How does a septic system work?
A septic tank is simply a big concrete or steel tank that is buried in the yard. The tank might hold 1,000 gallons (4,000 liters) of water. Wastewater flows into the tank at one end and leaves the tank at the other. The tank looks something like this in cross-section: In this picture, you can see three layers. Anything that floats rises to the top and forms a layer known as the scum layer. Anything heavier than water sinks to form the sludge layer. In the middle is a fairly clear water layer. This body of water contains bacteria and chemicals like nitrogen and phosphorous that act as fertilizers, but it is largely free of solids. Wastewater comes into the septic tank from the sewer pipes in the house, as shown here: A septic tank naturally produces gases (caused by bacteria breaking down the organic material in the wastewater), and these gases don’t smell good. Sinks therefore have loops of pipe called P-traps that hold water in the lower loop and block the gases from flowing back into
Water flows into the septic tank from the plumbing in the house. It funnels wastewater into the septic tank. In the tank, solids are separated from the liquids. Some solids float to the top and others settle to the bottom. Natural bacteria in wastewater break down the organic solids. Solids not broken down by bacteria are stored in the septic tank until the tank is pumped. They should be pumped out of the tank through the manhole cover (top) every one to three years. Septic tanks DO NOT destroy disease-causing pathogens. Septic tanks prepare the liquid for final treatment by the soil. Wastewater from septic tanks is distributed into the overflow cesspool. When owners don’t clean septic tanks often enough, too many solids clog the overflow cesspool. Liquids can’t pass through. This means the septic system will fail with untreated water coming to the surface or backing up into the home.
Septic systems typically have two major components: a septic tank and subsurface disposal field (also known as a leachfield or drainfield). The tank is a watertight receptacle designed to receive domestic wastes. The lighter solids called scum (mainly grease) floats to the top. The heavy solids settle to the bottom where bacterial action partially converts them to a digested sludge. The liquid portion in the middle called effluent or “gray water” flows out of the tank through perforated pipes to the leachfield which is composed of sewer rock. Here, remaining solids further decompose and the liquid is absorbed into the soil, evaporates or is taken up by plants. View diagram here. Proper maintenance through regular pumping will remove excess solids and sludge, thereby extending the life of the average septic system by many years. For more detailed information contact Paul Pinard at Pinard Engineering, (907) 357-3647, P.O. Box 871347, Wasilla, AK 99687-1347. TOP We often hear, “Well, if i
A septic system, properly installed and maintained, is a good way to treat wastewater and to protect groundwater quality when municipal sewer service is not available. A typical septic system consists of two major parts, the septic tank and drainfield. Waste from toilets, sinks, washing machines and showers enters the septic tank, which is a holding tank generally made of pre-cast concrete or fiberglass and is sized according to the estimated wastewater flow from a given-sized residence or business. The septic tank separates the wastewater into three general components — solids or “sludge”, floatables or the “scum layer”, and a zone of relatively clear water. Anaerobic bacteria (able to live in an oxygen-free environment) perform the first treatment of the wastewater, generating gas that is vented through the vent stack of the building’s plumbing, and breaking the solids into a liquid form. The oxygen-free conditions inside the septic tank also deactivate some of the disease germs tha
