A septic tank is essentially a smaller version of a municipal sewage treatment plant. The septic system is made up of two parts; the drain field and the septic tank. These types of waste management systems are common in rural settings and areas that do not have easy access to city services. The key to this type of sewage system is the septic tank, without it the outhouse would still be a common site along the many back roads and country lanes.
The most common type of septic tank is made of concrete and is essentially a rectangular box that is divided into chambers. You can also get tanks made of plastic and fiberglass which have the advantage of not weighing as much as a concrete one. They are easier to maneuver and don’t require heavy equipment to install. The disadvantage is that they can and will float, so areas that have high ground water or are prone to floods should avoid these types of tanks.
So how does a septic tank work?
Basically it works by running the waste effluent through various stages inside the chambers that separate its internal makeup. The first chamber is the largest as it collects all the household waste water from the inlet pipe. As organic solids, commonly called sludge, enter the first chamber they settle to the bottom. The sludge is then broken down and digested by different bacteria, some anaerobic but mostly facultative bacteria that produces a combination of carbon dioxide and methane gas. This helps stabilize the sludge and stops it from rotting. Most of the sludge will stay on the bottom of the tank but a small amount will float forming a layer of scum.
All septic tanks are designed to allow the sludge to spend a maximum amount of time being exposed to the digestive bacteria’s. They do this by locating the inlet, overflow and outlet pipes diagonally across from each other. The pipes for the overflow and outlet are also vertically placed, forcing waste material to flow upward between stages. This makes the effluent travel a longer distance before entering the next phase of processing, furthering the break down of waste products during each phase.
After the semi-processed waste water leaves the first chamber via the vertical pipe overflows it enters the second chamber. Forcing the waste water to go upward prevents large solids from getting into the second chamber. The same processes are in place in the second chamber as in the first as the organic matter is further digested and settled by bacterial microorganisms. The second chamber is normally about half the size of the first chamber and as a result the effluent only spends about half as long processing before being discharged into the drain field.
The outlet to the drain field is located in the opposite corner from the overflow into the second chamber. Only waste water should be flowing into the drain field as all solids should have settled out into one of the two septic chambers. The waste water is further filtered and purified by the soil in the drain field before it is taken in by plant roots or filters downward to any ground water that exists in the area. The size of the drain field will be dependent on soil types and porosity.
Most septic tanks and systems are designed to use the pull of gravity to allow a natural flow of waste effluent from the home to its final destination in the drain field. In some instances the lay of the land may not be conducive to a gravity fed system so a pump or pumps may be needed.
The way in which septic tanks work is pretty straight forward. They use natural processes and time to effectively break down household sewage. This protects not only homeowners and their families but also their property and the environment.