Facilities for biological wastewater treatment. Biofilters

Biofilters. They are rectangular or round structures with solid walls and a double bottom: the upper one is in the form of a grate, and the lower one is solid. The grate or perforated bottom, the drainage of biofilters is made of reinforced concrete slabs. The total area of ​​the drainage holes is assumed to be at least 5-8% of the filter surface area.

The filter material is crushed stone, rock pebbles, expanded clay, slag. The loading of the filter layer along its entire height should be carried out with a material of the same size (Table 61).

Table 61

Small things in the feed material should be no more than 5%. The bottom supporting layer in all types of biofilters should be used with dimensions of 60-100 mm.

Irrigation of biofilters with sewage is carried out at regular intervals. Wastewater distribution can be drip, jet or thin layer.

Oxygen, which ensures the vital activity of bacteria, enters the filter body by natural or artificial ventilation. The amount of oxygen obtained from 1 m3 of filter material per day to reduce the BOD of wastewater is called the oxidizing power. It depends on the temperature of wastewater, outdoor air, the nature of pollution (Table 62).

Table 62

Notes: 1. Specified in the table. 62 values ​​of oxidative power have been determined for wastewater with an average winter temperature of +10°. At a different average winter wastewater temperature, the values ​​of the oxidizing power should be increased or decreased in proportion to the ratio of the actual temperature to 10 ° C

2. If the value of the hourly coefficient of uneven inflow is more than 2, the volume of the filter material should be increased in proportion to the ratio of the actual coefficient of unevenness K=2.

At an average annual outdoor temperature below + 10°C and a wastewater recirculation ratio of more than 4, as well as at an average annual air temperature of up to +3°C, biofilters of any capacity, and at an average annual temperature of +3 to +6°C, biofilters with a capacity of up to 500 m3 per day must be placed in heated rooms with an estimated internal air temperature of +20C above the wastewater temperature and five air changes per hour. With a capacity of more than 500 m3/day and an average annual air temperature of +3 to +6°C, biofilters can be placed in unheated light-weight rooms.

When sewage enters intermittently during the day, the construction of biofilters in unheated premises or open type should be justified by heat engineering calculation. In this case, it is necessary to take into account the experience of operating treatment facilities located in the area or in other areas with similar conditions.

The oxidizing power of the OM biofilter can be determined by the formulas:

when working with recirculation

, (135)

without recirculation

, (136)

where LCM is the BOD5 of the incoming wastewater mixture, mg/l;

Ld - BODb of wastewater entering the treatment, mg/l;

Lt is BOD5 of treated wastewater, mg/l;

QcyT is the daily wastewater consumption, m3/day;

F is the filter area, m2;

H is the filter loading height, m;

q is the flow rate of wastewater, l/s;

n is the recirculation coefficient determined by formula (133).

When calculating biofilters for industrial wastewater from food industry enterprises, it is possible to recommend the rate coefficient of biochemical oxidation Kc.b, indicating the rate of growth of the biological film, determined by the formula

Ks.b = 21/a, (137)

where a is the difference, percent, between COD and BOD20 of wastewater.

Low values ​​of the coefficient indicate the inexpediency of biochemical methods of wastewater treatment. The reciprocal value of the biochemical oxidation rate coefficient characterizes the growth rate of the biological film.

The rate coefficient of biochemical oxidation of a mixture of wastewater with different sizes of contaminants is determined by the formula

, (138)

where Q1, Q2...Qn are the costs of wastewater of various concentrations;

a1, a2,...an are the corresponding differences, percent, between COD and BOD20.

The smaller the coefficient, the greater the intensity of the biofilm growth factor, so the coefficient affects the choice of filter material (Table 63).

Table 63. Dependence of the type of loading material on the rate coefficient of biochemical oxidation

Biofilters are divided into drip, high-load, air filters, tower.

A distinctive feature of drip biofilters is the small diameter of the loading material fractions (30–50 mm) and the loading height (2 m), while the lower supporting layer 0.2 m high is assumed to be 60–100 mm in size, as well as the low wastewater load from 0 .5 to 1.0 mg per 1 mg filter load.

Highly loaded biofilters differ from drip filters by a significantly higher hydraulic load. For drip biofilters, the load per 1 m2 of surface per day is 1–2 m3 of wastewater, for highly loaded ones it is 10–30 m3 per 1 m2 of surface per day, i.e., 10–30 times more.

