KR101978823B1 - Electric flocculation and filtration system - Google Patents

Abstract

The present invention relates to an electric coagulation and filtration system for removing fine particles such as suspended solids, heavy metals and the like of car washing wastewater. The system comprises: an oil-water separation tank (100) into which the car washing wastewater is introduced and in which oil and water are separated; and a raw water tank (200) in which the car washing wastewater removed with oil is stored.

Description

Technical Field [0001] The present invention relates to an electric flocculation and filtration system,

The present invention relates to an electrocoagulation and filtration system for removing fine particles such as suspended solids, heavy metals and the like of car waster wastewater.

As the recent developments in the industry have led to increased logistics and increased use of vehicles, air pollution has become a problem during the operation of the vehicle. However, water pollution caused by wastewater discharged at the time of car washing is discharged to sewage, It is emerging as an environmental issue.

Work sites for wastewater treatment related to water pollution are classified as one to five kinds of work sites according to the amount of wastewater discharged per day based on the day on which they are most discharged. As a result, the amount of wastewater discharged from the car wash is not more than 50 m ³ per day. Therefore, the car wash wastewater treatment area belongs to the five-kind business, which is a small-scale treatment facility.

However, the wastewater generation and discharge status is the second most common wastewater after the first operation site. This is due to the fact that most of the sedimentation is simplified in a small scale car wash using a small wastewater treatment facility or the wastewater generated is discharged through a sewer.

Although the wastewater generated during car washing of such vehicles contains less pollution than industrial wastewater generated in various industrial facilities, the wastewater is deteriorated by various pollutants contained therein. COD (Chemical Oxygen Demand) is increased, and SS (Suspended Solids) is increased by soil or dirt generated at the time of washing.

The wastewater discharged from the car wash is discharged by lowering the degree of pollution below a certain level according to the relevant laws and ordinances. For this purpose, most of the car wash is chemical wastewater treatment using chemicals. The pH is increased or decreased by the chemical used in the treatment of such wastewater, and it is changed into acidic or alkaline. When extracting n-hexane (n-HEXANE) and washing it with oil or wax attached to the car Anionic surfactants are generated in detergents.

On the other hand, in the prior art Patent Registration No. 10-0360535, there is disclosed a sedimentation and water separation tank 100 for separating oil and fine particles in the influent wastewater by gravity, a wastewater collection tank 100, The chemical water supplied from the chemical supply pump 510 and the chemical water supplied from the chemical water supply pump 510 are stored in the chemical water supply tank 500, A line mixer 300 for forming particles by chemical reaction, a filter 400 for receiving waste water containing the particles and separating the particles containing contaminants by treatment water, A blower 600 for supplying air for separating the filtered particles between the filter media 410, and a blower 600 for separating the particles-sludge separated from the filter media by the blower 600, - to A dehydrator 700 for dehydrating and dehydrating the dehydrated water using the dehydrated water, and a reusing water tank 800 for allowing the treated water separated from the filter 400 to flow into the car wash as reclaimed water. .

In such a wastewater treatment system, chemicals are injected based on the flow rate and the inflow time, but there is a difficulty in maintaining the reaction time and facilities of the chemical when coagulating foreign matters and chemicals in the wastewater.

Patent Document 1. Korean Patent Registration No. 10-0360535

SUMMARY OF THE INVENTION The present invention has been made in an effort to solve the problems of the prior art described above, and it is an object of the present invention to provide an electrocoagulation apparatus for electrochemically coagulating fine contaminants contained in wastewater from waste water to form flocs to remove contaminants, There is an object to distribute the wastewater of wastewater between the electrode plates by an equal amount and pressure.

Further, in order to compensate for the phenomenon that the solids are washed away and the specific gravity of the filter medium is low during the backwashing, the filter media is used for high pressure air in order to compensate for the phenomenon that the filter medium is removed together with foreign matters. The reverse bleeding efficiency and the separation loss of the filter material can be reduced.

