CN111689573A - Multiple-water-level-reduction backwashing method for thoroughly solving hardening of biological filter - Google Patents
Multiple-water-level-reduction backwashing method for thoroughly solving hardening of biological filter Download PDFInfo
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- CN111689573A CN111689573A CN202010603286.8A CN202010603286A CN111689573A CN 111689573 A CN111689573 A CN 111689573A CN 202010603286 A CN202010603286 A CN 202010603286A CN 111689573 A CN111689573 A CN 111689573A
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Abstract
The invention discloses a multiple-falling water level backwashing method for thoroughly solving the hardening of a biological filter, which is a method comprising falling water level backwashing, air washing, air-water combination, water lowering again, air-water combination again and water rinsing, and by adopting the method, a series of problems of hardening of a filter material of the biological filter, poor water passing capacity of the filter, high operating pressure, unobvious water pollutant removal effect, fluctuation and standard exceeding of effluent water quality and the like caused by hardening of the filter material are thoroughly solved, and the problem that the hardening cannot be thoroughly solved by the existing backwashing method is solved; the increase of the operation cost caused by high-strength multi-frequency continuous backwashing of the filter material in the filter tank is thoroughly controlled; the defect of insufficient washing of the filter head at the first precipitation level is thoroughly overcome; has great popularization and application value for the technical field of the biological filter.
Description
Technical Field
The invention belongs to the technical field of water pollution treatment, and particularly relates to a high-efficiency uniform and rapid water and gas distribution backwashing system of a biological filter and a using method thereof.
Background
The existing biological filter generally adopts a 'precipitation level + air water combination method' to carry out periodic backwashing, and suspended matters intercepted by the filter and an aged and fallen biological membrane are discharged out of a system so as to ensure the permeability of filter materials in the filter, but the biological filter still has a plurality of problems in operation, such as: (1) in the backwashing process of the filter, the phenomenon of uneven water distribution and air distribution, overlarge backwashing strength of a local area and even strong material spraying frequently occurs, and the phenomenon of insufficient backwashing strength of the local area and even no air is generated; in the back flushing process of some filter tanks, the water distribution and the gas distribution have hysteresis, the local area close to the gas inlet end distributes water and gas in advance, even the strength is far beyond the designed strength, and the water distribution and the gas distribution in other areas have obvious hysteresis and extremely uneven strength; (2) after the backwashing of the filter tank is finished, continuous bubbles often appear at a plurality of positions, the duration is long, the bubbles cannot be discharged through an exhaust system, the operation attractiveness of the filter tank is seriously influenced, and particularly in a nitrogen removal or denitrification biological filter tank system, the pollutant removal efficiency of a denitrification filter tank is reduced due to the continuous bubbles; (3) because the backwashing water distribution and air distribution are uneven, the backwashing strength of the local area of the filter tank is insufficient, the local backwashing strength is too high, the problems of hardening, material spraying, filter material loss, mixed bed of a supporting layer and a filter material layer and the like of a filter material of the biological filter tank are easily caused in the past, serious production accidents are caused even when the filter plate is turned over, the daily production operation is tired, and the problems of the current situation are thoroughly solved by an efficient uniform and rapid air distribution backwashing system and a using method of the biological filter tank.
Disclosure of Invention
The invention aims to solve the problems and provides a multiple-precipitation-level backwashing method for thoroughly solving the hardening problem of a biological filter so as to break through the current operation difficulty.
