CN115925086A - A method for degrading organic matter in wastewater - Google Patents

Abstract

The invention provides a method for degrading organic matter in wastewater, which belongs to the technical field of wastewater treatment. The scheme forms a divalent manganese ion/metal complex system in wastewater, and utilizes the divalent manganese ion/metal complex system to activate tetravalent sulfur The ions form sulfate radicals, which degrade organic matter through sulfate radicals. The method can effectively solve the problem of low activation efficiency when divalent manganese is used to activate tetravalent sulfur ions in the prior art.

Description

A method for degrading organic matter in wastewater

technical field

The invention belongs to the technical field of organic matter degradation, and in particular relates to a method for degrading organic matter in waste water.

Background technique

The advanced oxidation process (SR-AOPs) based on SO4 ^- radicals has a wider application pH range and higher redox potential than the hydroxyl radicals in the traditional Fenton oxidation process (SO4 ^- radicals are 2.5 to 3.1 V, OH ^· free radical is 1.8 ~ 2.7V) and longer half-life (SO4 ^{· -} free radical is 30 ~ 40μs, OH ^· free radical is 1μs), which has been extensively researched and developed. In SR-AOPs, persulfates (peroxydisulfate (PDS) and permonomonosulfate (PMS)) are often used as precursors to generate SO4 ^·- radicals. However, the application of persulfate still faces the defects of high cost, high acidity and residual biological toxicity. Sulfite (S(IV)) is a common industrial by-product derived from sulfur dioxide. Due to its environmental friendliness, low price and the ability to be activated to generate SO4 ^·-free radicals, how to efficiently activate S(IV) ) to produce SO4 ^·-free radicals has increasingly become the focus of research.

Common methods for activating S(IV) mainly include thermal activation, photoactivation, electrical activation, and transition metal activation. Manganese (Mn) is a common transition metal with low toxicity and abundant natural reserves. Mn is often used in SR-AOPs and is considered as an excellent metal catalyst. At present, most studies are devoted to combining permanganate, single or composite manganese oxides with S(IV). However, because Mn(II) activates S(IV), there is a conversion between Mn(II) and Mn(III), and Mn(III) in neutral alkaline solution is very unstable, and disproportionation will occur The formation of Mn(II) and MnO ₂ (equilibrium constant log K=7~9) has limited the research and application of Mn(II) activation of S(IV) in aqueous solution.

Contents of the invention

Aiming at the above-mentioned problems in the prior art, the present invention provides a method for degrading organic matter in wastewater, which can effectively solve the problem of low activation efficiency in the prior art when divalent manganese is used to activate tetravalent sulfide ions.

In order to achieve the above object, the technical solution adopted by the present invention to solve the technical problems is:

A method for degrading organic matter in wastewater, characterized in that, by forming a divalent manganese/metal complex system in wastewater, utilizing the divalent manganese/metal complex system to activate tetravalent sulfur to form sulfate radicals, base to degrade organic matter.

Further, the specific operation process is as follows: mix the water body containing organic matter, divalent manganese salt and metal complexing agent to obtain a mixed solution, adjust the pH value of the mixed solution to 4-10, then add sulfite to it, and stir to react .

Further, the molar ratio of the divalent manganese salt to the metal complexing agent in the mixed solution is 1:1-10.

Further, the concentration of the divalent manganese salt in the mixed solution is 10-100 μM.

Further, the concentration of tetravalent sulfide ions in the mixed solution is 100-800 μM.

Further, adjust the pH value of the mixed solution to 6-7.5.

Further, the reaction can be carried out under the condition of 25-35°C.

Further, the divalent manganese salt includes at least one of manganese sulfate monohydrate, manganese chloride and manganese nitrate.

Further, the metal complexing agent is nitrilotriacetic acid sodium salt.

Further, the sulfite includes at least one of anhydrous sodium sulfite, potassium sulfite, calcium sulfite, sodium bisulfite and potassium bisulfite.

