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Severn Trent Services has been selected to supply Tetra LP Block filter underdrain systems, for use in pre-treatment filtration systems at two desalination plants in North Africa and South America.

The Tetra LP Block system will form the floors of the rapid gravity sand filters that will treat seawater prior to desalination by reverse osmosis membranes.

The Tetra LP Block floor supports the sand media during filter operation and provides excellent distribution of air and water during backwashing, to enhance filter cleaning and extend run times.

The filter for the 300 million litres per day (MLD) plant in North Africa will employ more than 3,500 Tetra LP Blocks across 20 cells, each 5m wide and 15.5m in length, while the 400MLD South American plant will use a total of 4,500 blocks in 18 cells, each measuring 19m x 6m.

The Tetra LP Block is a dual parallel lateral underdrain system constructed from high-density polyethylene moulded plastic blocks that provide effective distribution of air and water for concurrent or sequential backwashing.

The lightweight construction and easy assembly and installation of the system make it suitable for new and retrofit filter underdrain applications.

A design for the backwash air and water distribution system, Tetra Flumeflow, has been introduced to the European market.

The Tetra Flumeflow will be installed at both plants, which will ensure further capital cost reductions.

The system design is employed with the Tetra LP Block filter floor system to negate the need for a separate air header for the distribution of backwash air and water from a central culvert.

Additional benefits of the Tetra Flumeflow system include increased flexibility when positioning laterals in the filter bed, prevention of air and water leakage, grout grip technology for additional stability, and even distribution between laterals, ensuring efficient and effective cleaning of dirty media.

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