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25 Person Marsh Ensign shallow dig sewage treatment plant.
  • 25 Person Marsh Ensign shallow dig sewage treatment plant.
  • Cross section of 25 Person Marsh Ensign sewage treatment plant.
  • Ensign shallow depth comparison.

25 Person Marsh Ensign Shallow Dig Sewage Treatment Plant

7-10 working days
7-10 working days
£7,114.82 ex. VAT
Free Delivery (Restrictions Apply)

Product Details

This item is supplied to order and additional refund & returns terms apply.


Inhabitants: Up to 25 people
Length: 4200mm
Width: 1912mm (+/- 50mm)
Height: 1600mm (+/- 50mm)
Depth to inlet invert level: 500mm (+/- 50mm)
Fall between inlet & outlet: 75mm
Pipe & Fittings: 160mm

Effluent Quality

BOD5: 11.5 mg/l
NH4: 8.4 mg/l
SS: 19.2 mg/l

This Marsh Shallow Ensign:Standard sewage treatment plant is designed to treat household wastewater for properties with up to 25 inhabitants. The Shallow Ensign:Standard is widely regarded as one of the most efficient, reliable and economical sewage treatment plants on the market.

Common sewage treatment plants on the market often exceed 2.3m high. Marsh Industries offer a range of shallow plants from 4-35PE that are only 1.6m in height, meaning installation is not only possible, but easier and safer too.

Shallow Ensign sewage treatment plants are often favoured when hard rock site conditions mean deeper alternatives, involving costly and time-consuming excavation.

Class leading performance

Tested and approved to BSEN12566-3/A1:2009 all Ensign units provide treatment well within national consent requirements. Published test results of 11.5:19.2:8.4mg/ltr (BOD: suspended solids: ammonia), with influent concentrations on test higher than those chosen by most competitor plants, effectively equates to 97% pollutant removal.

Unrivalled choice

Ranging in size from 4 to 35 PE in Ultra and Standard versions of each, and with a wide range of ancillaries, almost all site, consent and budget requirements can be met.

  • Optional risers to increase invert depth are available on request.
  • Optional pumped outlets are also available on request.

Why choose the Marsh Shallow Ensign:Standard?

End users, merchants and installers alike recommend the Ensign range due to its ease of installation, reliability, and cost-effective operation and maintenance. All backed by technical support from local contacts.

  • Inlets and outlets with ‘Forsheda seal’ 
    Forsheda seals provide flexibility in the joint for easier installation.
  • Low-energy compressor with alarm
    Near silent compressor ensures minimal running, maintenance and servicing costs. Integral alarm detects low pressure in air line.
  • External compressor housing
    Supplied as standard on all shallow and pumped outlet models.
  • PVC pressure pipe/diffuser(s)
    Provides a protective conduit for the air diffuser line. Can be easily removed for maintenance and cleaning.
  • Bio-media
    High specification bio-media (310m3 per m2) and membrane diffusers ensure even circulation to eliminate 'dead spots'.
  • Nylon mesh
    Retains media in aeration chamber during transportation and handling, and in the event of flooding.
  • 32mm sludge return
    Larger diameter sludge return prevents the possibility of blockages and improves system circulation. Provides higher effluent quality whilst balancing flow over a 24-hour period or periods of intermittent use.
  • Impermeable lid
    Regular lid/frame improves strength and durability whilst blending into the surrounding environment.
  • Integral lifting eyes
    For safe and secure on-site handling.
  • Stabilising feet
    Stabilising feet prevents the tank from rolling and allows safe and steady transportation and installation.
  • Unique ‘keying-in’ lip
    Assists anchoring into granular or concrete surrounds.

Operating Principle

The tank utilises a three-chamber design to produce its high-quality effluent. The first chamber is where primary settlement takes place and where anaerobic digestion produces clarified water. This water then filters into a second aeration chamber where, supported by diffused air and bio-media, bacteria treats the effluent to remove the dissolved constituents. The third chamber is where final settlement takes place before the effluent is discharged into a drainage field or local watercourse.

General guidance

Package Sewage Treatment Plant's (or PSTP's) are often a suitable option where groundwater in the surrounding environment is vulnerable, drainage field percolation values are restrictive, or direct discharge to a water course or surface water sewer is the preferred discharge method.

  • PSTP's should be sized using the latest version of British Water Flows & Loads which provides detailed information on sewage production figures and sizing calculations.
  • Regulatory authorities for the control of pollution in the UK normally require treatment plants conforming to BSEN12566:3 to be demonstrated as capable of producing a minimum effluent discharge quality of 20:30:20 (Biochemical Oxygen Demand: Suspended Solids: Ammoniacal Nitrogen in mg/ltr), although in certain areas more stringent site-specific qualities may be required.
  • No surface water should enter the system as this can reduce the system's capacity and cause solids to be flushed out which may prematurely block drainage field or cause pollution.
  • As with septic tanks sludge should be removed annually or in line with manufacturer’s instructions.


Please Note: Tank configuration and components shown for illustration purposes. Due to production processes, dimensions of finished units are within a tolerance of +/-2.5%.

7-10 working days
25+ Persons
Install Type:
Large Capacity
Product Type:
Sewage Treatment Plant