JP4147411B2 - Diluted wastewater treatment method - Google Patents

Description

  The present invention relates to a method for treating lean wastewater, and more particularly to a method for treating reusable wastewater containing volatile acids or alkalis such as hydrofluoric acid, nitric acid, and ammonia.

  Wastewater containing hydrofluoric acid, nitric acid, and ammonia discharged in the manufacturing process of electronic components such as semiconductors and liquid crystals is generally low in concentration and difficult to reuse. Therefore, sludge is generated and separated by neutralization and precipitation. After that, it was usually released. However, such a method has a problem that not only the facility space required for precipitation and dehydration becomes excessive, but also a large amount of waste is generated.

Therefore, in Patent Document 1, after adding sodium hydroxide to waste water containing hydrofluoric acid to form sodium fluoride (NaF), the hydrofluoric acid is recovered by processing with an evaporator and a reverse osmosis membrane device. Thus, a wastewater treatment apparatus configured to be reusable is disclosed.
JP 2002-143850 A

  However, according to the treatment method using the waste water treatment device disclosed in Patent Document 1, NaF is dissolved in the concentrated water obtained in the evaporator, so that hydrofluoric acid is recovered from the concentrated water and recycled. There was a problem that it could not be used and the recovery efficiency was not sufficient. Further, since the hydrofluoric acid is recovered from the distilled water generated by the evaporator using the reverse osmosis membrane device, the equipment cost and the maintenance burden are increased.

  DISCLOSURE OF THE INVENTION The present invention has been made to solve such a problem, and is capable of treating a dilute wastewater containing a volatile acid or alkali so as to be reusable with high efficiency and low cost. The purpose is to provide a method.

  The object of the present invention is a method for processing a dilute wastewater containing a volatile acid or alkali so as to be reusable, a storage step of storing a liquid to be treated containing a dilute wastewater in an evaporation chamber, A concentration step for evaporating and concentrating the liquid to be treated, a recovery step for recovering the concentrated water generated in the concentration step from the evaporation chamber, and a steam generated in the concentration step are introduced into the washing chamber, A dissolution step of generating an acid or alkali solution by bringing the solution into contact with the stored dissolution water, and the storage step recovers the concentrated water in the recovery step, and then the acid or alkali together with the diluted waste water. This is achieved by a method for treating diluted wastewater comprising a step of supplying a solution to the evaporation chamber.

  In the method for treating the diluted waste water, it is preferable to control the concentration so that the acid or alkali concentration of the produced concentrated water is in the range of 10 to 35% (more preferably 15 to 30%) in the concentration step. .

  Further, in the dissolving step, the ratio of the concentration of the liquid to be treated when the diluted waste water and the acid or alkali solution are supplied to the evaporation chamber to the concentration of the liquid to be treated when only the diluted waste water is supplied to the evaporation chamber. It is preferable to control the concentration of the acid or alkali solution so as to be in the range of 0.8 to 1.0 (more preferably 0.85 to 0.95).

  According to the method for treating diluted waste water of the present invention, the diluted waste water containing a volatile acid or alkali can be treated with high efficiency and low cost so that it can be reused.

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

  FIG. 1 is a schematic configuration diagram showing a wastewater treatment apparatus used in a method for treating diluted wastewater according to an embodiment of the present invention. As shown in FIG. 1, this waste water treatment apparatus includes a concentrating device 1 and a water contact device 2, and is used for treatment of diluted waste water containing volatile acids or alkalis such as hydrofluoric acid, nitric acid, and ammonia. It is done.

  The concentrating device 1 is, for example, a flash-type evaporating and concentrating device, and includes an evaporator 11 having an evaporation chamber for storing a liquid to be treated, and a waste water supply line 12 for supplying diluted waste water discharged from an electronic component factory or the like to the evaporator 11. And a heating device 13 for heating and evaporating the liquid to be treated contained in the evaporator 11 and a waste water collecting line 14 for collecting the concentrated water generated by the evaporation and concentration of the liquid to be treated.

  The heating device 13 is configured so that the liquid to be processed in the evaporator 11 passes through a heater 16 provided in the circulation line 15, and the liquid to be processed heated by the heater 16 is a nozzle (not shown) under reduced pressure. To the evaporator 11. Conveyance of waste water in the waste water recovery line 14 or the circulation line 15 is performed by the first pump 17, and switching of each line is performed by manual operation or automatic operation of the first switching valve 18.

  As the water contact device 2, various types of pure water scrubbers such as a spray type, a packed tower type, and a tray type can be used. The water contact device 2 is accommodated in the flush tower 21 having a flush chamber for storing dissolving water such as pure water, a steam supply line 22 for supplying steam generated in the evaporator 11 to the flush tower 21, and the flush tower 21. A dissolving water spraying device 23 for spraying the dissolving water and a return line 24 for supplying the dissolving water in the washing tower 21 to the evaporator 11 are provided. The water for dissolution to the water washing tower 21 can be supplied through a water supply line for dissolution (not shown).

