Cog Moors

The Cog Moors wastewater treatment works which treats wastewater for Dinas Powys, Sully, Penarth, Barry and the West of Cardiff is receiving an upgrade.

What is the Cog Moors Waste Treatment Works?

Cog Moors is a wastewater treatment works which treats wastewater for Dinas Powys, Sully, Penarth, Barry and the West of Cardiff.

Cog Moors Wastewater Treatment Upgrade

As part of our upgrade of the treatment works, we will be investing over £50 million to install an Advanced Anaerobic Digestion (AAD) plant along with other improvements to the existing site. Our AAD investment once completed will enable us to achieve an energy neutral wastewater site by recovering energy from the waste we process onsite. This will help manage the effects of climate change, reduce our running costs and carbon footprint and help keep your bills low.

Artist impression of the new Advanced Anaerobic Digestion plant once completed.

Here are figures for the new AAD plant once completed:

  • 1.5GWh capacity
  • Will produce 2.028MWh of electricity a year
  • Equivalent of power required to power 3,750 homes per year
  • Help meet Welsh Water renewable energy target.

What is Advanced Anaerobic Digestion (AAD)?

An AAD plant is part of a combined heat and power facility consisting of 2 engines that use biogas from the anaerobic digestion of sewage sludge collected from waste in our sewer system to produce biogas (mainly a mixture of around 60% methane and 40% carbon dioxide) and a biosolid “cake” (a sustainable fertiliser that can be recycled on farmland).

How Does It Work?

The biogas is created by the anaerobic digestion of sewage sludge which is then used in gas powered engines to generate electricity which will be used to power the plant. The left over sludge becomes a biosolid “cake” and is collected and used as a sustainable soil enhancer and environmentally friendly alternative to chemical fertilisers.

Here is a diagram explaining how Advanced Anaerobic Digestion works:

Project Update

September 2018:

Our AAD investment got underway! First, we cleared the site and removed any trees and shrubs. We replanted these trees and shrubs in a space which wouldn’t interfere with the new developments.

October 2018 – May 2019:

During this period, we demolished redundant tanks and other buildings to make space for the new AAD plant. We then laid the concrete foundations while the new AAD plant began being built off site.

May 2019 – December 2019:

We then started constructing the boiler house, chimney and other key AAD plant buildings onsite. Additional tanks and new digesters were also installed.

January 2020 – April 2020:

So far this year, amongst other works, we have installed and cladded two new digesters and Post Digestion Storage Tanks. We also began laying pipes and installing electrical works.

Here is a link to pictures outlining progress made in developing the AAD plant since the summer of 2019.

We have also produced a Frequently Asked Questions page to answer additional questions.

Next steps

As long as everything goes to plan, we’re hoping that our work at Cog Moors will be complete by the end of the year. Here’s an overview of what we have left to do:

Spring 2020 – Summer 2020:

Complete the installation of electrical equipment, lay all the pipes and lay roads across the site.

Summer 2020:

Start the commissioning of the new AAD plant.

Autumn 2020:

Complete the construction of the new AAD plant.

Winter 2020:

Once the AAD plant is built, we will carry out some tests to ensure it meets all the necessary standards. Once we have successfully completed testing, the new AAD plant will be ready to create energy from the waste we process on site.

Engagement with the Community


As part of the development of the works, we will be keeping you informed of developments to the AAD plant through bi-monthly newsletters.

Here is a link to the current newsletter.

Community schemes awarded by Welsh Water in Sully and Dinas Powys

Welsh Water’s Community Fund has been developed to give something back to the communities we are investing in. We have recently awarded various worthwhile community schemes throughout Sully and Dinas Powys, which you can find out more about here.

If you would like to find out more about our Community Fund and how you can apply, visit here.

Events and School Visits

As part of the scheme we aim to hold or attend several community engagements events to keep you informed of developments in Cog Moors. Please click here to find out more about the engagement events Welsh Water have attended so far. We have also visited local primary schools in Sully and Dinas Powys to teach children about the work of Welsh Water and our work at Cog Moors.

If you have a community event which Welsh Water could attend or interested in a school visit, please contact Tomos Davies on 07866818183.

Want To Know More?

If you have any queries regarding work on the site, please contact Tomos Davies, Community Engagement Officer on 07866818183. Alternatively, you can call the Welsh Water Call Centre on 0800 085 3968 and ask for Danielle Thomas or Camille Valmalle.

Additional information on the scheme is also available on the In Your Area section of our website.