Aerobic Septic System: Types, Cost and Working

What is an Aerobic Septic System?

An aerobic septic system, sometimes called an aerobic treatment system (ATS), is a compact wastewater treatment solution that operates much like a conventional septic tank only with a key difference.

Instead of relying solely on anaerobic bacteria (which work in oxygen-free conditions), these systems use aerobic bacteria, meaning they need oxygen to break down waste.

You’ll often find aerobic systems in rural settings, particularly where there’s no access to public sewer lines. They’re suitable for individual homes or even a small cluster of residences.

What sets the aerobic treatment system apart from a standard septic tank is the quality of its output: it produces secondary wastewater clean enough to be disinfected and reused for things like irrigating lawns or gardens.

This opens up more options for where you can put the leach field and can even reduce its required size by up to half.

If you take a closer look at how these systems work, you’ll notice that Aerobic Treatment Units (ATUs) borrow several principles from municipal sewage plants, but everything’s scaled down to fit residential needs.

The magic happens when oxygen is actively pumped into the treatment tank, ramping up the activity of aerobic bacteria. These little organisms do a much better job breaking down nutrients in the wastewater compared to their anaerobic counterparts.

Some setups go a step further by including an extra tank before the main treatment stage and another one at the end for disinfection. This helps lower the number of harmful microbes in the final effluent even more.

There are some clear advantages to choosing an aerobic system. They’re particularly useful for properties with small yards, poor soil conditions, high water tables, or homes near bodies of water that are sensitive to pollution.

Of course, it’s important to keep in mind that aerobic systems do require regular maintenance over their lifetime to keep things running smoothly but that’s a small trade-off for the added flexibility and environmental protection they offer.

How Does an Aerobic Septic System Work?

There are essentially two primary types of septic systems: conventional systems and the more advanced aerobic septic systems. The main distinction between them really comes down to one key element oxygen.

In a conventional septic system, wastewater treatment relies mainly on the septic tank itself, which is designed to separate out solids, fats, and grease from the liquid. This process takes place in an environment without oxygen, meaning it’s an anaerobic process.

On the other hand, aerobic treatment units (ATUs) take a different approach. These systems introduce oxygen into the treatment chamber, which encourages the growth of specific bacteria that thrive in oxygen-rich conditions. These bacteria play an active role in breaking down and digesting sewage much more efficiently compared to the conventional, oxygen-free approach.

Just like traditional systems, aerobic septic systems use natural processes to treat wastewater. However, by supplying additional oxygen, they create an environment where aerobic bacteria can flourish, leading to more effective and thorough breakdown of waste materials within the unit.

This Treatment is Done in Stages:

• Pre-Treatment: The process often begins with a pre-treatment stage, where wastewater first passes through a septic tank placed before the Aerobic Treatment Unit (ATU), or, in some cases, the ATU itself includes a dedicated setting or “trash” tank. The main goal here is to separate out the solids from the liquid wastewater, making it easier for the following treatment steps to work efficiently.
• Aeration Chamber: Next comes the aeration chamber. In this section, air is actively introduced into the wastewater typically using an air compressor or blower. By supplying oxygen, this stage creates a favorable environment for aerobic bacteria, which are essential for breaking down the remaining organic matter in the water.
• Disinfection: After aeration, the partially treated water (now called effluent) goes through a disinfection step. This is an added layer of protection, ensuring that any lingering pathogens are neutralized. Common disinfection methods include the use of chlorine or ultraviolet (UV) light, each aiming to further improve the quality of the treated water before it’s released.
• Final Treatment and Disposal: Finally, the treated effluent is ready for disposal. At this stage, it’s released into an appropriate drain field. Depending on the system design, this might be a sand filter, an absorption field, or even an evapotranspiration bed. Each of these methods helps to safely disperse the treated water into the environment.

What is an Aerobic treatment unit?

Aerobic treatment units are designed to handle household and small business wastewater in much the same way as large municipal systems just on a smaller scale.

These units are surprisingly effective, removing somewhere between 85 and 98 percent of the organic material and solids from the wastewater.

