CN106045002B - Method for catalyzing persulfate degradation of organic matter or ammonia nitrogen in sewage by sludge biochar - Google Patents

Abstract

The invention discloses a method for degrading organic matters or ammonia nitrogen in sewage by catalyzing persulfate through sludge biochar, which comprises the following steps: (1) drying the sludge to obtain dry sludge; then, pyrolyzing the dry sludge at 300-500 ℃ for at least 2 hours in a nitrogen environment, and cooling to obtain sludge biochar; (2) and putting the sludge biochar and persulfate into the sewage to degrade organic matters or ammonia nitrogen in the sewage. According to the invention, by improving the key preparation conditions of the sludge biochar, the application ratio of the sludge biochar to persulfate and the like, the persulfate can be used for efficiently catalyzing, oxidizing and degrading organic matters and ammonia nitrogen in sewage based on sulfate radical free radicals under the catalytic action of the sludge biochar, the problem of organic pollutants and ammonia nitrogen pollution in sewage is effectively solved, and the degradation effect is good.

Description

Method for catalyzing persulfate degradation of organic matter or ammonia nitrogen in sewage by sludge biochar

technical field

The invention belongs to the field of sewage treatment, and more particularly relates to a method for degrading organic matter or ammonia nitrogen in sewage by sludge biochar catalyzed by persulfate. Sulfate degrades organic pollutants and/or ammonia nitrogen in sewage.

Background technique

"Research Report on Status Quo Analysis and Development Prospects of China's Sludge Treatment and Disposal Industry (2016 Edition)" shows that during the "Twelfth Five-Year Plan" period, the total scale of sludge treatment and disposal in national planning and construction should reach 5.18 million tons per year, and by 2015, China The harmless treatment and disposal rate of sludge in key cities has reached 80%, other cities have reached 70%, and county-level key cities have reached 30%. However, according to the data in the "China Urban Statistical Yearbook", by the end of 2014, the construction of sludge treatment and disposal facilities nationwide had only completed 43.4% of the "Twelfth Five-Year Plan" target, or 2,248,100 tons per year. The "light mud" problem is still serious.

Among the current disposal methods, landfill accounts for 63.0%, sludge aerobic fermentation + agricultural use accounts for about 13.5%, natural drying and comprehensive utilization of sludge accounts for 5.4%, sludge incineration accounts for 1.8%, open-air storage and outbound transportation of sludge each accounted for 1.8% and 14.4%. In fact, most of the sludge in landfill, open storage and outbound transportation is disposed of at will, and the proportion of real safe disposal does not exceed 20%. The unsafely disposed sludge usually contains a wide variety of toxic and harmful substances, such as harmful Persistent organic pollutants such as microorganisms, inorganic metals, polychlorinated biphenyls and dioxins, etc. (CN 103725304 A).

Sludge carbonization refers to the process of releasing the water in the sludge by certain means, while retaining the carbon value in the sludge to the maximum extent, and greatly increasing the carbon content in the final product, which is a relatively safe sludge cleaning process. Handling new technologies. Among them, low-temperature carbonization has the advantages of low energy consumption, high degree of heavy metal stabilization, less dioxins and nitrogen and sulfur oxides (CN201670822 U), and high biochar yield. The main product of slow low-temperature sludge carbonization is biochar, which has a large specific surface area and abundant surface functional groups. At present, the main disposal methods of sludge biochar include landfill, incineration, etc., among which landfill consumes land and causes secondary pollution, and incineration consumes energy and releases dioxins, nitrogen and sulfur oxides and other pollutants.

