Method for treating organic wastewater through ferric salt reinforced thermal activation of persulfate

Abstract

The invention relates to a method for treating organic wastewater through ferric salt reinforced thermal activation of persulfate, which comprises the following steps: adding ferric salt into wastewater, adjusting the pH value of the solution to be acidic, then controlling the reaction temperature to be more than 60 DEG C, and adding persulfate into the reaction solution for reaction, and after the reaction is finished, carrying out solid-liquid separation on the reaction system to realize thorough removal of organic pollutants. On the basis of removing organic pollutants through polymerization of thermal activation persulfate, ferric salt is introduced to reinforce the polymerization removal process of organic matters. Compared with the prior art, through the synergistic effect of the ferric salt and the persulfate, the utilization efficiency of an oxidizing agent and the removal rate of organic pollutants are greatly improved, meanwhile, generation of toxic intermediate products is reduced, the application range of removing the organic pollutants in water through polymerization is widened, and the problem of carbon emission caused by CO2 generation is avoided.

Description

Technical Field

[0001] The invention relates to the technical field of water treatment, in particular to a method for treating organic wastewater with iron salt-enhanced thermally activated persulfate. Background Art

[0002] Industries such as pharmaceuticals, coking plants and refineries generate a large amount of organic wastewater during production activities. These wastewaters usually contain a large amount of organic pollutants, which are highly toxic and difficult to degrade, posing a serious threat to the environment. Although traditional wastewater treatment technologies such as biological, physical, chemical and enzymatic methods can remove organic pollutants to a certain extent, they have strict requirements on reaction conditions during the treatment process and the removal rate of organic matter is not high.

[0003] In recent years, persulfate-based advanced oxidation technology has been widely used in actual wastewater treatment due to its strong oxidation activity and wide pH range. Persulfate can be activated by heating, ultrasound, ultraviolet light, microwaves, transition metals or alkali to produce hydroxyl radicals ·OH (2.8V) and sulfate radicals SO4· - (2.5~3.1V), these free radicals will then attack organic pollutants to decompose them into small molecules, and finally mineralize into CO2 and H2O, achieving complete removal of pollutants. Among them, thermally activated persulfate technology can greatly reduce treatment costs because it can directly utilize the residual heat in the wastewater, and has great potential in actual wastewater treatment. However, the traditional method of treating organic wastewater with thermally activated persulfate based on mineralization requires the addition of a large amount of persulfate as an oxidant. Take phenol as an example: theoretically, 13 mol of peroxydisulfate (PDS) is required to treat 1 mol of phenol, the utilization efficiency of the oxidant is low, and the treatment cost is relatively high; in addition, the mineralization process of organic matter may produce intermediates with higher toxicity, and the carbon dioxide in the mineralized product will have problems such as carbon emissions, which poses certain safety hazards.

[0004] In recent years, studies have pointed out that the efficient removal of organic pollutants can be achieved by polymerization under the action of heat-activated persulfate. Chinese patent CN114477412A discloses a method for removing organic pollutants in water by heat-activated persulfate. This method does not seek to mineralize organic matter into small molecules, but rather causes most organic pollutants to undergo polymerization reactions to form solid organic particles. After the reaction is completed, most organic pollutants can be removed from water by solid-liquid separation, which has a high oxidant utilization efficiency. However, this method is limited in practical applications by the difficulty in controlling the activity of the reaction system, and is often accompanied by problems such as insufficient production of organic polymerization monomers or excessive oxidation of polymerization products, and the range of applicable reaction conditions is relatively narrow. Therefore, it is urgent to explore a new method for treating organic wastewater. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a method for treating organic wastewater with iron salt-enhanced thermally activated persulfate to achieve complete removal of organic pollutants in the wastewater.