According to an aspect of the present invention, there is provided an electrocoagulation and filtration system comprising: a water separator for separating oil and water from flowing wastewater; And a raw water tank into which raw wastewater from which oil has been removed is introduced and stored, wherein micro-pollutants contained in the wastewater supplied by the coagulation transfer pump of the raw water tank are sent to the raw water tank after the electrocoagulation treatment Electrocoagulation device; A filtration device for filtering the flocculation treatment water supplied by the coagulation treatment water transfer pump of the raw water tank by upward flow using an internal floating filter medium; And a backwash device for backwashing the filtration apparatus when the pressure difference between the coagulation water inflow section and the filtration water discharge section of the filtration apparatus is equal to or greater than a predetermined value; Further comprising:

The electric coagulation apparatus includes an electric wastewater inflow section, an electric coagulation section for electrochemically coagulating the wastewater wastewater, a distribution section connected to the wastewater inflow section for distributing wastewater to the electrocoagulation section, And an agglomerated water outlet portion through which the coagulated water is discharged, wherein the agglomerated portion includes an electrode plate having a plurality of openings arranged at predetermined intervals, a power source for supplying current to the electrode plate, The control unit adjusts a value of a current applied to the electrode plate according to a measured value of an electric conductivity sensor that measures an electric conductivity of the incoming wastewater, and the distribution unit has a spiral shape on the lower side of the electrode plate The discharge of the wastewater through the discharge holes formed at predetermined intervals in the longitudinal direction of the distributor is progressed The size of the discharge hole and the diameter of the distributing unit are adjusted to compensate for the pressure drop of the wastewater due to the flow of the wastewater so that the wastewater can be distributed between the electrode plates through the discharge holes with an equal amount and pressure In addition,

The backwash apparatus includes an air supply unit for supplying high pressure air of the compression tank to the inside of the filtration apparatus and a reverse osmosis transfer pump for supplying reverse osmosis water of the reverse osmosis storage tank to the filtration apparatus, An air inlet provided along the upper side of the filtration apparatus so as to circulate and flow the inflowing high pressure air, a high-pressure air supply pipe extending at a predetermined interval in the longitudinal direction of the air pipe, An air injection nozzle for spraying air around a strainer in the filtration apparatus, and a check valve provided between the air pipe and the air injection nozzle for preventing backflow of high-pressure air.

In addition, in order to prevent rain or natural rainfall, which is not wastewater, from flowing into the water separation tank, it is preferable that a sensor for sensing a predetermined component or a predetermined component of the wastewater is installed in the water separation tank, And an excellent shut-off valve for shutting off the shut-off valve.

The first water level sensor is operable to turn off the operation of the flocculation treatment water transfer pump and to provide a water level sensor on the upper side of the first water level sensor from the lower side of the raw water tank. The third water level sensor provided on the upper side of the second water level sensor turns ON the operation of the flocculation conveyance pump and the second water level sensor provided on the upper side of the third water level sensor The fourth water level sensor turns ON the operation of the flocculation treatment water transfer pump.

The distributing unit may include a spiral portion provided horizontally in a spiral shape, a converging portion converging the spiral portion, a first extending portion extending a predetermined length in the vertical direction from the converging portion, And a sludge discharge valve at an end of the second extension part.

Meanwhile, the backwashing method for the electrocoagulation and filtration system of the present invention includes: stopping the operation of the flocculation treatment water transfer pump; Closing the flocculation treatment water inflow section and the filtration treatment water discharge section of the filtration apparatus; Opening the air injection nozzle and injecting high pressure air for a predetermined time with the strainer; Opening the backwash inflow section and the backwash water discharge section of the filtration apparatus; Operating a reverse septic transfer pump to inject reverse septic water into the upper side of the filtration apparatus and inject air into the strainer through the air injection nozzle; Stopping the operation of the backwash transfer pump and closing the air injection nozzle; And discharging the reverse water to the lower side of the filtration apparatus.

Therefore, the electrocoagulation and filtration system of the present invention adopts an electrocoagulation device for electrocoagulating fine contaminants contained in car waster wastewater to form flocs to remove contaminants, It has an effect of increasing the electrocoagulation efficiency by distributing by an equal amount and pressure.

