The Framework
Yorkshire Water has issued a formal tender through Find a Tender (reference 2026/S 000-068534, internal reference CM3543) for an ASP Diffuser Asset Replacement Framework. The framework covers the full lifecycle of diffuser system replacement across Yorkshire Water's estate of Activated Sludge Plants — from initial condition assessment and design through to supply, installation, commissioning and ongoing replacement.
Yorkshire Water is seeking specialist contractors to join a framework for the replacement and maintenance of diffuser systems in its Activated Sludge Plant network. The framework is valued at £9.27m (ex VAT) over a 4+4 year term running from January 2027 to December 2034. Award criteria are split 50% Quality and 50% Commercial. The tender was published on 17 July 2026 via Find a Tender, the UK's mandatory above-threshold procurement portal under the Procurement Act 2023.
What Are Activated Sludge Plants — and Why Do Diffusers Matter?
The Activated Sludge Process (ASP) is the most widely used biological wastewater treatment method in the UK. In simple terms, it involves mixing incoming wastewater with a culture of microorganisms — the activated sludge — in a large aeration tank. The microorganisms consume the organic pollutants in the wastewater as a food source, cleaning the water before it passes to settlement and further treatment stages.
The aeration system — specifically the diffuser network installed across the floor of these tanks — is central to the whole process. Diffusers introduce compressed air into the mixed liquor, providing the oxygen that the microbial community needs to survive and function. Without effective aeration, the biological treatment process fails and the plant cannot meet its discharge consent.
Fine bubble membrane diffusers — the most efficient type — are made from EPDM rubber or polyurethane membranes stretched over a support plate. Over time, these membranes foul with biological growth, suffer chemical degradation, and lose their oxygen transfer efficiency. A diffuser that was 35% efficient at installation may drop to 20% efficiency after several years, significantly increasing energy costs and reducing treatment performance. Periodic replacement is not optional — it is a routine operational and capital requirement for every ASP operator in the UK.
Scope of Works
Yorkshire Water's framework covers the complete scope of diffuser asset replacement, from initial diagnosis through to commissioned replacement systems. The key work categories are:
- Assessment — condition surveys and performance testing of existing diffuser systems to determine replacement priority and specification
- Design — engineering design of replacement diffuser systems, including layout, density, air supply and control integration
- Supply — procurement and delivery of replacement diffuser assemblies, supporting hardware and ancillary components
- Installation — physical installation of new diffuser systems in live or dewatered ASP tanks, including associated pipework and connections
- Commissioning — testing, calibration and performance verification of installed systems to confirm oxygen transfer efficiency targets are met
- Replacement — ongoing asset replacement over the framework term as individual components reach end of life
This framework is suited to specialist wastewater treatment process contractors and diffuser system suppliers. The 50/50 quality/commercial split means that technical capability — demonstrated experience in ASP aeration systems, knowledge of fine and coarse bubble diffuser technology, and evidence of previous similar replacement programmes — will carry equal weight to price. Companies with a track record in water company wastewater treatment works, particularly those already working within Yorkshire Water's supply chain or holding relevant accreditations, are well positioned to compete.
Framework Details and Procurement Route
The framework has been published under the Procurement Act 2023 via Find a Tender, the UK's mandatory procurement notice portal for above-threshold contracts. The procurement was initiated by Yorkshire Water through its internal reference CM3543.
Key Framework Facts
- Client: Yorkshire Water Services Ltd
- Reference: 2026/S 000-068534 (CM3543)
- Framework value: £9.27m (ex VAT)
- Framework term: 4+4 years — January 2027 to December 2034
- Submission deadline: 12 August 2026
- Award criteria: 50% Quality / 50% Commercial
- Published: 17 July 2026 via Find a Tender
- Region: Yorkshire and Humber
Supply Chain Context
Yorkshire Water is one of England's largest water and wastewater companies, serving approximately 5.4 million customers across the Yorkshire region. Its AMP8 investment programme runs from 2025 to 2030 and includes significant expenditure on wastewater treatment asset renewal, driven by tightening discharge consent standards and the need to reduce storm overflow spills under the Environment Act 2021.
Diffuser replacement sits firmly within the asset maintenance and renewal category of AMP8 capital expenditure. Unlike large civil or mechanical schemes, diffuser replacement programmes are awarded on process knowledge and delivery efficiency — which means they are accessible to specialist SMEs and established process contractors alike.
The 4+4 year structure gives successful framework suppliers a potential 8-year relationship with Yorkshire Water's wastewater operations team — significantly longer than a single works contract. For companies seeking stable, recurring revenue from a major UK water company, this type of framework is a strategic priority.
This tender is published under the Procurement Act 2023, which replaced the Public Contracts Regulations 2015 from February 2025. Key changes affecting suppliers include new transparency requirements (all notices must appear on Find a Tender), updated award criteria rules, and new supplier debarment provisions. For water sector suppliers, the Act also introduces stronger requirements around payment terms and subcontractor protections.
How to Get Involved
The tender is live on Find a Tender (reference 2026/S 000-068534). Submission is via Yorkshire Water's procurement portal. The deadline for submission is 12 August 2026.
If you are a wastewater treatment specialist interested in this framework and would like guidance on the opportunity, to understand how it fits within Yorkshire Water's broader procurement pipeline, or to discuss whether your business is positioned to compete — contact Water Industry Hub. We track Yorkshire Water's full tender pipeline and can provide context on the procurement landscape.
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