Method for treating organic wastewater through cooperation of ultrasonic waves and Fenton-flocculation

Abstract

The invention discloses a method for treating organic wastewater by ultrasonic wave cooperating with Fenton-flocculation, which comprises the following steps: adding a 5% sulfuric acid solution or sodium hydroxide solution into wastewater to adjust the pH value to 2.0-4.0, and adding a compound reagent system polyaluminum chloride (PAC), poly dimethyl diallyl ammonium chloride (PDMDAAC), ferrous sulfate (FeSO4) and hydrogen peroxide (H2O2) with the mass concentration of 30% into the solution; ultrasonic treatment is applied to the solution while the compound reagent system is added, then a sodium hydroxide solution with the mass concentration of 5% is added into the solution, the pH value is adjusted to 7, and clear water is obtained after standing, precipitation and separation. According to the method, Fenton oxidation and flocculation processes are synchronously enhanced through ultrasonic cavitation, generation of iron sludge is reduced through a dynamic cooperation mechanism of ferric salt circulation and PAC, meanwhile, Fe < 3 + > and PAC form Al-Fe composite flocs, and the effects of electrostatic neutralization and netting are achieved. H2O2 is added in stages, so that the peak value duration time of the. OH concentration is prolonged by 2-3 times, and the effective utilization rate of H2O2 is remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of wastewater treatment, and specifically relates to a method for treating organic wastewater by using ultrasound in combination with Fenton-flocculation, which is particularly suitable for treating high-concentration, difficult-to-degrade organic wastewater (such as printing and dyeing, pharmaceutical, and petrochemical wastewater). Background Art

[0002] Among traditional wastewater treatment methods, the Fenton process can degrade some organic matter by catalyzing hydrogen peroxide with ferrous ions to produce hydroxyl radicals. However, ferrous ions are easily oxidized to trivalent ferrous ions, forming iron hydroxide precipitates, resulting in decreased catalytic efficiency, high reagent consumption, and a narrow pH range for the reaction system. The treatment effect on complex high-salt and high-alkali wastewater is unstable. On the other hand, the degradation efficiency of Fenton oxidation alone for large molecular organic matter with a molecular weight greater than 5000Da and structurally stable heterocyclic compounds (such as pyridine and quinoline) is less than 50%, and it cannot effectively remove suspended matter and colloidal substances in the wastewater. Subsequent flocculation processes are often required, resulting in lengthy processes and increased costs.

[0003] The water treatment process that combines ultrasonic technology with the Fenton process can effectively overcome the shortcomings of a single technology in practical applications, give full play to the advantages of each technology, and improve the efficiency and quality of water treatment. Existing ultrasonic-assisted treatment technologies mostly adopt a series mode of "oxidation first, then flocculation". This process separates the oxidation and flocculation processes, resulting in the escape of intermediate products and the inability to achieve synergistic efficiency. A more prominent problem is that traditional processes fail to fully utilize the micro-jets generated by the ultrasonic cavitation effect to break up and reorganize the floc structure, as well as the local high temperature and high pressure environment when the cavitation bubble collapses to promote the decomposition of hydrogen peroxide in the Fenton reaction, resulting in a double waste of energy and reagents. Summary of the Invention

[0004] An object of the present invention is to solve at least the above problems and / or disadvantages and to provide at least the advantages which will be described hereinafter.

[0005] The purpose of the present invention is to provide a method for treating organic wastewater with ultrasonic assisted Fenton-flocculation. By synchronously strengthening the Fenton oxidation and flocculation processes through ultrasonic cavitation, the formation of iron sludge is reduced through the dynamic synergistic mechanism of iron salt circulation and PAC. 3+ Forming Al-Fe composite flocs with PAC, it provides both static neutralization and netting. The phased addition of H2O2 prolongs the duration of peak OH concentration by 2-3 times, significantly increasing the effective utilization of H2O2.

