Abstract
Abstract:
Rapid sand filters are expected to continuously produce clean, safe water for many years, during
which time some of these filters will inevitably develop some problems. These problems are
usually only apparent once the damage is already done, thereby causing expenditure and
inconvenience due to rehabilitation. However, if the cleanliness of the media grains is routinely
measured, the potential for some of the more serious problems could be detected at an early stage
and measures taken to alleviate such problems before serious damage occurs.
In 2002 and 2003, the Water Research Group at the Rand Afrikaans University developed a
number of tests to quantify filter media cleanliness in a simple yet standard manner. These tests
provide information in two important areas. Firstly, they alert the operator when media does not
meet an acceptable standard for cleanliness after backwashing. Secondly, they provide pointers to
the nature of the residual deposit on the media, suggesting why the media have not been properly
cleaned during backwashing.
These tests are currently being benchmarked by a series of trials at a number of South African
water treatment plants. This paper will provide the details of these tests, together with practical
limits for the different parameters. It should make a valuable contribution towards early detection
and troubleshooting of filtration problems by operators and managers.