Further, in order to compensate for the phenomenon that the solids are washed away and the specific gravity of the filter medium is low during the backwashing, the filter media is used for high pressure air in order to compensate for the phenomenon that the filter medium is removed together with foreign matters. There is another effect that the backwash efficiency and the separation loss of the filter material can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing a wastewater treatment system of an electrocoagulation and filtration system according to the present invention. FIG.
2 is a view showing an embodiment of an electrocoagulation apparatus of an electrocoagulation and filtration system according to the present invention.
3 is a view showing a partial structure of a backwash apparatus of an electrocoagulation and filtration system according to the present invention.
4 is a diagram illustrating an embodiment of a backwashing method of an electrocoagulation and filtration system according to the present invention.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

Therefore, the embodiments described in this specification and the configurations shown in the drawings are merely the most preferred embodiments of the present invention and do not represent all the technical ideas of the present invention. Therefore, It is to be understood that equivalents and modifications are possible.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a view showing a wastewater treatment system of an electrocoagulation and filtration system according to the present invention, and FIGS. 2 (a) and 2 (b) are views showing an embodiment of an electrocoagulation apparatus of an electrocoagulation and filtration system according to the present invention And FIGS. 3 (a) and 3 (b) are views showing a partial configuration of the backwash apparatus of the electrocoagulation and filtration system according to the present invention.

1 to 3, the electrocoagulation and filtration system of the present invention includes a water separation tank 100 in which wastewater used for car washing flows into the water separation tank 100, and a water separation tank 100 And the fine contaminants contained in the wastewater supplied by the cohesive feeding pump 210 provided in the raw water tank 200 are electrochemically agglomerated into floc The flocculation apparatus 300 includes an electric flocculation apparatus 300 for forming flocculated flocculated flocculated water and discharging the coagulated flocculated water to the raw water tank 200 and an agglomeration treatment water transfer pump 220 provided in the raw water tank 200, A filtration device 400 for filtering the treated water in an upward flow fashion using the floating oil filter 410 inside the filtration device 400 and a filtration device 400 for filtering the coagulated treated water inflow part 420 and the filtered treated water discharge part 430 of the filtration device 400 When the pressure difference is equal to or greater than a predetermined value, a backwashing apparatus 500 for backwashing the filtration apparatus 400 is provided. .

A T-shaped valve 130 is installed in the water tank 100 to remove the oil-containing water from the waste water and to discharge the oil to the water tank 200 due to the difference in specific gravity between the oil and water contained in the waste water. And the optical oil (oil) remaining in the water separation tank 100 can be adsorbed and removed by the adsorbent.

In order to prevent rainwater or natural rainfall that is not wastewater from being introduced into the water separator tank 100, the water tank 100 is provided with a predetermined component (for example, iron powder, oil component, etc.) A sensor 110 for sensing a predetermined amount of water (for example, sodium, chlorine, calcium, magnesium, etc.) and an excellent shutoff valve 120 interlocking with the sensor 110 to block the inflow of rainwater. Therefore, it is possible to prevent the phenomenon that the efficiency of the wastewater treatment facility is remarkably increased due to the infiltration of rainwater and other rainfall-related substances into the bottom of the car wash.

The raw water tank 200 receives the wastewater from which the oil is removed while flowing through the water tank 100. Two wastewater pumps are provided in the raw water tank 200. Waste wastewater is sent to the electrocoagulation apparatus 300 by the coagulation transfer pump 210 to be coagulated and then returned to the raw water tank 200, The water is sent to the filtration apparatus 400 by the flocculation treatment water transfer pump 220).

In addition, four water level sensors 231, 232, 233, and 234 are sequentially provided from below to above in the raw water tank 200 to detect the respective water levels.

That is, the first water level sensor 231 provided at a predetermined height from the bottom of the raw water tank 200 turns off the operation of the flocculation treatment water transfer pump 220, and the upper side of the first water level sensor 231 The second water level sensor 232 provided at a predetermined height turns off the operation of the cohesion transfer pump 210 and the third water level sensor 233 provided at a predetermined height above the second water level sensor 232 is turned off, The fourth water level sensor 234 provided at a predetermined height above the third water level sensor 233 turns on the operation of the flocculation treatment water transfer pump 220. [

The electrocoagulant 300 is formed by flocculating the fine contaminants contained in the wastewater supplied by the coagulation transfer pump 210 of the raw water tank 200 by electrochemical agglomeration, (200).