The invention specifically comprises the following contents:
the invention aims to solve the problems and provides a multiple-precipitation-level backwashing method for thoroughly solving the hardening problem of a biological filter so as to break through the current operation difficulty. The specific contents are as follows: the biological filter backwashing system consists of a pressure sensor, a PLC system, a suspended matter detector, a liquid level meter, a backwashing gas system and a backwashing water system; the suspended matter detector is arranged in the clear water area; the pressure sensor is positioned below the filter plate and used for measuring the pressure value between the filter head and the water surface of the clear water area above the filter material layer; the liquid level meter is arranged at the top of the filter tank and used for monitoring the liquid level height of the filter tank when the water level of the filter tank is reduced; when data measured by an automatic monitoring system consisting of the pressure sensor and the suspended matter detector is fed back to the PLC system, and the PLC system determines that the biological filter needs backwashing through analysis, the system starts a backwashing program; the automatic back-flushing program of the filter tank comprises the following steps:
the biological filter backwashing system consists of a pressure sensor, a PLC system, a suspended matter detector, a liquid level meter, a backwashing gas system and a backwashing water system; the suspended matter detector is arranged in the clear water area; the pressure sensor is positioned below the filter plate and used for measuring the pressure value between the filter head and the water surface of the clear water area above the filter material layer; the liquid level meter is arranged at the top of the filter tank and used for monitoring the liquid level height of the filter tank when the water level of the filter tank is reduced; when data measured by an automatic monitoring system consisting of the pressure sensor and the suspended matter detector is fed back to the PLC system, and the PLC system determines that the biological filter needs backwashing through analysis, the system starts a backwashing program; the automatic back-flushing program of the filter tank comprises the following steps:
(1) and (3) backwashing at a reduced water level: firstly, opening a control valve on a water level reducing backwashing drain pipe, quickly reducing the water level in the biological filter at the moment, quickly reducing the water level in the biological filter through gravity, reversely washing impurities and fibrous materials in filter head gaps, filter cap gaps and filter rods, and arranging the impurities and the fibrous materials in the biological filter side by side to solve the problem of filter head impurity blockage; monitoring the descending height of the liquid level of the filter tank through a liquid level meter, closing a control valve on a descending water level backwashing drainage pipe when the liquid level descends to 0-80cm of the surface layer of the filter material, and stopping the descending water level backwashing;
(2) air flushing: opening a control valve on the backwashing air inlet pipeline, starting a backwashing blower to enable backwashing air to enter the biological filter from the backwashing air inlet pipeline, starting air washing, and loosening the plate-bound biological filter material layer;
(3) air-water combined backwashing: opening a control valve on a backwashing water inlet pipeline, feeding backwashing water from the bottom of a filter plate through the backwashing water inlet pipeline, starting air-water combined backwashing, enabling a hardened filter material layer to integrally float upwards and lift under the action of air-water combined backwashing, strongly washing the hardened filter material layer through the air-water cavity combined backwashing action at the lower part of the filter material layer, backwashing a part of slightly hardened filter material layer, and lowering loosened granular filter materials to the lower part of an air-water cavity under the action of gravity after the slightly hardened filter material layer is loosened through backwashing; the seriously hardened filter material layer can continuously keep a floating and lifting or suspension state under the combined backwashing action force of the air-water cavity because the filter material layer can not be washed away; monitoring the overflow of backwashing wastewater from the backwashing drainage channel by a liquid level meter, closing a backwashing blower and a corresponding pipeline control valve, a backwashing water pump and a corresponding pipeline control valve after backwashing drainage is carried out for 1-10min, and stopping air-water combined backwashing;
(4) reducing the water level for backwashing again: opening the control valve on the water level lowering back-flushing drain pipe again, and then leading the severely hardened floating filter material layer to rapidly sink along with the combined action of the water level lowering of the biological filter and the self gravity; in the process of sinking, a filter material layer close to the wall of the tank and the inner wall of the filter tank generate strong washing friction force, so that the sinking rate of the filter material layer close to the wall of the tank is reduced, and meanwhile, due to the friction action of the filter material and the wall of the tank, the hardened filter material layer at the periphery can be loosened; the filter material layer far away from the periphery of the tank wall can sink quickly due to the gravity action of the filter material layer but no friction force of the tank wall; because the difference between the acting force of the filter material layer close to the tank wall and the acting force of the filter material layer far away from the periphery of the tank wall is large, the seriously hardened filter material layer can be divided into a plurality of small hardened filter material layers by the acting force, thereby solving the problem of the seriously hardened filter material layer of the whole tank; meanwhile, sundries retained in the filter cap in the air-water combined backwashing stage are subjected to complete reverse backwashing and are arranged in the biological filter tank; monitoring the descending height of the liquid level of the filter tank through a liquid level meter, and closing a control valve on a water level descending backwashing drain pipe when the liquid level descends to 0-80cm of the surface layer of the filter material;
(5) secondary air flushing: opening the control valve on the backwashing air inlet pipeline again, starting the backwashing blower to start air washing, and loosening the small hardened filter material layers;
(6) and (3) performing air-water combined backwashing again: opening the control valve on the back washing water inlet pipeline again, feeding back washing water from the back washing water inlet pipeline from the bottom of the filter plate, and starting air-water combined washing back washing; the air-water combined backwashing is carried out on a plurality of small hardened filter material layers, and the air-water strong backwashing and the friction acting force among the filter materials can completely loosen and wash away the plurality of small hardened filter material layers, so that the hardening problem of the plurality of small hardened filter material layers is solved, and the hardening problem of a serious filter material layer is completely solved;
(7) rinsing with water: and finally, closing the back washing blower and the corresponding pipeline control valve, and performing water rinsing independently.
