The Differences Between Aerobic vs. Anaerobic Septic Systems

    One of the basic utilities you have to think about when you're building on acreage is sewage. You'll be choosing between either an anaerobic or aerobic septic system. Let's take a look at how both of these systems work, and then I'll give you some advantages, disadvantages and circumstances to consider.

    About Anaerobic Septic Systems

    Anaerobic septic systems involve the use of bacteria that don't require oxygen to live. In an anaerobic system, you've got a septic tank with two main pipes. One of these goes to the house, and the other heads out into your yard. That main pipe splits into several pipes that sit just below the surface of your lawn.

    Inside the septic tank, solid waste settles and is eaten by the anaerobic bacteria. Liquid waste floats to the top. Wastewater from the tank moves out to the smaller pipes under the surface, which have holes at their ends. The wastewater then filters or "percolates" out into the soil.

    Download a helpful guide on anaerobic septic systems (also called subsurface sewage treatment systems) from the State of Oklahoma here.

    About Aerobic Septic Systems

    The aerobic septic system involves three tanks. Waste enters the first tank and settles into layers like the anaerobic system. But when it moves to the next tank, the treatment tank, an aerator moves oxygen bubbles through the waste. This allows aerobic bacteria to consume the waste. From there, wastewater moves to a pump tank where it's treated once more.

    Then, often in the middle of the night, sprinkler heads pop up and distribute that wastewater out onto your lawn.

    Download a helpful guide on aerobic septic systems from the State of Oklahoma here.

    Comparing Aerobic and Anaerobic Systems

    1. Cost

    The first obvious difference is cost. Typically, installing an anaerobic system is simpler and therefore less costly. Aerobic septic systems involve a more complicated system with added machinery, and are more expensive.

    2. Land Requirements

    There are certain situations in which you might actually require an aerobic system based on your land. First, for an anaerobic system to work the soil must be able to allow for percolation.

    When you're deciding on a septic system, a company will come out and do a percolation test to see how quickly water is absorbed into the soil.

    If the water doesn't "percolate" through the soil quickly enough, a traditional subsurface system won't work. Depending on the land, an aerobic septic system may be more efficient, or might be your only choice.

    Another case in which you'd need an aerobic septic system is if your land is very flat. Anaerobic (subsurface) systems require at least a gentle slope to make sure that wastewater can move out into the septic field. For more information about how slope (or lack thereof) can affect your choice when buying land, and other things to watch out for, here is a comprehensive article on searching for, evaluating, and buying the right piece of land for your custom home.

    Outside of these situations, you'll most commonly see homes built with conventional anaerobic septic systems. These systems are cost effective and simple, and are used successfully in many country homes.

    If you're looking to build a custom home on your land, you'll definitely want to educate yourself on the options and the pros and cons of each.

    Comparing Septic System Contractors

    Finding the right installer or service contractor for your aerobic or anaerobic (subsurface) septic system can be a challenge. This isn't an area to skimp on. It needs to be right.

    Where we are located in the state of Oklahoma (and I'm sure every other state) there's a requirement that installers and servicers of septic systems to be licensed. The scary part is that in some cases (particularly in certain counties, and outside city limits) there's no building department, and no permit / inspection process when building a home. In those cases, it's easy to "bootleg" a septic system, installing it without a state permit or inspection.

    Ask any contractor you're considering whether they're licensed, and how the state inspection process works.

    Second, ask around... there are homes in the general vicinity of where you're building, already living, or installing a system. Ask those homeowners who they use and why.

    You'll get the unvarnished opinions of lots of people, and that will help you sort out the contractors with good reputations from the bad ones. You can also ask home builders - they'll know who installs the systems with the fewest callbacks and problems. In Oklahoma, the best choice is Biggs Backhoe.

    They do great work and stand behind their installations. 

    Many states, including Oklahoma, have a Certified Installer Program, where installers can become certified by the State of Oklahoma by fulfilling certain requirements above and beyond the basic licensing. You can read more about that program here.

    Look for a Certified Installer for even more peace of mind. 

    Additional Resources

    If you're researching septic systems because you're replacing or troubleshooting an existing system, here's one more site with some really good info.

    If you're researching septic systems because you're thinking of building a home on your land, please feel free to download our free guide, "From Raw Land to Forever Home", for useful information on how to navigate the confusing and scary process of finding a bank, a house plan, and a builder for your forever home. 


    Download Guide to Build Your Forever Home


    3 minute read