what happens in coagulation water treatment

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What is coagulation and flocculation in wastewater treatment?

What is coagulation and how is it used in water treatment?

• Works to treat particles that are suspended in the water — not just those which have already formed non-suspended solids.
• Forms clumps or flocs that can be removed from the water relatively simply.
• Cost-effective, as the chemicals required in coagulation are not difficult or expensive to obtain.

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What is conventional water treatment process?

conventional treatment processes in detail. 1. Raw water basins slow the water’s velocity after it passes through the intake structure, allowing heavy sediment and grit to settle to the bottom of the basins before the water enters the treatment plant. 2. Chemical coagulants are added to react with the remaining small particles in the water to form particles large enough to settle out.

What is 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 are flocculants and coagulants for wastewater treatment?

Removal of Inorganics

• Arsenic removal. Arsenic is a commonly occurring toxic element and long term exposure to arsenic is injurious to health.
• Fluoride removal. In 1975, the EPA named fluoride as a contaminant in the National Interim Primary Drinking Water Regulations.
• Chemical Phosphorus Removal. ...

What happens after coagulation in water treatment?

When this reaction occurs, the particles bind together, or coagulate (this process is sometimes also called flocculation). The larger particles, or floc, are heavy and quickly settle to the bottom of the water supply. This settling process is called sedimentation.

What is coagulation and flocculation in the water treatment process?

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.

What is the principle of coagulation?

At a glanceWorking PrincipleSuspended particles are destabilised by addition of a clarifying agent leading to the neutralisation of their charges. Particles thus agglomerate (flocs formation) and are able to decant.Main strengthRemoves solids and improves filtrationMain weaknessContinuous input of chemicals required6 more rows•May 24, 2019

Why is coagulant added to water?

Chemicals (coagulants) are added to the water to bring the nonsettling particles together into larger, heavier masses of solids called floc. 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.

What are Coagulation and Flocculation in Water Treatment?

Coagulation and flocculation are two processes that go together in water treatment. They are separate, but they are used one after the other to remove particles in water.

How Coagulation Water Treatment Works

Coagulation water treatment prevents the suspended particles from repelling one another and encourages them to form into clumps, or flocs.

How Flocculation Works

The flocculation process follows coagulation in water treatment. Coagulation is the charge neutralisation of fine particles, and flocculants are the agents that then promote the clumping of these particles together.

How Does Temperature Affect Coagulation in Water Treatment?

Temperature can have a significant effect on coagulation and flocculation.

Is Coagulation Caused by Bacteria in Water Treatment?

Suspended solids in water can be the result of natural causes, arising from organic materials such as algae, or inorganic materials such as sediment or silt.

How to Maximise the Effects of Water Treatment

Coagulation is a long-established water treatment, but it doesn’t remove all bacteria from water systems.

How is coagulation affected by pretreatments?

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.

What is the difference between coagulation and flocculation?

Coagulation (water treatment) In water treatment, coagulation flocculation involves the addition of compounds that promote the clumping of fines 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 ...

What is the SCD for coagulant dose?

The SCD measures the net surface charge of the particles and shows a streaming current value of 0 when the charges are neutralized ( cationic coagulants neutralize the anionic colloids ). At this value (0), the coagulant dose can be said to be optimum.

What force causes colloidal particles to cling together?

Once the repulsive charges have been neutralized (since opposite charges attract), van der Waals force will cause the particles to cling together (agglomerate) and form micro floc.

Why do colloidal particles settle slowly?

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 colloidal particles are negatively charged and alum is added as a coagulant to create positively charged ions. Once the repulsive charges have been neutralized (since opposite charges attract), van der Waals force will cause the particles to cling together (agglomerate) and form micro floc.

Is coagulation a physical process?

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 process can be used as a preliminary or intermediary step between other water or wastewater treatment processes like filtration and sedimentation.

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 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 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 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 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.

What is the pH of alum coagulant?

pH affects on the activities of coagulants. The optimum pH for alum coagulation is 6 to 7.5 whereas 5.0 to 8.0 are for iron. If the alkalinity is lower or higher, then the floc does not form properly. As a result, more coagulant is consumed. In this case, it is beneficial to correct the pH by adding acid or base.

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.

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.

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.

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 added to ferric chloride?

If ferric chloride is used, iron and chloride are added. And if aluminum sulphate is used, aluminum and sulphate are added. The majority of municipal water treatment plants use aluminum sulphate as the coagulation chemical. Generally, water treatment facilities have the coagulation process set up so that the coagulant chemicals are removed with ...

What is residual water?

Residuals are the by-products that remain in the water after substances are added and reactions occur within the water. The particular residuals depend on the coagulant that is used. If ferric sulphate is used, iron and sulphate are added to the water. If ferric chloride is used, iron and chloride are added.

Does DOC remove suspended particles?

Organic Carbon (DOC). 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.

What is coagulation in water treatment?

Coagulation water treatment is the first step in chemical wastewater treatment. Instead of passing over particles that would otherwise slip through the filter and fall too slowly to be trapped as sediment, coagulation clumps them together so they are more easily removed. Most of us know coagulation from anatomy class.

When was coagulation water used?

Yet coagulation water treatment is far from being a new process. In fact, it was in use by the Egyptians as early as 2,000 B.C. Later the Romans used the coagulation process in water treatment, as did the English in the 18th century.

What is a flocculant?

Flocculants are lightweight, medium weight and heavy polymers that cause the destabilized clumps of particles to agglomerate and drop out of the solution, removing them from the filtered water. The weight used depends on the type of particle.

Why is flocculation so popular?

Coagulation and flocculation processes have become more and more popular due to the increasingly stringent filtration requirements for industrial and municipal water treatment and wastewater treatment facilities levied by the U.S. Environmental Protection Agency (EPA.)

Is alum a good coagulant?

It’s the same principle with wastewater treatment. In coagulation treatment, a harmless chemical such as alum causes all of the particles to give off a positive charge and thus clump together, making them easier to filter. Coagulation is especially useful in removing the chemical phosphorus from water. Yet coagulation water treatment is far ...

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 is the best coagulant for organics removal?

Organics removal and enhanced coagulation are effective with traditional coagulants like aluminum sulfate, ferric chloride and ferric sulfate, as well as formulations like polyaluminum chloride (PACl) and acid alum. Acid alum formulations are aluminum sulfate with 1 to 15-percent free sulfuric acid.

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.

How does orthokinetic flocculation work?

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 extent of flocculation is governed by both applied velocity gradients and time of flocculation. These two parameters influence the rate and extent of particle aggregation and the rate and extent of breakup of these aggregates.

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:

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.

Overview

Factors

Mechanism

Determining coagulant dose

Limitations

See also