A method for treating furfural wastewater using ozone-Fenton coupling

Abstract

The present invention is a method for treating furfural wastewater by using ozone-Fenton coupling. The method comprises the following steps: (1) adding sulfuric acid or sodium hydroxide to the furfural wastewater to adjust its pH value to 3; (2) adding Fenton catalyst ferrous salt solid and oxidant hydrogen peroxide to the solution obtained in step (1) and introducing ozone for reaction; (3) adding sodium hydroxide solution to the solution obtained in step (2) to adjust the pH value to 10, and then discharging after forming flocculation precipitation. The method has significantly improved the ability to degrade organic matter, and only requires a single reaction device to complete the process, and the process is simple, economical, and reliable in operation.

Description

Technical Field

[0001] The invention belongs to the technical field related to furfural wastewater treatment, and more specifically, relates to a method for treating furfural wastewater by coupling ozone and Fenton process. Background Art

[0002] Furfural is a difuran liquid and oil with an almond odor that quickly turns into yellow furfural on contact with air and is soluble in water. Human exposure can be absorbed through inhalation, swallowing, skin or eye contact. Furfural (at concentrations of 1.9–14 ppm) can cause headaches, red eyes and tearing in some workers. Exposure to higher concentrations can cause pulmonary edema in the lungs. Several major methods have been studied for the removal of furfural, such as catalytic and photocatalytic methods, nanofiltration solvent extraction, circulating bioreactor (CBR), biodegradation methods, and adsorption methods. Studies have shown that furfural biodegradation includes both aerobic and anaerobic methods, but they are expensive. In addition, due to the influence of various parameters and the toxicity of furfural at high concentrations, it is almost impossible to remove furfural by biodegradation. As well as the difficulties caused by the degradability and toxicity of petrochemical industrial waste, biodegradability is reduced, causing serious environmental pollution.

[0003] In the past two decades, physical and chemical technologies have played an increasingly important role in wastewater treatment due to their high efficiency and low cost. In 1980, advanced oxidation processes (AOPs) were introduced into the field of wastewater treatment after their successful implementation in drinking water treatment. The main AOPs involved in the generation of ·OH include ozone (O3), hydrogen peroxide (H2O2), etc. Combining strong oxidants such as ozone, hydrogen peroxide, ultraviolet light, sunlight, radiation, ultrasound, Fenton, etc. with semiconductor catalysts can effectively improve the biodegradability of wastewater and reduce wastewater indicators such as chemical oxygen demand, biodegradability and color.

[0004] The Fenton process mainly involves a mixture of H2O2 and ferrous Fe(II) from ferrous sulfate (FeSO4) to form a high concentration of ·OH. The Fenton process has a strong oxidizing ability, can react at ambient temperature, and has simple process flow, equipment and operation. The combination of the Fenton process with other oxidants can promote the formation of ·OH and can be called an advanced Fenton process (AFP). The combination of the Fenton process with UV radiation is called the photo-Fenton process (PFP), and the combination of biological methods with the electro-Fenton process is called bio-electro-Fenton, while in the electro-Fenton process (EFP), both Fe(II) and H2O2 are produced by reduction electricity on the electrodes. Extensive research can be seen in the literature, among which electro-Fenton and photo-Fenton are widely used to treat landfill leachate. Ozone itself has a higher oxidation potential and selectivity for organic pollutants, and ozone has less secondary pollution and lower equipment operating costs. When ozone decomposes in water, free radicals such as ·OH and HO2· are produced, which can oxidize organic matter. This decomposition process is a free radical chain reaction process. It mainly includes: 1. The OH in water reacts with ozone to generate O2 - ; and HO2·; secondly, impurities in water trigger ozone decomposition to produce other free radicals (O3 - , HO3·, ·OH). It is precisely because of the presence of these free radicals that the free radical reaction of ozone is relatively complex, and it also plays an extremely important role in ozone oxidation. Ozone oxidation is selective, especially for N=N, >C—C<, >C—O, N—О and other groups. Some research papers use ozonation as a pretreatment of the Fenton experiment or a post-treatment of the Fenton experiment to improve the treatment efficiency. If used as a single system, the composition and subsequent complexity of the effluent may hinder the use of ozone or Fenton process. In the current technology, furfural wastewater is treated by evaporation or adsorption methods, such as using a high-efficiency evaporation device to evaporate the wastewater (patent publication number CN215479843U). This method uses steps (equipment) including a box, a water injection pipe, a cleaning block, a heating pipe and an air pump. Due to the complexity of the equipment and the high cost of evaporation, the adsorption method is less efficient, has strong selectivity, and the effect is not ideal. Summary of the invention

