A typical septic system is made up of two components: the septic tank and the leaching system. The most current style of septic tank contains two chambers with a baffle in-between; while older tanks may only have one compartment. The size of the tank will vary depending on the size of the house and household water use and have a liquid capacity averaging 1,800 to 5,700 litres. (500 to 1500 gallons)
From your house through the septic system, here’s how it works…
The wastewater comes from the house and flows through the inlet tee into the first chamber of the septic tank where the heavier solids settle to the bottom as “sludge” and lighter materials like grease and oil, called “scum,” floats to the surface. Anaerobic bacteria, present in wastewater work to digest and break down the sludge into a liquid, thus reducing the volume of solids in the tank. Wastewater, free from most solids and scum, passes through or over the baffle into the second chamber where it is filtered even more. The relatively clear liquid, called “effluent”, will then drain through to the leaching bed or drain field for further treatment. It should be noted that a tank that is too small, overfilled with solids or receives a high volume of water too quickly, can allow solids to pass through and contaminate and clog the drain field.
The leaching bed is typically made up of perforated plastic pipes for distribution.
The pipes are laid in gravel trenches over a layer of soil. The leaching bed acts as a soil filter using natural processes to treat contaminants in the wastewater including organic matter, harmful bacteria and viruses from the septic tank. The bottom of each distribution trench in the leaching bed forms a slime layer of bacteria called the “biomat”. It is in this layer of the biomat where much of the treatment occurs. It is important to use the right type of soil for the leaching bed so that the wastewater stays in there long enough to be treated yet still permits adequate draining.
To summarize, the septic system serves five different functions:
- The septic tank receives the wastewater from the house
- It separates the solids from the liquids
- It stores and breaks down the solids
- It sends effluent water to the drain field for distribution
- The drain field filters the wastewater for final purification