Mogden Sewage Treatment Works Digester Cleaning

MTS worked closely with the global engineering, consulting and construction company Black and Veatch and Thames Water on improvements to the Mogden Sewage Treatment Works in Twickenham.

The Mogden STW is the third largest in the UK, serving 1.9 million customers. The £150m Tidal Thames Quality Improvements Scheme was designed to increase treatment capacity by around 50% and produce more renewable energy from the site's combined heat and power units.

Thirteen of the sixteen Digesters at Mogden needed thorough cleaning to improve the efficiency of the gas off take system and to mitigate odour release from the Digester roof seals. A rolling programme of works allowed the Digester system to remain operational at all times.

Thames Water were responsible for the isolation and initial draining of each Digester. MTS were contracted to remove the remaining 200m3 of residue (sludge, grit and rag) and dispose of the material offsite. In addition, MTS would carry out a thorough internal wash down of the floors, walls and roof seals.

Complications arose when Thames Water were unable to drain the Digesters to the required residue volumes, leaving at least 500m3 volume in each one. MTS worked proactively with Black and Veatch and Thames Water to develop a cost effective solution where a pumping system and screening unit returned the liquors back to the head of the works and reduced the remaining volume.

MTS completed all works to the agreed programme, with no nuisance odour complaints and no safety issues arising on site, maintaining flexibility to meet the demands of the operational site.

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