CN110981092B - Biological phenol-reducing denitrification system and method for coal chemical wastewater - Google Patents

Abstract

The invention provides a biological phenol and nitrogen removal system and method for coal chemical wastewater. A biological phenol-reducing denitrification system for coal chemical wastewater comprises a composite phenol-reducing denitrification device with an inner cavity, a secondary enhanced denitrification device and a carbon source supplementing device; the composite phenol-reducing denitrification device is provided with a water inlet pipe and a water outlet pipe A, the middle part of the inner cavity of the composite phenol-reducing denitrification device is provided with a guide cylinder A and a guide cylinder B which are coaxial, and the bottom of the inner cavity of the composite phenol-reducing denitrification device is provided with a sludge hopper A and a sludge discharge pipe A; the secondary enhanced denitrification device is communicated with the composite phenol-degrading denitrification device through a water outlet pipe A, a water outlet pipe B is arranged on the secondary enhanced denitrification device, and a partition plate which divides the inner cavity of the secondary enhanced denitrification device into a reverse aeration carrier discrete area and a secondary upflow biological filtration area is arranged in the inner cavity of the secondary enhanced denitrification device. The invention improves the phenol reduction and denitrification efficiency through the functional division, gradually reduces the inhibition effect of the phenolic compound on nitrification and denitrification, and has short hydraulic retention time and strong impact load resistance.

Description

Biological phenol-reducing denitrification system and method for coal chemical wastewater

Technical Field

The invention relates to a phenol and nitrogen removal system and method for coal chemical industry wastewater, in particular to a biological phenol and nitrogen removal system and method for coal chemical industry wastewater.

Background

The coal chemical wastewater has complex components and high toxicity, and the effective removal of refractory organic pollutants, phenol and ammonia nitrogen needs to be considered. The problem of wastewater treatment is the bottleneck of the development of the coal chemical industry, and the wastewater regeneration and reuse and high-standard discharge have great difficulty. The coal chemical industry enterprises urgently need the wastewater treatment technology with strong applicability, low operation cost and stable treatment effect, effectively solve the water control crisis and relieve the worries of the future for production. At present, the process route of 'pretreatment + biological treatment + advanced treatment' is commonly adopted at home and abroad to treat the coal chemical wastewater. Biological treatment is a key unit of the coal chemical wastewater treatment process, and the treatment effect of the biological treatment is directly related to the operation condition of the whole treatment system and the effluent quality. The COD concentration of effluent water of the conventional biological treatment process is higher, and the phenolic compounds inhibit denitrification, so that flora starts a self-protection mechanism to generate more Extracellular Polymeric Substances (EPS), and the removal efficiency of ammonia nitrogen and total nitrogen is seriously influenced.

Therefore, how to provide a biological phenol and nitrogen removal system and method for coal chemical wastewater, which can realize the high-efficiency removal of total phenol, COD, ammonia nitrogen and total nitrogen with lower hydraulic retention time, improve the impact load resistance and reduce the investment and operation cost is a technical problem to be solved in the field at present.

Disclosure of Invention

The invention aims to provide a biological phenol and nitrogen removal system for coal chemical wastewater, which enriches dominant flora, realizes high-efficiency removal of total phenol, COD, ammonia nitrogen and total nitrogen with low hydraulic retention time, improves the anti-impact load capacity, and reduces the investment and operation cost.

The invention also aims to provide a biological phenol-reducing denitrification method for the coal chemical industry wastewater.

The technical scheme adopted by the invention for solving the technical problems is as follows:

a biological phenol-reducing denitrification system for coal chemical wastewater comprises a composite phenol-reducing denitrification device with an inner cavity, a secondary enhanced denitrification device and a carbon source supplementing device;

the composite phenol-reducing denitrification device is provided with a water inlet pipe and a water outlet pipe A, the middle part of the inner cavity of the composite phenol-reducing denitrification device is provided with a guide cylinder A and a guide cylinder B which are coaxial, and the bottom of the inner cavity of the composite phenol-reducing denitrification device is provided with a sludge hopper A and a sludge discharge pipe A;