In fact, the effluent they produce is often as clean as what you’d get from a city treatment plant, and it’s definitely cleaner than what comes out of a typical septic tank.

What sets Class I certified aerobic units apart is their ability to treat wastewater to a high enough standard that it can safely be used with spray irrigation systems those setups that disperse treated water across lawns.

This compatibility is actually one of the main reasons aerobic units are so commonly paired with spray systems for on-site wastewater management.

Components of Aerobic treatment unit

The aerobic treatment process includes four main components that work together to purify wastewater:

• Pretreatment tank: In most treatment systems, the first step is the pretreatment tank, often nicknamed the “trash tank.” Its job is pretty straightforward: it catches and holds on to the kinds of materials that the microbes downstream simply can’t break down. Think of it as a filter, keeping out the stuff that would otherwise just clog up the works later.
• Aeration chamber: Next, the process moves into the aeration chamber. This is where the real action happens—here, aerobic microbes get busy breaking down the waste in the water. To keep those microbes happy and active, an aeration system pumps air into the chamber. The system typically includes an air pump (usually sitting close by), a network of pipes, and diffusers. The pump pushes air through the pipes into the chamber, and the diffusers break up that air into small bubbles. As the bubbles float up, they mix the water and supply oxygen, which is crucial for the microbes to do their job.
• Settling chamber: After the aeration step, the water heads into the settling chamber, sometimes called a clarifier. Here, the microbes that have finished treating the wastewater have a chance to settle out. This step clears up the water before it moves on.
• Land application system: The last stop is the land application system. This part of the process takes the treated water and spreads it out into the soil, where nature takes over for the final bit of treatment and safe disposal or reuse. Most aerobic treatment units use spray systems to distribute the water. These setups typically feature a disinfection step (to knock out any lingering disease-causing microbes), a pump tank to help dose out the water, and spray heads that spread it evenly over the ground.

How Does an Aerobic Treatment Unit Work?

Aerobic treatment systems manage wastewater by relying on naturally occurring processes that depend on oxygen. In these systems, bacteria that flourish in oxygen-rich conditions actively break down and consume the organic matter found in wastewater, with the bacteria remaining suspended within the liquid inside the aerobic treatment unit (ATU).

Like many other onsite wastewater solutions, aerobic systems handle treatment in several distinct stages.

One of the main steps involves introducing compressed air into the tank, which bubbles through the liquid effluent. This process creates an environment full of oxygen—just what the bacteria need. The microorganisms then use the organic materials in the wastewater as their main energy source, efficiently breaking them down.

After this, there’s another phase where bacteria and solid particles settle out of the wastewater, resulting in cleaner liquid that’s then directed to a soil treatment system for further purification.

Compared to traditional septic tanks, ATUs involve more complexity. In a typical septic tank, solids separate from the liquid continuously.

As bacteria multiply, they eventually settle at the bottom along with larger pieces of organic matter, forming a layer of sludge. Meanwhile, lighter substances like fats and bits of toilet paper float to the surface and create a scum layer.

In contrast, an ATU uses constant bubbling to keep the water agitated. This agitation prevents solids from simply settling and keeps materials that would otherwise float mixed in with the rest of the liquid.

A well-designed aerobic treatment unit finds a balance: it provides enough time and space for certain solids to settle out, while ensuring that bacteria get both the oxygen they require and thorough mixing with their food source the incoming sewage.

Any bacteria that do settle are typically returned to the oxygen-rich part of the tank, where they can continue breaking down waste.

How To Maintain Your Aerobic Septic System?

To ensure an aerobic treatment unit continues to function properly, ongoing maintenance is essential. When these systems are neglected, the quality of the treated water often falls short of expectations.

The most reliable approach is to adhere to the maintenance instructions provided by the manufacturer. However, there are some universal guidelines that can serve as a helpful starting point for looking after your system.

Generally, upkeep responsibilities are divided into two main categories: those tasks handled by a maintenance professional, and those that fall to the homeowner. Understanding which duties belong to each group makes caring for your aerobic treatment unit much more straightforward.