[0005] The purpose of the present invention is to provide a method for treating furfural wastewater by ozone-Fenton coupling in view of the above wastewater treatment technical problems. The method couples ozone and Fenton methods to treat furfural wastewater; in an acidic environment, ozone is used to directly or indirectly oxidize simple organic matter in the wastewater, and the Fenton method is used to promote ozone decomposition to produce hydroxyl radicals to enhance the ability to oxidize complex organic matter; the method has a significantly improved ability to degrade organic matter, and only requires a single reaction device to complete the process, with a simple and economical process and reliable operation.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for treating furfural wastewater by ozone-Fenton coupling, the method comprising the following steps:

[0008] (1) adding sulfuric acid solution or sodium hydroxide solution to the furfural wastewater to adjust its pH to 3;

[0009] (2) adding Fenton catalyst ferrous salt solid and oxidant hydrogen peroxide to the solution obtained in step (1), and introducing ozone at the same time, and reacting for 0.5-1.5h;

[0010] (3) Add sodium hydroxide solution to the solution obtained in step (2), adjust the pH to 10, form flocculation precipitation, and discharge the clear liquid.

[0011] The clear liquid obtained in step (3) meets the secondary standard in the "Integrated Wastewater Discharge Standard" (GB8978-1996);

[0012] The ferrous salt is FeSO4·7H2O.

[0013] Preferably, the Fe added to the wastewater by the Fenton reaction 2+ The concentration is 3-11 mmol / L. That is, the dosage of solid FeSO4·7H2O (98%) added to each liter of wastewater is 4.2-15.3 g.

[0014] Preferably, the concentration of H2O2 added to the wastewater by the Fenton reaction is 2g / L-10g / L, that is, the amount of hydrogen peroxide solution H2O2 (mass percentage concentration of 30%) added to each liter of wastewater is 6-30ml.

[0015] Preferably, the ozone concentration after being added to the wastewater is 10-50 mg / (L·min), that is, the ozone flow rate per liter of wastewater is 10-50 mg / min.

[0016] The concentration of the hydrogen peroxide solution in step (2) is 30% by mass;

[0017] The concentration of the sodium hydroxide solution in step (3) is 5% by mass;

[0018] The main components of the furfural wastewater have a mass percentage concentration of 0.01-0.2% furfural, 1-2% furan carboxylic acid, 0.5-1% oxalic acid, and a COD of 500-2000.

[0019] The essential features of the present invention are:

[0020] The oxidizing ability of the ozone and hydrogen peroxide coupling process lies in the fact that hydrogen peroxide can induce the decomposition of ozone to produce more ·OH with extremely strong oxidizing properties. ·OH has strong oxidizing properties and is non-selective, and has a good removal effect on organic pollutants in water. Compared with ozone oxidation alone, ozone and Fenton coupling will greatly improve the oxidation effect, and the system also has a good removal effect on compounds that are not active in ozone. Studies have shown that hydrogen peroxide, in the form of anions HO2 - In this system, the reaction rate depends on the initial concentrations of the two oxidants. The catalytic mechanism can be summarized as follows:

[0021] H2O2→HO2 - +H +

[0022] HO2 - +O3→HO2·+O3 -

[0023] HO2 →O2 - +H +

[0024] O3 - +H + →HO3

[0025] HO3 →O2 + + OH

[0026] O2 - +O3→O2+O3 -

[0027] Overall reaction formula: H2O2+2O3→3O2+2OH

[0028] The addition of ferrous ions can catalyze the decomposition of hydrogen peroxide and produce more hydroxyl radicals.

[0029] Fe 2+ +H2O2→Fe 3+ +OH-+·OH

[0030] Fe 3+ +H2O2→Fe 2+ +H + +·O2H

[0031] There are many influencing factors in the process of ozone and hydrogen peroxide coupling oxidation of organic matter. The pH value of wastewater and the molar ratio of hydrogen peroxide and ferrous ions will have a great impact. The increase in H2O2 dosage may promote the formation of hydroxyl radicals. However, excess H2O2 does not produce more ·OH for further oxidation; the excess H2O2 reacts with ·OH to form ·HO2. The oxidation effect of ·HO2 is weaker than that of ·OH, which will lead to a decrease in COD removal rate. The dosage of ozone is also an important factor affecting the oxidative removal of organic matter. The increase in ozone flow promotes the production of ·OH and accelerates the number of hydroxyl groups produced, and ozone itself has oxidation capacity. However, as the ozone dosage continues to increase, the COD removal rate does not increase much. This is because when the ozone flux increases to a certain level, O3 will capture ·OH and consume a large amount of ·OH. The ·OH radicals produced in the early stage of degradation have an attack on organic matter, so the early degradation efficiency of the coupling method is relatively high. However, as the reaction proceeds, the Fe 3+ This affects the degradation efficiency and causes the removal efficiency to begin to decline. Therefore, this method requires a good control of the concentration ratio of hydrogen peroxide and ferrous ions and the ozone flux, so as to obtain both economical and efficient process conditions.

