Sewage Treatment Plant - Filter Feed Pumps Types and Operation And Maintenance Considerations

FILTER FEED PUMPS

Filter Feed Pumps are used to draw water from the clarified water sump and pass it through the Pressure Sand Filter (PSF) and Activated Carbon Filter (ACF), which are installed in series to improve water quality.PRESSURE SAND FILTER (PSF)

Working Principle:

The upper layers of sand perform the actual filtration function, while gravel layers provide physical support.

Specialized sand with a specific particle size is used to trap solid impurities present in water.

The particles get entrapped in the spaces between sand grains, eventually blocking water flow.

When the pressure drops beyond a set limit, the sand is cleaned by backwashing with water.

Backwashing reverses the flow, fluidizing the sand bed and removing lighter solid particles as waste.

Operation And Maintenance Considerations

• Filtration is followed by a short backwash sequence.
• The filter requires backwashing when the pressure drop across the filter reaches 0.5 kg/cm².
• Best practice: Backwash once per shift, regardless of pressure loss.
• A typical 5 to 10 minute backwash removes all accumulated impurities.

ACTIVATED CARBON FILTER (ACF)

Function:

The Activated Carbon Filter receives pre filtered water from the PSF and enhances water quality by reducing:

• Biochemical Oxygen Demand (BOD)
• Chemical Oxygen Demand (COD)
• Clarity (Turbidity)
• Colour and Odour

Uses adsorption action of activated carbon, typically derived from coconut shell or charcoal.

Working Principle:

Water flows through the activated carbon bed, where contaminants get adsorbed onto the surface.

Unlike sand filters, trapped molecules in the carbon cannot be backwashed.

Exhausted carbon is removed and replaced with fresh activated carbon.

Operation and Maintenance Considerations:

• Similar to PSF, the ACF also requires occasional backwashing to dislodge solid particles.
• When no improvement in water quality is observed, carbon replacement is required.
• Spent carbon must be disposed of properly, and new activated carbon should be charged into the filter.

Filter Feed Pumps play a crucial role in industrial water treatment, ensuring efficient removal of contaminants through Pressure Sand Filters and Activated Carbon Filters. Proper maintenance, routine backwashing, and timely replacement of filtration media ensure optimal performance and longevity of the system.