What To Do:

1. Regularly Inspect Your Septic System

Even if your aerobic system works really well, you’ll still need to have it checked out from time to time. That means regular inspections, as well as cleaning and emptying your septic tank as needed.

Staying on top of routine maintenance can really make a difference when it comes to how long your septic system lasts. For example, gravity systems usually only need cleaning every three years, while pressure distribution systems, along with mound or sand filter systems, should be cleaned once a year.

2. Pump Out Whenever Necessary

During a typical inspection, a septic service provider might suggest that your septic tank needs to be pumped. How often this needs to happen isn’t the same for every household; it can depend on things like the tank’s capacity and how much water your household uses day to day. For most homes, having the septic system pumped every three to five years is standard practice.

3. Be Water-Wise

It’s important to be mindful of how much water you use at home. Overusing water is actually one of the most common reasons aerobic systems don’t work as they should. Not only can this lead to system failure, but it also means your tank will fill up much more quickly, so you’ll find yourself needing to pump it out more often than you’d probably like.

4. Use Licensed, Certified Companies

It is important to ensure that your aerobic system is maintained or repaired exclusively by certified professionals. Proper servicing of a septic tank involves much more than simply adding chlorine tablets.

Before allowing a maintenance team to work on your system, take the time to research their qualifications and verify their experience. This extra step can help protect your home and ensure the job is done correctly.

What not To Do:

1. Flush Solids Down the Drains

It’s important not to dispose of random materials down your toilets or drains. When solids or grease make their way into the septic system, they can complicate the treatment process and add to the buildup of sludge over time. Remember, aerobic systems are specifically engineered to handle typical household wastewater—not everything that can fit down a drain.

2. Pour Harsh Chemicals into Your Toilets

Using chemicals can seriously harm the beneficial bacteria in your aerobic system—these microbes are essential for breaking down solid waste effectively. Additionally, harsh chemicals don’t just stop there; over time, they can actually corrode and damage your drainage pipes.

Instead of pouring unwanted chemicals down the drain, it’s best to look up proper disposal methods. Try reaching out to your local public health or hazardous waste hotline—they can guide you on safe and responsible disposal options.

3. Park Cars or Trucks On Your Drain field Or Reserve Area

Parking heavy equipment or vehicles over your septic tanks can compact the soil above your aerobic system, which might eventually cause the system to fail. It’s also a simple way to protect your pipes from being damaged by excess weight an issue that can lead to costly repairs down the road.

On a related note, it’s wise not to plant your flower garden directly above the septic tanks. If your tanks become full and require urgent servicing, you won’t want to choose between your garden and addressing a sewage issue. In such situations, septic professionals may have to dig up the area, and saving your flowers won’t be their top priority when your home’s plumbing is at risk.

4. Add Septic Tank Additives

It’s not uncommon for homeowners to experiment with different products when maintaining their septic tanks even though some of these products haven’t received approval from the local Department of Health.

The trouble is, using these unapproved items can actually do more harm than good, often introducing additional solids into the system that it simply isn’t designed to handle.

Beyond that, the chemicals in these products can seep out and end up contaminating both groundwater and surface water a risk that’s easy to overlook. For example, some people have tried using swimming pool chlorine tablets as a substitute for proper chlorinators.

However, it’s important to know that only calcium hypochlorite tablets are recognized as safe and effective for treating domestic wastewater. Using anything else may not just be ineffective; it could also create environmental hazards.

Types Of Aerobic Treatment Systems

When it comes to small-scale aerobic systems, there are usually two main types you’ll come across: fixed-film systems and continuous flow suspended growth aerobic systems, often referred to as CFSGAS. While both setups handle pre-treatment and effluent in much the same way, what really sets them apart is how they approach the aeration process.

1. Fixed film systems

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Fixed film systems work by using a porous material as a bed, which supports a layer of biomass that handles the digestion of waste in wastewater. While there are lots of different ways to design these systems, they generally fit into two main categories.

In the first approach, the media—the part that supports the biomass—actually moves through the wastewater. This means the biofilm gets dipped in the water and then lifted out to catch some air, over and over. The second type keeps the media still, but instead, the flow of wastewater changes. So, sometimes the film is under water, and other times it’s exposed to the air.

