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Documented Performance

Solutions that have been field-proven for decades.

Errol Scotland WWTP

Remote siting for the Errol project eliminated both the nuisance and costs of access roads for sludge lorries due to the no-sludge feature of Aero-Fac® . 23+ years of performance, now expanded and upgraded for another 20 years of low OPEX operations.

Client: Scottish Water
Date: Tuesday, 14 August 2001
Info: Remote mostly automated WWTP for village

Visitors to the Errol plant are typically amazed by the lack of odour. Many remark that it is hard to believe that they are at a sewage treatment plant.

The Aero-Fac® treatment system incorporates a number of highly unique features, not least of which is the self digesting sludge process that requires no pre-screening, sedimentation tanks or clarifiers, no sludge removal, dewatering or conditioning, and best of all, no routine sludge disposal and the associated lorry traffic in and out of the works. All sludge is continuously self-digested within the initial treatment stage.

Constructing The UK’s First Aero-Fac® Nature Based Solution WwTP in 2000-2001

North of Scotland Water (NoSWA), the Scottish water agency at the time of construction, had the vision to implement a fast-construction, innovative and economic solution for treating the wastewater from the community of Errol on the scenic Tay Estuary near Dundee, Scotland. The innovative Aero-Fac® approach provided significant reductions in both initial and ongoing costs, carbon footprint and other environmental benefits that came to have implications for wide application across both the rest of Scotland and the entire UK.

An analysis at the time by NoSWA and Montgomery-Watson Projects (now Stantec) of various options demonstrated a remarkable cost advantage for the Aero-Fac® option in both immediate CAPEX as well as ongoing OPEX (see project cost data below).

Following construction and commissioning of the new WwTP, the effluent from Errol routinely met rigid discharge requirements. Most importantly, it did so without the production of sludge that normally requires costly handling and highly-regulated disposal. The elimination of sludge handling also eliminated the need for access roads which allowed a more remote location of the WwTP off the main roads.

NoSWA’s adoption of a highly sustainable system with a completely biological process resulted in very little in the way of wear-prone mechanical equipment, operational manpower or energy needed for operation, thereby meeting the then needs of NoSWA in providing affordable public services. The technology provided reliable process control to achieve quality of effluent with both low capital and exceptional growth flexibility — and all with a net zero cost as compared to the other alternatives considered.

A follow-on independent study of the Aero-Fac® plant at Errol commissioned by Scottish Water early into the project confirmed the performance of the system. In the report, particular mention was given to the plant's class-leading disinfection performance together with its ability to destroy 99.99% of the solids entering the system.

No odours. No sludge lorries. No noisy mechanical equipment. Little operator attention. The Errol Aero-Fac® WwTP is an attractive, Nature Based Solution that fits within its sensitive environment and meets today’s Low Carbon Footprint concerns.

errol specs 1


Back in the late 1990s when Tayside Water (later merged into North of Scotland Water and eventually Scottish Water) first enquired about the possible use of Aero-Fac® for the local town of Errol, there was little discussion of carbon footprint, CSO/storm overflows and climate change challenges. Don McClean and his team at Tayside were interested in the technology essentially for its simplicity, low energy and lesser need for manpower, maintenance and its projected sustainability and total life-time cost.

NoSWA began work with Montgomery-Watson Projects (now Stantec) to evaluate the new-to-the-UK Aero-Fac® technology — a significant departure from the previously favoured options — to determine the benefits as opposed to traditional activated sludge options. 22+ years later, the numerous benefits and cost savings identified back in 1999-2000 have been more than realised for Scottish Water.

Meeting the Challenges of Climate Change

Aero-Fac® is uniquely suited to cost-effectively meet the challenges of projected growth and loading/flow swings (including CSOs), whilst also having an extremely low carbon footprint, dramatic energy savings, no sludge production or handling costs and complexities, plus energy-free disinfection, thereby making effluent suitable for irrigation water re-use or safe-bathing waters whether discharged to river or sea — or to the sensitive Tay Estuary reed area.

2021 marked 20 years of successful operation for the Errol facility. In 2023, Scottish Water engaged Gurney Environmental, the supplier of the Aero-Fac® system, to perform a 20-year refurbishment and expansion of the treatment works to accommodate a 50% increase in load and anticipated growth for the next 20 years of operations.


Complete Cost Recapture — Zero Net Cost


errol effluent


Errol filled  Errol difuser construct


Errol Celebrates 20th Anniversary in 2021

20-years is often referred to as the expected lifetime of a mechanical WwTP, yet after 20 years the Errol Aero-Fac® wastewater treatment plant continued to perform with incredibly low ongoing OPEX, no sludge, no odours and little in manpower and energy.

Errol, Scotland Aero-Fac® WwTP in 2021

2021 celebrated 20 years of successful operation for the Errol facility.











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Scottish Water's Errol Aero-Fac® WwTP Expanded and Upgraded in 2023 for Another 20 Years of Low Carbon Footprint, Low OPEX Service!

