WPL Hybrid SAF

Submerged aerated filtration for wastewater treatment

The modular WPL Hybrid SAF product range combines submerged aerated filter technology with the latest research to mitigate the risk of compliance failures. Process flexibility makes the the modular plant suitable for a range of applications from sewage to industrial wastewater treatment.

Each individual modular WPL Hybrid SAF is built to a standard size 2.8m (l) x 2.8m (w) x 3.1m (h), which allows for ease of transportation, site access and installation. The units can operate as an individual treatment plant or be designed to connect in series to form a larger plant, which takes in to account the footprint of each individual site requirements.

The WPL’s SAF plants have a proven track record of over 25 years in utilising submerged aerated filtration for wastewater treatment; compliant with WIMES, specific water utility asset standards, CDM regulations, European norms and directives.

Why you should choose the WPL Hybrid SAF:

Flexible design

  • Scalable – the modular WPL Hybrid SAF units can operate as an individual treatment plant or be designed to be connected in series to form a larger plant.
  • Reduced footprint – the WPL Hybrid SAF package can be designed to fit sites with a small or unusual shaped footprint or scaleable to accommodate a growing population of up to 10, 000 PE.
  • Moveable – can be used as a transportable asset during site modification and used elsewhere if an existing installation becomes redundant before the end of its life. This prevents premature scrappage and reduces waste.

Reduces civil installation time

  • Off-site build – The unique, above ground, WPL Hybrid SAF modules are manufactured, engineered and wet tested in a quality controlled environment, reducing on-site installation time and health and safety risk.
  • Ease of access – the modular design of the tanks are designed for ease of transportation and accommodates unusual height or width restrictive site access.
  • Ease of off-loading – The units can an be delivered and off-loaded by a lorry crane (Hiab), removing the need for large lifting equipment on-site during installation.
  • Control kiosks – blowers, panels and telemetry equipment are also pre-built to reduce on-site installation

Engineering design

  • Process – designed to meet on site specification and high treatment standards for biochemical oxygen demand (BOD), ammonium (NH4), nitrate (NO3) and soluble chemical oxygen demand (COD).  Additional equipment can be added to remove phosphorus (P) .
  • Process – The modular design can be combined with both upstream and downstream treatment equipment based on individual process requirements.
  • Running costs – option of allowing blowers to be driven by variable speed drives (VSD’s), controlled by dissolved oxygen (DO) and/or ammonia monitors, delivers further reductions in energy consumption, reducing overall carbon footprint and running costs.
  • BIM – modular construction and configuration can meet site-specific requirements incorporating BIM workflow principle.
  • Compliant –  all WPL SAF units meet WIMES, specific water utility asset standards, CDM regulations, European norms and directives.


  • No need for high level access for internal maintenance which significantly reduces health and safety risk.
  • No need to drain the tanks or remove the media, minimising maintenance.
  •  No internal moving parts or maintenance required within the tank.
  • GRP and galvanised steel or stainless steel frame reduces maintenance costs, no need for repainting of steel structure.

Continued Research and development

  • Research has proved that the unique hydrodynamics retains process fluids, in excess of the hydraulic retention time (HRT).
  • 25 years of process developments has led to the evolution of the WPL SAF process into the hybrid variant.


  • Manufactured, engineered and wet tested in WPL’s quality controlled factory environment, reducing on-site installation time which further reduces health and safety risk.
  • Modular units are a combination of UV stabilised external gel coat finish GRP (glass reinforced plastic) and galvanised steel or stainless steel structural ‘exoskeleton’ – design life of 25 years.
  • Units for international export are built to a standard size to fit five units in to a 40ft (12m) shipment container and two units in to a 20ft (6m) shipment container.
  • Standard UK unit size is 2.8m (l) x 2.8m (w) x 3.1m (h).


WPL SAF options

Our WPL SAF’s can also be manufactured in steel, stainless steel and GRP, both above and below ground.

WPL SAF hire options are also available in steel and stainless steel tanks.

Case study: at a glance

Modular installation at a United Utility site, Sandbach & Lawton Gate WwTW

Some 12 x WPL Hybrid SAF modules have been installed in four treatment streams at Sandbach wastewater treatment works (WwTW).

Meanwhile, six WPL Hybrid SAF modules are now providing two additional treatment streams at Lawton Gate WwTW.

Arrival of Modular Hybrid SAF at Sandbach site

Installation and commissioning  in 5 days

Offloaded over two days and was set up and commissioned within five days.

The plants are likely to be needed at these sites for approximately five years. However, they can be transported from site-to-site as required in the future.

Image of Modular Hybrid SAF (submerged aeated filtration) for BOD and ammonia removal being installed at Sandbach


Neil Wilkinson, Projects Manager, Nomenca said:

“The modular nature of WPL’s Hybrid SAFs gives the wastewater treatment plant managers at Sandbach and Lawton Gate flexibility in terms of operation along with the additional capacity required. They can work alongside existing process systems, so they were a good choice at these sites.

“Working in close partnership with WPL, each process plant was delivered on time and within budget.”


Technical director, Andrew Baird, returns to Sandbach WwTw site, post installation, to measure the performance through the dissolved oxygen levels of the WPL Hybrid SAF (submerged aerated filter).

Image of WPL Technical Director, Andrew Baird at Sandbach site

Read full case study Modular treatment plant delivers flexible upgrade for United Utilites

Meeting UK water utility site specifications

WPL recognise every site is different and each UK water utility has its own demanding requirements to meet AMP 6 targets.  Using our innovative WPL Hybrid SAF wastewater treatment plant, guarantees environmental compliance and is easily adapted to changing regulations and contributing to reduction in whole life costs.  The WPL Hybrid SAF plant is suitable for permanent or temporary applications, with a number of different hire and purchase options to meet customer requirement.

The WPL Hybrid SAFs flexible process suits both BOD and ammonia removal.