The electrocoagulation device 300 is connected to the clean wastewater inflow portion 310 of the wastewater supplied by the cohesion transfer pump 210, the coagulation portion 320 which coagulates the wastewater wastewater electrically, the wastewater inflow portion 310 A distributor 330 for distributing the wastewater to the electro-condenser 320, and a coagulation-treated water outlet 340 for discharging coagulation-treated water in the electro-condenser 320.

The electrocoagulation unit 320 includes an electrode plate 321 having a plurality of openings arranged at predetermined intervals, a power unit (not shown) for supplying current to the electrode plate 321, a control unit (Not shown), and the control unit adjusts the current value applied to the electrode plate 321 according to the measured value of an electric conductivity sensor (not shown) that measures the electric conductivity of the incoming wastewater.

As shown in FIG. 2, the distributor 330 may have a structure that converges on the lower side of the electrode plate 321 in a spiral shape. The distributor 330 may include a discharge hole The wastewater is discharged to the upper side through the openings 331. The size of the spray hole 331 and the diameter of the pipe of the distributor 330 are adjusted to compensate for the pressure drop of the wastewater in the distributor 330 according to the process of the spraying, 331 to distribute the wastewater to an equal amount and pressure between the electrode plates 321.

The distributor 330 includes a spiral portion 332 provided horizontally in a spiral shape, a converging portion 333 where the spiral portion 332 converges, a first extension portion 332 extending from the converging portion 333 in the vertical direction by a predetermined length, A second extension 335 extending in the horizontal direction at the upper end of the first extension 334 and a sludge discharge valve 336 at the end of the second extension 335.

That is, the electrocoagulation apparatus 300 is a mechanism in which Fe ³⁺ elutes from the electrode due to a minute current flow and coheres to Fe (OH) ₃ , and the wastewater is distributed equally to the electrode plate 321 in the electro- The density due to electricity can be increased and high coagulation efficiency can be expected.

The distribution unit 330 includes 32A The second extension part 335 was horizontally extended to the side part in order to compensate for the clogging of the sludge. In addition, A sludge discharge valve 336 is provided at the end of the second extension 335 so that clogging of the piping can be removed by using the valve opening / closing device when the piping is clogged by the sludge.

The retention time of the wastewater for washing was 10 minutes and the capacity was 0.5 m3. The material of the electrode plate 321 was iron (Fe) The electrode plate 321 had a size of 50 cm x 60 cm x 33, the interval between the electrode plates 321 was 1.5 cm and the current density was 0.0067 A / cm ² (current 30 A, voltage 50 V) After the electrodes were connected at pH 6.5 ~ 7.5, the treatment efficiency of the filtration device (filtration line speed 2m / hr, media diameter 1 ~ 2mm, specific gravity 0.3 polystylen) was as shown in Tables 1 and 2 below.

Treatment efficiency of filter without electrocoagulation device inflow remove exhaust unit Removal efficiency (%) SS (suspended solids) 151 111.74 39.26 Mg / L 74

Treatment efficiency of the filter provided with the electrocoagulation device (the present invention) inflow remove exhaust unit Removal efficiency (%) COD
(Chemical oxygen demand) 187 68.629 118.371 Mg / L 36.7 SS 151 144.075 11.325 Mg / L 92.7 T-P (total phosphorus) 0.095 0.08094 0.01406 Mg / L 85.2

The filtration apparatus 400 is configured such that the flocculation treatment water of the raw water tank 200 flows through the flocculation treatment water inflow section 420 and is filtered through the floating oil filter media 410 provided therein, (430). ≪ / RTI >

A strainer is provided on the upper side of the filtration device 400 to allow the filtration process water to be discharged without separating the floating filtration media 410 from the filtration process.

The backwashing apparatus 500 is provided with a filtration device (not shown) if the pressure difference between the coagulated water inflow section 420 of the filtration apparatus 400 and the filtration treatment water discharge section 430 is measured by a differential pressure gauge 400 is backwashed.

Although the conventional upflow type filtration apparatus can achieve an excellent linear velocity (28 m / sec) at the initial stage of filtration, the filtration linear velocity decreases and the desired flow rate can not be processed. If the filtration process is repeated, It was difficult to use because it formed occlusion or lumps. In addition, since a certain amount of wastewater is collected in the raw water tank, the wastewater is completely filtered and then converted into a backwash process. Therefore, the filtration pressure is excessively high before all of the filtration water is discharged, Respectively.