The backwashing period of the biological filter is 5-48h, the air washing strength is 25-50L/m 2 & s, and the water washing strength is 6-20L/m 2 & s.
The thickness of the filter material layer is 1.5-4.0 m, and the diameter is 3-10 mm.
The biological filter can be an upward flow biological filter or a downward flow biological filter, and can be an anaerobic biological filter, an anoxic biological filter or an aerobic biological filter.
And the flow velocity of the cross section in the filter rod at the lower end of each filter head is not less than 0.15m/s during the water level reduction backwashing.
The backwashing program of the steps (4), (5) and (6) can be continuously and alternately operated for backwashing for multiple times, and the alternate operation frequency is 2-5 times.
In the process of lowering the water level, the free liquid level lowering height of the biological filter during normal operation is controlled in a linkage manner through a liquid level meter and a PLC system which are arranged on the top of the biological filter.
The liquid level meter, the back washing blower, the back washing water pump and the regulating valve are respectively connected with the PLC system.
And the air-water combined backwashing time is 1-15 min.
The multiple-water-level-reduction backwashing method for thoroughly solving the hardening of the biological filter tank thoroughly solves a series of problems of hardening of the filter material of the biological filter tank, poor filter water passing capacity, high operation pressure, unobvious water pollutant removal effect, fluctuation and standard exceeding of effluent quality and the like of the filter tank due to hardening of the filter material; the increase of the operation cost caused by high-strength multi-frequency continuous backwashing of the filter material in the filter tank is thoroughly controlled; thoroughly solved the first time precipitation level filter head and washed insufficient drawback. Has great popularization and application value for the technical field of the biological filter.
Drawings
FIG. 1 is a program control flow chart of a multiple water level reduction backwashing system for thoroughly solving the hardening problem of a biological filter tank;
FIG. 2 is a schematic diagram showing the distribution of the filter material layer of the first water level lowering of the biofilter system according to the present invention;
FIG. 3 is a schematic diagram showing the distribution of the filter material layer before the biological filter system is lowered to the water level again;
wherein: 1. the biological filter comprises a biological filter, 2 parts of a water distribution chamber, 3 parts of a filter plate, 4 parts of a filter material layer, 4 parts of 1 part of a loose granular filter material, 4 parts of 2 parts of a hardened filter material, 5 parts of a clean water area, 6 parts of a filter head, 7 parts of a liquid level meter, 8 parts of a pressure sensor, 9 parts of a suspended matter detector, 10 parts of a lower water level drainage pipeline, 11 parts of a lower water level drainage pipeline control valve, 12 parts of a back flush blower, 13 parts of a back flush air inlet pipeline, 14 parts of a back flush air inlet pipeline control valve, 15 parts of a back flush water pump, 16 parts of a back flush water inlet pipeline, 17 parts of a back flush water inlet pipeline control valve, 18 parts of.
