Process Description
Gravity media filtration is effective in reducing turbidity, foul taste, and odor by removing impurities through chemical absorption and physical straining of the water between the media material. The example above illustrates a media filtration process utilizing a sand filter. In this, process water flows through a sand filter which is filled with select types of media material (depending on the application). The sand filter removes select impurities and/or flocculation from the treated water. Industrial applications can have as many as four sand filters in series, depending on process requirements. Common issues in media filtration include:
- Impurities such as: Silt, Clay, Flocculants, Colloids (bacteria, plankton), Iron, Manganese, Arsenic, Chlorine
- Types of media: Activated Carbon, Anthracite, Green Sand, Garnet sand, Gravel, Earth
- Gravity feed : Water height or head above the media forces the water through the filter media.
- Pressure Media Filtration: Is the same as gravity media filtration with the exception that the media is in a rated pressure vessel and dirty water is introduced under pressure through distributors at a point just above the media. This type of filter can process higher volumes of water than a comparable gravity filter. The pressure drop (ΔP) across the media in a pressure filter is critical to the life of the media. Backwash must be initiated when the ΔP reaches a predetermined set point.
Measurements in Media Filtration
Flow:
- Monitors the influent water stream and tracks the total volume of water processed through the media. This may be used for initiating backwash and planning maintenance on the system.
- Monitors the use of the product water being used in the application.
Pressure: Pressure and pressure differential are used to protect filter media and membanes in pressure filter and reverse osmosis units. When a pre-set level of pressure differential is reached across the filter bed, this condition initiates the backwash cycle. A second pressure differential switch can be used for an alarm.
Turbidity:
A Turbidimeter detects the presence of un-dissolved matter and suspended solids in water. These impurities make water opaque to light. These same impurities can also provide food and shelter for algae and pathogens. When sheltered, pathogens are less apt to be exposed to disinfectant and with an abundant food source, the pathogens are free to grow and flourish inside a water distribution system.
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