[0032] The invention has the following beneficial effects:

[0033] 1. Ozone and Fenton can react directly or indirectly with organic matter in furfural wastewater under acidic conditions. Ozone can use its own oxidation to selectively attack the aromatic rings and conjugated double bonds in furfural wastewater to generate aldehydes, carboxylic acids and other substances.

[0034] 2. The initial pH of furfural wastewater is around 3, and this process has a good effect on treating acidic wastewater, so there is no need to adjust the initial pH of the system too much.

[0035] 3. The ozone-coupled Fenton process is used to treat furfural wastewater, which promotes the production of oxidative free radicals in the system, especially ·OH, significantly enhances the treatment effect on COD in the wastewater, accelerates the treatment efficiency, and has a simple process and is economically feasible. The UV-visible spectrum of furfural wastewater after treatment with three processes is shown in the figure below. The light absorption in the shown range is mainly related to the unsaturated conjugated bonds present in organic molecules. The absorbance of the wastewater after 30 minutes of treatment by the coupling process is much lower than that of the wastewater treated by the single process. This difference shows that Fe 2+ It can enhance the oxidation ability of O3 and H2O2 on organic matter.

[0036] 4. According to Example 1, the COD removal rate of the coupling process can be increased from 32.6% of ozone alone and 42.7% of Fenton alone to 73.1. The use of ozone and Fenton processes to treat furfural wastewater in a coordinated manner significantly shortens the treatment time and has high treatment efficiency. The amount of sludge produced by the coupling process can be reduced by about half compared to the Fenton process alone, greatly reducing secondary pollution and reducing treatment costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a flow chart of the deep treatment steps of ozone-Fenton coupling in the present invention.

[0038] Figure 2 This is a diagram of the ozone-Fenton oxidation unit;

[0039] Figure 3 UV spectrophotometer test spectra of wastewater after coupling process, ozone alone and Fenton alone treatment;

[0040] In the figure: 1. Ozone tail gas absorption bottle; 2. Exhaust port; 3. Feed port; 4. Aeration head; 5. Drain port; 6. Magnetic stirrer; 7. Rotor flowmeter; 8. Ozone generator DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0042] like Figure 1 and Figure 2 As shown, an ozone-Fenton coupled oxidation deep treatment system is provided, in which a feed port 3 and an exhaust port 2 are provided at the upper part of the reaction tank, and a drain port 5 is provided at the lower part; an ozone generator 8 is connected to an aeration head 4 at the bottom of the reaction tank through a pipeline provided with a flow meter 7; a stirring device (magnetic stirrer 6) is also provided at the bottom of the reaction tank; the exhaust port 2 is connected to an ozone tail gas absorption bottle 1;

[0043] The device of the present invention is as follows Figure 2 As shown, the main components are ozone generator, aeration head, reactor, magnetic stirrer, flow meter, tail gas treatment bottle and other devices; its connection relationship is ozone generator, flow meter, aeration head, tail gas treatment bottle;

[0044] Example 1: Treatment of furfural production wastewater from a pharmaceutical factory (pH = 3.2; furfural 0.1%; furancarboxylic acid 1.3%; oxalic acid 0.8% (all mass percentages); COD 1210)

[0045] 1000 ml of the above wastewater was put into the oxidation unit, and the pH value was first adjusted to 3 using a 5% by mass sodium hydroxide solution;

[0046] The industrial wastewater after adjusting the initial pH value enters the reactor, and then ferrous sulfate powder (98%) and hydrogen peroxide (30% by mass) are added, stirred and ozone is introduced at the same time; the ferrous sulfate content added in the reactor is 7 mmol / L; the hydrogen peroxide content added is 4 g / L; the ozone concentration is 40 mg / (L·min); and the reaction time is 1 hour.

