What is coagulation and flocculation in wastewater treatment?
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).
What is conventional water treatment process?
Jan 10, 2017 · In a water treatment facility, the coagulant is added to the water and it is rapidly mixed, so that the coagulant is circulated throughout the water. The coagulated water can either be filtered directly through a medium filter (such as sand and gravel), a microfiltration or ultrafiltration membrane, or it can be moved to a settling tank.
What is coagulation process?
Mar 04, 2017 · Factors affecting coagulation water treatment. 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. Effect of pH on coagulation
What are flocculants and coagulants for wastewater treatment?
Coagulation is the process by which particles become destabilized and begin to clump together. Coagulation is an essential component in water treatment operations. Evaluation and optimization of the coagulation/rapid mixing step of the water treatment process includes a variety of aspects. Optimal coagulant dosages are critical to proper floc formation and filter …
How does coagulation work in water treatment?
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.Apr 14, 2022
What causes coagulation of 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 comes first flocculation or coagulation?
Coagulation and flocculation occurs in successive steps, allowing particle collision and growth of floc. This is then followed by sedimentation (see Sedimentation Chapter). If coagulation is incomplete, flocculation step will be unsuccessful, and if flocculation is incomplete, sedimentation will be unsuccessful.
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 are the steps involved in water treatment?
They typically consist of several steps in the treatment process. These include: (1) Collection ; (2) Screening and Straining ; (3) Chemical Addition ; (4) Coagulation and Flocculation ; (5) Sedimentation and Clarification ; (6) Filtration ; (7) Disinfection ; (8) Storage ; (9) and finally Distribution.
Which step does water treatment begin with?
Coagulation is often the first step in water treatment. During coagulation, chemicals with a positive charge are added to the water. The positive charge neutralizes the negative charge of dirt and other dissolved particles in the water.
What is the role of coagulation and flocculation in water treatment?
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 typical reaction time for coagulation and flocculation?
Once the floc has reached its optimum size and strength, the water is ready for the separation process (sedimentation, floatation or filtration). Design contact times for flocculation range from 15 or 20 minutes to an hour or more.May 24, 2019
Which water treatment process is done after filtration of water?
DisinfectionWhich water treatment process is done after filtration of water? Explanation: Disinfection is a process which is done to kill microorganism present in the water after the filtration process.
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.
Why is chlorine such an important part of the treatment?
Chlorine's use has seen it help to virtually eliminate waterborne diseases, such as cholera, typhoid and dysentery in developed countries. It also eliminates slime bacteria, molds and algae that commonly grow in water supply areas, on the walls of water mains and in storage tanks.Jun 28, 2010
What is the purpose of coagulation in drinking water treatment quizlet?
The purpose of coagulation and flocculation is to remove particulate impurities and color from the water being treated.
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.
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 charge of a colloidal particle?
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. 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 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.
Can a coagulant cause sludge?
It is very significant to determine the optimum dosage of a coagulant which will give the maximum clarifying effect. Insufficient amount of coagulant cannot able to destabilize properly of the colloidal particles. On the other hand higher dosage can cause excessive sludge production, corrosion and loss of money.
What is coagulation in water treatment?
Coagulation is the process by which particles become destabilized and begin to clump together. Coagulation is an essential component in water treatment operations. Evaluation and optimization of the coagulation/rapid mixing step of the water treatment process includes a variety of aspects. Optimal coagulant dosages are critical to proper floc ...
Why is the pH of water important?
The pH of the water plays an important role when alum is used for coagulation because the solubility of the aluminum species in water is pH dependent. If the pH of the water is between 4 and 5, alum is generally present in the form of positive ions (i.e., Al(OH)2+, Al8(OH)4+, and Al3+). However, optimum coagulation occurs when negatively charged ...
What is PACl used for?
Organic polymers, such as polyaluminum hydroxychloride (PACl), are typically used to enhance coagulation in combination with a primary coagulant. The advantage of these organic polymers is that they have a high positive charge and are much more effective at small dosages.
What is a jar test?
Jar Testing The raw water characteristics will affect the type and amount of chemicals used. Changes in raw water pH, temperature, alkalinity, total organic carbon, and turbidity will affect coagulation and, subsequently, filtration and finished water quality. Jar tests are an excellent way to determine the best type and amount of chemical ...
