Composite catalyst as well as preparation method and application thereof in sludge treatment

Abstract

The invention discloses a composite catalyst as well as a preparation method and application thereof in sludge treatment, and belongs to the technical field of sludge treatment and environmental protection. The iron-carbon nano composite catalyst is synthesized by taking iron nitrate nonahydrate, antibiotic mushroom dregs and melamine as precursors. On one hand, the obtained catalyst can activate ammonium persulfate to generate free radicals to destroy the water locking structure of sludge, enhance the hydrophobicity of the sludge and further enhance the dewatering effect, on the other hand, Fe species in the composite catalyst activate ammonium persulfate to form Fe < 3 + >, and Fe < 3 + > is hydrolyzed to generate ferric hydroxide colloid which can adsorb sludge particles and neutralize surface charges, so that the dewatering effect is improved. Therefore, repulsive force among particles is reduced, floc aggregation is promoted, and the dehydration effect is enhanced. And the advanced oxidation process of catalyzing ammonium persulfate by the iron-carbon nano composite catalyst also realizes removal of antibiotic resistance genes in the sludge.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of sludge treatment and environmental protection, and particularly relates to a composite catalyst, a preparation method thereof and application of the composite catalyst in sludge treatment. BACKGROUND

[0002] Activated sludge technology is widely used in wastewater treatment plants around the world for treating municipal wastewater, which produces a large amount of sewage sludge. Developing effective strategies to remove harmful pollutants in sludge and improve its dewatering performance is a major challenge for recycling sewage sludge to land. Among these harmful pollutants, antibiotic resistance genes (ARGs) can be widely detected in sewage sludge due to their rapid spread through mobile genetic elements (MGEs), which will exacerbate the prevalence of antibiotic resistance. Therefore, it is crucial to control the release of resistance genes during sludge treatment.

[0003] The current mainstream sludge dewatering technology mainly uses mechanical dewatering, but the mechanical dewatering process can only separate free water and part of the bound water, and a considerable part of ARGs still exists in the dewatered sludge cake. These resistance genes can quickly spread in the soil environment after the sludge cake is applied to the land. In addition, the resistance genes in the dewatering filtrate have great potential to spread into the water environment through the transformation process. Therefore, it is necessary to develop new efficient and low-cost sludge dewatering technology and simultaneously remove antibiotic resistance genes in sludge.

[0004] Antibiotic residue is a solid waste produced in the drug extraction process of antibiotic production, which is complex in composition and contains not only incomplete extraction of antibiotics, metabolites, unused medium components and bacterial residue, but also rich nitrogen elements. Because it contains residual antibiotics and toxic substances, it is listed as hazardous waste. If not properly disposed of, the antibiotics in it may spread through soil and water, induce drug-resistant bacteria and pollute the food chain. At the same time, if the nitrogen elements are not effectively treated, they may also cause environmental problems such as water eutrophication, which threatens the ecology and human health. At present, it is mainly treated by incineration, fertilizer, feed, anaerobic digestion, pyrolysis and fertilizer preparation, but all of them face challenges such as cost, secondary pollution or residual risk, and further safe and efficient harmless and resourceful technologies need to be developed. SUMMARY

[0005] The purpose of the present application is to provide a composite catalyst, a preparation method thereof and application of the composite catalyst in sludge treatment. The iron-carbon nanocomposite catalyst is synthesized by taking ferric nitrate nonahydrate, antibiotic residue and melamine as precursors. The obtained composite catalyst can activate ammonium persulfate to generate free radicals to destroy the water-locking structure of sludge, enhance the hydrophobicity of sludge and thus enhance the dewatering effect. On the other hand, the Fe species in the composite catalyst activates ammonium persulfate to form Fe 3+ , Fe3+ The hydrolysis generates iron hydroxide colloid which can adsorb sludge particles, neutralize surface charge, thereby reducing inter-particle repulsive force, promoting flocculation aggregation, and further enhancing dewatering effect. The composite catalyst catalyzes the advanced oxidation process of ammonium persulfate, and also realizes the removal of antibiotic resistance genes in sludge.

