What is a coagulant used in water treatment?
More coagulant can cause the pH to decrease, and more lime is typically added to compensate. Although finished water quality may be adequate when the raw water is stable, the plant pays a high cost in chemicals and sludge removal.
What happens when metal coagulants are added to water?
May 16, 2018 · When it comes to nutrient removal, it is all too common for wastewater utilities to overdose with ferric chloride, a chemical primarily used to combat the presence of phosphorus. If operators use too much of a coagulant like ferric chloride, they can cause a reversal in charge, forcing the stream’s suspended solids to destabilize and complicating the entire treatment …
What happens if you mix coagulants too much?
clump together and settle out of the water, unless proper coagulation and flocculation is used. 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,
What happens when you use too much coagulant in a water purifier?
When added to water, the acidic coagulant and the natural alkalinity of the water reacts to form an aluminium hydroxide floc, which usually consists of calcium bicarbonate. pH control is important in coagulation, for both the removal of turbidity and colour and also to maintain satisfactory minimum levels of dissolved residual aluminium in the clarified water.
What is the effect of adding coagulants to water?
What is the disadvantage of coagulation?
How does coagulation affect pH?
Why does coagulation play a key role in wastewater treatment?
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.
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In almost all things, wastewater treatment operators need to strike a delicate balance. They are asked to maintain cutting-edge processes but to remain within budget. They are expected to deal with the effects of climate change but remain energy efficient.
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.
What coagulants remove suspended solids?
Organic coagulants. Both polyamine and poly-DADMAC coagulants have been proven to be very effective at removing most suspended solids. Tannates are particularly good at oils and fats. Enable relatively low charge density to neutralise lower charged suspended particles, more effectively.
What are the two types of coagulants?
Types of coagulants. Today, there are two types of coagulants that are most commonly used in water and wastewater treatment. Organic and inorganic. Inorganic coagulants include: Iron coagulants - e.g. ferric sulphate, ferrous sulphate, ferric chloride and ferric chloride sulphate. Organic coagulants include:
Why do colloids repel each other?
The smallest particles (colloids) are stabilised by the action of physical forces (static electricity) on the particles themselves and, because they all have a negative charge when suspended in water, they repel each other. This causes them to remain suspended rather than clumping together and settling out of the water.
What is the purpose of coagulation and flocculation?
Coagulation and flocculation are essential components of both drinking water and wastewater treatment. They provide a reliable process for treating water turbidity (the cloudiness or haziness of a fluid typically invisible to the naked eye) which is a key test of water quality.
When were coagulants first used?
The use of coagulants for treating water goes all the way back to around 2000 BC when the Egyptians used almonds, smeared around vessels, to treat river water. These larger ‘clumps’ of particles are called micro-flocs and still cannot always be seen by the naked eye.
Who is James Greenwood?
James Greenwood as been working in the Water Treatment and Water Hygiene Industry for over 20 years. He is currently the Sales and Marketing Director for WCS Group the largest water hygiene and treatment Company in the UK. James has been instrumental in bringing significant innovations to the UK market over the years always focusing on enhancing client’s compliance and delivering true return on investment projects offering monetary and environmental savings.
What is the function of polymers in water?
Polymers are a range of water-soluble macromolecular compounds that have the ability to stabilise or enhance flocculation of the constituents in a body of water. They are added as part of the flocculation process to help strengthen and increase the settling weight of the floc. Polymers can be either natural or synthetic.
What are coagulants in water treatment?
Water Treatment Coagulants. Coagulant water treatment chemicals come in two main types –. primary water treatment coagulants and coagulant aids. Primary coagulants neutralize the electrical charges of particles in the water which causes the particles to clump together. Chemically, coagulant water treatment chemicals are either metallic salts ...
What are the factors that affect coagulation?
FACTORS INFLUENCING COAGULATION. Coagulation will be affected by changes in the water’s pH, salt content, alkalinity, turbidity, and temperature. Within the plant, mixing effects and coagulant effects will influence the coagulation/ flocculation process.
How long does it take to slake lime?
The slaking requires 15 – 30 minutes under optimum conditions. The slaked lime is diluted with water and stored in solution tanks.
What is the most commonly used coagulant?
Alum. One of the earliest, and still the most extensively used coagulant, is aluminum sulfate (Al/S04)3 ·14 HP), also known as alum. Alum is acidic with light tan to grey in color and available in blocks, lumps and powder with a density of 1000 -1100 kg/ m3 and specific gravity of 1.25 to 1.36.
What are the advantages and disadvantages of alum?
Advantages of alum are. It readily dissolves with water, and. It does not cause the unsightly reddish brown staining of floors, walls and equipment like ferric sulphate, Disadvantages of alum are. It is effective only at certain pH range, and.
What is ferrous sulphate?
Ferrous sulphate, ordinarily known as copperas, is granular acid compound and green to brownish yellow color available in granules, crystals and lumps. This is fed usually in solution form with strength of 4 to 8 %.
What is a coagulant aid?
Coagulant aid is an inorganic material, when used along with main coagulant, improves or accelerates the process of coagulation and flocculation by producing quick forming, dense and rapid-settling flocs. Coagulant aids when added increase the density to slow-settling flocs and toughness to the flocs so that they will not break up during the mixing and settling processes. Primary coagulants are always used in the coagulation/ flocculation process. Coagulant aids, are generally used to reduce flocculation time and when the raw water turbidity is very low. The particles of coagulant aids may become negatively charged making them subject to attraction by positively charged aluminium ions. It is especially useful for clear water with very low turbidity that does not coagulate well with usual processes. Nearly all coagulant aids are very expensive, so care must be taken to use the proper amount of these chemicals. In many cases, coagulant aids are not required during the normal operation of the water treatment plant, but are used during emergency water treatment of water which has not been adequately treated in the flocculation and sedimentation basin. Common coagulant aids are
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 coagulants are used in water treatment?
Commonly used coagulants include alum, lime, ferric sulfate, and polymers. Unfortunately, there are pitfalls to using this type of chemical coagulation treatment in a water treatment plant. ...
What are the disadvantages of coagulation?
One of the most prevalent and obvious disadvantages to any type of coagulation process is the resulting sludge. As the suspended solids cluster together and fall, they gather at the bottom of the tank. In a chemical coagulation water treatment process, the volume of the sludge produced can be significant.
What are the contaminants in wastewater?
Wastewater effluent often has many contaminants within it. These contaminants can range from organic compounds to heavy metals to oils, fats and hardness. Certain chemical additives are effective at coagulating certain constituents in the raw water.
Is sludge hazardous?
Sludge is hazardous and requires costly disposal. Not only is there a high volume of sludge, but often in the case of chemical coagulation, the sludge is hazardous. Non-hazardous sludge can actually be used in land applications. It can be applied to agricultural land or forest land as the case may be.
Can sludge be used as fertilizer?
This sludge material can condition the soil to facilitate nutrient growth as well as retain water. It can also act as a pseudo fertilizer, or be combined with an organic fertilizer to replace the more expensive chemical fertilizers.
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