JP7448129B2 - How to treat wastewater - Google Patents

Description

The present invention relates to a method for treating wastewater containing thiocyanate ions, salts thereof, and ammonium ions.

Industrial wastewater, particularly from chemical factories, oil refineries, steel factories, coke factories, etc., discharges wastewater of various properties. These wastewaters contain organic substances, for example, as measured by chemical oxygen demand (COD), and if these organic substances are directly discharged into sea areas, lakes, and marshes, they may cause environmental pollution. Therefore, under the Water Pollution Control Act, uniform wastewater standards have been established for the COD concentration of wastewater discharged from businesses with specified facilities into sea areas, lakes, etc., and it is necessary to reduce the COD concentration below the wastewater standards. It has been demanded.
Additionally, in areas where uniform wastewater standards alone are insufficient to prevent water pollution, prefectures have established additional wastewater standards through ordinances. Additional COD wastewater standards vary by industry and region, but in some cases strict standards of 20 mg/L or less have been established.

Conventionally, as a method for treating thiocyanic acid, which is listed as one of the COD components, for example, a method is known in which sodium hypochlorite is added to wastewater to oxidize and decompose thiocyanate ions.
However, with the treatment method using sodium hypochlorite, if the first stage reaction is not maintained at pH 10 to 11, highly toxic chlorine gas and cyanogen chloride gas will be generated, so constant pH control is necessary for safety. Moreover, a large amount of sodium hypochlorite was required to be added in order to prevent residual cyanide compounds such as cyanide, cyanogen chloride, and cyanic acid produced during the reaction.

Furthermore, as a method for treating wastewater containing thiocyanate, for example, Patent Documents 1 and 2 disclose a method of reacting copper ions in wastewater containing thiocyanate, and Patent Document 3 discloses a method for reacting copper ions in wastewater containing thiocyanate compounds. A method for reacting a substance containing ferric ions as a main component is disclosed. These patent documents describe that the COD value can be reduced by removing thiocyanic acid from the waste liquid.
However, in addition to thiocyanate ions, ammonium ions often coexist in wastewater containing thiocyanate, so in order to discharge treated wastewater into rivers or the ocean, the total nitrogen content in addition to COD in wastewater must be determined by the Ministry of the Environment. Although it is necessary to reduce the amount of nitrogen to below the established wastewater standard value, conventional methods for treating wastewater containing thiocyanate have not paid any attention to reducing the total nitrogen content in the wastewater.

Patent No. 50-18383 Japanese Patent Application Publication No. 58-159891 Japanese Unexamined Patent Publication No. 51-48564

Therefore, in treating thiocyanate ions, etc. in wastewater, the amount of added chemicals can be minimized, the treatment can be carried out safely and efficiently, and the amount of COD and total nitrogen in treated wastewater can be reduced to the uniform wastewater standards set by the Ministry of the Environment. The objective is to provide a method for treating wastewater that satisfies the following criteria.

As a result of extensive research to solve the above problems, the inventors of the present invention have found that by bringing a copper compound into contact with wastewater containing thiocyanate ions, their salts, and ammonium ions, the amount of chemicals added can be reduced. We have completed the present invention by discovering the fact that thiocyanic acid in wastewater can be removed as safely and efficiently as possible to ensure that the COD concentration and total nitrogen content in wastewater can meet the uniform wastewater standards set by the Ministry of the Environment.

(1) The present invention includes a step of bringing a copper compound into contact with wastewater containing thiocyanate ions, salts thereof, and ammonium ions, and monitoring the chemical oxygen demand (COD) and total nitrogen in the wastewater. A method for treating wastewater, comprising the steps of:
(2) The present invention is also the method for treating waste water according to (1), further comprising the step of bringing activated carbon into contact with the waste water.
(3) The present invention also provides the method for treating wastewater according to (1) or (2), wherein the copper compound is a monovalent copper salt or a divalent copper salt.

According to the present invention, wastewater containing thiocyanate ions, salts thereof, and ammonium ions can be treated safely and efficiently while minimizing the amount of chemicals added.
That is, according to the present invention, by removing thiocyanate ions and the like contained in the wastewater, the COD and total nitrogen content in the treated wastewater can be reduced to below the uniform wastewater standard value set by the Ministry of the Environment, and the method of the present invention The method of the present invention is extremely useful industrially because even if the treated wastewater is released into nature as it is, the impact on the environment is extremely small.

Hereinafter, the present invention will be explained in detail, but the present invention is not limited to the following explanation.

