JP2014079672A - Ammonia removal apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ammonia removal apparatus with a simple and low-cost apparatus configuration, which efficiently removes ammonia nitrogen in waste water without excessive addition of a chlorine agent.SOLUTION: An ammonia removal apparatus removes ammonia nitrogen in water to be processed by break-point chlorination. The ammonia removal apparatus includes chlorine agent addition means which adds a chlorine agent to a reaction tank for accommodating water to be processed, gas-liquid separation means which separates gas components in the sampled water to be processed from the reaction tank, ammonia gas detection means which detects the ammonia gas amount in the gas components separated by the gas-liquid separation means, and control means which controls the addition amount at the chlorine agent addition means on the basis of detection value of the ammonia gas detection means.

Description

  The present invention relates to an ammonia removal apparatus for removing ammonia nitrogen from wastewater by a discontinuous point chlorine addition method.

Conventionally, as a treatment method of waste water containing ammonia nitrogen (NH ₃ —N, the same shall apply hereinafter), a nitrification denitrification method that is a microbial treatment method, a discontinuous point chlorine addition method that is a physicochemical treatment method, ammonia A stripping method and a wet catalyst method are known. For example, any method is selected and used depending on the ammonia nitrogen concentration in the wastewater.

Above all, in the wastewater treatment by the discontinuous point chlorine addition method, a part of the wastewater is transferred from the wastewater tank storing the ammonia nitrogen-containing wastewater discharged unsteadily to the reaction tank, and the required amount of chlorine agent, for example By adding sodium chlorite, ammonia nitrogen in wastewater is oxidatively decomposed and removed as nitrogen gas.
At this time, the required amount of the chlorine agent is determined by measuring the ammonia concentration in the wastewater by the ammonia electrode method, the membrane concentration method, or the conductivity method.

  The oxidative decomposition reaction of ammonia nitrogen with hypochlorous acid is performed, for example, by the following formula.

  As shown in the formulas (1) and (2), 7.6 parts by mass of chlorine is required stoichiometrically to oxidize 1 part by mass of ammonia nitrogen in the wastewater.

  By the way, it is generally known that discontinuities (break points) exist in the reaction between ammonia and chlorine.

  For example, in the vicinity of neutral pH, when the ratio of chlorine to ammonia nitrogen (mass ratio, hereinafter the same) is gradually increased from 0, the amount of residual chlorine increases as the initial chlorine ratio increases. This is because most of the reaction product of ammonia and chlorine is monochloramine. As the proportion of chlorine is further increased, the amount of residual chlorine decreases through a maximum point and reaches a minimum point, that is, a discontinuous point. Increasing the percentage of chlorine beyond the discontinuity increases free chlorine and trichloramine. Thus, the reaction of chlorine and ammonia up to the discontinuity point is not only complicated, but the reaction product may change depending on the pH.

  In addition, since the concentration of ammonia nitrogen in the wastewater is fluctuating, actually, an excessive amount of chlorinating agent is added more than necessary. Then, after removal of the ammonia nitrogen by the chlorine agent, a post-process for adding a reducing agent such as sodium sulfite and sodium thiosulfate to the treated water is performed in order to remove residual chlorine. This reaction is represented, for example, by the following formula (3).

However, the excessive addition of the chlorine agent not only increases the burden on the environment and the cost, but also increases the amount of the reducing agent added in the subsequent process.
Furthermore, if the addition amount of the chlorinating agent is not appropriate, byproducts such as dichloramine, trichloramine, and nitric acid may increase as shown by the following formula.

  Therefore, in wastewater treatment by the discontinuous point chlorine addition method, in order to prevent excessive addition of chlorine agent, the required amount of chlorine agent is added in portions, or the oxidation reaction of ammonia by measuring the oxidation-reduction potential (ORP). The addition of the chlorinating agent is determined, and the addition amount of the chlorinating agent is controlled by measuring the concentration of monochloramine or dichloramine in the water to be treated. (For example, see Patent Document 1, Patent Document 2, and Patent Document 3.)