[0006] In order to achieve these purposes and other advantages according to the present invention, a method for treating organic wastewater by using ultrasound in combination with Fenton-flocculation is provided, comprising the following steps:

[0007] Step 1: Add 5% sulfuric acid solution or sodium hydroxide solution to the wastewater to adjust the pH value to 2.0-4.0, and control the pH fluctuation range to no more than ±0.5 during the reaction;

[0008] Step 2: Add a composite reagent system to the solution obtained in step 1, wherein the composite reagent system comprises polyaluminum chloride (PAC), polydimethyldiallyl ammonium chloride (PDMDAAC), ferrous sulfate (FeSO4) and 30% hydrogen peroxide (H2O2), and the mass ratio of PAC:PDMDAAC:ferrous sulfate:hydrogen peroxide is 1:1-6:1-5:0.5-2.5;

[0009] Step 3, adding the compound reagent system and applying ultrasonic treatment to the solution obtained in step 1,

[0010] The ultrasonic treatment produces an ultrasonic cavitation effect in the wastewater, generating local high temperature, high pressure and micro-jets, accelerating the decomposition of hydrogen peroxide into hydroxyl radicals (·OH) and simultaneously destroying the colloidal stability of pollutants in the wastewater;

[0011] The ultrasonic treatment simultaneously promotes the hydrolysis of polyaluminium chloride (PAC) and ferrous sulfate (FeSO4) to form Al-Fe composite hydroxyl complex, and then generates Al-Fe composite flocs, which have both electrostatic neutralization and net capture effects to adsorb pollutants in wastewater; the ultrasonic cavitation effect also drives Fe 3+ Reduction to Fe 2+ , reduce the formation of iron sludge;

[0012] When PDADMAC and PAC are used together as flocculants, they promote the aggregation of fine particles through adsorption bridging, forming a core structure with a larger specific surface area, enhancing the coagulation effect on colloids and suspended solids in water, and making them more easily decomposed by the hydroxyl free radicals.

[0013] Step 4: add 5% sodium hydroxide solution to the solution obtained in step 3, adjust the pH value to 7, let it stand and precipitate, and then separate to obtain clear water.

[0014] Preferably, the amount of hydrogen peroxide (H2O2) with a mass concentration of 30% is added in a range of 2 g / L to 8 g / L.

[0015] Preferably, the hydrogen peroxide (H2O2) with a mass concentration of 30% is added in a one-time addition or in a staged addition, wherein the first addition amount is 60% and the second addition amount is 40%.

[0016] Preferably, the ultrasonic treatment parameters are preferably a frequency of 20 to 40 kHz, a power density of 0.2 to 0.5 W / mL, and the ultrasonic probe is immersed below the liquid surface and continuously acts during the reaction process.

[0017] Preferably, the reaction time is 30 to 65 minutes.

[0018] The present invention has at least the following beneficial effects:

[0019] 1. Ultrasonic cavitation simultaneously enhances the Fenton oxidation and flocculation process. The local high temperature and high pressure and micro jet generated by cavitation accelerate the decomposition of hydrogen peroxide into hydroxyl radicals (·OH), increase the free radical yield, and simultaneously destroy the colloidal stability of pollutants, promoting the Al / Fe hydroxyl complex generated by the hydrolysis of polyaluminum chloride (PAC) and ferrous sulfate (FeSO4) to efficiently adsorb pollutants. The cavitation effect of ultrasound generates transient high temperature and high pressure, accelerating the reaction of H2O2 and Fe 2+ The Fenton reaction is stimulated by cavitation, increasing the yield of hydroxyl radicals (·OH). Cavitation microjets directly shear large molecular pollutants (such as azo dyes and polycyclic aromatic hydrocarbons), breaking them into small molecular fragments that are more susceptible to attack by ·OH and shortening the oxidation reaction time. Furthermore, the combination of PDMDAAC and PAC promotes the aggregation of fine particles through "adsorption bridging," forming a core structure with a larger specific surface area, which is more susceptible to decomposition by hydroxyl radicals.

[0020] 2. Through the dynamic synergistic mechanism of iron salt cycle and PAC, Fe 2+ Catalyze the Fenton reaction to generate OH, and ultrasonic cavitation drives Fe 3+ Reduction to Fe 2+ To reduce the formation of iron sludge, Fe 3+ It forms Al-Fe composite flocs with PAC, which has both static neutralization and net capture functions, and increases the adsorption capacity of hydrophobic organic matter by 25%-35%.

