Filtration field for septic tank - calculation and arrangement of filtration field

Few people need to explain how important it is to build a quality septic tank in a private house. Such a structure should always be working, because the breakdown or clogging of the septic tank can lead to the fact that the sewage system and drains entering it can then get into the environment. In addition, if the septic tank is unstable, it will affect the work of the sewer system in the house, and therefore - how the owners will have to use the system. Therefore, in such a situation, it is best to make a filtration field for a septic tank.

What is a septic tank? First of all, these are important parts of the wastewater treatment process. How to execute this field? Now we will understand.

In order to properly perform the drainage system around the septic tank, it is necessary to lay a sewer pipe underground at a depth of about 45-65 cm, making it a slope of 1.52 cm per linear meter. The whole structure will work as one, because the depth of the drainage and the main tank of the septic tank will be almost the same. At the same time, this depth should be no more than 2 m, but no less than 1.26 m. If you do not adhere to this range, difficulties with subsequent wastewater treatment will begin, even in the presence of anaerobic bacteria.

Filtration fields

Filtration field for septic tank - calculation and arrangement of filtration field Filtration field during construction

How field construction is performed filtering? A drainage system is being built, which can be closed, or it can also represent an unclosed pipeline system. The pipes are arranged drain holes. At the same time throughout the length of the pipe holes are made through the same distance.

Usually, pipes with perforations of Ø 10 cm are used for the installation of drainage. It is important to pay attention to what diameter the drain holes have and where they are located. This is due to the fact that in the first-encountered section of the system, the volume of all drains will be an order of magnitude larger, therefore, in order not to flood the soil below, it is necessary to make holes at the top of the pipe, and the size of the holes themselves should be slightly smaller.

Drainage areas remote from the septic tank have holes with a larger diameter, and these holes will be located at the bottom of the pipes, not at the top. If you follow these recommendations, you can make sure that the wastewater is distributed evenly along the entire length of the system.

Arrangement of the drainage system

Filtration field for septic tank - calculation and arrangement of filtration field

Before starting the design of the drainage system, remember a few simple but important rules:

  • the length of the drain (drainage pipe) must be no more than 25 m, counting from the fungi of ventilation to the distribution well;
  • between adjacent pipelines there must be a distance of at least 1.5 m;
  • the depth of the laid pipes also about 150 cm;
  • the trench width is calculated in the range of half a meter, but not wider than 1 m.

Why do they make a filtration field? It is necessary to give the ground the opportunity to clean itself. Work should be done in stages, in the following order:

  • a sand pad of small thickness is made inside the excavated trench (sand should not have impurities); ;
  • pipes are laid in a trench, after which they are poured with rubble 10 cm thick;
  • on top of pipes with a layer of rubble are poured over the usual soil.

Filtration field for septic tank - calculation and arrangement of filtration field Application of geotextiles

To prevent the system from silting, geotextiles are laid over the pipes.

What else needs to be remembered? Here are a number of tips to help you correctly perform the filtration field:

  1. The minimum depth of the drainage system should be 0.3-0.35 m, maximum 1.6 m (recommended depth is 1.5 m) . The smaller the depth, the greater the need for laying a layer of insulation.
  2. The system is mounted at an angle of 1.5 °.
  3. The drainage system runs from wells and wells with water at a distance of 30 m and more.
  4. There are no trees near the drainage system, otherwise their roots can later damage the pipes.
  5. Near the drainage, it is not allowed to drive or park vehicles of any dimensions.
  6. If, on the site where the installation of the drainage system will be done, the soil is clayey, it is necessary to dig it out and replace the soil that is able to absorb moisture normally.
  7. Ventilation pipes should extend at least half a meter from the ground, with protective visors over them.
  8. The pipes must have free access to air. In this case, they can be cleared by anaerobic bacteria. Then their degree of purification, which can be achieved by filtering devices, will be quite high, reaching almost 100%.

Given the different degrees of load, the drainage system may need to be updated periodically. What does this mean? Under the update refers to the replacement of a pillow of sand and rubble, as well as a layer of soil above the pipes. This replacement is performed once every 10 years, if necessary - once every 6 years.

Stages of filtration of effluents

Filtration field for septic tank - calculation and arrangement of filtration field

Filtration of wastewater is carried out in stages. Consider these processes:

  1. First, the liquid is settled (in the first section). The membrane of the septic tank prevents penetration of foam and accumulated gases further into the system.
  2. The effluent that continues to flow results in pressure on the already existing fluid, as a result of which the part that has undergone the primary cleaning is poured into the second zone of the septic tank. Under the influence of reagents impurities are split.
  3. Next, in the following zones, suspended impurities, obtained after a chemical reaction with reagents, precipitate, and purified water then goes through the pipes into the distribution well.

Filtration field for septic tank - calculation and arrangement of filtration field Bacteria for a septic tank

To increase the efficiency of the septic tank, add tools to it, in which there are anaerobic bacteria. The essence of their action is that they break down the thick drains contained in the septic tank and prevent them from forming sludge.

A septic tank must have a hatch. Since anaerobic bacteria do not act on 100%, undissolved particles will remain inside the septic tank in any case, and a hatch will be necessary in order to pump out these particles through it. It is necessary that the hatch was able to safely approach the vacuum. At the same time, the hatch must be tightly closed, otherwise, if insoluble residues of large sizes or large amounts of water after heavy rains, as well as toxic impurities, fall into it, the life of the septic tank and drainage can be significantly reduced, as a result of which the clogging can become more serious .


This video shows how to make a filtration field for a septic tank:


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