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Aerobic vs Anaerobic Septic Systems: What Actually Changes

An aerobic septic system and a conventional anaerobic septic system both rely on bacteria to break down household waste; the difference is whether those bacteria have oxygen to work with. A conventional tank runs anaerobic, without added oxygen, and its bacteria digest waste more slowly and produce hydrogen sulfide gas as a byproduct. An aerobic treatment unit (ATU) uses an air pump to keep oxygen moving through part of the tank, which speeds up digestion and cuts down that gas. Neither design changes the pumping schedule.

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Both digest waste with bacteria. Only one adds oxygen to do it.

A conventional septic tank runs anaerobic, meaning its resident bacteria digest waste without added oxygen.
An aerobic treatment unit uses a mechanical air pump to add oxygen to part of the wastewater, supporting a different set of bacteria that digest waste faster.
Hydrogen sulfide forms when bacteria strip oxygen from sulfate compounds in an oxygen-starved environment, producing the rotten-egg smell associated with sewage.
An aerobic treatment unit has moving mechanical parts, including an air pump, and typically needs a maintenance contract and periodic professional service that a conventional tank does not.
Both aerobic and anaerobic septic systems still require solids to be pumped out on a regular schedule regardless of how well the bacteria are digesting waste.
Aerobic treatment units are often required by local health departments on lots too small, too wet or too close to water for a conventional drain field to be approved.

The two designs, side by side

A conventional septic system is a tank and a drain field. Waste settles, anaerobic bacteria digest what they can without added oxygen, and the clarified liquid flows out to the drain field for the soil to finish treating. It has no moving parts to service, which is part of why it is the default design across most of the country. An aerobic treatment unit adds a step. Air is pumped into a chamber of the tank, or a separate chamber after it, so a different population of bacteria, the kind that need oxygen, can digest waste faster and more completely before it reaches the drain field. That extra step is also why an aerobic system usually costs more up front and needs a service contract: the air pump is a mechanical part, and most jurisdictions that permit ATUs require regular professional inspection to keep the permit valid.

Why oxygen changes what the bacteria produce

The bacteria at work in a septic tank are only part of the story; what they are short of matters just as much. In an anaerobic tank, once the easy oxygen is gone, some bacteria turn to sulfate compounds for the oxygen they need, and hydrogen sulfide is the byproduct: the gas responsible for a septic system's rotten-egg smell. An aerobic treatment unit's whole point is to keep oxygen available, so fewer bacteria are forced to strip it from sulfate, and less hydrogen sulfide forms in the first place. Our home treatment, DRP Accelerator, carries usable oxygen to the bacteria already living in your tank. We add no bacteria, no enzymes and no chemical additives. It works in a conventional anaerobic tank the same way an aerobic unit does mechanically: giving the resident bacteria oxygen so digestion runs faster and hydrogen sulfide has less chance to form, without the added equipment, power draw or service contract an ATU requires.

What each design does and does not change

Neither design changes what still has to happen on a fixed schedule. Grease, wipes, inorganic solids and the sludge bacteria never fully digest still accumulate in both aerobic and anaerobic tanks, and both still need pumping on the interval your county or installer sets. An aerobic unit does not eliminate that step; it changes how completely the liquid is treated before it reaches the drain field, and in some soil and lot conditions it is what makes a system approvable at all. Choosing between them, for a new system, is mostly a site and permitting question your installer and local health department settle together. For a system you already have, converting anaerobic to aerobic is a significant retrofit, not a small upgrade, so it is worth confirming with a professional whether your actual problem, whether that is smell, slow drains or a permitting requirement, needs a different design or just better-supported biology in the design you already have.

Published October 12, 2026

The Short Answer

An anaerobic septic system, the conventional design most homes have, digests waste with bacteria that work without added oxygen. An aerobic septic system uses a mechanical air pump to add oxygen to part of the tank, supporting a faster-digesting population of bacteria and producing less hydrogen sulfide gas along the way. Neither design removes the need to pump solids on a fixed schedule; the difference is in how completely the wastewater is treated before it reaches the drain field, and in how much mechanical maintenance the system needs to keep working that way.

What “Anaerobic” and “Aerobic” Actually Mean Here

A conventional septic tank is a sealed, buried box. Waste settles, and the bacteria already living in the tank, working in an oxygen-starved environment, digest what they can. That is anaerobic digestion: bacteria breaking down organic solids without added oxygen. It is slower than digestion with oxygen present, and it has a well-known side effect. When bacteria run out of easy oxygen sources, some of them strip oxygen from sulfate compounds instead, and hydrogen sulfide, the gas behind sewage’s rotten-egg smell, is the byproduct.

An aerobic treatment unit changes the environment rather than the bacteria you start with. A mechanical air pump, called a blower or aerator, pushes air into a chamber of the tank or into a separate aeration chamber that follows it. With oxygen available, a different, faster-digesting population of bacteria takes over that stage of treatment, and the wastewater leaving the unit is more completely broken down than water leaving a conventional tank at the same point in the process.