The higher oxidizing power of highly loaded biofilters is due to non-silting, better air exchange, which is achieved due to larger feed material and increased water load. Significant speeds of water passage through the feed material provide a constant removal of difficult-to-oxidize impurities and dying biofilm. The particle size of the load is assumed to be 40–60 mm, which provides a large pore volume.

The design and operational features of highly loaded biofilters and their difference from drip filters are as follows:

1. the height of the filter bed layer reaches 4 m. The amount of contaminants introduced per 1 m2 of filter area per day depends on the height of the filter. At a height of 4 m, the oxidizing power is 2400 g O2/m2, 3 m - 2200, 2.5 m - 2000, 1 m - 1800 g O2/m2;
2. grain size reaches 65 mm over the entire loading height;
3. artificial ventilation of the filter is provided by a special design of the bottom and drainage (fencing with blank walls with a water seal);
4. the intervals in filter irrigation with waste water should be reduced to a minimum. The water load must be increased and constant;
5. directing concentrated wastewater to filters is unacceptable, therefore, in order to maintain an increased water load, it is necessary to dilute them with conditionally pure or treated water using recirculation;
6. highly loaded biofilters can operate at a given degree of wastewater treatment;
7. are used for both complete and partial wastewater treatment.

Highly loaded biofilters can be one- (Fig. 19) and two-stage.

Rice. 19. Scheme of single-stage highly loaded biofilters: P.O. - primary sump; N.S. - pumping station; B - biofilter; IN. - secondary settling tank, K.B, - coagulation basin; 1,2 - possible options for recirculation of the purified liquid, 3 - removal of excess biofilm; 4 - chlorine; 5 - treated and disinfected wastewater and outlet.

The use of two-stage high-load biofilters is recommended in case of favorable terrain and if deeper wastewater treatment is required. A variety of highly loaded biofilters can be intermittent filtration facilities (Fig. 20).

Rice. Fig. 20. Scheme of two-stage high-load biofilters with intermittent filtration: PO - primary settling tank, K1, K2 - switching chambers, IS - pumping station, B - biofilters, VO - secondary settling tanks, KB contact pool, 1 - removal of excess bnoplenka, 2 - chlorination, 3 - treated wastewater for release

Air filters are a variety of highly loaded biofilters. A feature of this type of filters is their high height (3-4 m) and forced ventilation, which can be carried out by low-pressure fans.

The loading material of the air filter body should be as smooth as possible. Air filters are arranged two- and three-layer. It is recommended to arrange the lower layer with a thickness of 0.2 m from pieces of loading material 50–70 mm in size, and the upper layer 30–40 mm in size (Fig. 21).

Rice. 21. Scheme of the air filter: 1 - loading, 2 - jet water distributor, 3 - water seal

Stable operation and a high cleaning effect on air filters can be achieved if the wastewater sent for treatment has a BOD of no more than 150 mg/l. The calculation of air filters can be carried out according to their oxidizing power (Table 64).

Table 64

Table data. 64 are defined for wastewater with an average winter temperature of +10°C. When the wastewater temperature is more or less than +10°C, the oxidizing power of the air filter must be increased or decreased, respectively, in proportion to the ratio of the actual temperature to +10°C.

Comparison of biological treatment systems

Anyone who has at least once encountered the problem of cleaning sewer, industrial and domestic wastewater is familiar with the concepts of "biofilter" and "aerotank". These structures, used in the biological processes of water purification, have gained quite high popularity in recent years. They are actively used in private residential construction, providing autonomous wastewater treatment.

What is the biological method of wastewater treatment based on? It is based on the use of a special kind of microorganisms capable of processing substances of organic and inorganic origin dissolved in water as part of their own life support processes. In particular, these microorganisms are capable of destroying organic compounds (nitrites, sulfites, hydrogen sulfide), decomposing them into constituent elements - water, ions, carbon dioxide, etc. Substances that cannot be decomposed into constituent components become part of the biomass. And the process of destruction of substances of organic origin is called biochemical oxidation. It is the ability to oxidize that determines the possibility of biochemical destruction of certain substances.

Biofilter or aerotank - both of these options for biological treatment facilities serve the same purpose - wastewater treatment to a state that is safe for the environment, to MPC standards.

1. Biofilter

A biofilter is a treatment facility filled with filter elements and equipped with a certain supply of microorganisms that form a special film on the surface. In fact, it is the vital activity of the biomass present in this structure that determines the effectiveness of wastewater treatment processes.