[0006] The conception process of this application is as follows: Based on the thermally activated persulfate polymerization to remove organic pollutants, the present invention introduces iron salts to strengthen the polymerization removal process of organic matter. In this process, iron salts can form polyphenol chelates or iron-chelated organic free radicals with organic matter, which makes the organic free radicals more stable and continuously undergoes polymerization reaction. At the same time, the organic matter after iron chelation can undergo internal redox reaction, thereby converting Fe 3+ Reduction to Fe 2+ , further accelerating the activation of persulfate, generating more free radicals, thereby promoting the continuation of the reaction. Finally, the generated organic free radicals are coupled and polymerized to form solid polymer products, and the organic pollutants can be completely removed by solid-liquid separation. Through the synergistic effect of iron salts and persulfates, the utilization efficiency of oxidants is greatly improved, the generation of toxic intermediates is reduced, the scope of application of polymerization to remove organic pollutants in water is broadened, and the carbon emission problem caused by the production of CO2 is avoided.

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

[0008] In one aspect, the present invention provides a method for treating organic wastewater by using iron salt-enhanced thermally activated persulfate, comprising the following steps:

[0009] S1. Add iron salt to the wastewater to adjust the pH value of the solution to acidic;

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

[0011] S3. After the reaction is completed, the reaction system is subjected to solid-liquid separation to achieve complete removal of organic pollutants.

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

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

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

[0015] Furthermore, the heating temperature in S2 is 60-90° C., and the heating method is to directly utilize high-temperature wastewater whose temperature meets the requirements.

[0016] Furthermore, the persulfate in S2 includes at least one of peroxymonosulfate (PMS) and peroxydisulfate (PDS).

[0017] Furthermore, the ratio of the dosage of the persulfate in S2 to the mass concentration of the wastewater COD is 0.6 to 6.

[0018] Furthermore, the reaction time in S2 is 30 to 150 minutes.

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

[0020] Furthermore, the organic pollutants described in S3 are one or more of phenolic organic matter, aniline organic matter, alkoxybenzene organic matter, nitrobenzene organic matter, phenol ester organic matter, benzene or biphenyl organic matter and heterocyclic compounds.

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

[0022] (1) The present invention provides a method for treating organic wastewater with iron salt-enhanced thermally activated persulfate. By adding iron salt and controlling the dosage of persulfate, organic pollutants undergo polymerization reaction to generate separable solid polymers. Compared with the existing organic wastewater treatment technology, the present invention 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 byproducts, which is beneficial to subsequent treatment.

[0023] (2) Based on the removal of organic pollutants by thermally activated polymerization, the present invention introduces iron salts to strengthen the polymerization removal process of organic matter. The presence of iron salts can further activate persulfate to produce more organic free radicals to increase the activity of the reaction and allow the reaction to continue. Therefore, there is no need to add a large amount of persulfate, saving costs. In the heating process of the reaction, the residual heat of the wastewater can be effectively utilized, thereby improving energy utilization.

[0024] (3) The present invention converts most of the organic matter in the wastewater into separable solid polymers, which can achieve complete removal of organic pollutants, and the polymer products obtained after solid-liquid separation can be further recovered to achieve the reuse of carbon resources.

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

[0026] Figure 1This is a curve chart showing the removal of COD over time when eight common organic pollutants in organic wastewater are treated in Example 2 of the present invention;

[0027] Figure 2 This is a diagram showing the actual effects of treating eight common organic pollutants in organic wastewater in Example 2 of the present invention.

[0028] Figure 3 This is a graph of the oxidant utilization efficiency when no iron salt is added and different iron salts are added when treating 4-chlorophenol in Example 3 of the present invention. DETAILED DESCRIPTION

[0029] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. Any features such as preparation means, materials, structures or composition ratios not clearly described in this technical solution are regarded as common technical features disclosed in the prior art.

[0030] The present invention provides a method for treating organic wastewater by using iron salt-enhanced thermally activated persulfate, comprising the following steps:

[0031] S1. Add iron salt to the wastewater to adjust the pH value of the solution to 1-7;

[0032] S2, then heating the solution in S1 to a temperature of 60 to 90° C., and adding persulfate to the solution to react;

