How much septic tank is needed? Calculation for 3 people, 4 people, 5 people or a family.

Sewage generated during human activity must be removed from the premises. Problems with this do not arise in areas that provide central sewerage equipment. If this is not possible, owners of country houses have to solve this issue by other available methods. Most often, the choice is made in favor of local treatment facilities, and one has to decide what volume of septic tank is needed, what type of device to choose and how to maintain it. You will find answers to these and other questions in this article.

What to consider when choosing a septic tank

Today, many city dwellers choose to live in the countryside, but many are not prepared for the difficulties that arise, and this is, first of all, the lack of communal infrastructure. Issues of water supply and waste disposal have to be resolved using different methods, and in this case it is important to minimize the risk of sewage getting into the ground and water bodies. According to the provisions of SNiP 2.04.03-85, the degree of purification of liquid discharged into a reservoir must comply with the provisions of legislative acts regulating environmental protection issues. If water purified in a septic tank is reused, sanitary and hygienic standards will come into force.

The main advantage of local wastewater treatment systems is the possibility of maximum effective treatment for reusing water for technical purposes, including irrigation. When choosing a waste disposal unit, the following factors must be taken into account:

• the number of people living in the house;
• frequency of stay;
• soil characteristics and composition;
• terrain characteristics;
• deep water level;
• depth of soil freezing.

A local treatment facility is selected depending on the specific conditions and characteristics of the area. This can be a storage tank sufficient to cope with wastewater at a dacha intended for seasonal residence, settling tanks and full-fledged biological treatment stations. The latter guarantee almost one hundred percent wastewater treatment and significantly reduce the frequency of using special equipment. Therefore, when installing a septic tank, you also have to take into account the volume of the sewage truck, and the standard model can accommodate 3.75 “cubes” of sewage. It remains to find out how to calculate the volume of a septic tank, taking into account the main factors.

Advantages and disadvantages

Let's look at the reasons for choosing just such a concrete system. A concrete septic tank has a number of undeniable advantages:

• Autonomous operation of the structure, without electrical power supply.
• There is no need for additional drainage or pump.
• The dimensions of concrete rings are at the discretion of the owner.
• The service life of a concrete structure is much longer than that of a plastic or iron structure.
• Reinforced concrete structures are more effective at treating wastewater.
• The installation technology is so simple that the work can be done by a person with minimal construction skills.
• Minimum costs for the purchase of materials and construction work.
• Easy to maintain.

There is also a second side to the coin - shortcomings, you need to know them in person:

• The use of special equipment during installation makes it difficult to install concrete rings manually.
• Difficulty in installing pipes between sections (we make the holes for the pipes ourselves).
• Regular cleaning of solid waste chambers in septic tanks. When using special additives, the number of calls for sewer trucks is reduced due to the decomposition of the solid mass.

Calculation of the volume of a septic tank for a private house

The main task of a septic tank is to dispose of waste residues, so the device must have a capacity that allows it to accumulate and effectively clean the entire volume of sewage. To prevent the chambers from overflowing, it is necessary to correctly calculate the volume of the septic tank for a private home. It would seem that there is nothing complicated about this - you just need to add up the volume of all the chambers of the waste disposal unit, but that would be too simple.

In fact, it looks a little different: the volume of the first chamber is calculated from the bottom level to the overflow pipe, while the useful space of the second chamber is everything that is located between the bottom and the drain pipe. In addition, it is worth considering that over time, a large amount of solid particles accumulate in the first tank, which occupy a fifth of the usable space. Therefore, when calculating the liquid component, this 20% must be subtracted from the total volume. Now, in order to understand what a septic tank should be like, it remains to compare the expected amount of waste.

According to the provisions of the Sanitary Norms and Rules (SNiP), the daily water consumption for the average user is 200 liters, or 0.2 m3, but according to the rules, the minimum volume must be calculated with a reserve of 3 days. Thus, for a family of 3 people, the approximate water consumption is 1.8 m3, and this does not count the 20% that must be added to the bottom sediment.

How to calculate the dimensions correctly?

To dig a pit, you need to know the size of the septic tank

The following data can be applied to such a concept as size:

This is important in order to make the correct pit, you need to make a septic tank calculation along with all its additional details. And in order to find out the volume of waste per day, you need to look at the size of the body and tanks

If it is a one-piece design, then you can estimate the size of the equipment according to the technical data on the packaging and compare them with the dimensions of your garden plot or private premises.

Norms and rules when designing the installation of a septic tank for a summer residence:

• If you have a small area, then perhaps the calculations of another device will be useful;
• To make the correct calculations, you can use the tables of engineers;
• The minimum working depth should be 1.3 m and the width less than 1 m;
• The depth from surface to bottom should be no more than 3.2 m.