[0021] 3. The phased addition of H2O2 shows significant advantages in many aspects in this treatment process. By dividing the total dosage into a gradient addition method of 60% for the first time and 40% for the second time, the Fenton reaction is first started quickly in an acidic environment of pH = 3 to produce a large number of hydroxyl radicals (·OH), and then the consumed oxidant is replenished in the middle of the reaction, so that the duration of the ·OH concentration peak is extended by 2-3 times, and the effective utilization rate of H2O2 is significantly improved. This dosing strategy effectively inhibits the ineffective decomposition of H2O2, reduces treatment costs, and optimizes the degradation path of organic matter. More importantly, the technology has excellent adaptability to water quality fluctuations. It only needs to adjust the secondary addition ratio to maintain the stability of the effluent COD. The system's ability to resist shock loads is increased by 3 times, providing reliable technical support for industrial applications.

[0022] Other advantages, objectives and features of the present invention will be reflected in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. DETAILED DESCRIPTION

[0023] The present invention is described in further detail below so that those skilled in the art can implement the invention with reference to the description.

[0024] It should be understood that terms such as “having”, “including” and “comprising” used herein do not preclude the existence or addition of one or more other elements or combinations thereof.

[0025] Example 1

[0026] Step 1: Add 5% sulfuric acid solution to 1L of industrial wastewater (COD: 1800mg / L, PCU: 400) to adjust the pH to 2.0, and control the pH fluctuation range to no more than ±0.5 during the reaction;

[0027] Step 2: The solution obtained in step 1 is fed into a reactor and a composite reagent system is added, wherein the composite reagent system is 1.2 g of polyaluminum chloride (PAC), 1.2 g of polydimethyldiallyl ammonium chloride (PDMDAAC), 1.2 g of ferrous sulfate (FeSO4) and 2 g of hydrogen peroxide (H2O2) with a mass concentration of 30%;

[0028] Step 3: Ultrasonic treatment is applied to the solution obtained in step 1 simultaneously with the addition of the compounded reagent system. The ultrasonic frequency is 20 kHz and the power is 0.2 W / mL. The ultrasonic probe is immersed below the liquid surface and continuously applied. Ultrasonic treatment produces an ultrasonic cavitation effect in the wastewater, generating localized high temperature, high pressure, and microjets, accelerating the decomposition of hydrogen peroxide into hydroxyl radicals (·OH) and simultaneously destroying the colloidal stability of pollutants in the wastewater.

[0029] The ultrasonic treatment simultaneously promotes the hydrolysis of polyaluminium chloride (PAC) and ferrous sulfate (FeSO4) to form Al-Fe composite hydroxyl complex, and then generates Al-Fe composite flocs, which have both electrostatic neutralization and net capture effects to adsorb pollutants in wastewater; the ultrasonic cavitation effect also drives Fe 3+ Reduction to Fe 2+ , reduce the formation of iron sludge;

[0030] When PDADMAC and PAC are used together as flocculants, they promote the aggregation of fine particles through adsorption bridging, forming a core structure with a larger specific surface area, enhancing the coagulation effect on colloids and suspended solids in water, and making them more easily decomposed by the hydroxyl free radicals.

[0031] Step 4: After 65 minutes of reaction time, add 5% sodium hydroxide solution to the solution obtained in step 3, adjust the pH to 7, and allow the solution to settle before separating to obtain clear water. Testing of the treated water showed a COD removal rate of 80% and a color removal rate of 83%.

[0032] Example 2

[0033] Step 1: Add 5% sulfuric acid solution to 1L of industrial wastewater (COD: 1800mg / L, PCU: 400) to adjust the pH to 2.0, and control the pH fluctuation range to no more than ±0.5 during the reaction;

[0034] Step 2: The solution obtained in step 1 is fed into a reactor, and a composite reagent system is added, wherein the composite reagent system is 1.2 g of polyaluminum chloride (PAC), 1.2 g of polydimethyldiallyl ammonium chloride (PDMDAAC), 1.2 g of ferrous sulfate (FeSO4), and 1.2 g of hydrogen peroxide (H2O2) with a mass concentration of 30%;

[0035] Step 3: While adding the compounded reagent system, ultrasonic treatment is applied to the solution obtained in step 1 at a frequency of 20 kHz and a power of 0.2 W / mL. The ultrasonic probe is immersed below the liquid surface and the treatment is continued for 30 minutes before adding 0.8 g of hydrogen peroxide. Ultrasonic treatment produces an ultrasonic cavitation effect in the wastewater, generating localized high temperature, high pressure, and microjets, accelerating the decomposition of hydrogen peroxide into hydroxyl radicals (·OH) and simultaneously destroying the colloidal stability of pollutants in the wastewater.