Detailed Description
The invention is further described with reference to fig. 1, 2 and 3:
a backwashing system of a multiple water-level-reduction backwashing method for thoroughly solving the hardening of a biological filter (1) is composed of a pressure sensor, a PLC system, a suspended matter detector (9), a liquid level meter (7), a backwashing gas system and a backwashing water system; the suspended matter detector (9) is arranged in the clear water area (5); the pressure sensor (8) is positioned below the filter plate (3) and used for measuring the pressure value between the filter head (6) and the water surface of the clear water area (5) above the filter material layer (4); the liquid level meter (7) is arranged at the top of the filter tank (1) and is used for monitoring the liquid level height of the filter tank (1) when the water level falls; when data measured by an automatic monitoring system consisting of the pressure sensor (8) and the suspended matter detector (9) is fed back to the PLC system, and the PLC system analyzes and determines that the biological filter (1) needs backwashing, the system starts a backwashing program; the automatic back-flushing program of the filter tank comprises the following steps:
(1) and (3) backwashing at a reduced water level: firstly, a control valve (11) on a water level reducing backwashing drain pipe (10) is opened, at the moment, the water level in the biological filter (1) begins to be rapidly reduced, the water level in the biological filter (1) is rapidly reduced through gravity, impurities and fibrous substances in filter head gaps (6), filter cap gaps and filter rods are reversely washed clean, and the impurities and the fibrous substances are discharged from the biological filter (1) side by side, so that the problem of filter head impurities (6) blockage is solved; the descending height of the liquid level of the filter tank (1) is monitored by a liquid level meter (7), and when the liquid level descends to 0-80cm of the surface layer (4) of the filter material, a control valve (11) on a descending water level backwashing drainage pipe (10) is closed, and the descending water level backwashing is stopped;
(2) air flushing: opening a control valve (14) on a backwashing air inlet pipeline (13), starting a backwashing air blower (12), enabling backwashing air to enter the biological filter (1) from the backwashing air inlet pipeline (13), starting air washing, and loosening the plate-bonded biological filter material layer (4);
(3) air-water combined backwashing: opening a control valve (17) on a backwashing water inlet pipeline (16), feeding backwashing water from the backwashing water inlet pipeline (16) from the bottom of a filter plate (3), starting air-water combined backwashing, so that a hardened filter material layer (4) starts to integrally float upwards and lift under the air-water combined backwashing action, strongly washing the hardened filter material layer (4) through the air-water cavity (20) at the lower part of the filter material layer (4), backwashing part of the slightly hardened filter material layer (4), and lowering loosened granular filter materials (4-1) to the lower part of an air-water cavity (20) under the action of gravity after the slightly hardened filter material layer (4) is backwashed and loosened; the seriously hardened filter material layer (4-2) can continuously keep a floating and lifting or suspension state under the combined backwashing action force of the air-water cavity (20) because the filter material layer can not be washed away; monitoring the overflow of backwashing wastewater from the backwashing drainage channel by a liquid level meter (7), closing a backwashing blower (12) and a corresponding pipeline control valve (14), a backwashing water pump (15) and a corresponding pipeline control valve (17) after backwashing drainage is carried out for 1-10min, and stopping air-water combined backwashing; (4) reducing the water level for backwashing again: opening the control valve (11) on the water level-reducing backwashing water discharge pipe (10) again, and then leading the severely hardened floating filter material layer (4-2) to rapidly sink under the combined action of the water level reduction and the self gravity of the biological filter (1); in the process of sinking, the filter material layer close to the wall of the tank and the inner wall of the filter tank generate strong washing friction force, so that the sinking rate of the filter material layer close to the wall of the tank is reduced, and meanwhile, due to the friction action of the filter material and the wall of the tank, the filter material layer (4-2) hardened at the periphery is loosened; the filter material layer far away from the periphery of the tank wall can sink quickly due to the gravity action of the filter material layer but no friction force of the tank wall; because the difference between the acting force of the filter material layer close to the tank wall and the acting force of the filter material layer far away from the periphery of the tank wall is large, the filter material layer (4-2) which is seriously hardened can be divided into a plurality of small hardened filter material layers, thereby solving the problem of the serious hardened filter material layer of the whole tank; meanwhile, sundries retained in the filter cap in the air-water combined backwashing stage are subjected to complete reverse backwashing and are arranged in the biological filter tank; the descending height of the liquid level of the filter tank is monitored by a liquid level meter (7), and when the liquid level descends to 0-80cm of the layer of the filter material surface (4), a control valve (11) on a water level descending backwashing drain pipe (10) is closed;
