K category: Sewage treatment

Biofilters

Biological filters are facilities in which the process of biological wastewater treatment takes place under artificially created conditions. Biological filters are periodic (contact) and continuous action. Contact biofilters are not currently used due to their low throughput and high cost. Continuous biofilters in terms of throughput can be divided into drip and high-load, according to the method of supplying air to them, both can be with natural and artificial ventilation (air filters).

Drip biofilters. Drip - continuously operating biofilters in foreign practice are sometimes called irrigation or percolator.

Continuous drip biofilter consists of the following main parts: impervious base, drainage, side walls, filter material and distribution devices. Biofilters can be round, rectangular, square. The surface of the drip biofilter is irrigated from above evenly at short intervals; in this case, water is supplied in the form of drops or jets (drip or irrigation) or in the form of a thin layer of water (percolator).

In domestic practice, air enters drip biofilters in a natural way - from above through the open surface of the biofilter and from below through drainage. They have low water loads (no more than 0.5-1 m3 of waste water per 1 m3 of feed material), as well as a smaller size of load fractions (20-40 mm) compared to highly loaded biofilters.

Passing through the filtering load of the biofilter, contaminated water, due to adsorption, leaves in it suspended and colloidal organic substances that have not settled in the primary settling tanks, which create a biofilm densely populated by microorganisms. Biofilm microorganisms oxidize organic substances and obtain the energy necessary for their life. Some of the dissolved organic substances are used by microorganisms as a plastic material to increase their mass. Thus, organic substances are removed from the waste water, and the mass of the active biological film increases in the body of the biofilter. The spent and dead film is washed off by flowing waste water and removed from the biofilter.

The biofilter (Fig. 1) works as follows. The wastewater clarified in the primary settling tanks by gravity (or under pressure) enters the distribution devices, which periodically let water onto the surface of the biofilter. The water filtered through the thickness of the biofilter passes through the holes in the perforated bottom (drainage), enters the solid impermeable bottom, from which it flows down the drain trays located outside the biofilter. Then the water enters the secondary settling tanks, where the removed biofilm, separated from the treated wastewater, is retained. The cleaning effect of normally operating biofilters of this type is very high and can reach 90% or more in terms of BOD.

When calculating the biofilter, the required volume of feed material is determined for the treatment of incoming waste water, as well as distribution devices for irrigating the load with water, drainage and trays that collect clarified water are calculated. In the domestic practice of designing drip biofilters, the volume of the filter load is determined by the oxidizing power of the biofilter. Oxidizing power - the number of grams of oxygen that can be obtained from 1 m3 of feed material per day to reduce the biochemical demand of wastewater. The oxidizing power of a biofilter varies widely, since its value depends on many factors: the temperature of the waste water and the outside air, the properties of the incoming liquid, the load material, the method of air supply, etc.

Rice. 1. Biofilter 1 - distribution layer; 2 - supporting layer; 3 - concrete; 4 - drainage; 5 - collection tray; 6 - supply of waste liquid

Highly loaded biofilters. In 1929 in the USSR and in 1936 in the USA, new types of biofilters appeared, which in domestic practice were called air filters, and in foreign practice - highly loaded biofilters. In the USSR, air filters were proposed by professors N. A. Bazyakina and S. N. Stroganov. They were first built in 1929 at the Kozhukhov biofiltration station and have a clear advantage over drip, so they are widely used. Highly loaded biofilters differ from drip filters both in design and operational features.

The structural differences are:
1) increase in the grain size of the loading material (40-70 mm over the entire loading height); the material can be crushed stone of hard rocks;
2) artificial blowing of the loading material with air, and in connection with this, a change in the design of the bottom and drainage;
3) an increase (if necessary) in the height of the filter bed layer.

Operational features include:
1) mandatory irrigation of the entire surface of biofilters with incoming water and, if possible, reducing the duration of interruptions in the supply of water to the surface;
2) increasing the water load per 1 m2 of surface in order to create natural conditions for spontaneous filter washing;
3) dilution, if necessary, of the incoming effluent with treated wastewater, i.e., the introduction of recirculation.

Studies have established that high-load biofilters can provide any throughput and any degree of purification, depending on certain design features and their operating mode that are specified.

Highly loaded biofilters should be classified according to such criteria.

1. According to the principle of action - working with complete or incomplete biological treatment. Initially, biofilters of this type were designed only for incomplete biological treatment. It was assumed that the filters can have an increased throughput only if they remove easily oxidizable contaminants in the wastewater and the outgoing effluent has a WPC above 20 mg/l; in addition, the process of nitrification in biofilters does not occur. However, later studies2 found that highly loaded biofilters can provide a very high cleaning effect.

2. According to the method of air supply - with natural and artificial air supply; in the second case, they are often called air filters. If the loading height in biofilters is small (1.5-2 m), then artificial air supply is not necessary; at a high loading height, it is necessary to provide artificial air injection.