[0036] The ultrasonic treatment simultaneously promotes the hydrolysis of polyaluminium chloride (PAC) and ferrous sulfate (FeSO4) to form Al-Fe composite hydroxyl complex, and then generates Al-Fe composite flocs, which have both electrostatic neutralization and net capture effects to adsorb pollutants in wastewater; the ultrasonic cavitation effect also drives Fe 3+ Reduction to Fe 2+ , reduce the formation of iron sludge;

[0037] When PDADMAC and PAC are used together as flocculants, they promote the aggregation of fine particles through adsorption bridging, forming a core structure with a larger specific surface area, enhancing the coagulation effect on colloids and suspended solids in water, and making them more easily decomposed by the hydroxyl free radicals.

[0038] Step 4: After 65 minutes of reaction time, add 5% sodium hydroxide solution to the solution obtained in step 3, adjust the pH to 7, and allow the solution to settle before separating to obtain clear water. Testing of the treated water showed a COD removal rate of 89% and a color removal rate of 91%.

[0039] Example 3

[0040] Step 1: Add 5% sulfuric acid solution to 1L of industrial wastewater (COD: 1800mg / L, PCU: 400) to adjust the pH to 3.0, and control the pH fluctuation range to no more than ±0.5 during the reaction;

[0041] Step 2: The solution obtained in step 1 is fed into a reactor and a composite reagent system is added, wherein the composite reagent system is 2.25 g of polyaluminum chloride (PAC), 6.75 g of polydimethyldiallyl ammonium chloride (PDMDAAC), 3 g of ferrous sulfate (FeSO4), and 3 g of 30% hydrogen peroxide (H2O2);

[0042] Step 3: While adding the compounded reagent system, ultrasonic treatment is applied to the solution obtained in step 1 at a frequency of 40 kHz and a power of 0.5 W / mL. The ultrasonic probe is immersed below the liquid surface and the treatment is continued for 20 minutes before adding 2 g of hydrogen peroxide. Ultrasonic treatment produces ultrasonic cavitation in the wastewater, generating localized high temperature, high pressure, and microjets, accelerating the decomposition of hydrogen peroxide into hydroxyl radicals (·OH) and simultaneously destroying the colloidal stability of pollutants in the wastewater.

[0043] The ultrasonic treatment simultaneously promotes the hydrolysis of polyaluminium chloride (PAC) and ferrous sulfate (FeSO4) to form Al-Fe composite hydroxyl complex, and then generates Al-Fe composite flocs, which have both electrostatic neutralization and net capture effects to adsorb pollutants in wastewater; the ultrasonic cavitation effect also drives Fe 3+ Reduction to Fe 2+ , reduce the formation of iron sludge;

[0044] When PDADMAC and PAC are used together as flocculants, they promote the aggregation of fine particles through adsorption bridging, forming a core structure with a larger specific surface area, enhancing the coagulation effect on colloids and suspended solids in water, and making them more easily decomposed by the hydroxyl free radicals.

[0045] Step 4: After 40 minutes of reaction time, add 5% sodium hydroxide solution to the solution obtained in step 3, adjust the pH to 7, and allow the solution to settle before separating to obtain clear water. Testing of the treated water showed a COD removal rate of 96% and a color removal rate of 99%.

