Colloid
A colloid, in chemistry, is a substance in which one substance of microscopically dispersed insoluble particles is suspended throughout another substance.
What is coagulation normal values?
Oct 15, 2021 · Coagulation is one of the common methods used by water treatment plants to provide safe, clean drinking water to public water customers.This method is often used alongside processes including filtration, disinfection and sedimentation to remove select contaminants from water. This article will look at this method in water treatment: what it is, …
What are flocculants and coagulants for wastewater 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 does a coagulation test determine?
Drinking Water Treatment - Coagulation. Solids are removed by sedimentation (settling) followed by filtration. Small particles are not removed efficiently by sedimentation because they settle too slowly; they may also pass through filters. They would be easier to remove if they clumped together (coagulated) to form larger particles, but they don't because they have a negative …
What is the purpose of a coagulation test?
Apr 03, 2018 · 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.
What is the purpose of coagulation?
Coagulation is a process for combining small particles into larger aggregates (flocs) and for adsorbing dissolved organic matter on to particulate aggregates so that these impurities can be removed in subsequent solid/liquid separation processes.Feb 19, 2015
What causes coagulation of water?
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.
What is the purpose of coagulation and flocculation in 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 is coagulation or 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.
Why does coagulation play a key role in wastewater treatment?
In water treatment, coagulants are used to remove a wide variety of hazardous materials from water, ranging from organic matter and pathogens, to inorganics and toxic materials, like arsenic, chemical phosphorous and fluoride.
What does coagulant mean?
Coagulant meaning A substance that brings about coagulation. noun. An agent that causes a liquid or sol to coagulate.
Why is coagulation flocculation necessary?
Coagulation and flocculation are used to separate the suspended solids portion from the water. Suspended particles vary in source, charge, particle size, shape, and density. Correct application of coagulation and flocculation depends upon these factors.
What are advantages of using sodium aluminate as coagulant in the water treatment process?
Key benefitsGives high purity and quality of water.Excellent coagulation, flotation and sedimentation.Increases alkalinity – no need for lime and hydroxides.Excellent removal of phosphor.Minimal chemical sludge.Low transportation cost.
What is the principle of coagulation?
Coagulation is the process used to reduce the energy forces present around particles that tend to keep them from joining together to form a larger mass.Oct 1, 1983
Is coagulation and clotting the same thing?
Coagulation is the process of making blood clot. This is an important and complex process that enables the blood to plug and heal a wound. This is how the body stops any unwanted bleeding. Coagulation involves the action of cells and coagulation (clotting) factors.
What is coagulation and sedimentation?
Large, heavy particles settle out readily, but smaller and lighter particles settle very slowly or in some cases do not settle at all. Because of this, the sedimentation step is usually preceded by a chemical process known as coagulation.
What is the process of coagulation?
Coagulation-flocculation process in a water treatment system. 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 ...
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.
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.
Why are jar tests limited?
Despite its widespread use in the performance of so-called "dewatering experiments", the jar test is limited in its usefulness due to several disadvantages. For example, evaluating the performance of prospective coagulants or flocculants requires both significant volumes of water/wastewater samples (liters) and experimental time (hours). This limits the scope of the experiments which can be conducted, including the addition of replicates. Furthermore, the analysis of jar test experiments produces results which are often only semi-quantitative. Coupled with the wide range of chemical coagulants and flocculants that exist, it has been remarked that determining the most appropriate dewatering agent as well as the optimal dose "is widely considered to be more of an ‘art’ rather than a ‘science’". As such, dewatering performance tests such as the jar test lend themselves well to miniaturization. For example, the Microscale Flocculation Test developed by LaRue et al. reduces the scale of conventional jar tests down to the size of a standard multi-well microplate, which yields benefits stemming from the reduced sample volume and increased parallelization; this technique is also amenable to quantitative dewatering metrics, such as capillary suction time.
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.
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 process of coagulation?
The coagulation process involves the addition of the chemical (e.g. alum) and then a rapid mixing to dissolve the chemical and distribute it evenly throughout the water.
How are solids removed?
Solids are removed by sedimentation (settling) followed by filtration. Small particles are not removed efficiently by sedimentation because they settle too slowly; they may also pass through filters.
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.
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.)
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.
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 ...
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.
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).
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.
Is sand filtration biological?
sand filtration is a biological process, because it uses bacteria to treat the water. The bacteria. establish a community on the top layer of sand and clean the water as it passes through, by. digesting the contaminants in the water. The layer of microbes is called a schumtzdecke (or.
What is dissolved organic matter?
dissolved organic material, which is referred to as Natural Organic Matter (NOM) or Dissolved. 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 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.
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 the process of coagulation?
Coagulation is a chemical process used to neutralize charges and form a gelatinous mass to trap (or bridge) particles, thus forming a mass large enough to settle or be trapped in a filter. The words "coagulation" and "flocculation" are often used interchangeably, but they refer to two distinct processes. Coagulation is often used in combination ...
What is coagulation in science?
What Does Coagulation Mean? Coagulation is a chemical process in which the destabilization of non-settleable particles takes place. These particles form clumps with the help of a coagulant.
How is coagulation achieved?
Coagulation is commonly achieved by adding different types of chemicals (coagulants) to wastewater to promote destabilization of the colloid dispersion and agglomeration of the resulting individual colloidal particles.
When does coagulation occur?
Coagulation of colloids occurs when a stable colloid (because of the intrinsic stability of the colloid dispersion) or a stabilized colloid (because of the presence or a double layer) is destabilized.
Overview
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 flocculationis a physical process and does not involve neutralization of charge. The coagulation-flocculation proces…
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 turbidityof 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
• Alum
• Electrocoagulation
• Flocculation
• Industrial wastewater treatment
• Industrial water treatment