At present, domestic waste in my country is mainly disposed of by sanitary landfill technology. The biochemical effluent of leachate (ie leachate, also known as leachate) has been the main secondary pollution source of this technology and has always been concerned by environmental protection practitioners and scholars. Its main pollution indicators For organic matter and ammonia nitrogen. Most domestic waste landfills choose membrane technology to intercept pollutants as the final disposal of landfill leachate (ie, landfill leachate). In addition, the advanced oxidation method is another idea. The catalytic oxidation based on hydroxyl radicals is the most widely used advanced oxidation method. This method has the advantages of non-selectivity to organic pollutants and high efficiency. But there are also obvious shortcomings: first, the storage and transportation of the raw material hydrogen peroxide is relatively difficult; second, this method has little effect on ammonia nitrogen. Persulfate (S ₂ O ₈ ^2- ) is cheaper than hydrogen peroxide and is easy to store and transport. The sulfate radicals generated by suitable activation methods have strong oxidizing properties and can oxidize ammonia nitrogen. Advanced oxidation technology has received a lot of research in the past five years. It is of high academic significance and engineering practical application significance to study high-efficiency and low-cost sulfate radical catalytic oxidation system catalysts.

In the prior art, the manufacturing process of the heterogeneous catalyst based on the advanced sulfate radical oxidation technology is complicated and the cost is high. For example, bimetallic or multimetal heterogeneous catalysts prepared by co-precipitation of various metal salt solutions and active metal-activated carbon or active metal-biochar heterogeneous catalysts prepared by metal salt solution impregnation method, these technical processes not only require many The active components are fixed on the inert support by co-precipitation or impregnation and sintering, and the obtained heterogeneous catalysts generally have high pH selectivity, which limits the application of these heterogeneous catalysts.

SUMMARY OF THE INVENTION

For the above defects or improvement needs of the prior art, the object of the present invention is to provide a method for sludge biochar to catalyze persulfate degradation of organic matter or ammonia nitrogen in sewage, wherein by the preparation conditions of its key sludge biochar ( Such as sludge pre-treatment, pyrolysis temperature, pyrolysis environment), and the application ratio of sludge biochar and persulfate, etc., compared with the existing technology, it can effectively solve the problem of advanced oxidation technology based on sulfate radicals. The production process of heterogeneous catalysts is complex and the cost is high, and through the interaction of the sludge biochar and persulfate, the persulfate can be efficiently based on sulfuric acid under the catalysis of the sludge biochar. Radical radical catalytic oxidation degrades organic matter (such as p-chlorophenol) and/or ammonia nitrogen in sewage (especially high-concentration sewage, such as landfill leachate), effectively solving the problem of organic pollutants in sewage and ammonia nitrogen pollution, and the degradation effect is good In addition, the method of utilizing sludge biochar to catalyze persulfate to degrade pollutants in sewage in the present invention also provides a sludge treatment approach with good uses for the current situation that a large amount of sludge cannot be properly disposed of, which is beneficial for sludge disposal. Environmentally friendly reuse provides an effective and harmless disposal approach.

In order to achieve the above object, according to the present invention, a method for degrading organic matter or ammonia nitrogen in sewage by sludge biochar catalyzing persulfate is provided, which is characterized in that, comprising the following steps:

(1) Preparation of sludge biochar:

Drying the sludge to obtain dry sludge; then, pyrolyzing the dry sludge at 300° C. to 500° C. for at least 2 hours in a nitrogen environment, and cooling to obtain sludge biochar;

(2) Sludge biochar catalyzes persulfate degradation of sewage:

The sludge biochar and persulfate obtained in the step (1) are put into sewage to degrade organic matter or ammonia nitrogen in the sewage.

As a further preference of the present invention, in the step (2),

When the sewage is the biochemical effluent of landfill leachate, the ratio of the sludge biochar to the sewage is 5g/L, and the ratio of the persulfate to the sewage is 18.75mmol/L. L～150mmol/L;

When the sewage is a solution of p-chlorophenol, the ratio of the sludge biochar to the sewage is 0.2g/L to 1.2g/L, and the ratio of the persulfate to the sewage is 0.2g/L to 1.2g/L. The ratio is 0.74 mmol/L to 18.5 mmol/L.