[0046] Example 4

[0047] Step 1: Add 5% sulfuric acid solution to 1L of industrial wastewater (COD: 1800mg / L, PCU: 400) to adjust the pH to 4.0, and control the pH fluctuation range to no more than ±0.5 during the reaction;

[0048] Step 2: The solution obtained in step 1 is fed into a reactor and a compound reagent system is added, wherein the compound reagent system is 0.96 g of polyaluminum chloride (PAC), 5.76 g of polydimethyldiallyl ammonium chloride (PDMDAAC), 4.8 g of ferrous sulfate (FeSO4) and 4.8 g of hydrogen peroxide (H2O2) with a mass concentration of 30%;

[0049] Step 3: While adding the compounded reagent system, ultrasonic treatment is applied to the solution obtained in step 1 at a frequency of 40 kHz and a power of 0.5 W / mL. The ultrasonic probe is immersed below the liquid surface and the treatment is continued for 15 minutes before adding 3.2 g of hydrogen peroxide. Ultrasonic treatment produces ultrasonic cavitation in the wastewater, generating localized high temperature, high pressure, and microjets, accelerating the decomposition of hydrogen peroxide into hydroxyl radicals (·OH) and simultaneously destroying the colloidal stability of pollutants in the wastewater.

[0050] The ultrasonic treatment simultaneously promotes the hydrolysis of polyaluminium chloride (PAC) and ferrous sulfate (FeSO4) to form Al-Fe composite hydroxyl complex, and then generates Al-Fe composite flocs, which have both electrostatic neutralization and net capture effects to adsorb pollutants in wastewater; the ultrasonic cavitation effect also drives Fe 3+ Reduction to Fe 2+ , reduce the formation of iron sludge;

[0051] When PDADMAC and PAC are used together as flocculants, they promote the aggregation of fine particles through adsorption bridging, forming a core structure with a larger specific surface area, enhancing the coagulation effect on colloids and suspended solids in water, and making them more easily decomposed by the hydroxyl free radicals.

[0052] Step 4: After 30 minutes of reaction time, add 5% sodium hydroxide solution to the solution obtained in step 3, adjust the pH to 7, and allow the solution to settle before separating to obtain clear water. Testing of the treated water showed a COD removal rate of 83% and a color removal rate of 86%.

[0053] Comparative Example

[0054] Step 1: Add 5% sulfuric acid solution to 1L of industrial wastewater (COD: 1800mg / L, PCU: 400) to adjust the pH to 3.0, and control the pH fluctuation range to no more than ±0.5 during the reaction;

[0055] Step 2: The solution obtained in step 1 is fed into a reactor, and 3 g of ferrous sulfate (FeSO4) and 5 g of 30% hydrogen peroxide (H2O2) are added, and stirring is started;

[0056] Step 3: After 90 minutes of reaction time, add 5% sodium hydroxide solution to the solution obtained in Step 2, adjust the pH to 7, and allow the solution to settle before separating to obtain clear water. Testing of the treated water revealed a COD removal rate of 60% and a color removal rate of 30%.

[0057] Comparing Example 1 with Example 3, Control Example 1 only used the Fenton reaction to treat wastewater, without using ultrasonic action or adding a composite flocculant. This resulted in a longer degradation time in the organic wastewater and the absence of local high-temperature and high-pressure areas produced by the cavitation effect. As a result, less ·OH was generated in the system, the utilization rate of hydrogen peroxide was reduced, the COD removal rate was only 60%, and the chroma removal rate was 30%.

[0058] The number of devices and processing scales described herein are intended to simplify the description of the present invention. Applications, modifications, and variations of the present invention will be readily apparent to those skilled in the art.

[0059] As described above, the present invention provides a method for treating organic wastewater with ultrasonic assisted Fenton-flocculation, which simultaneously strengthens the Fenton oxidation and flocculation processes through ultrasonic cavitation. The cavitation effect of ultrasonic waves produces transient high temperature and high pressure, which accelerates the reaction of H2O2 with Fe 2+ The Fenton reaction increases the yield of hydroxyl radicals (·OH); cavitation microjets directly shear large molecular pollutants (such as azo dyes and polycyclic aromatic hydrocarbons), breaking them into small molecular fragments that are more easily attacked by ·OH, shortening the oxidation reaction time. In addition, the combination of PDMDAAC and PAC promotes the aggregation of fine particles through the "adsorption bridging" effect, forming a core structure with a larger specific surface area, which is more easily decomposed by hydroxyl radicals. Through the dynamic synergistic mechanism of iron salt circulation and PAC, Fe2+ catalyzes the Fenton reaction to generate ·OH, and ultrasonic cavitation drives the reduction of Fe3+ to Fe2+ to reduce iron sludge formation. At the same time, Fe3+ and PAC form Al-Fe composite flocs, which have both electrostatic neutralization and net capture effects, and the adsorption of hydrophobic organic matter is increased by 25%-35%. By dividing the total H2O2 dosage into a gradient addition of 60% for the first and 40% for the second, the Fenton reaction is rapidly initiated in an acidic environment of pH 3 to produce a large amount of hydroxyl radicals (·OH). The consumed oxidant is then replenished mid-reaction, extending the duration of the ·OH concentration peak by 2-3 times and significantly improving the effective utilization of H2O2. This dosing strategy effectively suppresses the ineffective decomposition of H2O2, reduces treatment costs, and optimizes the degradation pathway of organic matter.

