JP2023152734A - Wastewater treatment method - Google Patents

Abstract

An object of the present invention is to propose a wastewater treatment method that reduces the amount of unnecessary chemicals injected even when the properties of wastewater change significantly. The present invention is a wastewater treatment method in which the COD of wastewater before wastewater treatment is measured, and based on the COD or the amount of change in COD, the wastewater treatment is a coagulation-precipitation treatment, or an oxidation treatment and a coagulation-precipitation treatment. Further, the coagulation and precipitation treatment uses an iron-based flocculant containing ferric chloride, ferrous sulfate, and polyferrous sulfate, and the oxidation treatment generates hydroxyl radicals using an aqueous hydrogen peroxide solution and an iron-based catalyst. The Fenton reaction can be used. The COD of the wastewater is in the range of 200 to 10,000 (mg/L). [Selection diagram] Figure 1

Description

The present invention relates to a wastewater treatment method for reducing the amount of chemicals used for wastewater treatment in factories.

In industry, many chemical products are used, and the generated wastewater is mixed and treated as factory wastewater.
As a treatment method for industrial wastewater, ferric chloride is injected while adjusting the pH with dilute sulfuric acid, slaked lime, etc., and impurities in the wastewater coagulate and settle due to specific gravity, thereby treating the wastewater. Fenton treatment is an oxidation treatment in which hydrogen peroxide and ferric chloride are reacted in acidic conditions to cause the Fenton reaction that generates hydroxyl radicals, thereby oxidizing and decomposing organic matter in wastewater.

For wastewater that is assumed to have a high COD (Chemical Oxygen Demand) contained in the wastewater before wastewater treatment, the wastewater is subjected to Fenton treatment and then further treated to reduce COD by coagulation sedimentation treatment. On the other hand, for wastewater that is assumed to have a low COD, the COD is reduced by coagulation and sedimentation treatment.

However, in reality, the properties of wastewater are not uniform, so chemicals are generally injected assuming that high-load wastewater is to be treated, but when treating low-load wastewater, extra chemicals are injected. This means that you are injecting Here, as a method for eliminating waste caused by the injection of excess chemicals, a method has been proposed in which an optimum amount of chemicals to be injected is determined by calculating from data on wastewater components.

In the technology described in Patent Document 1, in the coagulation treatment step performed prior to the oxidation treatment step (Fenton treatment), an inorganic flocculant and activated carbon are added to the water to be treated so that they coexist, and an organic flocculant is further added to the wastewater to be treated. A processing method is disclosed.
Moreover, the technique described in Patent Document 2 discloses a water treatment system and a chemical injection control device that can inject an appropriate amount of chemicals into water to be treated.
Moreover, the technique described in Patent Document 3 discloses a method of measuring the COD or TOC value of wastewater and controlling the amount of chemical injection, etc.

JP2019-214020A JP2019-81140A Japanese Patent Application Publication No. 2010-179272

The above conventional technology has the following problems.
In the technology described in Patent Document 1, in the aggregation step before the oxidation step, recalcitrant COD is efficiently adsorbed and removed by activated carbon adsorption by the addition of activated carbon, and the oxidation efficiency by the oxidizer is further improved in the subsequent oxidation step. It also improves. However, this method is based on the premise that the oxidation step and the aggregation step including activated carbon adsorption are always carried out, and omitting the process does not result in a significant reduction in the amount of chemicals injected.

In addition, the method of determining the optimal amount of chemical injection using calculations described in Patent Document 2 is effective when changes in the properties of the wastewater to be treated can be predicted to some extent, but when dealing with industrial wastewater, etc., the properties of the wastewater vary greatly. Since the amount of chemicals varies, there is a problem in that it is difficult to derive the optimal amount of chemicals to be injected by calculation.
With the method described in Patent Document 3, it is possible to control the amount of medicine to be injected without performing difficult calculations. However, when dealing with industrial wastewater, etc., there is a problem that the properties of the wastewater may change in a short period of time, and the changes in the properties of the wastewater are so large that it is impossible to control the amount of chemical injection.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to propose a wastewater treatment method that reduces the amount of chemicals injected in excess even when the properties of the wastewater change significantly.

The inventors conducted extensive experiments and studies in order to solve the above problems. As a result, a system that can select the wastewater treatment method based on the COD of the wastewater before wastewater treatment has made it possible to select between only the coagulation-sedimentation treatment method or the coagulation-sedimentation treatment method that also includes oxidation treatment, and select the most suitable chemical. It was discovered that wastewater treatment can be done by adjusting the amount of injection.

