AWTS: aerated wastewater treatment systems explained
Written by Septic Help editors Last reviewed
An aerated wastewater treatment system (AWTS, also sold as a "home sewage treatment plant" or HSTP) is a miniature sewage works in your backyard. It treats all household wastewater to a secondary standard, disinfects it, and pumps it out through irrigation — clear enough to water the garden with, which is why it's the default on blocks too small or too heavy-soiled for absorption trenches. The trade-off is a machine that runs 24 hours a day and a legal obligation to have it serviced, usually every three months, for as long as you own it.
How an AWTS works
Inside one tank (or two), wastewater moves through four stages. A primary chamber settles solids like a conventional septic. An aeration chamber then bubbles air through the effluent — the blower is the heart of the system — so aerobic bacteria digest what anaerobic ones can't. A clarifier settles the remaining fines, and a disinfection stage (usually chlorine tablets, sometimes UV) knocks down pathogens before a submersible pump sends the treated water to the irrigation field. Systems sold in Australia must be certified to AS 1546.3 and accredited by your state's health or environment regulator before a council can approve them.
Power use and running costs
The blower runs continuously and the irrigation pump cycles daily, so an AWTS needs mains power at all times — councils explicitly require power to be maintained to the system. Modern blowers draw roughly 60–120 watts (Fuji Clean, for example, advertises a 68-watt unit), which works out to around 1.5–3 kWh a day. Installers commonly quote power at $200–$300 a year at 2026 tariffs. Add servicing, chlorine tablets, occasional pump or blower replacement and a de-sludge every few years, and the realistic all-in running cost is around $800–$1,200 a year averaged over the system's life — several times what a conventional septic costs to run.
Power outage or alarm?
An AWTS keeps accepting wastewater during an outage but stops treating properly. Cut water use until power returns, and never ignore the audible/visual alarm — it usually means the blower or pump has failed, and untreated effluent will reach your garden if it runs on for days.
The mandatory service contract
Every state ties an AWTS approval to ongoing servicing by a qualified technician — quarterly in most jurisdictions. NSW councils such as Camden state it plainly: "Have your AWTS serviced quarterly (every 3 months) by a qualified service technician." A service checks the blower, pumps, alarms and chlorinator, tests the treated water, and lodges a report — many councils require the service sheet to be submitted to them. Expect $300–$500 a year for a contract; some brands bundle the first year free. Skipping services can void your approval to operate and shows up when you sell. Full details in our AWTS servicing requirements guide and service contracts guide.
The irrigation area
Treated water still has to go somewhere on your land — usually surface sprinklers (purple-marked, low-throw) or subsurface drip in a dedicated, vehicle-free irrigation area. The size is set by your site assessment under AS/NZS 1547:2012, not by the brand brochure: soil, rainfall and household size drive it, and for a typical family home it commonly runs to several hundred square metres, with council buffer distances to boundaries, dwellings and waterways on top. Irrigation water is for gardens and lawns only — not vegetables you eat raw, and children shouldn't play on freshly irrigated grass.
What it costs in 2026
Supplied and installed on a reasonable site, most AWTS quotes land between $12,000 and $20,000. Express Wastewater, one of the larger Queensland installers, publishes $11,000–$15,000 for surface-irrigation installs and $13,000–$16,000 for subsurface; hillier or rockier sites in NSW and Victoria commonly quote higher. Converting an existing failed septic to an AWTS costs more again — often $22,000–$30,000 once decommissioning and new irrigation are included. See the full breakdown in our AWTS cost guide.
Cost snapshot
Installed: $12,000–$20,000 new build; $22,000–$30,000 for a septic changeover. Running: roughly $800–$1,200/year all-in, including the mandatory servicing.
Before committing, confirm the approval pathway with your council — every state requires an install approval and most issue an ongoing approval to operate. Start with your state's rules.
Common questions
Is AWTS servicing really compulsory?
Yes. Quarterly servicing by a qualified technician is a condition of approval in most states, and many councils require the service reports to be lodged with them. An unserviced AWTS can lose its approval to operate.
How much power does an AWTS use?
The blower runs 24/7 at roughly 60–120 watts, plus a daily irrigation pump cycle — typically 1.5–3 kWh a day, or around $200–$300 a year at 2026 tariffs.
Can I water my vegie garden with AWTS water?
No. Treated AWTS water is approved for lawns and ornamental gardens via the designated irrigation area only — not for edible crops eaten raw, and not for storage or hosing hard surfaces.
Does an AWTS still need pump-outs?
Yes — sludge still accumulates in the primary chamber. Most systems need a de-sludge roughly every 3–5 years depending on load; your service technician will flag it. A pump-out on an AWTS typically costs a little more than on a plain septic.
How long does an AWTS last?
Tanks last decades, but expect to replace blowers, pumps and diaphragms along the way — commonly every 5–10 years per component. A well-serviced AWTS keeps working indefinitely; a neglected one fails in years, not decades.