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General Information on Unsewered Treatment Systems

Unsewered Treatment Systems

HSTPs are also known as Aerated Waste Water Treatment Systems (AWTS) or All Waste Treatment Plants (AWTP). They are a system used for the treatment of sewage and liquid waste, and are basically a domestic version of a sewage treatment plant.

Aerobic Sand Filtration System (ASFS)

These systems usually follow the same processes as an AWTS but use a carefully graded and layered bed (filter) of gravel and sand to provide oxygen to micro-organisms that treat and purify the wastewater.


HSTPs have significantly better water quality than older style septics if properly maintained and therefore have far less environmental impact.

How do They Work?

There is living bacteria in a HSTP that make the system operate effectively. The HSTP imitates nature by using the naturally occurring bacteria that your household provides as part of your daily lifestyle. We provide them with oxygen and a happy home environment to breed and work properly and, in turn, they treat our wastewater by turning it into clean usable water.

What Do They Need? 

A Food Source - the food source is your natural household waste. Everything that you use in your house that goes into your drains, kitchen, laundry, toilet, shower etc. Too much food will kill the bacteria in the same manner that over fertilizing a plant will kill it. So garbage disposal, home brew kits etc are not good for them.

An Air Source - air is introduced into your HSTP to keep the bacteria populated, much in the same way an air pump works in a fish tank. If you were to have 10 fish in a small tank with an air pump operating in it, the system would have enough oxygen to support the tank life and keep it healthy. Turn off the air pump and there would not be enough oxygen in the water and the fish and plants would slowly die. Your HSTP works on the same principle.

It requires air, food and a happy home environment to work at its maximum potential. When working properly, your HSTP will work efficiently with no odours or problems. It needs a happy balance.

What Upsets the Balance? 

The greatest cause of problems with your treatment plant are cleaning products and the washing machine.

Cleaning Products

You must use environmentally friendly cleaning products as any product used that kills bacteria is harmful to your system. If you wish to use some of the harsher cleaning products, it is suggested that you use a bucket and discard the contents in the garden. This also applies to disinfectant, surface sprays and wipes.

Some other things that may cause problems are antibiotics or people who are on chemotherapy. We do not suggest that you stop medication, just expect that the treatment system may not function well for a short time.

Washing Machines

Try to evenly spread your washing over a period of a week. Avoid where possible to wash everything in one day. It puts too much water in the system in a short time and your HSTP will struggle to cope. Liquid soaps break down easier than granulate styles do. Try not to use too much soap.

How do You Look After Your HSTP? 

Things to Absolutely Avoid

Chlorine, disinfectant, ammonia, acids, bleaches, caustics and heavy chemical products, nappy pre-soaker products, antibacterial products, fat, oil, grease, milk, toilet deodorisers/cleaners etc are some of the types of products that will cause the bacteria to die off in your HSTP. It will recover but may cause some odours in the short term.

Don't allow foreign objects, (eg. Nappy liners, disposable nappies, tampons, pads, condoms etc) to enter the system. They do not breakdown and can cause problems.

Avoid pouring large quantities (1/2 litre or more) of beer, wine, milk or fruit juice or oils into the system. Products that are acidic may affect bacteria production.

Suitable Products

Use products that DO NOT contain disinfectants, bleaches &/or anti bacterials (harsh cleaners). All products should be used in moderation.

Surface cleaners - when using surface cleaners try to wipe excess cleaner with a disposable cloth and discard contents into the bin.

Toilet cleaners - cream cleaner or wash soda. Toilet fresheners, toilet deodorisers/ cleaners are not recommended.

Floor cleaners - use hot water and detergent.

Laundry powders and liquids - use suitable products.

Avoidable Products

Products that contain ammonia, acids, disinfectants, bleaches. chlorine, oil, paint and chemicals.

Antibacterial products - any cleaning product that contains any antibacterial chemicals will be harmful to your system. You should limit the use of such products. Please do not discard excess contents into your treatment plant.

Bleaches - if using bleaches, pre-soak washing detergents or nappy pre-soaker products please do not discard the excess in your treatment plant.

Other cleaners that are harmful - chlorine based products, spirits/alcohol, drain cleaning/ clearing products, bleaches, metho or kero, flea or tick wash, floor cleaners, caustic oven cleaners.

Servicing of Home Sewage Treatment Plants

All Home Sewage Treatment Plants are required to be serviced. All treatment plants in Queensland require an approval from the Department of Local Government, Planning, Sports and Recreation (DLGPSR). The service interval will be given when approval is granted.

Most of the All Waste Treatment Plants (AWTS) are required to be serviced every quarter. Most of the Aerobic Sand Filtration Systems (ASFS) are serviced yearly.

Treatment systems should only be serviced by registered licenced wastewater service personnel.

HSTP's Should Be Serviced for More Important Reasons Than Legislative Approval. 

Your service person will tend and monitor your HSTP to give your system the best chances of supplying the environment with the cleanest and best quality water (effluent) that your system can produce.

Please Ensure that You Do Not

1. Do not cover tanks with earth, cement, paver or any material.

2. Do not prevent quick and easy access to any inspection openings.

3. Do no allow roof or surface water to enter any part of the system.

4. Allow free access to your property for the service person. Ensure that the gates are unlocked, your dogs are locked up and your children are supervised.

5. Keep plants and grass monitored on dispersal areas.

Informational PDFs

Aerated Wastewater Treatment Systems

Composting Toilets

Defining Myths

Holding Tanks

Land Application Systems

New Installation and Alterations

Septic Tank Systems