The wastewater treatment method according to the present invention that advantageously solves the above problems is configured as follows.
[1] A wastewater treatment method that measures the COD of wastewater before wastewater treatment, and selects coagulation-sedimentation treatment, and either one of oxidation treatment and coagulation-sedimentation treatment based on the COD value.
[2] In [1] above, the COD is measured in the raw water tank, and based on the COD change amount ΔQ, which is the difference between the maximum value and the minimum value per hour, for the obtained COD value, This is a wastewater treatment method that selects the treatment.
[3] In the above [2], the wastewater treatment method selects oxidation treatment and coagulation-sedimentation treatment as wastewater treatment when the amount of change ΔQ in COD increases by 1000 mg/L or more.
[4] In any one of [1] to [3] above, the coagulation and precipitation treatment is a treatment using an iron-based flocculant containing ferric chloride, ferrous sulfate, and polyferrous sulfate. This is a certain wastewater treatment method.
[5] In any one of [1] to [3] above, the oxidation treatment is a wastewater treatment method that uses a Fenton reaction that generates hydroxyl radicals with an aqueous hydrogen peroxide solution and an iron-based catalyst. be.
[6] The wastewater treatment method according to any one of [1] to [3] above, wherein the COD of the wastewater is in the range of 200 to 10,000 mg/L.
[7] The wastewater treatment method according to [4] above, wherein the COD of the wastewater is in the range of 200 to 10,000 mg/L.
[8] The wastewater treatment method according to [5] above, wherein the COD of the wastewater is in the range of 200 to 10,000 mg/L.

According to the present invention, it is now possible to select a treatment method based on the COD value of the wastewater, so when the COD of the wastewater is low, the wastewater treatment method reduces the use of conventionally used Fenton treatment chemicals. can be realized. Further, the wastewater treatment method according to the present invention can be applied to the case of treating wastewater whose properties change greatly. Furthermore, the present invention can also reduce the use of chemicals such as pH adjusting chemicals during processing.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram of the wastewater treatment flow which is one embodiment of this invention. It is a flow chart of wastewater treatment of the present invention.

Hereinafter, a wastewater treatment method that is one embodiment of the present invention will be described in detail.

<Wastewater treatment equipment>
Figure 1 shows the wastewater treatment equipment. The raw water tank 1 stores wastewater from multiple factories. A COD measuring device 2 is installed to measure the COD of wastewater from the raw water tank. This measured COD value is transmitted to the control device 3. This control device 3 determines the steps of the coagulation sedimentation treatment 5 or the Fenton treatment 4 and the coagulation sedimentation treatment 5 regarding the wastewater treatment based on this COD, and controls the opening and closing of the solenoid valve 31 and the solenoid valve 32 of the drainage flow. .

The Fenton processing equipment 4 is shown from the top to the middle of FIG. The COD neutralization tank 41 performs neutralization treatment of waste water from the raw water tank. The chemicals used for pH adjustment are preferably dilute sulfuric acid, slaked lime, or caustic soda. A buffer pond 42 is provided to stir this waste water. It is preferable to use air for stirring. Neutralization tank 43 adjusts the pH of wastewater. It is preferable to use dilute sulfuric acid for adjustment. In the reaction tank 44, ferric chloride and hydrogen peroxide are injected into the waste water to cause a Fenton reaction to decompose organic matter. In place of ferric chloride, a chemical capable of causing the Fenton reaction, such as ferrous sulfate, may be used. In the decomposition tank 45, the wastewater is stirred and pH adjusted to remove hydrogen peroxide remaining in the wastewater. It is preferable to use caustic soda for pH adjustment, and it is preferable to use air for stirring. In the settling tank 46, impurities from the wastewater treatment settle.

Note that the solenoid valve is not limited to a two-way solenoid valve, and for example, a three-way solenoid valve may be used.

The coagulation and sedimentation treatment equipment 5 is shown in the lower part of FIG. Dilute sulfuric acid and ferric chloride are injected into the decomposition tank 51 to adjust the pH of the wastewater. It is preferable to use dilute sulfuric acid for pH adjustment. In the neutralization tank 52, the pH of the waste water is adjusted. In the sedimentation tank 53, impurities in the waste water are sedimented and separated.

