What simple media tests can tell you about filter problems and rehabilitation

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