What are polymers used for?
Polymers are often used in conjunction with other coagulants such as alum or ferric chloride to optimize solids removal. The table below provides some guidelines for selecting the proper chemical based on some raw water characteristics. 3 Cost may be a consideration when selecting chemicals.
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 is the EPA rule for Giardia?
The U.S. EPA surface water treatment rule requires 99.9-percent (3-log) Giardia removal or inactivation, and at least 99-percent (2-log) removal of Cryptosporidium. Adequately designed and operated water treatment plants, with coagulation, flocculation, sedimentation and filtration are assigned a 2.5-log removal credit for Giardia, leaving only 0.5-log inactivation to be achieved by disinfection.
When was alum used in water?
As early as 2000 BC the Egyptians used almonds smeared around vessels to clarify river water. The use of alum as a coagulant by the Romans was mentioned in around 77 AD. By 1757, alum was being used for coagulation in municipal water treatment in England.
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:
What is the sequence of chemical addition?
Traditionally, the sequence of chemical addition for coagulation operations is to first add chemicals for pH correction, then add the metal coagulant, then add the flocculant aid. Not all these chemicals are necessarily added, but the sequence logic is often as described. However, there are instances when other sequences are more effective, including inverting the sequence of metal coagulant and polymer addition, and the sequence of metal coagulant addition and pH adjustment. The best sequence for a particular application can be determined by jar test experiments.
What are some examples of coagulants?
Particles in water carry an electrostatic charge on their surface. Common examples include clay, silica, iron, paints, and even oil.
What is the process of removing solids from water?
Wastewater 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 is a 10 mm particle?
Particles over 100μm are generally considered “settleable solids” and readily settle out of suspension. Particles sized 10-100μm are generally considered “turbidity” and are often addressed in a wastewater treatment system with coagulation. Particles smaller than 10μm are “colloidal particles”, which are almost always treated with coagulation ...
What is a jar test?
Jar testing is an essential tool for comparing products, optimizing performance, estimating treatment costs, and planning operations.
What are some examples of suspended particles?
Common examples include clay, silica, iron, paints, and even oil. These small, suspended particles are stabilized in suspension & difficult to remove via mechanical methods. A suspension of solids in water typically contains a variety of particles sizes. A lab analysis of “particle size distribution” will help define the size ...
What is a colloidal particle?
Particles smaller than 10μm are “colloidal particles”, which are almost always treated with coagulation because it is quite expensive to remove small particles using only mechanical water treatment like filtration. Colloidal particles are further classified as hydrophobic and hydrophilic colloids.
Is there a coagulant for wastewater treatment?
There are many coagulants available for wastewater treatment, for a deep dive check out. Below is an introduction to the coagulants representing the variety of different formulations and charge densities.
Why are coagulant chemicals added to water?
Coagulant chemicals with charges opposite those of the suspended solids are added to the water to neutralize the negative charges on non-settlable solids (such as clay and color-producing organic substances).
What are the most commonly used coagulants?
Inorganic coagulants such as aluminum and iron salts are the most commonly used. When added to water, these highly charged ions to neutralize the suspended particles. The inorganic hydroxides that are formed produce short polymer chains which enhance microfloc formation.
What are polymers used for?
These can be used as coagulant aids along with the regular inorganic coagulants. Anionic (negatively charged) polymers are often used with metal coagulants. Low-to-medium weight cationic (positively charged) polymers may be used alone, or in combination with alumor ferric coagulants to attract suspended solids and neutralize their surface charge. Manufacturers can produce a wide range of polymers that meet a variety of source-water conditions by controlling the amount and type of charge and the polymers molecular weight.
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
- Temperature
Temperature significantly affects coagulation operations, particularly for low turbidity waters, by shifting the optimum pH. This can be mitigated by operating at an optimum pOH as given by: pH + pOH = pKW; where pKW = 0.01706xT + 4470.99/T – 6.0875 and T = temperature in °K = 273.15 … - Sequence of chemical addition
Traditionally, the sequence of chemical addition for coagulation operations is to first add chemicals for pH correction, then add the metal coagulant, then add the flocculant aid. Not all these chemicals are necessarily added, but the sequence logic is often as described. However, t…
Rapid Mixing
Flocculation
Testing and Control