Do-it-yourself septic tank from concrete rings: diagrams and device

Recommendation points

• Scheme and principle of operation of a septic tank with separate chambers
• What rings and how to dig them in
• Not all containers are equally sealed
• Septic tank aeration system
• Moving masses between chambers

If plastic septic tanks do not inspire confidence in you, make your own, with aeration and separate chambers. For these purposes, the most profitable option is concrete rings, and today we will tell you how to install them correctly, waterproof them and conduct a communications network inside.

Scheme and principle of operation of a septic tank with separate chambers

Septic tank is a generalized definition of multilevel wastewater treatment systems, which are based on the use of natural biological processes. Unfortunately, most of the “branded” products are just an attempt to standardize the work of the WWTP, although such structures have always been erected only according to an individual project, which takes into account:

• features of soil and relief;
• ground water level;
• temperature regime;
• chemical composition of effluents.

A number of more specific indicators are often added to this list..

In home construction, a septic tank made of concrete rings requires a sensitive approach, organization and planning of the structure in all possible modes, including emergency. All processes related to both water clarification and the protection of cameras from negative external influences must be worked out to the smallest detail.

The first chamber is a sealed column of the primary clarifier (PO). Its volume is determined at the rate of 200 liters per person per day for at least three days in case of emergency work. The capacity of the software is equivalent to the capacity of the second chamber (reactor or aeration tank), respectively, it is necessary to take into account the possibility of three-fold salvo discharge, protecting the septic tank from self-flooding.

A conventional septic tank uses the gravitational principle of moving water between chambers and does not contribute to the rapid development of bacterial colonies. Septic tanks equipped with a system of aeration and waste movement have an accelerated treatment mode due to the attraction of aerobic microorganisms to the process, but they require expensive technical equipment and are volatile: up to 1.4 kW · h / day and about 3-5 kW · h / day at working heating.

As a warning, we will make a small excursion on the preparation for the arrangement of a septic tank. Lay the underground part of the septic tank inlet line with HDPE pipe 125 mm SDR 17. Its inner diameter allows you to pull about 50 cm at the end of a 100 mm sewer pipe, free from the socket. It is better to drain the clarified water with the same pipe, but with a diameter corresponding to the drain pump fitting.

What rings and how to dig them in

One of the key properties of a septic tank is the tightness of the PO chambers and aeration tank. Without this, runoff will seep into the upper water, polluting drinking water sources, deteriorating soil characteristics, which will attract the attention of sanitary and epidemiological control services.

When dealing with rings, it is difficult to achieve a deaf waterproofing: winter heaving breaks the joints, the rings are displaced from the ground movements. High-quality insulation materials alone are not enough, a ring fastening system is needed.

Another problem with any sealed chamber is that its equivalent density may be lower than the density of the soil, therefore, over time, the septic tank will begin to squeeze out. All this leads to the conclusion that a standard ring well shaft using the sequential digging method is clearly not enough..

Rings must be used with a quarter (lock) for a secure fit. First, a hole is dug to the required depth, the diameter is one meter larger than the rings. The bottom is poured in two stages. The first lower layer is 80 mm, reinforced with mesh, with four anchor inserts, diametrically distant from the center to the outer radius of the ring. The second layer is poured the next day with sand concrete 30 mm, then, even before setting, the lower ring is lowered into the pit and installed between the mortgages.

Previously, the rings of the first two chambers must be treated with one or two layers of coating waterproofing. The locks on the ends are opened especially carefully, and a fresh layer of mastic is applied when installing each new ring. It is recommended to fasten through the walls of U-shaped brackets with thread at the ends from the final calculation every 40 cm.

After the installation of the shaft, it is covered with a cap with an outlet on the sides of at least 150 mm at a level of 100–120 cm below the ground. 16 mm holes are drilled according to the location of the embedded elements in the cap, then the container is pulled together with thermo-reinforced reinforcement with a diameter of 14 mm on threaded grips. The throat of each chamber can be assembled from rings, but with a high level of groundwater, it is better to cast it monolithically with a cap or arrange a clay lock at the level of the upper water.

From the outside, the columns are covered with a layer of foamed polyurethane foam, possibly with a foil backing. Not for the purpose of insulation, but as a means to compensate for the swelling of the soil, and prevent it from freezing to the rings. The remaining space can be filled with road rubble, but often it is filled with excavated clay – it depends on the type and composition of the local soil.

Not all containers are equally sealed

The water leaving the second chamber is 99% free of solid particles and fat, but it is biologically contaminated and requires additional treatment in the soil layer. So, contrary to the “heralds” from marketing, it is strictly not allowed to dump water from the septic tank onto the relief.

A well made of perforated rings will perfectly cope with the filtration field function. You can dig in the rings sequentially, but it is better to start with a pit and arrange a 20-cm dump on the sides with rubble, anticipating the silting of the holes. To simplify excavation work, you can replace one deep container with a pair of smaller ones. It is also preferable to remove the filter well from the septic tank chambers by 5-7 meters so that the soil around the chambers is less saturated with moisture.

When laying the upper rings, do not forget to leave mortgages connecting the first chamber with the second and the second with the third by means of 110 mm PVC pipe lengths located with a difference in level of 50 cm.Place a 70 mm HDPE pipe from the bottom of the second chamber to the middle of the first. Also, do not forget to connect the aeration tank with a HDPE pipe to the filter well. Outlets of pipes in the first chambers are sealed and sealed, then they are completed with vertically oriented tees so that the overflowing liquid is taken from the layer 2-3 meters below the surface, where there is no solid silt and light fragments.

1 – sewage inlet pipe; 2 – tee; 3 – primary settling tank; 4 – aerotank; 5 – drainage well; 6 – HDPE pipe O110; 7 – HDPE pipe O70; 8 – crushed stone (gravel)

Septic tank aeration system

To maintain the vital activity of aerobic bacteria, air must be periodically passed through the treated wastewater – about 1300 l³/ h The more the air bubbles are atomized, the more efficient and faster the aeration takes place. Diaphragm diffusers used in fish farms to supply oxygen to pools do this well. They need to be located one meter from the bottom of the aeration tank in an amount of one to three pieces, depending on the size and performance of the entire system.

1 – compressor; 2 – silicone tubes; 3 – membrane diffuser

The diffusers are connected by means of silicone pipes led through the overflow pipes to the neck of the container. The compressor can be located either on an equipped site inside the aeration tank, or in a caisson equipped next to the tanks.

Moving masses between chambers

The septic tank must be supplied with a submersible slurry pump, which will not only prevent flooding, but also help with periodic cleaning of accumulated waste sludge. By default, it is suspended in the middle of the second tank, but the float is brought out half a meter above the outlet. So the pump will urgently get rid of the excess clarified water by dropping it into the filter well, and will not allow the septic tank to flood itself.

1 – cable; 2 – float; 3 – drainage pump; 4 – tubular diffuser

Activated sludge is pumped into the primary sump through the second pipe between the chambers, which accelerates the growth of bacteria and the operation of the entire septic tank. In order not to use another pump, the end of the pipe is smoothly lowered 30 cm from the bottom, and a productive tubular diffuser is installed inside, which works as an airlift with a lift height of up to two meters.