the bottom of the guide shell A is closed, the top of the guide shell A is provided with an interception net A, the top of the guide shell B is closed, the bottom of the guide shell B is open, the guide shell B is sleeved outside the guide shell A, a space is arranged between the guide shell A and the guide shell B, at least two interception nets B are arranged between the guide shell B and the inner cavity wall surface of the composite phenol-degrading denitrification device, the guide shell A, the guide shell B and the interception nets B divide the inner cavity of the composite phenol-degrading denitrification device into a reinforced phenol-degrading area, a sludge primary settling area, a primary upflow biological filtering area and an overflow area, the reinforced phenol-degrading area is arranged in the guide shell A, an embedded carrier is arranged in the guide shell A, the bottom of the guide shell A is provided with an aeration pipe A, the sludge primary settling area is arranged between the guide shell A and the guide shell B, the primary upflow biological filtering area is arranged between the guide shell B and the inner cavity wall surface of the composite phenol-degrading denitrification device and is limited by the interception nets B, and the composite carrier is arranged between the interception nets B, the bottom of the first-stage upflow biological filtration area is provided with an aeration pipe B, and the overflow area is positioned in the area of the inner cavity of the composite phenol-degrading denitrification device above the interception net B;

the secondary enhanced denitrification device is communicated with the composite phenol-degrading denitrification device through a water outlet pipe A, the secondary enhanced denitrification device is provided with a water outlet pipe B, the inner cavity of the secondary enhanced denitrification device is provided with a partition board which divides the inner cavity of the secondary enhanced denitrification device into a reverse aeration carrier discrete area and a secondary upflow biological filtering area, the lower part of the partition board is provided with a bottom water flow channel which is communicated with the reverse aeration carrier discrete area and the secondary upflow biological filtering area, the reverse aeration carrier discrete area is provided with at least two intercepting nets C, a discrete carrier is arranged between the intercepting nets C, the lower part of the reverse aeration carrier discrete area is provided with an aeration pipe C and an aeration pipe D, the secondary upflow biological filtering area is provided with at least two intercepting nets D, a composite carrier is arranged between the intercepting nets D, the lower part of the secondary upflow biological filtering area is provided with an aeration pipe E, and the bottom of the secondary upflow biological filtering area is provided with a sludge hopper B and a sludge discharge pipe B, a sludge discharge branch pipe is arranged on the sludge discharge pipe B, and the sludge discharge pipe B is communicated with a water inlet pipe through the sludge discharge branch pipe;

the carbon source supplementing device is provided with a dosing pipe and is communicated with the bottom of the secondary upflow biological filtration zone through the dosing pipe.

Preferably, the embedding carrier is a polyvinyl alcohol gel carrier with the diameter of 9-12 mm, and the filling rate of the embedding carrier in the reinforced phenol-reducing area is 15% -30%; the discrete carrier is a porous sphere with the diameter of 30-40 mm and the pore diameter of 0.8-1.5 mm, and the filling rate of the discrete carrier in the reverse aeration carrier discrete area is 30-40%.

Preferably, the composite carrier comprises an outer sphere, a porous carrier A and a porous carrier B, wherein the porous carrier A and the porous carrier B are wrapped by the outer sphere, the outer sphere is a grid hollow sphere with the diameter of 150mm and the grid pore diameter of 10-15 mm, the pore diameter of the porous carrier A is 0.5-0.7 mm, and the pore diameter of the porous carrier B is 1.6-2.5 mm.

Preferably, the aeration pipe A, the aeration pipe B, the aeration pipe C and the aeration pipe E are transversely arranged, the aeration direction is upward, the aeration pipe D is vertically arranged, and the aeration direction is radially around.

Preferably, the upper part of the overflow area is provided with an annular water collecting tank.

