It’s easier to get your head around maintenance when you have a clear sense of parts and function. Here’s an overview of how a conventional home septic system works:
Instead of shunting wastewater into the sewer system, a septic system sends all water (and any waste) from sinks, showers, and toilets into a large watertight tank buried on the property. Depending on the conditions of the site and local regulations, the tank might be buried anywhere from four inches to four feet deep, according to Angi.
Liquids exit the tank to be distributed through perforated pipes, and filtered through gravel or sand, and ultimately, soil. This processing removes dangerous viruses and bacteria, purifying the output so it can trickle into the water table. Meanwhile, inside the tank, solids are partially digested by naturally occurring bacteria—and what’s left is pumped out by professionals, on a regular schedule.
Before we get more granular, here’s some essential terminology. There won’t be a quiz, but there will be tremendous satisfaction in knowing what you’re talking about when calling for service. Some keywords and phrases:
Main line: The underground pipe that connects the plumbing system in your home to the septic tank outside. Sinks, bathtubs, showers, and toilets all drain into the septic system through this main line.
Septic tank: Just the tank proper (not the whole system) into which wastewater drains. Sizes vary, but according to Angi, a typical tank for a home is about 5 feet wide, 8 feet long, and 6 feet tall. Septic tanks could be made of concrete, fiberglass, polyethylene (plastic), or steel. Capacities vary, but the average home septic tank is 1,250 gallons, which is usually big enough for a house with four bedrooms, according to Angi.
Access riser: Tightly capped plastic or concrete pipes that run from your septic tank up to the ground surface. They allow septic system professionals easy access (with minimal disruption to the yard) when they need to inspect or pump the tank. Not all systems have access risers; those that do, most often have a pair.
Drainfield: This includes the entire underground filtering system that controls the gradual release of wastewater into the ground. Sizes vary based on conditions, local regulations, and septic tank size: A 1,500-gallon tank can require a drainfield of 800 to 2,500 square feet. Other terms used for a drainfield: leach field, absorption field, soil absorption system, and disposal field.
Baffles: Pipes or walls with openings that direct the flow of liquid into and out of the septic tank. Tanks typically have two baffles: one that controls the flow of wastewater into the tank, and another that controls the flow out.
Effluent: Wastewater from sinks, showers, and toilets after it’s gone through the septic tank. The term refers only to the liquid, not the sludge or scum it leaves behind.
Sludge: The solid part of the waste flushed from your house into the septic tank, which settles on the bottom of the tank.
Scum: Substances like oil and grease (which may come from the kitchen sink) that rise to the top of the wastewater in the septic tank.
Effluent filter: A component, required in some locations, that filters liquid as it exits the tank, preventing scum and sludge from leaving the tank with the effluent.
Anaerobic bacteria: Naturally occurring bacteria that do not require oxygen to grow and function. Inside the tank, these bacteria thrive on sludge, helping to break it down.
Aerobic bacteria: Naturally occurring bacteria that require oxygen. Outside the tank, in the drainfield, these bacteria continue the breaking down of organic material.
Now to get a bit more detailed about the workings of the system: When wastewater flows into the tank, baffles and filters separate the scum (on top) and sludge (on the bottom) from the effluent.
In the tank, anaerobic bacteria consume some of the sludge, reducing its volume (byproducts of this process include gases that can be dangerous—one reason never to attempt to open the tank lid yourself). The effluent flows out of the tank into the drainfield’s filtering system, which might include gravel, sand, soil, a specialized textile called geofabric, and more. This is where aerobic bacteria come into play, breaking down the organic waste still in the liquid, as other microorganisms help eliminate harmful bacteria and digest waste.
Some systems might have more going on, such as a series of chambers that filter effluent, or a drip distribution system controlled by a timer. There are alternative systems in which aerobic treatment units (ATUs) inject oxygen into the septic tank so aerobic bacteria can operate inside, too. And some newer systems (which are more expensive to run and require more maintenance) use electric pumps.
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