All biofilters are divided into categories, according to:

• the declared number of purification levels is single- and two-stage options;
• according to the principle of providing air access - forced (artificially ventilated) and with natural ventilation;
• degree of purification (with full or partial loading);
• type of loading material / filler - with granular filling (expanded clay, crushed stone, slag, pebbles are used, or planar - filled with meshes, plastic sheets, metal sheet materials, prefabricated metal blocks (cellular or lattice), pipe trimmings, filling elements made of plastic, ceramics , metals.

All volumetric biofilters can be divided on the:

• drip - fine-grained, with a backfill height of 1-2 m and an element size of not more than 30 mm;
• high-load - aeration, with a more intense effect, equipped with a forced ventilation system (the size of the fractions in this case reaches 60 mm, and the loading height is 4 m);
• tower - deep structures, the loading height of which reaches 18 m with fraction sizes up to 80 mm.

In addition, there is a category of submersible biofilters that allow for local filtration of wastewater at the place of demand. They are drum or screw structures coated with a biofilm that provides the necessary level of microbial content during cleaning.

2. Aerotank

It is an aerated treatment plant made of fiberglass or reinforced concrete, the process of wastewater treatment in which is carried out by mixing active sludge biomass with aerated (oxygenated) wastewater.

Aerotanks can provide different levels of water purification - from partial (with the removal of elements that cause decay and purification to the level of decomposition of wastewater into water, nitrates and other components) to complete, providing deep biological water purification.

Aerotanks are equipped with various aeration devices - pneumatic, mechanical, mixed, providing the saturation of waste masses with oxygen necessary for their effective treatment.

The aeration tank can introduce effluents according to the principle of flow-through or semi-flow flow, by contact or on the basis of a variable working flow.

There are options with a different number of purification steps - usually no more than two.

In addition, they can have different loads on active biomass and subdivided into subspecies according to the selected hydrodynamic regime:

• displacing,
• mixing,
• with distributed release.

What to choose?

Biofilters and aeration tanks are the ideal solution for clay-dominated soils or areas with high groundwater levels. In fact, these are high-tech developments focused on the deepest wastewater treatment - within 60 - 98% .

If we talk about comparing a biofilter or an aerotank, then it all depends on what the operating conditions of the treatment plant will be. If the site needs a simple and non-volatile cleaning system, biofilters should be preferred. If the main emphasis is on quality, it is worth choosing an aeration tank that can provide the highest level of wastewater treatment, but requires constant access to power and requires maintaining a certain level of humidity in the system.

Argel

The process of removal and oxidation of organic wastewater contaminants in biological filters does not fundamentally differ from similar processes occurring during wastewater treatment in other biological treatment facilities, however, the course of the process in biological filters largely depends on the design features of these facilities. In particular, the design of a biological filter determines the specifics of the hydrodynamic conditions in it, and, consequently, the nature and speed of the supply of organic substances and oxygen from the air to the cells of microorganisms of the biological film, the removal of products of biochemical reactions from them, which in turn affects the speed of the wastewater treatment process and efficiency of buildings.

Cleaning is carried out when the flowing waste water comes into contact through the load with a biological film fixed on its surface. The course of mass transfer processes occurring in the elementary volume of a biological filter is schematically shown in Fig. 2.1 a. The transfer of pollution is determined by the laws of molecular and turbulent diffusion of matter. With molecular diffusion, mass transfer occurs both due to the difference in the concentrations of substances at the interface between liquid - air (maximum concentration of contaminants) and liquid - biofilm (minimum concentration). Turbulent diffusion occurs due to fluid mixing as it flows through the biological filter media. In this case, the rate of turbulent diffusion can be much higher than the rate of molecular diffusion.

t/Started Soda

Airyaoneni*

air

Ppo?f/ktmreactions -

Lorobos

I HjP?/dot I sTioplesnka

Oresniches/fue of the best biogenic j/sments MP da, Mg, b and dp.

Rislorod

And in I P I » I *u

biological

film

C0 Zl H;0, H0 2j Wj

Energy

Biomass growth

EnergyWMC

nonstructishexchange

Rice. 2.1.Schemes of mass transfer processes occurring during wastewater treatment on biological filters (a), and oxidative processes, occurring in the biofilm (b)

Air oxygen, necessary for the biological process, comes to the biofilm from the pore space of the biological filter loading. The transfer and fixation (sorption) of organic substances on the cell surface or in the pericellular space is accompanied by the hydrolysis of complex compounds under the action of various enzymes, as well as as a result of the diffusion of substances through the permeable cell membrane.

In the course of intracellular processes, organic substances are oxidized (energy metabolism) and new cell material is synthesized (constructive metabolism). The oxidation process is accompanied by the release of energy, the synthesis process comes with its consumption (Fig. 2.16).