The beneficial effects produced by the present invention are:

1. In the method of the present application, divalent manganese (Mn(II)) and metal complexes (NTA) are added to the wastewater. In the presence of NTA, Mn(II) forms a stable coordination form, which is not prone to hydrolysis and disproportionation Reaction, the coordination form of Mn(II) excites and activates tetravalent sulfur (S(IV)) to form sulfate radicals (SO ₄ ^·- ), and utilizes the strong oxidation of SO ₄ ^·- to decompose organic matter in water Degradation; due to the existence of metal complexes, the stable state of Mn(II) in water can be greatly improved, and then the excitation of S(IV) can be improved, and the degradation effect of organic matter can be improved.

2. In the method of this application, sulfite is used as a raw material to degrade organic pollutants in water bodies. The sulfite is stable in nature, convenient for transportation and storage, low in price, wide in source, and has no biological toxicity, which greatly improves the safety of use sex.

3. In this application, divalent manganese is used as raw material. Divalent manganese widely exists in groundwater and natural water, and is evenly distributed in water bodies, which can reduce the use of raw materials; and divalent manganese has a wide range of sources and low prices, which can reduce processing costs; Divalent manganese can quickly and fully activate sulfite, which makes up for the theoretical gap in the efficient activation of sulfite by divalent manganese ions.

Description of drawings

Fig. 1 is the statistical diagram of the degradation effect of organic matter in different reaction systems;

Fig. 2 is the UV-Vis spectrogram of Mn(III)-NTA and Mn(II)/NTA/S(IV) system at t=1min;

Fig. 3 is the degradation statistics diagram of RhB in Mn(III)-NTA and Mn(III)-NTA/S(IV) systems;

Among Fig. 4, a is the statistical diagram of EtOH and TBA to RhB degradation in the Mn(II)/NTA/S(IV) system; b is the statistical diagram of EtOH and TBA to the RhB degradation in the Mn(III)-NTA/RhB system;

Among Fig. 5, a is a statistical diagram of changing the concentration of Mn(II) on RhB degradation; b is a statistical diagram of RhB degradation after changing the ratio of [Mn(II)] and [NTA];

Fig. 6 is the statistical diagram of S(IV) dosage on the degradation of RhB by Mn(II)/NTA/S(IV) system;

Among Fig. 7, a is the statistical diagram of pH on Mn(II)/NTA/S(IV) system degrading RhB; b is the percentage content of Mn(II)-NTA and NTA species in the solution with pH change diagram;

Fig. 8 is a statistical diagram of the degradation of RhB by inorganic anions on the Mn(II)/NTA/S(IV) system.

Detailed ways

The specific embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings.

Example 1

A method for degrading organic matter in wastewater, the specific operation process is as follows: the water body containing organic matter, MnSO ₄ ·H ₂ O and NTA are mixed to obtain a mixed solution, and the molar ratio of MnSO ₄ ·H ₂ O and NTA in the mixed solution is 1 :3, and the concentration of MnSO ₄ ·H ₂ O in the mixed solution is 50 μM, use boric acid-sodium borate buffer to adjust the pH value of the mixed solution to 7.5, and then add anhydrous sodium sulfite (S(IV)) to it to make it in The concentration in the mixed solution is 500 μM, and it is sufficient to stir and react at 2000 r/min at 30° C.

Example 2

A method for degrading organic matter in wastewater, the specific operation process is as follows: the water body containing organic matter, manganese chloride and NTA are mixed to obtain a mixed solution, the molar ratio of manganese chloride and NTA in the mixed solution is 1:5, and the mixed solution The concentration of manganese chloride in the medium is 30 μM, and the pH value of the mixed solution is adjusted to 6 by using boric acid-sodium borate, and then anhydrous sodium sulfite (S(IV)) is added therein so that the concentration in the mixed solution is 300 μM. Under the conditions, the reaction can be stirred at 2000r/min.