(5) secondary air flushing: opening the control valve (14) on the backwashing air inlet pipeline (13) again, starting the backwashing blower (12), starting air washing, and loosening the small hardened filter material layers;
(6) and (3) performing air-water combined backwashing again: opening the control valve (17) on the backwashing water inlet pipeline (16) again, feeding backwashing water from the backwashing water inlet pipeline (16) from the bottom of the filter plate (3), and starting air-water combined washing backwashing; the air-water combined backwashing is carried out on a plurality of small hardened filter material layers, and the air-water strong backwashing and the friction acting force among the filter materials can completely loosen and wash away the plurality of small hardened filter material layers, so that the hardening problem of the plurality of small hardened filter material layers is solved, and the hardening problem of a serious filter material layer is completely solved;
(7) rinsing with water: finally, the back washing blower (12) and the corresponding pipeline control valve (14) are closed, and water rinsing is carried out independently.
The backwashing period of the biological filter (1) is 5-48h, the air washing strength is 25-50L/m 2 & s, and the water washing strength is 6-20L/m 2 & s.
The thickness of the filter material layer (4) is 1.5-4.0 m, and the diameter is 3-10 mm;
the biological filter (1) can be an upward flow biological filter or a downward flow biological filter, and can be an anaerobic biological filter, an anoxic biological filter or an aerobic biological filter; according to the selected form of the upward flow biological filter or the downward flow biological filter, the positions of a water inlet and a water outlet are determined, the upward flow biological filter adopts a downward water inlet and upward water outlet mode, and the downward flow biological filter adopts an upward water inlet and downward water collection and outlet mode; an aeration device or a non-aeration device can be arranged according to the oxygen supply mode of the anaerobic biological filter, the anoxic biological filter or the aerobic biological filter.
And the flow velocity of the cross section in the filter rod at the lower end of each filter head is not less than 0.15m/s during the water level reduction backwashing.
The backwashing program of the steps (4), (5) and (6) can be continuously and alternately operated for backwashing for multiple times, and the alternate operation frequency is 2-5 times.
In the process of lowering the water level, the free liquid level of the biological filter (1) in normal operation is lowered to a height which is controlled in a linkage manner through a liquid level meter (7) arranged on the top of the biological filter (1) and a PLC system.
The liquid level meter (7), the back washing blower (12), the back washing water pump (15) and the regulating valves (14 and 17) are respectively connected with the PLC system.
And the air-water combined backwashing time is 1-15 min.
Example 1: a certain municipal sewage upgrading and transformation treatment project in Beijing has the treatment scale of 20 ten thousand tons/day, adopts an upward flow denitrification biological filter with a water outlet at the rear end of a drainage channel and a water inlet in a water distribution chamber, and is provided with a carbon source dosing system.
Example 2: the invention relates to a sewage upgrading and reforming treatment project in a certain town of Jiangsu, wherein the treatment scale is 5 ten thousand tons/day, an upward flow denitrification biological filter water outlet channel is arranged at the rear end of a water drainage channel, a water inlet is arranged in a water distribution chamber, and a carbon source dosing system is arranged.
Example 3: a chemical wastewater advanced treatment project of Anhui province, the treatment scale is 2 ten thousand tons/day, the water outlet channel of the upward-flow aerobic carbon removal biological filter is arranged at the rear end of the water discharge channel, and the inlet water is arranged above the filter material layer of the filter.
Example 4: the scale of the treatment of the chemical wastewater treatment project in Henan is 1.5 ten thousand tons/day, the water outlet collecting port of the downward flow aerobic nitrification biological filter is arranged below the water distribution chamber, and the inlet water is arranged above the filter material layer of the filter.
