A method for treating organic wastewater

Abstract

The present invention discloses a method for treating organic wastewater, comprising soaking zero-valent iron in a solution containing a modifier, then filtering to obtain the modified zero-valent iron, and then adding the modified zero-valent iron and hydrogen peroxide to the organic wastewater. The modifier comprises one or more of ethylenediaminetetraacetic acid, ethylenediaminetetraacetate, butanetetracarboxylic acid, butanetetracarboxylic acid salt, methyliminodiacetic acid, methyliminodiacetic acid salt, nitrilotriacetic acid, and nitrilotriacetate. The present invention uses the modifier to modify the zero-valent iron. The modified zero-valent iron can synergistically remove organic pollutants from wastewater with hydrogen peroxide under near-neutral conditions, greatly broadening the application range of the zero-valent iron and hydrogen peroxide system. The treatment method of the present invention produces almost no secondary pollution, and compared to traditional zero-valent iron and hydrogen peroxide systems, both the removal rate and removal efficiency are improved.

Description

Technical Field

[0001] The present invention particularly relates to a method for treating organic wastewater. Background Art

[0002] With the rapid development of industries such as chemical, pharmaceutical, and printing and dyeing, an increasing number of organic pollutants are being discharged into the environment. This not only damages aquatic ecosystems but also harms the health of animals, plants, and humans. Treatment of organic wastewater is urgent. Advanced oxidation processes (AOPs) are simple and efficient water treatment technologies that generate highly oxidizing hydroxyl radicals (•OH), rapidly degrading or even completely mineralizing target pollutants. Therefore, they are widely used in organic wastewater treatment. Zero-valent iron (ZVI) is safe, readily available, inexpensive, has a strong reducing capacity, and produces no secondary pollution. In recent years, advanced oxidation processes based on ZVI have become a hot topic of research.

[0003] Currently, the zero-valent iron / hydrogen peroxide (hydrogen peroxide or H2O2) system has been widely used to treat organic pollutants such as phenols, antibiotics, and dyes. However, the traditional zero-valent iron / hydrogen peroxide system has the following main problems:

[0004] (1) The pH range of application is small, and organic pollutants can only be effectively removed under acidic conditions (pH ≤ 4). Usually, a large amount of acid needs to be added to the organic wastewater in advance to adjust the pH of the organic wastewater to below 4. However, the addition of a large amount of acid brings secondary pollutants to the water body, increasing the subsequent treatment cost of the wastewater.

[0005] (2) The time required to treat organic wastewater is long, which means that the removal efficiency of organic pollutants is low.

[0006] (3) The removal rate of organic pollutants is not high. Summary of the Invention

[0007] The object of the present invention is to provide a method for treating organic wastewater which produces almost no secondary pollution and still has high removal rate and removal efficiency under nearly neutral conditions.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is:

[0009] A method for treating organic wastewater comprises first modifying zero-valent iron using a modifier, and then adding the modified zero-valent iron and hydrogen peroxide to the organic wastewater. The method for modifying the zero-valent iron using the modifier comprises: immersing the zero-valent iron in a solution containing the modifier, and then filtering to obtain the modified zero-valent iron. The modifier comprises one or more of ethylenediaminetetraacetic acid, ethylenediaminetetraacetate, butanetetracarboxylic acid, butanetetracarboxylate, methyliminodiacetic acid, methyliminodiacetate, nitrilotriacetic acid, and nitrilotriacetate.

[0010] Traditional zero-valent iron / hydrogen peroxide systems have a narrow pH range of application, requiring a pH below 4 to remove organic pollutants. Conventional organic wastewater is generally near neutral, meaning that using this system requires adding large amounts of acid to the organic wastewater to reduce the system's pH to below 4, which limits the current application of zero-valent iron / hydrogen peroxide systems. The present invention modifies zero-valent iron using a modifier. The modified zero-valent iron can then work with hydrogen peroxide under near-neutral conditions to efficiently and effectively remove organic pollutants from wastewater, significantly expanding the application range of zero-valent iron and hydrogen peroxide systems. Furthermore, this treatment method produces virtually no secondary pollution.

