Mogden Sewage Treatment Works

Built in 1931–36 by Middlesex County Council and now operated by Thames Water, it is the third largest sewage works in the United Kingdom.

The Middlesex County Council Act 1931 is solely devoted to the scheme's construction and mitigations, comprising 78 sections and three schedules.

The sewerage district (catchment) was defined as those districts named after: Brentford & Chiswick, Ealing, Feltham, Harrow, Hayes & Harlington, Hendon (both), Heston & Isleworth, Kingsbury, Ruislip-Northwood, Southall-Norwood, Staines, Sunbury-on-Thames, Teddington, Uxbridge, Wealdstone, Wembley, Yiewsley & West Drayton.

[5] The council enlarged the sewage operation at Mogden Farm, buying 101 acres (41 ha) of it,[6] after the public and Duke of Northumberland objected to a Syon Park proposal.

[9] The plant began operations in late 1935[10] and was formally opened with the rest of the scheme on 23 October 1936 by the then Minister of Health, Sir Kingsley Wood.

[12] From 1935 the treatment facilities at Mogden comprised storm water tanks, primary sedimentation, sewage aeration, final separation and sludge digestion.

[11][20] In 1989 the Perry Oaks site was closed and the land reclaimed for Heathrow Terminal 5 with new sludge dewatering provided at nearby Iver South.

[26][27] In January 2022 a report published by the Environmental Audit Committee found that Mogden discharged enough sewage to fill 400 Olympic-sized swimming pools on 3 and 4 October 2020.