Example 5: the industrial waste water treating project of Jiangsu includes treating scale of 2 ten thousand tons/day, downward flow aerobic nitrifying biological filter with water outlet below the water distributing chamber and water inlet above the filtering material layer.
Example 6: the sewage treatment project of a certain town in Henan has the treatment scale of 18 ten thousand tons/day, the water outlet channel of the upward-flow aerobic nitrification biological filter is arranged at the rear end of the water discharge channel, and the water inlet is arranged in the water distribution chamber.
The multiple-water-level-reduction backwashing method for thoroughly solving the hardening of the biological filter tank thoroughly solves a series of problems of hardening of the filter material of the biological filter tank, poor filter water passing capacity, high operation pressure, unobvious water pollutant removal effect, fluctuation and standard exceeding of effluent quality and the like of the filter tank due to hardening of the filter material; the increase of the operation cost caused by high-strength multi-frequency continuous backwashing of the hardened filter material of the biological filter is thoroughly controlled; thoroughly solved the first time precipitation level filter head and washed insufficient drawback. Has great popularization and application value for the technical field of the biological filter.
The above-mentioned embodiments are merely illustrative of the technical ideas and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the protection scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.
Claims (9)
1. A multiple water level reduction backwashing method for thoroughly solving the hardening problem of a biological filter is characterized by comprising the following steps: the biological filter backwashing system consists of a pressure sensor, a PLC system, a suspended matter detector, a liquid level meter, a backwashing gas system and a backwashing water system; the suspended matter detector is arranged in the clear water area; the pressure sensor is positioned below the filter plate and used for measuring the pressure value between the filter head and the water surface of the clear water area above the filter material layer; the liquid level meter is arranged at the top of the filter tank and used for monitoring the liquid level height of the filter tank when the water level of the filter tank is reduced; when data measured by an automatic monitoring system consisting of the pressure sensor and the suspended matter detector is fed back to the PLC system, and the PLC system determines that the biological filter needs backwashing through analysis, the system starts a backwashing program; the automatic back-flushing program of the filter tank comprises the following steps:
(1) and (3) backwashing at a reduced water level: firstly, opening a control valve on a water level reducing backwashing drain pipe, quickly reducing the water level in the biological filter at the moment, quickly reducing the water level in the biological filter through gravity, reversely washing impurities and fibrous materials in filter head gaps, filter cap gaps and filter rods, and arranging the impurities and the fibrous materials in the biological filter side by side to solve the problem of filter head impurity blockage; monitoring the descending height of the liquid level of the filter tank through a liquid level meter, closing a control valve on a descending water level backwashing drainage pipe when the liquid level descends to 0-80cm of the surface layer of the filter material, and stopping the descending water level backwashing;
(2) air flushing: opening a control valve on the backwashing air inlet pipeline, starting a backwashing blower to enable backwashing air to enter the biological filter from the backwashing air inlet pipeline, starting air washing, and loosening the plate-bound biological filter material layer;
(3) air-water combined backwashing: opening a control valve on a backwashing water inlet pipeline, feeding backwashing water from the bottom of a filter plate through the backwashing water inlet pipeline, starting air-water combined backwashing, enabling a hardened filter material layer to integrally float upwards and lift under the action of air-water combined backwashing, strongly washing the hardened filter material layer through the air-water cavity combined backwashing action at the lower part of the filter material layer, backwashing a part of slightly hardened filter material layer, and lowering loosened granular filter materials to the lower part of an air-water cavity under the action of gravity after the slightly hardened filter material layer is loosened through backwashing; the seriously hardened filter material layer can continuously keep a floating and lifting or suspension state under the combined backwashing action force of the air-water cavity because the filter material layer can not be washed away; monitoring the overflow time of backwash wastewater from a backwash drainage channel by a liquid level meter, closing a backwash blower and a corresponding pipeline control valve, a backwash water pump and a corresponding pipeline control valve after the backwash drainage overflows for 1-10min, and stopping air-water combined backwash;