  The dissolving water spraying device 23 transports the dissolving water in the washing tower 21 upward through the spraying line 25 and sprays it from the nozzle 26 provided at the tip of the spraying line 25 to mist the steam in the washing tower 21. It is comprised so that it can be made to melt | dissolve in the shape of a microdroplet. The water for dissolution in the return line 24 or the spray line 25 is transported by the second pump 27, and switching of each line is performed by manual operation or automatic operation of the second switching valve 28.

  Next, a method of treating lean wastewater using the wastewater treatment apparatus having the above configuration will be described along the flowchart shown in FIG. A predetermined amount of water for dissolution (pure water in the present embodiment) is supplied to the washing tower 21 in advance, and both the first pump 17 and the second pump 27 are stopped.

  First, a storage step of supplying the diluted waste water from the waste water supply line 12 to the evaporator 11 and storing the liquid to be treated including the diluted waste water in the evaporator 11 is performed (step S1). As the diluted waste water, for example, one having a weight concentration of about 0.1 to 3 wt% containing volatile acid or alkali such as hydrofluoric acid, nitric acid, and ammonia discharged in the manufacturing process of semiconductors and liquid crystals is suitable. is there.

  Next, a concentration process for evaporating and concentrating the liquid to be processed stored in the evaporator 11 is performed (step S2). Specifically, the pressure of the evaporator 11 is adjusted so that the temperature of the liquid to be processed becomes a saturation temperature, and the first pump 17 is operated to cause the liquid to be processed to pass through the circulation line 15. By operating the switching valve 18, the liquid to be treated is heated by the heater 16 to be a supersaturated liquid of about 5 ° C. The supersaturated liquid is sprayed from a nozzle (not shown) and the supersaturated liquid becomes vapor, and the liquid to be treated stored in the evaporator 11 is gradually concentrated. When the liquid to be treated is, for example, hydrofluoric acid water, the pressure in the evaporator 11 is preferably set to about 0.0074 MPa corresponding to a saturation pressure of about 40 ° C. In this case, the hydrofluoric acid concentration of the hydrofluoric acid-containing steam when the liquid concentration in the can is about 3% is about 0.2%.

  Concentrated water is generated in the evaporator 11 by performing the concentration step described above until a predetermined time elapses or until the concentration of the liquid to be processed reaches a predetermined concentration. Then, the 1st switching valve 18 is operated and the collection process which discharges concentrated water from the waste_water | drain collection line 14 is performed (step S3). The concentration of the concentrated water recovered in the recovery step is preferably 10 to 35 wt%, more preferably 15 to 30 wt%. By controlling the concentration of the concentrated water within the above-mentioned desired concentration range, for example, it can be reused for various purposes such as for metal cleaning.

  On the other hand, the acid or alkali-containing steam generated in the evaporator 11 is introduced into the water washing tower 21 through the steam supply line 22. In the water-washing tower 21, a melting process is performed in which the steam is brought into contact with the dissolving water to be dissolved (step S4). That is, by operating the second pump 27 and passing the dissolving water through the spraying line 25, acid or alkali is added to the dissolving water droplets such as pure water sprayed from the nozzle 26 and filled in the washing tower 21. Contains steam. As a result, most of the acid or alkali contained in the vapor (for example, about 60 to 90%, depending on the liquid concentration condition in the can, for example) is dissolved and removed in the dissolving water.

  The concentration of the dissolving water stored in the washing tower 21 is gradually increased to become a dilute acid or alkali solution. This acid or alkali solution is obtained by switching the flow path from the spray line 25 to the return line 24 by operating the second switching valve 28 after recovering all the concentrated water from the evaporator 11 in the recovery step. Supply to the evaporator 11.

  Next, by supplying the diluted waste water again from the waste water supply line 12 to the evaporator 11, the above-described steps S <b> 1 to S <b> 4 are repeated until the end. That is, in step S <b> 1, the liquid to be treated in which the diluted waste water and the acid or alkali solution are mixed is stored in the evaporator 11 by supplying the acid or alkali solution together with the diluted waste water to the evaporator 11. Thus, dilute waste water containing volatile acids or alkalis can be sequentially treated by a batch method.

  Thus, according to the method for treating diluted waste water according to the present embodiment, the steam generated in the concentration step of the liquid to be treated is dissolved in the dissolution water in the dissolution step to generate an acid or alkali solution, and concentrated. After passing through the water recovery process, this acid or alkali solution is supplied into the evaporation chamber along with the diluted waste water, so that most of the vapor generated in the concentration process is recovered without using a reverse osmosis membrane device as in the past. The volatile acid or alkali can be recovered with high efficiency and low cost.