Therefore, in order to increase the durability and efficiency of the filter media 410, the coagulation water inflow part 420 and the filtration water discharge part 430 of the filtration device 400, (Not shown) capable of outputting 4 to 20 mA to the piping portion of the compressor, and operates so that the pressure difference between the inlet and the outlet is 0.5 kg / cm 2 or less. When the pressure difference is 0.5 kg / cm 2 or more, And can be selectively used.

3, the backwashing apparatus 500 includes an air supply unit 520 for supplying the high pressure air generated by the compression tank 510 to the inside of the filtration apparatus 400, And a reverse osmosis transfer pump 540 for supplying reverse osmosis water to the filtration unit 400.

The air supply unit 520 includes an air inlet 521 through which the high pressure air generated by the compression tank 510 flows, an air pipe 521 provided along the upper side of the filtration apparatus 400 so that the inflowed high- An air injection nozzle 524 which is formed at a predetermined interval in the longitudinal direction of the air pipe 522 and extends toward the filtering device 400 to inject high pressure air in the air pipe 522 into the interior of the filtering device 400, And a check valve 523 provided between the air pipe 522 and the air injection nozzle 524 to prevent backflow of the high pressure air in the process of injecting high pressure air into the filtering device 400.

Particularly, the upper strainer portion of the upflow type filter causes clogging of the filter material due to the filtration pressure, and even when backwashing is not completed, the periphery of the strainer is clumped together with the sludge, Pressure air is blown around the strainer 440 provided in the upper part of the filtering device 400 by the air injection nozzle 524 so that the filtering material 400 can be gathered or fixed around the strainer 440 (410).

That is, in order to compensate for the phenomenon that the solids are washed away and the specific gravity of the filter medium is low during backwashing and the filter media 410 is separated from the filtration device 400 together with foreign matters during backwashing, high pressure air of the compression tank 510 is used After the initial backwash air cleaning, a process capable of draining backwash water by a natural gradient method is constituted so as to reduce backwash efficiency and separation loss of filter media.

4 is a diagram illustrating an embodiment of a backwashing method of an electrocoagulation and filtration system according to the present invention. As shown in the figure, the backwashing method includes stopping the operation of the flocculation treatment water transfer pump 220, closing the inlet 420 and the outlet 430 of the filtration apparatus 400 (S30) of spraying air to the strainer 440 for a predetermined time by opening the air injection nozzle 524 and the step S30 of returning the water from the water withdrawn water inflow part 450 and the reverse water discharge part 460 The backwash water pump 540 is operated to flow the reverse water to the upper side of the filtering device 400 and the air is injected to the strainer 440 through the air injection nozzle 524 A step S60 of stopping the operation of the backwash water transfer pump 540 and closing the air injection nozzle 524 and a step S70 of discharging the backwash water to the lower side of the filtration apparatus 400, Are sequentially performed.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, Various changes and modifications will be possible.

100:
110: T type valve
120: Superior isolation valve
200: Circulating water tank
210: coherent feed pump
220: flocculation treated water transfer pump
231, 232, 233, 234: a water level sensor
300: electrocoagulation device
320: electric coagulation part
330:
331: Spout hole
332:
333: convergent part
334: first extension
335:
400: Filtration device
410: Filter media
440: Strainer
500: Backwash device
520: Air supply
521: Air inlet
522: air pipe
533: Check valve
534: Air injection nozzle

Claims (5)

