WPL Hybrid-SAF™

High-rate adaptable biological wastewater treatment

WPL’s Hybrid-SAF is a highly efficient wastewater treatment process that can deliver significant cost-savings over traditional submerged aerated filters (SAFs).

The technology comprises of a submerged moving-bed, fixed-film reactor which can treat wastewater with greater energy efficiency than standard SAFs, in a tighter site footprint whilst meeting environmental compliance.

Adaptable technology – above or below ground plants

A key advantage is that the modular technology cells can be retrofitted into any onsite vessel, regardless of shape or size. This reduces the high cost of rebuilding infrastructure, minimises onsite disruption, reduces waste and optimises site footprint.

WPL can also supply Hybrid-SAF as packaged wastewater treatment plant in steel, glass-reinforced plastic (GRP) or a combination of both materials (Hybrid-16 units) for new wastewater treatment plants.

A hire option for temporary and trial applications is available.

Examples of how the technology can be used:


  • Utilities and municipal
  • Industrial trade effluent
  • Commercial

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Technology advantage

  • High-rate process (submerged moving-bed, fixed-film reactor)
  • Achieving <0.4mg/l ammonia discharge
  • Site footprint requirement 30% smaller than comparable technologies 
  • Energy consumption reduced in line with footprint reduction
  • Fully optimising new or existing vessels regardless of shape or size
  • Interlocking modular units for larger capacities
  • UK water utility and industrial site references

Low Maintenance

  • Fully optimised plant – maximum of one visual check a week
  • No mechanical or electrical moving parts within the cells
  • No need to drain tanks or remove the media during maintenance
  • No need to desludge process technology cells
  • Does not require additional equipment or adaptation to scour within the biological reactor
  • Cells can be removed, repaired and reinstalled individually without impacting on the process and discharge standard
  • No need for high-level access for internal maintenance

Installation and commissioning

  • Technology installed within days
  • Modular cells overcome site access restrictions
  • Off-site build significantly reduces installation time
  • Health and safety risk minimised
  • Can be delivered by Hiab loader crane
  • Reduced commissioning times

Design and off-site build

  • UK manufacture in a quality-controlled environment
  • 25-year design-life
  • Technology is patent pending

Above ground standardised option

  • Scalable to accommodate growing populations
  • Cells can operate individually or connected in series to form a larger plant
  • Can redeploy elsewhere if existing installation becomes redundant before end-of-life

Repurpose of onsite vessels

  • CFD modelling carried out
  • Vessel scanned to ensure precision fit

Treatment standards

  • The technology meets high treatment standards for biochemical oxygen demand (BOD), ammonium (NH4), and soluble chemical oxygen demand (COD)
  • Additional equipment can be added to remove phosphorus (P)
  • The process can also be configured to provide anoxic conditions for nitrate (NO3) removal

Hydraulic design and control

  • Higher process treatment capacity achieved within each vessel, reducing the physical footprint, which in turn optimises energy per m³ treated
  • Hydraulic design ensures even and constant flows of nutrients and oxygen over the high specific surface area media, even during peak and low flow situations, providing ideal conditions for biological growth and treatment
  • The slow-moving media bed and hydraulic design ensure that the suspended solids that normally settle out are carried up and through the process to be captured in the final clarification stage


  • Secondary and tertiary treatment process
  • Standardised or repurpose options
  • Telemetry control system for the blowers
  • Variable speed drive blowers can deliver 50-100% of design requirements, allowing greater headroom for power optimisation
  • Control kiosks with blowers, panels and optional telemetry equipment are also factory built to reduce onsite installation time

Fully compliant

  • WIMES specification
  • British Standards
  • European Norms
  • Designed to meet individual UK water utility specifications
  • Designed to BS12255 – parts 1 to 15

Technical specification

For standardised asset options download the WPL Hybrid-SAF datasheet within the Assets section on this page.