Method for treating organic wastewater by using iron salt reinforced heat-activated persulfate

Abstract

The present application relates to a kind of iron salt reinforced heat-activated persulfate treatment organic wastewater method, the method includes the following steps: adding iron salt to wastewater, adjust the pH of solution to acidic, subsequently control the reaction temperature to be above 60 DEG C, and add persulfate to reaction solution to carry out reaction, after reaction, solid-liquid separation is carried out to reaction system, realize the complete removal of organic pollutants.The present application is based on heat-activated persulfate polymerization removal organic pollutants, introduce iron salt to strengthen the polymerization removal process of organic matter.Compared with prior art, by the synergistic effect of iron salt and persulfate, the utilization efficiency of oxidant and the removal rate of organic pollutants are greatly improved, while the generation of toxic intermediates is reduced, the application range of polymerization removal organic pollutants in water is widened, and the carbon emission problem caused by CO2 is avoided.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to a method for treating organic wastewater by iron salt-enhanced thermal activation of persulfate. Background Technology

[0002] Industries such as pharmaceutical manufacturing, coking plants, and oil refineries generate large amounts of organic wastewater during their production activities. This wastewater typically contains high levels of organic pollutants, which are highly toxic and difficult to degrade, posing a serious threat to the environment. Traditional wastewater treatment technologies, such as biological, physical, chemical, and enzymatic methods, can remove organic pollutants to some extent, but these methods require stringent reaction conditions and have low organic matter removal rates.

[0003] In recent years, advanced oxidation technologies based on persulfate have been widely applied in wastewater treatment due to their strong oxidizing activity and wide suitable pH range. Persulfate can be activated through heating, ultrasound, ultraviolet light, microwaves, transition metals, or alkalis to generate hydroxyl radicals ·OH (2.8V) and sulfate radicals SO4·2-, which have strong oxidizing capabilities. - (2.5–3.1V), these free radicals then attack organic pollutants, causing them to decompose into smaller molecules, and finally mineralize into CO2 and H2O, achieving complete removal of pollutants. Among them, thermally activated persulfate technology greatly reduces treatment costs because it can directly utilize the residual heat in wastewater, and has great potential in practical wastewater treatment. However, traditional mineralization-based thermally activated persulfate treatment of organic wastewater requires the addition of large amounts of persulfate as an oxidant. Taking phenol as an example, theoretically, treating 1 mol of phenol requires consuming 13 mol of perdisulfate (PDS), resulting in low oxidant utilization efficiency and relatively high treatment costs. In addition, the mineralization process of organic matter may produce intermediate products with higher toxicity, and the carbon dioxide in the mineralization products may pose carbon emission problems, which have certain safety hazards.

[0004] In recent years, studies have shown that thermally activated persulfate can efficiently remove organic pollutants through polymerization. Chinese patent CN114477412A discloses a method for removing organic pollutants from water using thermally activated persulfate. This method does not aim to mineralize organic matter into small molecules, but rather causes most organic pollutants to polymerize into solid organic particles. After the reaction, solid-liquid separation removes most of the organic pollutants from the water, demonstrating high oxidant utilization efficiency. However, in practical applications, this method is limited by the difficulty in controlling the activity of the reaction system, often resulting in insufficient yield of organic monomers or excessive oxidation of polymerization products, and its applicable reaction conditions are relatively narrow. Therefore, there is an urgent need to explore a new method for treating organic wastewater. Summary of the Invention

[0005] The present application aims to overcome the defects of the prior art and provide a method for treating organic wastewater by using iron salt to strengthen the heat-activated persulfate salt, so as to completely remove the organic pollutants in the wastewater.

[0006] The present application is based on the heat-activated persulfate salt polymerization removal of organic pollutants, and introduces iron salt to strengthen the polymerization removal process of organic matter. In this process, the iron salt can form polyphenol chelates or iron chelated organic free radicals with the organic matter, which makes the organic free radicals have better stability and continuously occur polymerization reaction. At the same time, the iron chelated organic matter can occur internal oxidation-reduction reaction, thereby Fe 3+ is reduced to generate Fe 2+ , further accelerates the activation of persulfate salt, generates more free radicals, thereby promoting the continuous reaction, and finally, the generated organic free radicals are coupled and polymerized to form solid polymerization products, so that the complete removal of organic pollutants can be realized through solid-liquid separation. Through the synergistic effect of iron salt and persulfate salt, the utilization efficiency of the oxidant is greatly improved, the generation of toxic intermediates is reduced, the application range of the polymerization removal of organic pollutants in water is widened, and the carbon emission problem caused by CO2 is avoided.

