What is slow sand filter water treatment system?
In the Water Treatment system as well as sewage treatment system Slow sand filter is the large-scale water filtration methods. Slow Sand media water treatment filter is very old type water filtration but very effective water treatment system.
Can slow sand filtration remove true colour?
Cleasby (1991) reported that true colour (caused by colloidal and soluble substances such as humic substances) is also not removed effectively by slow sand filtration (e.g. 30% removal, Ellis, 1985).
What is the filtration rate of sand filter?
Slow Sand filtration of water treatment process is very reliable which do not usually require coagulation/ flocculation before filtration. This Filtration rate is 0.0015 – 0.15 gpm/ft 2 Water treatments Filtration of Sand Filter is Minimum operation and maintenance requirements.
How does a sand filter remove organic particles from the water?
The multi sized layer (schmutzdecke break down and removes organic particles from the water through the mechanism of biological action, adsorption and straining methods. The absorption of biological microorganism in sand filter media should be reformed by the backwash with water.
How do you make a slow sand water filter?
0:026:06Building an Inexpensive Water Filter - Slow Sand Filter | Weekly Peek Ep4YouTubeStart of suggested clipEnd of suggested clipClean. Water then flows up and out of the spigot bricen gathers the supplies maril. We've got a fiveMoreClean. Water then flows up and out of the spigot bricen gathers the supplies maril. We've got a five gallon bucket.
What is a typical filtration rate for slow sand filters?
Process Description Slow sand filters require a very low application or filtration rate (0.015 to 0.15 gallons per minute per square foot of bed area, depending on the gradation of the filter medium and the quality of the raw water).
What is the design period of slow sand filter?
The frequency of cleaning is 1 to 3 months. Rate of filtration is 100-200 l/hr/m2 of filter area. It is used for smaller plants in villages.
What is effective size of slow sand filter?
between 0.15 – 0.35mmSlow sand filters on the other hand, should ideally have an effective size of between 0.15 – 0.35mm, and a Uniformity Coefficient of between 1.5 – 3, but preferably less than 2. Penetration of suspended matter into the sand bed is deeper for rapid sand filters, which are usually cleaned by backwashing.
How do you calculate the flow rate of a sand filter?
The filter flow rate is defined as the amount of water filtered over a given period of time, expressed in gallons per minute. Filter flow rate formula: Filter area x filter rate = filter flow rate in gpm. The “filter area” is the surface area of the filter medium. It is measured in square feet.
What are the essential components of a 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 sand size used in slow sand filter?
0.15 – 0.35mmMost literature recommends that the effective size of sand used for continually operated slow sand filters (COSSFs) should be in the range of 0.15 – 0.35mm, and that the uniformity coefficient should be in the range of 1.5 – 3, although a coefficient of less than 2 is desirable (Schulz and Okun, 1984 [ref.
What is slow sand filter in water treatment?
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.
What are the characteristics of slow sand filter?
Slow sand filters have a number of unique qualities: Unlike other filtration methods, slow sand filters use biological processes to clean the water, and are non-pressurized systems. Slow sand filters do not require chemicals or electricity to operate.
How do you calculate effective sand size?
The effective size of a given sample of sand is the particle size where 10% of the particles in that sample (by weight) are smaller, while 90% are larger. Usually this is denoted as the D10. The size distribution is represented by the Uniformity Coefficient, which enables you to see how well graded your sand sample is.
What is the thickness of bed in slow sand filter tank?
The filter media is supported on the base material (gravel) of a 30 to 75 cm thick bed. The gravel bed is graded and it is laid in different layers each 15 cm thick.
What are the advantages of slow sand filter?
The benefits of slow sand filtration are: High flow rate of up to 0.6 liters per minute. Simplicity of use and acceptability. Visual improvement of the water. Production of sufficient quantities of water for all household uses.
Slow Sand media Water filter
In the Water Treatment system as well as sewage treatment system Slow sand filter is the large-scale water filtration methods. Slow Sand media water treatment filter is very old type water filtration but very effective water treatment system.
Uses of Slow Sand filters
Slow Sand filtration of water treatment process is very reliable which do not usually require coagulation/ flocculation before filtration. This Filtration rate is 0.0015 – 0.15 gpm/ft 2
Lab Effectiveness, Field Effectiveness, and Health Impact
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.
