Conventional vs. Aerobic (ATU) Septic Systems in Florida

A conventional septic system lets wastewater settle in a tank and then lets the soil of the drain field finish the treatment. An aerobic treatment unit (ATU) pumps air into the tank so bacteria treat the wastewater more fully before it reaches the drain field. In Florida, an ATU costs more to buy and to run, and it comes with extra rules: an operating permit that is valid for 2 years and a service contract with a maintenance entity that inspects the unit at least twice a year. A conventional system has neither requirement.

Which one you have, or need, depends mostly on the lot: the soil, the water table, the space, and whether the property is in one of Florida's nutrient protection areas. This guide explains both systems, compares their costs, and covers the Florida rules that decide when a plain conventional system is no longer allowed.

How a conventional septic system works

The U.S. EPA describes a conventional system as a septic tank plus "a trench or bed subsurface wastewater infiltration system, known as a drainfield." Wastewater from the house flows into the tank. Solids sink to the bottom as sludge, and grease and oils float to the top as scum. The liquid in the middle flows out to the drain field, where, as EPA puts it, effluent "filters through the stone and is then further treated by microbes" in the soil.

There is no air pump and, on a gravity system, nothing that needs power. The main upkeep is pumping the tank: the EPA says household tanks are typically pumped every 3 to 5 years and inspected at least every 3 years. EPA also notes that gravel drain fields are large and "may not be suitable for all residential sites."

How a conventional septic system works

1. 1Wastewater from toilets, showers, sinks and laundry flows out of the house through one main drain pipe to the septic tank.
2. 2In the tank, solids settle to the bottom as sludge, and grease and oils float to the top as scum. Compartments and a T-shaped outlet (often called baffles) keep both inside the tank.
3. 3The liquid in the middle (effluent) flows out of the tank, in many systems through an effluent filter that holds back small solids.
4. 4In many systems, a distribution box splits the effluent evenly between the drain field lines.
5. 5The drain field is a shallow, covered area of unsaturated soil that accepts, treats and disperses the effluent. If it is overloaded or flooded, sewage can surface in the yard or back up into toilets and sinks.

How an aerobic treatment unit works

An aerobic treatment unit uses oxygen-loving bacteria instead of relying only on the bacteria that live in a sealed tank. EPA's page on septic system types says "an aerobic system injects oxygen into the treatment tank," which "increases natural bacterial activity within the system." EPA's technology fact sheet on aerobic treatment explains that, unlike septic (anaerobic) treatment, "the aerobic treatment process requires oxygen," so the units "use a mechanism to inject and circulate air inside the treatment tank."

According to that fact sheet, home units typically hold 400 to 1,500 gallons and include an aeration compartment, a settling chamber and, in some units, a pretreatment compartment. The treated water still goes to a drain field (or another approved disposal method). Power is needed to run the aeration equipment and pumps.

Where EPA says ATUs fit

EPA says ATUs "can be used in homes with smaller lots, inadequate soil conditions, in areas where the water table is too high," and for homes close to surface water that is sensitive to nutrient pollution. Its fact sheet adds that one of the most common reasons to choose one is to replace a failing septic system, and that an ATU may allow a smaller drain field or extend a drain field's life.

The trade-offs EPA lists

The same fact sheet lists these disadvantages of aerobic units compared with a septic tank:

• More expensive to operate
• Requires electricity
• Includes mechanical parts that can break down
• Needs more frequent routine maintenance
• Can be upset by sudden heavy loads or neglect
• May release more nitrates to groundwater than a septic system

That last point matters in Florida. A standard ATU is not automatically a nitrogen-reducing system, and the next sections explain why the difference counts.

Florida rules for aerobic systems

Florida's septic law, s. 381.0065, F.S., sets rules for ATUs that do not apply to a conventional system:

• Operating permit. "The operating permit for an aerobic treatment unit is valid for 2 years after the date of issuance," so it has to be renewed.
• Service contract. The owner must keep a current maintenance service agreement with a maintenance entity permitted by the department, and "the maintenance entity shall inspect each aerobic treatment unit system at least twice each year."
• Owner as maintenance entity. The owner of an owner-occupied, single-family home can be approved and permitted as the maintenance entity for their own unit, with written certification from the manufacturer's approved representative that they have been trained to install and service it.
• State inspections. The law also calls for the department to inspect buildings that use an ATU at least once a year, and the owner must allow it.