No matter which setup you’re looking at, the important thing is that the biomass needs to come into contact with both the wastewater and air for the aerobic digestion process to work. The porous material that forms the film bed can be made from all sorts of things—formed plastic and peat moss are a couple of common choices.

Some of the simplest setups use stationary media and let gravity do the work. Wastewater trickles in at intervals, allowing the film to switch between getting wet and airing out, just by how the flow happens.

A classic example of a moving media system is the rotating biological contactor, or RBC for short. In an RBC, you’ve got disks mounted on a horizontal shaft, slowly turning so that around 40 percent of each disk is underwater at any one time. The whole shaft turns just once or twice every minute, giving the biofilm the right balance of exposure to both air and wastewater.

2. Continuous flow, suspended growth aerobic systems

CFSGAS systems, true to their name, are built for continuous flow treatment and don’t use a traditional bacterial film bed. Instead, they rely on keeping bacteria suspended throughout the wastewater.

To keep the bacteria mixed and supplied with oxygen, these systems usually have an air pump. The pump continuously pushes air into the aeration chamber, which not only stirs the wastewater but also ensures there’s plenty of oxygen for the bacteria to thrive.

Some setups take it a step further and introduce a special medium to encourage bacteria to stick and grow, especially if the system needs to handle unusually high amounts of organic material. This extra step helps support even more bacterial activity when the wastewater is particularly loaded.

3. Retrofit or portable aerobic systems

One practical and increasingly widespread approach is to address malfunctioning or failed anaerobic septic systems by upgrading them with an aerobic treatment component. This method, often called aerobic remediation, targets the underlying biological issues in compromised anaerobic distribution systems.

By incorporating aerobic treatment, the system is able to significantly lower both the biochemical oxygen demand (BOD₅) and the total suspended solids (TSS) in the effluent. This step is crucial because bringing down these values helps break down the bio-mat that tends to accumulate in failed systems.

When the effluent leaving the treatment unit contains higher levels of dissolved oxygen and active aerobic bacteria, it enters the distribution section and begins to digest and clear out the problematic bio-mat buildup.

4. Composting toilets

Composting toilets are specifically designed to handle only human waste, rather than all types of household wastewater. You’ll usually find them paired with waterless toilets, not the typical flush toilets connected to standard aerobic treatment systems.

One key thing about composting toilets is that they process waste as a moist solid, instead of dealing with it as a liquid. Because of this, these systems actually separate urine from feces right at the source, which helps keep the moisture levels balanced inside the composting chamber.

A well-known example is the clivus multrum—its name literally means “inclined chamber” in Latin. True to its name, the design features a sloped chamber where urine and feces are directed into different areas. There’s also a fan built in, which isn’t just for show; it provides positive ventilation, so you don’t have to worry about unpleasant odors leaking back into the bathroom.

Inside this chamber, the breakdown of waste is handled by more than just aerobic bacteria. Fungi, arthropods, and even earthworms all play a role in the composting process. It’s a slow operation, though—the waste needs to stay in the chamber for at least a year before any solids are removed.

Over that time, about 90% of the solid waste actually disappears, mostly turning into water vapor and carbon dioxide. What’s left behind is much smaller in volume, and most harmful pathogens are destroyed thanks to the harsh, prolonged conditions inside the chamber.

What is a Conventional System?

A decentralized approach to wastewater management often involves the use of a septic tank paired with a subsurface infiltration system, commonly referred to as a drain field or leach field.

You’ll find this kind of setup most frequently at individual homes or smaller businesses, where centralized sewage infrastructure either isn’t available or simply isn’t practical.

One of the longstanding designs in this category is the gravel or stone drain field. The term itself hints at how the system is put together: after wastewater leaves the septic tank, it flows into a shallow trench filled with gravel or stone.

This isn’t just for show—the gravel provides a pathway for the effluent to move through, and there’s typically a layer of fabric or some sort of barrier on top. That barrier’s job is to keep out sand, soil, and other debris, making sure only the wastewater makes its way through the clean stone layer.

