Filter well: design, purpose, device technology
Unlike residents of multi-storey buildings, owners of private households are not provided with a centralized sewerage system and are forced to independently organize wastewater disposal on their property. A filter well plays an important role in the sewer and drainage system of a house.
However, it cannot be installed everywhere; there are certain rules that must be followed when constructing it.
In our material we will understand the types of filter wells, the rules for their installation on the site, and also tell you how to make such a structure yourself.
The content of the article:
Purpose and features of filtration wells
Issues of ecology and environmental protection are very acute today. Untreated wastewater, if it flows directly into water bodies or soil from the internal sewer system, can serve as a source of contamination of water and soil.
Therefore, doing this is strictly prohibited. Before entering open sources or going into the ground, dirty domestic water must undergo a purification system.
There are various methods for purifying wastewater, one of which is an absorption well, which acts as a kind of natural multi-layer filter. It retains dirt, debris and other particles, and allows purified water to flow into the soil.
A distinctive feature of filter structures is the absence of a sealed bottom. A bottom filter made of crushed stone, gravel, broken brick and other similar building materials is equipped at the bottom of the well. The total height of the filter filling should be up to one meter.
A filter well is usually installed in areas that are not equipped with a drainage system, as well as in places where there are no natural reservoirs nearby for water drainage.
It can be used as an independent structure when arranging a drainage system or storm sewer, or for post-treatment of wastewater that has been pre-treated in a septic tank.
Installation rules and regulations
The capabilities of filtration wells are very limited; the rules and features of their installation are regulated by building codes (SNiP behind the number 2.04.03-85).
They can only be installed on certain types of soil: sandy or sandy loam, which themselves have good absorption capacity. Absorption wells are not suitable for clay soils with low filtration properties.
For comparison, if 1 m² of medium-sized sand can absorb up to 80 liters of liquid per day, and sandy loam - up to 40, the absorption capacity of loam is 25, and fractured clay - only 5 liters. From the given data it follows that when installing a filtration well on clay soil, it will, of course, purify the water, but there will be nowhere for it to go.
To find out the type of soil in the area, do the following experiment: dig a small hole measuring 300x300 mm and about 150 mm deep. Pour liquid into it to the very top and note how long it takes for the water to go underground. 18 seconds – sandy soil, half a minute – sandy loam, 2 minutes – loam.
Particular attention should be paid to the groundwater level in the area. If the groundwater runs high enough, it is not recommended to install an absorption well, since its depth should be 2-2.5 m. In this case, it is necessary to ensure a distance of at least one and a half meters from its bottom to the groundwater.
Installation restrictions also apply to the average daily volume of wastewater. Their number should not exceed 1 m3. If the volume of wastewater to be treated is larger, it is recommended to choose a different filtration and liquid removal system.
If underground water is used for drinking or household needs, the construction of a well must be coordinated with the sanitary and epidemiological inspection services. But in any case, it must be done at a distance of at least 30 meters from wells and wells for drinking water. You can read about the features of installing a sewer pipeline on the site In this article.
Construction regulations stipulate the rules governing the location of the conditional bottom of the filter well. It must be 1.5 m or more above the groundwater horizon.
Types of filter structures
There are two types of well filtration structures that work on the same principle and are installed in a similar way. Their differences lie in the area of application. The former are used in the drainage and stormwater systems, the latter in the sewer system.
Absorption well in the drainage system
In this case, drainage absorption wells are the end point of a complex system site drainage, where groundwater or rainwater flows through a pipeline, so that later, after passing through a natural filter, it goes into the ground. Its main purpose is to remove water from the house and clean it from silt and sand.
The diameter of such wells, as a rule, is no more than one and a half, and the depth is up to two meters. It is allowed to drain both systems into one well. The filter container is installed at the lowest point of the site so that water flows into it by natural gravity.
Filtration structure in the sewer system
In the sewerage system of the site, absorption wells are used for post-treatment of wastewater coming from a hermetically sealed reservoir in which the wastewater undergoes primary biological treatment.The tank is made of concrete rings, brick or rubble stone, or a ready-made septic tank is used.
The principle of operation of the system is as follows: wastewater from the house sewer enters a sealed container, where it is oxidized for two to three days under the influence of anaerobic bacteria living in airless space.
Then the wastewater enters the filtration well, where other bacteria - aerobes - are already present. Their vital activity is activated under the influence of oxygen.
