Articles & Case Studies

Underdrain copes under pressure

Posted: Tuesday 15th December 2009

Hampton Advanced Water Treatment Works (AWTW) is one of the most technologically advanced of its kind. It is Londonís largest water treatment plant with a design capacity of 790,000 m≥/day. Owned by Thames Water, it has a key role as the control centre for the Thames Water Ring Main, the biggest single trunk water distribution system in the United Kingdom.

The works was originally built in the 1850s and the site includes old Victorian buildings, filter beds and some larger water storage beds. Thames Water has made several large investments in the works, particularly with the introduction of Granular Activated Carbon within the Slow Sand Filters.

The completion of a capital investment program in 1998 led to significant improvements. Hampton AWTW provides some of the highest quality drinking water in the world.

On arrival at Hampton, the stored water is fed into an on-site reservoir called the Grand Junction. This small reservoir is predominantly used to blend different source water and balance the flow into the works. There are 32 dual cell filters on site acting as roughing rapid gravity filters before the slow sand filtration process on site.

ITT Water & Wastewater supplied Leopold filter underdrains, together with the main air scour delivery piping and supervision of installation and training services to the contractor Black & Veatch. The filters were redesigned in conjunction with ITT Water & Wastewater to maximize the available underdrain area.

The water is filtered through Primary Rapid Gravity Filters. These filters function in biological mode with no coagulant dose applied. The filters are designed purely to reduce the load from large reservoir algae and thus to lengthen Slow Sand Filter bed run duration. The water from the primaries gravitates under the Grand Junction Reservoir into the K-Shaft, where six pumps lift the water into the Ozone Plant. Most of the Slow

Sand Filters contain a layer of granular activated carbon (GAC, for pesticide reduction) within the sand bed. The Slow Sand Filters are skimmed according to time or head-loss data. Filtrate water is then directed by low lift pumps from the Slow Sand Filters to the disinfection stage. The water is dosed with chlorine prior to the fine micro screens and then flows into the contact tank for disinfection. After disinfection, the water is sulphonated and then ammoniated, prior to being passed into supply with a combined monochloramine residual.

Next door to the works are two officially designated wildlife reserves, the Sunnyside Reservoir and the Stain Hill Reservoirs, which contain flower-rich grassland and habitats for water birds. The Hamptons AWTW well demonstrates the successful accommodation of nature conservation with operational considerations.
Tel: 0115 940 7324

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