Rice. 2. Scheme of single-stage operation of biofilters with recirculation

3. According to the mode of operation - with recirculation and without recirculation. If the concentration of the incoming polluted effluent to the biofilter is low and the water flow to the biofilter is sufficient for its spontaneous washing, then recirculation of the effluent is not necessary. With a heavily polluted effluent, recirculation is desirable, in some cases mandatory.

4. According to the number of steps - single-stage (Fig. 2) and two-stage. A two-stage operation of the biofilter is provided if complete biological treatment is necessary and the biofilters of the 1st stage cannot be designed with sufficient height. In this case, in stage I, incomplete treatment of the effluent will be carried out, and in stage II, its additional treatment.

5. In height - low up to 2 m, high from 2 m and above.

6. According to the design features of loading - with bulk loading (gravel, crushed stone, expanded clay, etc.) and with flat loading.

Biofilters with flat loading are subdivided: with rigid loading in the form of rings or pipe cuttings made of ceramic, plastic and metal filling elements; with rigid loading in the form of gratings or blocks of flat and corrugated sheets; with soft or roll loading from metal meshes, plastic films, synthetic fabrics, which are attached to frames or stacked in rolls.

High biofilters are designed for complete biological treatment, low - for partial.

Biofilters with plastic loading. A distinctive feature of these filters is that they work on a plastic material in the form of gratings, bags or plastic rings. Favorable conditions for air flow around the filter media provide higher throughput than other types of biofilters. The load in them for urban wastewater (according to the research of the Sewerage Department of the Moscow Institute of Civil Engineering) can be increased to 10 m3 of water per 1 m3 of material loading. As a loading material, plastic blocks made of polyvinyl chloride, polystyrene and other rigid plastics are used, as well as a plastic nozzle from shortly cut perforated pipes assembled into blocks or poured into a biofilter. Such biofilters are designed round or polygonal in plan with a height of 3-4 m. Usually they are located in a heated room.

Biofilter designs. In domestic practice, the most widely used biofilters are rectangular or round. On fig. Figure 3 shows a typical rectangular precast concrete biological filter developed by Soyuz-vodokanalproekt. A drainage is arranged on a concrete waterproof base, which drains water and provides favorable conditions for aeration of the biofilter load. Most often, drainage is performed from reinforced concrete slabs laid on concrete supports.

Rice. 3. Typical rectangular biological filter with sprinkler water distribution 1 - prefabricated blocks; 2 and 3 - beams and floor slabs; 4 - distribution chamber; 5 - service platform

Rice. 4. Highly loaded biofilter made of prefabricated reinforced concrete 1 - rubble foundation; 2 - drainage floor slabs; 3 - prefabricated wall elements; 4 - prefabricated plate; b - ventilation pipes; 6 - grate plates

The loading material must have a developed surface with particle sizes that ensure the rapid formation of a microbial film. At the same time, the feed material must be sufficiently porous, as this contributes to good aeration of the filter load and largely prevents filter silting. To load biofilters, it is recommended to use crushed stone, pebbles of durable rocks and expanded clay.

Highly loaded biofilters during preliminary treatment of partially purified waste liquid in aerotanks and biocoagulators, as well as high-loaded biofilters of the II stage and drip biofilters are loaded with material with a particle size of 30 - 50 mm. The lower support layer 0.2 m high in all cases has a loading size of 60-100 mm.

Highly loaded biofilters are made of precast concrete (Fig. 4). The biofilter is a cylindrical tank with a diameter of 17 m, a height of 2.3 m. The walls of the biofilter are made of 48 vertically arranged prefabricated cylindrical elements, the bottom is made of monolithic concrete, the drainage ceiling is made of prefabricated grates.

Reliable operation of the biofilter can only be achieved with uniform irrigation of its surface with water. Irrigation is carried out by special distribution devices, which are fixed and mobile. Fixed distributors include perforated chutes or pipes and sprinklers (sprinklers), while movable distributors include rocking chutes, moving filling wheels and rotating jet distributors (sprinklers). In domestic and foreign practice, sprinkler irrigation and irrigation with the help of mobile sprinklers are most widely used.

The sprinkler system consists of a dosing tank, distribution network and sprinklers. Sprinklers (sprinkler heads) are nozzles put on the ends of vertical branches branching off from distribution pipes laid on the surface or in the biofilter itself. Sprinkler head holes are made with a small diameter of 18-32 mm. On fig. 5 shows one of the types of nozzles used in domestic practice. Sprinklers are made of bronze or brass to prevent corrosion.

Rice. 5. Nozzle for irrigation of the biofilter surface 1 - reflective cone; 2 - head

Rice. 6. Jet sprinkler

In order to better distribute wastewater over the surface of the biofilter and improve its performance, wastewater should be fed into the sprinkler network periodically at short intervals. For this purpose, a dosing tank is provided that automatically supplies water to the sprinkler network when it is emptied.

