Articles & Case Studies

Hydrok ‘liftout grids’ give Chelmsford WwTW a bespoke solution

Posted: Tuesday 10th February 2009

Following the successful refurbishment of Anglian Water’s Witham WwTW, Hydrok UK were asked, as part of the tri-partnership with LES Engineering, to design a refurbishment package for the Chelmsford WwTW. The objective was to improve the plant efficiency whilst maintaining the current usage during the construction and installation stages. The Hydrok solution was to construct and install their own bespoke designed liftout grids incorporating the highly efficient AEROSTRIP® fine bubble diffusers.

Mark Lunn, Aeration Product Manager of Hydrok said “Anglian Water’s brief was to refurbish the two existing aeration tanks with Hydrok’s new liftout diffuser grids and airmain. To make matters more complicated, due to strict consent levels for the site, Hydrok had to install and commission the new aeration system whilst still maintaining and operating the old diffusers.”

The Hydrok liftout diffuser grids have been designed to be ‘future proof’, they allow Anglian Water to increase the number of diffusers as and when future load to ‘the works’ increases. Gary Wakley of Anglian Water said, “The Hydrok liftout grid mounted strip diffusers allowed Anglian Water to upgrade the aeration process with minimal interruption. Following lengthy discussions with the various interested parties such as the Environment Agency, Essex and Suffolk Water and Anglian Water senior staff, it became apparent that the consented discharge limits for the Chelmsford wastewater treatment plant would need to be maintained while the new system was installed. Therefore innovative thinking by the Asset Engineer provided a solution to install the Hydrok system. When brought on stream the replacement aeration process benefited from the increased oxygen transfer efficiency. As a secondary benefit it has also been possible to operate the aeration process on only one 90kW blower opposed to the normally operating two units. This should equate to power savings of £75,000 per annum. Once an additional treatment lane is constructed under the next phase of development it will be possible to simply lift out the diffuser assemblies and drain the old lanes one by one in order to remove the redundant diffuser system”.

Mark Lunn further commented “The scheme certainly was a challenge as we were unable to drain the tanks down and remove the redundant diffusers before installing the new liftout grids. It meant that we had to study the old “As Installed” drawings and engineer a solution to ensure the new grids did not damage the old diffusers whilst lowering them into the tanks. Our ingenious guiderail system ensures the liftout grids are located in the same location every time”.

The scope of the work entailed; the design, fabrication, installation and commissioning of a thin wall stainless steel grade 304 air main, 32 No. 9m x 2.8m stainless steel grade 304 liftout grids, manual and actuated valves and associated fittings. The pipe network is to supply air from existing centrifugal blowers to 336 AEROSTRIP® fine bubble diffusers.

All the design elements of the project were handled by the Hydrok in-house design team and engineers, with all pipe work fabrification and manufacture of the liftout grids, produced at the Hydrok manufacturing and engineering plant in Cornwall. Installation and commissioning was handled by the Hydrok teams of installers.

Hydrok UK can be contacted on 01726 861900, email: or the website

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