[0011] Preferably, the pH of the organic wastewater is controlled to be greater than or equal to 4.

[0012] Further preferably, the pH of the organic wastewater is controlled to be 4.5-8.5.

[0013] More preferably, the pH of the organic wastewater is controlled to be 6-7.

[0014] Preferably, the concentration of the modified zero-valent iron in the organic wastewater is controlled to be 0.1-0.5 g / L, preferably 0.25-0.5 g / L, and more preferably 0.25-0.4 g / L.

[0015] Preferably, the concentration of hydrogen peroxide in the organic wastewater is controlled to be 20-100 mM, preferably 40-80 mM, more preferably 50-80 mM, for example, 50 mM, 55 mM, 60 mM, 65 mM, 70 mM, 75 mM, etc.

[0016] Preferably, the concentration of the solution containing the modifier is 0.1-0.5 mol / L, preferably 0.2-0.3 mol / L, more preferably 0.2-0.25 mol / L.

[0017] More preferably, the solution containing the modifier is an aqueous solution containing the modifier.

[0018] More preferably, the soaking time is 0.5 to 1 hour.

[0019] Preferably, the zero-valent iron is reduced iron powder, and the particle size of the reduced iron powder is 30-100 μm. The reduced iron powder in the present invention is micron-sized reduced iron powder, which is cheaper than nano-sized reduced iron powder.

[0020] Preferably, the method of modifying the zero-valent iron using the modifier further includes washing the modified zero-valent iron obtained by filtration with water, and then drying the modified zero-valent iron, and controlling the drying temperature to be 70-85°C.

[0021] Preferably, the metal ions in the ethylenediaminetetraacetate, butanetetracarboxylate, methyliminodiacetate and nitrilotriacetate are independently selected from one or more of sodium ions, calcium ions, potassium ions and magnesium ions.

[0022] Preferably, the organic matter contained in the organic wastewater includes one or more of dyes with high concentration and large chroma, phenolic pollutants, drugs and personal care products, wherein personal care products include but are not limited to hand cream and / or shampoo.

[0023] Further preferably, the concentration of organic matter in the organic wastewater is 20-80 mg / L.

[0024] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0025] The present invention uses a modifier to modify zero-valent iron. The modified zero-valent iron can synergistically remove organic pollutants in wastewater with hydrogen peroxide under near-neutral conditions, greatly broadening the application range of the zero-valent iron and hydrogen peroxide system. The treatment method of the present invention produces almost no secondary pollution, and compared with the traditional zero-valent iron and hydrogen peroxide system, both the removal rate and removal efficiency are improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The effect of the EDTA-ZVI (modified zero-valent iron) / hydrogen peroxide system on the removal rate of tetracycline hydrochloride (TC) at different times in Example 1, where η (%) refers to the removal rate;

[0027] Figure 2 is the reaction rate constant of EDTA-ZVI and ZVI (zero-valent iron) at different concentrations in Example 1. DETAILED DESCRIPTION

[0028] Traditional zero-valent iron / hydrogen peroxide systems suffer from a narrow pH range and low removal efficiency and rate. The inventors unexpectedly discovered that by first modifying zero-valent iron with the modifiers described in this invention and then introducing the modified zero-valent iron and hydrogen peroxide into organic wastewater, organic pollutants can be removed from the system under near-neutral conditions. Furthermore, compared to traditional zero-valent iron / hydrogen peroxide systems, both the removal rate and efficiency are improved. The present invention's solution is further described below.

