RU2180895C2 - Method of biological treatment of waste water - Google Patents

Abstract

FIELD: biological cleaning of waste water. SUBSTANCE: waste water is passed through aerotanks containing activated sludge, after which water-and-sludge mixture is supplied to settler where biologically active elements are laid in two and more layers; biological elements are just bearing surface coated with biological film. Circulating space (spaces) is formed between biological active elements by taking water filtered through biological film and feeding water-and-air mixture to this space. Flow rate of circulating water in each circulating space is equal to 6-12% of flow rate of water fed to settler and flow rate of air is equal to 2-5% of flow rate of circulating water; velocity of water fed to settler and that at outlet of circulating space (space) are related as (5-8):1. EFFECT: enhanced efficiency of biological treatment of waste water; improved quality of cleaned water to requirements corresponding to tertiary treatment low cost of process.

Description

 The invention relates to the biological treatment of wastewater.

 A known method of biological wastewater treatment, including passing wastewater through activated sludge aeration tanks, retaining activated sludge using biologically active elements representing a bearing surface coated with a biological film in a sump, returning the delayed activated sludge to the aeration tank inlet (see Russian Patent 1551660, C 12 F 3/12, publ. 23.03.90).

 The method allows you to delay excess activated sludge, namely its "swollen" form, formed during the biological treatment of wastewater, and due to this ensures the normal operation of treatment plants with activated sludge, allows to increase the efficiency of water treatment.

The disadvantage of this method is that for wastewater with BOD _full ≥ 5 mg / l, it does not allow to obtain a water quality that meets the requirements of post-treatment, i.e. it requires an additional operation for water purification, including on strainers.

 A known method of biological wastewater treatment, including passing wastewater through activated sludge aeration tanks, additional treatment of activated sludge in autonomous aerated tanks, delayed activated sludge in settling tanks and returning it to aeration tanks, the additional treatment being a continuation of the biological treatment process, the flow mode of which is provided by changing the hydrodynamic conditions of movement of the water-sludge mixture (see Russian patent 2119460, C 02 F 3/02, publ. 09/27/98).

 The disadvantage of this method is the need for secondary sumps to separate activated sludge from water and the need for additional water treatment, i.e. tertiary treatment, due to the low quality of the resulting water.

 Closest to the proposed one is a method of biological wastewater treatment, including wastewater treatment using biologically active elements representing a load-bearing surface coated with a biological film, aeration of water, circulation of water through a biofilm, creating a vortex surface under the surface layer of treated wastewater, precipitation of suspended solids particles (see Russian patent 2111177, C 02 F 3/06, publ. 05.20.98).

 The disadvantage of this method is the need for additional water treatment in the precipitation chamber and low efficiency of water purification, the complexity of the equipment used.

 The objective of the present invention is to increase the efficiency of treatment and improve the quality of the water obtained to the requirements of the corresponding post-treatment, as well as reducing the cost of water treatment.

 The technical result of the invention is to increase the efficiency of biological water purification, ensuring the quality of the water obtained that meets the requirements of post-treatment, reducing the cost of water purification.

 The specified technical result is achieved due to the fact that in the method of biological wastewater treatment, including wastewater treatment using biologically active elements representing a bearing surface coated with a biological film, aeration of water, water circulation through a biofilm, creating a vortex surface under the surface layer of the wastewater being cleaned water, sedimentation of suspended solids, there are differences, namely: biological wastewater treatment with the use of biologically active elements, representing the bearing surface, covered with a biological film, is carried out after passing the wastewater through aeration tanks with activated sludge, the process of water treatment using biologically active elements is combined with the deposition of suspended solids, including activated sludge, for which the biologically active elements are placed in two tanks or more layers, in the space between which a circulating volume (s) is created by supplying a water-air mixture there, while the flow of recirculated water in each of the circulating volume of water is 6-12% of the flow rate of water supplied to the sump, air flow rate is 2-5% of the flow rate of recirculated water, and the speed of the water supplied to the sump and the water velocity at the outlet of the circulation volume (s) are correlated as ):1.

