Have you ever wondered how clean water gets to your taps? Water treatment plants use the process of coagulation to clean water and make it safe for consumption and use. What is coagulation exactly? Take a look:
Coagulation Definition: Water treatment plants add chemicals to wastewater to cause clumps of suspended solids to bind together and sink to the bottom of the treatment chamber. This process is called coagulation.
The coagulation process will remove certain contaminants from the water in conjunction with sedimentation, disinfection, and filtration processes.
High-quality water is essential for economic, social, and health development. However, as the world’s population keeps growing, clean water supply is continually becoming a challenge.
To curb this problem, processes like water coagulation are implemented. However, UN-Water’s research shows that 50% of household water is not treated safely.
In this blog, we will look at what coagulation is (a water treatment method), its importance, and the contaminants eliminated during the process.
Water treatment entails different operations — among them is coagulation. They can either be physiochemical, chemical, or physical.
Shortages in drinking water brought about water treatment. Research shows that about 0.4% of the 2.5% of freshwater is unsafe for drinking.
Therefore, water is treated mainly to eliminate contaminants so that the water is fit for drinking.
A coagulant is defined as an organic or inorganic chemical that initiates the congealing process during water treatment.
Coagulants are used during the coagulation process, and they aid in cleaning the water and removing contaminants.
Examples of coagulants used in water treatment include iron and aluminum salts like ferric chloride, aluminum sulfate, and ferric sulfate.
These chemicals aid in the removal of suspended solids from drinking water. They neutralize the water as they are made of positively charged molecules, and the suspended particles are negatively charged.
Before we discuss how the coagulation process works, let us expound on the different types of coagulants and the forms in which they are used.
To understand what coagulation is and how it works, you need to know there are two types of coagulants: organic and inorganic. Here’s a brief description of each so you can understand their pros and cons:
These include polyamines, polytannate, and poly DADMAC. They do not contain metal or hydroxide, and they can remove organic matter, making the disinfection process safer as fewer harmful byproducts are produced during this stage of water treatment. Finally, they do not affect the water’s pH levels.
While they come with many benefits, it’s important to note that organic coagulants are more expensive per unit, produce low-density floc (clumps of suspended solids) and must be used in higher dosages.
These include forms of aluminum and iron coagulants. Like organic coagulants in water, these chemicals can remove organic particles, improving the disinfection process. They also enhance the formation of micro-flocs and are extremely affordable and readily available.
Before adding an inorganic coagulant to water, water treatment plants must recognize that the floc produced will have a high metal content and will need to be disposed of carefully. Additionally, inorganic coagulants affect water’s pH, requiring the use of pH control in addition to the coagulant.
- Sodium Aluminate
- Ferric chloride
- Ferric sulfate
- Aluminum sulfate
This coagulant is a combination of aluminum oxide and sodium oxide. When it is in solid form, it contains 70-80% sodium illuminate, and in liquid form, it has 30% sodium aluminate.
Aluminum sulfate can be used in a block, kibbled, or ground form during water treatment. When added to alkaline water containing calcium bicarbonate, it produces aluminum hydroxide floc.
If aluminum sulfate is not available, ferric sulfate is the best alternative. It is often used with chlorine, and it produces a denser floc than its counterpart, aluminum sulfate. However, the hydroxide sludge produced by ferric sulfate is heavier.
This is a great alternative to ferric sulfate, but it is less popular because when the water has more chlorine, the corrosivity also increases.
Water treatment facilities usually select a coagulant based on its availability and affordability. Aluminum sulfate is the most affordable and readily available among all the coagulants.
Metal, biopolymer, and synthetic coagulants are also used. Natural biopolymer coagulants made from animals, fungi, and other plant sources can produce less sludge and are non-toxic.
To truly understand coagulation, you need to know how it is used during water treatment. Coagulation is usually done before filtration and sedimentation. The coagulant is added to the water and evenly distributed to enhance water treatment.
Like the name, this process entails the addition of a coagulant that contains positive charges. The positive charges of the coagulant will then be neutralized by the negative charges of the suspended solids; hence, the water is neutralized.
The suspended solids in the water will then coagulate or bind together to form clumps known as flocs. They will then sink to the bottom of the treatment chamber. From here, the flocs will be filtered out. Various filtration processes, such as microfiltration or ultrafiltration via a medium filter or a membrane, can be used.
After learning about the definition of coagulation as it pertains to water treatment, many people naturally wonder if this process is always necessary. The short answer is no. Not every water treatment plant uses the process of coagulation to purify water. However, creating coagulated water is a critical step in wastewater treatment. These plants will follow this necessary step to create potable water.
With that said coagulants are not always used during the treatment of drinking water. Some drinking water supplies come from groundwater sources and are naturally filtered as the water flows over rocks and soil. In some of these cases, using coagulation to treat groundwater isn’t always necessary. You can contact your local water treatment plant to determine which processes they use to treat wastewater and drinking water.
Various things are removed during the coagulation process before the water becomes clear. However, the main particles removed are suspended solids and organic matter like bacteria, protozoa, iron, clay, algae, sand, and gravel. When these contaminants are in the water in large amounts, they make the water have an unpleasant taste, and the color of the water becomes either orange or brown.
However, the coagulation process does not remove all contaminants in a specific time frame. For this reason, other processes have to be incorporated during water treatment. For example, contaminants like sand and gravel take about two minutes to be neutralized, while others, like protozoa, clay, and algae, may take up to 2 hours.
Did you know that it takes up to 8 days for bacteria and algae of 1 micron to coagulate and collect at the bottom of the water? Viruses with 0.1 microns may take up to 2 years to coagulate.
Because of these challenges, disinfection is used to kill the microorganisms before the coagulation process. The remaining pathogens will attach themselves to the coagulated particles and will be removed during filtration.
Remember that coagulation in water treatment does not guarantee the water is safe, but it is crucial. When the suspended solids are removed, it is easier to disinfect the water and add chlorine.
Coagulation is a vital process in water treatment, but it cannot work alone. Other processes that should be done are disinfection, sedimentation, and filtration. These ensure that your water is safe for drinking and general consumption.
While coagulation is a vital process for treating wastewater and drinking water and does a fantastic job alongside sedimentation and filtration, it may not be enough. Water can still pick up contaminants from the moment it leaves the treatment plant to the time it pours through your faucets. For this reason, it’s often beneficial to look into residential water treatment solutions.
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