NJ Home & Building Engineering Inspections - NJ License # 24 GI 00015500

SEPTIC TANK

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SEPTIC TANK

Did you know that anything and everything that goes down a drain in your home travels via the septic tank? A septic tank is a large watertight tank with the capacity to handle large volume flow. The septic tank is the first step in the process of household water treatment.

The Job of the Septic Tank
How Long is the Process?
What Happens to Solids?
Anaerobic Digestion
Flow of the Septic Tank
Effluent Filters
Flow Buffering
Waste Breakdown

The Job of the Septic Tank
The septic tank, as anyone who has ever had a septic tank failure will know, is a vital piece of the system of your home. Though not a necessarily complex system, it provides essential functions in the treatment and flow of all drains in your home. The septic tank receives all of the waste liquid form the phone and separates it from the solids. The treated water then leaves and enters the drain field where it is fully treated and disposed of. The water that passes to the drain field is referred to as Effluent. The solids that are separated are things like soil, grit, solid food debris, and unconsumed materials) 

How Long is the Process?
For the septic tank to properly separate the solids and liquids, it must sit in the tank long enough for the components to settle and the tank to begin the process. Therefore, it is not an instant process. The retention time (in the tank) will vary based on the volume produced by the household and flow of the water. When designing and installing septic tanks, it is most often set for at least 24 hours to sit in the tank. If there is a large volume of solids, it could take up to three days. However, on average, the process will complete on the second day. 

What Happens to Solids?
A quality septic tank will be designed to handle to a high volume of solids for an extended period of time. When installing a tank, the design should account for at least ½ of the tank to be reserved for solid storage for at least five years. The storage time and capacity will obviously vary from home to home depending on the tank and the volume.

Anaerobic Digestion
Anaerobic bacteria can live without oxygen and appear in places like the septic tank! The bacteria consume the materials found in the solids that are stored in the tank. As the materials are broken down, the gases that are created during the process are ventilated out of the tank by way of the inlet pipe. This process reduced the volume of solids over time in tank. However, scum and other materials can build up in the tank and eventually will have to be pumped out. 

Flow of the Septic Tank
The way the septic tank works is by three main components that keep the drainage materials and liquids flowing through the tank as they should. There are the inlets(1) which release the energy and gasses the build-up in the tank during the treatment and breakdown process. The inlets should always top out well above the water line in the tank to prevent backup of the tank. Next, there are the outlets(2). The outlet is in charge of the scum that enters the tank. The scum consists of anything lighter than water including oils, fats and grease. The outlets are located 2 to 3 inches below the top of the inlet. They stay closer to the bottom of the tank where the scum resides. Finally, there is the Gas Deflection Baffle(3). As gases are produced in the tank, the baffle prevents the gas from bubbling. Not all tanks have this component.

 Effluent Filters
Newer septic tank systems have an effluent filter in the system. This filter prevents the scum from entering the drain field with the treated water. 


Flow Buffering
When there are large surges of waste that enter the septic tank, the flow is buffered. This can happen when the toilet is flushed or the washing machine drains. The buffer slows the flow rate so that the surge does not enter the tank all at one time


Waste Breakdown
In the early years of the Twentieth Century, scientist, W. P. Dunbar tested the decomposition of the septic tank. For a peak into how the materials in the tank are broken down, he found, “… a large number of solid organic substances, such as cooked vegetables, cabbages, turnips, potatoes, peas, beans, bread, various forms of cellulose, flesh in the form of dead bodies of animals, skinned and unskinned, various kinds of fat, bones, cartilage, etc., and has shown that many of these substances are almost completely dissolved in from three to four weeks. They first presented a swollen appearance, and increased in weight. The turnips had holes on the surface, which gradually became deeper. The edges of the cabbage leaves looked as though they had been bitten, and similar signs of decomposition were visible in the case of other substances. Of the skinned animals, the skeleton alone remained after a short time; with the unskinned animals the process lasted rather longer. At this stage I will only point out that the experiments were so arranged that no portion of the substances could be washed away; their disappearance was therefore due to solution and gasification.”