 This method allows to increase the efficiency of biological water purification, to improve the quality of the water obtained to the requirements corresponding to post-treatment, due to the fact that the biological water purification that occurs in the volume of the aeration tank continues on biologically active elements that provide a bearing surface coated with a biological film, as well as in circulation volumes created in the sump in the space between biologically active elements, where active sludge has lost reactivity in aeration tanks l acquires it under the influence of subsurface aeration and circulation according to the proposed pneumohydrodynamic regime. Simultaneously with the process of absorption of contaminants, the process of sedimentation of suspended solids occurs, a considerable proportion of which are activated sludge particles. Particles of activated sludge are precipitated by the counterflow flocculation method, which occurs when wastewater with activated sludge particles contained in it passes through biologically active film elements due to the difference in electrostatic charges, particles of activated sludge and biofilm.

 The combination of the biological water treatment process with the deposition process by placing biologically active elements in the sump allows you to reduce the cost of water treatment. Ensuring the quality of the produced water that meets the requirements of post-treatment allows to simplify the complex of equipment used.

 The method is as follows.

 Wastewater is treated with activated sludge in an aeration tank, and then the water-sludge mixture is fed into a sump, where biologically active elements representing the bearing surface covered with a biological film are placed. Biologically active elements are placed in two or more layers, in the space between which a circulating volume (s) is created by taking water from there that has been filtered through a biofilm and supplying an air-water mixture there. The flow rate of recycled water in each of the circulation volumes is 6-12% of the flow rate of water supplied to the sump. The oxygen consumption in the supplied water-air mixture is 2-5% of the circulating volume of water. The ratio of the velocities of the water supplied to the sump and the water velocity at the outlet of the circulating volume (s) lies in the range (5-8): 1.

 Activated sludge, which entered the sump in a mixture with water, has already exhausted its reactivity and sorption capacity to a greater extent. The oxidation and absorption of contaminants at the first stage in the sump occurs on biofilm elements, the reactivity of which is maintained due to the pneumohydrodynamic regime created in the circulating (circulating) volumes. After filtering the water-sludge mixture through a biofilm, the purification process continues in the circulation volume, where the indicated pneumohydrodynamic regime ensures the regeneration of activated sludge in the mixture by eliminating oxygen deficiency.

 Simultaneously with the process of absorption of contaminants, the process of deposition of suspended solid particles of activated sludge and biological film. The process begins on biofilm elements, since the particles of activated sludge and biofilms have insignificant but opposite charges, in the place of their contact, the particles of activated sludge, due to electrostatic attraction, acquire the charge of the biological film and begin to flocculate nearby particles of activated sludge. Further, the flocs increase in size by combining them from small to larger, and under the influence of their ever-increasing specific gravity, their gravitational deposition occurs in the lower silt part of the sump. From here, activated sludge particles can be fed into the aeration tank for reuse in the purification of a new portion of contaminated water.

 EXAMPLE 1

The degree of contamination of the source wastewater BOD _full = 6.

 Carry out the method as described above.

 In this case, the biologically active elements are placed in a sump in two layers. The number of circulating volumes created is one.

The speed of water supplied to the sump is V ₁ = 15 mm / s, the speed of water at the outlet of the circulation volume is V ₂ = 1.9 mm / s. The flow rate of recycled water in the circulation volume is 7% of the flow rate of water supplied to the sump, and the air flow rate is 2% of the flow rate of recycled water.

The indicated pneumohydrodynamic parameters in this method allow to bring the quality of the purified water to BOD _full = 3 mg / l, which meets the requirements of post-treatment and allows you to discharge water into natural reservoirs.

 EXAMPLE 2

The degree of contamination of the original wastewater BOD _full = 8 mg / L. The method is carried out as described above, while the biologically active elements are placed in three layers. The number of circulating volumes created is two. The speed of water supplied to the sump is V ₁ = 14 mm / s, the speed of water at the outlet of the first circulation volume is equal to the speed of water at the outlet of the second circulation volume and is 1.8 mm / s.