It is advisable to design the distribution sprinkler network so that each section of the biofilter is served by a separate dosing tank. There are various designs of automatically operating devices (tanks), for example, machines with rotating sleeves, a cylindrical shutter, etc. The most widely used dosing tank with a siphon, which has no moving parts.

When calculating the distribution system, the water flow from the sprinkler (sprinkler), the required number of them, the distribution network, the volume and operating time of the dosing tank are calculated. For normal operation, biofilters must be provided with the necessary amount of air. In drip biofilters, natural blowing (ventilation) is created due to the temperature difference between the outside air and the biofilter body. The main mass of air enters the body of biofilters through the double bottom space and from above along with water as it moves in the filter. If the temperature of the wastewater is higher than the air temperature, then the air flow will be ascending (from the drainage to the surface), with the opposite ratio, descending, and if the temperatures are equal, there may be no ventilation at all. Studies of the operation of biofilters have shown that the required amount of air should be 8-12 m3 per 1 m3 of waste water.

Biofilters with a height of more than 2 m must be artificially ventilated. In this case, air is blown by a fan into the double-bottom space between the bottom and the drainage under a pressure of 100 mm of water. Art. (980 Pa). In the place of the outlet tray, where the water comes out from under the filter, a hydraulic seal 200 mm high is arranged, and the double-bottom space is closed from all sides. This is done so that the air blown by the fan enters completely into the filter body and does not break through along with the water coming out from under it.

Rice. Fig. 7. Scheme of the device of a disk biofilter 1 - a disk block of plates; 2 - shaft; 3-drive disk unit; 4 and 7 - inlet and outlet trays; 5 - bath; 6 - weir

The reactive rotating sprinkler consists of two or four perforated pipes cantilevered on a common riser (Fig. 6). Water from the distribution chamber enters under some pressure into a riser mounted on ball bearings; the riser can freely rotate around a vertical axis. From the riser, water enters the radially arranged pipes and pours through the holes in them onto the surface of the biofilter. Under the action of the reactive force that occurs when water flows out of the holes, the sprinkler rotates. The diameter of the holes in the pipes is taken 10-15 mm; the distance between the holes increases from the periphery to the center. Soyuzvodokanalproekt has developed standard designs for biofilters with a diameter of 15, 21, 27 and 29 m with rotating sprinklers.

In the practice of wastewater treatment at flow rates up to 500 m3/day, submersible (disk) biofilters are used (Fig. 7). On rotating discs immersed in waste water, a biological film is formed, with the help of which the oxidation of organic contaminants sorbed on it is carried out. Waste water enters the trough with a semicircular bottom through the inlet, and is discharged from the opposite side. The disks usually have a diameter of 2-3 m and rotate at a speed of 1-40 rpm. The distance between the discs is 15-20 mm. Disc biofilters are installed in the form of prefabricated prefabricated units.

Research conducted at MISI them. V. V. Kuibyshev and the Odessa Civil Engineering Institute, it was found that submersible biofilters are simple and reliable in operation and consume little energy to saturate water with oxygen.

Part 2

Biofilters are divided into batch biofilters, or contact, and continuous biofilters. Biofilters of continuous action, in turn, can be subdivided into: a) biofilters of the usual type; b) air filters; c) highly loaded.

Contact biofilters due to their low productivity and high cost are not currently used.

The conventional type continuous biofilter consists of the following main parts: impermeable base, drainage, side walls, filter material and distributors. In terms of biofilters can be in the form of a circle, rectangle, square or octagon. They can be arranged with waterproof or openwork walls. The flow of water into the devices that distribute it over the surface of the biofilter occurs continuously, while its surface is irrigated at short intervals of 3-5 minutes. water supplied from these devices in the form of separate drops or jets. Such irrigation contributes to better penetration into the body of the biofilter of air necessary for the oxidative process. Air also enters through the openwork walls of the biofilter and drainage. Scheme of operation of a continuously operating biofilter. ra is as follows: the wastewater clarified in the primary settling tanks by gravity (or under pressure) enters the distribution devices, through which the water is perio. is applied directly to the surface of the biofilter. Profilero. The water that has flowed through the thickness of the biofilter passes through the holes in the perforated bottom (drainage) and enters a solid impermeability. permeable bottom, from which flows down through the outlet trays located outside the biofilter.

The processes of oxidation occurring in the body of a biofilter are similar to those that occur with natural methods of water purification in irrigation or filtration fields, but differ from the latter in a much greater intensity. The effect of wastewater treatment with normally operating biofilters is very high, the BOD of the outflow is reduced by 90% or more.

The calculation of a biofilter consists in determining the required volume of feed material for cleaning incoming water, as well as calculating distribution devices for water irrigation, drainage and trays for passing and collecting clarified water.

The volume of feed material is determined by the so-called biofilter oxidizing power (OM), which refers to the number of grams of oxygen that can be given to 1 mg of feed material per day to reduce the biochemical demand of wastewater.

