The domestic sewage treatment plant is an individual wastewater treatment system that is very eco-friendly. Not only is this device quick to install, but it is also generally quite compact and therefore adapts to small areas.

In a few words, the domestic sewage treatment plant uses microorganisms attached to a bacterial carrier to remove pollutants from domestic wastewater.

To know exactly how a domestic sewage treatment plant works in detail, we will look at its main components and their respective functions.

Understanding how a domestic sewage treatment plant works

Generally speaking, this type of wastewater treatment has three compartments dedicated to settling large pollutants, eliminating micropollutants through biological reaction and clarifying wastewater.

After passing through these three steps, the treated water can be released into the natural environment without posing any risk to health and the environment.


The settling compartment

In this first compartment, all the water from the house (e.g. toilets, kitchens, bathrooms, etc.), undergoes primary settling through a gravitational process.

During this phase, the heavy materials are separated and settle to the bottom, forming a layer of sludge. This sludge must be removed when its volume reaches more than 30% of the useful volume of the settling compartment.

On the other hand, the lighter effluents remain on the surface and are discharged with the pre-treated water into the second tank.

The biological reaction compartment

In this second compartment, the water from the first compartment is supplied with oxygen via a compressor and diffusers, in order to allow aerobic bacteria that are naturally present in the water to develop.

These micro-organisms will have the mission of degrading impurities to reduce pollution. During this stage, sludge can also form. These will be settled and then stored with the sludge in the pre-treatment compartment.

The clarification compartment

Finally, the treated water arrives in a third basin to be clarified.

This is the last stage of treatment during which the purified water is separated from the rest of the light sludge. Thanks to the sampling chamber, specialists in wastewater treatment can easily monitor water quality.

At the end of the process, the treated water can be released into the natural environment or dispersed in the soil, without having negative effects on health or the environment.

The case of SBR sewage treatment plants

SBR (Sequential Batch Reactor) sewage treatment plants are a special case, and work differently.

With this technology, the plant has only two compartments: the primary clarifier, and a second compartment that combines the treatment and clarification stages. In this compartment, an electronic device alternates the treatment phases (aeration with oxygen supply) and the clarification phases (rest).

SBR plants are therefore often more compact than their fixed-film counterparts (as described above), and tend to consume less electricity. That said, their cost is higher at the time of purchase.


The domestic sewage treatment plant is the ideal wastewater treatment system for a primary residence. However, it does not appreciate variations in workload, i.e. long periods of absence. Therefore, it is not as well suited to secondary residences as it will not perform well if you are absent for half the year.

Despite this, and the fact that this device can also lead to additional costs for the electrical supply of the compressor, the domestic sewage treatment plant remains one of the most popular alternatives to septic tanks for ensuring individual sanitation.

Its few disadvantages are offset by its increased compactness (approximately 10 m² of floor space), its eco-friendly nature (no use of chemicals), its high purification efficiency (more than 95% reduction) and its durability (20 years or more), etc.

Whether it is better to choose an SBR or fixed-film sewage treatment plant is up to you!