The wastewater treatment method according to the present invention (hereinafter also referred to as the treatment method according to the present invention) includes a step of bringing a copper compound into contact with wastewater containing thiocyanate ions, salts thereof, and ammonium ions.
The wastewater to which the treatment method according to the present invention is applied is not particularly limited as long as it contains thiocyanate ions, salts thereof, and ammonium ions, and includes, for example, chemical factories, oil refineries, steel factories, etc. Examples include thiocyanate ion-containing wastewater and wet flue gas desulfurization wastewater discharged from coke factories and the like.

Conventional thiocyanic acid treatment methods such as those described in Patent Documents 1 to 3 mentioned above aim to reduce the amount of COD by removing thiocyanic acid, and do not take into account the reduction of the total nitrogen amount due to the presence of ammonium ions, etc. However, no consideration was given to what treatment conditions would be used to limit not only COD but also the total amount of nitrogen.
In contrast, the treatment method according to the present invention includes a step of treating wastewater containing thiocyanate ions, salts thereof, and ammonium ions with a predetermined chemical, and a step of monitoring COD and total nitrogen in the wastewater. By having this, it is possible to effectively remove COD and total nitrogen content in treated wastewater, and it is easy to reduce the amount to uniformly below the standard value set by the Ministry of the Environment. The present invention is the first method to focus on COD and total nitrogen in the treated waste liquid and to control these amounts to extremely small amounts.

The thiocyanate ion concentration and ammonium ion concentration in the wastewater to be treated in this process are not particularly limited, but it is preferable that the concentration exceeds the uniform wastewater standards for COD and total nitrogen set by the Ministry of the Environment. According to the present invention, even if the concentration of wastewater does not exceed the uniform wastewater standards for COD and total nitrogen content, the COD and total nitrogen in the wastewater can be sufficiently reduced.

In the present invention, the copper compound is preferably a cuprous compound or a cupric compound that is soluble or easily dispersible in water and capable of forming monovalent or divalent copper ions in water.
Examples of the cuprous compounds include cuprous chloride, cuprous fluoride, cuprous bromide, cuprous iodide, cuprous nitrate, cuprous sulfate, and the like. Examples of the cupric compound include cupric chloride, cupric fluoride, cupric bromide, cupric iodide, cupric nitrate, and cupric sulfate.
In addition, when using the cupric compound, it is preferable to use a reducing agent together to reduce divalent copper ions to monovalent copper ions in the waste water. Examples of the reducing agent include thiosulfates, sulfites such as sodium sulfite, divalent iron salts, thiosulfates, and the like.
Furthermore, since sulfuric acid is generated when the divalent copper ion is reduced to a monovalent copper salt, it is preferable to add a neutralizing agent to neutralize the waste water.
The neutralizing agent is not particularly limited, and examples thereof include sodium hydroxide, potassium hydroxide, calcium hydroxide, and magnesium hydroxide.
Moreover, sulfuric acid, hydrochloric acid, nitric acid, etc. are selected as the neutralizing agent depending on the pH before discharge.

The method of bringing the copper compound into contact with the waste water containing the thiocyanate ion, its salt, and ammonium ion includes, for example, using a stirrer to promote the reaction between the waste water and the mixed solution of the copper compound. Examples include methods that utilize aeration, mixing in a channel that allows drainage to stagnate, and the like.
The contact between the waste water and the copper compound is preferably carried out under conditions that allow the thiocyanate ions and ammonium ions in the waste water to come into contact with the copper compound. Contact with a cuprous compound is preferred.

In the present invention, the contact between the waste water and the copper compound is preferably carried out by uniformly stirring the mixed solution from the viewpoint of treatment effect during the reaction with the waste water, but if the mixed solution has already been treated to reduce COD and/or total nitrogen. A copper compound may be brought into contact with the water before and after the water is drained.
Further, in order to promote the reaction during stirring, the temperature of the mixed solution is preferably heated to some extent, but a temperature of about 20 to 60°C is sufficient.
The time required for the reaction during stirring varies depending on the amount and concentration of the wastewater, the form and scale of the treatment equipment, etc., but may be appropriately determined so that the above-mentioned wastewater comes into contact with the copper compound sufficiently. Generally, the stirring time may be 10 minutes to 6 hours, more preferably 15 to 60 minutes.

