Located on a vast site in North London, Deephams is one of the capital’s largest facilities. It provides sewage treatment and sludge processing to a population of 891,000 as well as storm water storage. The plant services three major sewers at different levels with a dry weather flow of 232,000 cubic metres a day.
Kier was involved in a Thames Water’s project at Deephams to upgrade the 50-year-old site to meet new Environment Agency sewage treatment standards. The site also needed to meet the needs of approximately one million people, reduce odour and improve the quality of discharge into the River Lea. The challenge at Deephams was to demolish and rebuild the sewerage works, whilst not compromising the quality of the treatment process. This involved having a good knowledge of the treatment process to intercept and change the route flows to suit the programme.
We aimed for a highly sustainable design to meet the client’s requirements. To achieve this each design was challenged and all options were considered to calculate whole life costs and to gain best value for money. A combined heat and power system turned methane gases into electricity to power the whole sewage treatment plant. This generated £1m revenue from surplus electricity by sending it back to the grid.
Directly next to the works there is a site of special scientific interest and a housing estate, so achieving planning permission was a significant challenge. To achieve consent we looked at each individual part of the works to learn the impact to the local environment and community.
The old finals settlement tanks were demolished and replaced by the largest in Britain. The walls were formed with 5m square precast panels. 600 precast panels created 10 settlement tanks, each 45 metres in diameter.
Construction activities included a large amount of temporary works including:
- De-watering works
- Sheet piled cofferdams
- Extensive diamond drilling
- Complex formwork and falsework designs
- Temporary flow diversion channels
- Soil stabilisation
- Muck storage
The permanent works involved:
- Large RC structures
- Sewer culverts
- Complex MEICA systems worth £50m
- Odour control systems that capture and treat the odour to achieve a 99% odour reduction
The project was achieved without expanding the footprint of the works and without interrupting the daily flow of sewage. The reconstruction of the works highlighted a range of cutting-edge innovations. We focused on increased operational safety, sustainable building techniques and extensive hydraulic modelling to provide significant capacity improvements to the sewage treatment works. We were told by our client, Thames Water, that our design – to put new plant within the existing footprint, with increased capacity – was “dripping with innovation.” The results of this approach enabled us to reuse and change existing structures by incorporating them into the final design. We added 2m of height to the treatment plant process to prevent a backflow of water into the treatment facility should the river flood.
By pre-casting a number of infrastructure elements we were able to achieve faster installation, unaffected by the vagaries of the Winter weather, with units arriving just in time to limit material storage. The intensity of construction operations was therefore reduced, and we were able to achieve enhanced durability, allowing the new structures to cope with fluctuating levels of liquid affecting these elements relentlessly. Our neighbours benefited from reduced lorry movements on the surrounding residential roads, as well as less noise, and the site was also a safer place of work through the elimination of working at height.
" The interface with the Thames Water Operations Team was critical to the works as sewage treatment never stops on site. In case of storm flow conditions - where there is a danger of flooding - an emergency plan was jointly developed to alter the sewage flow routes to accommodate the increased volume of water and provide a safe system of working for construction operatives. "
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