How does rapid sand filter work?
Rapid sand filters use relatively coarse sand and other granular media to remove particles and impurities that have been trapped in a floc through the use of flocculation chemicals—typically alum. Mixing, flocculation and sedimentation processes are typical treatment stages that precede filtration.
What is use of rapid sand filter?
Rapid filters are used primarily to remove turbidity after coagulation and flocculation in large water treatment plants. Rapid filters can either be open tanks (rapid gravity filters, see Figure 1) or closed tanks (pressure filters, see Figure 2), where water passes through a filter medium, most commonly sand.
How is backwashing done in rapid sand filter?
This is usually conducted through backwashing: the flow of water is reversed, so that treated water flows backwards through the filter. The sand is re-suspended and the solid matter is separated in the surface water. Often, air is injected additionally to support the cleaning process (WHO 1996).
Which is better slow sand filter or rapid sand filter?
A flow of between 4 – 21 m/h can be expected from a rapid sand filter, which is somewhere between 20 and 50 times faster than the range of slow sand filtration. Flow rates are usually around 0.1 m/h but can increase up to 0.4 m/h. Check out Flow Rates for more information.
How do you make a rapid sand filter?
- Coagulation: • Raw water is first treated with chemical coagulant such as alum.
- Rapid mixing. • The treated water is then subjected to violent agitation in a ‘Mixing Chamber’ for a few minutes.
- Flocculation.
- Sedimentation:
- Filtration: the partly clarified water is now subjected to rapid sand filtration.
What is the purpose of rapid sand filter bed fluidization?
The rapid sand filters are a polishing step that removes approximately 1 NTU or about 1 mg/L of solids. This is not to diminish the importance of filtration.
When should a backwashing operation be performed on a sand filter?
How Often Should I Backwash? A good rule of thumb is to backwash once the pressure displayed on your pressure gauge is 8-10 psi over the starting level. Backwashing after heavy rains, treating for algae, or when trying to clear cloudy water will keep your filter working efficiently.
What is efficiency of rapid sand filter?
The MPs removal efficiency of a bioreactor membrane (MBR) is about 99.9%; the rapid sand filter (RSF) is about 97%; dissolved air flotation (DAF) is about 95% and a disc filter (DF) is about 40–98.5%.
How effective is sand filter?
Slow sand filter lab effectiveness studies with a mature biolayer have shown 99.98% protozoan, 90-99% bacterial, and variable viral reduction. Field effectiveness studies have documented E. coli removal rates of 80-98%. Two health impact studies report 44-47% reduction of diarrheal disease incidence in users.