[0060] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and exemplary embodiments. They can be applied to a variety of fields suitable for the present invention. Further modifications will be readily apparent to those skilled in the art. Therefore, the present invention is not limited to the specific details shown and described herein without departing from the general concept defined by the claims and their equivalents.

Claims

1. A method for treating organic wastewater by using ultrasound in combination with Fenton-flocculation, characterized in that: The steps are as follows: Step 1: Add 5% sulfuric acid solution or sodium hydroxide solution to the wastewater to adjust the pH value to 2.0-4.0, and control the pH fluctuation range to no more than ±0.5 during the reaction; Step 2: Add a composite reagent system to the solution obtained in step 1, wherein the composite reagent system comprises polyaluminum chloride (PAC), polydimethyldiallyl ammonium chloride (PDMDAAC), ferrous sulfate (FeSO4) and 30% hydrogen peroxide (H2O2), and the mass ratio of PAC:PDMDAAC:ferrous sulfate:hydrogen peroxide is 1:1-6:1-5:0.5-2.5; Step 3: while adding the compound reagent system, ultrasonic treatment is applied to the solution obtained in step 1, wherein the ultrasonic treatment produces an ultrasonic cavitation effect in the wastewater, generating local high temperature, high pressure and micro-jets, accelerating the decomposition of hydrogen peroxide into hydroxyl radicals (·OH), and simultaneously destroying the colloidal stability of pollutants in the wastewater; The ultrasonic treatment simultaneously promotes the hydrolysis of polyaluminium chloride (PAC) and ferrous sulfate (FeSO4) to form Al-Fe composite hydroxyl complex, and then generates Al-Fe composite flocs, which have both electrostatic neutralization and net capture effects to adsorb pollutants in wastewater; the ultrasonic cavitation effect also drives Fe 3+ Reduction to Fe 2+， Reduce iron sludge formation; When PDADMAC and PAC are used together as flocculants, they promote the aggregation of fine particles through adsorption bridging, forming a core structure with a larger specific surface area, enhancing the coagulation effect on colloids and suspended solids in water, and making them more easily decomposed by the hydroxyl free radicals. Step 4: add 5% sodium hydroxide solution to the solution obtained in step 3, adjust the pH value to 7, let it stand and precipitate, and then separate to obtain clear water.

2. The method for treating organic wastewater by using ultrasound-assisted Fenton-flocculation as claimed in claim 1, wherein: The added amount of the hydrogen peroxide (H2O2) with a mass concentration of 30% is 2g / L to 8g / L.

3. The method for treating organic wastewater by using ultrasound-assisted Fenton-flocculation as claimed in claim 1, wherein: The hydrogen peroxide (H2O2) with a mass concentration of 30% is added in a one-time manner or in a staged manner. In the staged manner, the first addition amount is 60% and the second addition amount is 40%.

4. The method for treating organic wastewater by using ultrasound-assisted Fenton-flocculation as claimed in claim 1, wherein: The ultrasonic treatment parameters are preferably a frequency of 20 to 40 kHz, a power density of 0.2 to 0.5 W / mL, and an ultrasonic probe immersed below the liquid surface and continuously acting during the reaction process.

5. The method for treating organic wastewater by using ultrasound-assisted Fenton-flocculation as claimed in claim 1, wherein: The reaction time is 30 to 65 minutes.