SKETCH of a typical aerobic treatment unit tank, aerator, chamber AEROBIC Septic System Failure Rates & Costs

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Aerobic septic system or aerobic treatment unit (ATU) failure rates & repair costs: this article discusses Aerobic Septic System Failure Rates & Costs.

This website provides designs and products for aerobic septic treatment units (ATUs) for onsite waste disposal, also called fine bubble aeration systems. We address aerobic septic system design, features, inspection, repair, and maintenance. Product sources are also listed.

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Aerobic Treatment Unit Failure Rates and ATU Installation & Operating Costs

Failure Rates for Aerobic Septic Systems

Some readers have written expressing concern that they've heard that ATU's have a high failure rate, "as high as 95%". That number doesn't mean much to me without more specific data, in particular, one would need to know what was meant by "failure" and what was the cause of specific failures of ATUs. Important septic system failures are the failure to adequately treat wastewater or the failure to successfully dispose of it.

ATU Failures due to lack of maintenance: In the study discussed below, while a high failure rate was reported for ATUs (where failure here means the aerobic treatment system was not treating the effluent satisfactorily), the failures were specifically linked to a lack of proper maintenance.

Every type of septic treatment system requires periodic maintenance and repair, and I expect that every septic system eventually fails and needs extensive repair or replacement. So we could put the septic system failure rate at 100%. What would be more useful would be a statement of the typical operating cost for various alternative septic treatment systems, the typical component life, and the amount and cost of ongoing maintenance that are required.

NESC, in an issue of their Pipelines magazine (Note 1), , cited a 1998 survey conducted in West Virginia which looked at Aerobic Treatment Units to evaluate the quality of their effluent discharge. 419 ATUs were tested for TSS (total suspended solids) and BOD5 (5-day biochemical oxygen demand), and 92 percent of the systems were determined to be producing unacceptable effluent discharge.

The main cause of these aerobic septic system treatment unit failures was attributed to poor or improper ATU maintenance. I suspect that homeowners, accustomed to the tradition of inattention to septic systems until they are visibly failed, simply were performing no maintenance at all. However with proper inspection and maintenance, ATU's can continue to provide effluent which has been treated better than by a conventional septic tank and drainfield.

For example, of the 419 units, only 85 were selected for chemical tests. Of the 419 units inspected, field inspectors found (by visual inspection) deficiencies in 272 units (65%). 71% of the 85 units selected for testing were found to have deficiencies.

What was particularly remarkable, while 93% of the ATU's with a visually detectable deficiency were producing unacceptable effluent output, more stunning, another 80% of the ATU's with no apparent deficiencies by visual inspection, were producing unacceptable effluent discharge! (Op. Cit., p. 43). Here is a description of the study: "Of the 419 ATUs examined, 85 were sampled for additional laboratory analyses, which included BOD, TSS, and fecal coliforms (FC).

Approximately 150 units were tested for chlorine residual and turbidity. The survey was performed by the Environmental Services and Training Division and the Environmental Microbiology Laboratory, both at West Virginia University (WVU), and six county health departments, and with assistance from the West Virginia Bureau of Public Health. The project objectives were to survey existing ATUs for proper operation and maintenance and to determine the chemical and microbiological quality of their effluents."

Installation & Operating Costs for Aerobic Treatment Units ATUs

The NESC cites several obvious components in ATU installation and operating costs. Installation costs for an ATU include the cost of the ATU installation, including excavation and electrical wiring, the cost of construction of the post processing facility such as raised bed or sand bed.

Operating costs for aerobic septic systems include electricity for the ATU compressor or air pump, annual inspection and maintenance, usually by contract with the installer, and cost of effluent disinfection if that step is used. One website, which has some nice simple summaries of types of septic systems, cites a cost of $3200. to $5000. to install an aerobic treatment unit.

This number cannot possibly be correct for a complete system installation. More likely it is referring to the aerobic treatment unit itself, the tank and aeration system. Add to these the cost of excavation and piping for the sewer line from the building, from the ATU to the absorption system, and the installation of the wastewater absorption system, and you're probably looking at two to three times that number.

It is a bit tricky trying to compare alternative septic system costs. After all, we choose a particular system because it best fits the limitations of the site. A very limited site that requires installation of an ATU and a raised bed or septic mound system to handle the effluent, such as in a rocky building site in the Northeastern U.S., may involve a total installed cost of $25,000. This troubling number cannot be compared with the probably lower cost of a conventional septic tank and drain field ($10,000) because the latter simply won't work on the site in question.

What we can say about ATUs is that if regular inspection and maintenance are not performed, the system has a good chance of not working properly.

The cost of electricity to operate the septic aeration system is likely to be trivial, perhaps $4./month. We can also say that the trash tank or primary treatment tank will require more frequent pumping than a conventional septic tank. I expect that septic tank cleaning or tank pumping cost, often $125. to $250. per pumpout depending on location and tank size and effort to access the tank, probably is more significant than the operating cost to supply electrical power to the equipment.

Failures & operating or maintenance difficulties with Aerobic Septic Systems or ATUs

Question: Having an ATU installed, worried.

