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Technical information

Evaluation method of filter media in use

We evaluate the management of filter media according to the filter media for water supply (JWWA A 103-1988) established by the Japan Water Works Association.
The table below summarizes the test methods for each item and the meanings of those items.

item Description
appearance Visually check the appearance (shape) of the filter media and whether impurities are mixed.
There are different standards depending on the filter material. In the case of filtered sand, there are few impurities, flat or fragile sand, and iron sand, and in the case of anthracite, there are few fine powder, flat, and scaly ones. It is determined that the content of impurities such as crushed stone and peat is low.
Effective diameter The 10% passage diameter of the particle size addition curve is expressed in mm, and is widely used as a representative diameter of filter media.
Equal coefficient The ratio of the 60% pass diameter to the 10% pass diameter of the particle size addition curve is an index showing the uniformity of the filter media particle size.
Cleaning turbidity The dirt that peels off by mixing the filter material and purified water and shaking vigorously is quantified as turbidity.
It is an index of the cleanliness (dirt limit) of the filter material.
Ignition weight loss It is calculated from the mass lost when the filter material is heated at 925 ± 25 ° C for 30 minutes.
It is an index of the degree of contamination of organic impurities contained in the filter medium and impurities such as coal grains, limestone and shells.
density Indicates the mass per unit volume of the filter medium.
In the case of anthracite and filtered sand, ores such as limestone and heavy metals may be mixed in if the density changes.
The density without voids in the filter media is called the density or true density, and the density with voids in the filter media is called the apparent density.
Abrasion rate Put 5 6.5mm steel balls and 50g of filter media in a brass or stainless steel cylinder that can be sealed, shake vigorously up and down, and calculate from the ratio of crushing (0.300mm or less). This is an index of the resistance to crushing and wear due to backwashing.
Hydrochloric acid solubility The filter medium is immersed in hydrochloric acid (1 + 1) at 36 ± 1 ° C for 1 hour, and is calculated from the rate of dissolution and loss.
It is an index of the content of substances (metals such as limestone, shells and iron) that are dissolved by hydrochloric acid.


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