As a result of double purification, the liquid entering the soil from the absorption well is almost completely free of harmful microorganisms and organic substances.
Wastewater disposal can be organized in two ways:
- Separate. Water from the kitchen, bath, and washing machines goes into the septic tank, and sewage with feces goes into the cesspool.
- Joint. All household waste goes to septic tank or storage tank.
As a rule, in the first case, gray wastewater is sent to different sewerage facilities. For example, fecal waste - into a storage well with subsequent pumping and removal, gray domestic wastewater from kitchen sinks, bathtubs, washbasins, etc. devices - into absorption wells.
In the second case, a septic tank consisting of at least from two chambers, each of which sequentially carries out its own cleaning stage. Fecal matter settles in the first chamber, from where it is periodically pumped out using a sewer truck.
Liquid waste without suspended particles with a minimum amount of impurities enters the second chamber, where it is further purified. After this, the water passes through the pipes into a filtration well, from where, after passing through a natural filter, it goes into the soil.
The second option of the joint scheme is complete pumping and removal of wastewater.
Calculation of the number of filter wells on the site
The number of filtration wells depends on the daily water consumption in the house. One septic tank is usually equipped with two to four absorption wells. In turn, the volume of the septic tank should be three times the daily flow of water waste.
If we assume that one person in a private house has 250 liters per day, then for four family members a septic tank with a volume of at least 3 cubic meters is needed. meters.
Load per 1 sq. m. area of the absorption well is calculated based on the type of soil. (sandy - up to 80, super sandy - up to 40 l) If the distance from groundwater to the bottom of the well is more than two meters, the load can be increased by 20%. It is also permissible to increase the load in dacha farms where the well is used only in the summer.
Alternative filter units
In addition to the filtration well, aerobic wastewater treatment under natural conditions can be carried out using:
- ground drainage;
- filter trenches;
- biological filter.
In the first case, wastewater from the septic tank first enters the distribution well, and then is distributed through drains - pipes with slots, laid with a slope into trenches, previously filled with gravel or crushed stone.The top of the pipes is also sprinkled with crushed stone, then with earth and covered with geotextile. Read more about how to correctly calculate the slope of a drainage pipe In this article.
If there is a body of water near the site where purified water can flow, then filter trenches are installed. Drainage pipes are laid in the bottom layer on a gravel bed, which are then covered with gravel and sand. Lay on top of a layer of gravel drainage pipes with slots, cover them with geotextile and cover them with earth.
If it is impossible to organize filter fields on the site, install a biofilter. It receives pre-purified water from the septic tank for further biological treatment. As a result of filtration, wastewater is purified to the level of technical water, which then goes into the ground.
How to make a filtration well
Absorption wells can be built from baked bricks or rubble stones, but their construction requires considerable effort. Therefore, more often the walls of the well are made of reinforced concrete rings. Today, plastic structures are also widespread. You can make them yourself from plastic pipes or buy ready-made ones.
Option No. 1 - brick structure
The brick structure can be either round or square. Usually round wells are built, which are most convenient to use. The structure for filtering sewage should be buried 2.5 meters into the ground, with a diameter of no more than 2 x 2 meters.
The pit is dug in such a way that between the ground and the outer walls of the well there will be a layer of crushed stone, gravel or broken brick up to 40 cm thick. The height of the backfill is one meter. The walls at the filter level must be water permeable.
To do this, the masonry to a height of one meter is not made solid, but with small holes ranging in size from 2 to 5 cm. They must be placed in a checkerboard pattern. After the structure is erected, crushed stone or gravel is poured into the cracks.
At the bottom of the structure, a filter layer of crushed stone or gravel is backfilled to a height of one meter. In this case, large fractions of the material are placed at the bottom, small ones at the top. The hole for the pipe through which drainage from the septic tank will flow is made in such a way that water flows in a stream from a height of 40-60 cm.
A plastic sheet must be placed in the area where the water flows to prevent the filter from being washed away. The structure is closed from above with a lid or hatch with a diameter of 70 cm. It is also necessary to make a ventilation pipe in the well with a cross-section of 10 cm. It should rise above the ground by 50-70 cm.
You will find step-by-step instructions for constructing a brick drainage pit in this material.
Option No. 2 - construction of concrete rings
To construct a filtration well, you will need three reinforced concrete rings. One of them should have holes with a diameter of about 5 cm. You can buy a perforated ring or make holes using a concrete crown. You also need to make a hole for the inlet pipe.
