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Run Phase
Once the rinse phase has completed the filter may be placed back into service mode. The transition should be slow; a
minimum time of 30 to 60 seconds should be taken to avoid any disturbance of the bed.
The water flow through media bed filters should never be turned off to avoid the development of anoxic conditions. By way
of example, if a filter was removing arsenic from the water, the arsenic is in the form of As5+ which is insoluble. If the filter
flow was stopped, organic matter and bacterium growing on the media and in the filter, would consume the oxygen, the
redox potential would drop and the arsenic would be reduced to As3+ which is soluble. When the filter goes back-on-line
the arsenic would be released into the product water. The issues are not as serious for media that do not biofoul. however,
it is good practice never to turn off the water flow. The schematic below displays a possible configuration for a filtration
systems that runs continuously but delivers a variable flow.
If the filters are turned off for a long period, it is best to backwash before they are turned off and/or when they are turned
back on again.
Water flow through the filters should be smooth and constant, if a change of flow is required, then take at least 30 seconds
to regulate the flow down or up.