CN112850856B

CN112850856B - Method for improving efficiency of electro-Fenton removal of organic pollutants by sulfite

Info

Publication number: CN112850856B
Application number: CN202011618115.9A
Authority: CN
Inventors: 周明华; 宋格; 杜雪冬
Original assignee: Nankai University
Current assignee: Nankai University
Priority date: 2020-12-31
Filing date: 2020-12-31
Publication date: 2022-05-24
Anticipated expiration: 2040-12-31
Also published as: CN112850856A

Abstract

The invention relates to the field of environmental engineering, in particular to a method for improving the efficiency of removing organic pollutants by electro-Fenton through sulfite. The method solves the problems of narrow pH application range (pH2.8-3.5) and low iron ion reduction speed of the traditional electro-Fenton process, generates various free radicals such as hydroxyl radical and sulfate radical through an electro-Fenton/sulfite system, improves the electro-Fenton reaction rate by tens of times, widens the application range of pH, and can obtain better pollutant removal effect under acidic, neutral and slightly alkaline conditions. And ferric iron is reduced through sulfite, so that the iron circulation is accelerated. Meanwhile, the method also has the advantages of simple operation, low cost and the like.

Description

Method for improving efficiency of electro-Fenton removal of organic pollutants by sulfite

Technical Field

The invention relates to the field of environmental engineering, in particular to a method for improving organic pollutant removal efficiency of electro-Fenton by sulfite.

Background

In the sewage treatment, the traditional physical method and chemical method can only partially remove or separate suspended particles and pollutants in water, but the treatment efficiency of the refractory organic matters in the sewage is not high, so that the conventional water treatment process is difficult to realize standard discharge or advanced treatment of the refractory organic wastewater.

The electro-Fenton technology is a novel electrochemical advanced oxidation technology, hydrogen peroxide generated by oxygen in-situ reduction reacts with ferrous ions to generate hydroxyl radicals with strong oxidizing property, so that organic pollutants are mineralized into carbon dioxide and water, risks of reagents such as hydrogen peroxide in the aspects of transportation, storage or treatment are avoided, and the electrochemical advanced oxidation technology has the advantages of high efficiency, environmental friendliness and the like. However, the traditional electro-Fenton has the defects of narrow pH application range (pH 2.8-3.5), slow iron ion reduction speed, difficult catalyst recovery and the like, which greatly limits the wide application of the traditional electro-Fenton.

On the other hand, the advanced oxidation technology based on sulfate radicals is widely concerned because of its high efficiency, mild reaction conditions, wider application range of pH value, and longer effective time than that of hydroxyl radicals in the environment. The sulfite is used as a desulfurization byproduct, has the advantages of low price, low toxicity and the like compared with persulfate, can be used as a source for generating sulfate radicals, and is a water treatment agent with low price and environmental protection. The existing research shows that the sulfate radical can be generated by activating sulfite with transition metal under the aerobic condition, thereby realizing the decolorization of organic dye and degrading organic pollutants. However, the activation process usually requires additional energy or aeration, and has the problems of narrow pH adaptation range (pH <5), high operation cost and the like, which restricts the practical application of the activated sulfite process.

Disclosure of Invention

The invention aims to overcome the defects of narrow pH application range and low iron ion reduction speed of the traditional electro-Fenton, widens the pH application range of an electro-Fenton system, accelerates the iron circulation process, improves the removal efficiency of the iron circulation system and develops a method for improving the efficiency of removing organic pollutants by using sulfite.

The object of the invention is achieved by the following steps:

adding 0.5-3.0mM of sulfite into an electro-Fenton system for efficiently producing hydrogen peroxide at a cathode, adjusting the pH of the organic wastewater to be treated to 3-10, and adding 0.025-0.4mM of Fe²⁺/Fe³⁺Ion or heterogeneous iron-based catalyst of 10-200mg/L, controlling current to 5-100mA, and carrying out pollutant degradation experiment for 10-300 minutes.