Example 3

A method for degrading organic matter in wastewater, the specific operation process is as follows: the water body containing organic matter, manganese nitrate and NTA are mixed to obtain a mixed solution, the molar ratio of manganese nitrate and NTA in the mixed solution is 1:1, and nitric acid in the mixed solution The concentration of manganese is 20 μM, and the pH value of the mixed solution is adjusted to 7 using boric acid-sodium borate buffer solution, and then anhydrous sodium sulfite (S(IV)) is added thereto so that the concentration in the mixed solution is 200 μM. The reaction can be stirred at 2000r/min.

Example 4

A method for degrading organic matter in wastewater, the specific operation process is as follows: the water body containing organic matter, MnSO ₄ ·H ₂ O and NTA are mixed to obtain a mixed solution, and the molar ratio of MnSO ₄ ·H ₂ O and NTA in the mixed solution is 1 :10, and the concentration of MnSO ₄ ·H ₂ O in the mixed solution is 100 μM, use boric acid-sodium borate or acetic acid-sodium acetate buffer to adjust the pH value of the mixed solution to 6.5, and then add anhydrous sodium sulfite (S(IV) ), so that the concentration in the mixed solution is 800 μM, and the reaction can be stirred at 2000 r/min under the condition of 30 ° C.

Test case

1. Configure organic solution

Rhodamine B (RhB) is a common artificial dye, because its structure is similar to most organic pollutants, it has a benzene ring and a variety of active sites, and the detection method is convenient, so RhB is used as a model organic pollutant, and its Add water to prepare a RhB solution with a RhB concentration of 1 mM, and set aside.

2. Test

2.1. Control experiment

Get the RhB solution, adopt the method in embodiment 1 to carry out degradation treatment to the RhB in the solution, this group is as experimental group;

Take the RhB solution, add MnSO ₄ ·H ₂ O (Mn(II)) to it to degrade the RhB in the solution, and this group is used as the control group 1;

Get the RhB solution, add metal complexing agent (NTA) therein to degrade the RhB in the solution, and this group is used as the control group 2;

Take the RhB solution, add anhydrous sodium sulfite (S(IV)) to it to degrade the RhB in the solution, and this group is used as the control group 3;

Take the RhB solution, add MnSO ₄ ·H ₂ O (Mn(II)) and anhydrous sodium sulfite (S(IV)) to it to degrade RhB in the solution, and this group is used as the control group 4;

Take the RhB solution, add MnSO ₄ ·H ₂ O (Mn(II)) and metal complexing agent (NTA) to it to degrade the RhB in the solution, and this group is used as the control group 5;

Take the RhB solution, add metal complexing agent (NTA) and anhydrous sodium sulfite (S(IV)) to it to degrade the RhB in the solution, and this group is used as the control group 6;

Samples were taken at 0, 1, 2, 3, 4, 5, 7, 10, and 15 minutes after the drug was injected, and immediately added to a colorimetric tube containing 1 mL of 200 mM Na ₂ S ₂ O ₃ solution. The role of Na ₂ S ₂ O ₃ solution is to quench the active species that may exist in the system, thereby stopping the further oxidation of RhB. Use a UV-visible spectrophotometer to measure the absorbance of RhB at 554nm, and also use a UV-visible spectrophotometer to measure the UV-visible light absorption spectra of different systems in the reaction process; count the content of RhB in the solution after the reaction, and the specific results are shown in Figure 1.

It can be seen from Figure 1 that in the single system of Mn(II), NTA and S(IV) and the binary system of Mn(II)/S(IV), Mn(II)/NTA and NTA/S(IV), In the element system, RhB was not significantly degraded. In the experimental group, namely the Mn(II)/NTA/S(IV) system in Example 1, the degradation rate of RhB reached 86.05%. Therefore, Mn(II)-NTA formed by introducing ligand NTA and Mn(II) can effectively react with S(IV) and generate active oxidative species to degrade RhB.

2.2. Formation of Mn(III)

During the process of activating S(IV) to generate SO ₄ ^·- free radicals, Mn(II) itself will also be oxidized to Mn(III). Mn(III) itself has strong oxidizing properties, and Mn(III) Prone to disproportionation (formula (1)), resulting in very little Mn(III) content in the solution, unable to achieve the purpose of degrading RhB.