As a further preference of the present invention, in the step (1), the nitrogen environment is a flowing nitrogen environment, and preferably, the flow rate of the nitrogen is 1 L/min.

As a further preference of the present invention, in the step (1), the temperature of the heat preservation treatment is 400°C; the drying in the step (1) is drying at 105°C for 24 hours.

As a further preference of the present invention, the specific surface area of the sludge biochar obtained in the step (1) is 46.98m ² /g～80.25m ² /g.

As a further preference of the present invention, the sludge biochar obtained in the step (1) is also subjected to grinding treatment to obtain sludge biochar with a mesh number greater than 200 meshes.

As a further preference of the present invention, in the step (2), when the sewage is the biochemical effluent of landfill leachate, the ratio of the sludge biochar to be put in and the sewage is 5 g/L. The ratio of the persulfate to the sewage is 150 mmol/L.

As a further preference of the present invention, in the step (2), when the sewage is a p-chlorophenol solution, the ratio of the sludge biochar to be put in and the sewage is 1.0 g/L, and The ratio of the persulfate to the sewage is 1.85mmol/L.

As a further preference of the present invention, in the step (2), the persulfate is Na ₂ S ₂ O ₈ .

The above technical solution conceived by the present invention, compared with the prior art, degrades sewage by directly utilizing transition metal elements in sludge (such as municipal sludge, sludge in domestic sewage plants, etc.) to activate peroxodisulfate Organic matter or ammonia nitrogen, the preparation is simple and convenient, no traditional methods such as multi-step co-precipitation or impregnation and sintering are required, and there is no need to use additional carriers (such as activated carbon, biochar, etc.) to support transition metals, only the "one-step method of pyrolysis of sludge" ” to prepare a heterogeneous catalyst (ie, sludge biochar). At the same time, the present invention improves the key sludge treatment conditions in the sludge biochar preparation method, such as sludge pretreatment, pyrolysis temperature, pyrolysis environment, etc., so that the prepared sludge biochar has a good ratio. surface area, and then by using the sludge biochar in combination with persulfate, the persulfate can efficiently degrade organic matter and/or ammonia nitrogen in sewage based on the catalytic oxidation of sulfate radicals under the catalytic action of the sludge biochar , suitable for high-concentration organic wastewater or ammonia nitrogen wastewater treatment, the method is simple and easy, and the degradation effect is good.

The sludge used in the present invention can come from municipal sludge such as municipal sewage treatment plants, and is prepared by uniform heating and pyrolysis under saturated nitrogen environment to prepare sludge biochar; after the sludge biochar is crushed and ground, it is mixed with persulfuric acid The salt is added to the organic model compound and leachate together, and stirred to oxidatively degrade organic pollutants (model compounds or total organic carbon TOC) and ammonia nitrogen; the sludge biochar is in high concentration of organic model compounds and leachate. The liquid has a uniform removal rate of organic pollutants and ammonia nitrogen. The invention integrates the degradation and removal effects of organic pollutants and ammonia nitrogen in sewage, the specific surface area and catalytic effect of sludge biochar, as well as the energy consumption and nitrogen consumption of pyrolysis in the preparation process of sludge biochar. The optimum pyrolysis temperature, and the optimum ratio of sludge biochar to persulfate. The sludge biochar/persulfate system in the present invention has obvious catalytic oxidation effect on organic pollutants and ammonia nitrogen, and the catalytic oxidation hardly depends on the pH value, and is suitable for various types of sewage; the sludge biochar prepared by the present invention The catalytically active components on the surface of the carbon are mainly transition metal elements (such as amorphous iron) and oxygen-containing functional groups. The catalytic oxidation is a free radical oxidation reaction and sulfate radicals dominate. It can be seen that the sludge biochar is based on sulfate radicals. The field of advanced oxidation of free radicals has a good application prospect as a heterogeneous catalyst with high practical value.