[0029] A method for treating organic wastewater comprises the following steps:

[0030] (1) adding reduced iron powder to a solution containing a modifier having a concentration of 0.1 to 0.5 mol / L, soaking the solution for 0.5 to 1 hour, cleaning the solution and drying the solution to obtain modified zero-valent iron, wherein the modifier comprises one or more of ethylenediaminetetraacetic acid, ethylenediaminetetraacetic acid salt, butanetetracarboxylic acid, butanetetracarboxylic acid salt, methyliminodiacetic acid, methyliminodiacetic acid salt, nitrilotriacetic acid and nitrilotriacetic acid salt;

[0031] (2) Adding the modified zero-valent iron and hydrogen peroxide obtained in step (1) to organic wastewater having a pH greater than or equal to 4, wherein the concentration of the modified zero-valent iron in the organic wastewater is controlled to be 0.1-0.5 g / L, and the concentration of hydrogen peroxide is controlled to be 20-100 mM.

[0032] The method for treating organic wastewater of the present invention has at least the following advantages:

[0033] (1) The treatment method of the present invention can remove organic pollutants at normal temperature and pressure and different pH conditions, and has a wide range of applications. Compared with the traditional method of removing organic pollutants using a zero-valent iron / hydrogen peroxide system, the present invention can effectively remove organic pollutants in organic wastewater even under near-neutral conditions, with a removal rate of more than 90%, which can reduce or even eliminate the need for additional acid or alkali to be added to the system to adjust the pH of the system.

[0034] (2) The treatment method of the present invention produces almost no secondary pollution and is environmentally friendly. Compared with the method of directly adding a modifier to a water body, the present invention uses a modifier to pre-modify the reduced iron powder so that the modifier is complexed with the reduced iron powder. The modifier complexed with the reduced iron powder can synergistically remove organic pollutants with iron and hydrogen peroxide while almost never entering the water environment. Even if it enters the water environment, it is only a very small amount and will not cause secondary pollution to the water environment. In addition, the direct complexation contact between the modified reduced iron and the modifier greatly enhances the synergistic effect of the modifier, iron and hydrogen peroxide. The modified reduced iron powder added to the water body of the present invention can be recovered by filtration, and the hydrogen peroxide can be naturally degraded by heating or light, etc., without introducing secondary pollutants into the water environment.

[0035] (3) The treatment method of the present invention has high removal efficiency, and its reaction rate constant k can reach 0.04min -1 The reaction rate constant k of the traditional zero-valent iron / hydrogen peroxide system is less than 0.005 min -1 .

[0036] (4) The zero-valent iron, modifier, and hydrogen peroxide of the present invention are all easily available and inexpensive, and the treatment method of the present invention is simple.

[0037] The present invention is further described below with reference to the following examples. However, the present invention is not limited to the following examples. The implementation conditions used in the examples may be further adjusted according to the specific requirements of the application. Unspecified implementation conditions are conventional conditions in the industry. The technical features involved in the various embodiments of the present invention may be combined with each other as long as they do not conflict with each other.

[0038] Unless otherwise specified, the particle size of the reduced iron powder in the following examples and comparative examples is 30-100 μm.

[0039] Example 1

[0040] (1) Add 2.0 g of reduced iron powder (ZVI) to 25 mL of a 0.2 mol / L aqueous solution of disodium ethylenediaminetetraacetic acid (hereinafter referred to as EDTA-sodium salt). Soak for 1 hour, filter, and then wash with deionized water 2-3 times, then filter using a suction filter. After filtration, place the reduced iron powder in an oven and dry it at 80°C to obtain the modified zero-valent iron (EDTA-ZVI) for later use.

[0041] (2) Take 500 ml of deionized water and 0.025 g of tetracycline hydrochloride (TC), mix them evenly, and prepare a TC solution with a concentration of 50 mg / L. Use 0.1 mol / L NaOH solution and H2SO4 solution to adjust the pH of the system to 6.5.

[0042] (3) Adding EDTA-ZVI and H2O2 prepared in step (1) into the system of step (2), wherein the concentration of H2O2 in the system is controlled to be 60 mM and the concentration of EDTA-ZVI is controlled to be 0.3 g / L.

