Types of Septic Systems

Septic systems are categorized into conventional and alternative systems. Conventional systems include gravity systems and pressure distribution systems. Aerobic treatment unit (ATU), mound system and sand filter system are classified under the alternative systems. It is important and beneficial if you can grasp a basic understanding about the types of septic systems you are using. I have presented a brief description about the most common types of septic systems that are in use.

Before we come to the different types of septic systems, let us know what are septic systems? Septic systems are defined as systems that are built to carry liquid wastes from our homes and prevent soil and water pollution. They are basically used for wastewater treatment and for preventing biological and nutrient contaminants.

Conventional Systems Category

Gravity Septic System
As the name suggests, gravity systems make use of the force of gravity for the drainage purpose. Due to gravity, the effluent (water mixed with waste water) 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 septic tank. The reason being, the working of the system using gravity. The trenches must have their bottoms lying on natural undisturbed soil. Water table or a hard pan acts as a restrictive layer for the system. For this reason, the bottom of the trenches must be situated at a location that is three to four 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 the gravity system. It is utilized in the final treatment of the effluent or the waste water. 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 septic system. Sufficient amount of oxygen in the soil also provides additional benefit to the cleaning process.

Pressure Distribution System
Pressure distribution system is common in most of the new systems because of its ability to make optimum use of the drainage field. This system makes use of pump for uniform distribution of effluent throughout the drainage field, at the same time. This system provides dosing and resting cycles. This means that the pump tank dose the entire drain with effluent. The pump holds waste water until it is accumulated enough, 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 system is most suitable.

Alternative Systems

Aerobic treatment unit (ATU)
The aerobic treatment unit 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 systems. 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 system has a water tight tank that consists of an aeration chamber. Inside the chamber, air is forced and is mixed with waste water. This technique creates a 'free-floating' conditions for bacteria in the liquid. Here, the bacteria grow as they break down and digest the waste. The waste water leaving the system is cleaner because of the rapid decomposition of the organic wastes.

Mound Septic System
Certain areas cannot provide conditions where soil is deep enough for installation of traditional septic systems. For such places, mound septic 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 waste water 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.

Sand Filter Septic System
Sand filter system 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 is separated by sand. So, the effluent that discharges from the pump tank, gets pre-treatment by the intermediate sand before it enters the drainage field. The system can be regarded as a biological treatment for natural cleansing of effluent. Places where the soil is in sufficient for waste water treatment, sand filter system 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 above description it is clear, that the installation and the types of septic systems are mainly influenced by the physical characteristics of the location. Many other factors also govern the life span of a septic system. The soil type of the site, landscape, amount of utilized water and water disposal habits and septic system maintenance are governing factors in selecting a septic system. You can extend the life of your septic system by having it inspected after every interval of 5 years. For proper maintenance of your septic system, it is advisable to hire a certified operator. For additional information, you can always contact your local health department.