A method for performing biological phenol-reducing denitrification on coal chemical industry wastewater by adopting the biological phenol-reducing denitrification system for coal chemical industry wastewater specifically comprises the following steps:

enabling the coal chemical wastewater subjected to physicochemical pretreatment to flow into an enhanced phenol reduction zone of the composite phenol reduction denitrification device through a water inlet pipe, embedding carrier immobilized phenol reduction bacteria, and controlling the dissolved oxygen concentration of the enhanced phenol reduction zone to be 2-3 mg/L through an aeration pipe A to perform phenol reduction and nitrification;

secondly, the wastewater flows into a sludge primary settling zone through the enhanced phenol reduction zone to be primarily settled, and sludge settled in a sludge hopper A is periodically discharged through a sludge discharge pipe A;

thirdly, the wastewater flows into a first-level upflow biological filtering area through a sludge primary settling area, the dissolved oxygen concentration of the first-level upflow biological filtering area is controlled to be 2 +/-0.2 mg/L through an aeration pipe B, the composite carrier forms a local anaerobic microenvironment under the external aerobic condition, and phenol-reducing bacteria, nitrifying bacteria and denitrifying bacteria are enriched to perform the functions of phenol reduction, nitrification and denitrification;

the wastewater flows into the overflow area through the first-stage upflow biological filtering area and flows into the reverse aeration carrier discrete area of the second-stage enhanced denitrification device through the water outlet pipe A;

controlling the dissolved oxygen concentration of the reverse aeration carrier discrete zone to be 2-2.5 mg/L through an aeration pipe C and an aeration pipe D, strengthening aerobic phenol reduction and nitrification in the reverse aeration carrier discrete zone, and enabling the aeration direction to be opposite to the water flow direction; when the dissolved oxygen concentration is higher than 2.5mg/L, closing the aeration pipe C and maintaining the aeration pipe D for continuous aeration, maintaining the discrete carrier in a dispersed and moving state through the aeration pipe D, and opening the aeration pipe C when the dissolved oxygen concentration is lower than 2 mg/L;

and sixthly, the wastewater flows into the secondary upflow biological filtration zone through the bottom water flow channel through the reverse aeration carrier discrete zone, a carbon source is added to the bottom of the secondary upflow biological filtration zone through a carbon source supplementing device by a medicine adding pipe, the dissolved oxygen concentration of the secondary upflow biological filtration zone is controlled to be 1 +/-0.2 mg/L through an aeration pipe E, the composite carrier forms more anaerobic micro-environments under the condition of lower dissolved oxygen, the denitrification effect is enhanced while phenol reduction and nitrification are performed, the wastewater passes through the secondary upflow biological filtration zone, passes through a water outlet pipe B discharge system, and is periodically discharged at a sludge hopper B through a sludge discharge pipe B, and part of sludge flows back to the enhanced phenol reduction zone through a sludge discharge branch pipe to improve the sludge concentration.

The invention has the beneficial effects that:

compared with the prior art, the biological phenol and nitrogen removal system and the method for the coal chemical industry wastewater have the following advantages and beneficial effects,

(1) the system and the method improve the phenol reduction and denitrification efficiency through functional division, gradually reduce the inhibition effect of the phenolic compound on nitrification and denitrification, and enrich the dominant flora in the division, so that the hydraulic retention time is short, the volume load is high, and the impact load resistance is strong;

(2) the system and the method can strengthen the synchronous nitrification and denitrification, improve the total nitrogen removal efficiency and reduce the dosage of the external carbon source;

(3) the system and the method realize effective control of the activated sludge through sludge backflow and biological filtration, combine the advantages of an activated sludge method and a biofilm method, and realize efficient removal of total phenol, COD, ammonia nitrogen and total nitrogen under the condition of not arranging a nitrification liquid backflow pipeline and a secondary sedimentation tank.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.

FIG. 1 is a schematic front view of the present invention;

FIG. 2 is a schematic structural view of the composite carrier of the present invention.

In the figure: 1. a composite phenol-reduction denitrification device 11, a water inlet pipe 12, an enhanced phenol-reduction zone 121, guide cylinders A, 122, an embedding carrier 123, aeration pipes A, 124, interception nets A, 13, a sludge primary settling zone 131, guide cylinders B, 132, sludge hoppers A, 133, sludge discharge pipes A, 14, a primary upflow biological filtration zone 141, a composite carrier 1411, an outer sphere 1412, a porous carrier A, 1413, a porous carrier B, 142, interception nets B, 143, aeration pipes B, 15, an overflow zone 151, an annular water collecting tank 16 and a water outlet pipe A,

2. a secondary enhanced denitrification device 21, a reverse aeration carrier discrete area 211, a discrete carrier 212, interception nets C and 213, aeration pipes C and 214, aeration pipes D and 22, a bottom water flow channel 23, a secondary upflow biological filtering area 231, interception nets D and 232, aeration pipes E and 233, sludge hoppers B and 234, sludge discharge pipes B and 2341, sludge discharge branch pipes 24 and a water outlet pipe B,

3. a carbon source supplementing device 31 and a dosing tube.