(4) reducing the water level for backwashing again: opening the control valve on the water level lowering back-flushing drain pipe again, and then leading the severely hardened floating filter material layer to rapidly sink along with the combined action of the water level lowering of the biological filter and the self gravity; in the process of sinking, a filter material layer close to the wall of the tank and the inner wall of the filter tank generate strong washing friction force, so that the sinking rate of the filter material layer close to the wall of the tank is reduced, and meanwhile, due to the friction action of the filter material and the wall of the tank, the hardened filter material layer at the periphery can be loosened; the filter material layer far away from the periphery of the tank wall can sink quickly due to the gravity action of the filter material layer but no friction force of the tank wall; because the difference between the acting force of the filter material layer close to the tank wall and the acting force of the filter material layer far away from the periphery of the tank wall is large, the seriously hardened filter material layer can be divided into a plurality of small hardened filter material layers by the acting force, thereby solving the problem of the seriously hardened filter material layer of the whole tank; meanwhile, sundries retained in the filter cap in the air-water combined backwashing stage are subjected to complete reverse backwashing and are arranged in the biological filter tank; monitoring the descending height of the liquid level of the filter tank through a liquid level meter, and closing a control valve on a water level descending backwashing drain pipe when the liquid level descends to 0-80cm of the surface layer of the filter material;
(5) secondary air flushing: opening the control valve on the backwashing air inlet pipeline again, starting the backwashing blower to start air washing, and loosening the small hardened filter material layers;
(6) and (3) performing air-water combined backwashing again: opening the control valve on the back washing water inlet pipeline again, feeding back washing water from the back washing water inlet pipeline from the bottom of the filter plate, and starting air-water combined washing back washing; the air-water combined backwashing is carried out on a plurality of small hardened filter material layers, and the air-water strong backwashing and the friction acting force among the filter materials can completely loosen and wash away the plurality of small hardened filter material layers, so that the hardening problem of the plurality of small hardened filter material layers is solved, and the hardening problem of a serious filter material layer is completely solved;
(7) rinsing with water: and finally, closing the back washing blower and the corresponding pipeline control valve, and performing water rinsing independently.
2. The multiple water-level-lowering backwashing method for thoroughly solving the hardening of the biological filter tank as claimed in claim 1, wherein: the backwashing period of the biological filter is 5-48h, the air washing strength is 25-50L/m 2 & s, and the water washing strength is 6-20L/m 2 & s.
3. The multiple water-level-lowering backwashing method for thoroughly solving the hardening of the biological filter tank as claimed in claim 1, wherein: the thickness of the filter material layer is 1.5-4.0 m, and the diameter is 3-10 mm.
4. The multiple water-level-lowering backwashing method for thoroughly solving the hardening of the biological filter tank as claimed in claim 1, wherein: the biological filter can be an upward flow biological filter or a downward flow biological filter, and can be an anaerobic biological filter, an anoxic biological filter or an aerobic biological filter.
5. The multiple water-level-lowering backwashing method for thoroughly solving the hardening of the biological filter tank as claimed in claim 1, wherein: and the flow velocity of the cross section in the filter rod at the lower end of each filter head is not less than 0.15m/s during the water level reduction backwashing.
6. The multiple water-level-lowering backwashing method for thoroughly solving the hardening of the biological filter tank as claimed in claim 1, wherein: the backwashing program of the steps (4), (5) and (6) can be continuously and alternately operated for backwashing for multiple times, and the alternate operation frequency is 2-5 times.
7. The multiple water-level-lowering backwashing method for thoroughly solving the hardening of the biological filter tank as claimed in claim 1, wherein: in the process of lowering the water level, the free liquid level lowering height of the biological filter during normal operation is controlled in a linkage manner through a liquid level meter and a PLC system which are arranged on the top of the biological filter.
8. The multiple water-level-lowering backwashing method for thoroughly solving the hardening of the biological filter tank as claimed in claim 1, wherein: the liquid level meter, the back washing blower, the back washing water pump and the regulating valve are respectively connected with the PLC system.
9. The multiple water-level-lowering backwashing method for thoroughly solving the hardening of the biological filter tank as claimed in claim 1, wherein: and the air-water combined backwashing time is 1-15 min.
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