The sludge biochar in the present invention is obtained by thermally treating the dried sludge in a nitrogen environment (especially a flowing nitrogen environment, the flow rate of nitrogen is preferably 1L/min) at 300°C to 500°C for at least 2 hours The sludge is pyrolyzed to generate sludge biochar. The sludge biochar has a high specific surface area (specific surface area is 46.98m ² /g～80.25m ² /g), surface functional groups (especially oxygen-containing functional groups) Abundant and with more transition metals, it can be used as a heterogeneous catalyst for advanced oxidation; then the sludge biochar is combined with persulfate, so that persulfate can be highly efficient under the catalysis of the sludge biochar based on the catalytic oxidation of sulfate radicals to degrade organic matter and/or ammonia nitrogen in sewage. Using the "one-step method" in the present invention to use the sludge biochar prepared by pyrolysis of sludge as a catalyst can avoid the consumption of chemical agents and the pH selectivity of the catalytic system, and the catalytic application range is also wider. Taking the municipal sludge in the domestic sewage plant as an example, the general domestic sewage plant needs to put ferrous salt in the phosphorus removal, so the iron content in the sludge will be high; and in the present invention, the sludge is anaerobic pyrolysis to prepare biochar It can retain its ferrous iron content to the greatest extent and make it an active ingredient in the persulfate activator, which can not only avoid the input of other chemicals, but also can make the sludge biochar content due to the one-step pyrolysis method. The combination of iron is more stable, so that the iron element in the sludge biochar is more stable under different pH environments, and the selectivity to pH environment is small.

The method of using sludge biochar to catalyze persulfate to degrade pollutants in sewage in the present invention also provides a sludge treatment approach with good uses for the current situation that a large amount of sludge cannot be properly disposed of, and is environmentally friendly and reused for sludge. Provides an effective and harmless disposal method. Compared with the current mainstream preparation method of activated carbon (such as commercial activated carbon), the preparation method of sludge biochar in the present invention can greatly reduce the cost; the method of utilizing the sludge biochar to catalyze persulfate to degrade pollutants in sewage, It can effectively degrade organic pollutants and ammonia nitrogen pollutants in sewage, and has the double added value of sewage treatment and municipal sludge disposal. In addition, because the sludge biochar in the present invention has high stability after high temperature pyrolysis, it can be directly landfilled after use, which greatly reduces the cost of sludge disposal.

Description of drawings

FIG. 1 is a schematic flow diagram of the method for the sludge biochar to catalyze persulfate degradation of organic matter or ammonia nitrogen in sewage according to the present invention.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

Example

The production steps of the sludge biochar adopted in the present invention are:

(1) Dry municipal sludge with a moisture content of about 80% at 105°C for 24 hours;

(2) Put the dried sludge into the muffle furnace which was evacuated in advance, then filled with nitrogen to atmospheric pressure and kept closed, and heated to 300, 350, 400, 450, 500 °C at a rate of 10 °C/min. , and continued the temperature for 2 hours, naturally cooled to 25 °C, and then opened the furnace and taken out. During the firing process, 1L/min nitrogen was uniformly introduced into the muffle furnace until the temperature in the furnace dropped to 25 °C, and the exhaust gas was taken over to the exhaust gas absorption device;

(3) Grind the taken out biochar through a 200-mesh sieve (that is, the particle size of the sludge biochar should be finer than 200 mesh), rinse with distilled water three times, and dry at 105° C. for later use. The specific surface areas of the fired biochar are: 46.98m ² /g, 54.73m ² /g, 75.34m ² /g, 77.42m ² /g, 80.25m ² /g (corresponding to 300°C, 350°C, 400 ℃, 450℃, 500℃); considering the electricity consumption and nitrogen consumption in the pyrolysis process, sludge biochar at 400℃ was selected as the heterogeneous catalyst.