In the invention, the sulfite comprises one or a mixture of several of sodium sulfite, sodium bisulfite, potassium sulfite and potassium bisulfite. The cathode is a carbon cathode for efficiently producing hydrogen peroxide, such as graphite, an air diffusion electrode, carbon black modified carbon felt and the like. The ferrous ion or ferric ion can be ferrous sulfate, ferrous chloride, ferric sulfate, ferric chloride, etc., and the molar ratio of the concentration of the ferrous ion or ferric ion to the concentration of the sulfite is 1:2.5-1: 40. The added heterogeneous iron-based catalyst comprises ferroferric oxide, ferric oxide, zero-valent iron, iron-carbon heterogeneous catalyst and the like. The organic wastewater to be treated comprises medical wastewater, phenol-containing wastewater, dye wastewater, chemical wastewater and the like.

The invention relates to the following principles:

the ferrous ions and hydrogen peroxide generated by the cathode oxygen reduction reaction generate Fenton reaction to generate hydroxyl free radicals and ferric ions. Ferric ions react with sulfite to reduce into ferrous ions, and sulfite radicals are generated at the same time. Sulfites can also generate sulfite radicals by anodic oxidation losing one electron. Sulfite radicals are further converted to persulfate and sulfate radicals in the presence of oxygen. The combined action of hydroxyl radical, sulfate radical and other radicals can mineralize pollutant.

Fe²⁺+H₂O₂→Fe³⁺+·OH+OH^-

The invention has the following outstanding characteristics:

(1) the method generates hydroxyl free radicals, sulfate free radicals and other free radicals, improves the rate of electro-Fenton, and can improve the rate constant by tens of times.

(2) The method widens the application range of pH, and can obtain better pollutant removal effect under acidic, neutral and alkaline conditions; and ferric iron is reduced by sulfite, so that iron circulation is promoted.

(3) The method can be operated in a conventional electro-Fenton system, is simple to operate, has the prices of industrial-grade sodium sulfite and sodium bisulfite of 1.8-2.2 yuan/kg, and has low cost.

Drawings

FIG. 1 shows the effect of an electro-Fenton/sodium sulfite system and an electro-Fenton system on the removal of carbamazepine using ferrous and ferric ions as homogeneous catalysts;

FIG. 2 shows the change of ferrous ions in an electro-Fenton/sodium sulfite system and an electro-Fenton system when ferric ions are used as a homogeneous catalyst;

FIG. 3 shows the effect of electro-Fenton/sodium bisulfite system and electro-Fenton system on the removal of carbamazepine using ferrous ions as homogeneous catalyst;

FIG. 4 shows the effect of electro-Fenton/sodium sulfite system and electro-Fenton system on the removal of carbamazepine using Fe-C, zero-valent Fe, iron trioxide and ferroferric oxide as heterogeneous catalysts;

FIG. 5 is a graph of the effect of an electro-Fenton/sodium sulfite system on the removal of carbamazepine at different pH with iron-carbon as a heterogeneous catalyst;

FIG. 6 shows the effect of electro-Fenton/sodium sulfite system and electro-Fenton system on removing different pollutants when iron-carbon is used as heterogeneous catalyst.

Detailed Description

Example 1

0.28g of carbon black was mixed with 2mL of ethanol, 2mL of deionized water, and 0.5mL of PTFE and coated on a carbon mat (4 cm. times.5 cm). The modified carbon felt is naturally dried and then calcined for 30min at 360 ℃ in air atmosphere.

Using DSA as an anode, using a carbon black coated modified carbon felt as a cathode, adding 50mM sodium sulfate as a supporting electrolyte and 1.0mM sodium sulfite, adjusting the pH to 7, degrading carbamazepine under the condition of an applied current of 10mA, using 0.05mM ferrous ions or 0.1mM ferric iron as a homogeneous catalyst, and increasing the removal rate of the carbamazepine from 55.83 percent and 15.55 percent of an electro-Fenton system to 83.74 percent and 78.29 percent of the electro-Fenton/sulfite system at 60 minutes and increasing the rate constants by 2.07 and 9.68 times respectively as shown in figure 1. As shown in fig. 2, the sulfite in the electro-fenton/sulfite system reduces ferric iron and produces ferrous iron.

