WPL HiPAF® compact

1 up to 60 population equivalent (PE)

The WPL HiPAF packaged wastewater (sewage) treatment range is regularly specified by the highly regulated UK water utilities, and the range meets stringent European environmental discharge consent standards.  This makes our products the preferred choice for sensitive locations such as Sites of Special Scientific Interest (SSSI).

The WPL HiPAF compact plant uses no chemicals during the treatment process and is ideal for locations which need extra consideration such as a burn, nature reserve, fisheries, salmon river or close proximity to water extraction (well).

The fully compliant, below ground WPL HiPAF compact (HPC) sewage treatment plant is ideal for 1 up to 60 population equivalent where mains drainage is unavailable.   Each wastewater treatment plant includes a primary settlement, biological treatment and final settlement processes all in one compact unit.

The HPC is manufactured in glass reinforced plastic (GRP) which is ultra violet (UV)  stabilised with an external gel coat finish which extends the asset life to 25 years.


Why you should choose the WPL HiPAF compact (HPC):

Ease of installation

  • Overall compact design minimises excavation required offering small footprint and lower installation costs

Low maintenance

  • No internal mechanical or electrical moving parts
  • Optional low energy compressors with adjustable timers
  • Tankering made easier because primary sludge and humus are stored together

Robust process

  • Proven WPL technology based on over 25 years empirical data
  • Rectangular shape of the midi and modular plants reduces dead zones
  • Use of high quality blowers and pumps underpins reliability of the plant
  • No odours – most other treatment plants have a separate primary tank which store settled solids and can emit odours; however our WPL HiPAF compact design has no separate primary tank and is therefore odour-free

Minimal visual impact

  • Below ground installation means the plant does not impede views of the landscape which means the plant requires minimal annual maintenance making it economical to run
  • Emptying of the tank is also not required during maintenance of air distribution system


  • Fully compliant with UK Building Regulations and Environment Agency guidelines
  • WPL uses British Water’s Code of Practice – Flows & Loads
  • Designed and manufactured to BS EN 12566-3
  • Meets all current legislation under the Environmental Permitting Programme
  • WPL HiPAF treatment plants are CE marked where applicable

Technical specification

For technical specification information (including indicative drawing), please download  the WPL HiPAF brochure (available on this page).

Typical uses for the WPL HiPAF compact (HPC) include:

  • Domestic housing
  • Commercial buildings and offices
  • Stately homes and country estates
  • Small hotels and bed and breakfasts
  • Small retail such as farm shops
  • Small villages, rural communities and housing associations

Image of WPL HiPAF Midi compact sewage treatment plant at a campsite for off mains drainage

Installed WPL HiPAF compact wastewater treatment plant

Read our simple guide to the Do’s and Don’ts usage compact wastewater (sewage) treatment plant.

WPL HiPAF compact treatment process

Image of HiPAF Compact process showing sewage and wastewater treatment process

1.  Primary settlement tank

2.  Settled solids at the bottom

3. Biological treatment unit (biozone)

4. Air diffusers at the bottom of each chamber

5. Filter media

6. Settled sludge air lift back to primary

7. Final (humus) settlement tank

  • Primary – Primary settlement is in accordance with EN12255-4, giving the required hydraulic retention time and ensuring that 30% of the BOD will settle out in the primary tank.  WPL HiPAF plants below 500 persons will have sludge storage integral to the primary tank. The primary settlement tank is equipped with baffles to prevent floating scum entering the biological phase of the treatment process. It also incorporates WPL’s unique forward feed system which lowers the level in the tank, during periods of low flow, to provide a buffering capacity for possible surges in the influent.
  • Biological – After primary settlement, the settled liquor flows to the biological treatment unit by displacement and via the air lift forward feed. The biozone is fully segmented internally to eliminate the risk of process short cuts. Each biozone segment is filled with high voidage plastic filter media, where both carbonaceous and nitrifying processes take place, mitigating process risks associated with variable loads. Air to oxygenate the influent and to scour excess biomass from the filter media is introduced continuously below each chamber by a series of diffusers.
  • Final – Following biological treatment the effluent flows into the final (humus) settlement tank where the excess biomass settles out. The humus tank is equipped with air lifts which are arranged to automatically transfer settled humus sludge to the primary tank for co-settlement. The treated effluent flows under gravity to the works outfall.