Implementation Examples
The BioSand Filter was designed by Dr. David Manz at the University of Calgary.
Economics and Scalability
The average slow sand filter’s construction cost ranges from US $15-$60, depending on whether local or imported materials are used. Filter programs are either fully subsidized or operated at partial cost recovery (with users paying $2-$10) using donor funds.
Additional Resources
For more information about slow sand filtration systems for developing countries visit:
How deep is a filter?
The filter is confined within a tank, typically rectangular or circular in shape and will be 2.5 to 4 metres deep (Figure 1.1). Water enters at the top of the tank, where it resides for a number of hours due to the slow percolation of water through the bed of sand beneath.
How to fill a SSF tank?
Begin to fill the SSF tank from the top using water from the header tank (tank 1), but ensure that this is done slowly and that the influent flow of water is directed onto the splash plate (stone) so as to avoid disturbing the sand. Completely fill the SSF tank.
Why is SSF performance compromised?
SSF performance may be compromised in countries with a temperate climate, due to a seasonal decline in microbiological activity (during cold periods, Section 2.2.7), as well as due to problems associated with seasonal algal growth (e.g. during the spring and later summer, Section 2.2.6).
What is an ejector type sand washer?
Huisman and Wood (1974) provide examples of ejector type sand washers where sand is placed in a tank into which water is ejected into the bottom. The sand sinks and the dirt attached to the sand becomes suspended in the water and is carried up to the surface of the tank, where it overflows and is thus removed.
What is water wash?
Water-washed– a transmission route for a disease (e.g. of the intestinal tract, skin, eyes or disease carried by lice) where improvements in hygiene significantly reduce its transmission between people. Hence the transmission depends on the quantity of water used rather than the quality (Feachem & Cairncross, 1993).
What is slow sand filter?
Design and operation simplicity—as well as minimal power and chemical requirements—make the slow sand filter an appropriate technique for removing suspended organic and inorganic matter. These filters also may remove pathogenic organisms. Slow sand filtration reduces bacteria, cloudiness, and organic levels—thus reducing the need for disinfection and, consequently, the presence of disinfection byproducts in the finished water.
What are the limitations of slow sand filters?
Slow sand filters do have certain limitations. They require a large land area, large quantities of filter media, and manual labor for cleaning. Water with high turbidity levels can quickly clog the fine sand in these filters. Water is applied to slow sand filters without any pretreatment when it has turbidity levels lower than 10 NTU. When slow sand filters are used with surface waters that have widely varying turbidity levels, infiltration galleries or rough filters—such as upflow gravel filters—may be used to reduce turbidity. Waters with a very low nutrient content may impair turbidity removal since some nutrients must be present that promote biological ecosystem growth within the filter bed. Slow sand filters do not completely remove all organic chemicals, dissolved inorganic substances, such as heavy metals, or trihalomethane (THM) precursors—chemical compounds that may form THMs when mixed with chlorine. Also, waters with very fine clays are not easily treated using slow sand filters.
Why is filtered water important in a sand filter plant?
First, because of the importance of establishing biological activity, using chlorine ahead of the filter is inappropriate, and the operator must provide disinfectant contact time in a storage basin. Second, storage is needed for production equalization and demand.
What is slow sand filter?
Slow sand filtration is a simple and effective technique for purifying surface water. It will remove practically all the turbidity from water, together with virtually all harmful eggs, protozoa, bacteria and viruses without the addition of chemicals and may frequently be constructed largely with local materials.A slow sand filter consists basically of three different layers within a filter box. These layers are from bottom to top: the underdrainage system, the gravel layer and the sand. It is only the sand which plays any part in the treatment process.
How is the size of a slow sand filter determined?
The size of a slow sand filter is determined by several factors. For example:Population of 1000 with water consumption of 100 litres/capita day.Wastage can be assumed to be 30 per cent of production.
How is the outlet flow maintained?
The outlet flow is maintained at the design flow rate by a hand-operated gate valve which is adjusted every day . It is essential to provide an outlet weir which is above the height of the sand bed.