DIY septic tank filtration field

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DIY septic tank filtration field
DIY septic tank filtration field

The device of the filtration field from the drainage pipes for the efficient operation of the septic tank. The design and features of such a system, the principles of its design and installation. A septic tank filtration field is an area of ​​land allocated for secondary wastewater treatment. It is often included in the overall design of an autonomous sewage system and has a positive effect on the condition of the local area. How to make a filtration field for a septic tank, our article.

Features of the filtration field for a septic tank

Filtration field construction

Without a septic tank that performs the primary processing of polluted wastewater, the device of such a field is meaningless, since its direct purpose is to purify waste. For a more understandable presentation, consider the principle of the structure's operation.

The cleaning mechanism starts in the drive. Here, the fractional separation of effluents takes place: solid particles create sediment, light fats form a film on the surface, and the rest of the substances form suspensions.

As the storage tank fills up, the drains are poured into an adjacent tank equipped with ventilation. Here, they are processed by aerobic bacteria. They create activated sludge. Later it can be used as fertilizer.

The result of two degrees of purification is a cloudy liquid that is not yet usable. In order to turn it into ordinary water or simply drain it into a ditch, additional treatment is required, which is carried out in three ways: in a filter well, in the ground, in a special infiltrator. The standard multi-stage cleaning scheme is available in many options. It is good for its efficiency, economy and ability to preserve a clean environment of the suburban area.

The main value of the filtration field for a septic tank is the natural nature of the purification and the absence of the need to purchase filters or any additional devices. Its design is a system of parallel-laid perforated pipes. At equal distances, they are located in special ditches with a powerful cement-sand cushion more than 1 m thick. All pipes extend from a common collector. The material for their manufacture can be asbestos cement or plastic. For access to the air pipes, they are equipped with vertically installed ventilation risers.

The main purpose of such a system is the uniform distribution of sewage over the filtration field and the possibility of realizing their maximum cleaning.

For this, the design of the field provides for several important technical points:

  • The distance between the pipes is 1.5 m, their diameter is 0, 11 m, and the length is up to 20 m.
  • The distance between the risers is up to 4 m.
  • The height of the part of the risers protruding above the ground is from 0.5 m.
  • The distance from the septic tank to the filtration field is 1-3 m.

Important! To ensure the natural movement of drains, pipes must have a slope of 2 cm for each running meter. The drainage is protected from getting into the soil by wrapping geotextiles. For the construction of a system with a filtration field, soils with good permeability are suitable. For example, for loose detrital soils, such a design is suitable, but not for clayey soils.

When creating a field, it is absolutely not necessary to make a collector yourself. There are ready-made plastic containers, so it is not difficult to choose the right volume of the tank. If the filtration area is small, you can do without a collector by connecting the drainage pipes to the septic tank directly.

Designing a filtration field for a septic tank

Filtration field diagram for a septic tank

Making a project is a necessary stage of any construction. It helps to mark the object on the ground, calculate financial costs and take into account many other important nuances. A well-written document will help to avoid mistakes common to people without experience. Therefore, let's figure out how to correctly calculate the filtration field for a septic tank.

The choice of the layout of the elements of the filtering field depends on the type of septic tank, the area of ​​unoccupied territory and certain requirements for wastewater treatment.

Each type of septic tank is characterized by a certain degree of waste treatment. For example, BO stations such as Astra or Eurobion do not require a filtering field at all. The liquid clarified in them by 98% can immediately go into the reservoir or open ground. Septic tanks made of bricks, tires, or concrete rings cannot be counted among efficient treatment plants. Therefore, the effluents coming from them need secondary treatment by a filtration field.

Usually, all the elements that make up the sewer system are lined up one by one in one line from the house: first there is a septic tank, and then a filtration field. Therefore, when designing a sedimentation tank, it is necessary to provide for the presence of a free territory behind it for arranging a field for secondary wastewater treatment.

Note! With a large discharge of sewage waste, the principle works: an increase in the length and number of pipe branches contributes to more efficient cleaning. For such a calculation, it is necessary to know the composition of the soil and the daily volume of runoff. If the first parameter is known, the size of the septic tank can be used as the second. The table will help to make approximate calculations:

Soil type Septic tank volume, cubic meters
1, 5 2 3 4 5 6 8 10 12 15
Sand 1 1 2 2 3 3 4 5 8 10
Sandy loam 1 2 3 4 5 6 8 10 12 15
Loam 2 3 4 6 6 9 12 15 16 20

Let's say the volume of the septic tank is 8 m3 in the presence of sandy soil on the site. Therefore, based on the data in the table, it can be determined that for high-quality wastewater treatment, at least 4 m of drainage pipes or two 2-meter pipes are required.

For more accurate calculations of the field area, use the following data that take into account the permeability of soils:

Name of breeds Soil filtration coefficient, m / day Permissible design load per 1 sq. M. filtering surface, l / day
Clay soils
Clay Less than 0.001 Less than 20
Heavy loam 0, 001-0, 05 20-30
Light to medium loam 0, 05-0, 4 30-40
Dense sandy loam 0, 01-0, 1 25-35
Loose sandy loam 0, 5-1, 0 45-55
Sandy soils
Silty clayey sand with a predominant fraction of 0.01-0.05 mm 0, 1-1, 0 35-55
Homogeneous silty sand with a predominant fraction of 0.01-0.05 mm 1, 5-5, 0 60-80
Fine-grained clayey sand with a predominant fraction of 0, 1-0, 25 mm 10-15 80-100
Fine-grained homogeneous sand with a predominant fraction of 0, 1-0, 25 mm 20-25 105-110
Medium-grained clayey sand with a predominant fraction of 0.25-0.5 mm 35-50 115-130
Medium-grained homogeneous sand with a predominant fraction of 0.25-0.5 mm 35-40 115-120
Coarse sand, slightly clayey with a predominant fraction of 0.5-1.0 mm 35-40 115-120
Coarse-grained homogeneous sand with a predominant fraction of 0.5-1.0 mm 60-75 60-75

According to these data, it can be seen that clay bases are completely unsuitable for mounting fields, sandy ones are more suitable. Crushed stone and gravel are characterized by the maximum water permeability: they have a filtration coefficient of about 200 m3 / day. Their loose structure is capable of passing a significant volume of liquid.