In an electrocoagulation and filtration system,
A water separator (100) for separating the oil and water from the incoming wastewater; And a raw water tank (200) into which the wastewater from which the debris is removed is introduced and stored,
An electrocoagulation device 300 for passing micro-contaminants contained in the wastewater discharged from the coagulation transfer pump 210 of the circulating water tank 200 to the circulating water tank 200 after the electrocoagulation process;
A filtration device 400 for filtering the flocculation treatment water supplied by the flocculation treatment water transfer pump 220 of the raw water tank 200 in an upward flow manner using the floating oil filter media 410 therein; And
A backwash apparatus 500 for backwashing the filtration apparatus 400 when the pressure difference between the coagulation water inflow section 420 of the filtration apparatus 400 and the filtration treatment water discharge section 430 is a predetermined value or more; Further comprising:
The electrocoagulation apparatus (300)
(330) connected to the clean wastewater inlet (310) and distributing the wastewater to the electric flocculation unit (320). The wastewater inflow unit (310) includes an electric flocculation unit And an agglomerated water outlet (340) through which the agglomerated treatment water is discharged from the agglomerated portion (320)
The electrocoagulation unit 320 includes an electrode plate 321 having a plurality of openings arranged at predetermined intervals, a power supply unit for supplying a current to the electrode plate 321, and a control unit for controlling a voltage or a current of the supplied power supply The control unit adjusts the current value applied to the electrode plate 321 according to the measured value of the electric conductivity sensor for measuring the electric conductivity of the incoming wastewater,
The distributor 330 is disposed below the electrode plate 321 so as to converge in a spiral shape. The distributor 330 includes a plurality of discharge holes 331 formed at predetermined intervals in the longitudinal direction of the distributor 330, The size of the spray hole 331 and the diameter of the distributor 330 are adjusted to compensate for the pressure drop of the car wash wastewater due to the flow of the spray water through the spray holes 331 So that the wastewater is distributed between the electrode plates 321 at equal amounts and pressures,
The backwashing device (500)
An air supply unit 520 for supplying high pressure air of the compression tank 510 to the inside of the filtration apparatus 400 and a circulating water conveyance pump 500 for supplying the reverse water of the reverse oily water storage tank 530 to the filtration apparatus 400, (540)
The air supply unit 520 includes an air inlet 521 through which high pressure air flows, an air pipe 522 along the upper side of the filtration apparatus 400 so that the introduced high pressure air circulates, An air injection nozzle 524 formed at predetermined intervals in the longitudinal direction of the strainer 440 and extending to the filtration device 400 to inject high pressure air around the strainer 440 in the filtration device 400, And a check valve (523) provided between the air injection nozzle (522) and the air injection nozzle (524) to prevent backflow of high-pressure air.
The method according to claim 1,
A sensor 110 for detecting a predetermined component or a predetermined component of the clean wastewater to prevent rainfall or natural rainfall that is not wastewater from flowing into the water separation tank 100, And an excellent shutoff valve (120) interlocking with the sensor (110) to block the inflow of stormwater.
The method according to claim 1,
And four water level sensors for sensing different water levels of the raw water tank 200,
The first water level sensor 231 from the lower side of the raw water tank 200 turns off the operation of the flocculation treatment water transfer pump 220 and the second water level sensor 232 provided on the upper side of the first water level sensor 231 The third water level sensor 233 provided on the upper side of the second water level sensor 232 turns on the operation of the flocculation conveyance pump 210 and the third water level sensor 233 provided on the upper side of the second water level sensor 232 turns ON the operation of the flocculation conveyance pump 210, And the fourth water level sensor (234) provided on the upper side of the water level sensor (233) turns on the operation of the flocculation treatment water transfer pump (220).
The method according to claim 1,
The distributor 330 includes a spiral portion 332 formed horizontally in a spiral shape, a converging portion 333 for converging the spiral portion 332, A second extension 335 extending in the horizontal direction at the upper end of the first extension 334 and a sludge discharge valve 336 at the end of the second extension 335. The first extension 334, ). ≪ / RTI >
1. A backwashing method for the electrocoagulation and filtration system of claim 1,
Stopping the operation of the flocculation treatment water transfer pump 220;
Closing the flocculation-treated water inflow section (420) and the filtered-water discharge section (430) of the filtration apparatus (400);
Opening the air injection nozzle 524 and injecting high-pressure air for a predetermined time to the strainer 440;
Opening the water inlet 450 and the water outlet 460 of the filtering device 400;
Injecting backwash water to the upper side of the filtration apparatus 400 by operating a reverse water wash transfer pump 540 and injecting air to the strainer 440 through the air injection nozzle 524;
Stopping the operation of the reverse water transfer pump 540 and closing the air injection nozzle 524; And
And discharging backwash water to the lower side of the filtration unit (400).

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