JP 2001-225085 A JP-A-10-28981 Japanese Patent Laid-Open No. 10-28982

  However, in the conventional method, a great amount of labor and time are required to obtain the ammonia concentration and the like in the wastewater by analysis and determine the amount of the chlorinating agent added each time. Even in the case of measuring the oxidation-reduction potential (ORP), it is only used as a measure for the completion of the reaction, and it is difficult to appropriately adjust the addition amount of the chlorine agent. Furthermore, since analysis requires time, there is a problem that it is difficult to make the addition amount of the chlorine agent appropriate.

  The present invention has been made to solve the above-described problems, and can remove ammonia nitrogen in wastewater efficiently with a relatively inexpensive and simple apparatus configuration, and an excessive addition of a chlorine agent. An object of the present invention is to provide an ammonia removing apparatus capable of suppressing the above.

  The ammonia removing apparatus of the present invention is an ammonia removing apparatus for removing ammonia nitrogen from the water to be treated by a discontinuous point chlorine addition method, and a chlorine agent adding means for adding a chlorine agent to a reaction tank containing the water to be treated. A gas-liquid separation means for separating the gas component in the water to be collected collected from the reaction tank, an ammonia gas detection means for detecting the amount of ammonia gas in the gas component separated by the gas-liquid separation means, and the ammonia Control means for controlling the addition amount of the chlorinating agent addition means based on the detection value of the gas detection means.

  In the ammonia removing apparatus of the present invention, when a chlorine agent is added to wastewater in a reaction tank to oxidatively decompose ammonia, unreacted ammonia in the liquid is gasified by a gas-liquid separation means, and the amount of the gasified ammonia gas is reduced. Detected by ammonia gas detection means. Since the volume of ammonia in the liquid is greatly increased by gasification, the amount of ammonia gas can be accurately detected. And based on this detected value, the addition amount of a chlorine agent is proportionally controlled by a control means. At this time, since the ammonia gas amount is accurately detected, the amount of the chlorinating agent can be adjusted continuously and appropriately in accordance with the ammonia amount in the liquid with a relatively simple apparatus configuration.

  According to the ammonia removing apparatus of the present invention, the addition amount of the chlorinating agent can be set to an appropriate amount, so that the equipment for reducing the residual chlorine can be simplified or omitted.

  In the present invention, the gas-liquid separation means preferably includes an aeration device. In this case, ammonia in the liquid can be sufficiently gasified. The gas-liquid separation means preferably includes a heating means for heating the water to be treated to 45 to 80 ° C., and pH adjusting means for adding an alkaline agent to make the pH of the water to be treated 10.5 or more. It is preferable to provide. In this case, the amount of ammonia gas can be detected stably, and the correlation between the amount of ammonia gas detected by sufficiently gasifying ammonia in the liquid and the concentration of ammonia nitrogen in the liquid is further increased, so that a timely and appropriate amount of chlorine agent can be added. Can be added.

  Furthermore, it is preferable that the ammonia gas detection means includes a plurality of ammonia gas detectors. Thereby, the amount of ammonia gas can be detected stably.

  In addition, the gas amount in this specification is the value converted into 25 degreeC and 1 atmosphere.

According to the ammonia removing apparatus of the present invention, ammonia nitrogen in wastewater can be efficiently removed with a relatively inexpensive and simple apparatus configuration, and excessive addition of a chlorine agent can be significantly suppressed.
Therefore, it is possible to simplify the wastewater treatment apparatus for ammonia nitrogen-containing wastewater and reduce the wastewater treatment cost.

It is a flowchart of the wastewater treatment using the ammonia removal device of the embodiment. It is a schematic block diagram of the ammonia removal apparatus of embodiment. It is a graph which shows the relationship between the elapsed time after sodium hypochlorite addition in an Example, a residual chlorine concentration, and the ammonia nitrogen concentration in a liquid. It is a graph which shows the correlation of the ammonia nitrogen density | concentration in a liquid and ammonia gas detection density | concentration in an Example. It is a graph which shows the relationship between the addition amount of sodium hypochlorite in a comparative example, ammonia nitrogen concentration in liquid, residual chlorine concentration, and total nitrogen concentration. It is a graph which shows the relationship between the addition amount of sodium hypochlorite in a comparative example, residual chlorine concentration, and pH.

  An embodiment of an ammonia removing apparatus according to the present invention will be described below with reference to the drawings. The present invention is not limited to the following embodiments. In addition, the apparatus which has the same function in drawing is attached | subjected with the same code | symbol, and abbreviate | omits detailed description.

