A positive impact on everything we touch
Over 2000 dedicated people nationwide
Providing critical infrastructure for the UK
A positive impact on everything we touch
Over 2000 dedicated people nationwide
Providing critical infrastructure for the UK

Wessex Water

Berry Hill, Sludge Treatment Centre


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Wessex Water has a regulatory output to generate more renewable electricity. To achieve this output three existing gas digesters were upgraded and a fourth digester installed. Berry Hill STC is a sludge treatment centre receiving both indigenous and imported sludges. Indigenous co-settled sludge is pumped to the site from Holdenhurst Sewage Treatment Works (STW), while imports are received via road tanker.

The site screen and thicken the indigenous sludge before it is blended with the imported sludge and digested. Digested sludge is dewatered to a cake and disposed to land.

Key Information


Berry Hill, Sludge Treatment Centre


Wessex Water




June 2014 - December 2016

Benefits at a Glance

The scheme delivered C£281K of CAPEX and C£31K of OPEX
Overall programme saving of 5 weeks
Pipework fabricated off-site to reduce installation time


All works were designed, programmed and constructed so as to ensure the works remained fully operational and able to continue to receive all imports and indigenous sludges.

The original project scope was to carry out the detailed design and construction of;

  • new sludge transfer pumping (various locations)
  • sludge screen (both indigenous and imported sludges)
  • 1 nr new screened sludge holding tank
  • New raw sludge thickening to 5.5% DS using gravity belt thickeners
  • New powder polymer storage, preparation and dosing equipment
  • New sludge transfer pipelines and pipe bridges
  • I nr new 300 m3 sludge blending tank and associated pump mixer


  • New digester feed
  • 1 nr new 2, 364 m3 mesophilic anaerobic digester c/w gas mixing system and recirculation pump
  • Refurbishment of existing 3nr concrete digesters including purging, emptying and cleaning, remedial civil repairs, new gas mixing systems, gas pipework, fixing of the existing floating roof, hand railing, recirculation pumps and new feed pipework
  • New shell and tube heat exchangers to all digesters and modification so the hot water system including new shunt pumps, distribution manifold and primary plate heat exchanger.
  • New gas flowmeters and pipework
  • 1nr 1360m3 double membrane gas holder
  • Refurbishment and capacity increase of existing gas flare stack
  • 3nr new secondary digesters


Existing redundant civil assets were refurbished and or reused where possible to allow offline construction and provide TOTEX benefits. Other benefits included;

  • Existing import holding tanks converted to secondary digesters, existing sludge holding tank civil base modified to form new reception tank.
  • Existing digester feed converted into new secondary sludge transfer.
  • Existing hot water pipework modified and re-used to serve new heat exchangers.
  • Large amounts of pipework were fabricated off-site to reduce installation time on site and reduce construction risk.
  • Nomenca now engaged to carry out a similar project at Poole STW including online design and feasibility.
  • The site was fully laser scanned and 3d modelled at the start of the design process.


We believe that by being flexible to our clients’ needs, and by close liaison at the onset of a project, we will be able to plan, design and deliver a service that is flexible and designed to focus on any additional needs, such as providing on call service, night shifts, dedicated service numbers, and provide resource availability.

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