Preferably, the present invention further includes a step of bringing activated carbon into contact with the wastewater.
The step of bringing the activated carbon into contact with the waste water may be performed during the above-described step of bringing the waste water into contact with the copper compound, or may be performed after the step of bringing the waste water into contact with the copper compound.
When the step of bringing the activated carbon into contact with the waste water is performed during the step of bringing the waste water into contact with the copper compound, it is preferable that the activated carbon is further brought into contact when the copper compound is brought into contact with the waste water.
By contacting the above-mentioned copper compound, CuSCN becomes cloudy and precipitates in the above-mentioned wastewater, and copper compounds derived from excess chemicals and copper compounds solubilized by ammonium ions in the wastewater and complex ions of copper thiocyanate remain. do. Therefore, it is necessary to treat the compound, for example, to insolubilize and remove copper by adjusting the pH, or to dilute it, but by using the activated carbon in combination, it is possible to prevent copper from remaining due to the compound. Further, the effect of promoting the sedimentation of the cloudy precipitate due to CuSCN and facilitating solid-liquid separation can be expected.

The raw material and shape of the activated carbon to be brought into contact with the wastewater are not particularly limited, and coal-based, coconut shell-based, and other granular or powdered materials can be used.

Known devices such as thickeners and turbidity/sedimentation basins can be used to remove suspended solids generated from the waste water and copper compounds.

In the step of bringing the copper compound into contact with the wastewater, an inorganic coagulant such as aluminum chloride, polyaluminum chloride, ferric chloride, or polyferric sulfate, or a water-soluble cationic polymer compound is further added to the reaction. Wastewater treatment can be accelerated by collecting fine particles of suspended solids and promoting sedimentation.

The water-soluble cationic polymer compound is not particularly limited as long as it is water-soluble and has cationic properties in an aqueous solution, such as a copolymer of acrylamide and diallyldimethylammonium chloride, polyethyleneimine, and its like. Modified products, copolymers of epichlorohydrin and dimethylamine, diallyldimethylammonium chloride, polydialkylaminoethyl acrylate (methacrylate) quaternary salts, polyvinylpyridine quaternary salts, cationized starch, chitin, chitosan, etc. In addition, a cationic flocculant usually called an organic flocculant (molecular weight of about 500 to 100,000) or a polymer flocculant (molecular weight of about 100,000 to 10,000,000) can also be applied.

In the present invention, an oxidizing agent may be further added to the waste water.
As mentioned above, methods of reducing COD by adding sodium hypochlorite (oxidizing agent) to wastewater containing thiocyanate ions, etc., and by air oxidation through aeration have been known for a long time, but there are still insufficient methods to reduce COD. In order to obtain a treatment effect, a large amount of sodium hypochlorite is required to be added, but in the present invention, since wastewater is treated with the copper compound described above, the amount of oxidizing agent added is small compared to conventional methods. Also, sufficient COD and total nitrogen reduction effects can be obtained.
The above-mentioned oxidizing agent is not particularly limited and conventionally used ones can be used, such as sodium hypochlorite, sodium hypobromite, N-monochlorosulfamate, chlorine dioxide, sodium chlorite, peroxide, etc. Examples include hydrogen oxide.

The present invention includes monitoring chemical oxygen demand (COD) and total nitrogen (TN) in the wastewater.
By feeding back the information on COD and total nitrogen in the wastewater obtained through this process to the process of bringing the wastewater into contact with the copper compound mentioned above, the contact conditions between the copper compound and the wastewater can be adjusted, making it more efficient. Efficient treatment of wastewater is possible.

The step of monitoring the chemical oxygen demand (COD) and total nitrogen in the wastewater can be carried out, for example, by measuring CODMn and total nitrogen in accordance with JIS K0102 Sections 17 and 45.1. can.

In the present invention, the step of monitoring the chemical oxygen demand (COD) and total nitrogen in the wastewater may be performed immediately before releasing the wastewater treated with the copper compound into the natural world, It may be carried out immediately after the step of contacting with. Furthermore, by performing a step of monitoring the chemical oxygen demand (COD) and total nitrogen in the wastewater before and after contacting the wastewater with the copper compound, the process of bringing the wastewater into contact with the copper compound can be improved. This is preferable because the processing conditions can be determined in more detail.

The present invention will be further explained below using Examples. However, the present invention is not limited to the following examples.

(Preparation of test water)
Test water with the water quality shown in Table 1 below was prepared as wastewater containing thiocyanate ion, its salt, and ammonium ion to be used in the following test example (pH 7.0, COD: 260 mg/L, TN : 140mg/L, thiocyanate ion 230mg/L). Specifically, test water was prepared using potassium thiocyanate, sodium chloride, sodium sulfate, and ammonium chloride.

