Calculation of a septic tank for a private house

Most owners of suburban buildings know that septic tanks used for the collection and partial disposal of household waste can have a variety of designs. They can be mounted both from reinforced concrete rings of standard size and from plastic tanks of various capacities. In this case, the most common option is considered to be a 2 or 3 section septic tank made of reinforced concrete rings. Particular attention when choosing a septic tank configuration should be paid to the fact that the efficiency of such a sewage treatment plant largely depends on its volume, so it is very important to correctly calculate the septic tank for a private house, regardless of the selected septic tank and the shape of its components. When choosing this indicator, you should focus on the useful volume, which is calculated on the basis of tripled water consumption per person permanently living in a dwelling.

Given that the average rate of water consumption per person is about 200 liters per day - the total consumption is determined by multiplying it by the number of residents (see Appendix).

Application:

Full calculation

The final or full calculation of the septic tank, produced in accordance with the existing technical standards, involves a comprehensive account of the existing factors that manifest themselves in specific operational situations (as opposed to an indicative definition of its volume according to the table. The following factors, as a rule, are subject to comprehensive accounting:

• deviation of the average value of water flow in one direction or another;
• availability of free spaces for a septic tank of the required volume.

When considering the first of these factors, it should be noted that the table above is used only for an approximate determination of the volume of the tanks of the future sewage treatment plant. Depending on the specific conditions, this value may deviate both in the direction of larger and in the direction of smaller values. To account for such deviations, a special correction factor is introduced, which corrects the average statistical value by simply multiplying it.

When using water metering devices, in particular, you will need to introduce an amendment to its mass flow, which, accordingly, will reduce the indicator of the volume of wastewater. In such situations, a so-called reduction factor of about 0.6–0.8 is introduced. For lovers of daily intake of refreshing showers and baths, on the contrary, you will need to introduce a multiplying factor of 1.5? 2. The presence of water-intensive household appliances (washing machine or dishwasher, for example) leads to the same result.

Taking into account the average daily water consumption by one user, as well as an additional adjustment for unforeseen expenses (another 200 l), the size of the sump tanks significantly increases not only in terms of volume, but also in the area occupied by the entire sewage treatment plant. With a significant increase in water consumption (up to 5 m³ per day), you will need to use a local treatment plant, consisting of two or three chambers, providing accelerated processing of wastewater.

Accounting for space

In the case of a limited area of ​​land allocated for the placement of a sewage treatment plant, you, in one way or another, will have to decide the question of optimizing its linear dimensions (or, more precisely, the usable area it occupies).

For this purpose, with a fixed volume, its linear dimensions can vary in any way. So as a settling tank can be used a concrete pipe with a diameter of 1? 1.5 meters, dug into the ground vertically. The depth of immersion of such a pipe into the ground can reach 2.5 m.

In accordance with the shape of the used sump, its volume can be calculated using standard formulas.

For example, consider the calculation of the volume for a family of 4 permanently residing in a country building:

1. Taking into account the average daily water consumption per person, as well as the data given in the table annex, a family of 4 people will need a sump with a total volume of at least 2 m³.
2. To accommodate such a tank you have to prepare a pit of 2 m? and one meter deep.
3. In that case, if you do not have the specified area - under the sump it will be possible to allocate 1 m? the area on which the pit is dug two-meter depth.

With an increase in the required volume of the septic tank, the value of the prepared recess, respectively, increases.

Video

For more information on the device, the operation of the septic tank and the calculation of its volume, you can get it by watching the video below: