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Oct
24
2011

The Wastewater Treatment Process

by Karl Holt

The key to understanding septic tank problems requires an understanding of the wastewater treatment process. Once the facts of the process are known, evaluating potential solutions becomes easier.

When wastewater first enters an anaerobic septic tank from the home, it is held for approximately two days. During this initial holding period, the anaerobic bacteria break down the organic material in the wastewater, reducing the organic strength of the wastewater by about forty percent.

Hold time is greatly affected by high hydraulic flow rates. During high hydraulic flow rates due to house guests or excessive amounts of laundry or showering, the holding period is significantly reduced. This is because the high flow of incoming wastewater into the septic tank displaces an equal volume of wastewater already in the septic tank.

Because of the separation distance between the inlet and outlet pipes in the septic tank, the wastewater that is closer to the outlet pipe has been in the tank the longest period, and therefore is the cleanest. This cleaner water (still containing sixty percent of the original organic material) flows out into the distribution field for further treatment.

After a short period of time, a layer begins to form at the bottom of the gravel bed of the distribution field. This layer is known as the biomat. The biomat is made of anaerobic bacteria and its by-product, a black slimy substance. This slimy substance protects the bacteria from oxygen. If the anaerobic bacteria were to come in contact with oxygen, it would quickly die. The anaerobic continue to live because the wastewater entering the distribution field contains a high level of organic material dissolved or suspended in the water coming from the septic tank. The biomat helps to further clean the wastewater, removing some of the sixty percent of organic material contained in the incoming wastewater.

Septic tank issues start to occur, however, with the growth of the biomat. The anaerobic bacteria within the biomat do not have high metabolisms and, as a result, do not consume the organic material at a fast rate. The residual organic matter, combined with the black, slimy by-product of the anaerobic bacteria, begin to close some of the soil pores, reducing the amount of water flow passing through it back to the water table. Note: the water passing through the soil pores is clean and eventually mixes with ground water.

Another problem occurs because of another by-product of the anaerobic bacterial metabolism: the production of hydrogen sulfide gas. This is the rotten egg odor that is emitted from your septic system and is unique to anaerobic bacteria respiration. In addition to being an obnoxious odor, the hydrogen sulfide gas combines with atmospheric oxygen to form hydrochloric acid. This highly corrosive acid forms at and above the water line and destroys the concrete and steel components of the septic system. This issue can be more prevalent in areas of high sulfur and high iron content in the fresh water supply.

The common element in septic tank troubles are the anaerobic bacteria. Changing the bacterial environment from anaerobic to aerobic bacteria well eliminate the root cause of the most common septic tank issues.

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