SAN ENGINEERING COMPANY
Pioneers in water treatment since 1964
San Filter Media
Silica Sand
Used universally to form the granular matrix required for filteration the process for
separating suspended and colloidal impurities from water by passage through a porous granular media. The required grain size of Silica sand is manufactured by crushing quartzite of high silica content and sieving the granules to
the desired effective size and Uniformity Coefficient as per IS 8419 ( part 1). The high Silica content of about 99% makes
it very durable and the silica sand is completely free of any imputities and dirt normally found in river sand . Standards: IS 8419 (Part 1) 1977
Physical Parameters :
• Effective Size: 0.5
• Uniformity Coefficient : 1.5
• Bulk Density : 1.5 approx
• Density : 2.65
• pH value: 6.5
• Loss on ignition : , 0.44 %
Chemical Analysis :
• Silica Content : > 92%
• Iron as Fe2O3 : < 0.56%
• Alumina as Al2O3 : <0.17%
• Phosphorus as P2O5 : < 0.01%
• Magnesium as MgO : Not detected.
• Sodium as Na2O : Not detected
Anthracite
Anthracite coal for dual media filters is of a specially hard variety of coal mined from over 500m deep in the earth. It is imported from Germany and is manufactured as per the European standards for filter media - DIN 19605, DIN 19643, DIN 2000. Standards : DIN 19605, DIN 19643, DIN 2000
Chemical Analysis :
• Carbon: approx 92%
• Moisture: approx 2.0%
• Ash: approx 3.5%
• Volatile Matter: approx 5.5%
• Acid Solubility: (19% HCl):0.5%
• Physical Parameters : Bulk density: approx 730 kg/cum
• Bulk volume : 1.37m^3 /tone
• Density : 1.4-1.45 gms/cm^3
• Porosity < 10%
• Hardness: approx : 4 Mohs
• Hardgrove : 32-34 HGI
• Grain size : 0.8 to 1.6 mm
Grannular Activated Carbon (GAC)
Shell carbon is activated by exposing it to a steam air mixture and crushed and
screened to obtain the desired particle size. GAC is used
like filter media. It can be
used as a partial or complete replacement for existing media in a conventional based on types of organic compounds and suspended impurities to be removed in the plant layout. It can also be installed in separate closed pressure vessels .
A minimum depth of 600 mm
of GAC suggested to provide effective removal of turbidity and most organic compounds causing tastes and odours.
GAC has proven to be as good
a filtering media as sand or anthracite coal and is available in the same particle size ranges. The bed expansion of 600 mm is to be allowed for during backwash and wash water troughs to be located suitably.
• Oversize % 5 Max
• Undersize% 5% Max
• Moisture% 5 Max
• Ash % 5 Max
• Apparent density 450 min
• Iodine Value 500/800
All the filter media are securely packed in bags of 25/50 kg and despatched within 4 to 6 weeks of order.
Unit Process
Filtration
It is basically a process for separating suspended and colloidal impurities from water
by passage through a porous granular media. The granular media in use include Sand, Anthracite (hard) coal, granular activated carbon used in single or multiple layers.
A. The Sand Filter comprises of a bed of sand serving as
a single medium granular matrix, supported on gravels overlaying an under drainage system. When water containing suspended and colloidal
solids is applied to the top
of the filter bed, suspended and colloidal solids are left behind in the sand matrix.
The standard rate of filtration through a rapid sand filter is 80 to 100 lpm/sqm. (4.8 -6 m/hr). The effective size of the sand may vary between 0.45 and 0.8 with 0.45mm being preferred. The sand is silica sand with a specific gravity 2.65.
The filter gravels are placed between the sand and the underdrainage system to prevent sand from entering the underdrains and to aid uniform distribution of wash water. The gravels should accomplish both these purposes without being displaced by the backwash mechanism. Sizes of gravel vary from 50mm size at the bottom to 2 to 5 mm size at top and
an over all depth of 450mm. (Ref IS : 8419 (Part 1) 1977). The filter gravels shall be as spherical as possible, hard, clean and uniform in quality and shall not contain impurities such as dirt and clay.
B . Dual Media filters are filters containing two media and have been successfully operated at rates of filtration ranging from 15 to 20 m^3/m^2/hr with acceptable filtrate quality. In general it is recommended to operate dual media filters at higher rates of 7.5 to 12 m^3/ m^2/hr.
With a view to maintain coarse to fine gradation of pore
sizes and pore volume with increasing depth of filter bed, two different granular media of different density and sizes are chosen. The top layer consists of a lower density material anthracite coal having larger particle size over a layer of high density material like silica sand having smaller diameter particles. It is recommended that 0.3 -0.5 m of anthracite coal of effective size 1.0 to
1.6 mm ( specific gravity 1.4 to 1.55) be used above a sand layer 0.15 to 0.3m.
Capping of Sand Filters
Rapid sand filters can be converted for mixed media operation to increase capacity by 100%.
Adsorption
Amajor goal in water treatment is to produce clear, good tasting water. Adsorption has been used for many years to achieve this goal by removing organics that cause tastes, odours and colours in drinking water. It is also an important method for protecting public health by removing toxic organic chemicals from drinking water. Adsorption works on the principle of ADHESION. The organic contaminants are attracted to the adsorbing material and adhere to its surface by a combination of complex physical forces and chemical action. Activated carbon is an excellent adsorbent since it has a vast network of pores that vary in size to accept large and small molecules of contaminants. A kilogram of activated carbon has a total surface area of about 300 acres which can trap and hold over half a kilogram of carbon tetra chloride. These pores are created during the manufacturing process by exposing the carbon to very high heat of 900 deg C in the presence of steam. This process known as activation oxidizes all the particles on the surfaces of the carbon particles, leaving the surfaces free to attract and hold organics. Once the surface of the pores are covered , it loses its capacity to adsorb. The spent carbon must then be replaced or it can be reactivated by essentially the same process.