This value of the oxidative power of the biofilter will be greatly reduced even in each biofilter, since its value depends on many factors, for example, on the temperature of the outside B03 tank and waste water, the concentration and properties of the incoming liquid, on the material of the load, the method of air supply, etc. Its value only in general terms displays the processes of oxidation of organic substances occurring in the body of the biofilter. We can only talk about the average value of the oxidizing power, determined experimentally on the basis of full-scale measurements.

Rice. 1. Rectangular biofilter

A necessary condition for the normal operation of the biofilter is their air purge. In biofilters of the usual type, their purge or ventilation occurs naturally due to the temperature difference between the outside air and the biofilter body.

In domestic practice, rectangular filters are most widely used (Fig. 1).

Rice. 2. The bottom of the biofilter from reinforced concrete slabs

The best type of drainage is drainage from reinforced concrete slabs, which are laid on concrete or brick supports (Fig. 2). The plates have holes of square or cylindrical shape. Other types of drainage (made of bricks, ceramic pipes) are rarely used.

The bottom of the biofilter is given a slope of 0.02 to collection trays located at a distance of 2.5-4 m from each other (depending on the size of the biofilter) with a slope of 0.005-0.02. From the collection trays, water enters the outlet trays with a slope of 0.003-0.005. Sometimes prefabricated trays under the biofilter are not satisfied and its bottom is given a general slope of 0.01 towards the outlet trays. Filters can be both ground and underground type.

The walls of ground filters are sometimes made openwork, i.e. with holes through which air enters. Reinforced concrete, brick, rubble, etc. can serve as materials for the walls.

The loading material must have a developed surface with particle sizes that ensure the rapid formation of a microbial film. On the other hand, the feed material must be sufficiently porous, as this contributes to good filter blowing and largely prevents silting. The material must also have sufficient strength, resistance to weathering; in addition, it must not contain impurities that could affect the baroflora of the biofilters. Should be used whenever possible | call local inexpensive material. Up to now, boiler slag and coke have been predominantly used as feed materials for biofilters. However, we can also accept crushed stone of hard rocks, crushed stone from brick-iron ore, gravel! pebbles.

Rice. 3. Round biofilter

Normal operation of the biofilter can only be achieved with uniform irrigation of its surface with water. This irrigation is carried out by special distribution devices, which are divided into two main groups: fixed and movable distributors.

Fixed distributors include: a) perforated chutes or pipes and b) sprinklers or sprinkler; to mobile: a) swinging gutters; b) a moving filling wheel and c) rotating jet distributors (petitioners). When distributing water over the surface using gutters or

Recently, movable inactive distributors have begun to be used abroad, operating on the principle of the PpGierov wheel. The riser, where the clarified waste water enters, is mounted on ball bearings and can freely rotate around a vertical axis. Two or four cantilevered horizontal pipes are connected to the riser, located oadally at a distance of 0.15 m above the surface of the biofilter. The pipes are held in a horizontal position by metal braces. The pipe has holes located at a certain distance from each other. When water flows out of these holes under a certain pressure (from 0.25 to 0.8 m), the distributor moves in the opposite direction under the action of a reactive force. The disadvantage of such distributors is the possibility of silting holes and, as a consequence, uneven irrigation of the surface of the biofilter.

On fig. 4 shows another type of movable distributor, a distributor in the form of a moving filling wheel. The filling wheel is a long hollow cylinder with paddles on the surface. The cylinder is located above the biofilter and, when sewage is fed into it, moves along rails laid on the longitudinal walls of the biofilter. The distributor is fed with waste water from the chute using a siphon, the end of which is lowered into the chute. Waste water, entering the blades of one side of the sprinkler, causes it to rotate. The sprinkler begins to move along the rails along the biofilter. To change the direction of movement of the sprinkler, a special device is used, which consists of a pallet with handles and a buffer; the handle, bumping into the buffer, turns the pan, as a result of which the waste water enters the other side of the movable wheel and it moves in the opposite direction.

The advantages of such distributors include a small amount of pressure required for their operation, and a uniform distribution of water. Their disadvantage is unreliable operation in winter, since the apparatus may stop when the rails freeze. Therefore, these distributors can be used mainly for biofilters installed in the southern regions, or for biofilters of small dimensions, installed indoors.

To calculate the combined network of trays that drain the purified liquid from under the biofilter (bottom), it is necessary to know the water flow rates.

Rice. 4. Movable distributor

In the place of the outlet tray, where the water comes out from under the filter, a water seal 200-250 mm high is arranged, and the double-bottom space is closed from all sides. This is done so that the air blown by the fan enters completely into the body of the air filter and does not break through together with the purified water coming out from under it. In addition, in order to create additional resistance to air movement along the inner surface of the air filter walls, they are made with horizontal ribs. The double-bottom space is usually made 0.5-0.6 m high and covered with reinforced concrete slabs with holes. The slabs rest on concrete posts or ribs. Water is supplied to such biofilters, as a rule, using a sprinkler distributor.

