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Types of Septic Systems

Rajib Singha Oct 30, 2018
Septic systems are categorized into two main types: conventional and alternative systems. Read on to know about these types and their subtypes to optimize your drainage system!
Septic systems are defined as facilities that are built to carry liquid wastes from our homes and prevent soil and water pollution. They are typically used for wastewater treatment and for preventing biological and nutrient contaminants.
The conventional type includes gravity and pressure distribution systems. Aerobic treatment unit (ATU), mound, and sand filtration facilities are classified under the alternative type category.

Conventional Systems


As the name suggests, these make use of the force of gravity for the drainage purpose. Due to gravity, the effluent (water mixed with wastewater) flows through the septic tank into the drainage field.
The drainage field consists of a series of trenches. The location of the drainage must be such that it lies below the outlet level of the tank; the reason being the working of the facility using gravity. The trenches must have their bottoms lying on natural, undisturbed soil. A water table or hard pan acts as a restrictive layer in this process.
For this reason, the bottom of the trenches must be situated at a location that is 3 - 4 feet above any such restrictive layer. The soil that lies between the foot of the trenches and the water table plays an important role in this process. It is utilized in the final treatment of the effluent or the wastewater.

Pressure Distribution

This is common in most of the new systems because of its ability to make optimum use of the drainage field. It makes use of a pump for uniform distribution of effluent throughout the drainage field, at the same time.
When the effluent makes its way through the soil, it gets filtered in the process. Since the effluent has to reach the ground water, it is cleaned and purified through chemical and biological processes. Dry and permeable soil works best for such a system. Sufficient amount of oxygen in the soil also provides additional benefit to the cleaning process.
This system provides dosing and resting cycles. This means that the pump tank doses the entire drain with effluent. The pump holds wastewater until it accumulates, before the next dose to the drainage field.
Topography of certain areas does not allow to set the level of the drainage field lower than that of the septic tank outlet. For such areas or sites, the pressure distribution facility is most suitable.

Alternative Systems

Aerobic Treatment Unit (ATU)

This system uses oxygen as its key product for its operation. Here, waste is broken down by the use of oxygen, so that the treated wastewater is cleaner than that of conventional facilities.
This is an important factor when environmentally sensitive areas or locations are considered. The working of this system can be regarded as a lower version of the municipal wastewater treatment. The most common type of ATU that is used for household purposes uses the "suspended growth" process.
In this process, the facility has a water tight tank that consists of an aeration chamber. Air is forced into the chamber and mixed with wastewater. This technique creates "free-floating" conditions for bacteria where they thrive, breaking down and digesting the waste. Wastewater leaving the system is cleaner due to the rapid decomposition of organic wastes.

Sand Filter

It can be installed above and below the ground and is based upon a principle similar to that of a mound system. The pump tank and the drainage field are separated by sand.


Certain areas cannot provide conditions where soil is deep enough for installation of traditional systems. For such places, mound system fits the bill. Here, the drainage system is raised above the natural soil surface or ground level.
On top of the natural soil, specific sand fill material is placed for the effluent or wastewater treatment. This sand fill consists of a gravel bed, which in turn, consists of a network, driven by pressurized pipes. Septic tank's effluent reaches the mound through the pump in a dosing tank.
The pump ensures controlled amount of doses for uniform distribution throughout the gravel bed. So, the waste gets filtered when it traverses through the sand fill and into the natural soil.
So, the effluent that discharges from the pump tank gets pre-treatment by the intermediate sand, before it enters the drainage field. This facility can be regarded as a biological treatment for natural cleansing of effluent.
Places where the soil is insufficient for wastewater treatment, it is a good alternative for them; this is because the dearth of soil is made up by the sand that is used in the process.
From the information here, it is clear that the installation and the type of septic system are mainly influenced by the physical characteristics of the location. Many other factors also govern its lifespan. The soil type of the site, landscape, amount of utilized water, water disposal habits, and maintenance are important considerations.
You can extend its life by having it inspected after every interval of 5 years. For proper maintenance, it is advisable to hire a certified operator.