Detailed Description

The technical solution of the present invention is further specifically described below by way of specific examples in conjunction with the accompanying drawings. It is to be understood that the practice of the invention is not limited to the following examples, and that any variations and/or modifications may be made thereto without departing from the scope of the invention.

In the present invention, all parts and percentages are by weight, unless otherwise specified, and the equipment and materials used are commercially available or commonly used in the art. The methods in the following examples are conventional in the art unless otherwise specified. The components or devices in the following examples are, unless otherwise specified, standard parts or parts known to those skilled in the art, the structure and principle of which are known to those skilled in the art through technical manuals or through routine experimentation.

Example (b):

the biological phenol-reducing denitrification system for the coal chemical industry wastewater as shown in the figure 1 comprises a composite phenol-reducing denitrification device 1, a secondary enhanced denitrification device 2 and a carbon source supplementing device 3; the composite phenol-degrading denitrification device is sequentially provided with a water inlet pipe 11, a reinforced phenol-degrading area 12, a sludge primary settling area 13, a primary upflow biological filtration area 14, an overflow area 15 and a water outlet pipe A16 along the water flow direction; the water inlet pipe is communicated with the enhanced phenol reduction area, the enhanced phenol reduction area is separated from the sludge primary sedimentation area through a guide cylinder A121, an embedding carrier 122 is arranged in the guide cylinder A, the bottom of the guide cylinder A is closed and is provided with an aeration pipe A123, and the top of the guide cylinder A is provided with an interception net A124; the sludge primary settling zone and the primary upflow biological filtration zone are separated by a guide cylinder B131, the top of the guide cylinder B is closed, the bottom of the guide cylinder B is open, a sludge hopper A132 is arranged at the bottom of the sludge primary settling zone, and a sludge discharge pipe A133 is arranged at the bottom of the sludge hopper A; the primary upflow biological filtration zone is provided with a composite carrier 141, an interception net B142 and an aeration pipe B143, the composite carrier is limited by the interception net B, and the aeration pipe B is fixed at the bottom of the primary upflow biological filtration zone; the upper part of the overflow area is provided with an annular water collecting tank 151, and a water outlet pipe A is communicated with a secondary enhanced denitrification device; the secondary enhanced denitrification device is sequentially provided with a reverse aeration carrier discrete area 21, a bottom water flow channel 22, a secondary upflow biological filtering area 23 and a water outlet pipe B24 along the water flow direction, and the reverse aeration carrier discrete area is communicated with the secondary upflow biological filtering area through the bottom water flow channel; the reverse aeration carrier discrete area is provided with a discrete carrier 211, an interception net C212, an aeration pipe C213 and an aeration pipe D214, the secondary upflow biological filtration area is provided with a composite carrier, an interception net D231 and an aeration pipe E232, the bottom is provided with a sludge hopper B233 and a sludge discharge pipe B234, and the sludge discharge pipe B is communicated with a water inlet pipe through a sludge discharge branch pipe. The carbon source supplementing device is provided with a dosing pipe 31 and is communicated with the bottom of the secondary upflow biological filtration zone through the dosing pipe.

The embedding carrier is polyvinyl alcohol gel carrier with the diameter of 10mm, and the filling rate in the reinforced phenol reduction area is 25 percent. As shown in figure 2, the composite carrier comprises an outer sphere, a porous carrier A and a porous carrier B, wherein the outer sphere is a grid hollow sphere with the diameter of 150mm and the grid aperture of 10-15 mm, the diameter of the porous carrier A is 30mm, the aperture of the porous carrier A is 0.5-0.7 mm, the diameter of the porous carrier B is 30mm, the aperture of the porous carrier B is 1.6-2.5 mm, and the filling volume ratio of the porous carrier A to the porous carrier B is 1.37. The filling rate of the discrete carrier in the discrete region of the reverse aeration carrier is 35%, and the discrete carrier is a porous sphere with the diameter of 30mm and the pore diameter of 0.8-1.5 mm. Aeration pipe A, aeration pipe B, aeration pipe C, aeration pipe E transversely arrange to the aeration of upper portion, aeration pipe D vertical arrangement is to aeration all around.

