The principle of operation of septic tanks. Varieties of cleaners and common elements in their design. Waste water purification process in various types of sedimentation tanks. A septic tank is a structure designed for the disposal of household wastewater from individual houses, cottages, summer cottages in the absence of access to a centralized sewage system. To choose the right purifier, you need to study the septic tank device and the features of its operation. Information on the design and principles of its operation can be found in this article.
How a septic tank works
A septic tank for a home is one or more tanks that receive waste water for temporary storage and processing. The principle of operation of the facility is to separate dirty water into solid, liquid and gaseous fractions.
The inclusions are separated and processed using gravity sedimentation and bioferment preparations based on special microorganisms - anaerobic and aerobic bacteria. Each method is used individually or in combination with another. After the septic tank, the liquid can be sent for additional treatment to the ground filters.
Gravity settling is the first step in fluid handling. In the storage section suspended fine particles and large elements settle to the bottom. At the bottom, small fragments of vegetables and fruits, sand, etc. accumulate.
The anaerobic bacteria used in the septic tank can live and multiply without oxygen. Such microorganisms decompose sediment on the bottom of the product and in other places where there is no air and sunlight. They recycle organics in two stages. At the stage of acid fermentation, carbohydrates, protein and fats are decomposed to a number of lower fatty acids, and at the stage of methane fermentation they decompose to hydrogen, carbon dioxide and methane. Some of the formations are removed from the septic tank through the ventilation system, the other is dissolved in water and removed to the outside. The remaining organic and inorganic inclusions after processing by bacteria are transformed and precipitate in the form of silt.
Another type of bacteria used in septic tanks (aerobic microorganisms) cannot live without oxygen, so it settles on the surface of the liquid. They process non-settling substances floating on top - fats, films, surfactants, etc. Aerobes process them with little or no sludge formation. Decomposition products of organic matter are discharged outside with water or evaporate.
To speed up the processing process, a certain amount of bioenzymes is added to the chambers, but the decomposition of waste takes place even without external intervention.
Note! The activity of microorganisms depends on several factors: the presence of organic substances in the chambers, the appropriate temperature (+ 10 … + 35 degrees), the acidity of household wastewater, the absence of substances that destroy bacteria in them. In order for the septic tank to work stably, it is recommended to keep the microorganisms active. For this, it is necessary that the product constantly receives waste, which serves as food for bacteria. Periodically add a small amount of biological products to the chambers to maintain the balance of active microorganisms.
The main structural elements of a septic tank
There are many types of septic tanks, which differ in size, design, the presence of additional elements to improve the quality of cleaning, ease of use, improve installation technology, etc. However, in the schematic diagram of septic tanks of all types, the same parts are present, listed below:
- Reservoirs … Needed for temporary storage of effluents. The compartments can be built with your own hands from brick, concrete, stone, etc. A classic septic tank is a two-chamber product, in which the sections are interconnected by overflow pipes at the level of the middle of the tank for independent overflow of water. The factory-made design is a single tank, divided internally by partitions.
- Pipelines … They are needed to supply liquid from the house to the sump and drain the purified water from the tank to the outside.
- Septic tank service elements … This category of elements of a septic tank includes hatches, inspection wells.
- Ventilation system … It is required to remove the gas formed as a result of the processing of organic substances from the chamber. Also, with the help of a ventilation pipe, air is supplied to the septic tank to maintain the activity of microorganisms. It must be able to move through holes in the walls throughout the sump. To equalize the pressure in the tank and the atmosphere, water seals are installed on the structure. They do not allow air into the sewer system, so there is no unpleasant smell in the house.
- System for draining the purified liquid from the septic tank to the site … The way of removing water depends on the modification of the device. It can flow independently from the last compartment, be removed by a pump or taken out by a sewer truck. If the degree of water purification is insufficient, the liquid after the sump is passed through post-treatment filters, which are built next to the septic tank.
Brief information about such devices is given in the table:
| Post-treatment filter | Application | Design |
| Filter well | Built on sand and sandy loam, cleaning efficiency - 100% | The wall of the well is made of concrete, at the bottom there is a layer of sand and gravel |
| Absorption trench | Built on sand and sandy loam, cleaning efficiency - 98% | Long perforated pipes are buried in the ground or laid on a site of sand and gravel |
| Filter trench | Built on soils with low filtering characteristics, cleaning efficiency - up to 98% | Two perforated pipes, between which a layer of sand with gravel is poured, one by one, water flows out of the septic tank, then passes through the filter layer and is removed from the site through the second |
| Infiltrate | Built on sand and sandy loam, cleaning efficiency - up to 98% | A metal or concrete box is turned upside down, installed on a platform of sand and gravel, water is directed inside the structure, where it is purified by passing through a soil filter |
Features of the functioning of septic tanks of various types
There are several types of sedimentation tanks, therefore, for the correct choice of the product, it is necessary to understand the mechanism of operation of the septic tank and knowledge of its structure. Depending on the degree of processing of mud, they are divided into 3 categories: storage tanks, sedimentation tanks with soil tertiary treatment, deep biological treatment stations. Let's consider what happens to dirty water in each of the listed products.
