An aerobic treatment unit, often called an ATU, is the tank that adds air so bacteria can break down household wastewater. People searching for an aerobic treatment unit in Oklahoma often use that name for the whole aerobic septic system. In the state rules it is one stage: the treatment tank. It is not the spray heads, the pump, or the yard by itself.
This site does not install systems. Oklahoma Aerobic Guide is a directory. It does not design, install, repair, or maintain an aerobic treatment unit. A name on this page is a roster match, not a bid and not a coverage map.
What DEQ means by an aerobic treatment unit
Oklahoma’s on-site sewage rules, OAC 252:641, define an aerobic treatment unit in 252:641-1-2. It is a treatment unit that digests organic matter through oxidation. An ANSI-accredited certifier has to test it to the current NSF/ANSI Standard 40. The definition still applies when the unit also reduces nitrogen. Standard 40 is the baseline. NSF/ANSI Standard 245 is the extra nitrogen-reduction certification, and the design rule calls for it when a waterbody restriction requires nitrogen reduction.
That certification is about the unit, not about a company’s service area. The paperwork from installation, or the installer who set the unit, is the practical way to see which model is in the ground and whether Standard 245 was required on that lot.
Where the treatment unit sits
- 1
Trash tankSolids settle out before treatment.
- 2
Aerobic treatment unitAir and bacteria treat what remains.
- 3
DisinfectionRequired when the yard uses spray.
- 4
DispersalTreated water goes to spray, drip, or another allowed field.
OAC 252:641-10-2 lists the pieces of an aerobic treatment system. There is a trash tank, then the aerobic treatment unit, then a dispersal field. The unit has to be rated for the design daily flow, built so sewage does not leak out and groundwater does not leak in, and produce effluent clear enough that the bottom of the pump tank is visible when that tank is full. The maintenance opening has to extend above the ground and have a locked or tool-only cover.
Disinfection is not automatic for every aerobic treatment unit. The rule requires a certified disinfection step when spray irrigation is the dispersal method, between the unit and the pump tank, or inside the pump tank. If the method is chlorine, the pump tank has to keep a free chlorine residual of 0.2 mg/L. Other disinfection methods have to reduce fecal coliform to fewer than 200 colonies per 100 milliliters. Drip irrigation and spray irrigation both have to be preceded by an aerobic treatment unit. A pressurized dispersal method also needs a pump tank with a high-water alarm.
DEQ limits these systems to sewage. The average daily flow has to be at least 100 gallons and no more than 1,500 gallons, and the wastewater cannot exceed 2.5 pounds per day of biochemical oxygen demand (252:641-10-1). Designs outside that range, including many commercial kitchens and laundries, use a different permit path. The chapter also says its design standards are minimum criteria and do not guarantee that a system will perform.
How an ATU differs from conventional septic
A conventional system and an aerobic treatment unit solve different soil problems. OAC 252:641-1-2 describes a conventional subsurface absorption field as a gravity-fed dispersal field that treats sewage in media-filled trenches. It may be preceded by a lift station. It is not an evapotranspiration field and it is not a shallow extended field. The soil is the treatment step after a septic tank settles solids.
- Treatment
- Conventional treatment happens in the soil trench. An aerobic treatment unit treats inside a tank by oxidation before water is dispersed.
- Power
- A gravity conventional field does not need a blower. An aerobic treatment unit uses air and electricity. If the power is off, treatment stops.
- Dispersal
- A conventional field is a gravity trench. Spray and drip fields in Subchapter 12 must be preceded by an aerobic treatment unit. Spray also disinfects.
- Upkeep
- A new aerobic treatment system has a two-year installer maintenance duty under OAC 252:641-10-3. That aerobic duty does not apply to a passive conventional tank and field.
- Who decides
- Soil, lot size, and the approval for that property decide which system is allowed. This directory does not choose a system for a lot.
Aerobic systems usually cost more attention because parts move: the aerator, the pump, the disinfectant, and the spray heads or drip emitters. A company that pumps conventional tanks may not work on those parts. Ask about the aerobic treatment unit before you book. For the cost and buying questions, see aerobic versus conventional septic. For the full flow of tanks, see how aerobic septic systems work.
Oklahoma rules homeowners actually feel
01 · New installationKeep the installer name, the date, and the unit paperwork with the house.
02 · First two yearsThe installer maintains the new aerobic treatment system at no additional cost to the owner.
03 · After two yearsThe owner maintains the system or hires someone. A forever paid contract is not a statewide mandate.
That two-year duty is OAC 252:641-10-3, and it covers aerobic treatment systems that reduce nitrogen as well as those that do not. During those two years the installer repairs, adjusts, or replaces broken or malfunctioning parts. On the schedule in the rule, the installer also measures trash-tank sludge, measures sludge in a forced-air unit, and writes the owner after each visit. When the system sprays, the installer tests free chlorine residual in the pump tank at least every six months. When there is a pump tank, the installer runs a clarity check on that same six-month rhythm. The installer keeps those notes at the business for three years. The installer is not responsible for damage the owner alone causes, such as a smashed spray head, too much water, or harmful items poured into the system.
After those two years, keeping the system working is the owner’s job, done by you or by someone you hire. The maintenance guide covers that handoff in more detail: aerobic septic maintenance in Oklahoma. 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. The owner rule in Chapter 641 still expects a malfunctioning system to be repaired so sewage does not surface or reach surface water.
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.
Chapter 641 is authorized in part by 59 O.S. § 1158. In these rules, a certified installer is a person in the business of installing or constructing on-site sewage treatment systems who has been certified by the Department of Environmental Quality to inspect and approve their own installations. Confirm the current certification and permit steps with DEQ or the installer before you treat this page as the permit. The public installer search is on the DEQ certified installer list. For a new unit or a replacement, start with aerobic septic installation and then confirm the exact job.
Quick answers
What is an aerobic treatment unit in Oklahoma?
An aerobic treatment unit digests organic matter by adding oxygen. OAC 252:641-1-2 says it must be tested and certified to the current NSF/ANSI Standard 40, whether or not it also reduces nitrogen. It is the treatment tank, not the spray heads, the pump, or the whole yard.
How does an ATU differ from a conventional septic system?
A conventional subsurface absorption field is a gravity-fed soil trench. An aerobic treatment unit is a certified oxidation tank. Spray and drip dispersal in these rules are preceded by an aerobic treatment unit. Spray also needs disinfection. The unit needs power and, for a new system, two years of installer maintenance under OAC 252:641-10-3.
Is an ATU the same as the whole aerobic septic system?
No. OAC 252:641-10-2 also requires a trash tank and a dispersal method. Spray systems add disinfection. Pressurized dispersal adds a pump tank with a high-water alarm.
Who maintains a new aerobic treatment unit?
The installer maintains the aerobic treatment system for two years at no additional cost to the owner. After that, the owner maintains it or hires someone. A forever paid contract is not a statewide mandate.
Does Oklahoma Aerobic Guide install aerobic treatment units?
No. This site is a directory of Department of Environmental Quality roster matches. It does not design, install, or service aerobic treatment units.
Does a listing mean the company covers my address?
No. The city on the card is the roster mailing city. Confirm the aerobic treatment unit job, the address, timing, and price when you call.
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. How we check the list explains the roster method. The six cards below are examples, not the full Oklahoma list.