[0047] Sodium hydroxide solution (concentration of 5% by mass) was added to the solution after the reaction to make the pH value 10, and flocculation precipitation was formed to obtain sludge treatment; the solution was tested for its COD value and the treatment effect was analyzed using an ultraviolet spectrophotometer:

[0048] In order to study the changes of pollutants during oxidation, it is necessary to study the UV-visible spectrum during the degradation process. Figure 3 This is the change in the UV-visible absorption spectrum of furfural wastewater treated with O3 / Fenton. The compound shows strong absorption at 220-250nm, indicating the presence of conjugated double bonds (conjugated dienes, unsaturated aldehydes). The compound shows moderate absorption at 250-290nm, indicating the presence of benzene rings in the compound. The compound shows medium to low intensity absorption at 250-350nm, indicating the presence of carboxyl groups or conjugated carboxyl groups in the compound. There is high intensity absorption above 300nm, indicating that the compound has a larger conjugated system. Due to the strong oxidizing effect of hydroxyl radicals, the absorption intensity of organic pollutants such as conjugated systems, conjugated bonds, unsaturated aldehydes, and aromatic rings in the wastewater is continuously reduced and eventually disappears, achieving a significant degradation effect and a relatively high degradation efficiency. Figure 3 As shown, it shows that the organic pollutants in the wastewater are constantly degrading.

[0049] The indicators of COD, BOD5, chromaticity and suspended solids of the treated wastewater are 278, 23, 16 and 31 respectively. The main components and contents are acetaldehyde (0.03 mg / L) and formic acid (0.01 mg / L). That is, the treated wastewater meets the secondary standard of the "Comprehensive Sewage Discharge Standard" (GB8978-1996).

[0050] Comparative Example 1

[0051] A single Fenton control group was set up: the same drug composition and dosage as in Example 1 were maintained, the same amount of ferrous sulfate powder (98%) and hydrogen peroxide were added, and sampling was performed at the same reaction time. This control group did not have an ozone generator and did not introduce ozone.

[0052] Comparative Example 2

[0053] A single ozone oxidation control group was set up: the same drug composition and dosage as in Example 1 were maintained, an equal flow of ozone was introduced using an air source ozone generator, and samples were taken for testing after the same reaction time.

[0054] After the above groups reacted for 1 hour, the COD content in the wastewater was detected, and the removal results are shown in Table 1 below:

[0055] The COD removal rates of ozone-coupled Fenton, single Fenton and single ozone for furfural production wastewater from a pharmaceutical factory were 73.1%, 43.7% and 32.6%, respectively, indicating that the coupling technology significantly enhanced the COD removal rate of wastewater under acidic pH conditions.

[0056] Table 1:

[0057] COD(mg / L) Ozone coupled Fenton Fenton Ozone oxidation Initial concentration 1210 1210 1210 Reaction 0.5h 486 909 1174 Reaction 1h 278 690 869 Sludge production 2.1g 3.9g

[0058] Example 2: Treatment of furfural production wastewater from a fertilizer plant (pH = 4; furfural 0.15%; furancarboxylic acid 1.5%; oxalic acid 0.5% (all mass percentages); COD 1520)

[0059] 1000 ml of the above wastewater was put into the oxidation unit, and the pH value was first adjusted to 3 using a 5% by mass sodium hydroxide solution;

[0060] The industrial wastewater after adjusting the initial pH value is introduced into the reactor, and then ferrous sulfate powder (98%) and hydrogen peroxide (30% by mass) are added, stirred and ozone is introduced at the same time; the ferrous sulfate content added in the reactor is 8 mmol / L; the hydrogen peroxide content added is 5 g / L; the ozone concentration is 40 mg / (L·min); and the reaction time is 1.5 h.

[0061] A sodium hydroxide solution (concentration of 5% by mass) was added to the solution after the reaction to make the pH value 10, and flocculation precipitation was formed to obtain sludge treatment; the COD value of the solution was tested and the treatment effect was analyzed using an ultraviolet spectrophotometer.

[0062] Comparative Example 3

[0063] A single Fenton control group was set up: the same drug composition and dosage as in Example 2 were maintained, the same amount of ferrous sulfate powder (98%) and hydrogen peroxide were added, and sampling was performed at the same reaction time. This control group was not equipped with an ozone generator and ozone was not introduced.

[0064] Comparative Example 4

[0065] A single ozone oxidation control group was set up: the same drug composition and dosage as in Example 2 were maintained, an equal flow of ozone was introduced using an air source ozone generator, and samples were taken for testing after the same reaction time.