  FIG. 1 is a flowchart of wastewater treatment using the ammonia removing apparatus 1 of the present embodiment. Ammonia nitrogen-containing wastewater stored in the wastewater tank 10 flows into the reaction tank 11 and is added with a chlorinating agent by the chlorinating agent adding means 12 and stirred to oxidize and remove ammonia nitrogen. Further, the reaction tank 11 is provided with pH measuring means and ORP measuring means for measuring the pH of the water to be treated and the residual chlorine concentration, respectively, and the treated water treated by the discontinuous point chlorine addition method is used as needed. Is supplied to a reduction tank 13, which is reduced and discharged outside the system.

  In the present embodiment, the ammonia removing apparatus 1 is configured to control the amount of chlorinating agent added by the chlorinating agent adding means 12 in the reaction tank 11.

  The ammonia removing apparatus 1 shown in FIG. 2 includes gas-liquid separation means (vaporizer 21) that separates a gas component from at least a part of the water to be treated treated in the reaction tank 11. Further, a chlorine agent tank 22 and a chlorine agent supply pump 23 are provided as the chlorine agent adding means 12.

  Further, an ammonia gas detection means 24 for detecting the amount of ammonia gas in the gas component separated by the vaporizer 21 and a control means 25 for controlling the supply amount of the chlorinating agent supply pump 23 based on the detected value of the ammonia gas detection means 24 I have.

The reaction tank 11 is provided with a sample pump 26 that allows the water to be treated to flow into the vaporizer 21 at a constant flow rate. As the sample pump 26, it is preferable to use a tube pump which can easily supply a fixed amount.
In addition, when there is a contaminant such as dust in the treated water, a sample tank for temporarily storing the treated water may be provided, and the treated water in the reaction tank 11 may be supplied to the vaporizer 21 through the sample tank. .

  In the present embodiment, the vaporizer 21 includes an aeration device 27, a temperature sensor (not shown) that is a heating unit, a heater 28, and an air supply pipe 29 that introduces air into the vaporizer 21. As described above, the vaporizer 21 is configured to raise the temperature of the water to be treated as necessary and to perform aeration.

As the aeration apparatus 27, an aeration apparatus that diffuses gas components in the liquid into the air can be used. The aeration apparatus 27 of the present embodiment sucks the gas phase gas from the upper vapor phase of the vaporizer through the intake pipe 27a through the air diffusion pump (air pump) 27b and discharges it to the lower part of the vaporizer 21 through the air diffusion pipe 27c. It is configured to circulate aeration.
In the present embodiment, since circulation aeration is performed using gas phase gas, ammonia in the liquid can be gasified to achieve a gas-liquid equilibrium state in a short time. Furthermore, the ammonia gas detection amount can be stabilized. Note that a diffuser plate may be used as the aeration apparatus 27.

  Although the aspect of a heating means is not specifically limited, In this embodiment, the heater 28 is arranged in the lower part in the vaporizer 21, and since it arrange | positions in the vaporizer 21, the sheathed heater is used. It is preferable that the heater 28 is by resistance heating because it is easy to control.

  Further, the vaporizer 21 includes an alkaline agent supply pump 30 and an alkaline agent tank 31 as pH adjusting means so that the pH of the water to be treated can be adjusted.

The capacity of the vaporizer 21 is preferably 100 to 1,000 mL, and more preferably 100 to 500 mL. If the capacity of the vaporizer 21 is too small, the ammonia gas detection amount may be likely to fluctuate. If the capacity is too large, the sampling amount must be increased, which is not efficient.
Further, the water to be treated which has flowed into the vaporizer 21 is circulated from the vaporizer 21 to the reaction tank 11 through an overflow pipe 32.

  The gas component separated by the vaporizer 21 flows into the ammonia gas detection means 24 from the gas supply pipe 34 through the auto drain 33. Thereby, for example, problems due to dew condensation in the ammonia gas detection means 24 can be suppressed, and the accuracy of the ammonia gas detection amount can be ensured.

The ammonia gas detector 24 is not particularly limited as long as it can measure the amount of ammonia in the gas component. For example, an ammonia gas detector based on a constant potential electrolytic method is used.
Since the volume of ammonia greatly increases when gasified, the amount of ammonia can be accurately measured by gasifying ammonia in the liquid. Furthermore, in recent years, the progress of gas sensor technology has been remarkable, and more precise gas sensors are also known. By using such a gas sensor, the amount of ammonia gas can be detected more precisely.

