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Aerobic treatment units


Application forms and fact sheets

Aerobic Treatment Units (ATUs) are a more advanced multi stage alternative to conventional septic tanks and provide an improved quality of effluent treatment. As the units are still an onsite effluent disposal system they are not accepted as an alternative to sewer requirements.

Only Department of Health WA approved systems can be used in WA. Approved systems for single dwelling units below 10 persons are listed in the List of Approved Systems for Single Dwelling Units(PDF 117KB). Larger systems which cater for more than 10 persons are assessed and approved by the Department on a case by case basis.

The chlorinated effluent from ATUs may be used to surface irrigate garden areas but can only be used below grassed areas. It is not approved for any use in vegetable gardens.

Due to environmental concerns, usually associated with the potential degradation of environmental water bodies, some developments are required to use a wastewater system which is capable of removing phosphates. Some ATUs are approved as Phosphate removing. These ATUs may use an in system phosphate removing process or an approved phosphate binding amended soil in the irrigation area.

The type of phosphate removing system can affect the choice of effluent irrigation methods available e.g. amended soil systems cannot be used with drippers.

Aerobic Treatment Units must be serviced regularly to ensure that they are operating effectively and that the quality of the final effluent is maintained. The maintenance protocol is set down in the Code of Practice for the Design, Manufacture, Installation and Operation of Aerobic Treatment Units (PDF 405KB).

The quarterly servicing can only be carried out by authorised persons (PDF 214KB) who have received approval from the Department of Health.

Service reports are provided to the property owner and the local government so that any problems can be followed up. Copies of service reports for larger commercial systems are also provided to the Department of Health.

System installations are only permitted with local government or Department of Health approval (the Department of Health assesses larger development proposals). Persons wishing to install ATUs or septic tank systems need to lodge an Application to Construct or Install an Apparatus for the Treatment of Sewage (PDF 257KB) with the relevant local government.

This is to ensure that the system is of an approved design and manufacture, is properly sized and is suitably located.

It is an offence to commence construction of a wastewater system without an approval and it is also an offence to commission an illegally installed system or to commission a system prior to a final inspection and approval to use from the local government.

Onsite treatment and disposal of effluent systems will not be approved if a property can be reasonably connected to sewer.

How to become an authorised person

The operation and maintenance of an ATU requires more than a ‘hands on’ knowledge and ability to perform simple service tasks to ensure the adequate maintenance of the system. ATU authorised persons, staff and service agents have access to technical knowledge and expertise regarding the operating principles and design of each system including repair and maintenance requirements.

Under the Health (Treatment of Sewage and Disposal of Effluent and Liquid Waste) Regulations 1974 (PDF 0.99KB)  (External link)a person seeking to be an authorised person needs to demonstrate that they are duly qualified to carry out maintenance work on each type of ATU for which approval is sought.

Applicants need to have completed an appropriate training course, have relevant experience in the industry and may be required to attend an interview.

For further information contact the Water Unit of the Environmetnal Health Directorate on (08) 9388 4999 or email

AS/NZS 1546.3:2001 Australian New Zealand Standard On-site Domestic Wastewater Treatment Units Part 3:Aerated Wastewater Treatment Systems, Please See Standards Australia Limited website.

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Last Updated: 10 November 2008

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