Important! If you pay attention to the size of the sump, then you are paying attention to the scale of the device. This could be some kind of hint

Refined formula for calculating the volume of a septic tank for a country house

Sanitary standards indicate that the release of purified water outside the device should be carried out no more than once every two weeks. When making calculations, no one uses this provision, because in this case, for a family of 4 people, you need a device with a minimum volume of 8 “cubes”. It is also not a fact that each resident uses 200 liters of water per day, and experts even believe that we can proceed from the figure of 0.1 m3/day. In this case, for 3 people you will need a “cube” septic tank, but the installation of such devices is not encouraged.

There are other exceptions to the rules in the form of an unexpected increase in the number of residents and an expansion in the range of household appliances (purchase of a dishwasher, for example). Therefore, it is necessary to calculate the required volume of the septic tank, taking into account possible changes. Experts recommend using a more precise formula:

V septic tank = (Number of residents * 0.2 + 0.2) * 2

To add a margin of safety, you need to add the cost for one more conditional person, after which the resulting result is multiplied by two, taking into account the fact that some residents really like to take water procedures. Thus, for 5 people, for example, the minimum volume of a septic tank is 2.4 m3; the ideal solution for 6 people would be a 2.8 m3 waste disposal unit. As practice shows, these are real numbers that allow you to accurately buy a septic tank that will make living in the house as comfortable as possible. There is another formula that takes into account the consumption of all used instruments and devices, presented in the table:

Calculations are carried out based on the consumption of 150 liters per day per person and occur in several stages. The first calculates the average consumption per person, taking into account the fact that he will use a shower for 7 minutes a day (flow rate 10 l/min), a bidet for 5 minutes (flow rate 8 l/min) and a bathtub, which takes 110 liters of water. Based on this, the average consumption per person, excluding household appliances, is 150 l (average) + 10*7 + 8*5 + 110 = 370 l/day. To obtain the required volume of the septic tank, all that remains is to multiply this figure by the number of residents.

It’s even easier to calculate the required volume of a septic tank for a summer house intended for periodic residence. In this case, low-functional storage tanks are most often installed, which must be selected taking into account how many cubic meters the sewage disposal equipment can dispose of at a time.

What factors need to be taken into account?

As it becomes clear from the above, the volume of the tanks directly depends on how much water the residents use. Consumption is affected by:

• the number of users, that is, how many people live permanently and also come periodically. Naturally, in a facility for a family of 3-4 people, the amount of sewage will be significantly lower than in a residential building of a holiday home designed for 20 guests and 15 staff;
• equipping the house with plumbing. It is clear that in a house equipped with a 350-liter jacuzzi, the volume of wastewater will be greater than in a house that only has a shower, even if the same number of people live in these houses.

Required volume of septic tank for a bath

Today we hear more and more often about a healthy lifestyle, so even in the countryside you can find a Russian bathhouse or sauna. Their presence significantly increases water consumption. In order for the local sewage system to work efficiently, the volume of the septic tank for the bathhouse will have to be added to the calculated indicators. In this case, it is better to use two-chamber septic tanks or biological treatment stations rather than storage tanks. The minimum consumption in the bathhouse is 100 liters of water per day, so the productivity of the device must be increased by 300 l/day. For bathhouses, plastic septic tanks are most often chosen, although many prefer durable devices made of concrete rings.

How many cameras should there be?

The number of chambers, as well as the total volume of the treatment plant, directly depends on the volume of wastewater to be disposed of. For private residential properties (houses, dachas), as a rule, two sealed settling tanks are built.

In addition, a third element is included in the system; this can be a filter well or filtration platforms. If a large septic tank is being built to serve 15 or 20 users, then the number of settling tanks should be increased.

When building a two- or three-chamber installation, the dimensions of the chambers are made unequal. So, the largest should be the receiving compartment. In the two-chamber version, it should occupy 75% of the total volume, since it is in this compartment of the septic tank that the heaviest and largest inclusions settle. If a three-chamber version of a septic tank is being built, then the receiver should account for 50% of the total capacity, and the remaining two chambers should be made identical.

Advice! Not in all cases, chambers are made different in volume. For example, when building a treatment plant from reinforced concrete well rings or Eurocubes, all compartments of the installation will be the same.

