WPL HiPAF® compact

1 up to 60 population equivalent (PE) where mains drainage is unavailable

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


  • Domestic homes
  • Small business
  • Ideal for environmentally-sensitive areas

The 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).

Why choose the WPL HiPAF compact (HPC):

Ease of installation

  • Overall compact design minimises excavation
  • Small footprint size units
  •  Below ground installation does not impede views of the landscape

Low maintenance

  • No internal mechanical or electrical moving parts within the tank
  • Tankering made easier because primary sludge and humus are stored together

Robust process

  • No odours – most other treatment plants have a separate primary tank which store settled solids and can emit odours; however our compact design has no separate primary tank and is therefore odour-free*
  • Warranty 25 years on the tank and air blower (housed in the kiosk) 2 years*
  • High quality blowers and pumps underpins reliability of the plant


  • UK Building Regulations and Environment Agency guidelines
  • British Water’s Code of Practice – Flows & Loads
  • CE marked to BS EN 12566-3
  • Meets all current legislation under the Environmental Permitting Programme
  • 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

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

*subject to correct installation, ventilation, consistent influent conditions and regular plant maintenance as per the manufacturers’ instructions.

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

The compact unit is a three-stage wastewater 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.