Blog: Offsite SECBE Awards 2019 finalist - Deephams Waste Water Treatment Works

28 May 2019

Sponsored by Heathrow Limited

Deephams Waste Water Treatment Works - submitted by Kier

A lot happened at Deephams as it was a huge upgrade project on a 170-acre site. They had to bring it up-to-date in terms of output, energy generation and odour control, while continuing to process the waste of the 800,000 people. Achieving this took a lot of effort by everyone on site - from the customer liaison operation working to keep Deephams’ neighbours on board during the work to the men and women of AMK, the joint venture of AECOM, Murphy and Kier that carried out the project.

The joint venture worked closely with Thames Water to design and build the solution that met the requirements of the client’s brief within a congested operational site. The many civil and hydraulic technical design challenges of the project were overcome through clever thinking, to provide operational flexibility and added value. The design team worked closely with the construction team to ensure that designs could be built safely.

The new works use only two thirds of the original footprint and freed up valuable land for Thames Water to potentially build additional treatment facilities on the site in the future, as may be required to meet further potential water quality improvements and treating sewage flows from the ever-increasing population.

Choice of precast concrete

It was beneficial to precast the concrete elements of this project offsite for a number of reasons. The greater speed of construction of so many repetitive structures involving curves and complex shapes was a persuasive factor. The units arrived on site based on the just-in-time delivery system, according to a reliable schedule unaffected by the winter weather conditions. This control over the schedule, the casting conditions and the logistics was an overriding factor considering the intensity of the construction operations in such a short period. In tandem with a reduction in the need for skilled trades people, time consuming site operations associated with in-situ concrete were eliminated such as formwork erection and stripping periods, implementing curing measures and waiting for strength gain.

The enhanced durability of the precast concrete was a benefit for Kier's client as owner of a sewage works with fluctuating levels of liquid affecting the structural elements relentlessly. This influenced both the enriched content of the concrete and its finish. The site's neighbours benefited from reduced lorry movements on surrounding residential roads, less noise from concrete vibrators, pumps and trucks. The site was a safer place of work through the elimination of working at height. The need to send finished drawings to the precast factory provided a discipline that was built in to the design process.

Extra value

A combined heat and power engine system that is essentially a mini-power station turns captured methane gases into electricity to power the whole sewage treatment plant and generate £1m revenue from surplus electricity by sending it back to the grid.

AMK JV aimed for a highly sustainable design to meet the client’s requirements. Each design was challenged and options considered to calculate the whole life costs for each part of the infrastructure to gain best value for money. The results of this approach enabled Kier to reuse and modify existing structures incorporating them into the final design. They calculated the most hydraulic profile for the process works when producing the design, adding 2m of height to the treatment plant process to prevent a backflow of water into the treatment facility should the river flood.

Highlights:

• Deephams waste water treatment plant was the subject of Thames Water’s £196m upgrade project. The upgrade enabled the works to: meet the new Environment Agency sewage treatment standards that came into force from 2017, meet the needs of approximately one million people in the near future, and reduce odour and improve the quality of discharge into the River Lea.
• Located on a vast but constricted urban site in North London, Deephams sewage treatment works is one of the capital’s largest facilities. It provides primary, secondary and tertiary treatment, plus sludge processing, to a current population of 891,000 as well as storm water storage. The plant services three major sewers entering the works at different levels with a dry weather flow of 232,000 cubic metres per day.
• Kier's challenge at Deephams was to demolish and rebuild the sewerage works whilst not compromising the quality of the treatment process. This involved having a complete knowledge of the sewage treatment process to enable smart flow management strategies to intercept and change the route flows to suit the construction programme. 21 other sites for a completely new treatment plant were considered before opting for the upgrade of the existing location while it remained in operation.

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The SECBE 2019 Offsite Award is sponsored by Heathrow Limited.