After determining the size of the field, it is easy to calculate the number of drainage pipes, ventilation risers, the thickness of the backfill, the amount of geotextiles, and then deduce the real cost of the materials required for work.

How to make a secondary wastewater treatment field?

In addition to the above, you will need devices for excavation and removal of soil: construction buckets, wheelbarrows, bayonet and shovels. Drainage trenches have a much shallower depth than a septic tank pit. Therefore, it is quite possible to do without the involvement of earth-moving equipment, but a few assistants can reduce the duration of the process.


Digging a trench under a filtration field for a septic tank

Before installing with your own hands the filtration field for a septic tank, first of all, you will need to prepare a site for laying drains. To do this, there are two ways: with shovels to dig one common pit or several trenches for each pipe. In the first case, it will be more convenient to assemble the drainage system. The second option will significantly reduce the overall operating time.

The depth of the pit must be made such that the sewage in the drainage does not freeze in winter. The branches of the system should be below the level of soil freezing. When digging ditches for pipes, you should remember about the slope, which allows the drains to overflow naturally.

The drainage system usually consists of several branches. This is done due to the fact that the length of each of them should not exceed 20 m, which is not enough to filter the total volume of wastewater.

Note! The field must have the correct geometric shape. This is usually a rectangle or square. All trenches should be the same length. Suppose the required pipe length is 60 m. In this case, four 15-meter branches or six 10-meter branches can be made. The length of each of them is the distance from the sewer collector to the extreme ventilation riser.

The bottom of the dug trenches should be covered with sand at 0.1-1 m, then with gravel or pebbles at 0.5 m. If drainage pipes are required, they should be placed under the sand in the soil, but not less than a meter above the level of the aquifer. The drainage pipes must be connected to a storage tank, which is located on the other side of the septic tank.

Installation of pipes for the filtration field

Installation of pipes for the filtration field

When installing the filtration field for a septic tank, plastic drains must be laid on the finished base. The procedure itself is simple, the main thing is their correct choice. It is possible to purchase ready-made perforated pipes in the form of corrugation or smooth. If this is not possible, you can take standard 110 mm sewer pipes and make many holes in their walls with a drill.

In the kit for these products, you need to buy connecting fittings - corners and plastic tees.

After laying the drains, install ventilation pipes. They are necessary for the supply of oxygen to the filtration system. Without it, aerobic bacteria that process wastewater into a harmless liquid lose their viability.

For the manufacture of risers, you can take ordinary gray plastic pipes with a diameter of 110 mm. To close them from the penetration of precipitation and debris, special conical visors are used.

If the length of the pipes is less than 4 m, the risers should be placed at the end of each branch. Products over 4 m long must be equipped with a large number of risers, cutting them into the network using plastic tees. Optimally - from 2 to 4 risers per pipe.

The minimum elevation of ventilation pipes above the ground is 0.5 m. It is recommended to install the risers carefully and decorate, thereby preserving the attractiveness of the surrounding landscape.

Backfilling of pipes and system maintenance

Backfilling of pipes and septic tank service systems

When the filtering and ventilation elements of the system are assembled, it is necessary to backfill the trenches. Top and sides of each drainage pipe should be covered with rubble and covered with geotextiles. The thickness of the top layer of crushed stone should be about 50 mm.

Geotextiles are necessary to prevent siltation of the inner cavity of the pipes. After laying it, the remaining space of the trench must be covered with soil, and then tamped down, being careful. The main thing is not to overdo it, otherwise the pipes can be damaged. After that, the device of the filtration field for the septic tank is considered complete.

The system is turned on as the tanks are filled with waste liquid. There are no special measures for drainage maintenance. The filtration field is capable of operating reliably for 6-7 years. Then the structure can be disassembled and the crushed stone filter can be replaced.

Alternative solutions for secondary wastewater treatment

Biological treatment station

Not every site owner will be able to perform secondary wastewater treatment using a filtration field. There are two main reasons for this: the presence of clay soil and a high level of soil water.

Often, the most optimal way is to purchase an SBO, a biological treatment plant that does not require secondary wastewater treatment. Its scheme of work involves the passage of contaminated liquid through a number of tanks equipped with filters, aerators and other devices. As a result of this process, the water is purified by 98%. As in conventional septic tanks, the main function of waste decomposition is performed by aerobic microorganisms.

Another option is to create an autonomous sewerage system with the inclusion of a filter well. However, certain conditions are also required for its construction. For example, the soil should not be clayey and the aquifer should be 1 m below the bottom of the tank.

What is a filtration field for a septic tank - see the video:

Now that you know how to properly make a filtration field after a septic tank, you can do this work yourself. To select a sump and determine the type of soil, we recommend that you contact a specialist. A well-functioning cleaning system always guarantees environmental safety, and therefore comfort.

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