Aerobic treatment system

An aerobic treatment system or ATS, often called (incorrectly) an aerobic septic system is a small scale sewage treatment system similar to a septic tank system, but which uses an aerobic process for digestion rather than the anaerobic process used in septic systems. These systems are commonly found in rural areas where public sewers are not available, and may be used for a single residence or for a small group of homes.

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Process

The ATS process generally consists of the following phases:

• Pre-treatment stage to remove large solids and other undesirable substances from the wastewater.
• Aeration stage, where the aerobic bacteria digest the biological wastes in the wastewater.
• Settling stage to allow any undigested solids to settle. This forms a sludge which must be periocally removed from the system.
• Disinfecting stage, where chlorine or similar disinfectant is mixed with the water, to produce an antiseptic output.

The disinfecting stage is optional, and is used where a sterile effluent is required, such as cases where the effluent is distributed above ground. The disinfectant typically used is tablets of calcium hypochlorite, which is specially made for waste treatment systems. Unlike the chlorine tablets used in swimming pools, which is stabilized for resistance to breakdown in ultraviolet light, the tablets used in waste treatment systems is intended to break down quickly in sunlight. Stabilized forms of calicum hypochlorite will persist after the effluent is dispersed, and can kill off plants in the leach field^[1].

Since the ATS contains a living ecosystem of microbes to digest the waste products in the water, excessive amounts of items such as bleach or antibiotics can damage the ATS environment and reduce treatment effectiveness. Non-digestable items should also be avoided, as they will build up in the system and require more frequent sludge removal.^[2]

Comparison to traditional septic systems

The aeration stage and the disinfecting stage are the primary differences from a traditional septic system to the user of the system. These stages increase the initial cost of the aerobic system, and also the maintenance requirements over the passive septic system. As opposed to most biofilters the aerobic treatment systems require a constant supply of electricity to drive the air pump increasing overall system costs, and the disinfectant must be periodically renewed and electrical components periodically replaced. On the positive side, the aerobic system produces a higher quality effluent, and the leach field can be smaller than that of a similar capacity septic system, and the output can be discharged in areas too environmentally sensitive for septic system output. Some aerobic systems recycle the effluent through a sprinkler system, using it to water the lawn where regulations approve.

References