WCS WPL VSF04, Руководство по эксплуатации и обслуживанию, Страница: 16 / 26

Operation & Maintenance Manual
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8. PLANT DESCRIPTION
This description is only supplied for interest and is not essential reading for plant installation, operation or
maintenance.
8.1 Plant Description
The sand filter will be supplied as a one-piece unit, the function and operation is as follows: -
The WPL sand filter has been designed to physically filter an effluent that has already undergone primary
settlement and biological treatment. The sand filter is composed of two chambers; the inner filter
chamber contains a graded granular material referred to as sand. The sand sits on a perforated steel
plate, which is installed approximately 450mm above the floor of the inner chamber.
Effluent flows into the inner chamber, where the head differential between the water level in the inner
and outer chambers forces it through the sand and the perforated steel plate, into the outer holding
chamber and ultimately out of the outlet.
As the filtering sand becomes blocked by contaminants, the passage of effluent is restricted and causes a
backup in the filter chamber. This back up is monitored by a sensing device and at a pre-determined level
the device activates a relay in the control panel to open one part of the “back - wash cycle” circuitry. The
other part of the back-wash cycle circuitry is activated by a timer. Both the relay and the timer must be
activated to initiate a back-wash cycle. During a back-wash cycle, a pump in the inner chamber pumps
the effluent back to the beginning of the entire treatment system. This lowers the level in the filter
chamber causing a reversal of flow through the sand. In conjunction with this, air is introduced under the
steel plate, which bubbles through the sand and “scours” the contaminates off of the sand and puts them
back into suspension in the effluent, which in turn is removed by the pump.
The timer should be set to come on during the periods of a low flow entering the beginning of the entire
treatment system. This is to prevent a combination of new effluent and back-wash water overloading the
system.
WPL sand filters are immediately effective once they are commissioned.