How does a slow sand filter work?
Slow sand filtration is a simple and reliable process. They are relatively inexpensive to build, but do require highly skilled operators. The process percolates untreated water slowly through a bed of porous sand, with the influent water introduced over the surface of the filter, and then drained from the bottom.
What are the components of slow sand filter?
The ecosystem in a slow sand filter includes bacteria, protozoa such as rhizopods and ciliates, rotifers, copepods, and aquatic worms. A biological layer develops on the sand surface and is known as the schmutzdecke (German for ‘dirt layer’).
What is the drawbacks of slow sand filter?
The drawbacks of slow sand filtration are: Not as effective against viruses. No chlorine residual protection – can lead to recontamination. Routine cleaning can harm the biolayer and decrease effectiveness. Difficult to transport due to weight – high initial cost.
What is slow sand filter and rapid sand filter?
Rapid filters typically have an effective size of greater than 0.55mm and a Uniformity Coefficient of less than 1.5. Slow sand filters, on the other hand, should have an effective size of 0.15–0.35mm and a Uniformity Coefficient of 1.5–3, with a preference for less than 2.
What is SSF and RSF?
Rapid Sand Filters. Base material: In SSF it varies from 3 to 65 mm in size and 30 to 75 cm in depth while in RSF it varies from 3 to 40 mm in size and its depth is slightly more, i.e. about 60 to 90 cm.
Which is the heart of slow sand filter?
The vital layer is the “heart” of the slow sand filter. It removes organic matter, holds back bacteria and oxidizes ammoniacal nitrogen into nitrates and helps in yielding a bacteria-free water. Until the vital layer is fully formed, the filtrate is wasted.
What is backwash in filtration?
One of the best ways to clean a drinking water system’s filter is to backwash it, meaning reversing the flow and increasing the velocity at which water passes back through the filter. This, in effect, blasts the clogged particles off of the filter.
What is the function of SSF slow sand filter?
Slow sand filtration is a type of centralised or semi-centralised water purification system. A well-designed and properly maintained slow sand filter (SSF) effectively removes turbidity and pathogenic organisms through various biological, physical and chemical processes in a single treatment step.
Who discovered slow sand filter?
In 1827, what are known as slow sand filters were invented in Scotland by a civil engineer named Robert Thom. Two years later, a civil engineer known as James Simpson developed a similar filter which was adapted for use around the world.
What is a Schmutzdecke layer?
A layer of trapped matter at the surface of a slow sand filter in which a dense population of microorganisms develops. These microorganisms within the film or mat feed on and break down incoming organic material trapped in the mat.
What is backwash rate?
Backwashing is the reversal of flow through the filters at a higher rate to remove clogged particles from the filters. Backwash run times can be anywhere from 5–20 minutes with rates ranging from 8 to 25 gallons per minute per square foot of filter bed area, depending on the quality of the pre-filtered water.
What is Zoogleal layer?
Vital layer (Zoogleal layer, Biological layer, Schmutzdecke) is a slimy gelatinous layer formed on the sand bed. It is 2 to 3 cm thick. It is formed by algae, planktons, diatoms and bacteria. It is a very important part of slow sand filter. It purifies water by removing organic matter and holding back bacteria.
What is the ratio of chlorine to water?
To disinfect water, add one part of the chlorine solution to each 100 parts of water you are treating.
How do you calculate backwash?
Filtration and backwash rates are calculated by dividing the flow rate through the filter by the surface area of the filter bed. Typically these rates are measured in gallons per minute per square foot of filter bed area.
What is filter volume?
The volume filter is used to filter out stocks which show insufficient activity (ie. stocks with low liquidity): The Minimum field represents volume (in number of shares), so 1 million should be entered as “1000000”.