WPL Hybrid-SAF™

Process quality

WPL’s submerged biological treatment process technology inside the Hybrid-SAF units 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.

Flexibility of design

WPL Hybrid-SAF units can either operate as individual treatment plants or the modular design means they can be connected in series to form larger plants. The flexibility of the modular design means units can be designed to an unusual footprint shape and installed even where site access face height and width constraints. In certain circumstances, WPL can increase the height or width of individual units at the design stage to accommodate site constraints.

Built off site, the modular units are simple to transport and install, reducing on-site installation time, which in-turn reduces health as safety risk. Units can be redeployed elsewhere if an existing installation becomes redundant before the end of its life.


Why you should choose the WPL Hybrid-SAF:

Flexible design

  • Designed to fit sites with a small or unusual footprint
  • Scalable to accommodate a growing population
  • Transportable asset during site modification
  • Can redeploy elsewhere if an existing installation becomes redundant before the end of its life
  • Modular units can operate as an individual treatment plant or be designed to be connected in series to form a larger plant

Custom design and off-site build

  • Can overcome installation challenges, both height and width restrictions in to and onsite
  • Can be combined with both upstream and downstream treatment equipment
  • Option of allowing blowers to be driven by variable speed drives (VSD’s), controlled by dissolved oxygen (DO) and/or ammonia monitors. This delivers further reductions in energy consumption; reducing overall carbon footprints and running costs

Reduces civil installation time

  • Modular tanks  can be installed on-site within days (off-site build) inturn reducing on-site health and safety risk
  • Can be delivered and off-loaded by a lorry crane (Hiab), removing the need for large lifting equipment
  • Control kiosks with blowers, panels and optional telemetry equipment are also pre-built to reduce on-site installation

Low operator maintenance

  • When the plant is fully optimised – max requirement visual check once a week, however this is not a requirement
  • No mechanical or electrical moving parts within the modular tanks
  • No need for high level access for internal maintenance
  • No need to drain the tanks or remove the media
  • No need to desluge the tanks


  • Meets stringent environmental discharge standards
  • The process consistently achieves final effluent Ammonia concentrations of less than 1 mg/l on a 95%ile basis.
  • Fully compliant WIMES specification, British Standards and other European Norms
  • Designed to meet individual UK water utility specifications
  • Designed to BS12255 – parts 1 to 15

Continuous research and development

  • The process technology inside the modular Hybrid tanks is 30% smaller footprint compared with equivalent technologies
  • Due to the smaller footprint, the energy consumption is reduced in line with the 30% – optimising  energy per m³ treated
  • Developments in hydraulic control and retention times have also enabled WPL’s process technology to consistently achieve final effluent Ammonia concentrations of less than 1 mg/l on a 95%ile basis.


  • Manufactured, engineered and wet tested in WPL’s quality controlled factory
  • Modular vessels are a combination of UV stabilised GRP with an external gel coat finish and galvanised steel or stainless steel structural ‘exoskeleton’ – design life of 25 years
  • Standard unit size (UK) is 2820mm (l) x 2820mm (w) x 3300mm (h)

Technical specification

For technical specification information (including indicative drawing), please download  the WPL Hybrid-SAF datasheet (available on this page).

Case study: at a glance

Image of WPL Technical Director, Andrew Baird at Sandbach site

United Utilities (UU) Wastewater Treatment Works – Sandbach in Cheshire and Lawton Gate in Staffordshire.

Each of the two site installations was delivered and offloaded over two days and was set up and commissioned within five days.

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