Aerobic Septic Systems: How They Work and What Maintenance Involves

Most septic systems around Coquille and Coos Bay are a tank and a drainfield, but not all of them. Coos County's Onsite Septic Program lists aerobic treatment units alongside sand filters and pressure distribution as advanced or alternative system components, and an aerobic septic system in Coos County comes with inspection and contract rules that a conventional tank does not.

An aerobic treatment unit uses an air pump to supply oxygen to bacteria that break down wastewater faster and more thoroughly than a conventional septic tank, before the treated water moves on to a drainfield. In Coos County, Alternative Treatment Technology (ATT) systems must be maintained by a DEQ certified maintenance provider, inspected at least once a year, and kept under a service contract for as long as the system is in use.

This guide covers how these units work, what the maintenance actually involves, and what to ask before you sign a service contract.

1. How an aerobic treatment unit works

An aerobic treatment unit (ATU) works like a small treatment plant installed ahead of the drainfield. Texas A&M AgriLife Extension describes the same basic stages across most units:

1. Pretreatment. Wastewater first enters a trash tank or septic tank, where solids settle to the bottom or float to the surface.

2. Aeration. Air is pumped into the aeration chamber. The bacteria in this chamber need a continuous supply of oxygen to stay healthy and keep breaking down waste.

3. Clarification. A clarifier separates out microbial cells and other solids, and the settled solids are returned to an earlier stage for further treatment.

4. Disinfection, where the design calls for it. Some systems include a disinfection step, most commonly chlorine or ultraviolet light.

5. Dispersal. The treated effluent goes to a drainfield or other approved dispersal area.

The difference that matters most to an owner is the air pump. A conventional septic tank relies on bacteria that work without oxygen. An aerobic system depends on a powered pump running continuously, which is why it needs electricity and regular service.

2. Aerobic system vs. conventional septic tank

Oregon DEQ describes ATT systems as typically designed to perform as well as a sand filter or to provide additional treatment.

3. Why a property ends up with an aerobic system

Homeowners rarely choose an aerobic unit out of preference. The system type comes out of the site evaluation and the permit. According to the Environmental Finance Center Network, aerobic systems can be built on a wider range of soils than conventional systems, because they do not rely on soil infiltration as the primary treatment step. That makes them an option on rocky or clay-heavy ground where a conventional drainfield may struggle.

If you are planning a new system or replacing a failed one, a septic site evaluation is where that decision starts.

4. What aerobic septic system maintenance involves

Maintenance on these units splits into what the owner does day to day and what the service provider does on each visit.

What the provider handles in Coos County. Under the county's Operation and Maintenance (O&M) Program, a DEQ certified maintenance provider must inspect ATT systems at least once per year and submit the report to OnlineRME, the state's online reporting system. The provider also inspects and documents the system and drainfield, makes repairs under Oregon Administrative Rules, and submits the annual report fee on the owner's behalf. For ATT systems, the provider must also hold the manufacturer's certification for that unit.

Pumping. Aerobic units still collect solids that need to be pumped out. Rather than following a fixed calendar, some manufacturers base pumping on how much solid material has built up. One manufacturer's owner manual filed with Oregon DEQ, for example, sets pump-out by a settling test. Your provider should tell you when solids are getting close to that point and coordinate septic pumping when it is due.

The air pump. The air pump is the part that keeps the whole system working, and it needs routine care such as cleaning or replacing its air filter on the schedule in your unit's manual. The same Oregon-filed manual warns that the air pump should not be turned off for more than a few days without removing the tank contents.

What owners can do between visits:

• Keep wet wipes, paper towels and other non-flushable paper out of the system.

• Go easy on toilet paper, since excess paper makes sludge build up faster.

• Avoid harsh chemical drain cleaners and heavy bleach use, which can kill the bacteria the unit depends on.

• Limit food waste and coffee grounds, which add to the solids that have to be pumped out.

• Keep the alarm panel powered and visible, and know what its light and sound mean.

5. The service contract, and what you should get for it

For many owners, the required contract is the least welcome part of having an aerobic system. It helps to know what the rule actually says and what it obliges a provider to do.

Coos County's O&M Program requires a minimum two year contract with a DEQ certified maintenance provider when an ATT system is installed, and the initial contract is submitted with the septic construction permit. After that, the owner must keep a valid, active contract for the life of the system. When the property sells, the new owner either takes over the existing contract or signs a new one with a certified provider.

The rule also sets expectations for the provider, including emergency service within 48 hours of a request. A contract should leave you with a clear record of each inspection, confirmation that your annual report was filed, and a plain explanation of anything that needs repair.

If you are buying a home with an aerobic unit, ask for the current contract and recent inspection records before closing. A septic inspection during the sale is a good time to confirm the system's condition and contract status.

6. Signs your aerobic system needs attention

• The alarm light or buzzer is on. On some units this signals a loss of air pressure from the air pump or a high water level in the tank.

• The air pump is silent when it would normally be running.

• Drains are slow, or water is backing up into the house.

• You notice a change in smell or wet ground near the tank or drainfield.

• Your annual inspection is overdue, or you are not sure whether a report was filed.

• You recently bought the property and do not know who holds the maintenance contract.

7. Questions to ask before you hire a maintenance provider

1. Are you a DEQ certified maintenance provider?

2. Are you certified by the manufacturer of my specific unit?

3. Will you file my annual report to OnlineRME and handle the report fee?

4. What does each visit include, and what costs extra?

5. Is pumping part of the contract, or scheduled and billed separately?

6. How do you handle alarm calls and emergency service requests?

7. How will you notify me if repairs are needed?

8. What affects the cost of owning an aerobic system

Costs vary from property to property, so the most useful thing to understand is what drives them:

• The service contract. Required for the life of the system in Coos County, with terms that differ between providers.

• Electricity. The air pump runs continuously.

• Pumping frequency. Driven by household size and habits, including food waste and how much paper goes down the drain.

• Consumables. Systems with chlorine disinfection need it replenished.

• Parts. The air pump, alarm and controls are mechanical and electrical parts that eventually need repair or replacement.

For a quote on your system, contact the office directly.

Frequently asked questions

What are the disadvantages of an aerobic septic system?

Aerobic septic systems need electricity to run the air pump, have more mechanical parts than a conventional tank, and cost more to install and maintain. In Coos County, ATT systems also require an ongoing contract with a DEQ certified maintenance provider and an inspection at least once a year.

Can you flush toilet paper in an aerobic septic system?

Yes, toilet paper can go into an aerobic septic system in normal amounts. Excess toilet paper makes sludge build up faster, and wet wipes and other paper products should not be flushed at all.

Which is better, a conventional or aerobic septic system?

Neither type is better in every situation. An aerobic system provides additional treatment and can work on a wider range of soils, while a conventional system needs no electricity and less maintenance. The right type for a property is set by its site evaluation and septic permit.

How much do aerobic septic systems cost?

Aerobic septic system costs depend on the unit, the site, the drainfield design and local permit requirements, and ongoing costs depend on the service contract, electricity, pumping frequency and parts. Contact a local provider for a quote on your specific property.

Get help with your aerobic septic system

Econo Rooter Services provides scheduled maintenance for advanced treatment units, along with septic pumping and site evaluations, across Coos County and the South Coast. You can see the full list on our septic services page. If you have an aerobic septic system and questions about its alarm, pumping or annual inspection, call (541) 396-4804 or contact our office with your unit's make and model, and we can tell you whether it is one we service.