The calculation of the air filter is also carried out according to the oxidizing power. Due to the fact that the oxidation process in the air filter is more intense than in other types of biofilters, OM usually takes up to 600 g of oxygen per day per 1 m3 of feed material. Air consumption per day averages 25-30 m3 per 1 m3 of load. Such air filters usually work with increased loads (up to 4-5 m3 of water per day per 1 m3 of load), therefore, in order to avoid rapid silting of the load body, the wastewater entering the air filters should not be highly concentrated, i.e. The BOD of incoming water should not exceed 100-120 mg!l. To do this, highly concentrated wastewater is either subjected to preliminary treatment in aeration tanks (as is done at the Kozhukhovskaya aeration station), or concentrated wastewater is diluted with purified water (Shchukinskaya biological station).

Air filters can be loaded with slag or crushed stone. Loading grain sizes are different. So, for example, at the Kozhukhovskaya station, the main layer is loaded with crushed stone or slag with a particle size of 25 mm; at the Shchukinskaya station in some sections there is a load with a particle size of 50-60 mm, in others - 25-45 mm, etc.

Highly loaded biofilters have begun to be introduced into construction practice recently. Their difference from conventional filters lies primarily in the fact that they sometimes provide not for complete biological treatment, as in conventional biofilters, but for partial purification. The process of mineralization of organic pollutants in these biofilters essentially ends with the stage of oxidation of easily oxidized organic substances; in this case, the waste water is not completely cleaned. As a result, the load of both water and pollution per 1 m2 of the biofilter surface is assumed to be increased.

Rice. 5. Scheme of highly loaded filters operating with recirculation

With an increased load in the body of the biofilter, a rapid accumulation of the biological film occurs, which can lead to silting of the biofilter. Its flushing is provided by diluting the incoming wastewater with purified water, i.e. the so-called recirculation and loading of the biofilter with smooth material (crushed stone). It should be noted that in some cases, increasing the height of the biofilter can give the same results as the use of recirculation.

Experiments conducted by the Academy of Public Utilities have shown that for the successful operation of such filters, it is necessary that the concentration of incoming water according to the WPC does not exceed 200 mg/l. If the concentration of wastewater is higher, then dilution of the wastewater must be applied, i.e. recycling.

Studies of such biofilters under the operating conditions of the Shchukin Biological Station, carried out by the Department of Sewerage of the Moscow Institute of Urban Construction Engineers together with a team of workers from the Shchukin Station, showed that even at a load of up to 4.5 m3 per 1 m3 of material, the quality of the treated effluent is quite satisfactory. As a load, it is most rational to use crushed granite stone with a particle size of 25-50 mm. When the concentration of wastewater according to the VPK is up to 170 mg/l, recirculation is not required.

- Biofilters

Biofilters are a fairly important design that has been successfully used for wastewater treatment. Therefore, it is important to understand the features of their action and application.

The filter for biological wastewater treatment is a design that serves to purify wastewater using a special biofilm consisting of colonies of microorganisms. The above biofilm decomposes organic components, which later serve as a source of nutrients for colonies of microorganisms. Over time, part of the bioreactor film dies and peels off.

In the future, these parts are washed off with sewage and are not retained in the filtration system. As a load for a biofilter, those materials that have a low density, coupled with high porosity, can be used - for example, gravel, expanded clay, crushed stone, slag or rolls of plastic mesh are perfect.

What are biofilters

In order to choose the right biofilter for you, you should refer to their classification. There are the following types:

• two-stage biofilters are indispensable in cases where it is necessary to achieve a high degree of purification, but it is impossible to increase the height of the system;
• drip filtration bioreactors, which have a relatively low productivity, however, are able to provide complete purification.

According to the type of feed material used for installation in the biofilter, they can be classified as follows:

• biofilters with a volumetric load, in which crushed stone of strong rocks, slag, pebbles, expanded clay are widely used;
• plane-loaded biofilters, for which plastics are used that can withstand temperatures from 6 to 30 degrees C, without losing a margin of safety.

Biofilter design

Knowledge of the design of the biofilter is necessary for its proper installation. What constituent parts does it consist of?

• the filter body, or the load, is a material of high porosity and low density placed in the tank, for example, expanded clay, gravel, slag, etc.;
• a water distributor that will be responsible for uniform irrigation of the loading surface of the bioreactor with wastewater;
• a drainage device is required to remove already filtered water;
• an air distributor necessary for a sufficient supply of oxygen to the system, in the presence of which oxidative processes occur.

Principle of operation

After the wastewater has undergone primary treatment in a special settling tank, in which heavy and large fractions of pollutants are removed, they are subsequently fed to subsequent biological treatment. Contaminated water on its way passes through the biofilter loading and leaves the undissolved impurities contained in it, which did not settle in the sediment in the water sump.

