3-Chamber septic tank - mode of operation

Septic tanks may no longer be operated as sole wastewater treatment from 2015 onwards.
Three-chamber wastewater treatment plants, however, can often be retrofitted without any problems, and they can continue to be used as a pre-treatment for a biological wastewater treatment process, as long as they are intact. In the following, therefore, their principle of operation will be explained.

Three-chamber principle

A three-chamber sewage treatment plant has a better effect than older one-chamber models. The wastewater passes through all three chambers in turn. These can either be in a container, or even be designed annularly as a single container with connecting pipes.

The wastewater first enters the first chamber, where the solids are deposited by sedimentation. The forming primary sludge degrades over time, thereby greatly reducing its volume. Klar The clear water produced by the separation of the solids enters a second chamber, where in turn the solids dissolved in the water are deposited as sediment over time. Decisive for the degree of cleaning here is the residence time.

Via an overflow, the water, which has been cleaned for the second time, enters a secondary clarifier, from where it can then drain off or be pumped out. So no sediments can get into the clarified water more.

Reasons for the ban on operation

From 2015, domestic sewage treatment plants will only be allowed in Germany if they work with biological wastewater treatment processes.

The reason for this is a Europe-wide harmonized framework directive for water management adopted by the EU.

Mechanical forms of wastewater treatment are no longer allowed as sole wastewater treatment. They have too many dangerous pollutants for waters, especially nitrate.

However, systems can either be retrofitted and incur costs of around 3,500 EUR for small systems. However, they can also remain in operation as pre-clarification for downstream biological wastewater treatment plants.

While SBR plants are the most frequently sold, the share of constructed wetlands in the last few years is increasing.

Tips & Tricks Bavaria, Thuringia, Saxony and Schleswig-Holstein all offer subsidies for the new construction as well as for the retrofitting.

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