefits of working at lower doses and having no effect on the pH of your water.
Inorganic Coagulants
Inorganic coagulants are typically cheaper than their organic counterparts, making them a cost-effective solution for a broad range of water treatment applications. They are especially effective when used on raw water with low turbidity.
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What happens when you add coagulants to water?
When metal coagulants are added to water the metal ions (Al and Fe) hydrolyze rapidly but in a somewhat uncontrolled manner, forming a series of metal hydrolysis species. The efficiency of rapid mixing, the pH, and the coagulant dosage determine which hydrolysis species is effective for treatment.
Why is coagulation important?
Coagulation is also important in several wastewater treatment operations. 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.
What are the variables in coagulation?
The efficiency of the coagulation-flocculation process is dependent on many variables. For a particular water these may include: 1 Type of coagulant used 2 Coagulant dosage 3 Final pH 4 Coagulant feed concentration 5 Type and dosage of chemical additives other than primary coagulant (e.g. polymers) 6 Sequence of chemical addition and time lag between dosing points 7 Intensity and duration of mixing at rapid mix stage 8 Type of rapid mix device 9 Velocity gradients applied during flocculation stage 10 Flocculator retention time 11 Type of stirring device used 12 Flocculator geometry.
What are some examples of coagulation operations?
Coagulation operations can be useful in some cases for the removal of inorganics. Examples of successful applications are copper and mercury reductions from wastewaterplant effluents. Two applications discussed in more detail below are arsenic and fluoride removals in potable water treatment:
When was alum used as a coagulant?
The use of alum as a coagulant by the Romans was mentioned in around 77 AD.
Why are synthetic polymers more effective than flocculants?
They are, in general, more effective as flocculants because of the level of control made possible during manufacture. Important mechanisms relating to polymers during treatment include electrostatic and bridging effects.
Does cationic polyelectrolyte inactivate viruses?
Metal coagulants or polyelectrolytes do not fully inactivate viruses. Therefore, a potential health hazard exists with the ultimate disposal of water treatment plantsludges.
What is the purpose of coagulation and flocculation?
The primary purpose of the coagulation and flocculation is to destabilize the charged colloidal particles in water and make them to settle so as to remove turbidity from the water. In addition to removing turbidity from the water, coagulation and flocculation process removes many bacteria which are suspended ...
What process removes bacteria suspended in water?
In addition to removing turbidity from the water, coagulation and flocculation process removes many bacteria which are suspended in the water and can be used to remove color from the water. Characteristics of Colloids. The principal phenomena that control the behaviour of the colloids are zeta potential (electrostatic force), ...
What are the three types of suspended particles in water?
In the order from smallest to largest, these particles are chemicals in solution, suspended colloidal solids, and suspended discrete solids.
What are the particles that settle out of water?
Some discrete particles of sizes bigger than 0.01 mm such as silt and fine sand causing turbidity would settle out of the water on their own by gravity, if retained for enough time.
What are some examples of chemical solutions?
An example of a chemical in solution is sugar in water.
Do colloids dissolve in water?
Colloids, also known as non settleable solids, do not dissolve in water although they are electrically charged. Still, the particles are so small that they will not settle out of the water by gravity even after several years of retention and they cannot be removed by filtration alone.
What are some examples of solids that can cause water to be colored?
Examples include bacteria, fine clays, and silts. Colloidal solids often cause colored water, such as the “tea color” of swamp water. Suspended settle able solids will settle out of water over time, though this may be so slow that it is impractical to merely allow the particles to settle out in a water treatment plant.
What is the process of adding coagulants?
Coagulation is carried by the addition of certain chemicals which are called as coagulants. Coagulation is a process in which coagulants are added for the purpose of rapid settlement of aggregates out of finely divided dispersed matter with slow or negligible velocity.
What is the purpose of coagulation?
Coagulation purpose is to increase the settling velocity. When size of aggregates increases, their settling velocity automatically increases. Coagulation is completed in two steps. Particle de-stabilization. Particle transportation (Flocculation).
What is the process of aggregation of small particles into a few large ones called?
Coagulation. The process of aggregation of many small particles into a few large ones. Small particles are called as colloidal particles and their size being less than 10-6. These colloidal particles have lesser velocity and more detention period. Detention period is a time taken by the particles to settle down.
When two particles approach each other, the net repulsive force exists?
When two particles approach each other, the net repulsive force exist. If repulsive force is dominant, then the system is stable. So we have to de-stabilize the system by adding the chemicals which are called coagulants. There are four methods by which chemicals can destabilize.
What are the counter ions in a diffused layer?
Sodium, calcium and Aluminum ions are the counter ions for negatively charged surfaces. These counter ions are absorbed on the surface of particles. In this mechanism, the charge of particle is not changed. Electrostatic interaction is important. The precipitation of particles depend upon the change of ions.
Is water a negative or positive charge?
Most of the particles in water have a charge which may be negative or positive. Under most natural conditions, this charge is negative. If the chemicals we added, have the same charge as that of particles. Then they don’t combine with each other. The charge of the particles may result from the various processes.
Why is coagulation important in water treatment?
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.
Can coagulant be added to water?
In the picture below, the coagulants have been added to the water, and the particles are starting to bind together and settle to the bottom. Coagulation jar test in a water treatment plant. As coagulation does not remove all of the viruses and bacteria in the water, it cannot produce. safe drinking water.
What is the most widely used water treatment technology?
Many water treatment plants use a combination of coagulation, sedimentation, filtration and disinfection to provide clean, safe drinking water to the public. Worldwide, a combination of coagulation, sedimentation and filtration is the most widely applied water treatment technology, and has been used since the early 20th century.
What is the charge of a coagulant?
The positive charge of the coagulant neutralizes the negative charge of dissolved and suspended particles in the water. When this reaction occurs, the particles bind together, or coagulate (this process is sometimes also called flocculation).
Does coagulation remove particles?
Coagulation can also remove suspended particles, including inorganic. precipitates, such as iron. A large amount of DOC can give water an unpleasant taste and odour, as well as a brown discolouration. While coagulation can remove particles and some dissolved matter, the water may still contain pathogens.
Why are pathogens removed from water?
Usually, the pathogens that are removed from the water are removed because they are attached to the dissolved substances that are removed by coagulation. In the picture below, the coagulants have been added to the water, and the particles are starting to bind together and settle to the bottom.
Is coagulation safe for drinking?
As coagulation does not remove all of the viruses and bacteria in the water, it cannot produce. safe drinking water. 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.
Coagulation and Flocculation in Water and Wastewater Treatment
The Coagulants
Removal of Natural Organic Matter
Pathogen Removal
Removal of Inorganics
Wastewater Treatment
Factors Affecting Coagulation Operations
Rapid Mixing
Flocculation
- Orthokinetic flocculation arises from induced velocity gradients in the liquid. It is here that primary particles are induced to approach close enough together, make contact and progressively form larger agglomerates, or flocs. The principal parameter governing the rate of orthokinetic flocculation is the velocity gradient applied. The degree or ex...
Testing and Control