Example 2

Example 2 the procedure was essentially the same as in example 1, except that 0.05mM ferrous ion was used as the homogeneous catalyst and sodium bisulfite was used as the sulfite, as shown in figure 3, 87.45% carbamazepine was removed at 60 minutes in the electro-fenton/sodium bisulfite system, which was improved over the electro-fenton system.

Embodiment 3

The procedure of example 3 was substantially the same as in example 1, except that 100mg/L of ferroferric oxide, ferric oxide, zero-valent iron, and iron-carbon were used as heterogeneous catalysts, wherein the iron-carbon heterogeneous catalyst was synthesized by a hydrothermal method, and the element contents were 88.95% carbon, 3.22% iron, and 7.83% oxygen, respectively. As shown in fig. 4, the electro-fenton/sulfite system removed 30.76%, 66.53%, 98.98%, and 100% carbamazepine at 60 minutes with a rate constant that was increased by 1.82, 1.46, 5.42, and 5.65 times, respectively, compared to the electro-fenton system.

Example 4

Example 4 was performed substantially the same as example 1, except that the pH was adjusted to 3-10 using 100mg/L of an iron-carbon heterogeneous material as a catalyst, as shown in fig. 5, after introduction of sulfite, both of them rapidly removed carbamazepine at pH 3-8, and the electro-fenton/sulfite system achieved good contaminant removal under acidic, neutral and slightly alkaline conditions.

Example 5

The steps of embodiment 5 are substantially the same as those of embodiment 1, except that 100mg/L of an iron-carbon heterogeneous material is used as a catalyst, and the pollutants are changed into sulfadimidine, carbamazepine, 2, 4-dichlorophenoxyacetic acid, phenol, p-chlorobenzoic acid, rhodamine B and the like, as shown in fig. 6, the pollutants can be removed in 60 minutes by the electro-fenton/sulfite system, the rate constants are respectively increased by 12.21, 10.74, 2.78, 5.32, 13.01 and 6.87 times compared with the electro-fenton system, and the electro-fenton removal efficiency is greatly improved, so that the method is suitable for removing various pollutants.

The above description is only an example of the present invention, and is not intended to limit the present invention in any way; one of ordinary skill in the art can readily practice the present invention as illustrated and described herein with reference to the accompanying drawings; however, those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiments as a basis for designing or modifying other structures for carrying out the same purposes of the present invention without departing from the scope of the invention; meanwhile, any equivalent changes, modifications, and evolutions made to the above embodiments according to the substantial technology of the present invention are within the protection scope of the technical solution of the present invention.

Claims

1. A method for enhancing the efficiency of electro-Fenton removal of organic contaminants with sulfite, comprising the steps of:

in an electro-Fenton system for generating hydrogen peroxide at a cathode, 0.5-3.0 mM of sulfite is added to adjust the pH of the organic wastewater to be treated to 3-8, and 0.025-0.4 mM of Fe is added²⁺/Fe³⁺Ion or heterogeneous iron-based catalyst of 10-200 mg/L, controlling current to 5-100 mA, and carrying out pollutant degradation experiment for 10-300 minutes.

2. The method of claim 1, wherein the sulfite comprises one or more of sodium sulfite, sodium bisulfite, potassium sulfite, and potassium bisulfite.

3. The method of claim 1, wherein the cathode is a hydrogen peroxide-producing carbon cathode, which is graphite, an air diffusion electrode or carbon black modified carbon felt.

4. The method according to claim 1, wherein the ferrous ion is ferrous sulfate or ferrous chloride, and the ferric ion is ferric sulfate or ferric chloride, and the molar ratio of the concentration of the ferric sulfate or ferric chloride to the concentration of the sulfite is 1:2.5 to 1: 40.

5. The method according to claim 1, wherein the heterogeneous iron-based catalyst comprises ferroferric oxide, ferric oxide, zero-valent iron or iron-carbon.

6. The method according to claim 1, wherein the organic wastewater to be treated comprises medical wastewater, phenol-containing wastewater, dye wastewater or chemical wastewater.