WPL HiPAF Midi (60 up to 300 PE)

Compact sewage treatment plant


The WPL HiPAF Midi compact sewage treatment plant offers sewage and wastewater treatment for properties of 60-300 people equivalent for where mains drainage is unavailable. The sewage treatment system is a packaged plant containing primary settlement, biological treatment (biozone) and final settlement modules suitable for larger applications and manufactured in glass reinforced plastic (GRP), installed below ground.

The HiPAF Midi sewage system treats wastewater using no chemicals to a high standard for more stringent standards stipulated by the Environmental Agency.

Our cutting-edge, ‘off-the-shelf’ HiPAF Midi packaged plants are tailored to your requirements to offer environmentally-friendly, legislation-compliant solutions that are simple to install, easy to live with and economical to maintain.

The HiPAF Midi sewage treatment plant is an EU compliant wastewater treatment system as per the statutory requirements. Designed and manufactured in the UK, they are easily transported to the continent.


Features and Benefits of the WPL HiPAF Midi:

Low running cost and maintenance

  • The design has no internal mechanical moving parts therefore the plant requires minimal annual maintenance
  • Emptying of the tank is also not required during maintenance of air distribution system

Discrete and low installation costs

  • Only a small excavation is required due to its compact design

Tailored applications

  • Energy saving options and chemical dosing packages can be tailored to the design for site specific requirements

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


  • Robust operation and stand-by facility

Easy access

  • Safe, clean, accessible air diffuser system with large access lids for easy maintenance
    (examples at the bottom of this page)

Simple tankering operation

  • Humus and primary sludge are stored in one place for simple tankering operation

Tank 25 years life

  • GRP is UV stabilised with an external gel coat finish which extends the asset life to 25 years
  • WPL HiPAF sewage 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 HiPAF Midi sewage treatment plant include:

    • 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

 The WPL HiPAF Midi Standard

The WPL HiPAF Midi range meets the following industry standards:

  • Fully compliant with UK Building Regulations and Environment Agency (EA) guidelines
  • The WPL HiPAF Midi compact sewage treatment plant is 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

Three stage system for safer processing

Each 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
  • High-voidage plastic media, contained between two floors within the biozone, encourages the growth of bacteria and other organisms which treat the
  • 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

The WPL HiPAF™ brand (High Performance Aerated Filter) references the unique hydrodynamic profile within the filter bed.  The benefit is a stable even biomass growth, during high or low flows meaning WPL is offering higher treatment efficiencies over other similar solutions on the market.

WPL’s robust biological treatment process guarantees to suit BOD and Ammonia removal and is underpinned by 25 years of empirical data offering treatment for carbonaceous ﴾BOD﴿ removal, nitrification and de‐nitrification ﴾Total N﴿ when strict standards are required.

Technical Specification of the 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.

HiPAF Midi Sewage treatment plant

Standard Kiosk Design

Each HiPAF Midi sewage treatment plant comes complete with a discreet, weatherproof, acoustically lined GRP kiosk, situated above ground. This houses the blower(s), a Form 2 control panel and air distribution manifold.

Included as standard is 10m of airline, to connect the blowers to the tank. Blower and airline upgrades are available if the kiosk is sited further than 10m from the plant.

The Form 2 control panel automatically controls the operation of the plant.  Form 4 is also available.

Kiosks upgrades available on request

Example of a standard (large) kiosk

Image of WPL standard kiosk, a component of a WPL sewage and wastewater treatment system

 The WPL HiPAF Midi Commercial Applications

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

MK2 lids for commercial application:

  • 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 lids  Image showing the internal configuration of a WPL HiPAF sewage treatment plant

 WPL HiPAF Midi Water Utility Specification

WPL HiPAF Midi with Mk 3 lids at Hycemoor WWTW

WPL HiPAF midi with Mk3 lids designed for the UK water utilities

MK3 lids for the UK Water Utilities specification:

  • Anti-slip pads on the lids
  • All lids are lockable
  • Two lids per width of the tank – lids less than 25 kilo’s to lift
  • Lockable stainless steel stays
  • Grating held in position under the lid when in the down position allows ease of access to all air distribution pipework
  • Grating when in place prevents risk of fall
  • Raised air distribution pipework allows for ease of maintenance

Image of WPL MK3 lids with grating showing air distribution pipework, part of the bespoke wastewater treatment system, the WPL HiPAF  WPL MK3 lids showing grates to walk on

HiPAF packaged sewage treatment plant installation | 3 villages in Slovenia

  • Total of three HiPAF packaged sewage treatment plants and walk-in kiosk housing blowers, manifolds and control panels being installed
  • Each village will have an individual plant treating sewage for approximate 235 population equivalent.
  • Final (3rd) stream installed early January 2016