2Mn(III)+2H ₂ O=MnO ₂ +Mn(II)+4H ⁺ (1)

The Mn(III)-NTA system was prepared in situ through the reaction process in the following formula (2), and the Mn(III)-NTA system prepared in situ and the Mn(II) in Example 1 were scanned using a UV-visible spectrophotometer The UV-Vis spectrum of the /NTA/S(IV) system at t=1min, the results are shown in Figure 2.

It can be seen from Figure 2 that a characteristic absorption peak appears at about 280 mm in the spectrum of the in situ prepared Mn(III)-NTA, which is consistent with the absorption peak of the coordinated form of Mn(III). The results show that the Mn(III)-NTA prepared in situ by formula (2) can exist stably in the presence of NTA. At the same time, in the spectrogram of the Mn(II)/NTA/S(IV) system, the characteristic absorption peak of Mn(III)-NTA was observed at the same position, so it can be confirmed that the Mn(II)/NTA/S(IV) Mn(III)-NTA was produced in the system.

The Mn(II)/NTA/S(IV) system in Example 1, the Mn(III)-NTA system prepared in situ and the Mn(III)-NTA/S(IV) system were directly reacted with RhB respectively, RhB in the Mn(III)-NTA system did not obviously degrade, but RhB in the Mn(III)-NTA/S(IV) system degraded. The specific results are shown in Figure 3.

It can be seen from Figure 3 that in the Mn(III)-NTA/S(IV) system, RhB was rapidly degraded, and even the degradation efficiency was higher than that of the Mn(II)/NTA/S(IV) system, reaching 95.72%. It can be seen that Mn(III)-NTA cannot directly oxidize and degrade RhB, but after adding S(IV) to react with Mn(III)-NTA, other active oxidative species may be generated to degrade RhB. It is speculated that Mn(III) in the coordination state with NTA is more stable and can activate S(IV) faster than Mn(II), thus leading to the degradation of RhB. Therefore, the stable Mn(III)-NTA plays an important role in promoting the circulation of Mn species and effectively activating S(IV).

3. Exploration of active oxide species

It is speculated that sulfate radicals (SO ₄ ^·- ) and hydroxyl radicals (OH ^· ) may be generated in the Mn(II)/NTA/S(IV) reaction system, and the free radical scavengers interact with SO ₄ ^·- radicals and OH· Free radical reactions have different second-order rate constants. Therefore, using tert-butanol (TBA) as a specific scavenger for ^OH radicals (k _(TBA,SO4·-) = 8.5×10 ⁵ M ^-1 s ^-1 , k( _TBA,OH· )=6.0×10 ⁸ M ⁻¹ s ⁻¹ ). However, absolute ethanol (EtOH) can simultaneously quench SO ₄ ^·- radicals and OH ^· radicals (k _{(EtOH,SO4·-)} = (1.6～7.7)×10 ⁷ M ^-1 s ^-1 , k _{(EtOH ,OH·)} = (1.2～2.8)×10 ⁹ M ^-1 s ^-1 ), see Figure 4 for the specific results.

As shown in Figure 4a and Figure 4b, when 20mM TBA was added to Mn(II)/NTA/S(IV) and Mn(III)-NTA/S(IV) systems, the degradation rate of RhB was only reduced by 6.13 % and 5.18%, which shows that OH ^· free radicals are not the main active oxidation species. However, when 20mM EtOH was added as a radical scavenger to both systems, the degradation of RhB was almost completely inhibited, thus confirming that SO ₄ ^· -radical is the decisive oxidative species in both systems.

4. Effect of Mn(II) and NTA concentration

Fixed [Mn(II)]:[NTA]=1:3, when increasing the concentration of Mn(II) step by step, the change of the degradation rate of RhB is shown in Figure 5a, the change of the degradation rate of RhB is gradually improved, but, when When the concentration of Mn(II) increased to 100μM, the degradation efficiency dropped sharply to 53.27%. It is speculated that the increase of Mn(II) concentration will increase the concentration of subsequent Mn-NTA complexes, which is conducive to the activation of S(IV) and the degradation of RhB. However, when the concentration of Mn(II) continued to increase to 100 μM, a large number of ligands introduced would compete with RhB to consume SO ₄ ^·- free radicals, resulting in hindering the degradation of RhB.

