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Harlequin CAP9 (up to 9 Person)

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 The Harlequin CAP9 or 'Continuous Aeration Tank' is a compact sewage treatment system is designed specifically for domestic households with up to 7 bedroooms or to serve up to 9 people. 

 Harlequins unique bio media system delivers a pollutant removal level of 96.2% whilst also combatting common problems associated with small packaged domestic plants. Contemporary design engineering and analysis software and state-of-the-art manufacturing facilities combine to create this unique product which dominates the domestic sewage treatment plant market. Market-leading performance, easy installation, super quiet operation, low maintenance costs, reliable bio media system and durability are all qualities that make the product best suited for a wide range of off-mains sewage treatment requirements.

 The CAP9 is available in gravity or pumped outlet versions and with the option of a low pressure alarm. The standard invert depth of the CAP6 is 0.65m. If necessary this invert can be increased up to 1.55m by adding additional risers.

 Please call us if you are need additional risers on 01388 537 050.

 Harlequin CAP6 and CAP9 Installation Guide

Harlequin CAP9 Specification

 Commissioning and Servicing Information

 Product Specification

Nominal hydraulic daily load  1,800 Litres / day
Nominal organic daily load 510g BODs / day
Inhabitants served up to 9
De-sludging interval 12 months *
Electronic consumption 1.8 kWh / day
Overall dimensions Dia. 1840 mm H 2180 mm
Net Weight 350 kg


  • Tank body moulded in one piece from durable medium density polyethylene material
  • 110mm inlet and outlet connections
  • 110mm services duct
  • Integrated lifting eyes for ease of handling and installation
  • Fully secured 450mm pedestrian duty flush fitting manhole cover to comply with statutory regulations
  • Above ground air blower housing delivers more reliable and efficient operation; allows easy access for maintenance
  • A MBBR system - there is no fixed media, eliminating blockages
  • Easy access to the bubble diffuser within the tank
  • Compact size and light weight reduces installation costs
  • Super quiet when installed correctly
  • Cost-effective installation
  • 12-month service period reduces operating costs
  • Mechanically reliable with no moving parts or electrics within the tank
  • Certified to EN12566-3

 How to Harlequin CAP9 works

Chamber 1 Primary Settlement:

Raw sewage flowing to the CAP unit is received in the primary settlement zone. Here, gross solids (primary sludge) settle to the bottom of the tank, where they remain until the tank is desludged. The settled sewage displaced from the primary zone then flows into the submerged filter zone, passing under a scum baffle.

Chamber 2 Reactor Vessel
Flow circulation in the submerged filter zone is generated by the hydraulic effect of the outlet air diffuser. This causes settled sewage entering the filter zone at high level to be drawn down through the media, aerating the sewage in the process. The flow circulation ensures that the influent sewage receives several passes through the filter bed at low flow.
In the filter zone, as the sewage passes over the filter media it is purified by micro-organisms growing on the surface of the media. Growth of these micro-organisms results in an excess which is shed as solid particles known as humus solids. Humus solids settling at the bottom of the filter zones are recirculated with the flow of incoming sewage and are deposited on the top of the primary settlement zone.

Chamber 3 Final Settlement
Sewage displaced from the submerged filter zone flows via a DIP pipe into the final settlement zone. Liquid displaced from the humus zone has now been fully treated and is known as final effluent. It is suitable for discharge to a watercourse or soakaway as defined in the consent to discharge issued by the Environment Agency.
Humus solids from the final settlement tank are recirculated to the primary tank via the recirculation pipework. This helps reduce the sludge build up in the humus tank and prevents stagnation during very low inflow.


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