Case Study

Clifton Wastewater Treatment Works

Sector: Built Environment; Coastal Resilience & Climate Adaptation; Water
Highlights: Waste reduction, biodiversity, ecological uplift, community engagement, community wellbeing, carbon mitigation
Project owner: Yorkshire Water
Project start: July 2020 – November 2021
Location: Yorkshire, UK
Community impacted: Urban, Rural
Hazards mitigated: Flooding
Number of people made more resilient: 180
Case study provided by: Stantec UK Ltd

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Clifton Wastewater Treatment Works (WwTW) is the first nutrient-reduction Integrated Constructed Wetland (ICW) in the UK designed to treat all flows. It was created as an alternative sustainable wastewater treatment works, demonstrating performance and gain against conventional solutions. It has achieved an operational carbon savings of 79%, embodied carbon of 50% and 24,000+ plants used, creating an innovative, low-carbon, ground-breaking nature-based solution.

About the Project

As part of Yorkshire Water’s £700M Water Industry National Environment Programme (WINEP), 80 regional wastewater treatment works require nutrient reduction measures. This is the largest and most complex environmental programme that Yorkshire Water has ever delivered. Yorkshire Water’s commitment to achieving net-zero carbon by 2030, coupled with the challenging Price Determination, means that the business cannot rely on traditional, high-carbon, chemical dosing methods to meet the nutrient reduction requirements.

Clifton WwTW ICW is the first nutrient-reduction ICW in the UK designed to treat all flows. The project’s ambition was to create an alternative sustainable wastewater treatment works. It demonstrates both performance and gain against more conventional solutions and has made Clifton one of the most environmentally friendly villages in Yorkshire.

The Environment Agency (EA), BarhaleEnpure JV, Stantec, and Yorkshire Water worked together to create a nature-based solution to fully replace the existing conventional treatment process. Working extensively with the EA, Yorkshire Water was granted the first ever constructed wetland Operating Techniques Agreement (OTA) in the UK.

The EA and England and Wales Sewerage Undertakers are collaborating to utilise ICWs for wastewater treatment. This is with the aim of achieving water quality objectives, whilst reducing energy use and carbon emissions and obtaining additional benefits associated with nature-based solutions, such as increasing biodiversity and improving natural capital.

The primary aim of the ICW at the WwTW is to reduce phosphorus to achieve the WINEP limit for phosphorus, but there is uncertainty regarding the efficacy of phosphorus treatment provided by ICWs. Therefore, the EA has agreed that ICWs for implementing phosphorus removal should be operated under an OTA, as a flexible approach to utilise ICW technology to achieve WINEP phosphorus targets.

An OTA includes the WINEP target and sets out the monitoring and reporting requirements for the operator to demonstrate if the target has been achieved or not. It sets out the techniques that must be complied with as part of the conditions within the current Environmental Permit for a water discharge activity to discharge sewage and/or trade effluent from the WwTW and applies to the ICW.

Clifton comprises five ponds (over 3,000m²), with open water ponds and shallow vegetated marshes, providing aerobic and anaerobic environments sustaining a diverse population of microbial activity and plant life. Wastewater treatment within ICWs is achieved by a combination of filtration, biological treatment, sedimentation, plant absorption, and adsorption to sediment and plant surfaces. The project aimed to achieve the EA phosphorus target of 4mg/l, with current performance on average being 1.8mg/l.

Unlike conventional treatment processes that use pumping and chemicals to treat the wastewater, the ICW is a fully passive process with flows gravitating through the system with no automatic control elements. The treatment process utilises an existing primary tank with an open water deeper pond providing 24 hours of primary settlement, reducing the solids and organics load into the wetland cells by 15-20%. Secondary treatment provided in the next two ponds works in parallel. These are limited to fewer plant species which are more robust and can tolerate higher organic load. These focus on the reduction of Biological Oxygen Demand (BOD) and nitrogen through filtration, sedimentation, and biodegradation processes. The last two ponds incorporate a diverse array of plants to provide tertiary treatment and increase biodiversity. Clay bunds surrounding the ponds are covered with a geojute and planted to create a flower-rich grassland helping to stabilise slopes, creating additional biodiversity and aesthetic appeal. The local clay environment is also harnessed to seal the wastewater activity and topography of the site to naturally aerate the wastewater, avoiding all need for pumping.