[0066] After the above groups reacted for 1.5 hours, the COD content in the wastewater was detected, and the removal results are shown in Table 2 below:

[0067] The COD removal rates of ozone-coupled Fenton, single Fenton and single ozone for furfural production wastewater from a pharmaceutical factory were 81.1%, 45.5% and 26.6%, respectively, indicating that the coupling technology significantly enhanced the COD removal rate of wastewater under acidic pH conditions.

[0068] Table 2:

[0069] COD(mg / L) Ozone coupled Fenton Fenton Ozone oxidation Initial concentration 1520 1520 1520 Reaction 1h 597 1022 1331 Reaction 1.5h 292 836 1117 Sludge production 2.8g 4.5g

[0070] Comparative Example 5

[0071] Set up control groups with different initial pH values ​​in the coupling system: keep the same drug composition and dosage as in Example 2, add the same amount of ferrous sulfate powder (98%) and hydrogen peroxide, use an air source ozone generator to introduce the same flow of ozone, and take samples for testing after the same reaction time. As can be seen from Table 3, the COD removal rate first increases and then decreases with the increase of pH. When pH = 3, the removal rate is the highest. As the reaction removal rate continues to increase, but the efficiency gradually decreases, the pH value does not have a great effect on the removal rate when ozone is used alone to treat wastewater. The Fenton system can promote the production of ·OH under acidic conditions and can have a higher efficiency. However, under conditions where the acidity is too strong, due to H + The concentration is too high, so Fe 3+ Fe 2+ When the pH rises to neutral or alkaline, Fe 3+ It begins to precipitate in the form of Fe(OH)3 and loses its catalytic ability.

[0072] The reaction equation is roughly

[0073] Fe 2+ +H2O2→Fe 3+ +OH-+·OH

[0074] Fe 3+ +H2O2→Fe 2+ +H + +·O2H

[0075] RH+H2O2→ROH+·OH

[0076] Fe 2+ +·OH→OH-+Fe 3+

[0077] Table 3

[0078]

[0079] Comparative Example 6

[0080] A control group with different hydrogen peroxide dosages was set up in the coupling system: the same drug composition and dosage as in Example 2 were maintained, the same amount of ferrous sulfate powder (98%) was added, and the same flow of ozone was introduced using an air source ozone generator. After the same reaction time, sampling was performed for detection. With the increase in the amount of hydrogen peroxide added, COD removal first increased and then decreased. With the increase in the amount of H2O2, the formation of hydroxyl radicals may have been promoted. However, excess H2O2 did not produce more ·OH for further oxidation; the excess H2O2 reacted with ·OH to generate ·HO2. The oxidation effect of ·HO2 is weaker than that of ·OH, resulting in a decrease in COD removal rate.

[0081] Table 4

[0082]

[0083] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should be included in the scope of protection of the claims of the present invention.

[0084] Matters not covered by the present invention are known technologies.

Claims

1. A method for treating furfural wastewater using ozone-Fenton coupling, characterized in that the method comprises the following steps: (1) Add sulfuric acid solution or sodium hydroxide solution to the furfural wastewater to adjust its pH to 3; (2) Add Fenton catalyst ferrous salt solid and oxidant hydrogen peroxide to the solution obtained in step (1), and introduce ozone at the same time, and react for 0.5-1.5 hours; in, Fe after Fenton reaction added to wastewater 2+ The concentration is 3-11mmol / L; the H2O2 concentration is 2g / L-10g / L; the ozone ventilation volume is 10-50mg / (L·min); (3) adding sodium hydroxide solution to the solution obtained in step (2) to adjust the pH to 10 to form flocculation precipitation, and discharging the clear liquid; The main components of the furfural wastewater have a mass percentage concentration of 0.01-0.2% furfural, 1-2% furancarboxylic acid, 0.5-1% oxalic acid, and a COD of 500-2000 mg / L.

2. The method for treating furfural wastewater using ozone-Fenton coupling as claimed in claim 1, characterized in that the ferrous salt is FeSO4·7H2O.

3. The method for treating furfural wastewater by ozone-Fenton coupling as claimed in claim 1, characterized in that The concentration of the hydrogen peroxide solution in step (2) is 30% by mass.

4. The method for treating furfural wastewater by ozone-Fenton coupling as claimed in claim 1, characterized in that The concentration of the sodium hydroxide solution in step (3) is 5% by mass.

5. The method for treating furfural wastewater by ozone-Fenton coupling as claimed in claim 1, characterized in that The clear liquid obtained in step (3) meets the secondary standard in the "Integrated Wastewater Discharge Standard" (GB8978-1996).

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