  In this embodiment, the ammonia gas detection means 24 has two ammonia gas detectors connected in parallel, and the ammonia gas is detected by alternately using the two ammonia gas detectors. Each ammonia gas detector is connected to an air supply pipe 35 for supplying air and a gas supply pipe 34 through valves 36 and 37 so as to be switched.

  In addition, a small amount of ammonia gas in the external atmosphere may be detected by the ammonia gas detector on the air inlet side of the air supply pipe 35 of the ammonia gas detector 24 and the air supply pipe 29 of the vaporizer 21. An apparatus for removing components, for example, an activated carbon tower 38 is provided, and external air is supplied through the activated carbon tower 38. As a result, components affecting the detection in the external atmosphere are removed and supplied to the ammonia gas detector, so that the zero base value of the ammonia gas detection means 24 does not fluctuate.

Based on the detection value of the ammonia gas detection means 24, the discharge amount of the chlorinating agent supply pump 23 is proportionally controlled by the control means 25. By using a pulse pump capable of controlling the discharge amount as the chlorinating agent supply pump 23, the discharge amount can be controlled appropriately.
It is preferable that the control means 25 is based on PID control because the addition amount of the chlorine agent can be precisely controlled according to the detected ammonia gas amount.

  As described above, in this embodiment, when removing ammonia nitrogen from wastewater using the discontinuous point chlorine addition method, the amount of chlorinating agent is controlled according to the unreacted ammonia concentration in the liquid. Can be adjusted to an appropriate amount.

  Next, an embodiment of the ammonia removal method will be described mainly based on FIG.

  First, the stirrer 39 in the reaction tank 11, the wastewater pump 40 that supplies the wastewater to the reaction tank 11, the sample pump 26, and the chlorine agent supply pump 23 are put into operation.

  Waste water is introduced into the reaction tank 11 and an aeration pump (air pump) 27b is started. When a method of diffusing a gas component into the air is used as the aeration device 27, the aeration amount by the aeration pump 27b is preferably a ratio (G / L) indicated by the aeration flow rate / treated water flow rate of 10 to 100. To be. If the aeration amount is too small, the ammonia vaporization amount is not sufficient, and if the aeration amount is too large, it is difficult to detect a stable ammonia gas amount.

  Further, the heater 28 is turned on, and the heating output of the heater 28 can be controlled by a signal from the temperature sensor in the vaporizer 21. The alkaline agent is added by the alkaline agent supply pump 30 so that the liquid property of the water to be treated in the vaporizer 21 is pH 10.5 or more, preferably 11 to 13. Thereby, since unreacted ammonia dissolved in the water to be treated can be sufficiently gasified, it is possible to accurately measure the amount of ammonia gas.

  In this state, the water to be treated is supplied from the reaction tank 11 to the vaporizer 21 through the sample pump 26 at a constant flow rate and circulated. The temperature of the water to be treated in the vaporizer 21 is controlled to a substantially constant temperature (about ± 1 ° C.) in the range of preferably 45 to 80 ° C., more preferably 55 to 70 ° C. by controlling the heater 28. If the temperature of the water to be treated is too low, ammonia is not sufficiently vaporized and it becomes difficult to detect a stable amount of ammonia gas. On the other hand, if the temperature is too high, for example, water vapor is mixed in the gas component, so that the ammonia gas ratio in the gas component fluctuates, making it difficult to detect an appropriate amount of ammonia gas.

  Then, after the temperature of the water to be treated in the vaporizer 21 is stabilized, the ammonia gas detection means 24 is operated to collect the gas component, and the amount of ammonia gas in the gas component is detected. The detection value of the ammonia gas detection means 24 is input to a PID control device 25 which is a control means. Based on the ammonia gas detection value, the PID control device outputs a signal at 4 to 20 mA to proportionally control the discharge amount of the chlorinating agent supply pump 23.

  In the present embodiment, the gas component separated by the vaporizer 21 is sampled alternately every one hour, for example, by switching the valve 37 on one of the ammonia gas detectors, and the valve 36 is switched. Fresh air is collected from the air supply pipe 35 in the ammonia gas detector from which the gas component is not collected. Thereby, since the detection part of the ammonia gas detector can be kept clean, the amount of ammonia gas can be detected more precisely.

