A standard test for filter media cleanliness

Abstract

Rapid sand filters are expected to produce clean, safe water, without interruption, for many years. Unfortunately, filters very often develop some problems during this time, most of which only become apparent when the damage is already done. Routine measurement of filter media cleanliness could provide the necessary early warning, which is the reason why the American Water Works Association (AWWA) suggested a media cleanliness test for inclusion in a structured filter assessment programme at drinking water treatment plants. After performing such assessments at 3 South African water treatment plants, the authors found that the results were not consistent, the turbidity could not be measured easily and the guideline values seemed to be excessively conservative. This led to an investigation to find a method for stripping the filter deposits from the media grains with an easy, reproducible method, and for characterising the stripped deposits.

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