The present invention selects p-chlorophenol (molecular formula: C ₆ H ₅ ClO) as the model compound of organic pollutants, and the biochemical effluent of leachate from the sanitary landfill of domestic waste (Wuhan Chenjiachong sanitary landfill of domestic waste, 114.40° east longitude, 30.52 north latitude) °) As the actual wastewater, the catalytic oxidative degradation and removal rates of sludge biochar and persulfate to p-chlorophenol and TOC and ammonia nitrogen in leachate were observed at 25 °C, respectively.

The p-chlorophenol solution with a concentration of 5 ppm was selected as the organic model compound, and the sludge biomaterials at doses of 0.2 g/L, 0.4 g/L, 0.6 g/L, 0.8 g/L, 1.0 g/L and 1.2 g/L were selected respectively. Carbon was used as a heterogeneous catalyst, and [Na ₂ S ₂ O ₈ ] ₀ = 0.74 mM, 1.48 mM, 1.85 mM, 3.7 mM, 7.4 mM, 11.1 mM, 14.8 mM and 18.5 mM (can be added by adding the corresponding [Na 2 S 2 O 8 ] 0 ₂ S ₂ O ₈ amount, obtained after stirring), pH=6.3, temperature 25°C, the results show that 1.0g/L sludge biochar, 1.85mM Na ₂ S ₂ O ₈ system, p-chlorophenol is removed within 100 minutes reached 90.8%.

The selected sludge biochar dosage is 1 g/L, [Na ₂ S ₂ O ₈ ] ₀ =1.85mM, and the temperature is 25°C. The removal rate of p-chlorophenol was tested at pH=3.0, 4.2, 5.2, 6.3, 7.3, 8.4 and 9.4, respectively. The results show that the alkaline conditions have a slight improvement in the removal rate (about 4% higher than that of the acidic conditions), but the difference is small, so it can be considered that the catalytic oxidation system does not depend on pH value.

Catalytic oxidation effect of sludge biochar on TOC and ammonia nitrogen in leachate of domestic waste landfill: without pH adjustment (sludge biochar with a dosage of 5 g/L was selected as the heterogeneous catalyst, [Na ₂ S ₂ O ₈ ] ₀ = 18.75mM, 37.5mM, 75mM and 150mM, test the removal rate of TOC and ammonia nitrogen. The results show that 5g/L sludge biochar, [Na ₂ S ₂ O ₈ ] ₀ = 150Mm system can remove TOC and ammonia within 12 hours. The removal rates of ammonia nitrogen were about 53% and 98%, respectively; and the catalytic oxidation system was not pH-dependent.

The main pollutant parameters of landfill leachate are shown in Table 1.

Table 1 Main pollutant parameters of landfill leachate biochemical effluent

The composition and proportion of the main elements on the surface of the sludge biochar prepared in the above-mentioned examples are shown in Table 2.

Table 2 Composition of main elements on the surface of sludge biochar (in terms of atomic weight)

The sludge biochar was analyzed by SEM-EDS, XRD and XPS, and it was found that the surface of sludge biochar contained amorphous iron with uneven distribution, and the bivalent and trivalent coexisted. The main reason for the catalytic activity of sulfate; FTIR analysis of sludge biochar found that the surface of sludge biochar contains a large number of oxygen-containing functional groups, which also contribute to the activation of persulfate; The free radical scavenger was added to the reaction system for EPR analysis, and it was found that the catalytic oxidation reaction was a free radical reaction, and sulfate radical was the main free radical. contribute.

It can be seen that the main active components of the sludge biochar in the present invention as persulfate activator are amorphous iron and surface oxygen-containing functional groups, and the catalytic oxidation is a free radical reaction, and sulfate radicals dominate; Charcoal and persulfate are put into the sewage at the same time, and under the catalytic action of the sludge biochar, the persulfate can oxidatively degrade organic pollutants and/or ammonia nitrogen in the sewage based on the catalytic oxidation of sulfate radicals.