Clifton demonstrates that there is an alternative way, which can serve as inspiration for the industry. This ambition is already being embedded in national regulation and guidance and is being used to inform ICW use across the water sector, with lessons being shared with other water companies, regulators, and stakeholders and to help inform Price Review 24 (PR24). Within Yorkshire Water, there are eight similar projects in the pipeline.

Achieved Outcomes

Clifton has been operational and treating wastewater since November 2021, exceeding performance expectations. An intensive ecology and chemical monitoring programme has commenced, running for three years, enhancing industry knowledge, and informing guidance on new nature-based solution designs. The project was completed with 35% lower costs than building conventional solutions and 40% lower operational costs.

This project is also being used as a best practice model for the industry, shaping projects, regulation and innovation. These benefits have no bounds when it comes to reach, affecting community members, water companies, consultants, designers, local authorities, The Environment Agency, OFWAT, the UK Government, The Rivers Trust and other industry professionals. Clifton is a flagship project offering opportunities for research across many areas, including climate impact, and evapotranspiration, and providing environmental, social, and economic benefits through influencing the industry.

Clifton improved the resilience of people through a systems-thinking approach. At its core, the project delivers water treatment naturally, avoiding the need for chemical dosing, while also breaking down matter on-site, mitigating transport measures and decreasing pressure on global supply chains.

At a higher level, Clifton is ensuring wider resilience as it is being replicated all throughout the UK and provides education opportunities through inclusion in and reports, as well as welcoming visitors from other water companies to the site, who are interested in developing similar solutions.


Community engagement has been an important aspect of the project; key stakeholders have been engaged with the aim of improving public understanding of the project and the challenges involved in decarbonisation. Letters were sent to properties in the local village outlining information on the project and benefits in comparison to traditional developments, and a tour was hosted for the local Parish Council. Additionally, an open day was attended by the Rivers Trust, local residents and local and national news outlets who promoted the scheme. OFWAT has visited the site and aims to encourage this type of solution in PR24. Water companies have also visited the site to understand how they can apply the solution in their own areas.

Directly, the people of Clifton will benefit from an improved wastewater treatment service, which has less carbon emissions than a conventional plant, provides educational opportunities and blends into the vista. Additionally, no waste was removed from the site, protecting the local community from disruption and carbon emissions, utilising a materials management plan under the process.


The project utilises over 24,000 plants, offering biodiversity enhancements and creating resilience against climate change. Clifton enhances the local natural environment with a BNG of 2.28. This is an improvement compared to a traditional activated sludge plant (ASP). Additionally, an ASP would also include significant amounts of concrete, which has been avoided.

Additionally, an ecological wilding area was created and planted adjacent to the site, using surplus waste materials. The flora and fauna in this area help to create natural climate resilience and have resulted in a second biodiversity net gain (BNG) habitat equal in size to the wetland. This habitat also enhances the climate resilience of local communities through engagement with schools and professionals andthrough educational site visits to study wildlife and plant bug houses.

Being a fully ‘green’ solution and incorporating waste-reduction measures has also enhanced the promoting the use of nature-positive infrastructure over conventional ‘grey’ ones. It decreases the amount of power needed, reduces concrete poured, avoids reliance on chemical supply chains and reduces lorry movements. .

Almost two years of performance data has shown that the target nutrient reduction concentration is being achieved. There are several academic studies programmed to continue informing the future of more sustainable water treatment. Since Clifton, another eight projects have adopted the nature-based design in Yorkshire Water and there has been interest from academics, regulators, designers, and other water companies. It is envisaged that up to 1,000 ha of wetlands will be created in the next decade, modelled on the Clifton design  and 40 designs are already in progress across the UK.


Clifton WwTW ICW has also generated notable economic outcomes. The project was completed within budget, two years ahead of the original plan and with 35% lower costs than conventional building solutions and operational costs 64% lower over its lifetime. This cost-saving boosts economic growth through reinvestment of savings and passing savings onto the customer.

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