Cotton Valley Water Recycling Centre

Teamwork overcoming challenges at Cotton Valley Water Recycling Centre.

The project team at Cotton Valley Water Recycling Centre were tasked with upgrading the sludge treatment centre, taking its capacity from 20,600 TDS to 25,000 TDS, and upgrade the existing pre-digestion Cambi treatment plant from MKI to MKII.

A new 16m high digester tank was designed with the associated pumps and mixing system which would tie into the existing digester systems, thus retaining as much of the original works as possible.

The solution did require a new MCC kiosk and controls as well as a new biogas line to enable the new digester to tie into the existing gas line. There was also a need for an additional cooling tower and heat exchanger with controls, above ground pipes and pipe-bridges as part of the scheme.

To support the construction of the new digester tank, there was a need for excavation of earth and the construction of a new sheet piling retaining wall in order to reinforce the base and structure.

During the excavation, the site team located a number of small services and high voltage cables. This posed a challenge and required the digester to be relocated, the diversion of two high voltage cables and the need for additional retaining walls. There were as many as 16 unidentified cables that were found and the team worked carefully and safely to ensure there were no cable strikes on site. The design team worked quickly to prioritise the redesign in order to keep the project to programme.

Due to the movement of the digester tank, which put it closer to an existing and listed glass incinerator building, the planned piling technique had to be adjusted to reduce vibration.

A bespoke concrete mix was designed for the digester base slab ,due to the density of the steel reinforcement within it. A self levelling compound was used with a dappling technique. The 175m3 concrete pour took four men six hours to place and complete, which reduced plant hire and labour costs as well as a reduction in manual handling and HAVs risks.

The team encountered adverse weather on site which risked delaying the completion of the new digester tank. The team pulled together and worked in shifts to get the scheme back on programme.

The team also encountered a further challenge as the work took place during Anglian Water’s annual Cambi shut down. This normally takes two weeks, but was extended to six weeks to allow for the works. To keep the plant running, temporary centrifuges, tractors, trailers and a temporary cake bay were hired. This ensured the site was running efficiently and was compliant during the shut down.

The project was designed in the most efficient and sustainable way,  with off-site fabrication of pipework, and cable racks, which arrived in three pieces and installed by crane in three hours. This eliminated the need to work from height and reduced the health and safety risk associated with building in situ.

The MCC kiosk was a standard product, taking four hours to be installed after arriving on site, pre-made. The cooling tower was built off-site and installed in five hours and the heat exchanger was also built off-site and installed within one hour.

The team work encouraged and supported by David Wright, Site Manager, at Cotton Valley was instrumental to keeping its flawless health and safety record and completing on time. ‘Coming from the tools’ himself, there wasn’t a job that David wouldn’t get stuck into, always on had to help with construction and tidying away at the end of the day. Keeping a safe, tidy and happy site is really important to David and the benefits were clear to see.

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