In 2001, Montgomery-Watson Projects (now Stantec) and then North of Scotland Water (NoSWA) christened the very first Aero-Fac® WwTP in the UK, a unique “greener” approach to wastewater treatment. The idea was to provide consistent effluent quality for the sensitive Tayside Estuary area, eliminate bothersome sludge lorry movements in and out of the WwTP including the major access road costs and issues, accommodate both long-term growth and peak load/flow swings spanning 20+ years – whilst at the same time requiring minimal manpower on site, ongoing maintenance and expensive capital equipment replacements, and all whilst incorporating amazingly little energy usage. Plus it was important to also install a treatment works that would not create any odour issues for the area. In fact, over the years visitors to the Errol plant are quite amazed by the lack of odour, many remarking that it is hard to believe that they are actually at a sewage treatment plant!

Long Term Proven Performance

2021 marked 20 years of successful operation for the Errol facility. In 2023, Scottish Water engaged Gurney Environmental, the supplier of the Aero-Fac® system, to perform a 20-year refurbishment and expansion of the treatment works to accommodate a 50% increase in load and anticipated growth for the next 20 years.

In reporting on the 20-year track record of service and performance of the Errol Aero-Fac® WwTP,  the Scottish Water’s spokeperson had this to say, "(Aero-Fac®) offered high process performance, but with low OPEX costs compared to a traditional plant, both in terms of operator attendance, maintenance and power usage, and in the fact the plant only needed sludge removal at intervals of several decades.

“In the 20 years since the plant was brought into service, it has indeed had both low maintenance costs, and low operator input. At the last testing it has been found to have very low sludge build up and at this anniversary, there has had to be no consideration of emptying to remove sludge build-up. We have never had any odour complaints at Errol.

“In tandem, it has given consistent performance with a 100% record in terms of compliance with consent conditions.
“Another important element of the Aero-Fac® system was low energy costs and with the wind-driven SERIES 3 aerators augmenting the mains-powered blowers, it has reduced the potential energy costs. Although it was not such a high consideration 20 years ago, Errol also supports Scottish Water’s moves to becoming carbon neutral.”

The spokesperson went on to say, “The Aero-Fac® system also uses much less concrete than traditional forms of construction. The aforementioned reduction in OPEX costs and the renewable energy element means that in both CAPEX and OPEX terms, the Aero-Fac® system accords with Scottish Water’s carbon-neutral vision.”

Selecting a Truly Sustainable Solution

North of Scotland Water (NoSWA), the Scottish water authority at the time of construction, implemented a solution that provided substantial cost and environmental benefits that soon came to have implications for wide application across the rest of Scotland and the UK for both immediate CAPEX as well as 20-year-life CAPEX and OPEX — and a lower carbon footprint.

Errol is a good example of just how good a neighbour the Nature Based Solution Aero-Fac® WwTP can be! No odour. No sludge lorries. No noisy mechanical equipment. The Errol WwTP routinely processes the community's wastewater with little operator attention and is an attractive, Nature Based Solution that fits within its sensitive natural environment.

Meeting the Many Challenges of Climate Change Including Serious Stormwater Overflows

Aero-Fac® has also been shown to be uniquely suited to meet the many challenges of climate change, including meeting new legal requirements for stormwater overflow containment (CSOs).

As an example, Northumbrian Water’s 2018 Waren Mill Aero-Fac® WwTP has been operating odour-free and sludge-free with over 10x flow/load variation, and automatically handles storm surges/CSOs without operator intervention or problematic discharges.

The designers at Gurney Environmental developed this specific Aero-Fac® wastewater system for Northumbrian Water to meet a normal winter population of 200, but rising to a summer population of almost 3,000! This dramatic variation in flow from winter to summer can create serious issues for many WwTP designs. At this particular location, Northumbrian Water had been tankering away excess wastewater flows over the 150-pe SAF design with an associated high operating cost and carbon footprint.

In the analysis by Northumbrian Water’s consultants, Aero-Fac® offered a well-proven and time-tested system with the flexibility and robustness of operation to be able to cost-effectively and easily accommodate this large flow variation. In the past few years, especially with the covid pandemic, the nearby caravan site was full, so the WwTP has had high load summers. However, with the new Aero-Fac® system, Northumbrian Water have finally had no tankering and associated costs!

Yorkshire Water’s Withensea 15,000 PE Aero-Fac® Wins Global ICE Award for Sustainability and Also Finalist For “Net Zero Carbon Initiative of the Year” Award

Yorkshire Water’s new in 2021 15,000 PE Withernsea Aero-Fac® WwTP likewise has been designed to automatically accommodate a 2x flow/load variation plus CSO/storm surges without operator intervention. The joint Yorkshire Water-Stantec-Gurney Environmental project was selected over other more traditional options. Yorkshire Water’s Communications Advisor John Bond had this to say: “Our proposal is a step away from traditional treatment works and means we are opting for a much greener, more environmentally friendly option. The new proposal means construction times will be reduced, traffic movements can be minimised and once finished, the site will be virtually noise free.”

