Woolston Wastewater Treatment Works

Work is well underway on our multi-million redevelopment of the treatment works which started in September 2014.

Picture above is an artist's impression of the completed redevelopment

The existing site was built in 1966 and was in need of modernisation. The redevelopment project once completed will:

  • Reduce smells coming from the site
  • Ensure the treated wastewater leaving the site meets new, higher environmental standards
  • Ensure the redesigned works fits in with the ongoing redevelopment of the area.

The end result will be a modern wastewater treatment works that will serve the area long into the future. Our film below gives a 3D virtual tour of how the works will appear from the street or estuary when construction is complete.

Temporary works

More than half of the temporary treatment works have now been demolished and we will continue to be phased out as we progress the construction of the permanent site.


The redevelopment will significantly reduce the smells coming from the site and residents should start to see improvements as the redevelopment progresses.

While we are still using parts of the original and temporary processes, and during warmer or particularly wet weather, we’ll continue to experience some odour issues from the site, due in part to accumulation and breakdown of fats, oils, and grease (also known as FOG) in the flows arriving for treatment.

As the new site will be completed in stages we need to ensure we are able to continue cleaning your wastewater and there will be occasions where we need to do undertake activities that are normally not required. These activities could cause additional smells, but should only be temporary. We’ll also be cleaning the old tanks before they’re demolished and you may notice some additional smells during this time.

The new site will see the open air tanks, where the majority of the smells originate from, replaced with new treatment processes fully odour controlled and contained within the building.

We’ll do everything we can to keep smells to minimum during construction.

Local Engagement

An Employment and Skills plan is in place which will encourage the participation of local contractors, sub-contractors and suppliers and provide employment opportunities for Southampton residents.

We’ll be keeping residents updated on progress and plan to hold regular drop-in sessions with the project team at the Community Liaison Group meeting. The project is being carried out by contractor 4Delivery.

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Community Liaison Group

As agreed with local community groups and Southampton City Council, we have created a Community Liaison Group. The aim of the group is to create a link between Southern Water, 4D and the local community. Regular meetings allow us to receive feedback from the community and provide progress updates.

The group meets every three months at the site offices and includes representatives from all parties involved.

Members of the project team will also be on hand to answer questions and discuss the ongoing activities. The chair for the group is Councillor Warwick Payne.

For anyone interested in attending or finding out more information, please call our site office number (during office hours) on 02380 420856.

For all other enquiries please see our contact us page.

Frequently asked questions

The Environment Agency has specified tighter standards on the treatment of wastewater before it can be recycled into the environment, in line with the latest European Union requirements.

We must improve the treatment processes at the site so it can meet these new standards. We also want to reduce the smells that sometimes come from the works, which we know cause problems for residents and businesses nearby.

The best way of doing this is to completely redevelop the site. The end result will be a modern wastewater treatment works which will be able to serve Woolston long into the future.

The sewer system which feeds into the works collects wastewater from homes and businesses in Woolston. The wastewater is treated in three stages before it is released through an outfall into the River Itchen Estuary.

The by-products produced from the treatment process are:

  • Screenings: collected at the first stage of treatment and consists of the large materials removed from the wastewater, including items such as wet wipes and sanitary products
  • Sludge: which is transferred by pump via the jetty, for removal by barge for further treatment at Millbrook Wastewater Treatment Works where it is converted into a soil conditioner.

We are proposing a redevelopment that will:

  • Completely modernise the wastewater treatment works
  • Ensure it meets new, tighter environmental standards
  • Address the odour issues at the plant.

The new treatment processes are the most efficient and cost effective and take into account the limited working space.

As well as improving the quality of the treated wastewater, one of the main goals of the redevelopment is to address the odour problem that has been affecting local residents for a long time.

The new buildings have been designed to blend into the urban area, taking into account the new developments already under construction. Fencing, walls and trees will minimise views into the site.

See our film above for a virtual tour of the area once construction is complete.

Originally, the Environment Agency’s National Environment Programme (NEP) specified that we transfer flows from Woolston to Peel Common Wastewater Treatment Works in Gosport.

This proposal was challenged by our regulator, Ofwat, and following an assessment it was agreed that an on-site redevelopment would be the best option.

Our appointed contractor 4Delivery Limited (a consortium comprising of industry leaders Veolia Water, Costain and Stantec) has vast experience in delivering works on our behalf and is fully committed to keeping customers and stakeholders up to date.