What is the definition of flocculation?
In simple terms, flocculation is the process by which individual solid particles in liquid clot together into bigger particles known as ‘clots’ or ‘flocs’ which can then be separated off to leave a cleaner and clearer liquid behind.
What is flocculation used for?
Conventional coagulation, flocculation or sedimentation practices are essential pre-treatments for a range of water purification systems. Flocculent chemicals are used in water treatment processes for removal of unwanted solids and contamination to produce cleaner, safer and potentially drinkable water. Other applications include sewage treatment, cheese production, and brewing. It is also used in surface and physical chemistry, biology, and civil engineering.
What are the processes in flocculation?
Flocculation, or sometimes referred to as clarification, consists of four distinctive processes – coagulation, flash mixing, flocculation, and clarification. Sufficient time and velocity are necessary to maximise the effectiveness of the flocculent so that the individual parts come together.
- Step 1. Adding the Flocculent
During the coagulation process, chemical coagulants, also known as flocculants, are added to the water to destabilise the smaller individual particles and cause them to begin aggregating.
- Step 2. Flash Mixing
After the flocculent is introduced, the water is mixed vigorously by the flash mixer so that the chemicals are evenly dispersed throughout the water. This particular step plays a large role in the effectiveness of the water treatment. So that the chemicals are evenly distributed it is flash mixed from 30-60 seconds. Coagulation actually begins during the flash mixing process as the coagulants neutralise the electrical charge of the fine particles. This stops the repulsion of the individual particles and allows them to begin sticking together to form bigger ‘flocs’.
- Step 3. Flocculation
After the initial more aggressive mixing, flocculation begins after slowing down the mixing so that the smaller particles produced during the coagulation start adhering together. The flocculation stage usually goes continues for around 30-45 minutes in a flocculation tank that may have several compartments. Each of these compartments has a different mixing speed, and the speed decreases as the water flows from the top of the basin to its bottom. This approach allows the growing flocs to form without being shattered by the mixing blades.
After the flocculation process, most of the particles should have bonded together which is called the Floc. Floc consists of larger masses of particulates bonded together in clusters of about 0.1 to 3 mm in size. It is critical that the floc is not too small otherwise it doesn’t settle well enough or too big otherwise it will likely break apart in the flocculation tank.
- Step 4. Clarification
Clarification is the last of the steps in the flocculation process. Clarifiers typically consist of polyethylene cone tanks which hold the water long enough to allow the floc and other particulates to move to the bottom of the tank. The clarification process makes the water clear by removing all kinds of particles, sediments, oil, natural organic matter and colour.
Enduratank offer a complete clarification tank design service based on your system requirements. As manufacturers of polyethylene cone tanks, we have in-house CAD engineers who can help you create bespoke solutions or, if you’re looking for a more standard system, we hold large stocks for quick delivery nationwide.
For more information or to talk to one of our sales team, call 01778 562810.