<Wastewater treatment method>
FIG. 2 shows a wastewater treatment flow according to an embodiment of the present invention. First, the COD of the wastewater is measured in the raw water tank 1 (step S1), this COD value is sent to the control device 3, and the control device compares the value set in advance in the control device 3 with the measured COD value of the wastewater. (Step S2). Here, the COD of the waste water in the raw water tank 1 is measured at a specific time or every specific time within the waste water treatment time.
If the COD of the wastewater is equal to or higher than the set value, open the solenoid valve 31 leading from the raw water tank 1 to the Fenton treatment equipment 4, and close the solenoid valve 32 leading from the raw water tank 1 to the coagulation sedimentation treatment equipment 5 (step S3). At the same time, a signal is sent from the control device 3 to start a pump for injecting chemicals used in the Fenton processing equipment 4 (step S3). If the COD of the wastewater is less than the set value, the solenoid valve 31 leading from the raw water tank 1 to the Fenton treatment equipment 4 is closed, and the solenoid valve 32 leading from the raw water tank 1 to the coagulation sedimentation treatment equipment 5 is opened (step S5 ). At the same time, a signal is sent from the control device 3 to stop the pump for injecting the chemicals used in the Fenton processing equipment 4 (step S5).

In addition, based on the amount of change ΔQ in the COD of the wastewater, the means leading to the wastewater treatment equipment is controlled to select either coagulation-precipitation treatment, oxidation treatment, or coagulation-precipitation treatment, and select the selected wastewater treatment. You can set wastewater treatment conditions and treat wastewater using the treatment method. Here, the amount of change in COD ΔQ refers to the difference between the maximum value and minimum value per hour of the COD of the raw water tank measured within the wastewater treatment time.
For example, the COD of a raw water tank is measured at a specific time or every specific time period from before wastewater treatment to within the wastewater treatment time, and the difference between the maximum and minimum values per hour of the measured COD is analyzed and changes are made. Outputs the quantity ΔQ.

If the amount of change ΔQ in the wastewater COD is equal to or greater than the set value, the solenoid valve 31 leading from the raw water tank 1 to the Fenton treatment equipment 4 is opened, and the solenoid valve 32 leading from the raw water tank 1 to the coagulation sedimentation treatment equipment 5 is closed. (Step S3). At the same time, a signal is sent from the control device 3 to start a pump for injecting chemicals used in the Fenton processing equipment 4 (step S3). If the COD of the wastewater is less than the set value, the solenoid valve 31 leading from the raw water tank 1 to the Fenton treatment equipment 4 is closed, and the solenoid valve 32 leading from the raw water tank 1 to the coagulation sedimentation treatment equipment 5 is opened (step S5 ). At the same time, a signal is sent from the control device 3 to stop the pump for injecting the chemicals used in the Fenton processing equipment 4 (step S5).
In addition, when selecting the wastewater treatment, if the amount of change ΔQ in COD is 1000 mg/L or more based on 1000 mg/L, it is preferable to select oxidation treatment and coagulation sedimentation treatment.

With this wastewater treatment control system, the wastewater treatment method is based on the COD value of the wastewater, that is, if the COD value is above a predetermined set value or above a predetermined amount of change, Fenton treatment (Step S4) and coagulation sedimentation treatment (Step S6) are performed. Both are performed, and if the COD value is less than a predetermined set value or less than the amount of change, it is possible to select only the coagulation-sedimentation treatment (step S6) and implement the wastewater treatment (step S7).

Further, the cause of the increase in COD is thought to be caused by organic substances such as surfactants and metal ions such as iron. If COD increases due to metal ions, it can be treated only by coagulation and precipitation treatment, and treatment by Fenton reaction has almost no effect in reducing COD. Among the COD causes of wastewater, when metal ions are dominant, the COD of wastewater is 200 to 1500 mg/L. Here, the COD in the embodiment of the present invention is a value that takes into account the origin of organic substances and the origin of metal ions, and is in the range of 200 to 10,000 mg/L.
Therefore, it is preferable that the preset value is 1500 mg/L, but the set value may be changed so as to meet the wastewater standard during actual operation.

Before carrying out the above wastewater treatment and discharging the treated wastewater, the COD of the treated wastewater is measured, and if the discharge standards are met, the wastewater is discharged, and if it is not, the COD of the present invention is again carried out. Treat wastewater.

In the Fenton treatment 4, the waste water from the raw water tank 1 is neutralized in the COD neutralization tank 41, and the pH is adjusted to 7 to 9. Next, the waste water is stirred in the buffer pond 42. The pH of the agitated wastewater is adjusted to 2 to 3 in a neutralization tank 43. After adjusting the pH, processing is performed in the reaction tank 44 to decompose organic matter by Fenton reaction. After this decomposition treatment, the pH is adjusted to 7 to 9 and stirred in a decomposition tank 45 to remove residual hydrogen peroxide, and impurities are precipitated in a precipitation tank 46.

In the coagulation and precipitation treatment 5, dilute sulfuric acid and ferric chloride are injected into the decomposition tank 51 to adjust the pH of the wastewater. Next, in the neutralization tank 52, slaked lime is added to adjust the pH of the wastewater to 7 to 9. A flocculant is injected into the sedimentation tank 53 to form flocs, thereby sedimenting and separating impurities in the waste water.

