Moulded air and water distribution blocks that form the filter tank bottom — how the brick layout works, how the bottom is installed, specification data and applications.
← Back to Denitrification Filter BrickA denitrification filter brick is a moulded block that is laid in rows on the concrete floor of a filter tank to build the filter bottom, or underdrain. In this application the tank is usually a deep-bed down-flow filter for nitrogen removal, or a biological aerated filter (BAF) working on the same principle: the water passes down through a granular bed, and the bed is periodically cleaned by backwashing with water, with air or with both together.
Unlike a nozzle deck, which distributes through individual nozzles fitted into a plate, a brick bottom is made of repeated identical blocks. Each block is a moulding of a fixed profile, and the blocks are placed side by side and end to end so that the channels formed inside the mouldings join up along the row. The result is a continuous collection and distribution surface that reaches the full plan area of the tank.
Within this product family the common block profiles are known as S-type, T-type and U-type filter bricks. They are also sold under the names air-water distribution block, filter block and underdrain block. The profile, block dimensions and channel arrangement are confirmed against the project, not taken from a fixed catalogue.
A brick bottom works as a secondary distribution stage. Water or air enters the filter tank plenum or inlet channel, then moves along the channels moulded inside the brick rows before being released through the slots of each block and into the support gravel and media above. Distributing in two stages is what allows the flow to be spread evenly over a large tank floor.
The number of distribution stages, the slot arrangement and the open area of the blocks are set by the tank designer together with the media depth and the backwash rates. They are confirmed for each project.
The exact sequence is set by the contractor's method statement for the project; the steps below describe how a brick bottom is normally built, and match the site photographs in the product gallery.
Bricks are supplied in banded and strapped units on pallets; a damaged block can be lifted individually during maintenance.
Where a continuous cast-in-place concrete nozzle deck is preferred instead of a brick bottom, see the BS Cast-in-place Filter Plate; the matching nozzles are shown on the ABS Filter Nozzle page.
Configuration is confirmed against the project drawing. Parameters marked on request are quoted for the specific tank, block profile and backwash duty rather than taken from a fixed catalogue, and no performance figures should be read into them.
| Parameter | Value |
|---|---|
| Product type | Moulded air and water distribution filter brick (underdrain block) |
| Typical use | Denitrification filters, biological aerated filters (BAF), deep-bed down-flow filters |
| Block profile | S-type and T-type profiles; U-type on request — final profile confirmed per project |
| Material | On request — moulded thermoplastic (HDPE) compound, confirmed by grade |
| Nominal block dimensions (L × W × H) | On request |
| Block mass | On request |
| Joint between blocks | On request — locating edges and any capping plate confirmed with the profile |
| Water distribution channel | On request — confirmed against the tank layout and backwash duty |
| Air distribution / air-scour channel | On request |
| Slot / orifice arrangement and open area | On request |
| Block compressive strength | On request |
| Colour | On request — grey, blue and black mouldings are shown in the gallery |
| Support gravel grading above the blocks | On request — matched to the media and the backwash rate |
| Media type and depth above the blocks | On request — chosen for the denitrification or filtration duty |
| Bricks per square metre of tank floor | On request — calculated from the tank plan and the block footprint |
| Installation | Blocks laid by hand in rows on the prepared tank floor, with support gravel and media placed above |
| Export packing | On request — banded and strapped units on pallets |
| MOQ / price | On request — confirm the tank plan, quantity & destination |
Send the following and we will come back with the brick layout, the number of blocks and the export packing:
If those details are not fixed yet, tell us the filter duty and the tank size instead — we will work from that.
Parameters are confirmed per project; items shown as on request are not fixed catalogue values and should not be read as published performance figures. Block profile, dimensions, material grade, slot arrangement and support gravel grading are confirmed against your project specification before order. Price is on request and is not published on this site.