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Technical information

Deterioration analysis of filter media

If you continue to use the filter media, it will gradually become contaminated by the substances contained in the raw water. If pollution progresses beyond a certain level, the quality of treated water will deteriorate and the filter layer will be blocked in a short time, which will have a great effect on filtration.
We analyze the filter media received from our customers in accordance with the regulations of the Japan Water Works Association (JWWA A 103: 1988) and evaluate the filter media in use.
Unlike new filter media, there are no clear standards for the filter media in use, so we have set our own safety standards to suggest customers to replace the filter media and improve cleaning methods. I will.
The table below summarizes the test methods for each item and the meanings of those items.

item Description
appearance Visually check the appearance (shape, color, etc.) of the filter media and whether foreign matter is mixed with a microscope.
Deposit test
(Washing turbidity,
amount of adhered substances, etc.)
In the deposit test, the dirt that peels off by mixing the filter material and purified water and shaking vigorously is quantified as turbidity or SS.
Adhesion is defined as a turbid substance that is relatively easy to exfoliate and adheres to the filter medium based on the measurement method.
In other words, it can be considered that the high value of the deposit test is a measure of the turbidity remaining in the tower without being discharged by backwashing, so it is verified whether the washing (backwashing) is carried out stably.
In addition, if the backwash conditions are appropriate, you can see the accumulation of turbidity that cannot be discharged by backwash.
It is also possible to identify the attached substances by performing a water quality analysis of water that measures turbidity and SS.
Adhesion test
(Hydrochloric acid solubility, etc.)
The amount of adhering substance is obtained by immersing the filter material from which the deposits have been peeled off in the deposit test with hydrochloric acid, dissolving the cohesive substance remaining on the filter material, and determining the weight reduction. It is an index of things that cannot be removed by backwashing or airwashing).
An increase in the amount of cohesive material indicates that heavy metals such as iron, manganese, and aluminum derived from a flocculant are attached to the filter medium.
As the particle size and density of the filter media increase, the quality of treated water is likely to deteriorate and cleaning failure is likely to occur.
Madball test In order to estimate how much mudballs are accumulated in the filter layer, the collected filter media is sieved in water, and the ratio is calculated from the volume of mudballs remaining in the sieve net.
If the volume ratio of the madball exceeds 0.2%, the cleaning method needs to be reviewed.
Sieve test Perform a sieving test to calculate the particle size (effective diameter, uniformity coefficient) of the filter media. Evaluate the measurement results by comparing them with new values.
If the particle size is large, it will lead to poor backwashing and deterioration of filtration accuracy.
In addition, if the particle size is small, there is a concern that the filter material may be significantly worn, the thickness of the filter layer of the treated water may be insufficient, and the rate of rise of the head loss may be mixed with fine sand.


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