Concrete ring septic tank: design and construction tips

How does a septic tank work? How does a two-chamber septic tank of concrete rings differ from a single-chamber? What should be the size of the rings, what is the optimal depth of the chambers? These and many other questions we have to find answers together with the reader.

Scheme of work

The principle of operation of the septic tank of concrete rings, in general, is no different from any other overflow septic tank:

1. Effluents enter the primary sedimentation tank, where they are kept for a long time. Their separation gradually occurs: the light fractions form a crust on the surface; heavy - settle to the bottom as sludge. The water in the middle of the settler is relatively clean (the degree of purification is 60%).
2. Through a special form of overflow, which draws water below the surface, purified water falls on the soil aftertreatment. With sufficient soil absorbency for this purpose, the so-called filtering well is used; if the ground absorbs water slowly, a filtration field is constructed.

Pay attention: we have described the simplest, single-chamber septic tank of concrete rings. Serial connection into a single chain of two or more sedimentation tanks will improve the quality of wastewater treatment.

Design

What problems we have to solve at the design stage?

• The location of the septic tank on the site.
• The choice of the method of disposal of treated wastewater.
• The choice of the sizes of a settler (settling tanks) and the filtering well or a filtration field.

Location

A few wishes for the location of the septic tank are pretty obvious:

• On a plot with a slope it is better to place it below the house on a slope. The instruction is connected with the fact that the water in the sewage moves by gravity: if you choose a location higher up the slope, the sump will have to be buried much deeper.
• It is better that the prevailing wind direction does not carry smells from the septic tank to the house.
• The depth of the bottom of the settling tank and the filtering well or filtration field must be below the freezing level. Otherwise, in winter, the sewers will be paralyzed.

In addition, the arrangement of a septic tank of concrete rings is impossible in close proximity to some objects:

Sump volume

In order for the effluent to pass through a complete separation, the volume of the primary clarifier (or, in the case of a multi-chamber septic tank, the total volume of the clarifier) ​​must be equal to or exceed the three-day volume of effluent.

How to calculate it?

• If water meters are installed at the cold water supply and hot water supply, the volume of wastewater can be considered equal to the sum of the flow of hot and cold water for the corresponding period of time.
• In other cases, it is calculated on the average daily water consumption of 200 liters per person. So, for a family of 3 people the minimum volume of the settling tank is 200 x 3 x 3 = 1800 liters, or 1.8 m3.

Typical dimensions of concrete rings for septic tank - diameter 1.6 meters at a height of 0.9 meters.

Объем, соответствующий одному кольцу, равен произведению квадрата радиуса цилиндра на число «пи» и высоту цилиндра: 0,8^2 х 3,14 х 0,9 = 1,84 метра; в теории, таким образом, для отстойника хватит одного кольца.

Tip: in practice, in the described case, it is still better to put two. The real water level in the sump will be much lower than the top edge, which will reduce the volume used. In addition, an increase in the sump will lead to improved quality of wastewater treatment.

Utilization of treated wastewater

The main parameter influencing the choice of the method of disposal and the calculation of the absorbing surface is the absorbency of the soil. It is easy to guess, it depends on the type of soil:

Suppose that in the case described above (a family of 3 people, the average daily volume of wastewater is 600 liters) we are dealing with sandy soil. With an absorbing capacity of 50 liters per day per square, the wetting area of ​​the soil must be at least 600/50 = 12 m2.

It is clear that concrete rings for a septic tank with such a cross-sectional area, which gives us the bottom of the desired size, are simply not available.

However, it can absorb not only the bottom, but also the walls of the pit; we only need to provide her with access:

1. The bottom ring is installed on the bedding of gravel with a thickness of at least 30 cm.
2. After installing all the rings, the pit around them is filled with not the ground, but the drainage - the same rubble.

In this case, we need a pit with a wall area below the overflow level of 12 m2. A simple calculation will show that the walls and the bottom of the cubic pit will have a side of just 1.55 m. The size and number of rings installed in it do not play a special role.

Now let's look at a more complicated case - clayey soil. With an absorption capacity of 10 liters per square, the absorption area must be at least 60 m2; trench size of 3.5x3.5x3.5 meters - a clear search.

In this case, it will be more rational to construct a filtering field. Instead of the excavation, a trench is being dug deep below the level of freezing; 10-20 cm of crushed stone fit into it; perforated drainage pipes are laid on it; above - another 30-40 cm of rubble and a layer of soil.

How to calculate the filtration field with your own hands? The principle is the same as that of the well: the wetted surface of the soil is taken into account.

So, for a trench 50 cm wide, filled with water up to half a meter in height, the minimum length in our case is 60 / (0.5 + 0.5 + 0.5) = 40 m. If the section size is insufficient, several parallel trenches dig.

Construction Tips

Каким должен быть септик из железобетонных колец - мы в общих чертах разобрались (см.также статью «Пескобетон М300 и его особенности»).

Now we delve into the subtleties of construction.

• For the sump it is better to purchase rings with seam locks that prevent horizontal displacement. The presence of a lock almost does not affect how much a concrete ring for a septic tank costs: the price differs by no more than 100-150 rubles.

• If a crane is used for installation, it is better to use not a through CS as the bottom ring, but a QDC equipped with a bottom. In this case, the sealing of the septic tank from concrete rings will be much more effective..

However: manual installation of wells with undermining of the edges is possible only with through-rings. In this case, the bottom is filled with sand, reinforced with steel mesh and poured with a layer of 8-10 cm of concrete.

• Overflow from the sump is supplied with a vertically oriented tee. The lower outlet will allow to take water below the surface, the upper one will be used for cleaning when clogged.
• Waterproofing a septic tank of concrete rings, as a rule, is reduced to the seal of the sutures of the settler cement-sand mortar with the addition of liquid glass. Bitumen coating is needed only at high seasonal groundwater levels.
• Most often, the ventilation of a septic tank of concrete rings is a pipe with deflectors, passed through the covers of wells. However, the same function will be perfectly fulfilled by the fan pipe, which is brought to the roof from the top of the house sewer system.

Conclusion

Надеемся, что предложенный вниманию читателя материал окажется полезным (см.также статью «Плотность бетона кг м3: что означает эта важнейшая характеристика материала и как она влияет на его качества»).

The video in this article will allow you to more clearly get acquainted with how the overflow septic tank is constructed from concrete rings. Successes!