The decay products of organic pollutants are carried out of the biogas tank into the liquid layer and removed with the liquid flow (dissolved substances) and with the air flow (gaseous). At the same time, the excess (growing) biofilm is washed out by the liquid flow, which is removed from the biological filter along with purified water. To separate excess biofilm, treated wastewater after biological filters is settled in secondary settling tanks.

The nature of the process of wastewater treatment on a biological filter is shown in fig. 2.2. As can be seen from the figure, the concentration of organic contaminants b n first, it rapidly decreases with the duration of the process from r 0 to which indicates high rates of pollution removal in this area. At the same time, the amount of biofilm sharply increases (curve 2) compared with the initial C n, and the growth rate of biosilane microorganisms as the concentration of contaminants in the liquid decreases gradually. By time /1, the amount of biofilm becomes stable, since the lack of nutrition inhibits further cell growth.

Rice. 2.2.

1 - concentration of organic contaminants; 2 - the total mass of the biomass fixed on the feed and circulating; 3 - mass of biofilm fixed on the biological filter loading; 4 - concentration of nitrites and nitrates; 5 - ash content of biomass

The increase in biomass at this point in time is maximum. With a further increase in the duration of the wastewater treatment process in the biological filter, the concentration of organic contaminants continues to decrease (curve /), but the speed in sections b - / 2 and / 2 - b significantly lower than at the beginning of the process. Due to the low residual concentration of contaminants in the liquid, the lack of sufficient nutrition for the vital activity of biofilm microorganisms, the process of biomass death (self-oxidation) begins in these areas. Part of the biofilm is washed off from the biological filter loading and enters the treated liquid. Due to the decay of biomass, its total amount decreases (curve 2), the amount of biofilm fixed on the load also decreases (curve 3), the ash content of the biomass increases (curve 5).

Section I (see Fig. 2.2) with a duration of the wastewater treatment process from /] to? 2 characterizes the mode of operation of biological filters at incomplete biological treatment. When operating in this mode, the concentration of contaminants according to the VPK decreases to 100...30 mg/l, a large increase in biomass is observed, the process proceeds without nitrification.

With the duration of the cleaning process from to b(section II) biological filters operate in the mode complete biological treatment; The MIC of the liquid is reduced to b 0 -= 15...25 mg/l, nitrites and nitrates appear in the purified liquid (curve 4). The amount of biomass, both fixed on the biological filter loading and carried out with the purified liquid, decreases due to autoxidation processes.

Increasing the duration of the process from and up to / 4 is accompanied by further decay and, consequently, a decrease in the amount of biomass in the biological filter (curves 2 and 3), its ash content increases. This section III characterizes the regime biomass stabilization, similar to the mode of continued aeration in wastewater treatment with activated sludge. When biological filters operate in this mode, it is possible to obtain the smallest increase in biofilm, a high degree of mineralization of excess biofilm removed from the biological filter, which makes it easier to further process it. Stabilized excess biomass removed from biological filters operating in this mode does not require additional fermentation and can be immediately sent to sludge beds for drying.

The concentration of wastewater pollution in section III not only does not decrease compared to the concentration of pollution in section II, but may even increase somewhat (curve 1 ) due to secondary contamination of the treated liquid with biomass decay products. At the end of section III with the duration of the process C in the biological filter, microorganisms develop that are adapted to the residual hard-to-oxidize pollution of wastewater, which leads to a further decrease in the concentration of pollution.

Section IV characterizes the operation of biological filters in the mode post-treatment of waste water up to the value of residual pollution according to the military-industrial complex b th= 15...5 mg/l. In this mode, the increase in biomass is extremely insignificant, the ash content of excess biomass is high, and the nitrification process proceeds intensively.

The considered course of the process of wastewater treatment on biological filters at the contact illustrates the possibility of operating these facilities in various modes, and their mode of operation, adopted on the basis of local conditions and the required quality of treated wastewater, determines the choice of the design of these facilities, the technological parameters of their operation, the scheme of the entire cleaning station.

The main technological parameters that determine the mode of operation of biological filters are: load on organic contaminants, oxidizing power, hydraulic load, average duration of wastewater flow, recirculation coefficient, flow rate of supplied air.

is measured by the amount of organic pollutants supplied with wastewater to the biological filter per unit time, and is the main indicator that determines the regime and conditions of the biological process (see Fig. 2.2). Usually, they use the specific load according to BOD full, referred to 1 m 3 of the volume of the biological filter: N - b en QJW, where N- specific

load according to BOD P0L11, g / day-m 3; b en- BOD is full of initial sewage, g/m 3 ; 0^, - wastewater consumption, m 3 / day; ]G- biological filter volume, m 3 .