I am having an ATU unit installed tomorrow. Against my better judgment, but due to wonderful regulations, that was the plan the engineer said we HAVE to have. Total install for a 500 gallon trash tank, 1000 gallon septic tank, ATU, 176 feet of drainfield piping with Q36 equalizer is $18,519. Just in case anyone was wondering. - Steve Woodward 10/4/2011

Question: ATU performance query

Steve, how is your ATU unit working so far? Was this a replacement for a failed system? How many people in household for that size. I'm guessing 5 to 6? Are you in the North and if so did you insulate the unit for winter? How big is your lot? Lastly, did you also have a well?
Dawn2nd 1/14/2012

Question: has trouble getting maintenance on Aerobic Treatment Unit ATU



Michele, I'm so sorry to read about your difficulty with an aerobic septic system. In fact aerobic treatment units can function to a very high level of treatment of sewage, but indeed independent research about various types of septic system failures confirms that most often, when there are failures in advanced systems and designs, it's because of lack of or improper maintenance.

We could argue that the problem is you haven't found the right maintenance contractor, and certainly that's what needs your attention. But it is fair to say that an innate problem with the design of some systems in just about any field (computers to zone valves) is that some designs, by their complexity, have trouble finding people who will install and maintain them properly - it could be lodged as a complaint against the designer as well.

Good design of any system includes making it easy to maintain it.

Question: complaints about ATUs & ATU Aerator pump problems, costs, frequency

Stay away from these units with a 10 foot pole, they may work fine if you have 3 people or less in your household, however, that is not guaranteed. They are not designed for family usage. This is the greatest nightmare of my home purchase from 2006, worse than being underwater on your mortgage.

When it rains your toilets don't flush. You have to have it pumped once or twice a year at at rate of $250.00 each time, also, in Florida, you are required to pay a septic maintenance company $200.00 every year, plus $100.00 for a two year permit from the Health Department. Sooner or later everyone will have to acknowledge these systems are a failure. Charlotte County, Florida got rid of their mandate that all new residences install these units for a reason. They were also installing these systems on properties without enough room for a big enough drain field during the housing boom. Do yourself a favor and stay away from these things.

Concerning the above stating the failure is only due to improper maintenance is simply not true, with all respect! I have lived in my home with an ATU since 2006, it has been a pure nightmare, waiting for my county to sewer up my street, slowly they will get to me. Older septic systems last much longer and do not require so much $$ in maintenance. Either have a sewer or an older septic system, but not an ATU. This was confirmed by the very owner of the septic company that installed my system. She told me they are a life changing headache! - guest 6/27/2012

The aerator pump in my ATU causes so much turbulence in the tank that it stirs the contents in each baffled chamber in the tank and this causes solid particles to flow into the drain field array. This has caused blockages and back ups which require Roto-Rooter style cleaning at the cost of $535.00 per visit.

Three times in 5 years. ATUs are a design nightmare and any county or municipality which requires them should be investigated. In my opinion there is not enough bang for your buck here when you consider the prohibitive cost. As far as the purity the ATU is supposed to give, it is way over-rated and is overkill. The old style systems have been working fine for years. When was the last time that a cholera or dysentery epidemic occurred because of a non-ATU style system? - George Kachmar 6/27/2012


Guest, and George, thanks for sharing your views about Aerobic septic treatment units. Reports of actual user experience are very very valuable as they bring "real world" considerations and experience in to balance with "theory".

Aerobic treatment units are very widely used in some areas, such as parts of Texas. I imagine that perhaps where there are many users there are more competent experienced service companies and people's use experience may be better.

Our own research finds that studies show that ATU systems can work to a high level of treatment - in the 90% range compared with 40% treatment in a conventional septic tank; but frequent failures of the system occur, usually traced to lack of proper maintenance.

My OPINION is that any product or system that relies on installers or users to do something that most people are not going to do is, at the end of the day, not the best design. We have to design buildings and mechanical systems for what people are going to do (or not do), not what they should do.

Question: Trouble with Clearstream ATU installed in Florida

I built my home in 2007 . I too have the nightmare known as ATU . The builders advice was to get a Clearstream ATU . One of the WORST mistakes I have ever made in my life . The pump only lasted 3 years . I have already had a circuit board go bad and now the filter housing is cracked . We also have to pay a permit fee with the state and a maintenance contract which also is expensive . Along with that is the hassle of dealing with the Health Department SURPRISE inspections . THIS IS NOTHING BUT A DISASTER . PLEASE STAY AWAY FROM THESE SYSTEMS AT ALL COST ! - Alan 3/21/2013


Alan, thank you for the report of your experience with Clearstream ATUs. Indeed surveys of septic system failures that focused on aerobic treatment units found a high failure rate, but asserted that the problem was lack of maintenance or owners not following the manufacturer's instructions. Of course if a product is designed to require maintenance that people are going to find burdensome or costly that design might be itself questioned.

Given that Clearstream will perform inspection and basic maintenance for the first two years at no charge, there wouldn't be much excuse for not having had maintenance performed and in turn I'd speculate that therefore the warranty should apply.

In the Clearstream ATU instance, can you tell us what was your experience when you went to the company to ask for assistance or advice?

If you have not done so, you can contact Clearstream, a Texas company, by calling them direct at 800-586-3656 or by writing to Clearstream at Clearstream Wastewater Systems, Inc.
4899 US Hwy 69 South
Lumberton, Texas 77657.

At ATU MAINTENANCE PROCEDURES we quote Clearstream's List of Aerobic Treatment Unit ATU Maintenance Requirements & Schedule. Can you give us any details on how working on each of these was easy or difficult?
Keep us posted - what you report will help other readers.


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