Multi Media Filter

Pre Treatment Before Adsorption Polishing

The SorbiTech Multi Media Filter is the pre treatment workhorse that sits upstream of every activated carbon polishing bed, reverse osmosis membrane, and process reuse train. The graded media bed (anthracite on top for the coarse retention, silica sand in the middle for the fine retention, garnet at the bottom for the underdrain support) captures suspended solids and turbidity that would otherwise blind the downstream adsorbent. Outlet turbidity below 1 NTU protects the carbon bed campaign life and the membrane element service interval.

Bed Design and Backwash Cycle

The standard bed is 600 mm anthracite at the top, 400 mm silica sand in the middle, 100 mm garnet at the bottom, supported on a wedge wire underdrain. Service flow runs at 10 to 20 m/h face velocity; backwash flow at 30 to 50 m/h lifts the bed by 20 to 30 percent to restratify and discharge the captured solids. Backwash interval is typically 24 to 72 hours depending on the inlet load. Air scour before water backwash improves the cleaning efficiency on biologically active raw waters.

Scope of Supply

The complete package includes:

• Pressure vessel (ASME VIII) or open gravity basin (concrete or steel)
• Graded media charge: anthracite, silica sand, garnet
• Wedge wire or strainer underdrain
• Inlet diffuser and outlet collector
• Backwash valves, flow meter, and controls
• Air scour blower and distribution lateral
• Differential pressure transmitter and turbidity meter

Where It Fits

Upstream of coalescing filtration for oily water polishing; upstream of GAC 1240 for taste, odour, and dissolved organic carbon removal; upstream of reverse osmosis to protect the membrane element. Applications span drinking water treatment across the municipal water and industrial water sectors.

Lifecycle

The graded media bed gives 5 to 8 years of service before partial replacement. Anthracite and garnet typically last the longest; silica sand needs makeup every 3 to 5 years to compensate for backwash loss. SorbiTech supplies the media replacement charge through SorbiTech with documented size grading.