A method for treating wastewater by adopting the system specifically comprises the following steps:

the method comprises the following steps that firstly, coal chemical wastewater subjected to physicochemical pretreatment enters a biological phenol reduction and denitrification system of the coal chemical wastewater, flows into an enhanced phenol reduction zone from a water inlet pipe, entraps immobilized Acinetobacter phenol reduction bacteria, and controls the concentration of dissolved oxygen in the enhanced phenol reduction zone to be 2-3 mg/L through an aeration pipe A to perform phenol reduction and nitrification;

secondly, the wastewater flows into a sludge primary settling area from the reinforced phenol reduction area for primary settling, and the sludge settled in a sludge hopper A is periodically discharged out of the system through a sludge discharge pipe A;

thirdly, the wastewater flows upwards from the sludge primary settling zone and passes through the primary upflow biological filtering zone, the dissolved oxygen concentration of the primary upflow biological filtering zone is controlled to be 2 +/-0.2 mg/L through the aeration pipe B, the composite carrier can form a local anaerobic microenvironment under the external aerobic condition, and phenol-reducing bacteria, nitrifying bacteria and denitrifying bacteria are enriched to perform the functions of phenol reduction, nitrification and denitrification;

the wastewater enters an overflow area after being treated by a first-stage upflow biological filtering area and flows into a reverse aeration carrier discrete area through an annular water collecting tank and a water outlet pipe A;

fifthly, strengthening aerobic phenol reduction and nitrification in a reverse aeration carrier discrete area, wherein the aeration direction is opposite to the water flow direction, controlling the dissolved oxygen concentration of the reverse aeration carrier discrete area to be 2-2.5 mg/L through an aeration pipe C and an aeration pipe D, closing the aeration pipe C and maintaining the aeration pipe D for continuous aeration when the dissolved oxygen concentration is higher than 2.5mg/L, maintaining the discrete carrier in a dispersed and moving state through the aeration pipe D, and opening the aeration pipe C when the dissolved oxygen concentration is lower than 2 mg/L;

and sixthly, the wastewater enters a secondary upflow biological filtration zone from a reverse aeration carrier discrete zone through a bottom water flow channel, a carbon source supplementing device adds a carbon source to the bottom of the secondary upflow biological filtration zone through a medicine adding pipe, the dissolved oxygen concentration of the primary upflow biological filtration zone is controlled to be 1 +/-0.2 mg/L through an aeration pipe E, the composite carrier can form more anaerobic micro-environments under the condition of lower dissolved oxygen, the denitrification effect is enhanced while phenol reduction and nitrification are performed, the wastewater is discharged out of the system after the reaction of the secondary upflow biological filtration zone, sludge precipitated in a sludge hopper B is periodically discharged out of a secondary enhanced denitrification device through a sludge discharge pipe B, and part of sludge is returned to the enhanced phenol reduction zone through a sludge discharge branch pipe and the sludge concentration is improved.

The Acinetobacter phenol-reducing bacteria is MKHZPDA-1, and is produced by Hangzhou environmental research institute, Inc. of coaly.

In the case that the total hydraulic retention time is 39 hours, the pilot water is the fixed bed gasification wastewater treated by phenol ammonia recovery, oil removal precipitation and air flotation, and the water quality monitoring data of this example after running for 51 days are shown in table 1.

Water quality monitoring data (unit: mg/L) during test run in Table 1

Index of water quality	System water intake	Effluent of composite phenol-reducing denitrification device	Effluent of secondary enhanced denitrification device
				Total phenols	226~305	12.3~21.9	2.35~6.72
COD	2731~3566	176~235	39.6~68.7
				Ammonia nitrogen	157~239	12.6~28.3	0~2.89
Total nitrogen	178-266	27.1~39.6	4.35~12.6

As can be seen from Table 1, the total phenol concentration of the effluent of the composite phenol-reducing denitrification device is less than or equal to 21.9mg/L, the inhibition effect of phenolic substances on microorganisms of the secondary enhanced denitrification device can be effectively avoided, and the higher removal rate of ammonia nitrogen and total nitrogen is also kept. The quality of the effluent of the secondary denitrification device is stable, and the deep removal of ammonia nitrogen and total nitrogen is realized. On the whole, the system stably realizes the high-efficiency removal of total phenol, COD, ammonia nitrogen and total nitrogen under the condition of not arranging a nitration liquid return pipeline and a secondary sedimentation tank, and has short hydraulic retention time and strong impact load resistance.