[0043] At set times (the set times in this embodiment are 2 min, 5 min, 10 min, 20 min, 30 min, 45 min, and 60 min, respectively), 4 mL of sample was taken. 0.3 ml of methanol was immediately added to the sample to terminate the reaction. The TC concentration in the sample was determined by high performance liquid chromatography, and the TC removal rate was calculated. The TC removal rate is shown as follows: Figure 1 As shown in the figure, after 60 min, the removal rate of TC was 90.8%.

[0044] The reaction rate in this example is shown in Figure 2 , where k refers to the reaction rate constant, which is calculated as: ln(C t / C0)=-k*t, where C t and C0 are the reaction time t and initial organic matter concentration respectively, and t is the reaction time (t is 20 min). Figure 2It can be seen that the EDTA-ZVI / H2O2 system in this embodiment can remove TC in the system in a relatively short time with good removal efficiency, and the reaction rate constant can reach 0.04min -1 The above is much higher than the traditional ZVI / H2O2 system.

[0045] Sampling was done at the set time (60 min), and the EDTA content in the sample was detected to be 0.01 mM.

[0046] Example 2

[0047] The difference from Example 1 is that the concentration of EDTA-ZVI in step (3) is 0.2 g / L. After 60 minutes, the TC removal rate is 68.4%.

[0048] Example 3

[0049] The difference from Example 1 is that the concentration of EDTA-ZVI in step (3) is 0.5 g / L. After 60 minutes, the removal rate of TC is 87%.

[0050] The EDTA content detected in the sample was 0.1 mM.

[0051] Example 4

[0052] The difference from Example 1 is that the concentration of H2O2 in step (3) is 20 mM. After 60 minutes, the removal rate of TC is 65.0%.

[0053] Example 5

[0054] The difference from Example 1 is that the concentration of H2O2 in step (3) is 100 mM. After 60 minutes, the removal rate of TC is 86%.

[0055] Example 6

[0056] The difference from Example 1 is that the pH of the system is not adjusted in step (2). The TC solution is an acidic solution with a pH of 4.5. After 60 minutes, the TC removal rate is 92.6%.

[0057] Example 7

[0058] The difference from Example 1 is that in step (2), 0.1 mol / L NaOH is used to adjust the pH of the system to 8.5. After 60 minutes, the TC removal rate is 50%.

[0059] Example 8

[0060] The difference from Example 1 is that the concentration of EDTA-sodium salt in step (1) is 0.1 mol / L. After 60 minutes, the removal rate of TC is 76%.

[0061] Example 9

[0062] The difference from Example 1 is that the EDTA-sodium salt concentration in step (1) is 0.3 mol / L. After 60 minutes, the TC removal rate is 90.96%.

[0063] Example 10

[0064] The difference from Example 1 is that in step (2), some water from Nanjing Xuanwu Lake is collected. The antibiotic concentration in natural fresh water is usually in the range of ng L -1 -μg L −1 Therefore, a certain amount of TC was added to the water of Nanjing Xuanwu Lake to control the TC concentration in the water to 50 mg / L. The pH of the system was adjusted to 6.5 using 0.1 mol / L NaOH solution and H2SO4 solution. The actual wastewater was used in the experiment. After 60 minutes, the TC removal rate was 80.1%.

[0065] Example 11

[0066] The difference from Example 1 is that the disodium ethylenediaminetetraacetic acid aqueous solution in step (1) is replaced by an ethylenediaminetetraacetic acid aqueous solution.

[0067] After 60 min, the removal rate of TC was 90.2%.

[0068] Example 12

[0069] The difference from Example 1 is that the disodium ethylenediaminetetraacetic acid aqueous solution in step (1) is replaced by a butanetetracarboxylic acid (BTCA) aqueous solution.

