Wastewater Sludge Europe

Waste to value: Biogas helps Scottish Water power ahead to Net Zero

Thursday, 2 December 2021

Utility Scottish Water is pushing ahead with ambitions to achieve net zero emissions by 2040. Its wastewater treatment works at Nigg proves how biogas will play a significant role in decarbonising wastewater treatment.

Creating a circular economy

Servicing over a quarter of a million people in Aberdeen and the surrounding area, the Nigg wastewater treatment plant (WWTP) is proving to be a pivotal contributor to Scottish Water's long-term environmental plans.

By 2040 the utility has committed to achieving net zero emissions, five years ahead of the Scottish government’s plans for carbon neutrality by 2045.

Following various upgrades, the Nigg site is now producing 80-90 per cent of its electricity via two Combined Heat and Power (CHP) engines.

“Creating a circular economy is a key strand of our route map towards net zero.”

Over 20 years ago, a thermal hydrolysis plant was installed by the Norwegian company Cambi. Since a programme of upgrade work was carried out over the past couple of years, the WWTP has now halved its CO2 emissions since 2019.

"When you consider the quantity of wastewater that we are treating on a daily basis, being able to turn that into something with a tangible use and creating a circular economy is a key strand of our route map towards net zero," said Simon Wrigglesworth, wastewater operations manager in Grampian.

Recognising value from waste

The improvements have allowed additional sludge to be treated on-site, increasing the amount of biogas produced by between 25-30 per cent.

"We are determined to do all we can to make our sites as green as possible as we focus on reaching our target of net zero emissions by 2040, and recognising the value we can generate from waste is absolutely vital to that," added Wrigglesworth.

Last year, Water UK launched the world’s first sector-wide plan to deliver net zero carbon emissions by 2030, including a 10-point plan for decarbonisation.

Furthermore, the Portuguese water utility group, Águas de Portugal Group (AdP), is joining the "2030 club" and has set out the target to be energy neutral within a decade.

Achieving Net Zero emissions

To reach net zero emissions by 2040, Scottish Water has published a route map as part of a strategic plan entitled ‘A Sustainable Future Together’.

This includes five focus areas:

  • Becoming more energy efficient
  • Embracing low carbon construction
  • Using lower-carbon energy products
  • Storing emissions that cannot be avoided
  • Investing in renewable power technologies.

The utility said it plans to embrace new technology and “invest in renewable energy”, including a solar scheme at the Erskine wastewater treatment works. (See video)

Regarding plans to reduce process emissions, the utility currently treats 983 megalitres of wastewater per day, generating both nitrous oxide (N2O) and methane.

From 2025 to 2040, it plans to move from demonstrating optimisation of WWTPs and sludge treatment centres to fully optimising the sites to decrease the production of N2O.

Achieving Net Zero emissions

By using the biogas produced as part of the treatment process as fuel for the new boiler, as well as recovering and reusing heat from the two CHP engines, Scottish Water said it had halved the amount of oil used in the boiler.

“This has cut 1300 tonnes of CO2 and led to a cost saving of over £250,000.”

This has cut around 1300 tonnes of CO2 emissions per year and led to a cost saving of over £250,000 per annum.

Wrigglesworth added: “In addition, we have increased our production of electricity on the site by between a quarter to one third since the new digester mixing system was installed and are producing around 12 GW a year of green energy, further reducing the carbon footprint of the site by 1000 tonnes of CO2 a year.”

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