An ATU treats effluent with air and bacteria before it reaches the ground, so what leaves is far cleaner than tank effluent. That is what allows a smaller dispersal area on a site a conventional bed cannot serve.
An aerobic treatment unit is cleaner, with moving parts
A conventional tank and bed has nothing to fail but time. An ATU has a blower, diffusers and usually a pump and control panel, which means it needs power, it needs servicing on a schedule, and it can fail in ways a gravity system cannot.
That is a genuine trade and it should be made with the running cost in view, not just the install price. Blower and diffuser checks, and any disinfection the permit requires, are ongoing work covered under aerobic maintenance, often with a mandatory service contract attached to the approval.
In exchange you get a system that fits where a conventional bed does not, and effluent clean enough that the dispersal area can be a fraction of the size. On a lot that cannot pass a perc test for a standard bed, that is often the difference between building and not.
Treatment unit
How it works
How an ATU install runs
Confirm it is needed
Soil result and setbacks checked first, because a conventional bed is simpler and cheaper to run where one will fit.
Design, permit, service plan
Unit sized and drawn, permit filed, and the servicing the approval requires set out before anything is ordered.
Install and power
Unit set, blower and controls mounted, the power connection made by a licensed trade, and the dispersal field built to drawing.
Commission and hand over
Started up, alarm tested, service interval set and the owner shown what the panel means before we leave.
What owning one is actually like
The alarm is a feature, not a fault
An ATU tells you when it is unhappy, which is more than a gravity system ever does. A blower that has stopped, a diffuser that has blinded or a pump that is struggling all raise an alarm well before anything reaches the ground, and that warning is most of the value.
It only works if the alarm is left enabled and somebody responds to it. Muted panels are the single most common reason an ATU fails its inspection, and a unit running without aeration is doing less than the plain tank it replaced. That is why servicing is not optional here, and why it is set out on aerobic maintenance.
When the lot is too small, the percolation too poor, the water table too high or the rock too shallow for a conventional bed. Where a standard bed fits, it is simpler and cheaper to run.
There is continuous electricity for the blower plus scheduled servicing, and often a mandatory contract attached to the approval. Those running costs should be part of the decision, not a surprise afterwards.
Set by the manufacturer and the permit, typically a few visits a year for blower, diffuser and disinfection checks. See aerobic maintenance.
Yes. Solids still settle and still have to be removed on an interval. The unit treats effluent, it does not eliminate sludge.
Treatment stops while the power is off and resumes after. A short outage is not a problem; a long one means reducing water use until it is back.
Sometimes, because cleaner effluent puts far less load on the soil, and it is worth assessing before committing to a full rebuild. See drain field rejuvenation.
Our lot was too small for a conventional bed. The aerobic unit went in with the wiring handled by a licensed trade they brought, and passed inspection.
Ben Y.
Saanich
★★★★★
They explained the yearly maintenance before we signed, not after. The unit has run quietly for two years with two service visits.
Sofia Z.
Victoria
★★★★★
Installation took four days including the tank, the unit and the spray field. Alarm panel mounted where I can see it from the kitchen.
Gita Q.
View Royal
★★★★★
The crew tested the aerator and the timer in front of me and left a laminated card explaining each light on the panel.
