Block filter underdrain used at two large RO desalination plants

Tetra® LP Block™ filter underdrain systems for use in pretreatment filtration systems are being supplied to two desalination plants in North Africa and South America by Severn Trent Services.

The desalination plants have been designed and constructed by Acciona Agua of Spain.

The contracts are the latest of a number of recent orders for the systems in the desalination market, including an order for their use at the largest desalination plant in Europe.

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. The block floor supports the sand media during filter operation and provides good distribution of air and water during backwashing to enhance filter cleaning and extend run times.

The desalination plants are scheduled for commissioning in 2009. The filter for the 300,000 m³/d plant in North Africa will employ more than 3,500 blocks across 20 cells, each 5 x 15.5m, while the 400,000 m³/d South American plant will use a total of 4,500 blocks in 18 cells, each measuring 19 x 6m.

The Tetra LP Block is a dual parallel lateral underdrain system constructed from high-density polyethylene moulded plastic blocks. The lightweight construction and easy assembly and installation of the system make it ideal for both new and retrofit filter underdrain applications.

A new design for the backwash air and water distribution system, Tetra® FlumeFlow™ has been introduced to the European Market. This will be installed at both plants, ensuring further capital cost reductions. The new system design is employed with the 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.

The desalination plants are scheduled for commissioning in 2009.

For more information, contact: Lori Doppelt at Severn Trent Services
Tel: +1 215-007-3727
Email: [email protected]