Storage of effluents in a reservoir
The drive is an improved version of the sump. It consists of a robust, sealed single chamber tank and a water inlet pipe. Prefabricated devices are equipped with a valve that prevents the contents from flowing out in the opposite direction, and a sensor for filling the container.
The effluent enters the storage tank through the sewer pipe and is temporarily stored in it. The contents of the chamber are partially processed by bacteria, but are removed only after the compartment is full. Waste is taken out by a sewage truck and dumped into a pre-prepared place outside the site.
The dimensions of the septic tank are small - within 1 m3… It is usually installed in summer cottages, where the owners rarely come. Such a purifier is used when it is impossible to remove purified water into the soil, for example, with a high level of groundwater or the presence of clay layers in the area that are poorly permeable to liquids.
Purification of sewage in a gravity septic tank
Self-flowing products belong to septic tanks with ground post-treatment. They consist of several compartments in which sedimentation and biological treatment of effluents takes place.
Water moves from one chamber to another on its own, so such a device can be installed in places where there is no electricity. After the septic tank, water must be passed through a soil filter.
Two-chamber products are installed at a water flow rate of up to 5 m3 per day, three-chamber - more than 8 m3… In a two-section device, the first part should occupy at least 2/3 of the total volume, in a three-section device - 1/2.
How a septic tank works in gravity systems is written below:
- Primary cleaning … It takes place in a storage tank, where the drains are discharged from the sewer pipe. At the entrance to the septic tank, a flow damper is mounted - a tee that directs the flow down. If it is not installed, the greasy layer on the surface will constantly break up, and a large amount of suspended matter will enter the next chamber, which should remain in the receiver. Heavy particles, insoluble in water, sink to the bottom of the storage tank. Light fractions (oils, fats) float up and through the overflow pipe into the second chamber.
- Processing of solid sludge … The particles that have fallen to the bottom begin to decompose and, after a few days, turn into a thick mass. This work is done by anaerobic bacteria that are present in the human body. They enter the septic tank with human waste products. The sediment at the bottom forms fermented activated sludge from microbes and other microorganisms that contribute to the processing of organic matter. But over time, the layer becomes very thick, so the sediment must be removed periodically. However, it is not recommended to thoroughly clean the drive. In the sump, up to 20% of activated sludge should remain in order for the bacteria to quickly restore their numbers. If you correctly calculate the volume of a septic tank for a home, all organic inclusions in the containers will be processed within 3 days. The process takes place better at a positive temperature, so it is recommended to insulate the device for the winter.
- Light ends decomposition … From the receiving chamber, water enters the second compartment, in which the floating inclusions are processed by aerobic bacteria. With their help, water is purified from organic components of natural origin and waste of personal care products. This is also where the detergents dissolve. The process is accompanied by the release of carbon dioxide, heat and the formation of the smallest particles that precipitate.
After the second stage of cleaning, up to 65% of inclusions are removed from the effluent, but this is not enough to pour it onto the surface. Therefore, the liquid is directed to the soil filters. They all have the same structure - a thick layer of a mixture of crushed stone and sand. Passing through them, the water is purified by 98% and seeps into the ground already clean.
If it is not possible to organize additional cleaning, a third tank can be installed, in which the clarified water is collected. After filling it, the liquid is taken out for disposal to a pre-prepared place by a sewer truck. To move water from one section to another, holes are drilled in the walls and a tee is installed in them, which takes water from the middle of the container, and not from the bottom or from the surface. The connecting pipe is positioned at 1/3 of the tank height, so no solids can enter the second compartment.
In some septic tanks, oxygen deficiency is artificially maintained, which has a very beneficial effect on the anaerobic process taking place in the reservoir.
Deep cleaning station operation
The station is designed for high quality wastewater treatment. The basic principle of operation of a septic tank of this type is the active effect of aerobic microbes on inclusions. Typically, this is a factory-made device, consisting of one chamber, internally divided into several compartments.
In the first compartment, solid elements settle to the bottom and are processed by anaerobic microbes. In the second, the remaining inclusions are processed by aerobic microbes, which need oxygen. Therefore, the station has a pump that constantly supplies fresh air to the chamber and mixes the liquid. Under its influence, aerobic bacteria multiply rapidly and actively process organic matter. The running water does not wash away the bacteria as it they live in fine-grained textile shields.
The longer the drains are mixed in the aerobic chamber, the better the cleaning. Often, a second stream of air is created in the tank, which drives it through the compartment for the second and third time.
Note! The minimum amount of time it takes to process waste is 5-6 hours. If you remove water from the sump earlier, the cleaning quality will deteriorate. The air compressor supplying air to the septic tank is powered by electricity, so it is not recommended to install the station in places where the lights are often turned off. Without oxygen supply, aerobic microbes die very quickly, and the device will have to be restarted for subsequent operation.
In the last tank, the water is settled and clarified. In the future, it can be used for irrigation without soil treatment, because the degree of purification reaches 95-99%.
How a septic tank works - look at the video:
So, you learned from our article that local sewage systems work thanks to bioferment preparations that accelerate the process of processing organic matter in a liquid. This is a modern solution for the disposal of sewage waste, which is available to the owner of a summer cottage or private house.
