Severn Trent Water has opened a £44.4 million procurement for membrane aerated biofilm reactor systems, seeking suppliers to support wastewater treatment upgrades across its operating region.
The company intends to establish a multi-supplier framework for membrane aerated biofilm reactor (MABR) technology and associated services. Approximately 11 wastewater treatment sites have been identified in the anticipated programme, although the number of installations and their final requirements remain subject to change.
Published on 6 November, the contract notice follows earlier procurement planning and forms part of Severn Trent’s AMP8 Activated Sludge Plant Intensification Programme and wider Net Zero Investment Programme.
The framework is expected to begin in March 2027 and run for an initial four years. Severn Trent may extend the arrangement by up to a further four years, creating a potential eight-year procurement route for equipment and services.
The estimated £44.4 million is the value of the framework opportunity, not the amount of work already awarded. Severn Trent has expressly stated that the agreement will not guarantee any future call-offs, expenditure or purchase volumes.
Suppliers appointed to the framework would become eligible for subsequent procurement activity as individual treatment projects progress. The company may also use the arrangement for additional MABR requirements during AMP8 and future AMP9 investment programmes.
The specified scope includes design support and the manufacture and supply of MABR systems. Detailed arrangements for installation, integration and commissioning will depend on the requirements of subsequent projects and the services procured under the framework.
MABR technology is designed to improve biological treatment by delivering oxygen through gas-permeable membranes that support microorganisms growing as an attached biofilm. This provides an alternative oxygen supply mechanism to the air bubbles commonly used in conventional activated sludge treatment.
In conventional systems, blowers introduce air into wastewater through diffusers. Oxygen must transfer from those bubbles into the surrounding liquid before microorganisms can use it. The transfer efficiency depends on factors including diffuser design, bubble behaviour, water depth and operating conditions.
Membrane aerated systems transfer oxygen across the membrane to the biofilm growing on its surface. Oxygen is supplied from the membrane side, while wastewater constituents reach the microorganisms from the surrounding liquid.
The resulting concentration gradients can support different biological processes within the biofilm. Ammonia-oxidising microorganisms use oxygen to convert ammonia through the nitrification process, while organisms operating in areas with limited oxygen can contribute to denitrification under suitable conditions.
Nitrification converts ammonia into oxidised forms of nitrogen, principally nitrite and nitrate. Denitrification subsequently converts nitrate or nitrite towards gaseous nitrogen, provided an appropriate source of organic carbon and suitable operating conditions are available.
These processes are important where wastewater treatment works must remove nitrogen compounds to meet the quality requirements of their treated discharge. The extent of treatment required depends on the incoming wastewater and the permit conditions applying to an individual site.
MABR modules can be introduced into some existing activated sludge tanks, offering a route to increase biological treatment capability within established infrastructure. The practicality of this arrangement depends on tank dimensions, hydraulic behaviour, available space and the treatment performance required.
Adding membranes does not remove the need for engineering changes elsewhere in a treatment works. Air supply equipment, pipework, controls, instrumentation and access arrangements may require modification, while the operation of existing biological treatment stages must remain compatible with the new system.
Biofilm management introduces a further operating requirement. Microorganisms must be able to grow and remain active on the membrane surface, but excessive accumulation can affect the transfer of oxygen or wastewater constituents through the biological layer.
Operating procedures may therefore incorporate methods for managing biofilm thickness and maintaining suitable treatment conditions. The required approach varies with the membrane system, wastewater characteristics and reactor configuration.
Temperature, organic loading, ammonia concentration and changes in wastewater flow can also influence biological performance. A process that operates effectively under steady conditions must be evaluated against the variations experienced at the treatment works.
MABR technology can offer opportunities to improve oxygen transfer and reduce some aeration requirements, but Severn Trent has not published a guaranteed energy saving or treatment performance figure for the prospective installations.
The final outcome at each site will depend on engineering design, the condition of the existing assets and the operation of the complete treatment process. A lower energy requirement in one biological stage does not automatically establish an equivalent reduction across the whole treatment works.
The use of a framework provides Severn Trent with a route to procure equipment for a series of projects without committing immediately to the full indicative programme. It also allows the company to determine project-specific requirements as treatment designs and investment decisions develop.
Companies interested in supplying the technology must participate in the formal procurement process. The submission deadline is 16 December 2026, with the published notice setting out the competitive procedure and associated requirements.
The development is part of a wider programme to intensify wastewater treatment within existing infrastructure while managing the energy demands of biological processing. The selected systems will need to demonstrate their suitability for the treatment conditions and installation constraints at each proposed site.
Framework appointments are anticipated from March 2027, but Severn Trent has not confirmed the suppliers, the final number of treatment works or the commissioning timetable for individual MABR installations.
