One of the first treatment methods to treat wastewater is the use of a septic tank. Individual households, small facilities, schools and other small groups use septic tanks to treat their wastewater. Currently, this technique is no longer practiced. They are designed to hold wastewater at low rates under anaerobic conditions for at least 36 hours. During this time, a significant amount of settled solids is removed. These particles are decomposed at the bottom of the tank, causing the gas to become entangled, making them float on the surface of the wastewater and settle in the form of scum until the gas is exhausted, at which time the solids settle out. Due to the constant floating and settling of solids, some of them are carried by the current towards the outlet and are discharged with the wastewater. Underground techniques are used to remove the final wastewater. The effectiveness of this technique is determined by the leaching capacity of the soil. Devices of this type require only the most basic of maintenance routine, which includes annual inspection and cleaning of sludge and sludge build-up every 3 to 5 years. Septic tank sizes for single-family homes (up to 20 users) and residences are recommended.
The septic tanks are a primary treatment system, intended to treat wastewater to a modest extent and consists mainly of a separation of solids and some early anaerobic operations (without oxygen). Many municipal governments no longer allow the installation of septic systems, instead requiring the installation of complex or anaerobic treatment systems that provide a higher level of treatment.
What are septic tanks and how do they work?
Solids and liquids separate when the wastewater enters the septic tank. Sludge forms at the bottom of the tank as partially decomposed particles sink, while lighter particles such as grease create a floating scum. Wastewater flows from the septic tank to an application site, where it may still contain small particulate matter. It filters through the soil, where bacterial activity processes it.
Depending on usage, the partly decomposed particles that collect at the bottom of the tank must be pumped out every 3–5 years.
So that the quantity of particles that are spread into the ground is restricted, the septic tank outflow should be below the level of the floating scum layer. The majority of septic tanks are gravity-fed. As a result, they must be put below the house’s level. Waste must be piped to the tank if this is not possible. To delay incoming wastewater and decrease sludge disturbance, tanks may have tees or baffles at the inlet and exit pipes. To prevent gas from escaping via the outlet, gas baffles might be used.
Installation and Construction of Septic Tanks
- Prefabricated septic tanks can be made from reinforced cement mortar, fiberglass, steel or polymers such as polyethylene and polypropylene.
- Tanks can be buried or built on the ground.
- The most common type of system is the one that is installed underground, and which must withstand the stresses of the surrounding soil and groundwater as well as hydraulic lift (the tendency to float).