Dissolved and colloidal organic components also remain in the feed, which are adsorbed by the biofilm of the bioreactor. Colonies of microorganisms of the biological film actively absorb organic materials and consume the energy received for their life activity. There is an active growth of colonies of microorganisms of the bioreactor system - thus, a constant renewal of the number of microorganisms is achieved, without which the operation of the filter is simply impossible.

Microorganisms can be divided into types, depending on their interaction with oxygen:

• Aerobic microorganisms need oxygen for their life activity, without it their existence is impossible. Anaerobic microorganisms are used in the bioreactor system;
• anaerobic microorganisms feel comfortable in the absence of free circulation of oxygen, on the contrary, in conditions where there is no access to oxygen, they actively reproduce.

Therefore, when installing a biofilter, it is necessary to ensure sufficient access of oxygen to the filtration system - for this, the design is equipped with an air distributor. This contributes to active reproduction and full life support of the aerobic microflora of the biofilter, and prevents the activity of anaerobes. The latter are responsible for the appearance of putrefactive formations and the fetid smell of sewage - make sure that the air distributor is in good condition.

Principles for effective wastewater treatment

Water is the source of life for all inhabitants of our planet. And in this case, we are not only talking about humans, animals or plants - microorganisms also need moisture, which is an excellent environment for their reproduction. Often, microorganisms belong to the group of pathogens, so you should worry about high-quality and efficient wastewater treatment in your home.

Even doctors of the distant past noticed that the health of the population in a certain area is directly related to the water reserves of the area. To carry out the installation of biological filtration means to reliably protect yourself from the reproduction of pathogens.

What determines the efficiency of wastewater treatment in such a filter? This is influenced by a whole group of factors:

• biological oxygen demand of the treated water;
• the rate of oxidative reactions in a given medium;
• the need of microorganisms for oxygen;
• thickness of the biological film of the biofilter;
• temperature of water and environment;
• composition of biofilm microorganism colonies.

As we can see, many factors influence the cleaning efficiency. Therefore, it is worth taking a responsible approach to the choice of this biological purifier, which is suitable specifically for your conditions in order to achieve the highest quality cleaning.

This Flotenk-BF treatment plant is used in the design and construction of complex systems for the treatment of domestic wastewater.

In the work of treatment facilities, the method of gravitational settling and biological treatment using bioenzymatic preparations is used.

Specifications

The biofilter is a waterproof container made by machine winding. Material: polyester fiberglass, made using polyester resins and glass reinforcing materials. The calculations for the treatment plant were made in accordance with SNiP 2.04.03-85 Sewerage. External networks and structures.

The delivery set of the "Flotenk-BF" biofilter includes:

• hull, with built-in fiberglass hatch
• inlet pipe, with tee, PVC
• PVC plug on outlet
• pump
• water disinfection plant
• expanded clay

Don't forget to see:

Wastewater from a residential building after cleaning in a septic tank flows by gravity through sewer pipes into a biofilter, where it is evenly distributed over the surface of an inert load. Due to the presence of bacteria in the feed water, a biofilm forms on the feed during the first two to three weeks of operation. Bacteria, as well as possible fungi, form the lower trophic level. They oxidize organic compounds entering the biofilter, serve as food for various types of protozoa, rotifers, ciliates, etc., which are in the biofilm, due to which the biofilm is constantly rejuvenated.

As wastewater seeps through the feed, aerobic oxidation of carbon and hydrogen occurs to form carbon dioxide and water, then the ammonium nitrogen is oxidized first to nitrite and then to nitrate.

From the biofilter, wastewater flows into a water intake well, in which a pump is located that pumps the treated wastewater to the discharge point.

If a biofilter is used as a post-treatment and disinfection unit in the BioPurit and BioDrafts complexes, a UV lamp is additionally installed in the chamber.

The FloTenk-BF treatment plant is serviced after the 1st year of operation (at a load of less than 20% of the maximum per day, the service life of the treatment plant can be extended up to 1.5-2 years).

Maintenance of the FloTenk-BF biofilter consists of a visual inspection of the expanded clay surface at least once a year. With an increase in the volume of biofilm on the surface of expanded clay to a volume that prevents the free passage of wastewater flow, it is necessary: ​​1-to dispose of excess biofilm from the surface of expanded clay. 2- rinse the claydite load with a jet of water. When an inert load (expanded clay) is clogged with building mixtures (chalk, cement, etc.) as well as untreated sewage, expanded clay must be replaced. On visual inspection, the biofilm appears as dark brown silty deposits.

The operation of any wastewater treatment system, including biological, is based on the fact that various cultures of microbes decompose and remove colloidal and dissolved organic substances from wastewater. The operation of the plant, the degree of wastewater treatment, as well as the presence or absence of unpleasant odors depend on the activity of the microflora.