To compare the operating modes of biological filters, it is more correct to determine the specific load per unit area of ​​the biofilm surface or the surface area of ​​the loading fractions: S = b e „ 0, ^ a, where - specific load, g / day-m 2; /in - loading surface area, m 2 .

oxidation power, or the performance of a biological filter in terms of the amount of organic contaminants removed in the wastewater treatment process, expressed in grams of BOD full per 1 m 3 load per day: OM = (b en ~ () * / no., where OM - oxidizing power, g / day-m 3; A^-BODtotal treated wastewater, g/m 3 .

- the amount of wastewater entering the biological filter, referred to 1 m 2 of the area of ​​\u200b\u200bthe structure in the plan: c - () „ / Г, where q- hydraulic load, m 3 /m 5 -day; biological filter area, m 2 .

Average duct duration wastewater through a biological filter Gco depends on the hydraulic load, the height of the biological filter, the method of supplying wastewater to the surface of the load, the type of load and the distribution of biofilm in it. The value of g cf is an indicator of the duration of the wastewater treatment process in the biological filter. With an increase in hydraulic load, the speed of fluid movement through the biological filter increases and the duration of the flow decreases; with an increase in the height of the biological filter, the residence time of the wastewater in the load increases. The load, as well as the biofilm fixed on it, by resisting the movement of the flowing liquid, thereby determine the path along which the flow of the liquid moves, and therefore, affect the duration of the duct.

Recirculation ratio- the ratio of the flow rate of the recycled purified liquid to the total flow rate of the initial wastewater entering the biological filter, P= (2u-

Recycling, i.e. repeated passage of a part of the purified LIQUID through a biological filter makes it possible to increase the duration of the purification process, reduce the initial concentration of contaminants in the source wastewater and increase the hydraulic load, which ensures that the loading of the structure is flushed during its operation. The recirculation coefficient is taken depending on the maximum permissible concentration of contaminants according to the BOD of a mixture of initial and recycled wastewater, which can be directed to a biological filter without fear of silting of the pores of the load as a result of biofilm growth. The recirculation coefficient is determined by the formula P = (L en - L mix)/ (L mix - Lex), where L mix-BOD p0LN mixture of initial and recycled wastewater, g/m 3 .

The amount of oxygen required for the oxidation of organic wastewater pollution by biofilm microorganisms, must be provided by supplying an appropriate amount of air to the body of the biological filter. The lack of oxygen slows down the rate of the biological process. However, the influence of the amount of air supplied on the speed of the cleaning process is only effective until the process is fully supplied with the required amount of oxygen. If sufficient air exchange in the pore space of loading biological filters is not provided by natural ventilation, then forced air supply is provided.

The most important structural element of a biological filter is the loading. The type and characteristics of the load significantly affect the flow of the wastewater treatment process. Biofilter loading is characterized by the following main parameters: layer height, specific surface area, porosity and loading density. The height of the loading layer, or the working height of the biological filter, determines, along with other parameters, the residence time of wastewater in the biological filter.

The total surface area of ​​the biofilm fixed on it and, consequently, the area through which the transfer of organic contaminants from the fluid flowing around the load to bacterial cells also depends on the specific surface area of ​​the load. As a rule, the process of mass transfer is a factor limiting the rate of removal of contaminants, and therefore the oxidizing power of the biological filter largely depends on the surface area of ​​the load.

It should be noted that for the wastewater treatment process, it is the surface area of ​​the biofilm that is important, and not the total amount of biomass in the feed. With the accumulation of biomass, the thickness of the biofilm increases, and only the outer aerobic layer remains actively working. Inside, at the surface of the load, an anaerobic zone is formed (Fig. 2.1a), which almost does not participate in the process of removal and oxidation of contaminants. An increase in the amount of biomass reduces the volume of the pore space of the load, makes it difficult for air exchange in the biological filter, as well as the supply of microorganisms with atmospheric oxygen. The porosity of the biological filter loading should be such that, under the steady state operation of the structure (when the amount of biofilm in the loading remains constant and its growth corresponds to the removal), the volume of free pores is sufficient to supply the biofilm with atmospheric oxygen.

The loading used for biological filters can be conditionally divided into two types: volumetric and planar. Crushed stone, gravel of strong rocks, coke, expanded clay and other materials are used as volumetric loading, characterized by a certain size of fractions, mechanical strength and resistance to destruction. Such material has a porosity of 40...50%, a density of 500...1500 kg/m3, and a specific surface area of ​​30...120 m2/m3 depending on the size of the loading fractions.

