Extended Aeration treatment system works by providing ideal conditions for aerobic bacteria and other micro-organisms; these micro-organisms then decompose the biological contaminants in the raw sewage.
The treatment plant provides the proper environment, sufficient oxygen and other elements which allow the bacteria to consume the organic matter and to live and multiply within the treatment plant. In this way the aerobic bacteria and microbes decompose the sewage and waste to a stable form - odor and nuisance free.
The aeration chamber is the key part where 90% of the treatment occurs. This process operates under the following theory: Waste in domestic wastewater is generally organic (biodegradable), which means that aerobic microorganisms in the presence of oxygen can use the organic material as their food source. In nature, if the waste were discharged untreated to a stream, the bacteria in the stream would decompose the sewage and deplete dissolved oxygen levels to a point which could kill all aquatic life in the stream. Similar to nature, in an extended aeration treatment system, air (29% oxygen) is introduced by blowers and bacteria are grown to feed on incoming sewage from your business or dwelling. Bacteria in the aeration tank decompose the sewage to form a suspended sludge. The liquid in the aeration chamber, called mixed liquor, will have the consistency of a thin milk shake and a brown color similar to that of coffee with cream. However, it should be noted that the color will vary from system to system depending on the types of wastes.
A settling chamber (clarifier) is placed after the aeration chamber to allow the microorganisms that are grown in the
aeration chamber to settle by gravity, forming a sludge on the bottom of the clarifier. Most of the microorganisms settle to the bottom of the settling chamber where they are then pumped back to the head of the aeration chamber. The
microorganisms then begin the cycle of feeding on incoming organics in the wastewater. This material is known as return activated sludge (RAS).
The clear liquid at the top of the settling chamber (85-90% treated) will then usually flow to a dosing pump station/ slow surface sand filter or polishing pond where further treatment is provided (95%). The treated discharge is then
disinfected with chlorine, and the chlorine is removed by a dechlorination unit. Some facilities are now replacing chlorination/dechlorination units with ultraviolet forms of disinfection. Disinfection is the process of killing disease causing
microorganisms. Final discharge is normally to a stream with sufficient dilution to safely assimilate the remaining 5% of the pollutants without measurable harm to the environment.
Poor operation and maintenance normally results in serious environmental and public health problems. Your sewage disposal system is not a magical device. It requires inspection and proper care and maintenance, much like your car or home, in order to operate effectively. Proper installation and maintenance of a sewage treatment and disposal system is essential to protect our water resources.
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