WPL HiPAF® midi – 60 up to 300 PE

Compact package sewage treatment plant


The below ground WPL HiPAF midi compact sewage treatment plant for properties of 60-300 people equivalent, where mains drainage is unavailable.

The WPL HiPAF range meets stringent European environmental discharge consent standards and is regularly specified by UK water utilities. This makes
the range the preferred choice for sensitive locations such as a Sites of Special Scientific Interest (SSSI).

Each WPL HiPAF wastewater treatment plant includes primary settlement, biological treatment and final clarification.

UK designed and manufactured in the glass reinforced plastic (GRP).


Why you should choose the WPL HiPAF midi system:

Low cost installation

  • Compact design minimises excavation required offering small footprint and lower installation costs
  • Modular design allows ease of transportation within the UK and to the continent

Low maintenance

  • The design has no internal mechanical moving parts within the tank – requiring minimal annual maintenance
  • Option of isolating and removing sections of the air distribution so it is not necessary to empty the tank
  • Safe, clean, accessible air diffuser system with large access lids for easy maintenance
  • Humus and primary sludge are stored in one place for simple tankering operation
  • Emptying of the tank is also not required during maintenance of air distribution system
  • Optional low energy compressors with adjustable timers
  • Chemical dosing packages can be tailored to the design for site specific requirements

Energy efficiency

  • Optional duty-standby blower arrangement minimises energy use
  • Variable speed drives can be used to optimise power use

Minimal visual impact

  • Does not impede views due to the below ground installation

Variable flows and loads

  • The unique design of the flow balancing in the primary tank means it can cope with variable flows and loads making it ideal for caravan sites and other seasonal venues.


  • Fully compliant with UK Building Regulations and Environment Agency (EA) guidelines
  • Designed using the British Water Code of Practice Flows and Loads, to ensure correct sized tanks
  • Designed to BS EN 12255 – 1/15 and manufactured using BS 4994


  • Proven WPL technology based on over 25 years empirical data
  • Unique internal circulation system leads to increased process performance
  • Use of high quality blowers and pumps underpins reliability of plant
  • Robust operation and stand-by facility
  • GRP is UV stabilised with an external gel coat finish which extends the asset life to 25 years
  • Plants and kiosks are produced in a quality controlled environment at the WPL factory
  • WPL tailor our robust and reliable wastewater treatment solutions to meet our clients’ demanding specifications and expectations

Typical commercial uses for the WPL HiPAF midi sewage treatment plant:

    • Animal waste options such as stables and kennels
    • Agricultural growers and garden centres
    • Camping and caravanning sites
    • Custodial establishments
    • Golf courses and fishing lodges
    • Hotels, restaurants and public houses
    • Motorway service stations
    • Care homes and retirement villages
    • Commercial buildings and offices
    • Housing developments
    • Schools, colleges and training centres
    • Stately homes and large country estates
    • Villages and rural communities
    • Visitor centres
    • Water utilities
    • Zoos, theme parks and leisure attractions and leisure centres

Design options:

  • Inverts up to 1.5m with turret extensions
  • Pumped inlet flow control
  • Single or three phase electrics depending on size
  • Alarm beacon for mechanical failure and loss of air pressure
  • Duty/standby blowers with automatic changeover to ensure an uninterrupted air supply
  • Energy-saving options such as variable speed drive blowers
  • GSM telemetry for remote monitoring of the plant
  • WPL’s Robust Aerobic Digestion System (RADS) can reduce de-sludge frequencies on the biological treatment plants
  • WPL Sand Filters can improve final effluent for strict consent requirements

Standard commercial kiosk design

Each WPL HiPAF treatment plant comes with a weatherproof kiosk to house the control panel and air blowers on site. The standard issue kiosk, which is acoustically-lined, houses:

  • Control panel, which automatically manages the operation of the plant
  • Air distribution manifold
  • One or more air blowers as required

Features include:

  • Thermostatic cut-off controls and air filtering monitoring which can alert the operator to loss of air pressure.
  • Ten meters of airline hose is supplied to connect blowers to the treatment plant – extra length can be supplied if the kiosk is sited further than 10m from the treatment unit.
  • The Form 2 control panel automatically controls the operation of the plant.  Form 4 is also available.

MK2 lids for commercial specification:

  • All lids are lockable
  • Large lids for easy access to each zone
  • Assisted lifting with gas struts
  • Fully serviceable due to easy access
  • Easily removable air diffusers
  • Optional safety grating when in place prevents risk of fall

WPL HiPAF sewage treatment plant showing gas strut open lidsImage showing the internal configuration of a WPL HiPAF sewage treatment plant

About the WPL HiPAF®

The HiPAF brand name refers to High Performance Aerated Filter, which is a unique hydrodynamic flow through the biological filter bed.  This helps provide even distribution across the media that is housed in the tank; ensuring strong even growth of the bacteria used in the treatment process and providing a robust stable treatment.
Feeding the biological zone is WPL’s unique airlift forward feed, maintaining a stable and even food source that enhances bacterial performance to degrade contaminants.
WPL’s robust biological treatment process is guaranteed to meet specified discharges of BOD5, ammonia and suspended solids, underpinned by over 25 years of experience and empirical data.

Three stage system for safer processing

Each WPL HiPAF treatment plant includes a three-stage process – primary settlement, biological treatment (biozone) and final settlement. The segmented biozone process chambers in stage two eliminate the risk of process short-cuts and mitigates risks associated with variable loads.


Stage 1 – Primary settlement

  • Incoming wastewater enters the primary settlement stage where organic and inorganic matter settles
  • The sludge is held in this section until it requires de-sludging
  • A unique forward-feed arrangement uses an airlift to deposit wastewater into the biological treatment stage (biozone), which keeps peak flows from entering the system and prevents hydraulic surges

Stage 2 – Biological treatment

  • Settled liquor enters the biological section either by displacement or via the airlift
  • High-voidage plastic media, contained between two floors within the biozone, encourages the growth of bacteria and other organisms which treat the wastewater
  • Air required for the treatment process is delivered by air-blowers housed in a weatherproof kiosk
  • The air also helps to scour the media bed, preventing the filter from blocking
  • A series of diffusers installed beneath the media bed ensure an even distribution of air

Stage 3 – Final settlement

  • The treated wastewater (final effluent) enters the final settlement section
  • Dead biomass (humus sludge) from the process settles out
  • An airlift automatically transfers settled humus sludge back to the primary settlement section for co-settlement
  • The final effluent is discharged through gravity displacement to either a watercourse or a sub-surface irrigation field

Technical Specification for the WPL HiPAF midi Sewage Treatment Plant



The table is an indicative guide only; all applications are specified to comply with the British Water Code of Practice for Flows and Loads.  For further advice please contact our experienced technical sales team.

Commercial application examples

Image of WPL Midi compact sewage system installed at McDonalds  WPL HiPAF midi installed at a public house

WPL HiPAF midi installed at an out of town fast food restaurant and public house.

West Gate WPL HiPAF Midi system installed below ground for off mains sewage treatment   Image of WPL HiPAF Midi sewage treatment plant at a campsite for off mains drainage

The below ground installation does not impede views.