Lower-cost, More Sustainable, Natural/Greener Disinfection Utilised

As an example of the “Greener”, nature-based, lower maintenance and cost approach, the UV system typically required by the Environment Agency was engineered out of both the Errol and the Withernsea WwTPs. Monitoring carried out by Stantec at other Aero-Fac® wastewater treatment plants around the UK demonstrated that the WwTP had met the discharge requirements via a greener, nature-based method without the need for expensive, higher carbon footprint traditional UV.

The unique combination of inherent disinfection provided by the natural biochemical process, enhanced by sun exposure provided by the continual gentle mixing and combined with longer retention/stabilisation times produces an effluent that is safe for irrigation water reuse. This also has the advantage where wastewater treatment systems can operate with better disinfection capabilities and require smaller or even no costly tertiary disinfection.

The Search for Sustainability

When initial costs, ongoing 20-year costs, plus Carbon Footprint considerations are all examined in order to make the best decisions for wastewater treatment, what are considered “greener”, Nature Based Systems like Aero-Fac® can truly offer well documented and well proven significant long-term cost and performance advantages.

CLICK HERE to learn about our various low-energy wastewater treatment systems and options.



Sample Projects Portfolio

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  • Source Management
  • Wastewater
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  • Date
  • Yorkshire Water's first new WwTP in many years is a No-Odour, No Sludge Aero-Fac® WwTP for the area around Withernsea. The new 15,000 population equivelant (PE) WwTP has been successfully treating sewage whilst automatically
    Read More
    • Wastewater
  • The No-Odour, No Sludge Aero-Fac® WwTP operated by Northumbrian Water for the area around Waren Mill has been successfully treating sewage whilst automatically handling flow/loading fluctuations of up to 10x due to local tourism,
    Read More
    • Wastewater
  • The success of Anglian Water’s wwtp at Sutton St James prompted the company to install three additional Aero-Fac® systems in treatment works including one at East Harling in Norfolk. The decision to choose the
    Read More
    • Wastewater
  • The ResMix “Source Management” System is used at South Staffordshire Water's Blithfield Reservoir for manganese reduction and general water quality improvement. Two units are deployed to cover the reservoir.
    Read More
    • Source Management
  • Accel-o-Fac® wastewater treatment upgrade to the Harbour View WWTW located just outside Kingston Town, owned and operated by the National Water Commission.
    Read More
    • Wastewater
  • In 2019 South West Water joined other water companies by employing new options to improve water quality at their Wistlandpound Reservoir whilst reducing both CAPEX and OPEX. In 2023 the Meldon Reservoir order became
    Read More
    • Source Management
  • Welsh Water installs first ResMix 5000cc Source Management System at the Pontsticill Reservoir to improve water quality prior to treatment works.
    Read More
    • Source Management
  • In July 2016, Gurney Environmental installed a 2nd installation of the ResMix 5000cc ‘source management ‘ system for Welsh Water at Llangdegfedd Reservoir in Wales.
    Read More
    • Source Management
  • The Accel-o-Fac® wind-powered WWTP operated by GWM Water for the community of Donald, Australia has been successfully treating sewage since installation of the upgrade in the Fall of 2018, and with virtually no significant
    Read More
    • Wastewater
  • The Accel-o-Fac® wind-powered WwTP for the village at Holkham Estate, England has been treating sewage since the spring of 2006, and with virtually no significant ongoing operating cost.
    Read More
    • Wastewater
  • Following use of an Aero-Fac® system on Sandringham Estate for 6 years, Gurney Environmental was contacted by the Crown Estate to examine solutions for Windsor Estate and Cumberland Lodge complex. The old 1960-era filter
    Read More
    • Wastewater
  • Southern Water's Weir Wood Reservoir is a 1.5-mile (2.4 km) long stretch of water storage, situated close to Forest Row, East Sussex, England, on the north-western margins of Ashdown Forest. In 2016 Gurney Environmental
    Read More
    • Source Management
  • The Aero-Fac® Sludge Digestion System (SDS) at Sandringham has solved the issues of sludge handling and disposal, as well as peak flow and load issues for over 15+ years.
    Read More
    • Wastewater
  • Accel-o-Fac® wastewater treatment system for the Severn & Wye Smokery in Gloucestershire providing a zero carbon footprint strategy for the business.
    Read More
    • Wastewater
  • Accel-o-Fac® upgrades at South Gippsland Water for implementation at two of their wwtp's located just outside Inverloch, Victoria in Southeastern Australia.
    Read More
    • Wastewater
  • Burncrooks WTW is located near Strathblane on the outskirts of Glasgow and is fed by a series of reservoirs. It serves a nearby population of more than 50,000. It was identified that the WTW
    Read More
    • Source Management
  • Early in 2013 United Utilities placed its first order for the unique ResMix 'source management' system following successful use of the system by Scottish Water since 2009 and over 15 years in Australia.
    Read More
    • Source Management

What Our Clients Say

Aero-Fac® Wastewater Treatment System

"For 20 years the Aero-Fac@ system at Errol has met our consent discharge levels, had no odour issues and we have not required any sludge removal. Although it was not such a high consideration 20 years ago, Errol also supports Scottish Water’s moves to becoming carbon neutral."

Robert Dey, Scottish Water

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