Why choose septic tanks from Septic Topas Plus

In Moscow and the Moscow region, many companies offer services for the sale and installation of septic tanks, but you need to trust this difficult issue to the best. It’s easy to imagine the consequences of installing a low-quality device. The Septic Topas Plus company catalog contains only proven septic tanks from domestic manufacturers: Topas, Unilos Astra, Eurolos, Termit, Tver, Diamant, Dochista, Terra, Biozon and Kolovesi. The company's managers will visit the site free of charge, and after making preliminary calculations, they will help you choose the most suitable recycler. As proof of the quality of our services, we offer a three-year guarantee, affordable prices and discounts for regular customers.

What can errors in calculations lead to?

If the volume of the settling tanks is determined incorrectly, the installation will perform worse. So, if the capacity of the installation is insufficient, the liquid will not have time to settle properly and poorly purified water will be supplied to the outlet.

This will lead to the fact that the soil filter used for post-treatment will quickly become silted and will become worse at filtering water. Restoring the system will require labor-intensive repairs.

It is not practical to build sedimentation tanks with a large reserve volume for economic reasons, since the construction of a large-capacity septic tank will cost much more than the construction of a compact model.

So, in the process of designing a local sewerage system, a septic tank is calculated. It is very important to do this work correctly, since the quality of the treatment plant will depend on it. If you plan to buy a ready-made septic tank, then there is no need to carry out calculations; the manufacturer must indicate the performance parameters of the model in the documentation.

Installation of an object made of concrete rings

Since concrete rings are the most common option for constructing a cesspool, it makes sense to consider it in detail.

Here is the general scheme for performing installation work:

1. Perform markup.
2. Dig a pit.
3. Install the rings.
4. Bring a sewer pipe to the property.
5. Make a hole for the pipe and insert it into the container.
6. Seal all connections.
7. Apply a layer of waterproofing material.
8. Place a sand and gravel filter at the bottom of the structure.
9. Backfill the pit.
10. Install the top cover with cover.
11. Cover the ceiling with soil or decorate it.

You can also dig a pit for a small hole by hand. You will need a bayonet shovel to dig, a bucket on a rope to remove the soil, a shovel to pour it into the bucket, and a partner on top to pull the bucket out. The concrete ring is placed on the ground and dug inside.

If a large pit is needed for a cesspool without a bottom, it makes sense to rent an excavator so that the work goes faster

As a result, the ring gradually lowers, preventing the walls of the pit from collapsing. For a large cesspool, it is still better to spend money on renting an excavator. The speed of work will increase significantly. Here you can also first place the ring on the ground and then begin work. You will need an excavator with the appropriate bucket size and an experienced operator.

The trench for the sewer pipe should have a slight slope, 2 - 3 cm per linear meter. If soil freezing in winter is typical for this area, then the pipe above this mark should be insulated.

A hole for the pipe is punched in a suitable place after it is laid. If you make such a hole in advance, you may simply not guess the height of the pipe entry.

Concrete rings at the bottom of the cesspool pit should be installed very carefully using a crane so as not to damage them

The joints of the concrete rings, as well as the pipe entry point, are treated with a solution. Then a layer of waterproofing material should be applied. Inexpensive coating insulation will do.

This step is not considered necessary if all joints are securely sealed. However, the waterproofing layer will protect the structure from damage, and this will significantly increase its service life.

The joints between the concrete rings of the cesspool are fastened with mortar, then all joints are carefully covered with a layer of waterproofing material

The bottom filter is formed from river sand and gravel. You can also use crushed stone of suitable fractions. First, sand is poured in a layer of about 30–35 cm, then two layers of gravel or crushed stone of approximately the same thickness.

Small particles should be at the bottom, and large ones at the top. Now you need to install the top floor. Usually, for this purpose, a ready-made concrete slab of suitable size and configuration is taken.

There should be a hole in the ceiling large enough so that you can not only lower the suction hose, but also send a person to inspect the condition of the container after cleaning it. This hole is covered with a lid so that foreign odors do not disturb others.

A concrete floor with a hole for the lid is the best option for installing a cesspool made of concrete rings. Such structures are also used in the construction of sewers from other materials.

Some owners prefer to make a double lid. It reliably protects against odors and freezing of drains in winter. A layer of soil is usually applied on top of the ceiling so as not to spoil the landscape.

The lid, of course, must be left free; it must be 20–30 cm above ground level. Now you just need to monitor the level of waste in the container and remove it in a timely manner.

The double lid over the cesspool container without a bottom has increased heat-insulating properties and reliably cuts off unpleasant odors

If everything is calculated correctly, then cleaning will only be necessary a couple of times a year. After the cesspool is cleared, do not allow a person in overalls to be lowered down. His task is to inspect the walls of the structure and check their integrity.

Periodically wash the bottom filter or replace it completely. All work inside the cesspool must be done only in the presence of a partner, who is at the top for insurance.