The present invention utilizes the original transition metal elements (especially iron elements) of sludge (such as municipal sludge, etc.) to form active sites on the surface of sludge biochar, and avoids multi-step co-precipitation or impregnation and sintering on the carbon framework. This "one-step method" is convenient for preparing sludge biochar for persulfate activation, which is economical, applicable and stable, and effectively provides a high value-added reuse method of sludge.

Those skilled in the art can easily understand that the above are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, etc., All should be included within the protection scope of the present invention.

Claims (8)

1. A method for degrading organic matters or ammonia nitrogen in sewage by catalyzing persulfate through sludge biochar is characterized by comprising the following steps:

(1) preparing sludge biochar:

drying the sludge to obtain dry sludge; then, pyrolyzing the dry sludge at 300-500 ℃ for at least 2 hours in a nitrogen environment, and cooling to obtain sludge biochar; wherein the sludge is municipal sludge or sludge in a domestic sewage plant; the sludge biochar can be prepared by a one-step pyrolysis method only by adopting dry sludge without adopting multi-step coprecipitation or impregnation sintering and additionally adopting a carrier to load transition metal;

(2) degrading sewage by catalyzing persulfate through sludge biochar:

putting the sludge biochar and persulfate obtained in the step (1) into sewage, using amorphous iron and surface oxygen-containing functional groups contained in the sludge biochar to enable the sludge biochar to be used as a persulfate activator, and oxidizing and degrading organic matters or ammonia nitrogen in the sewage based on sulfate radical catalytic oxidation under the catalytic action of the sludge biochar by persulfate;

the specific surface area of the sludge biochar obtained in the step (1) is 46.98m²/g～80.25m²/g；

In the step (2), the step (c),

when the sewage is the biochemical effluent of the landfill leachate, the ratio of the added sludge biochar to the sewage is 5g/L, and the ratio of the added persulfate to the sewage is 18.75 mmol/L-150 mmol/L;

when the sewage is a parachlorophenol solution, the ratio of the added sludge biochar to the sewage is 0.2-1.2 g/L, and the ratio of the added persulfate to the sewage is 0.74-18.5 mmol/L.

2. The method for degrading organic matters or ammonia nitrogen in sewage by catalyzing persulfate through sludge biochar as claimed in claim 1, wherein in the step (1), the nitrogen environment is a flowing nitrogen environment.

3. The method for degrading organic matters or ammonia nitrogen in sewage by catalyzing persulfate through sludge biochar as claimed in claim 2, wherein the flow rate of the nitrogen is 1L/min.

4. The method for degrading organic matters or ammonia nitrogen in sewage by catalyzing persulfate through sludge biochar as claimed in claim 1, wherein in the step (1), the temperature of the heat preservation treatment is 400 ℃; the drying in the step (1) is drying at 105 ℃ for 24 h.

5. The method for degrading organic matters or ammonia nitrogen in sewage by catalyzing persulfate through the sludge biochar as claimed in claim 1, wherein the sludge biochar obtained in the step (1) is further subjected to grinding treatment to obtain the sludge biochar with the mesh number of more than 200 meshes.

6. The method for degrading organic matters or ammonia nitrogen in sewage by catalyzing persulfate through sludge biochar as claimed in claim 1, wherein in the step (2), when the sewage is landfill leachate biochemical effluent, the ratio of the sludge biochar to the sewage is 5g/L, and the ratio of the persulfate to the sewage is 150 mmol/L.

7. The method for degrading organic matters or ammonia nitrogen in sewage by catalyzing persulfate through sludge biochar as claimed in claim 1, wherein in the step (2), when the sewage is a p-chlorophenol solution, the ratio of the added sludge biochar to the sewage is 1.0g/L, and the ratio of the added persulfate to the sewage is 1.85 mmol/L.

8. The method for degrading organic matters or ammonia nitrogen in sewage by using the sludge biochar to catalyze persulfate according to claim 1, wherein in the step (2), the persulfate is Na₂S₂O₈。

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