  Thus, in the ammonia removal apparatus of the present embodiment, the ammonia nitrogen concentration in the reaction tank 11 can be continuously and accurately detected. Therefore, the addition amount of the chlorine agent to the reaction tank 11 can be made an appropriate amount according to the ammonia nitrogen concentration in the liquid. As a result, excessive addition of the chlorine agent can be suppressed, and the configuration of the reduction tank 13 in FIG. 1 can be simplified or omitted.

Next, an embodiment using the apparatus shown in FIG. 2 will be described.
The specifications and experimental conditions of each device used in the examples are as follows.
Reaction tank capacity: 2,000 mL,
Vaporizer capacity: 100 mL,
Ammonia gas detector: Constant potential electrolytic ammonia gas detector (Aquatech Co., Ltd., AQAM ammonia gas detector),
pH measuring device: manufactured by TOA-DKK, HM-21P,
Ammonia nitrogen (NH ₃ -N) concentration in liquid, measurement of residual chlorine concentration, total nitrogen concentration measurement: DR-5000 manufactured by HACH.

Example 1
An example using the above-described embodiment will be described.
First, raw water having an initial ammonia nitrogen concentration of 74 mg / L was continuously introduced into the reaction tank 11 of the apparatus shown in FIG. 2 at 2,000 mL / hour. The discharge amount of the pulse pump (chlorine agent supply pump 23) for supplying sodium hypochlorite with the ammonia gas concentration of the PID control device set to 5 mg / L was PID controlled by the control device 25.

  The amount of aeration by the air diffusion pump 27b was 60 L / hour (G / L = 30), and the temperature of the water to be treated in the vaporizer was made to be almost constant at 55 ° C. In addition, sodium hydroxide was added from the alkaline agent tank 31 so that the pH of the water to be treated in the vaporizer 21 was approximately 12.5.

Further, the water to be treated was sampled from the bottom of the reaction tank 11 every 15 minutes, and the ammonia nitrogen concentration in the liquid was measured by the salicylic acid method (colorimetric method), and the residual chlorine concentration was measured by the DPD method (colorimetric method).
FIG. 3 shows the relationship between the elapsed time, the residual chlorine concentration (Cl mg / L), and the ammonia nitrogen concentration in the liquid.

  As shown in FIG. 3, after 75 minutes, the ammonia nitrogen concentration in the reaction tank was about 20 mg / L, and then gradually decreased. After 140 minutes, a discontinuous point was reached, and the ammonia nitrogen concentration was reduced to 6.3 mg / L and the residual chlorine concentration was reduced to 6.4 mgCl / L. Furthermore, even if it exceeds the discontinuous point, the residual chlorine concentration is stable at 10 mg Cl / L or less, and it can be seen that excessive addition of the chlorine agent can be greatly suppressed. In FIG. 3, the black circles indicate the residual chlorine concentration in the liquid, and the black triangles indicate the ammonia nitrogen concentration.

FIG. 4 shows the correlation between the ammonia nitrogen concentration in the liquid at this time and the ammonia gas concentration detected by the ammonia gas detector.
FIG. 4 shows that in this example, a high correlation of r ² (correlation coefficient) = 0.8976 is obtained between the ammonia nitrogen concentration in the liquid and the ammonia gas concentration.

(Comparative Example 1)
First, 1,000 mL of raw water having an ammonia nitrogen (NH ₃ -N) concentration of 41 mg / L was introduced into the reaction tank, and 2 mL of sodium hypochlorite 5% solution was added every 10 minutes by a chlorine agent supply pump. It was. At this time, the ammonia nitrogen concentration and the residual chlorine concentration in the liquid were measured in the same manner as in Example 1, and the total nitrogen concentration was oxidized to nitrate nitrogen with potassium peroxodisulfate and then measured by ultraviolet absorption.

FIG. 5 shows the relationship between the amount of sodium hypochlorite added (Cl / (NH ₃ —N), (mass ratio), the same applies hereinafter), the ammonia nitrogen concentration in the liquid, and the residual chlorine concentration. In FIG. 5, black circles indicate the residual chlorine concentration in the liquid, white triangles indicate the ammonia nitrogen concentration, and black squares indicate the total nitrogen concentration.