For comparison, the EPA generally recommends inspecting alternative systems with mechanical parts about once a year. Florida's twice-a-year contract inspection goes further. If you are buying a home with an ATU, ask the seller for the current operating permit and the service contract. Our aerobic system service page lists what a maintenance visit covers.

What each system costs

The figures below are published planning ranges, not quotes. The ATU install range spans two national guides: the low end is Fixr's table, which labels its figures materials-only, and the high end is HomeGuide's installed cost, which it leaves open ("or more"). Engineered systems on difficult sites can cost considerably more.

Cost	Conventional	Aerobic (ATU)
New system (published range)	$3,500–$9,000	$10,000–$40,000 or more
Maintenance contract, per year	Not required	$175–$600
Aerator or air pump replacement	No aerator	$300–$900
State base fee for the operating permit, every 2 years	No operating permit	$100
Example county operating permit (Seminole, FY 2025-2026), every 2 years	No operating permit	$150
Routine pumping	Every 3–5 years (EPA)	Ask your maintenance entity

The maintenance contract range comes from InspectApedia. Chlorine and parts are often extra. The county operating permit is separate. The state base fee comes from Rule 62-6.030, F.A.C. County health departments add their own fees, so the operating permit costs more than the state's part in most counties. Seminole County is shown as one example. In Marion County, Florida DEP has issued septic permits directly since July 1, 2025.

For a conventional system, the bigger long-term risk is a failed drain field. The EPA puts the cost of repairing or replacing a malfunctioning conventional system at $5,000–$15,000. See our Florida septic cost guide for pumping, repair and drain field prices, or try the septic cost calculator.

Conventional vs. aerobic: side by side

	Conventional system	Aerobic treatment unit
How it treats	Settling in the tank; the soil finishes treatment	Air pumped into the tank boosts bacterial treatment
Power	None on a gravity system	Needed for aeration equipment and pumps
Moving parts	Few or none	Aerator, pumps, alarms and controls
Florida operating permit	No	Yes, valid 2 years
Service contract	No	Yes, inspections at least twice a year
Suited to	Sites with enough suitable soil and space	Small lots, poor soil, high water tables, sites near sensitive water (EPA)
Install cost (published range)	$3,500–$9,000	$10,000–$40,000 or more
Meets Florida's nitrogen-reducing standard?	No	Only Florida-approved nitrogen-reducing models

When Florida requires more than a conventional system

Most of the decision comes down to the lot. EPA lists the factors that shape a system's design, including household size, soil type, site slope, lot size and nearness to sensitive water. For shallow soil or high groundwater, EPA names alternatives such as an ATU or a raised (mound) system. In parts of Florida, the law now adds a second test: nitrogen.

Nutrient (BMAP) areas

Since July 1, 2023, new septic systems on lots of 1 acre or less in Florida's nutrient (BMAP) areas must be nitrogen-reducing where sewer is not available. State law defines an enhanced nutrient-reducing system as one that removes at least 50% of total nitrogen before the drain field, or at least 65% counting the tank and drain field together.

Here is where ATUs and nitrogen rules meet. DEP lists three kinds of systems that can meet the standard: in-ground nitrogen-reducing biofilters, Florida-approved nitrogen-reducing aerobic treatment units certified under NSF 245, and Florida-approved nitrogen-reducing performance-based treatment systems. So an ATU only counts if it is one of the approved nitrogen-reducing models. DEP publishes a list of NSF 245-certified units. Ask the installer which product they propose and whether it is on DEP's list.

Springs areas with stricter rules

• Silver Springs and Rainbow Springs (Marion and nearby counties). DEP adopted this springs plan by final order on June 27, 2025, and declared it final and effective on April 27, 2026, after the last legal challenge was dropped. It is stricter than the statewide rule: DEP's August 2026 table lists the nitrogen-reducing requirement for repairs on any size lot, and for new systems on any size lot as of July 27, 2026. The plan area includes Ocala and Belleview.
• Wekiwa and Rock Springs (Orange County). Since March 1, 2025, a repair or modification permit for a conventional system on a lot under 1 acre in the Priority Focus Area requires an upgrade to a nitrogen-reducing system. Orange County has offered upgrade payments to eligible homes; check its page to see whether applications are open, and see our repair assistance and financing page.