[0070] After 60 min, the removal rate of TC was 89.8%.

[0071] Example 13

[0072] The difference from Example 1 is that the disodium ethylenediaminetetraacetic acid aqueous solution in step (1) is replaced by a methyliminodiacetic acid (MIDA) aqueous solution.

[0073] After 60 min, the removal rate of TC was 80.3%.

[0074] Example 14

[0075] The difference from Example 1 is that the disodium ethylenediaminetetraacetic acid aqueous solution in step (1) is replaced by a nitrilotriacetic acid (NTA) aqueous solution.

[0076] After 60 min, the removal rate of TC was 87.1%.

[0077] Comparative Example 1

[0078] (1) Take 500 ml of deionized water and 0.025 g of tetracycline hydrochloride (TC), mix them evenly, and prepare a TC solution with a concentration of 50 mg / L. Use 0.1 mol / L NaOH solution and H2SO4 solution to adjust the pH of the system to 6.5.

[0079] (2) Reduced iron powder (ZVI) and H2O2 are added to the system of step (1), wherein the concentration of H2O2 in the system is 60 mM and the concentration of reduced iron powder is 0.3 g / L.

[0080] The TC removal rate was tested using the method of Example 1. After 60 min, the TC removal rate was 19.84%. Figure 2 As shown, where k is the reaction rate constant at 20 min.

[0081] Comparative Example 2

[0082] (1) Take 500 ml of deionized water and 0.025 g of tetracycline hydrochloride (TC), mix them evenly, and prepare a TC solution with a concentration of 50 mg / L. Use 0.1 mol / L NaOH solution and H2SO4 solution to adjust the pH of the system to 6.5.

[0083] (2) Reduced iron powder (30-100 µm), disodium ethylenediaminetetraacetic acid, and H2O2 are added to the system of step (1), wherein the concentration of H2O2 in the system is 60 mM, the concentration of reduced iron powder is 0.3 g / L, and the concentration of disodium ethylenediaminetetraacetic acid is 20 mM.

[0084] At set time intervals (the set times in this comparative example were 2 min, 5 min, 10 min, 20 min, 30 min, 45 min, and 60 min, respectively), 4 mL of the sample was sampled. Immediately after sampling, 0.3 ml of methanol was added to the sample to terminate the reaction. The TC concentration in the sample was determined by HPLC, and the TC removal rate was calculated. After 60 minutes, the TC removal rate was 36.8%.

[0085] The EDTA content in the sample was detected to be 20 mM.

[0086] Comparative Example 3

[0087] (1) Add 2.0 g of reduced iron powder (30-100 µm) to 25 mL of a 0.2 mol / L aqueous solution of disodium ethylenediaminetetraacetic acid. Soak for 1 hour, filter, and wash with deionized water 2-3 times. Filter the mixture using a vacuum filtration device. After filtration, dry the iron powder in an oven at 80°C to obtain modified iron (EDTA-ZVI) for later use.

[0088] (2) Take deionized water and 0.025g (TC), mix them evenly, and prepare a TC solution with a concentration of 50mg / L. Use 0.1mol / L NaOH solution and H2SO4 solution to adjust the pH of the system to 6.5.

[0089] (3) Adding the EDTA-ZVI prepared in step (1) into the system of step (2), wherein the concentration of EDTA-ZVI is 0.3 g / L.

[0090] The TC removal rate was tested using the method of Example 1. After 60 minutes, the TC removal rate was 30.5%.

[0091] Comparative Example 4

[0092] (1) Add 2.0 g of reduced iron powder (30-100 µm) to 25 mL of 0.2 mol / L boric acid solution. Soak for 1 hour, filter, and wash with deionized water 2-3 times. Filter the solution with a vacuum filtration device. After filtration, dry the iron powder in an oven at 80°C to obtain modified iron (B-ZVI) for later use.