As shown in FIG. 5, when the amount of sodium hypochlorite added is gradually increased, the residual chlorine concentration increases as the initial chlorine ratio increases. This is because most of the reaction product of chlorine and ammonia is monochloramine. When Cl / (NH ₃ -N) = 6 is exceeded, the residual chlorine concentration is decreased, and when Cl / (NH ₃ -N) = 7.5, the residual chlorine concentration is the lowest, that is, a discontinuous point. Yes.

FIG. 6 shows the relationship between the amount of sodium hypochlorite added, residual chlorine concentration, and pH at this time.
As shown in FIG. 6, the pH increases until Cl / (NH ₃ −N) = 4.6, and then decreases. Then, Cl / (NH ₃ −N) = 7.5, pH = 9.4, and thereafter becomes constant. In FIG. 6, the black circles indicate the residual chlorine concentration in the liquid, and the black triangles indicate pH.

  The increase in pH is due to sodium hydroxide produced by the reaction of ammonia and sodium hypochlorite, indicating that monochloramine is produced. Further, the subsequent decrease in pH indicates that monochloramine becomes nitrogen gas and hydrochloric acid is generated. Therefore, the ammonia nitrogen concentration in the liquid is also reduced as shown in FIG. Thus, the production of monochloramine and the reaction mechanism of ammonia and chlorine in the discontinuous chlorine addition method were confirmed.

5 and 6, in the batch formula, when the chlorine agent is added beyond the discontinuity point, the residual chlorine concentration rapidly increases. When Cl / (NH ₃ −N) = 8, 18 mgCl / L, Cl / It can be seen that (NH ₃ −N) = 8.3 increases to 27 mgCl / L.

  As described above, according to the present embodiment, an appropriate amount of chlorinating agent can be continuously added according to the concentration of ammonia nitrogen in the liquid, so that excessive addition of chlorinating agent can be significantly suppressed. it can. Furthermore, it is possible to remove ammonia nitrogen from wastewater efficiently by using a relatively inexpensive and simple ammonia removing device. Therefore, the apparatus and operation for reducing the treated water can be simplified or omitted, and the wastewater treatment cost can be reduced.

  DESCRIPTION OF SYMBOLS 1 ... Ammonia removal apparatus, 10 ... Waste water tank, 11 ... Reaction tank, 12 ... Chlorine agent addition means, 13 ... Reduction tank, 21 ... Vaporizer, 22 ... Chlorine agent tank, 23 ... Chlorine agent supply pump, 24 ... Ammonia gas Detection means, 25 ... control means, 26 ... sample pump, 27 ... aeration device, 28 ... heater, 29 ... air supply pipe, 30 ... alkali agent supply pump, 31 ... alkali agent tank, 32 ... overflow pipe, 33 ... auto Drain, 34 ... gas supply pipe, 35 ... air supply pipe, 36, 37 ... valve, 38 ... activated carbon tower, 39 ... stirrer, 40 ... wastewater pump.

Claims (5)

An ammonia removal apparatus that removes ammonia nitrogen from water to be treated by a discontinuous point chlorine addition method,
A chlorinating agent adding means for adding a chlorinating agent to a reaction vessel containing treated water;
A gas-liquid separation means for separating a gas component in the water to be collected collected from the reaction tank;
Ammonia gas detection means for detecting the amount of ammonia gas in the gas component separated by the gas-liquid separation means;
Control means for controlling the addition amount of the chlorinating agent addition means based on the detection value of the ammonia gas detection means;
An ammonia removing apparatus comprising:   2. The ammonia removing apparatus according to claim 1, wherein the gas-liquid separating means includes an aeration apparatus.   The ammonia removal apparatus according to claim 1 or 2, wherein the gas-liquid separation means includes a heating means for heating the water to be treated to 45 to 80 ° C.   4. The ammonia removing apparatus according to claim 1, wherein the gas-liquid separating unit includes a pH adjusting unit that adds an alkali agent to adjust the pH of the water to be treated to 10.5 or more. 5. .   The ammonia removal apparatus according to any one of claims 1 to 4, wherein the ammonia gas detection means includes a plurality of ammonia gas detectors.

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