The above-described embodiments are only preferred embodiments of the present invention, and are not intended to limit the present invention in any way, and other variations and modifications may be made without departing from the spirit of the invention as set forth in the claims.

Claims (5)

1. The utility model provides a biological phenol nitrogen removal system that falls of coal chemical industry waste water which characterized in that: the biological phenol-reducing denitrification system for the coal chemical industry wastewater comprises a composite phenol-reducing denitrification device with an inner cavity, a secondary enhanced denitrification device and a carbon source supplementing device; the composite phenol-reducing denitrification device is provided with a water inlet pipe and a water outlet pipe A, the middle part of the inner cavity of the composite phenol-reducing denitrification device is provided with a guide cylinder A and a guide cylinder B which are coaxial, and the bottom of the inner cavity of the composite phenol-reducing denitrification device is provided with a sludge hopper A and a sludge discharge pipe A; the bottom of the guide shell A is closed, the top of the guide shell A is provided with an interception net A, the top of the guide shell B is closed, the bottom of the guide shell B is open, the guide shell B is sleeved outside the guide shell A, an interval is arranged between the guide shell A and the guide shell B, at least two interception nets B are arranged between the guide shell B and the inner cavity wall surface of the composite phenol-degrading denitrification device, the guide shell A, the guide shell B and the interception nets B divide the inner cavity of the composite phenol-degrading denitrification device into a reinforced phenol-degrading area, a sludge primary settling area, a primary upflow biological filtering area and an overflow area, the reinforced phenol-degrading area is positioned in the guide shell A, an embedded carrier is arranged in the guide shell A, the bottom of the guide shell A is provided with an aeration pipe A, the sludge primary settling area is positioned between the guide shell A and the guide shell B, the primary upflow biological filtering area is positioned between the guide shell B and the inner cavity wall surface of the composite phenol-degrading denitrification device and is limited by the interception nets B, and the composite carrier is arranged between the interception nets B, the bottom of the first-stage upflow biological filtration area is provided with an aeration pipe B, and the overflow area is positioned in the area of the inner cavity of the composite phenol-degrading denitrification device above the interception net B; the secondary enhanced denitrification device is communicated with the composite phenol-degrading denitrification device through a water outlet pipe A, a water outlet pipe B is arranged on the secondary enhanced denitrification device, a partition plate for dividing the inner cavity of the secondary enhanced denitrification device into a reverse aeration carrier discrete area and a secondary upflow biological filtering area is arranged in the inner cavity of the secondary enhanced denitrification device, a bottom water flow channel for communicating the reverse aeration carrier discrete area with the secondary upflow biological filtering area is arranged at the lower part of the partition plate, at least two intercepting nets C are arranged in the reverse aeration carrier discrete area, a discrete carrier is arranged between the intercepting nets C, an aeration pipe C and an aeration pipe D are arranged at the lower part of the reverse aeration carrier discrete area, at least two intercepting nets D are arranged in the secondary upflow biological filtering area, a composite carrier is arranged between the intercepting nets D, an aeration pipe E is arranged at the lower part of the secondary upflow biological filtering area, and a sludge hopper B and a sludge discharge pipe B are arranged at the bottom of the secondary upflow biological filtering area, a sludge discharge branch pipe is arranged on the sludge discharge pipe B, and the sludge discharge pipe B is communicated with a water inlet pipe through the sludge discharge branch pipe; the carbon source supplementing device is provided with a dosing pipe and is communicated with the bottom of the secondary upflow biological filtration zone through the dosing pipe; aeration pipe A, aeration pipe B, aeration pipe C and aeration pipe E transversely arrange, the aeration direction is upwards, aeration pipe D vertical layout, the aeration direction is radially all around.

