Continuous Sand Filters

The dirty sand is continuously removed from the active sand bed (A) thanks to the action of the air-lift pump (C), which sucks the contaminated sand from the bottom (B) of the filter body. A mixture of sand, dirty particles and water is transported upward through the air-lift pipe into the washing chamber at the top of the filter.

The separation of impurities from the sand takes place in the exclusive washing system. This is accomplished through the simultaneous action of both counter current water and air injected at the bottom of the washing chamber. The sand is returned by gravity to the top of the active sand bed (A) after being directed downward through a labyrinth of several settling steps.

The feed water is fed into the filter at the base of the active sand bed through the distribution ring (D). It then flows upward through the downward moving sand bed where the solids are intercepted. The clean filtrate exists the filter through the overflow weir (E). The continuous reject flow of washing water is discharged through a separate outlet.

Main Advantages

• Unique continuous back-washing system uses 50% raw water in place of filtered water
• High efficiency in removing fine solids including colloidal particles
• Easy maintenance thanks to an external sand air-lift system
• Easy installation
• Very low operational head loss allows gravity feed in many instances
• Low capital and operating costs

Typical Applications

• Surface water filtration
• Drinking water treatment
• Municipal/industrial WWTP (primary filtration)
• Municipal/industrial WWTP (tertiary treatment)
• Mill scale cooling water treatment
• Algae removal
• Pre-treatment for membrane ultra-filtration plant
• Pre-treatment for ozonisation treatment plant
• Final treatment with active carbon
• Biological denitrification

Materials

All wetted parts are in stainless steel ASI 304.

Special constructions available on request.