 The flow rate of recycled water in each of the circulation volumes is 10% of the flow rate of water supplied to the sump, while the air flow rate is 4% of the flow rate of recycled water.

The indicated pneumohydrodynamic parameters in this method allow to bring the quality of the purified water to BOD _full = 2 mg / l, which meets the requirements of post-treatment and allows you to dump purified water into natural water bodies.

 EXAMPLE 3

The degree of contamination of the source of wastewater BOD _full = 10 mg / L.

Carry out the method as described above. In this case, biologically active elements are placed in a sump in three layers. The number of circulating volumes created is two. The speed of water supplied to the sump is V ₁ = 20 mm / s, the speed of water at the outlet of the first circulation volume is equal to the speed of water at the outlet of the second circulation volume V ₁ = V ₂ = 2.2 mm / s.

 The flow rate of recirculated water in the circulation volumes is 11% of the flow rate of water supplied to the sump, and the air flow rate is 4.3% of the flow rate of recirculated water.

The indicated pneumohydrodynamic parameters in this method allow to bring the quality of the purified water to BOD _full = 3 mg / l, which meets the requirements of post-treatment and allows you to discharge water into natural reservoirs.

 EXAMPLE 4

The degree of contamination of the source wastewater supplied from the laundry, BOD _full = 312 mg / l.

Carry out the method as described above. Biologically active elements are placed in three layers. The velocity of water supplied to the sump is V ₁ = 18.5 mm / s, the velocity of water at the outlet of the first circulation volume is equal to the velocity of water at the outlet of the second circulation volume V ₁ = V ₂ = 2.1 mm / s.

 Due to the large contamination with the pile, the aeration pump clogged, because of which the flow rate of recirculated water decreased to 5%, and the flow rate of the supplied air was 1.5%.

 As a result, the quality of purified water was 6.8 mg / l, which does not meet the requirements for water discharged into natural reservoirs.

 EXAMPLE 5

The degree of contamination of the source wastewater BOD _full = 312 mg / L.

 The method is carried out as described above, while the biologically active elements are placed in three layers. The number of circulating volumes created is two.

The speed of water supplied to the sump V ₁ = 18.5 mm / s, the speed of water at the outlet of the first circulation volume is equal to the speed of water at the outlet of the second circulation volume and is 2.1 mm / s.

 Due to improper selection of the pump characteristics, the circulation flow rate increased to 20%, and the amount of air supplied increased to 7%. As a result, a flotation effect is observed (sludge rises), and the cleaning effect has decreased to 9.5 mg / l, which does not satisfy the requirements for water discharged into natural water bodies.

 Thus, the proposed method of biological wastewater treatment, subject to the specified pneumohydrodynamic regime, which is illustrated by examples 1-3, can increase the efficiency of biological water treatment, improves the quality of the water to the requirements corresponding to post-treatment, reduces the cost of treatment.

 Non-compliance with the specified pneumohydrodynamic regime in this method does not allow to achieve the desired technical result, as illustrated by examples 4-5.

Claims (1)

 A method of biological wastewater treatment, including the treatment of wastewater using biologically active elements representing a bearing surface coated with a biological film, aeration of water, circulation of water through a biofilm, creating a vortex surface under the surface layer of the treated wastewater, sedimentation of suspended solids, characterized in that biological wastewater treatment using biologically active elements representing the bearing surface covered with a biological film is carried out by After passing wastewater through aeration tanks with activated sludge, the process of water treatment using biologically active elements is combined with the process of sedimentation of suspended solids, including activated sludge, for which the biologically active elements are placed in a settling tank in two or more layers, in the space between which create a circulation volume (s) by supplying a water-air mixture there, while the flow rate of recycled water in each of the circulation volumes is 6-12% of the flow rate of water supplied to the sump, and the air flow is 2-5% of the recirculated water flow rate, and the speed of the water supplied to the sump and the water velocity at the outlet of the circulation volume (s) are correlated as (5-8): 1.