If your lot is in one of these areas, the choice may not be "conventional or aerobic" at all, but which approved nitrogen-reducing system fits the site. The county septic resource finder shows the springs rules and permit office for each county we cover, and our Florida septic regulations page explains the rules in more detail.

Living with each system

Conventional

• Pump the tank on schedule. The pumping interval calculator gives an estimate for your tank and household.
• Keep vehicles and heavy loads off the drain field.
• Watch for slow drains, odors or soggy ground over the field.

Aerobic

• Keep the service contract current and the operating permit renewed every 2 years.
• Leave the power on. EPA notes power is required to operate the aeration equipment.
• Treat an alarm as a call to your maintenance entity, not something to switch off.
• Budget for parts. Aerators and air pumps wear out, and parts are often extra under a contract.

Questions to ask an installer

1. What does the soil evaluation show, and why does my lot need this type of system?
2. Is my lot in a BMAP or springs area that requires a nitrogen-reducing system?
3. If you propose an ATU, is the model on DEP's list of approved nitrogen-reducing units?
4. What will the maintenance contract cost each year, and what does it leave out?
5. Who applies for the construction and operating permits, and are the fees in the quote?
6. Are you registered with Florida DEP as a septic tank contractor?

You can check a contractor's registration with our registration checker or the verification worksheet. For the cost of a new system with permits, read our installation cost guide.

Frequently asked questions

Is an aerobic septic system better than a conventional one?

Not in every case. EPA says an ATU can give a higher level of treatment and works on sites where a conventional system will not. It also costs more to run, needs power and has parts that can break. On a lot with good soil outside the nutrient areas, a conventional system may be all that is needed. The lot and the local rules usually decide.

Do I need a maintenance contract for an aerobic system in Florida?

Yes. Florida law requires an ATU owner to keep a service agreement with a permitted maintenance entity that inspects the unit at least twice a year. The one exception: the owner of an owner-occupied, single-family home can be approved as the maintenance entity for their own unit after manufacturer-certified training.

How often does an ATU operating permit renew?

Every 2 years. The state base fee is $100, and counties add their own fees. Seminole County, for example, lists $150.

Does every ATU count as a nitrogen-reducing system?

No. DEP accepts Florida-approved nitrogen-reducing ATUs certified under NSF 245, along with in-ground nitrogen-reducing biofilters and approved performance-based systems. EPA's fact sheet notes that aerobic units in general may release more nitrates to groundwater than a septic system.

Can I switch my ATU back to a conventional system?

Any change to a septic system usually needs a permit, and the lot may not support a conventional system, especially in a nutrient area. Ask your county septic permit office before planning a change. Our permit offices page lists who to contact.

Sources

Cost figures are planning estimates from the published sources below. Rules sources were opened and checked in November 2026.

• U.S. EPA: How to Care for Your Septic System (updated August 2026)
• U.S. EPA: Why Maintain Your Septic System (updated March 2026)
• HomeGuide: How Much Does a Septic Tank System Cost? (updated September 2025)
• HomeGuide: How Much Does a Leach or Drain Field Replacement Cost? (updated December 2025)
• Fixr: Septic System Installation Cost (updated January 2025)
• Bob Vila: How Much Does It Cost to Replace a Septic Tank and Drain Field? (updated December 2023)
• InspectApedia: Aerobic (ATU) Septic Maintenance & Repair Costs (updated May 2024)
• Florida Administrative Code: Rule 62-6.030, F.A.C. (Fees) (updated June 2026)
• Florida Department of Health in Seminole County: Environmental Public Health Fee Schedule 2025-2026 (updated FY 2025-2026)
• U.S. EPA: Types of Septic Systems
• U.S. EPA: Decentralized Systems Technology Fact Sheet, Aerobic Treatment (EPA 832-F-00-031, September 2000)
• Florida Statutes s. 381.0065: Onsite sewage treatment and disposal systems
• Florida DEP: Onsite Sewage Program
• Florida DEP: Onsite Sewage FAQ, Permitting
• Florida DEP: Permitting enhanced nutrient-reducing onsite sewage systems
• Florida DEP: 245 Certified Aerobic Treatment Units (list, October 2026)
• Florida DEP: Enhanced Nutrient-Reducing Requirements for OSTDS, by BMAP (August 2026)
• Florida DEP: Amended Order Closing File, Silver Springs and Rainbow Springs BMAP challenge (April 2026)
• Orange County: Septic Pollution Prevention (Wekiwa Springs)