IWOX Clear

Viltra’s IWOX Clear is a 3-stage sewage treatment plant in a three-tank configuration that uses a biological process to effectively treat sewage. Containing a de-nitrification chamber which enhances BOD and nitrogen removal, it is a highly efficient, reliable and cost-effective way to dispose of domestic sewage where there is no access to a main sewer. The IWOX Clear sewage treatment plant is tested and certified to European standards with a certified average effluent quality of 3/4 BOD/SS, with removal efficiencies up to 99.8%.


  • Minor footprint

  • Bespoke-made in the UK and Ireland from robust, impact-resistant polyethylene

  • Can be custom-made to suit individual sites

  • Certified for up to 8 people (1200 litres per day)

  • Easily fitted due to lightweight material

  • Quiet in operation

  • Extremely low maintenance and running costs; only one mechanical part (energy-efficient air pump – 50-55W)

How it works

The IWOX Clear sewage treatment plant is based on the activated sludge principle.

Pre-settlement tank

The wastewater influent flows straight into the settlement tank. Larger and heavier pieces of waste in the flow will sink to the bottom of the compartment. Once a year, the presence of these materials has to be checked (sludge judge test). If the water flow from the pre-settlement tank to the oxidation compartment is blocked, these materials have to be removed from the tank.

Denitrification and Nitrification tank

In the Nitrification compartment, purification of waste particles in the wastewater is carried out by bacteria in the activated sludge. Here, COD and BOD are removed, ammonia (NH4) is transformed into nitrate (NO3). Due to the denitrification, the SS in the effluent is also lowered.

Biozone (BZ)

In the oxidation compartment, the purification of waste particles in the wastewater is carried out by bacteria in the activated sludge. Here, Chemical Oxidation Demand pollutants (COD) and Biological Oxidation Demand pollutants (BOD) are removed, and ammonia (NH4) is transformed into nitrate (NO3). The oxidation compartment also features a tube diffuser which provides the water with continuous airflow. The desired oxygen concentration (minimum of 1.5 mg O2/l) can be created with the adjustment of a valve.


A two-stage clarifier has been developed so that the water and suspended solids are separated with maximum efficiency. In the clarifier tank, the activated sludge formed settles on the bottom and is returned to the aerobic compartment, where pollutants are removed more efficiently. The circulation is performed by an airlift pump, increasing the system power efficiency. Once the pollution is removed, the treated water (effluent) is discharged in the outer clarifier to increase the solid removal efficiency, and the treated wastewater is discharged into the environment via outlet pipe.

Key features

  • Only one mechanical part - (energy-efficient air pump – 50-55W)

  • Strong and secure access covers

  • One-piece mould with no joints below water level

  • Rotationally moulded in tough, durable tank-grade polyethylene for easy and cost-effective installation

  • Contains a de-nitrification chamber which enhances BOD and nitrogen removal

  • Features an external air compressor failure beacon – which can be fitted anywhere on the premises

  • 1 Year Warranty (Blower and small parts)

  • Removal efficiencies up to 99.8%

  • Our unique flow buffering technology (ALF) ensures a constant steady flow 24 hours a day through your system with a gradual release to the natural environment

Environment Agency Standard

Northern Ireland

The Department of Agriculture, Environment and Rural Affairs (DAERA) currently require one of two minimum standards of 97.5% and 95% BOD removal efficiency depending on receiving watercourse and catchment size. Viltra's IWOX Clear is a three-tank sewage treatment plant that is tested and certified to exceed the current DAERA requirement, with average removal efficiencies of:

-3mg/l Biological Oxygen Demand (BOD)
-4mg/l Suspended Solids (SS)

Scotland and Wales

Viltra's IWOX Clear sewage treatment plant is tested and certified to exceed current SEPA and NRW regulations with an overall average:

-3mg/l Biological Oxygen Demand (BOD)
-4mg/l Suspended Solids (SS)

NH4 removal up to:
-Up to 0.1mg/l Ammoniacal Nitrogen (NH4)

Why choose a Viltra sewage treatment plant?

  • Exclusively created products that are designed in the UK and Ireland

  • First-class products and services that are exclusively made to meet and exceed customer needs

  • Verified history in providing affordable and resourceful sewage treatment plants within the wastewater business across the UK and Ireland

  • Our domestic products are tried, tested and certified to EN12566-3 European standards

  • All-inclusive mechanical and electrical set-up with professional assistance from planning right through until installation and final commissioning

  • We organise the Consent to Discharge process for our clients, liaising with the all-regulatory bodies to certify compliance with any requirements enforced

  • At Viltra we have a team of passionate and expert process, civil, electrical, mechanical and environmental engineers with over 100 years of collective experience in the wastewater business

  • Round-the-clock emergency breakdown service

  • Loyal after-sales service to provide our clients with valued guidance

  • Affordable servicing and maintenance packages available to ensure your system is achieving predictable functions all year long

  • Viltra have an admired internal civils crew who can provide a comprehensive end-to-end procedure when needed. This package can implement a complete installation pack from start to finish, saving you the trouble of completing each component individually.

Our latest projects

A sewage treatment plant installation and civil works for a homeowner

Replacement of an existing septic tank and installation of a sewage treatment plant

The installation of a sewage treatment plant and removal of an existing septic tank

Start an IWOX Clear sewage treatment plant project with us

At Viltra, we are specialists in separating waste and water. Whether you have an individual household, a business or a development, we all need and rely on water, we all create and dispose of waste and we all must keep these two worlds apart.

Viltra are a dedicated team who design, manufacture and install wastewater treatment solutions for a wide range of sectors across the UK and Ireland, including the commercial and industrial sector, education sector, conservation sector, domestic sector, agricultural sector and the tourism and hospitality industry. Offering an end-to-end service, the experienced team at Viltra ensure our customers receive a premium service and a robust solution to their wastewater management requirements.

To make an enquiry or to book a FREE site visit by our expert engineers who will find a solution for you, please get in touch with Viltra through the contact form provided.

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