Filtec :: Media
Media selection and its placement are two of the most important aspects of any filter refurbishment project as these directly affect the resulting efficiency and quality of output.
Treatment plant custodians should consider all aspects of the work as short term cost savings can lead to an overall increase in life cycle costs where compromises in either filter media quality or the choice of contractors are made.
| Media Selection |
| The choice of filter media and support layers is dependant on the required filtration rate, the water being treated and the use for the resulting filtered water. Other factors affecting the media choice include the ambient temperature and the local environment which can, seasonally, change the treatment water significantly as to warrant additional filter media to be able to handle changes. |
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Filtration Sand
The standard filter medium for water treatment normally available from suppliers in various grades depending on application e.g. slow sand filter, rapid gravity filters. Size defined as either a mesh size or, more commonly, as a BS ( British Standard ) spec e.g. BS16/30 |
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Support Gravels
Various sizes of gravel are available . Support gravel used as the first layer in filter bed and should be installed and levelled off prior to any other media placement. During the backwash cycle this layer of support media should not be disturbed ( this is why the selection of grade size is very important ) . |
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Garnet Sand
Normally used in multimedia filter applications to trap smaller particulates where normal filter sands do not provide the required inter-grain sizes. Its specific gravity and small size will ensure that it is found closest to the filter nozzles which must be chosen to prevent media migration. |
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Anthracite
Typically found in dual media filters it is used to increase filter runs due to its relative bulk density and coarseness which makes it suitable to trap larger particulates at the top of the filter bed. |
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Activated Carbon
Relatively expensive filter media used , primarily , for taste and odour removal with other uses such as dechlorination and organics removal. Manufactured from coconut shell and coal based carbons using a thermal process it contains thousands of pores. It is these pores which trap organics and chlorine. |
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Manganese Dioxide
Principally found mixed with normal filter sand to remove both iron and manganese from potable water where there is an increased concentration of those elements in the treatment liquor. The use of manganese dioxide will normally reduce the concentration of Manganese and Iron in water from 0.5mg/l and 3mg/l to 0.02mg/l and 0.05mg/l respectively ( given the correct conditions of alkalinity and pH ). |
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Media Placement -Typical Process |
| Typical process in filter media placement project is shown in the diagram opposite. Please click on the stages of interest in the diagram for more information on the actual process involved. |
| 1.
Air Scour pattern tests conducted to ensure that the current filter plant is operating normally so that any subsequent backwashes and pattern tests can be conducted. |
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| 2.
Any problems identified in the air scour tests are investigated and a report provided detailing causes and recommended remedial work together with any anticipated costs associated with the repairs |
| 3.
Existing media is removed using appropriate plant equipment ( dry or wet vacuum tankers ) and disposed of according to appropriate legislation and industry recommendations. |
| 4.
Powerwashing existing structures removes slime build up for any subsequent inspections. |
| 5.
After washing both the filter walls / structures and filter components are inspected to determine their status. Endoscopic inspections ( if required) may be carried out at this point to determine the status of lateral pipework/plenum chambers. |
6.
Any problems e.g. damaged nozzles, wall structure problems, sealant joint integrity etc. are identified and a report submitted to the client for their information.
The client will be encouraged to inspect any remedial works carried out on their behalf. |
| 7.
Support layer(s) are installed using approved grades of media to ensure proper operation after commissioning. Support layer(s) are levelled off correctly to minimise localised problem areas in operation. Deformations in the support layer(s) can lead to early refurbishment requirements and lower efficiency in backwash cycles. |
| 8.
Filter media ( filter sand, anthracite ) is now placed carefully to prevent distortion to the support layers. Media grade(s) are carefully selected to give optimum filter efficiencies. |
9.
Filter is now backwashed ( normally twice ) to remove any fine particles of filter media which may present in any new filter media. Backwashing also forms part of the customer acceptance and gives confidence in the overall operation of the plant.
Summary of the whole project is supplied to the client for their information and acceptance. |
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