  The dissolution step described above is preferably performed so that the concentration of the acid or alkali solution supplied to the evaporator 11 is approximately the same as the concentration of the diluted waste water supplied to the evaporator 11. That is, the ratio of the concentration of the liquid to be treated when the diluted waste water and the acid or alkali solution are stored in the evaporator 11 to the concentration of the liquid to be processed when only the diluted waste water is stored in the evaporator 11 is 0.8 to. It is preferably in the range of 1.0, and more preferably in the range of 0.85 to 0.95.

  By controlling the concentration of the acid or alkali solution in this way, the concentration of the liquid to be treated can be maintained substantially constant even when the above-described steps S1 to S4 are repeatedly performed. Can be efficiently recovered.

  Further, the time until the concentration of the acid or alkali solution becomes approximately the same as the concentration of the diluted waste water supplied to the evaporator 11 is substantially the same as the time until the concentrated water having a recoverable concentration is generated. It is preferable. Thereby, since the acid or alkali solution can be supplied to the evaporator 11 immediately after collecting the concentrated water, a good treatment speed of the diluted waste water can be obtained.

  The rate of increase in the concentration of the acid or alkali solution generated in the washing tower 21 depends on the amount and concentration of dilute wastewater supplied to the evaporator 11 and the amount of dissolved water stored in the washing tower 21 and sprayed from the nozzle 26. Control is possible by appropriately setting the flow rate and the like.

  As an example of the method for treating diluted waste water according to the present embodiment, waste water treatment was actually performed using the waste water treatment apparatus shown in FIG. Diluted waste water was used as hydrofluoric acid waste water, and pure water was used as dissolving water. The operation time of the waste water treatment apparatus was 22 hours per day, and 19 hours of the operation time was defined as the liquid supply time to the evaporator 11. During the liquid supply time, all the hydrofluoric acid solution stored in the washing tower 21 was supplied to the evaporator 11 while supplying the hydrofluoric acid waste water to the evaporator 11, and then the water for dissolution was supplied to the washing tower 21. The last one hour of the liquid supply time was set as an operation preparation time such as starting up a vacuum in the evaporator 11. As a result, 1980 L of dilute hydrofluoric acid having a hydrofluoric acid concentration of 1.28 wt% was stored in the evaporator 11, and 990 L of pure water was stored in the flush tower 21.

  Next, the liquid supply to the evaporator 11 was stopped, and the evaporation of the hydrofluoric acid water in the evaporator 11 was performed for 2 hours. As a result, 649 L of concentrated hydrofluoric acid having a hydrofluoric acid concentration of 14.43 wt% was generated in the evaporator 11. Further, 990 L of dilute hydrofluoric acid having a hydrofluoric acid concentration of 1.565 wt% was generated in the washing tower 21 by dissolving hydrofluoric acid vapor in pure water.

  Next, the evaporation concentration in the evaporator 11 was stopped, and the concentrated hydrofluoric acid water was recovered in about 1 hour. In addition, the diluted hydrofluoric acid water produced | generated in the water-washing tower 21 is supplied to the evaporator 11 in the liquid supply time of the next day.

  When the recovery rate of hydrofluoric acid in such a method for treating diluted wastewater was measured, the amount of hydrofluoric acid charged was 112.5 kg, whereas the amount of hydrofluoric acid recovered was 109.1 kg, and the recovery rate was It was as good as 96.99%.

It is a schematic block diagram which shows the waste water treatment apparatus used for the processing method of the diluted waste water which concerns on one Embodiment of this invention. It is a flowchart for demonstrating the action | operation of the waste water treatment apparatus shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Concentrator 11 Evaporator 12 Wastewater supply line 13 Heating device 14 Wastewater recovery line 2 Water contact device 21 Flush tower 22 Steam supply line 23 Dissolving water spray device 24 Return line

Claims (3)

A method for reusable treatment of dilute wastewater containing volatile acids or alkalis,
A storage step of storing the liquid to be treated including dilute wastewater in the evaporation chamber;
A concentration step of evaporating and concentrating the liquid to be treated in the evaporation chamber;
A recovery step of recovering the concentrated water generated in the concentration step from the evaporation chamber;
The steam generated in the concentration step is introduced into a washing chamber, and is dissolved in contact with the dissolution water stored in the washing chamber to generate an acid or alkali solution,
The storage step is a treatment method of diluted wastewater, comprising: collecting concentrated water in the recovery step; and supplying an acid or alkali solution to the evaporation chamber together with the diluted wastewater. The processing method of the diluted waste water of Claim 1 which performs density | concentration control in the said concentration process so that the acid or alkali density | concentration of the produced | generated concentrated water may be in the range of 10 to 35%. In the dissolution step, the ratio of the concentration of the liquid to be treated when the diluted waste water and the acid or alkali solution are supplied to the evaporation chamber to the concentration of the liquid to be processed when only the diluted waste water is supplied to the evaporation chamber is 0. The processing method of the diluted waste water of Claim 1 or 2 which performs density | concentration control of an acid or an alkali solution so that it may become the range of 8-1.0.

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