[0007] The purpose of the present application can be achieved by the following technical solutions:

[0008] On the one hand, the present application provides a method for treating organic wastewater by using iron salt to strengthen the heat-activated persulfate salt, comprising the following steps:

[0009] S1, adding iron salt to the wastewater, and adjusting the pH value of the solution to be acidic;

[0010] S2, then heating the solution in S1, and adding persulfate salt to the solution to react;

[0011] S3, after the reaction is completed, the solid-liquid separation is performed on the reaction system, so that the complete removal of the organic pollutants is realized.

[0012] Further, the iron salt in S1 is ferric nitrate, ferric chloride, ferric sulfate, ferrous nitrate, ferrous chloride or ferrous sulfate.

[0013] Further, the ratio of the mass concentration of iron in the iron salt in S1 to the mass concentration of the wastewater COD is 0.25-2.5.

[0014] Further, the pH value of the solution in S1 is adjusted to 1-7.

[0015] Further, the heating temperature in S2 is 60-90℃, and the heating mode is to directly use the high-temperature wastewater meeting the requirements.

[0016] Further, the persulfate in S2 includes at least one of permonosulfate (PMS) and perdisulfate (PDS).

[0017] Further, a ratio of a dosage of the persulfate to a mass concentration of the COD in S2 is 0.6-6.

[0018] Further, a time of the reaction in S2 is 30-150 min.

[0019] Further, the solid-liquid separation in S3 is coagulation sedimentation, filtration, centrifugal separation or standing sedimentation.

[0020] Further, the organic pollutant in S3 is one or more of phenolic organic matter, aniline organic matter, alkoxybenzene organic matter, nitrobenzene organic matter, phenolic ester organic matter, benzene or biphenyl organic matter and heterocyclic compound.

[0021] Compared with the prior art, the present application has the following beneficial effects:

[0022] (1) The present application provides a method for treating organic wastewater by iron salt reinforced heat-activated persulfate, which makes organic pollutants undergo polymerization reaction by adding iron salt and controlling the dosage of persulfate, and generates solid polymers that can be separated. Compared with existing organic wastewater treatment technologies, the present application does not need to add a large amount of oxidant to completely degrade organic pollutants into small molecules or even mineralize them into CO2 and H2O to improve the COD removal rate in wastewater. The method has high oxidant utilization efficiency and can effectively reduce the generation of toxic by-products, which is beneficial to subsequent treatment.

[0023] (2) Based on the heat-activated polymerization removal of organic pollutants, the present application introduces iron salt to strengthen the polymerization removal process of organic matter. The presence of iron salt can further activate persulfate to generate more organic free radicals to improve the activity of the reaction, so that the reaction can continue to proceed, thus saving the cost of adding a large amount of persulfate. During the heating process of the reaction, the residual heat of the wastewater can be effectively utilized, improving the energy utilization rate.

[0024] (3) The present application converts most of the organic matter in the wastewater into solid polymers that can be separated, which can achieve complete removal of organic pollutants, and the polymerization products obtained after solid-liquid separation can be further recycled, realizing the reuse of carbon resources.

[0025] (4) The process of the present application is simple to operate and does not require additional equipment. It can also treat various types of organic pollutant wastewater, has a wide range of applications and good application prospects. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1The figure of COD removal with time for treating 8 kinds of common organic pollutants in organic wastewater in Example 2 of the present application;

[0027] Figure 2 The actual effect figure for treating 8 kinds of common organic pollutants in organic wastewater in Example 2 of the present application.

[0028] Figure 3 The figure of oxidant utilization efficiency for treating 4-chlorophenol without adding iron salt and adding different iron salts in Example 3 of the present application. DETAILED DESCRIPTION

[0029] The present application will be described in detail below with reference to the accompanying drawings and specific examples. In the present technical solution, the preparation means, materials, structures or component ratios and other features not explicitly described are considered as common technical features disclosed in the prior art.

[0030] The present application provides a method for treating organic wastewater by iron salt reinforced heat-activated persulfate, comprising the following steps:

[0031] S1, adding iron salt to wastewater, and adjusting the pH value of the solution to 1-7;

[0032] S2, subsequently heating the solution in S1 to a temperature of 60-90℃, and adding persulfate to the solution for reaction;

[0033] S3, after the reaction is completed, performing solid-liquid separation on the reaction system to achieve complete removal of organic pollutants.

[0034] The solid is a carbon-containing organic polymer, and the liquid is treated wastewater.

[0035] Example 1

[0036] In this example, actual coking wastewater is selected as the research object, and the removal of COD in coking wastewater in the heat / PDS system, the ferric chloride / PDS system and the (ferric chloride+heat) / PDS system is compared. The results show that in the ferric chloride / PDS system, the COD is almost not removed, while in the (ferric chloride+heat) / PDS system, the treatment effect of coking wastewater is better than that in the heat / PDS system, and the COD can be almost completely removed after 90 minutes, and more than 80% of the COD is converted into separable solid polymers through polymerization. The results show that ferric chloride alone cannot remove organic pollutants in the solution, and only when heated and PDS is present can the removal of COD in coking wastewater be achieved, and the addition of ferric chloride can strengthen the polymerization removal process of organic matter.