Sheet material (plastic, asbestos cement, etc.), soft roll materials (plastic film, synthetic fabrics), as well as filling elements (rings, pipe sections, etc.) are used as flat loading. Loading from sheet materials is performed in the form of various blocks and cassettes, which are placed in the body of the biological filter, soft roll materials are fixed on frames or freely suspended.

The porosity of flat loading from sheet materials is 80...97%, from rolled materials - 94...99, from filling elements - 70...90%. The specific surface of sheet and roll loading - 80 ... 130 m 2 /m 3, backfill - 70 ... 100 m 2 /m 3, sheet loading density 40-100 kg / m 3, roll - 5 ... .60 kg / m 3, filling - 100 ... 600 kg / m 3.

The use of flat loading makes it possible to simplify the design of the biological filter, reduce construction and installation costs.

What is a biofilter? This device has a container of a certain shape, which, using biomaterials, purifies wastewater.

What is a biofilter? This device has a container of a certain shape, which, using biomaterials, purifies wastewater. These biomaterials are composed of various microorganisms. With the help of changes in the temperature of the atmosphere and the liquid being cleaned, uninterrupted air circulation is carried out during the cleaning work. This is necessary so that the microorganisms in the container receive the oxygen they need to live.

Types of biological filters.

In biofilters, there are various materials that are loaded into them. You can highlight such as:

1. Filters using volumetric loading. They may contain pebbles, rubble and so on.
2. Flat load technology. They are made from strong types of plastic, functioning in the temperature range from 6 to 30 degrees.

According to technological schemes, they are divided into:

• Biofilters with two stages of purification, producing water of high purity. They are usually used in severe weather conditions or when the height of the instrument is limited.
• Biological filters with one stage.

According to the quality of cleaning, the following types are divided:

• Complete cleaning.
• Not a complete cleaning.

By type of air transmission filters are divided into:

• With natural delivery.
• With artificial air circulation.

It is also possible to distinguish 2 modes of functioning of biofilters:

• With recirculation - heavily contaminated liquid is supplied in small volumes for better cleaning.
• Without recirculation - used if the water is not very polluted.

Depending on the amount of purified water over a period of time, the following are distinguished:

• Drip - with a small permeability of water.
• Highly loaded - with the ability to clean large volumes.

Biological filters applying volume load are divided into:

• Drip. They have little performance. If the layer size is 2 meters, then their loading will be 2-3 centimeters.
• Highly loaded. With a 4-meter layer, their loading will be 4-6 centimeters.
• Tower filters are produced 16 meters high and have a grain size of 4-6 centimeters.

All of the above types of biofilters can be implemented, installed and launched by our company site.

Filters using flat loading.

Reinforced loading is performed by pipe elements, rings and similar components. Metal or plastic chips are placed in the tank. The cleaning layer can be up to 6 meters.

The softened load is produced by a metal mesh, synthetics or plastic film. The load is laid by the roll method or attached to the body. The height of the load will be 8 meters, and the porosity will be at least 95 percent.

Biological filters for immersion - containers with a concave bottom. Metal, plastic or asbestos discs are attached above the level of the liquid to be cleaned. These discs are attached at a distance of 1-2 centimeters from each other.

Scheme of functioning of the biofilter.

Water supply can be of two types: jet and drip. Air masses are collected from the surface. The previously treated low-pollution wastewater flows by itself into the distribution compartment, which discharges it in parts over the load mass. After that, the water mass flows into the drainage system, then to the trays outside the boundaries of the biofilter. The biofilm is removed from the other sump.

Biological filters of drip type imply work with a small, organic load. In order for the filter to be cleaned of dead film in a timely manner, hydraulic loading is performed.

Drip-type biofilters cannot be adjusted to the variability of external factors. When using, look at the degree of contamination and the condition of the filters. It is much more profitable to make a complete change of the load, since its cleaning is very expensive. Waste water with a concentration of suspended particles of no more than 100 milligrams per liter should be poured into the filter.

A very important factor in use is the aeration of the biofilter. The amount of oxygen should not be lower than 2 milligrams per litre. From time to time it is important to clean the recess under the drain and above the bottom.

The drip-type biofilter reacts very hard to cold winter winds. For high-quality operation of the filter, wind protection is installed. A different load leads to swamping of the biofilter, which can be removed by changing the load. The operation of the filter can also be affected by foreign matter in the feed and dosing containers.

