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How Septic Tanks Function

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There are many innovations in the modern world that are easily taken for granted and barely given a second thought. One that many prefer not to dwell on is how sewage is dealt with in locations that are not connected to a larger network of sewage treatment plants. The use of a self-contained septic system allows human waste to be treated on site and is particularly convenient for those located in rural areas without access to more mainstream solutions.

Development of the first septic tank

The septic tank was first patented in 1881 by a Frenchman named John Louis Mouras, who experimented with a sewage tank he installed in his back yard. Mouras was surprised when he opened his tank after 12 years of use to find there were barely any solids remaining. It was this discovery that convinced him to patent his invention. Over the next decade septic tanks began to be utilised all over the United States, Europe and parts of Africa

What happens inside a septic tank?

Septic tanks function in various ways, although the most basic design is very much the same as that patented by Mouras. A septic system is a sealed tank buried beneath the ground that captures waste water and effluent from the plumbing that is connected to a dwelling. Every time a toilet is flushed or a drain inside the home empties, the water and solids get transported into the underground tank.

The material inside the tank is comprised of three distinct layers. The heavier solids or sludge sink to the bottom of the tank and form the first layer. This sludge is slowly digested by naturally occurring bacteria that thrive on organic waste matter. The middle portion is the second layer which is all liquid and on the very top is the third and final layer of floating fats, oils and other scum.

How does a septic tank work?

Septics have an inlet that allows the tank to receive wastes and an outlet that is strategically positioned to allow only the liquid layer to flow out and slowly disperse beneath the ground to a drain field, which is a large network of leech pipes spread over a wide area. The drain field is generally constructed of permeable materials such as sand, gravel or peat moss and is completely covered with soil and grass. The soil of the drain field needs to be loose enough to ‘percolate’ for the liquids to leech from the tank and be effectively dispersed.

Innovations and change

Innovations in septic systems include the addition of a baffle in the tank and a pump chamber with an electric sump pump. The baffle is a dividing wall inside the tank that helps keep the sludge in the main portion of the tank and ensures that it cannot build up and exit from the outlet. Because only liquids should flow from the system, unintended sludge overflow can block the system and compromise its ability to properly drain.

What is a pump chamber and sump pump?

Some modern septic systems are fitted with a dosing or pump chamber which is a secondary tank between the main tank and the drain field. Inside is a float mechanism that rises and falls along with the level of effluent. When the level rises to a set point, the float activates a sump pump that sends the effluent out into the dispersal field in a set amount called a dose. As the liquid is pumped away, the level in the tank falls and the lowering float shuts the pump off. Mechanical failure of pumps does happen and these pumps need to be checked, maintained and serviced with some regularity.

Without innovations such as the septic tank, modern people would be exposed to all manner of diseases. Thanks in part to the innovative spirit of John Louis Mouras, the times when open sewerage was the norm have long since passed.

 
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