How the Two Designs Compare

Factor	Anaerobic (conventional)	Aerobic (ATU)
Oxygen	None added; bacteria digest waste without it	A mechanical air pump adds oxygen to part of the system
Digestion speed	Slower	Faster, and more complete before the drain field
Hydrogen sulfide	More likely to form, especially with a long gap since pumping	Less likely to form, since oxygen is available
Moving parts	None	An air pump or blower that runs continuously
Maintenance	Pumping and inspection on schedule	Pumping and inspection on schedule, plus a service contract for the mechanical parts
Typical cost	Lower to install; no service contract	Higher to install; ongoing service contract usually required by the permit
Where it fits	Adequate soil and lot size for a standard drain field	Small, wet or environmentally sensitive lots where a conventional drain field will not be approved

Why a Health Department Might Require an Aerobic System

An aerobic treatment unit is not usually a homeowner’s first choice; it is often a permitting requirement. Soil that drains too slowly, a lot too small for a standard drain field, or proximity to a well, a lake or a wetland can all push a local health department to require the more thorough treatment an ATU provides before it will approve a septic permit. In those situations, the extra equipment and the service contract are the cost of building on a lot that a conventional system cannot serve, not an upgrade the homeowner is choosing for its own sake.

What Neither Design Changes

Both designs still send effluent, water clarified of larger solids, out to a drain field, and soil does part of the final treatment either way. Both still accumulate sludge and scum that bacteria never fully digest: grease, wipes and other solids their systems cannot break down. That means both still need pumping on the interval your county or installer sets, no matter how well the bacteria inside are performing. A biological treatment or a mechanical aerator can keep digestion running well between pumpings; neither one is a substitute for the pump truck.

Where a Biological Treatment Fits in Either Design

DRP Accelerator carries usable oxygen to the bacteria already living in your tank. We add no bacteria, no enzymes and no chemical additives. In a conventional anaerobic tank, that oxygen does mechanically what an aerobic treatment unit does with a pump: it gives the resident bacteria what they need to digest waste faster and reduces the conditions that let hydrogen sulfide form, without adding equipment, power draw or a service contract. In an aerobic treatment unit, the same accelerator supports the bacteria that are already working with the oxygen the blower provides, on the same schedule you would otherwise use to keep any tank’s biology fed. Either way, it is a supplement to the system you have, not a replacement for pumping or for mechanical service the unit’s manufacturer or your permit requires.

When to Call a Licensed Septic Professional

Some situations are not a design or a treatment question. Sewage backing up into the house, wastewater surfacing over the tank or the drain field, ground that stays wet or spongy in dry weather, a system alarm on an aerobic unit, or drains that stay slow after the traps are cleared all call for a licensed septic professional today. That holds for either design: a treatment supports the bacteria that are already there, and it does not diagnose or repair a failed blower, a cracked tank, a broken baffle or a drain field that has stopped taking water.

Where to Buy

The home version of DRP Accelerator is sold as Accelerator by Dr. Pooper at doctorpooper.com, made by DRP Seven. The buttons on this page take you there. It works alongside a conventional anaerobic tank or an aerobic treatment unit, on a schedule you keep, between the pumpings both designs still need.

COMMON QUESTIONS

Straight answers.

What is the difference between an aerobic and an anaerobic septic system?+

An anaerobic septic system, the conventional design, has bacteria digest waste without added oxygen. An aerobic septic system uses a mechanical air pump to add oxygen to part of the tank, which supports faster-digesting bacteria and produces less hydrogen sulfide gas. Both still need solids pumped out on a schedule.

Is an aerobic septic system better than a conventional one?+

Better fits the situation. An aerobic system treats wastewater more completely and is often required on lots where soil or lot size will not support a conventional drain field. A conventional system has no mechanical parts to fail and no service contract to keep up, which suits a straightforward lot with adequate soil.

Do aerobic septic systems smell less than conventional ones?+

Often, yes, because added oxygen means fewer bacteria are forced to strip it from sulfate, which is what produces hydrogen sulfide's rotten-egg smell. A conventional tank can reach a similar result by keeping its resident bacteria well supplied with oxygen through a biological treatment, without adding mechanical equipment.

How much maintenance does an aerobic treatment unit need?+

More than a conventional tank. An ATU has a mechanical air pump and typically requires a service contract with a licensed provider for periodic inspection, most jurisdictions make that a condition of the permit. A conventional tank still needs pumping and inspection on schedule, but has no pump or blower to maintain.

Can I convert my conventional septic tank to an aerobic system?+

It is possible but it is a significant retrofit involving new equipment, wiring and typically a new permit, not a simple add-on. Before committing to it, a licensed septic professional can tell you whether your actual problem, such as odor or slow drains, is something a biological treatment or a repair can resolve in the system you already have.

Does a biological treatment work in both aerobic and anaerobic septic systems?+

Yes. DRP Accelerator carries usable oxygen to the bacteria already living in a tank, whether that tank is a conventional anaerobic design or an aerobic treatment unit, supporting faster digestion in either setup. It supports the bacteria present; it does not replace pumping or repair mechanical or structural faults.

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