Highly loaded biological filters

This type of biofilters is characterized by increased air exchange and, consequently, oxidizing power. Increased air exchange is carried out with a large fraction of the load and an increased load of water.

Purified water masses move at high speed and carry away difficult-to-oxidize substances and biofilm. Oxygen is wasted for the rest of the pollution.

Filters with a high load are characterized by a high loading layer, increased drainage granularity and a special type of bottom in order to artificially circulate air masses.

Flushing of this type of biofilter can only be carried out with an uninterrupted and constant supply of water.

The higher the loading height, the more efficient the biological filter and vice versa.

Design and operation of filters

Biofilters may include:

• The body of the biofilter is a load for filtration, which is located in a container that is open for water masses to enter it. Fillers must be of low density and increased surface area.
• A device that distributes water. It provides systematic irrigation of the load with untreated water.
• Drainage.
• A device that distributes air masses. Produces oxidation reactions with the help of oxygen. These reactions in biological filters are similar to irrigation of land, but at a higher rate.

The principle of operation of the biological filter

Loading purifies water from undissolved substances that have passed through the settling tanks. Microorganisms exist in it by means of the oxidation of organic matter. The remaining organic substances serve to increase the biological mass. 2 effective processes are carried out: unnecessary organic substances are killed in the water and the biofilm is increased. Masses of sewage will take with them the dead part of the biofilm. Ventilation supplies oxygen in two ways: artificial and natural.

Filter calculation

Drip type biofilters

The calculation is needed in order to find the effective size of the load and the parameters of the water distribution device, as well as the size of the tray to drain the liquid. The load size is calculated from the oxidation power - OM. Oxidation power is the amount of obligatory oxygen per day. It is influenced by the temperature of the liquid and air, loading materials, air supply methods, and so on. When the average annual temperature is below three degrees, the biological filter should be moved to a more heated environment with 5 times the air supply.

For biological filters with a high load, there is an exact calculation method:

The limiting concentration of pollution of the incoming water mass is calculated. Further, using the formulas, the recirculation coefficient is determined. There are methods for counting biofilters, which use complicated formulas, but which will give results of high accuracy.

Ventilation of biofilters

As mentioned above, biological filters have 2 types of oxygen transfer, natural and artificial. The type of ventilation is chosen depending on the type of biofilter and weather conditions.

For filters with a high load, ventilation with low pressure is used. As for air filters, artificial ventilation is used for them. Installing a filter in a confined space implies the mandatory supply of air masses into it.

There must be constant air circulation, because interruptions can raise the temperature to 60 degrees and cause unpleasant odors from the decay of the biological film.

The filter functions effectively at temperatures over six degrees. In cases where the temperature of the liquid is below six degrees, it is necessary to heat it before serving.

In order to prevent the biofilter from freezing during the cold seasons, wind protection is used and the coefficient of uneven water supply is reduced. Then carry out restrictions on the flow of cool air: 60 minutes per 1 sq. meter is supplied no more than 20 cubic meters. meters. Ventilated grilles are equipped with blinds, fabric protection.

The width of the biological film directly affects the balance in the biofilter. The greater the width, the more likely it is that the air masses will stop flowing and the process of decay will begin. This problem is more often encountered when using filters of the drip type.

It used to be thought that the natural supply of oxygen was possible only because of the different temperatures. But in the end it became known that it is influenced by diffusion processes.

They do their job well and show high performance. The water purified by the septic tank can be used for useful purposes or simply soaked into the ground. In addition to the septic tanks themselves, it is sometimes necessary to use additional equipment for post-treatment. If it is necessary that the water goes into the ground or any other place as clean as possible, you should install a wastewater treatment system in the form of a biofilter for a septic tank. It happens that the water absorption of the soil is such that the effluents after the sewerage are not absorbed, and this is a fairly common option, or you intend to use the water to irrigate the garden plot or dump it into the reservoir. For some reason it is impossible to install a biological treatment plant, we recommend that you think about purchasing a biofilter for water purification. On this page you will find up-to-date material on these two types of additional equipment for septic tanks.

Varieties of wastewater disposal systems

It is advisable to use treated wastewater disposal systems with low soil permeability. They allow more efficient removal of purified water and, in addition, contribute to its filtration. Let's consider four main types of treated water drainage systems.

1. Field absorption

This system is popular with many of our customers. It is easy to install, inexpensive and yet effective.