Control the concentration of Mn(II) to 50 μM, and change [Mn(II)]:[NTA]=1:1～1:10, the change of the degradation rate of RhB is shown in Figure 5b, when the ratio of the two changes from 1: When 1 was reduced to 1:3, the RhB degradation rate increased from 64.23% to 86.04%. When [Mn(II)]:[NTA] was 1:5 and 1:10, the degradation rates of RhB were 86.3% and 85.66%, respectively, showing that the degradation of RhB was negligible. When [Mn(II)]:[NTA]=1:1, it may be due to the low concentration of Mn(II)-NTA and Mn(III)-NTA generated in the case of insufficient NTA, and the concentration of S(IV) The activation efficiency is not high, so RhB cannot be effectively degraded. When the ratio of the two reaches 1:3-1:10, under the condition of an appropriate excess of NTA, the concentration of the generated Mn species can remain sufficient and stable, which is conducive to the subsequent activation of S(IV).

5. The effect of S(IV) dosage

As shown in Figure 6, when the S(IV) concentration was 100, 200, 300 and 500 μM, the RhB degradation rates were 13.79%, 56.36%, 83.88% and 86.24%, respectively. However, when the concentration of S(IV) reached 800 μM, the degradation rate of RhB dropped sharply to 16.89%. S(IV) is closely related to the formation of SO ₄ ^·- free radicals and Mn(III), sufficient S(IV) can be activated to produce a large number of SO ₄ ^·- free radicals to participate in the degradation of RhB. However, excess S(IV) may compete with RhB for SO ₄ ^·- radicals (Equation (3)), causing internal friction of free radicals, reducing the utilization rate of SO ₄ ^·- radicals, and resulting in a decrease in the degradation rate of RhB . In addition, the addition of excessive S(IV) will lead to a large consumption of dissolved oxygen, thereby reducing the production of SO ₅ ^·- radicals and SO ₄ ^·- radicals (Equation (4) and Equation (5)), and limiting the subsequent Generation of reactive oxidative species.

SO ₄ ^·- +SO ₃ ^2- → SO ₃ ^·- +SO ₄ ^2- (3)

SO ₃ ^·- +O ₂ -----→SO ₅ ^·- (4)

SO ₅ ^·- +SO ₃ ^2- → SO ₄ ^·- +SO ₄ ^2- (5)

6. The influence of pH

The effect of pH on the degradation of RhB by the Mn(II)/NTA/S(IV) system is shown in Figure 7. From Figure 7a, it can be seen that when the pH of the solution is 4, the degradation rate of RhB is only 11.79%. When the pH of the solution was 6, the degradation rate of RhB was significantly increased to 99.31%. When the pH of the solution is 7.5, the degradation rate of RhB is 86.05%, but at pH = 9, the degradation rate of RhB drops to 49.33%. The pH has a great influence on the ionization balance of the substances in the solution. Fig. 7b is a graph showing the percentage of Mn(II)-NTA and NTA in solution as a function of pH, drawn by the professional chemical balance software Medusa. The molecular structure of NTA is (CH ₂ COOH) ₃ N. At a lower pH value, a large amount of NTA exists in the form of tribasic acid in aqueous solution, so when pH=4, there is only a small amount of Mn(II)-NTA Formation, the subsequent S(IV) activation reaction is difficult to carry out, resulting in low degradation efficiency of RhB; with the increase of pH, the content of Mn(II)-NTA gradually increases, and S(IV) can be effectively activated to generate SO ₄ ^{· -} Free radicals degrade RhB. However, when the pH=9, the hydrolysis and disproportionation reaction of Mn(III) produced in the Mn(II)/NTA/S(IV) system is intensified, which is not conducive to the stable formation of Mn(III)-NTA and subsequent reactions.