[0037] The specific experimental parameters of the (ferric chloride+heat) / PDS system are as follows:

[0038] COD of coking wastewater: 2460 mg / L

[0039] PDS concentration: 3000 mg / L

[0040] Ferric chloride concentration: 5000 mg / L

[0041] Reaction temperature: 90°C

[0042] pH value of solution: 3

[0043] The specific experimental parameters of the heat / PDS system are as follows:

[0044] COD of coking wastewater: 2460 mg / L

[0045] PDS concentration: 3000 mg / L

[0046] Reaction temperature: 90°C

[0047] pH value of solution: 3

[0048] The specific experimental parameters of the ferric chloride / PDS system are as follows:

[0049] COD of coking wastewater: 2460 mg / L

[0050] PDS concentration: 3000 mg / L

[0051] Ferric chloride concentration: 5000 mg / L

[0052] Reaction temperature: 25°C

[0053] pH value of solution: 3

[0054] Example 2

[0055] In this example, eight common organic pollutants in organic wastewater were selected, including phenol, 4-chlorophenol, 2-chlorophenol, 4-nitrophenol, 4-hydroxybenzoic acid, 4-aminophenol, bisphenol A and resorcinol, and the removal of the eight organic pollutants in the (ferric chloride + heat) / PDS system was investigated. Please refer to Figure 1 and 2 The results show that the (ferric chloride + heat) / PDS system has achieved good removal effect for the eight common organic pollutants, among which the best treatment effect 4-AP has achieved complete removal of organic pollutants within 30 min, and more than 80% of the pollutants are formed into solid polymers through polymerization to achieve the recovery of pollutants.

[0056] The specific experimental parameters of this example are as follows:

[0057] Organic pollutant concentration (COD): 800 mg / L

[0058] PDS concentration: 1900 mg / L

[0059] Ferric chloride concentration: 3240 mg / L

[0060] Reaction temperature: 90℃

[0061] pH value of the solution: 3

[0062] Example 3

[0063] In this example, 4-chlorophenol was selected as the research object, and the COD removal and oxidant utilization efficiency (the amount of COD removed by a unit amount of PDS, oxidant utilization efficiency = removed COD amount (ΔCOD) / consumed PDS amount (ΔPDS)) of the heat / PDS system under four conditions of no iron, adding ferric chloride, adding ferric sulfate or adding ferric nitrate were compared. The higher the oxidant utilization efficiency, the better. The oxidant utilization efficiency is shown in Table 1. Figure 3 The results show that the COD removal effect after adding iron salt is better than that without adding iron, and the oxidant utilization efficiency after adding iron salt is higher than that without adding iron, and from high to low, it is ferric chloride > ferric nitrate > ferric sulfate > no iron.

[0064] The specific experimental parameters of this example are as follows:

[0065] Initial 4-chlorophenol concentration (COD): 800 mg / L

[0066] PDS concentration: 1900 mg / L

[0067] Iron salt concentration (calculated as iron mass concentration): 1117 mg / L

[0068] Reaction temperature: 90℃

[0069] pH value of the solution: 3

[0070] Example 4

[0071] For the (ferric chloride + heat) / PDS system, this example compared the removal of 4-chlorophenol at four different temperatures of 60℃, 70℃, 80℃ and 90℃. The results show that as the reaction temperature increases, the removal effect and rate of 4-chlorophenol are improved, and at 90℃, the complete removal of 4-chlorophenol can be achieved within 30 min. The amount of solid polymer generated in the reaction increases with the increase of temperature.

[0072] The specific experimental parameters of this example are as follows:

[0073] 4-chlorophenol concentration (COD): 800 mg / L

[0074] PDS concentration: 1900 mg / L

[0075] Ferric chloride concentration: 3240 mg / L

[0076] Reaction temperature: 60°C, 70°C, 80°C, 90°C

[0077] pH of solution: 3

[0078] Example 5

[0079] For the (ferric chloride + heat) / PDS system, this example compares the effects of PDS at five different concentrations, 950, 1900, 2375, 2850, and 4750 mg / L, on the removal of 4-chlorophenol. The results show that as the PDS concentration increases, both the removal efficiency and rate of 4-chlorophenol increase. The amount of solid polymer produced in the reaction increases first and then decreases as the PDS concentration increases.

