Aerobic Septic Tank
This is a mix of the correct term, which is an aerobic treatment unit, or an aerobic system. An aerobic treatment unit (ATU) is the main component. It's a tank full of sewage into which air is bubbled. That's it. No more fancy salesmanship.
Aerobic treatment units (ATU) first came into Texas in the 70's, so they're not new. ATUs became popular begining in 1997 due some "convenient" changes in the State regulations. Again, they're not so new.
For us, we started designing, installing, and maintaining ATUs in the early 1980s, so they're definitely not new to us. All the companies who started before or shortly after we did are all out of business. We're the only one still in business with this depth of experience.
Okay, so let's set aside the sales brochures and pursue some of real-life and technical issues with these “new” (not) OSSFs.
They undergo standardized testing to determine if they can meet the standards set for cleaning up wastewater. The test methods used in their testing is nowhere close to the conditions they're asked to handle in actual installed operations. In a 6 month test, they only go through 1 week of workday stress testing. When installed, many of these units go through workday stress every day of their life. Same story with wash day stress testing - one week out of 6 months for testing, then wash day every week of their life.
Can you figure out where I'm going with this? The testing that "proves" how well they work is nowhere near as demanding as their actual installed operation. Not surprisingly, they way we install them here in Texas, they don't perform in the field nearly as well as they work in their testing.
How does the system accommodate peak flows? How many gallons per minute or per day, above the average daily flow, is the system capable of handling without adverse effects?
How does the system accommodate for solids management? How many gallons (or days) of solids will accumulate before the system must be pumped? What do the calculations show about the probable pump-out frequency? Has the homeowner been advised of this requirement? To increase solids retention, what additional steps must be taken to maintain treatment performance?
What is the required level of homeowner participation in the operation of their system? Do they know this? Does the system require them to clean the filters or refill the chlorinator even when you know they won't do it? As a regulator, do you require devices or programs that complicate, and do not improve, system performance?
Does the system provide for odor control? Can your customers have a dispersal field that satisfies their desire for something other than a flat slab of grass in their otherwise beautiful landscaping?
Statewide, ATUs with surface application, or spray heads, are often the cheapest systems and are therefore the systems of choice for most builders. When a surface application field won't fit because of site constraints, the most common alternative is to use the same ATU, tanks, and controls, strap on some additional parts, and pretend we now have a subsurface drip dispersal field. Designers and installers of such systems often are not aware of their limitations. Eventually, the system produces alarms, soggy yards, or bad odors -- and the homeowners are dissatisfied.
On the other end of the spectrum, there are times when the choice of a system is based only on the biased opinions of the designer (and occasionally the regulator). The system chosen is extremely costly and needlessly complex. Once again the homeowner ends up dissatisfied. In either scenario, homeowners are left with the results of a decision making process that often completely excludes them.
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