The most important factors affecting the biological activity of microorganisms are:

• waste water temperature (optimally 10-35 C)
• the presence of organic matter in wastewater
• supply of oxygen to the plant
• pH value (acidity)
• no toxic substances

In order to create the most favorable conditions for microorganisms and the operation of a biological treatment plant, it is recommended that the following conditions be met:

• do not throw leftover food, garbage into the sewer
• avoid underloading or overloading the installation. With a long absence of effluents, bacteria begin to die
• use hot water regularly so that the temperature of the drains is optimal
• wash with powders with normalized foaming (for automatic machines)
• do not use chlorine-based bleaches, formaldehyde-based chemicals
• do not allow strong acids (such as oxalic acid), solvents, alkalis, toxic substances to enter the sewer

For the treatment of plumbing and pipe cleaning, it is preferable to use preparations specially designed for biological systems. The appearance of a strong odor from the air of the installation indicates a decrease in the efficiency of the biofilter as a result of a violation of one of the above operating conditions.

Biofilter for post-treatment of household wastewater to concentrations acceptable for disposal into reservoirs for fisheries, household and cultural purposes.

№	Name		Cost, rub. VAT included	Note
1	FloTenk-BFU, biofilter ∅ 1200 mm (up to 12m3/day)	with supply pipe up to 1000 mm	199 900	Post-treatment filter
2	FloTenk-BFU, biofilter ∅ 1600 mm (up to 24m3/day)	with supply pipe up to 1000 mm	279 900	Post-treatment filter
3	FloTenk-BFU, biofilter ∅ 2000 mm (up to 32m3/day)	with supply pipe up to 1000 mm	449 900	Post-treatment filter
4	FloTenk-BFU, biofilter ∅ 2300 mm (up to 48m3/day)	with supply pipe up to 1000 mm	549 900	Post-treatment filter
5	FloTenk-BFU, biofilter ∅ 3000 mm (up to 60m3/day)	with supply pipe up to 1000 mm	699 900	Post-treatment filter

Under the order, biofilters are made with any supply pipes from the ground level. Price on request.

A biofilter is a fixed bed reactor with a biological effect for purifying air or water. Its main purpose is to filter gaseous impurities and substances dissolved in the substance to be purified, and not solid particles.

The idea to purify exhaust air in a biological way originated in the seventies of the twentieth century, but was first put into practice only in 1980 thanks to intensive research by scientists. Based on the microbiological method, a few years later the concept of a modular plant with the possibility of universal use was developed.

Biofiltration is a relatively simple and economical process for cleaning exhaust air containing VOCs and odors. At the same time, microorganisms decompose harmful and odorous substances into harmless products such as carbon dioxide and water. Biofilters are mainly used for air purification. For specific cases, biological wastewater treatment based on a similar principle is also possible.

Biological exhaust air treatment uses microorganisms to remove harmful substances from the air through microbiological degradation. Various microorganisms, such as bacteria or fungi, act as degraders.

The whole process boils down to the following: microorganisms convert harmful substances with the help of oxygen into carbon dioxide and water, which means that we are talking about a decay reaction of matter.

This reaction can proceed only when harmful substances pass from the gaseous state to the liquid state, since water constitutes the living space of microorganisms. That is why the transition of harmful substances into a liquid state is the most important factor in all biological methods. Only those microorganisms survive that can best adapt to the prevailing conditions and to the nutrient base. In this case, we are always talking about a mixture of various heterotrophic species that use harmful substances in the air as a source of carbon and energy.

Types and methods of operation of biofilters

There are different types of biofilters depending on the way they are used and the area of ​​application. For example:

• flat sleeve,
• container type,
• for wells,
• storey,
• cellular,
• tower.

But in all types of devices, the exhaust air passes through some kind of filter material.

In some cases, an air-washing chamber is located in front of the biofilter, in which the gas acquires a relative humidity of almost 100%. This should prevent the material from drying out. In addition, if necessary, solid particles are removed from the gas in the air-washing chamber. Saturated with water vapor and cleaned of dust, the raw gas enters directly into the biofilter, which contains the filter material. Thanks to additional irrigation, it always remains moist. This is where microorganisms live. When passing through the filter layer, the substances in the composition of the exhaust air are sorbed on the surface of the material, thus becoming a nutrient base for the bacteria living here.

In order to guarantee a high microbial activity in the filter, the optimal conditions for the life of microorganisms must be observed: pH level, humidity, temperature and a regular supply of nutrients. Practice shows that microbial mixed populations developing in biofilters are very hardy, if the above conditions are observed.

Filter material

Certain requirements are also imposed on the filter material.

It should have a large specific surface and, at the same time, a comfortable breeding zone for microorganisms, which:

• retains moisture well
• allows only a slight pressure drop during the passage of gas,
• independently regulates fluctuations in the pH value,
• ensures uniform passage through the filter layer,
• has a low decay rate.

In addition, microorganisms must be supplied with inorganic nutrients and trace elements. The following materials can be used as a filter layer:

• Compost from wood or trash
• Heather, brushwood or coir
• Peat products
• Paper granulate

Additionally, inert materials are added for loosening, such as expanded clay, styrofoam or foam. At the same time, the filter layer is not only a carrier for microorganisms, but also a supplier of nutrients.