2. The biological phenol-degrading and nitrogen-removing system for the coal chemical industry wastewater as claimed in claim 1, wherein: the embedding carrier is a polyvinyl alcohol gel carrier with the diameter of 9-12 mm, and the filling rate of the embedding carrier in the enhanced phenol reduction area is 15% -30%; the discrete carrier is a porous sphere with the diameter of 30-40 mm and the pore diameter of 0.8-1.5 mm, and the filling rate of the discrete carrier in the reverse aeration carrier discrete area is 30-40%.

3. The biological phenol-degrading and nitrogen-removing system for the coal chemical industry wastewater as claimed in claim 1, wherein: the composite carrier comprises an external sphere, a porous carrier A and a porous carrier B, wherein the porous carrier A and the porous carrier B are wrapped by the external sphere, the external sphere is a grid hollow sphere with the diameter of 150mm and the grid pore diameter of 10-15 mm, the pore diameter of the porous carrier A is 0.5-0.7 mm, and the pore diameter of the porous carrier B is 1.6-2.5 mm.

4. The biological phenol-degrading and nitrogen-removing system for the coal chemical industry wastewater as claimed in claim 1, wherein: the upper part of the overflow area is provided with an annular water collecting tank.

5. A method for biologically reducing phenol and denitrifying coal chemical industry wastewater by using the biologically reducing phenol and denitrifying system for coal chemical industry wastewater according to any one of claims 1 to 4, which is characterized by comprising the following steps: the method specifically comprises the following steps of,

enabling the coal chemical wastewater subjected to physicochemical pretreatment to flow into an enhanced phenol reduction zone of the composite phenol reduction denitrification device through a water inlet pipe, embedding carrier immobilized phenol reduction bacteria, and controlling the dissolved oxygen concentration of the enhanced phenol reduction zone to be 2-3 mg/L through an aeration pipe A to perform phenol reduction and nitrification;

secondly, the wastewater flows into a sludge primary settling zone through the enhanced phenol reduction zone to be primarily settled, and sludge settled in a sludge hopper A is periodically discharged through a sludge discharge pipe A;

thirdly, the wastewater flows into a first-level upflow biological filtering area through a sludge primary settling area, the dissolved oxygen concentration of the first-level upflow biological filtering area is controlled to be 2 +/-0.2 mg/L through an aeration pipe B, the composite carrier forms a local anaerobic microenvironment under the external aerobic condition, and phenol-reducing bacteria, nitrifying bacteria and denitrifying bacteria are enriched to perform the functions of phenol reduction, nitrification and denitrification;

the wastewater flows into the overflow area through the first-stage upflow biological filtering area and flows into the reverse aeration carrier discrete area of the second-stage enhanced denitrification device through the water outlet pipe A;

controlling the dissolved oxygen concentration of the reverse aeration carrier discrete zone to be 2-2.5 mg/L through an aeration pipe C and an aeration pipe D, strengthening aerobic phenol reduction and nitrification in the reverse aeration carrier discrete zone, and enabling the aeration direction to be opposite to the water flow direction; when the dissolved oxygen concentration is higher than 2.5mg/L, closing the aeration pipe C and maintaining the aeration pipe D for continuous aeration, maintaining the discrete carrier in a dispersed and moving state through the aeration pipe D, and opening the aeration pipe C when the dissolved oxygen concentration is lower than 2 mg/L;

and sixthly, the wastewater flows into the secondary upflow biological filtration zone through the bottom water flow channel through the reverse aeration carrier discrete zone, a carbon source is added to the bottom of the secondary upflow biological filtration zone through a carbon source supplementing device by a medicine adding pipe, the dissolved oxygen concentration of the secondary upflow biological filtration zone is controlled to be 1 +/-0.2 mg/L through an aeration pipe E, the composite carrier forms more anaerobic micro-environments under the condition of lower dissolved oxygen, the denitrification effect is enhanced while phenol reduction and nitrification are performed, the wastewater passes through the secondary upflow biological filtration zone, passes through a water outlet pipe B discharge system, and is periodically discharged at a sludge hopper B through a sludge discharge pipe B, and part of sludge flows back to the enhanced phenol reduction zone through a sludge discharge branch pipe to improve the sludge concentration.

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