[0080] The specific experimental parameters of this example are as follows:

[0081] 4-Chlorophenol concentration (COD): 800 mg / L

[0082] PDS concentration: 950, 1900, 2375, 2850, 4750 mg / L

[0083] Ferric chloride concentration: 3240 mg / L

[0084] Reaction temperature: 90°C

[0085] pH of solution: 3

[0086] Example 6

[0087] For the (ferric chloride + heat) / PDS system, this example compares the effects of ferric chloride at five different concentrations, 1620, 2430, 3240, 4050, and 4860 mg / L, on the removal of 4-chlorophenol. The results show that as the ferric chloride concentration increases, both the removal efficiency and rate of 4-chlorophenol increase. The amount of solid polymer produced in the reaction increases as the ferric chloride concentration increases.

[0088] The specific experimental parameters of this example are as follows:

[0089] 4-Chlorophenol concentration (COD): 800 mg / L

[0090] PDS concentration: 1900 mg / L

[0091] Ferric chloride concentration: 1620, 2430, 3240, 4050, 4860 mg / L

[0092] Reaction temperature: 90℃

[0093] pH of the solution: 3

[0094] Example 7

[0095] For the (ferric chloride + heat) / PDS system, this example compares the effects of five different initial 4-chlorophenol concentrations (COD) of 40, 80, 160, 480, and 800 mg / L on the removal of 4-chlorophenol, while keeping the ratio of PDS and ferric chloride dosage to the initial 4-chlorophenol concentration (COD) constant. The results show that solid polymers are generated during the reaction at all concentrations, and the amount of solid polymer generated increases with increasing initial 4-chlorophenol concentration.

[0096] The specific experimental parameters for this embodiment are as follows:

[0097] Initial 4-chlorophenol concentration (COD): 40, 80, 160, 480, 800 mg / L

[0098] PDS concentrations: 95, 190, 380, 1140, 1900 mg / L

[0099] Ferric chloride concentrations: 162, 324, 648, 1944, 3240 mg / L

[0100] Reaction temperature: 90℃

[0101] pH of the solution: 3

[0102] Example 8

[0103] This example compares the effects of five different pH values ​​(1, 3, 5, 7, and 9) on the removal of 4-chlorophenol in the (ferric chloride + heat) / PDS system. The results show that 4-chlorophenol was effectively removed under both acidic and neutral conditions, with solid polymers generated during the reaction. However, under alkaline conditions, the removal effect of 4-chlorophenol was relatively poor, and the amount of solid polymer generated was less.

[0104] The specific experimental parameters for this embodiment are as follows:

[0105] Initial 4-chlorophenol concentration (COD): 800 mg / L

[0106] PDS concentration: 1900 mg / L

[0107] Ferric chloride concentration: 3240 mg / L

[0108] Reaction temperature: 90℃

[0109] pH values ​​of the solutions: 1, 3, 5, 7, 9

[0110] The foregoing description of the embodiments has been presented for the purposes of illustration and description. It is apparent to those skilled in the art that various modifications can be practiced as set forth in the foregoing description, and that the generic principles described herein can be applied to other embodiments without departing from the scope of the application. Therefore, the description is not intended to be exhaustive or to limit the application to the precise forms disclosed. Persons skilled in the art will readily devise other ways to implement the application without the application departing from the scope of the application in its broadest aspects.

Claims

1. A method for treating phenolic organic wastewater by a ferric salt- enhanced heat-activated persulfate process, characterized in that, The method comprises the following steps: S1, adding an iron salt into wastewater to adjust the pH value of the solution to be acidic; wherein: the iron salt is ferric nitrate, ferric chloride or ferric sulfate; the ratio of the mass concentration of iron in the iron salt to the mass concentration of COD in the wastewater is 0.25-2.5; S2, subsequently heating the solution in S1 and adding a persulfate salt into the solution to react; wherein: the heating temperature is 60-90 ℃, and the ratio of the dosing amount of the persulfate salt to the mass concentration of COD in the wastewater is 0.6-6; S3, after the reaction is completed, performing solid-liquid separation on the reaction system to realize complete removal of organic pollutants; The method introduces an iron salt on the basis of heat-activated persulfate salt polymerization to remove organic pollutants, and the iron salt forms polyphenol chelates or iron-chelated organic free radicals with organic matters, so that the organic free radicals have better stability and continuously occur polymerization.

2. The method according to claim 1, wherein the method is characterized by, The pH value of the solution in S1 is adjusted to 1-7.

3. The method according to claim 1, wherein the method is characterized by, The persulfate salt in S2 comprises at least one of peroxymonosulfate and peroxodisulfate.

4. The method for treating phenolic organic wastewater by ferric salt enhanced heat-activated persulfate according to claim 1, characterized in that, The reaction time in S2 is 30-150 min.

5. The method according to claim 1, wherein the method is characterized by, The solid-liquid separation in S3 is coagulation sedimentation, filtration, centrifugal separation or standing sedimentation.

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