An aerobic treatment unit, often called an ATU, is the tank that adds air so bacteria can break down household wastewater. Homeowners sometimes use the name for the whole aerobic septic system. In Oklahoma the unit is one stage of that system, not the spray heads, the pump, or the yard by itself.
What an aerobic treatment unit is
Oklahoma’s on-site sewage rules (OAC 252:641-1-2) describe an aerobic treatment unit as a treatment unit that digests organic matter through oxidation. It has to be tested and certified to the current NSF/ANSI Standard 40. Some units also reduce nitrogen. That extra step is NSF/ANSI Standard 245, and the design rules call for it when a waterbody restriction requires nitrogen reduction. The paperwork from installation, or the installer who set the unit, is the practical way to see which one is in the ground.
Where the treatment unit sits
- 1Trash tankSolids settle out before treatment.
- 2Aerobic treatment unitAir and bacteria treat what remains.
- 3DisinfectionSpray systems disinfect before water leaves.
- 4DispersalA pump sends treated water to spray or drip.
A typical aerobic treatment system has a trash tank, the aerobic treatment unit, and a dispersal field. When the yard uses spray, the rules also require a disinfection step. When dispersal is pressurized, there is a pump tank with a high-water alarm so you know if that tank is getting too full. The treatment unit is the stage after solids settle and before treated water is sent to the yard.
Oklahoma homeowner basics
That two-year duty is OAC 252:641-10-3. During it, the installer repairs malfunctioning parts and, on the schedule in the rule, checks items such as sludge, spray-system chlorine residual, and pump-tank clarity. You should get a written note of each visit. The installer is not responsible for damage the owner alone causes, such as a smashed spray head or a system overloaded with water.
After those two years, keeping the system working is the owner’s job, done by you or by someone you hire. Some cities add local paperwork. Edmond describes a yearly check for properties inside the city limits. A mailing address that says Edmond does not, by itself, prove the house is inside those limits.
You do not have to become a technician. Do notice sewage at the surface, an alarm that stays on, or a smell that does not go away, and call before wastewater sits in the yard. Do not open electrical panels or tank lids unless you are qualified to do that work.
When to call a certified installer
Call for a new aerobic treatment unit, a replacement, a backup, or sewage discharging where it should not. During the first two years, start with the installer who set the system. After that, call a company that confirms it works on aerobic systems at your address.
In Oklahoma, a person who installs individual sewage systems as a business must be certified by the Department of Environmental Quality (59 O.S. § 1158). DEQ also describes a narrow case: someone who is not certified may install one on-site system in a calendar year, and DEQ inspects that job. A certified installer may inspect their own work in the categories they hold. Confirm the current rule with DEQ or the installer before you treat this page as the permit.
A name here is a roster match. The company name and phone line up with the Department of Environmental Quality aerobic spray list. The mailing city is not a promise they cover your street. Ask what they will do, whether they cover the property, when they can come, and what it costs.
Quick answers
What is an aerobic treatment unit?
An aerobic treatment unit digests organic matter by adding oxygen. Under OAC 252:641-1-2 it must be certified to the current NSF/ANSI Standard 40. It is the treatment tank, not the whole septic system.
Is an ATU the same as the whole aerobic septic system?
No. The system also has a trash tank and a dispersal method. Spray systems add disinfection and usually a pump tank with a high-water alarm.
When should I call a certified installer?
Call for a new aerobic treatment unit, a replacement, or sewage at the surface. During the first two years, start with the installer who set the system. After that, hire someone who confirms aerobic work at your address.
Use the directory as a starting point.
Ask the company to confirm your system type, exact task, property coverage, timing, and price. A directory record does not replace an on-site evaluation.
Start at the Oklahoma Aerobic Guide home page for the statewide roster. Open the company directory for names and phones that match it. For a new aerobic treatment unit or a replacement, see aerobic septic installation.