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

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

[0035] Example 1

[0036] This embodiment selected actual coking wastewater as the research object, and compared the removal of COD in the coking wastewater of the heat / PDS system, the ferric chloride / PDS system and the (ferric chloride + heat) / PDS system. The results show that in the ferric chloride / PDS system, COD is almost not removed, while the (ferric chloride + heat) / PDS system has a better treatment effect on the coking wastewater than the heat / PDS system. COD can be almost completely removed after 90 minutes, and more than 80% of COD is converted into separable solid polymers through polymerization. The results show that ferric chloride alone cannot remove organic pollutants in the solution. The removal of COD in the coking wastewater can only be achieved when heated and PDS is present, 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] Coking wastewater COD: 2460mg / L

[0039] PDS concentration: 3000mg / L

[0040] Ferric chloride concentration: 5000mg / L

[0041] Reaction temperature: 90℃

[0042] pH of the solution: 3

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

[0044] Coking wastewater COD: 2460mg / L

[0045] PDS concentration: 3000mg / L

[0046] Reaction temperature: 90℃

[0047] pH of the solution: 3

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

[0049] Coking wastewater COD: 2460mg / L

[0050] PDS concentration: 3000mg / L

[0051] Ferric chloride concentration: 5000mg / L

[0052] Reaction temperature: 25℃

[0053] pH of the solution: 3

[0054] Example 2

[0055] This example selected 8 common organic pollutants in organic wastewater, including phenol (Phenol), 4-chlorophenol (4-CP), 2-chlorophenol (2-CP), 4-nitrophenol (4-NP), p-hydroxybenzoic acid (4-HBA), 4-aminophenol (4-AP), bisphenol A (BPA) and resorcinol (RES), and explored the removal of the 8 organic pollutants under the (ferric chloride + heat) / PDS system. Please refer to Figure 1 and 2 The results showed that for the eight common organic pollutants, the (ferric chloride + heat) / PDS system achieved good removal effects. Among them, 4-AP, which had the best treatment effect, completely removed the organic pollutants within 30 minutes, and more than 80% of the pollutants formed solid polymers through polymerization to achieve pollutant recovery.

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

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

[0058] PDS concentration: 1900mg / L

[0059] Ferric chloride concentration: 3240mg / L

[0060] Reaction temperature: 90℃

[0061] pH of the solution: 3

[0062] Example 3

[0063] This example selected 4-chlorophenol as the research object, and compared the COD removal and oxidant utilization efficiency (the amount of COD that can be removed by a unit amount of PDS, oxidant utilization efficiency = the amount of COD removed (ΔCOD) / the amount of PDS consumed (ΔPDS)) of the heat / PDS system in four conditions without iron, with iron chloride, with iron sulfate or with iron nitrate. The higher the oxidant utilization efficiency, the better. Please refer to the oxidant utilization efficiency Figure 3 The results showed that the COD removal effect after adding iron salts was better than that without adding iron, and the oxidant utilization efficiency after adding iron salts was higher than that without adding iron, from high to low: ferric chloride > ferric nitrate > ferric sulfate > no iron added.

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

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

[0066] PDS concentration: 1900mg / L

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

[0068] Reaction temperature: 90℃

[0069] pH of the solution: 3

[0070] Example 4

[0071] For the (ferric chloride + heat) / PDS system, this example compares the removal of 4-chlorophenol at 4 different temperatures of 60°C, 70°C, 80°C, and 90°C. The results show that with the increase of the reaction temperature, the removal effect and rate of 4-chlorophenol are improved. Among them, at 90°C, 4-chlorophenol can be completely removed within 30 minutes. The amount of solid polymer generated by the reaction increases with the increase of temperature.

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

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

[0074] PDS concentration: 1900mg / L

[0075] Ferric chloride concentration: 3240mg / L

[0076] Reaction temperature: 60℃, 70℃, 80℃, 90℃

[0077] pH of the solution: 3

[0078] Example 5

[0079] For the (ferric chloride + heat) / PDS system, this example compares the effects of 950, 1900, 2375, 2850, 4750 mg / L of these 5 different concentrations of PDS on the removal of 4-chlorophenol. The results show that with the increase of PDS concentration, the removal effect and rate of 4-chlorophenol are improved. The amount of solid polymer generated by the reaction shows a trend of first rising and then falling with the increase of PDS concentration.