[0093] (2) Take deionized water and 0.025g (TC), mix them evenly, and prepare a TC solution with a concentration of 50mg / L. Use 0.1mol / L NaOH solution and H2SO4 solution to adjust the pH of the system to 6.5.

[0094] (3) Adding B-ZVI and H2O2 prepared in step (1) into the system of step (2), wherein the concentration of H2O2 in the system is 60 mM, and the concentration of B-ZVI is 0.3 g / L.

[0095] The TC removal rate was tested using the method of Example 1. After 60 minutes, the TC removal rate was 59.0%.

[0096] Comparative Example 5

[0097] (1) Add 2.0 g of reduced iron powder (30-100 µm) to 25 mL of 0.2 mol / L sodium dihydrogen phosphate aqueous solution. Soak for 1 hour, filter, and wash with deionized water 2-3 times, then filter with a vacuum filtration device. After filtration, dry the iron powder in an oven at 80°C to obtain modified iron (P-ZVI) for later use.

[0098] (2) Take deionized water and 0.025g (TC), mix them evenly, and prepare a TC solution with a concentration of 50mg / L. Use 0.1mol / L NaOH solution and H2SO4 solution to adjust the pH of the system to 6.5.

[0099] (3) P-ZVI and H2O2 prepared in step (1) are added to the system of step (2), wherein the concentration of H2O2 in the system is 60 mM and the concentration of P-ZVI is 0.3 g / L.

[0100] The TC removal rate was tested using the method of Example 1. After 60 minutes, the TC removal rate was 30.9%.

[0101] Comparative Example 6

[0102] The difference from Example 1 is that the disodium ethylenediaminetetraacetic acid aqueous solution in step (1) is replaced by a triethanolamine (TEA) aqueous solution.

[0103] After 60 min, the removal rate of TC was 26%.

[0104] Comparative Example 7

[0105] The difference from Example 1 is that the disodium ethylenediaminetetraacetic acid aqueous solution in step (1) is replaced by a tetramethylethylenediamine (TMEDA) aqueous solution.

[0106] After 60 min, the TC removal rate was 32%.

[0107] The above detailed description of the present invention is intended to enable persons familiar with the art to understand the contents of the present invention and implement them. It does not limit the scope of protection of the present invention. Any equivalent changes or modifications made based on the spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for treating organic wastewater, characterized in that: The steps include: (1) adding reduced iron powder to a solution containing a modifier having a concentration of 0.2 to 0.3 mol / L, soaking the solution for 0.5 to 1 hour, filtering, cleaning, and drying the solution to obtain modified zero-valent iron, wherein the modifier comprises one or more of ethylenediaminetetraacetic acid, ethylenediaminetetraacetate, butanetetracarboxylic acid, butanetetracarboxylate, methyliminodiacetic acid, methyliminodiacetic acid, nitrilotriacetic acid, and nitrilotriacetate; (2) Adding the modified zero-valent iron and hydrogen peroxide in step (1) to organic wastewater to remove tetracycline hydrochloride in the organic wastewater, controlling the pH of the organic wastewater to 6-7, and controlling the concentration of the modified zero-valent iron in the organic wastewater to 0.25-0.5 g / L and the concentration of hydrogen peroxide to 40-100 mM.

2. The method for treating organic wastewater according to claim 1, wherein: The concentration of hydrogen peroxide in the organic wastewater is controlled to be 50-80 mM.

3. The method for treating organic wastewater according to claim 1, wherein: The particle size of the reduced iron powder is 30-100 μm.

4. The method for treating organic wastewater according to claim 1, wherein: The cleaning liquid used in step (1) is water; And / or, the drying temperature in step (1) is 70-85°C.

5. The method for treating organic wastewater according to claim 1, wherein: The metal ions in the ethylenediaminetetraacetate, butanetetracarboxylate, methyliminodiacetate and nitrilotriacetate are independently selected from one or more of sodium ions, calcium ions, potassium ions and magnesium ions.

Images