(Examples 1 to 4)
Weighed 200 mL of test water into a beaker, added the chemicals shown in Table 2 below and activated carbon (Examples 2 and 4, manufactured by Futamura Chemical Co., Ltd., product name IP) in the amounts shown in Table 2, and stirred for 30 minutes. Stirred.
Next, solid-liquid separation was performed using 5C filter paper, and the filtrate was collected.
In Examples 1 and 2, sodium hypochlorite was added in the amount shown in Table 2 to the filtrate collected above, the pH was adjusted to 10 to 11, stirred for 20 minutes, and then the pH was adjusted to 6 to 7. The mixture was stirred for 40 minutes to obtain treated water.
After the stirring was completed, CODMn and TN (total nitrogen) of the treated water were measured in accordance with JIS K0102 Sections 17 and 45.1.
In Examples 3 and 4, the collected filtrate was adjusted to pH 10 to 11 and aerated for 120 minutes, and after the aeration was completed, CODMn and TN (total nitrogen) were measured according to JIS K0102 Section 17 and 45.1. Measured in accordance with Section 1.

(Comparative example 1)
200 mL of test water was weighed into a beaker, and the chemicals shown in Table 2 below were added in the amounts shown in Table 2, the pH was adjusted to 6 to 7, and the mixture was stirred for 30 minutes.
Next, NO. Solid-liquid separation was performed using 5C filter paper, the filtrate was collected, and CODMn and TN (total nitrogen) were measured in accordance with JIS K0102 Sections 17 and 45.1.

(Comparative example 2 )
200 mL of test water was measured into a beaker, and the chemicals shown in Table 2 below were added in the amounts shown in Table 2, the pH was adjusted to 10 to 11, and the mixture was stirred for 20 minutes.
Next, the pH was adjusted to 6 to 7, stirred for 40 minutes, and after the stirring was completed, CODMn and TN (total nitrogen) were measured in accordance with JIS K0102 Sections 17 and 45.1.
(Comparative example 3 )
200 mL of test water was weighed into a beaker, adjusted to pH 10 to 11, and aerated for 120 minutes. After the aeration, CODMn and TN (total nitrogen) were measured in accordance with JIS K0102 Sections 17 and 45.1. .
(Comparative example 4)
200 mL of test water was weighed into a beaker, and CODMn and TN (total nitrogen) were measured in accordance with JIS K0102 Sections 17 and 45.1.

From the test results in Table 2, the following was found.
(1) By performing the treatment with a copper compound or a copper compound and activated carbon (Examples 1 to 4), a sufficient treatment effect can be obtained for both CODMn and TN contained in wastewater.
(2) Activated carbon treatment alone (Comparative Example 1), sodium hypochlorite treatment alone (Comparative Example 2), aeration treatment alone (Comparative Example 3), and no treatment (Comparative Example 4) were sufficient for both CODMn and TN. The processing effect cannot be obtained.
(3) By performing treatment with a copper compound, copper compound, and activated carbon (Examples 1 to 4), the amount of sodium hypochlorite added can be reduced compared to treatment with sodium hypochlorite alone (Comparative Example 2). Also, sufficient processing effects can be obtained for CODMn and TN.

Claims (4)

A step of bringing a copper compound into contact with wastewater containing thiocyanate ions, salts thereof, and ammonium ions;
monitoring chemical oxygen demand (COD) and total nitrogen in the wastewater ;
Information on the chemical oxygen demand (COD) and total nitrogen in the wastewater obtained in the step of monitoring the chemical oxygen demand (COD) and total nitrogen in the wastewater is obtained by contacting the wastewater with a copper compound. Feedback to the process adjusts the contact conditions between copper compounds and wastewater to reduce chemical oxygen demand (COD) and total nitrogen in the wastewater.
A wastewater treatment method characterized by: 2. The method for treating wastewater according to claim 1, wherein in the step of bringing the copper compound into contact with the wastewater, the thiocyanate ions and ammonium ions in the wastewater are brought into contact with the copper compound. The method for treating wastewater according to claim 1 or 2 , further comprising the step of bringing activated carbon into contact with the wastewater during and/or after the step of bringing the wastewater into contact with a copper compound. The method for treating wastewater according to claim 1 or 2, wherein the copper compound is a monovalent copper salt or a divalent copper salt.