It is necessary to dig a pit, the width of which is 40 cm greater than the diameter of the ring. A perforated ring is installed at the bottom of the structure. You don’t have to dig a hole, but only slightly deepen the area where you plan to make a well.
Place the first ring on the ground and select the ground from the inside. Gradually it will fall down under the weight of its own weight. The two upper rings are installed in the same way.
After this, you need to make a bottom filter from crushed stone or gravel up to one meter high and fill the outer walls of the well with the same material to the level of the filter layer. The hatch and ventilation pipe are installed in the same way as in a brick well.
Another option for arranging a septic tank made of concrete rings can be read Here.
Option No. 3 - a well made from old tires
The most inexpensive way to make a filter well is to make one from used tires. This design can provide filtration of sewage for a family of three. Basically, such a well is made in summer cottages, since in winter the rubber freezes and the activity of bacteria slows down, and at very low temperatures it stops altogether.
The well is made very simply - the tires are installed one on top of the other and fastened together with plastic clamps. The joints are coated with sealant. All other structural elements are made in the same order as in wells made of other materials.
Option No. 4 - plastic filter containers
Today you can purchase ready-made filter wells made of plastic, equipped with everything necessary for effective wastewater treatment. Of course, they cost a lot, but they are reliable, convenient, easy to install and maintain. There are many companies producing such equipment on the market.
For example, the Russian company POLEX-FC, whose products received good consumer ratings. Filter wells are produced in different volumes (from 1200x1500 to 2000x3000 mm), which allows you to select a product based on the daily water consumption of an individual household.
The containers are made of corrosion-resistant durable plastic, the walls of the shaft are made of primary polyethylene. The lower compartment of the tank is covered with biofilm and filled with a filter layer of crushed stone, gravel and slag.
Conclusions and useful video on the topic
Watch the video and learn how to build a brick well:
Video about the construction of a concrete structure:
You will learn how to make a well from old tires from the following video:
Filter structures perform a very important function - they provide effective wastewater treatment and do not allow dirty, untreated water to enter the ground, which, when released into the soil, causes significant harm to the environment.
It’s not that difficult to make a filtration well yourself, but if you don’t want to bother with arranging it and you have the financial opportunity, you can buy a ready-made plastic well.
If, while studying the material, you have questions about setting up filtration structures yourself, you can ask them in the comments section. There you can also share your experience in arranging filter wells.
This is the first time I've heard that such a thing even exists. When I built a house 3 years ago, the workers said that the water was centralized, but there was no sewage system. Right next to the house, a few meters away, they dug a rather deep and large hole for drainage, lined it with bricks, and covered it with a very dense concrete lid. Tell me, is it better for me to leave everything as is or install a filter well?
Lina, you already have a filter well. A filter well is a structure without a bottom, where the water gradually drains away on its own.
I recently purchased a country house, and I really want to solve the problem with wastewater.Water supply has been installed both in the house and on the street, but sewerage facilities, without which the water supply network cannot be used, are not yet available. Therefore, I’m wondering what would be better: a storage tank with pumping out all wastewater or a septic tank with a filter well. Tell me at what distance the filter well should be placed from the drinking water well and the house itself to avoid getting into the aquifer.
Good afternoon, Igor. If possible, it is better to arrange the disposal of treated wastewater into a ditch.
If this is not possible, the filtration well is installed 12 meters from the foundation and 50 meters from the drinking water well. In this case, the well should be 8-10 meters away from the septic tank. Please note that the minimum distance of the septic tank itself from the foundation is 3-5 meters, from the well the same 50 meters.
Igor, just don’t pump out all the drains (when the system is completely sealed) - you’ll get tired of calling the pumping machine all the time (and it’s not free).
Calculate, a person needs about 160 liters of water per day. Multiply by 30 days and you get 4800 liters, that's 4.8 cubic meters per month for ONE person! This is the volume of a standard car. Multiply by the number of people and the cost of the sewer flight =).
It is clear to make systems with two wells - the main one (with a bottom) and the overflow into the filter well (without a bottom). In this case, if the filtering capacity of the soil is sufficient (sand), pumping out water may not be necessary at all (only a suction pump to remove insoluble sediment - sludge from the bottom of the well as it accumulates, i.e. very, very rarely).Or, if the filtering capacity of the soil is low, you will have to call a sewage disposal machine, but MUCH less often than if there was no filter well.