Ashford Common water treatment works
Ashford Common water treatment works is located in Ashford Surrey and supplies potable water to west London via the local distribution network and the Thames Water ring main. The works were constructed in the 1950s, and were modernised in the 1990s to increase the output.
History
In the immediate post second world war period it was envisaged the demand for water in London would increase significantly. In 1947 the Metropolitan Water Board proposed to construct a new water treatment works between Ashford and Sunbury-on-Thames, Surrey, (51.41772°N 0.43802°W) The works would draw water from the adjacent Queen Mary Reservoir or from the Staines Reservoir Aqueduct.[1] The plant and treatment processes would comprise: aeration of the feed water, fine screen filtration to remove algae, slow sand filtration, granular carbon treatment, sterilization and contact tanks. Rotating screens were identified as the most effective primary filtration for algal removal.[1]
By 1953 the Ashford Common works were under construction.[2] There were 23 micro-strainers and 32 slow sand filter beds each of about ¾ of an acre (3345 m2). The slow sand filters were cleaned on a 25 to 30 day cycle. This entailed skimming off the top 25 to 40 mm of sand which was cleaned and returned. The works were fully commissioned in 1958. The total treatment capacity was 108 million US gallons per day (409 Ml/d). The peak output was 480 Ml/d, higher flows up to 550 Ml/d were possible but significantly increased the frequency of filter cleaning.[2]
Modernisation
The Ashford Common water works operated effectively for four decades. In the early 1990s the projected increase in demand for water was met by increasing the hydraulic capacity of Coppermills, Hampton and Ashford Common water treatment works.[3]
The facilities at Ashford Common comprised:[3]
- Stored water pumps from Queen Mary and Wraysbury reservoirs, 730 Ml/d
- Pre Ozonisation (5 minutes contact)
- Rapid gravity primary filters, dual media, air scour and water backwash
- Main Ozonisation (16 minutes contact)
- Slow sand filters with granular activated carbon sandwich (300 mm lower sand, 135 mm GAC, 420 upper sand)
- Low lift pumps
- Hypochlorite dosing
- Contact tank screens 400 μm mesh
- Chlorine contact tank
- Hypochlorite, Sodium bisulfite and Ammonia dosing
- High lift pumps
- Water distribution and supply
Subsidiary plant included Ozone generation, washwater treatment plant, and SCADA to monitor and control the flow of water.
With all these facilities operational the peak supply increased from 480 Ml/d to 690 Ml/d.[3]
See also
References
- Schliessmann, D. J. (1948). "Public Health Engineering Abstracts". Public Health Engineering Abstracts. 28: 68.
- Hazan, Richard (July 1953). "Application of the Microstrainer to Water Treatment in Great Britain". Journal of the American Water Works Association. 45 (7): 723–37. doi:10.1002/j.1551-8833.1953.tb20172.x.
- Glendinning, D. J. (February 1996). "Uprating water treatment works supplying the Thames Water ring main". Water and Environment Journal. 10: 17–23. doi:10.1111/j.1747-6593.1996.tb00003.x.