Further, wastewater that requires Fenton treatment has always been treated as having a high COD, but in reality, depending on the timing of wastewater collection, the COD may be so low that Fenton treatment is not required. Even in that case, using the wastewater treatment method based on the COD set value of the present invention, it is possible to perform only the coagulation and sedimentation treatment without performing the Fenton treatment.

The treated water that has undergone coagulation and sedimentation treatment is discharged outside from the drain after confirming that the COD concentration is below the standard value using a COD meter. Since this COD measuring instrument requires accuracy, it is preferable to use chemical analysis in accordance with JIS K0102-1:2021.

[Example 1]
Wastewater from multiple factories was collected in a raw water tank and COD was measured. Switching of wastewater treatment method The set value of COD is 1500mg/L. If COD is 1500mg/L or more, both Fenton treatment and coagulation sedimentation treatment are performed, and if COD is less than 1500mg/L, only coagulation sedimentation treatment is performed. carried out. Wastewater treatment was carried out for three months using the wastewater treatment method according to the COD value of the present invention. The COD was measured after wastewater treatment and before discharge, and the COD was below the discharge standard for all charges.

[Example 2]
Wastewater from multiple factories was collected in a raw water tank, and COD was constantly measured. Furthermore, the difference between the maximum value and the minimum value of COD was calculated from the COD data converted per hour from the start of COD measurement.
The timing for switching the wastewater treatment method is set as the difference between the maximum and minimum COD values per hour at 1200 mg/L, and if the difference in COD increases by 1200 mg/L or more, Fenton treatment and coagulation sedimentation treatment are performed. Both treatments were performed, and if the difference in COD was less than 1200 mg/L, only the coagulation and precipitation treatment was performed. Processing time is approximately 1-2 hours. For 3 months, wastewater treatment was carried out using the wastewater treatment method based on the amount of change in COD of the present invention. The COD was measured after wastewater treatment and before discharge, and the COD was below the discharge standard for all charges.

In the embodiment of the present invention, it is now possible to select a treatment method based on the COD value of wastewater or the amount of change in COD, so when the COD of wastewater is low, the conventionally used Fenton treatment chemicals can be used. Because there was no need to do this, the amount of Fenton treatment chemicals used could be reduced by more than 25% in both treatment methods.

Note that although the embodiments of the present invention have been described in the above examples, the present invention is not limited thereto.

According to the present invention, the present wastewater treatment control system can be applied even when the number of options for wastewater treatment increases, such as when a new wastewater treatment method is developed or when the wastewater treatment method is improved. be.

W Waste water 1 Raw water tank 2 COD measuring device 3 Control device 31 Solenoid valve leading to Fenton treatment equipment 32 Solenoid valve leading to coagulation sedimentation treatment equipment 4 Fenton treatment equipment 41 COD neutralization tank 42 Buffer pond 43 Neutralization tank 44 Reaction tank 45 Decomposition Tank 46 Sedimentation tank 5 Coagulation sedimentation treatment equipment 51 Decomposition tank 52 Neutralization tank 53 Sedimentation tank

Claims (8)

A wastewater treatment method comprising: measuring the COD of wastewater before wastewater treatment; and selecting one of coagulation and sedimentation treatment, oxidation treatment, and coagulation and sedimentation treatment based on the COD value. A claim characterized in that the COD is measured in the raw water tank and the wastewater treatment is selected based on the amount of change ΔQ in the COD, which is the difference between the maximum value and the minimum value per hour, for the obtained COD value. The wastewater treatment method according to item 1. The wastewater treatment method according to claim 2, characterized in that when the amount of change ΔQ in COD increases by 1000 mg/L or more, oxidation treatment and coagulation-sedimentation treatment are selected as the wastewater treatment. The wastewater treatment method according to any one of claims 1 to 3, wherein the coagulation and precipitation treatment is a treatment using an iron-based flocculant containing ferric chloride, ferrous sulfate, and polyferrous sulfate. The wastewater treatment method according to any one of claims 1 to 3, wherein the oxidation treatment is a treatment that utilizes a Fenton reaction that generates hydroxyl radicals using an aqueous hydrogen peroxide solution and an iron-based catalyst. The wastewater treatment method according to any one of claims 1 to 3, wherein the COD of the wastewater is in the range of 200 to 10,000 mg/L. The wastewater treatment method according to claim 4, wherein the COD of the wastewater is in the range of 200 to 10,000 mg/L. The wastewater treatment method according to claim 5, wherein the COD of the wastewater is in the range of 200 to 10,000 mg/L.

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