As the effluent travels downward, it passes through the gravel and is gradually filtered. But the treatment doesn’t stop there—once the water reaches the soil underneath, naturally occurring microbes step in to break down and further treat whatever’s left in the wastewater.

It’s worth noting, though, that gravel and stone systems can take up quite a bit of space. They have a larger physical footprint compared to some other designs, so they’re not always a perfect fit for every property or site condition. Homeowners or builders need to keep this in mind when weighing their wastewater treatment options.

How Much Does It Cost Aerobic Septic System?

Aerobic septic systems rely on oxygen-loving bacteria and use an air pump to ensure the tank stays well-aerated, which helps break down waste efficiently. Compared to anaerobic systems, aerobic setups are a bit more complex they need extra components and careful installation.

Because of this, and depending on factors like system size, soil type, and where you’re located, you’ll usually find that aerobic systems come with a higher price tag.

• Site evaluations and permits have an average cost between $200 and $400.
• An aerobic septic system has an average cost between $10,000 and $20,000.
• You need to have the system professionally inspected and pumped every one to three years, which has an average cost of $200.
• Aerobic systems may need motor & timer replacements from time to time. Motor replacements have an average cost between $500 & $600 and timers average $100.

How to Pick the Best Septic Air Pump?

The septic air pump serves as the essential component of an aerobic treatment system, and without it, the system simply cannot operate as intended. Its function is actually twofold.

Primarily, the air pump infuses oxygen into the water, which is necessary for the growth and sustainability of aerobic bacteria. These bacteria play a critical role: they are responsible for breaking down and consuming the waste material present in the tank.

Notably, aerobic bacteria are both larger and more effective at waste decomposition than the anaerobic bacteria typically found in conventional septic systems.

In addition to oxygenation, the air pump helps agitate the water within the tank. This agitation breaks down larger solid materials into much smaller particles, thereby making it easier for the bacteria to access and process the waste efficiently.

If the air pump stops functioning, the consequences can be significant. Within approximately two weeks, the environment inside the aerobic system will start to revert to an anaerobic state.

This transition poses a particular issue because, unlike traditional anaerobic septic systems, aerobic systems do not have an additional treatment stage after the main tank.

As the system becomes anaerobic, the quality of the effluent changes dramatically. Rather than a clear, odorless output, the discharge will begin to resemble untreated sewage.

Understandably, releasing raw sewage whether it ends up in a ditch, body of water, or is sprayed onto a lawn poses clear environmental and health risks.

For these reasons, maintaining the proper operation of the air pump is essential to the performance and safety of your aerobic treatment system.

7 Reasons Why You Need Aerobic Septic Systems on Your Property

Septic systems play an essential role in maintaining the health and functionality of both commercial and residential properties. Without a properly operating septic system, waste cannot be managed safely, creating potential health risks for anyone in the building—whether that’s your family, your tenants, or your clients.

Regular maintenance is key if you want your septic tank to function as it should. Typically, it’s recommended to have your home’s septic tank pumped every three to five years, which helps prevent issues down the line.

When the time comes to select a septic tank system for your property, you’ll usually be deciding between a couple of main types. One option worth considering is the aerobic septic system. If you’re curious about the benefits of this type, keep reading—we’ll look at why an aerobic septic system might be the right fit for your needs.