The installation of the system is carried out as follows: a trench of the required width and depth is excavated near the installed biological wastewater treatment plant or septic tank. A layer of large rubble is poured at the bottom, forming a pillow for the drainage system. Then the system itself is installed. If the depth at which it is located does not exceed 120 cm, the system must be insulated (most often with sand). Then she carefully digs in.

The principle of operation of the absorption field: the water purified in the septic tank enters the soil through the drainage system, passing through sand and gravel. This contributes to its filtration (post-treatment) and rapid absorption.

2. Absorption well

This system is best suited for sandy soils with moderate water tables. More difficult to install than field absorption, however, and more efficient.

The installation of the system is carried out as follows: at a certain distance from the sewer station, a pit is dug. Through a trench, it connects to the station foundation pit. A container without a bottom is installed in the pit (essentially a well). It can be made of fiberglass, concrete rings or other waterproof materials. A layer of rubble is poured at the bottom of the well.

The cleaning station and the well are connected by a pipe located at a slight slope. The principle of operation of the absorbent well: the treated drains, flowing down the pipe, enter the well, and then, passing through the layer of rubble and being filtered, go into the ground.

3. Filter field

In fact, this treated wastewater disposal system is a modernized and improved Absorption Field system. It is more voluminous and time-consuming, however, and much more effective. The installation of the system is carried out as follows: a pit of the required shape and size is dug near the cleaning station. A layer of gravel is poured at the bottom. A two-level pipe system is installed on it. Then the sand layer is poured. After that, another layer of rubble is laid. The final step is to fill the remaining space in the pit with soil.

The principle of operation of the filtration field: the same as that of the absorption field. The only difference is that the water, before entering the ground, also passes through the sand and gravel layer.

4. Filter cassette

Another type of withdrawal systems. It will be convenient for those who have little space on the site for the absorption / filtration field.

The installation of the system is carried out as follows: from the cleaning station, a pit is dug of the required shape and size. The bottom of the pit is covered with rubble. A cassette is installed on it (a structure made in the form of a box with several compartments and an outlet pipe). Cassette sections are filled with filter materials (sand, crushed stone). After installing and connecting the inlet pipe, the pit is buried.

The principle of operation of the filter cassette: treated wastewater enters the filter cassette through the inlet pipe. Passing through all sections with filter materials, they are subjected to post-treatment. Then, through the outlet pipe, the treated effluents enter the ground.

The principle of operation of the biofilter and its design features

The biofilter performs post-treatment of wastewater. Used in conjunction with septic tanks. A biofilter for water is especially convenient where it is impossible to install a system for removing treated effluents. And such cases are possible with the following factors:

• The site has a high level of groundwater;
• On the site there is a well or a well with drinking water;
• The soil of the site has low filtration and absorption rates (for example, clay);
• Discharge of treated effluents into the water protection zone (in such cases, additional UV treatment is often used; treatment of processed effluents up to 100%).

The biofilter for sewage treatment is a special type of container filled with expanded clay. Through the inlet pipe, clarified wastewater (purified by 65-70%) is supplied (usually by gravity) to the biofilter. The liquid fills the entire biofilter loading area and undergoes aerobic oxidation. The wastewater is then treated with aerobic bacteria. After the filter is put into operation, in the first 2-3 weeks in the area of ​​​​inert loading, in the first chamber of the biofilter, a biofilm is formed from bacteria, microorganisms and various fungi. Bacteria and fungi oxidize organic compounds that come with wastewater. They are also food for various microorganisms. For example, ciliates or rotifers. Thanks to this biological activity, the biofilms are constantly rejuvenated and the water purification process is permanent. To accelerate the development of bacteria, special enzyme additives are used. The supply of oxygen necessary for the activity of bacteria and microorganisms is provided by a natural ventilation system. There is no need to use any technical means for its functioning. After cleaning, water enters the second chamber, and from there it is discharged from the filter with the help of an outlet hose. As a result of the considered processes, wastewater is purified by 90-95%.

It is important to remember that the biological treatment filter is only supplementary equipment for septic tanks. Its use without a septic tank is strictly prohibited and is fraught with clogging of the chambers and even failure of the entire filter. Thinking about buying a septic tank? Visit the relevant pages of our website - we have something to offer you.

Where to buy biofilters and wastewater disposal systems?

In our company, you can purchase the treated wastewater disposal systems discussed on this page, as well as "Flotenk" biofilters, designed for a different number of users. By purchasing septic tanks, drainage systems or biofilters for wastewater treatment in our company, you get free professional advice, free departure (up to 50 km) and measurement, design of an autonomous sewage system, as well as high-quality installation from experienced and competent specialists.