7. Influence of inorganic anions

Figure 8 shows the effect of common inorganic anions on the degradation of RhB by the Mn(II)/NTA/S(IV) system. Even in the presence of 1 ~ 10mM Cl ^- , the degradation of RhB was hardly affected, but slightly enhanced. This may be because Cl ^- captures SO ₄ ^·- free radicals, resulting in active chlorine species such as Cl ^· , Cl ₂ ^·- and HOCl, which may participate in the oxidation process of RhB.

HCO ₃ ^- is generally considered to be an interfering ion in the S(IV) activation system, because SO ₄ ^·- can react with HCO ₃ ^- to generate CO ₃ ^·- (formula (6)). However, the presence of high concentration of HCO ₃ ^- not only did not interfere with the degradation of RhB, but slightly promoted the degradation of RhB. This may be because the reaction rate constant of SO ₄ ^·- with RhB is two orders of magnitude higher than that of SO ₄ ^·- with HCO ₃ ^- (k _(RhB,SO4·-) = 3.02×10 ⁸ M ^-1 s ^{- 1} , k _{(HCO3-,SO4·-)} = 2.8×10 ⁶ M ^-1 s ^-1 ), so the effect of HCO ₃ ^- on RhB degradation is not significant. In the presence of HCO ₃ ^-, the degradation effect of RhB is slightly improved, probably because the HSO ₅ ^- present in the Mn(II)/NTA/S(IV) system reacts with HCO ₃ ^- to produce HCO ₄ ^- , thereby oxidizing Part of the organic matter (formula (7)). SO ₄ ^·- +HCO ₃ ^- →H ⁺ +SO ₄ ^2- +CO ₃ ^·- (6)

HSO ₅ ^- +HCO ₃ ^- →SO ₄ ^2- +HCO ₄ ^- +H ⁺ (7)

Adding NO ₃ ^- to the system will slightly inhibit the degradation effect and reaction rate of RhB, probably because NO ₃ ^- will react with SO ₄ ^·- to generate NO ₃ ^· with a lower redox potential (Formula (8), thus inhibiting some Degradation of RhB.

SO ₄ ^·- +NO ₃ ⁻ → SO ₄ ^2- +NO ₃ ^· (8).

Claims (10)

1. A method for degrading organic matters in wastewater is characterized in that a divalent manganese/metal complex system is formed in the wastewater, tetravalent sulfide ions are activated by the divalent manganese/metal complex system to form sulfate radicals, and the organic matters are degraded by the sulfate radicals.

2. The method for degrading organics in wastewater according to claim 1, wherein the specific operation process is as follows: mixing the water body containing organic matters, the divalent manganese salt and the metal compounding agent to obtain a mixed solution, adjusting the pH value of the mixed solution to 4-10, then adding sulfite into the mixed solution, and stirring for reaction.

3. The method for degrading organic matters in wastewater according to claim 1, wherein the molar ratio of the divalent manganese salt to the metal complexing agent in the mixed solution is 1.

4. The method for degrading organic substances in wastewater according to claim 1, wherein the concentration of the manganous salt in the mixed solution is 10 to 100 μ M.

5. The method for degrading organic matters in wastewater according to claim 1, wherein the concentration of the tetravalent sulfide ions in the mixed solution is 100 to 800 μ M.

6. The method for degrading organic substances in wastewater according to claim 2, wherein the pH of the mixed solution is adjusted to 6 to 7.5.

7. The method for degrading organic matters in wastewater according to claim 1, wherein the reaction is carried out at 25 to 35 ℃.

8. The method for degrading organics in wastewater of claim 1, wherein the divalent manganese salt comprises at least one of manganese sulfate monohydrate, manganese chloride, and manganese nitrate.

9. The method for degrading organics in wastewater of claim 1 wherein the metal complexing agent is sodium nitrilotriacetate.

10. The method for degrading organics in wastewater of claim 1 wherein the sulfite comprises at least one of anhydrous sodium sulfite, potassium sulfite, calcium sulfite, sodium bisulfite and potassium bisulfite.

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