• Longevity: A well-installed and properly maintained septic tank system is remarkably durable, often lasting up to four decades. The key to such longevity lies in regular cleaning and inspection, which are crucial for keeping aerobic systems running smoothly over the years. From the outset, investing in correct installation pays dividends by ensuring the system’s extended lifespan.
• Minimal Space Requirements: The capacity of a septic tank generally depends on the number of people living in a household or occupying a building. While some systems can demand a considerable footprint, this is not always the case. Aerobic septic systems, in particular, are notably compact making them a practical solution for properties where space is limited.
• Superior Treatment Efficiency: Aerobic septic systems excel in delivering a higher standard of wastewater treatment. This means the treated water released from the system is significantly cleaner, which substantially reduces the risk of groundwater contamination. For properties situated in areas with a high water table, installing an aerobic system is highly recommended, as it helps prevent potential water pollution.
• Environmental Benefits: These systems also appeal to those looking for more sustainable options. For example, water used in household activities such as laundry or showers can be safely recycled for purposes like lawn irrigation. After passing through the aerobic treatment process, this water is suitable for reuse, which both conserves resources and supports environmentally friendly practices.
• Rapid Waste Breakdown: One major advantage of aerobic septic systems is their ability to break down solid waste more efficiently than conventional systems. This accelerated process means waste accumulates much more slowly, reducing the need for frequent pumping and making ongoing maintenance simpler and less frequent.
• Adaptability to Various Land Types: Perhaps one of the most flexible features of aerobic septic systems is their compatibility with all soil types. Unlike traditional septic systems, which often struggle on land with high groundwater levels or particular soil conditions, aerobic systems are engineered to function reliably across a diverse range of environments.
• Cost Savings: Finally, because aerobic systems treat most wastewater within the tank itself, the associated drain field endures much less strain. This reduces the frequency and expense of repairs to the drain field, providing significant long-term cost savings for homeowners.

Advantages of Aerobic Septic Systems

• Provides a Higher Standard of Effluent Treatment: These systems are capable of treating wastewater to a more advanced level, ensuring that what is released meets stricter environmental standards.
• Suitable for Marginal or Poor Soil Conditions: Unlike traditional methods that rely on ideal soil, this approach works well even when the soil is less than perfect.
• Adaptable to Small or Challenging Lots and Unusual Terrain: Whether a property has limited space or difficult topography, these systems can be tailored to fit where conventional options might struggle.
• Effective in Areas with Setback Limitations: When properties are close to boundaries, bodies of water, or aquifers, these solutions are designed to operate safely within those tighter restrictions.
• Environmentally Friendly with Smaller Drain Field Requirements: By needing a much smaller footprint for the drain field, these systems help conserve land and minimize the impact on the surrounding environment.
• Demonstrated to Prolong Drain Field Lifespan: Research and field experience show that these systems can help drain fields last significantly longer.
• Significantly Lowers the Risk of Clogging: Because of the way the treatment process works, the likelihood of the drain field becoming clogged is greatly reduced.
• Supports Water Conservation—Some States Permit Irrigation: Many areas now allow treated water from these systems to be reused for irrigation, making them a practical option for saving water.
• Helps Minimize Nitrogen Discharge: These systems are designed to reduce the amount of nitrogen that enters the environment, addressing a key pollution concern.
• Offsets Upfront Costs by Enhancing System Durability and Efficiency: While the initial investment may be higher, the extended performance and longevity of the system can provide long-term cost savings.

Disadvantages of Aerobic Septic Systems

• Blower noise: One issue that often comes up with these systems is the noise generated by the blower. Depending on the setup and quality of installation, this can be noticeable and, for some users, quite distracting especially in quieter environments.
• Slight odor if not properly vented: If the ventilation isn’t handled correctly, there’s a chance you might notice an unpleasant smell. This is something that’s often overlooked but can be a real nuisance in daily use.
• Higher power consumption: Compared to some alternatives, these systems tend to draw more electricity. Over time, this can add up on your utility bills, so it’s worth considering the long-term costs.
• Maintenance limitations: Regular maintenance is not always straightforward—or sometimes, not even an option. If something goes wrong, you might find yourself facing bigger issues or higher repair costs down the road.
• Significant upfront installation expense: The initial cost to install these systems is generally on the higher side. While you might recoup some of that over time, the upfront investment can be a barrier for many.
• Contamination risks with poor upkeep: If the system isn’t maintained properly, there’s a risk of contamination whether that’s from mold, bacteria, or other pollutants. Staying on top of regular checks is crucial to avoid health concerns.
• Overload from excessive water: Introducing too much water into the system can overwhelm it, leading to operational problems. It’s a detail that’s easy to overlook, but it can have a major impact on performance.
• Vulnerability to cold weather: Cold weather can pose significant challenges unless the system is well insulated. If not properly protected, components may not function as intended, which could result in inefficiency or even damage.

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