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

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

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

[0083] Ferric chloride concentration: 3240mg / L

[0084] Reaction temperature: 90℃

[0085] pH of the solution: 3

[0086] Example 6

[0087] For the (ferric chloride + heat) / PDS system, this embodiment compares the effects of 1620, 2430, 3240, 4050, 4860 mg / L of these 5 different ferric chloride concentrations on the removal of 4-chlorophenol. The results show that with the increase of ferric chloride concentration, the removal effect and rate of 4-chlorophenol are improved. The amount of solid polymer generated by the reaction increases with the increase of ferric chloride concentration.

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

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

[0090] PDS concentration: 1900mg / 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 embodiment compares the effects of 40, 80, 160, 480, 800 mg / L these 5 different initial 4-chlorophenol concentrations (COD) on the removal of 4-chlorophenol, and controls the ratio of PDS and ferric chloride dosage to the initial 4-chlorophenol concentration (COD) to be constant. The results show that solid polymers are generated during the reaction process at different concentrations, and the amount of solid polymer generated increases as the initial 4-chlorophenol concentration increases.

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

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

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

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

[0100] Reaction temperature: 90℃

[0101] pH of the solution: 3

[0102] Example 8

[0103] For the (ferric chloride + heat) / PDS system, this example compares the effects of 1, 3, 5, 7, and 9 pH values ​​on the removal of 4-chlorophenol. The results show that under acidic and neutral conditions, 4-chlorophenol has achieved good removal effects, and solid polymers are generated during the reaction; while under alkaline conditions, the removal effect of 4-chlorophenol is relatively poor and the amount of solid polymer generated is small.

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

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

[0106] PDS concentration: 1900mg / L

[0107] Ferric chloride concentration: 3240mg / L

[0108] Reaction temperature: 90℃

[0109] Solution pH: 1, 3, 5, 7, 9

[0110] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for treating organic wastewater by using iron salt-enhanced thermally activated persulfate, characterized in that: The following steps are involved: S1. Add iron salt to the wastewater to adjust the pH value of the solution to acidic; S2, then heating the solution in S1, and adding persulfate to the solution to react; S3. After the reaction is completed, the reaction system is subjected to solid-liquid separation to achieve complete removal of organic pollutants.

2. The method for treating organic wastewater by using iron salt-enhanced thermally activated persulfate according to claim 1, characterized in that: The iron salt in S1 is ferric nitrate, ferric chloride, ferric sulfate, ferrous nitrate, ferrous chloride or ferrous sulfate.

3. The method for treating organic wastewater by using iron salt-enhanced thermally activated persulfate according to claim 1, characterized in that: The ratio of the mass concentration of iron in the iron salt in S1 to the mass concentration of COD in the wastewater is 0.25 to 2.

5.

4. The method for treating organic wastewater by using iron salt-enhanced thermally activated persulfate according to claim 1, characterized in that: The pH value of the solution in S1 is adjusted to 1-7.

5. The method for treating organic wastewater by using iron salt-enhanced thermally activated persulfate according to claim 1, characterized in that: The heating temperature in S2 is 60 to 90°C.

6. The method for treating organic wastewater by using iron salt-enhanced thermally activated persulfate according to claim 1, characterized in that: The persulfate in S2 includes at least one of peroxymonosulfate and peroxydisulfate.

7. The method for treating organic wastewater by using iron salt-enhanced thermally activated persulfate according to claim 1, characterized in that: The ratio of the dosage of the persulfate in S2 to the mass concentration of the wastewater COD is 0.6 to 6.

8. The method for treating organic wastewater by using iron salt-enhanced thermally activated persulfate according to claim 1, characterized in that: The reaction time in S2 is 30 to 150 minutes.

9. The method for treating organic wastewater by using iron salt-enhanced thermally activated persulfate according to claim 1, characterized in that: The solid-liquid separation in S3 is coagulation sedimentation, filtration, centrifugal separation or static sedimentation.

10. The method for treating organic wastewater by using iron salt-enhanced thermally activated persulfate according to claim 1, characterized in that: The organic pollutants described in S3 are one or more of phenolic organic matter, aniline organic matter, alkoxybenzene organic matter, nitrobenzene organic matter, phenol ester organic matter, benzene or biphenyl organic matter and heterocyclic compounds.

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