Advantages and disadvantages of biofiltration

During the operation of the biofilter, the main problem is to prevent drying or excessive moisture of the filter layer, and, consequently, ensuring uniform passage of polluted air through it.

This can be achieved primarily by encapsulation of biofilters. The disadvantages of these devices include the following:

• large footprint
• energy costs for boosting pressure
• the need for additional irrigation

However, compared to other methods, such as air ionization with ionizing tubes, a permanent biological cleaning process is more advantageous due to CO2 savings and numerous economic aspects (average acquisition costs, long service life, average production costs).

Technological foundations

The technological basis is essentially biochemical oxidation and at the same time the decomposition and transformation of materials by bacteria, fungi and yeast into harmless and odorless substances.

The prerequisites are that the harmful materials are water-soluble, biodegradable and non-toxic to microorganisms.

The rapidly growing population of microorganisms living on the filter layer uses the volatile organic compounds contained in polluted air for their own metabolic processes. Decomposition occurs under aerobic conditions and sufficient oxygen. The latter is ensured by its sufficient content directly in the air. Exhaust air saturated with water vapor must be used because the filter material must be damp.

Areas of application for biofilters

• Biofilters are used for biological air purification in the following areas:
• Wastewater treatment plants
• Solid waste landfills, waste processing plants
• Solvent painting plants (metal, wood, plastics)
• Food processing, mushroom farms, smokehouses
• Oil mills and malting companies
• Agricultural installations
• Biogas plants, gas processing from organic waste
• Cattle farms
• Feed factories
• slaughterhouses
• Sludge dryers
• Industrial production complexes

Biofiltration to eliminate odor

The main area of ​​application of biological filtration devices is the purification of air from unpleasant odors. The microbiological breakdown of malodorous substances into carbon dioxide and water takes place at ambient temperature, so there is no need for additional energy or additives. Therefore, the production costs of this process are very low. In many areas, biofiltration is becoming an integral part of the technical equipment of production.

Thousands of biofiltration devices are used in Europe to eliminate unpleasant odors from a wide variety of emission sources. Odor problems are common in the vicinity of sewage treatment plants, landfills, foundries, breweries, food processing plants, animal housing, waste processing plants, agricultural operations and slaughterhouses. Biofiltration is the most cost-effective and most reliable method for eliminating unpleasant odors - its efficiency reaches 99%.

Biofilters for sewer wells

Biofilters for wells are installed directly under the splash guard in the well shaft, thereby preventing strong odors from escaping from the sewer. They contain an integrated mudguard and a filter layer (a mixture of peat and a composite for microorganisms). The water coming from the surface is directed to the suction socket under the sludge collector and is discharged through the waste pipe. The rubber seal prevents uncleaned air from escaping. Modern filters no longer prevent air seepage. Modern paper-based filters do not require additional maintenance and function from 5 to 6 years without constant monitoring and care. Their efficiency is about 99%.

Application

Designed to effectively eliminate unpleasant odors from municipal or industrial sewers.

Action

Microorganisms in the biofilter neutralize unpleasant odors before they go outside.

Design

HDPE (High Density Poly-Ethylene) and stainless steel construction ensures durability (~7 years)

Container type biofilters

The main purpose of biofiltration is the contact of microorganisms with contaminants contained in the air stream. The filtration material constituting the soil for growing microorganisms is placed inside the biofilter. During the biofiltration process, a jet of polluted air enters the biofilter, where the absorption process takes place through the filter material. In the effect of decomposition, metabolic intermediates appear in the form of CO2 and H2O.

Advantages:

• There is no waste requiring special treatment.
• Pollution is decomposed into neutral compounds such as: H2O, CO2 and biomass.
• The biomass is stored inside the apparatus and after a certain period of time it is composted together with the filter material.
• Properly designed biofilters require virtually no maintenance.
• Exceptionally low cost of investment as well as low operating costs compared to traditional air purification methods.

Exhaust Air Requirements

The most important prerequisites for the functioning of biofilters are:

• Compliance with a favorable temperature regime (+5°C - +55°C).
• Irrigation of the filter layer to prevent it from drying out.
• Preventing the formation of cracks and cracks in the filter layer.
• The substances to be purified must be water soluble.
• Substances to be purified must be biodegradable.
• Regular supply of nutrients to the habitat of microorganisms.

Links

H.C. Flemming and J. Wingender (2010). Nature Reviews Microbiology.

Joseph S. Devinny, Marc A. Deshusses and Todd S. Webster (1999). Biofiltration for Air Pollution Control.

Hermann Bubinger, Hans-Gerd Schwinning (1992). Grundlagen und Anwendungsbeispiele der Biofiltertechnologie.

Andreas Oberhammer (1997). Verfahren zur gleichmäßigen Befeuchtung ener Filtermasse

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.