How do onion septic tanks work

The septic tank - how it is constructed, how it works and what you have to pay attention to

Use of septic tanks

Septic tanks are used purely for the treatment of household wastewater. They are still very common systems, especially in older houses.

According to the new EU Water Framework Directive, they will no longer receive a permit under water law from 2015. The new water framework guideline stipulates that from this point onwards every small wastewater treatment plant must have a biological purification stage.

Older systems must be retrofitted accordingly by this point in time. In the case of three-chamber sewage treatment plants, however, this is possible without any problems in most cases.

In some federal states, the cost of retrofitting is covered by appropriate funding.

In Bavaria and Thuringia this is 1,500 EUR each, in Schleswig-Holstein and Mecklenburg-Western Pomerania 770 EUR and 750 EUR, respectively. The state of Saxony is making EUR 1,000 available for retrofitting.

The prerequisite for retrofitting, however, is that the existing septic tank is still completely sealed. If this is not the case, it is more worthwhile to build a new small wastewater treatment plant.

How the septic tank works

A septic tank basically works through sedimentation. This means that all solid dirt particles that are present or dissolved in the wastewater settle within the septic tank after a certain time.

They then form what is known as sewage sludge. Above the water surface there is usually a layer of floating sludge.

Rotting after about two to three months reduces the volume of sludge to a fraction of the original amount.

The so-called clear water can then be sucked off with the help of a suction vehicle, fed into a receiving water or trickled into it. However, due to its very high nitrate content, it is a heavy burden both for water and for the soil.

This is why such disposal is no longer permitted in the future.

Three-chamber septic tanks have a slightly different mode of operation, and the septic tank is also a widespread special form of septic tank. It will also no longer be permitted in the future.

Alternatives to the septic tank

If retrofitting the septic tank is not possible, there are various alternatives.

Since the excavation and supply and discharge are already in place, it can often be exchanged for an SBR system without any problems. Plants using the activated sludge process that are not fed intermittently are also an option.

However, attention should be paid to the non-existent power connection at the septic tank, which must also be set up. But there are also small wastewater treatment plants that work with an existing or artificially created gradient, even without electricity, only with the help of gradient or water pressure.

Another alternative is the installation of a plant-based sewage treatment system. However, a relatively large amount of space is required here. Approximately four to five square meters of area must be expected per population equivalent (PE).

The existing septic tank can also be used as mechanical wastewater treatment for the plant-based sewage treatment plant. This means that only minor modifications are required. For plant-based sewage treatment systems, there are also do-it-yourself kits from around 1,000 EUR in stores.

Since a retrofitting or a new construction of the sewage treatment plant is absolutely necessary from 2015, it is worthwhile in any case to deal with the subject of small sewage treatment plants in more detail. In this way you can make an informed decision about the type of future wastewater treatment system for your own home.