[0006] To achieve the above object, the present application provides the following technical scheme:

[0007] One of the technical schemes of the present application: a preparation method of a composite catalyst is provided, comprising the following steps:

[0008] Iron nitrate nonahydrate, antibiotic residue and melamine are added to hydrochloric acid ethanol, mechanically stirred, then dried, and calcined at 700-1100 DEG C under inert atmosphere, the calcined product is pickled, dried and ground to obtain the composite catalyst.

[0009] Preferably, the volume fraction of concentrated hydrochloric acid in the hydrochloric acid ethanol is 2%; the amount ratio of the iron nitrate nonahydrate, antibiotic residue, melamine and hydrochloric acid ethanol is 0.1-1g:0.5-2g:1-3g:50-70mL.

[0010] The concentrated hydrochloric acid used in the present application is a commonly used commercially available concentrated hydrochloric acid reagent (mass fraction of hydrochloric acid is 36-38%).

[0011] Preferably, the stirring speed of the mechanical stirring is 500-700 rpm, and the time is 3-8 h.

[0012] Preferably, the temperature of the drying after the mechanical stirring is 60 DEG C, and the time is 12-24 h.

[0013] Preferably, the heating rate of the high-temperature calcination is 2.5-8 DEG C / min, and the holding time is 2 h.

[0014] Preferably, the acid pickling uses 6mol / L hydrochloric acid as the acid solution.

[0015] Preferably, the temperature of the drying after the acid pickling is 60 DEG C, and the time is 12 h.

[0016] Preferably, the grinding is ground to pass through a 100 mesh sieve.

[0017] The second technical scheme of the present application: a composite catalyst prepared according to the preparation method of the above composite catalyst is provided.

[0018] The third technical scheme of the present application: the application of the above composite catalyst in sludge treatment is provided, comprising the following steps:

[0019] The composite catalyst and the ammonium persulfate solution are added into sludge, and stirring reaction is carried out to realize sludge dewatering and synchronous removal of antibiotic resistance genes in the sludge.

[0020] Preferably, the adding amount of the composite catalyst is 8-12% of the mass of the sludge; the concentration of the ammonium persulfate solution is 0.75-1.25 mol / L; and the adding amount of the ammonium persulfate solution is 0.1-0.3 mL / g of the sludge.

[0021] Preferably, the stirring rate of the stirring reaction is 100-300 rpm, and the time is 20-60 min.

[0022] Preferably, the ammonium persulfate in the ammonium persulfate solution is obtained by electrolysis of an electrolyte containing ammonium sulfate and sulfuric acid.

[0023] More preferably, the concentration of sodium sulfate and sulfuric acid in the electrolyte containing ammonium sulfate and sulfuric acid is 0.5-1.25 mol / L; the current density of the electrolysis is 0.5-1 A / m 2 , the voltage is 5-10 V, and the time is 4-6 h.

[0024] The beneficial technical effects of the present application are as follows:

[0025] 1. The present application realizes rapid dewatering of sludge by using extremely simple components and means, improves the dewatering capacity of sludge, and reduces the transportation pressure of sludge.

[0026] 2. The present application realizes removal of antibiotic resistance genes in sludge by using extremely simple components and means, and significantly reduces environmental pressure.

[0027] 3. The sludge treatment method of the present application can realize sludge dewatering and pollutant removal simultaneously within 1 h, and reduces the treatment time and cost.

[0028] 4. The present application realizes sludge dewatering and harmless treatment, and also realizes high-value utilization of antibiotic residue, and provides an innovative solution for developing an economic and efficient green catalytic material system. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The change of the moisture content of sludge before and after treatment in Example 1.

[0030] Figure 2 The change of the capillary suction time of sludge before and after treatment in Example 1.

[0031] Figure 3 The removal rate of antibiotic resistance genes in sludge after treatment in Example 1.

[0032] Figure 4The changes in sludge capillary suction time after treatment in Examples 1, 2, 3, and 4 are shown.

[0033] Figure 5 The changes in sludge capillary suction time after treatment in Examples 1, 5, 6, 7, and 8 are shown. Detailed Implementation

[0034] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0035] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0036] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0037] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this invention.

[0038] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0039] Unless otherwise specified, "room temperature" in this invention refers to a temperature of 20±10℃.

[0040] The sludge used in this embodiment of the invention was taken from Jinan City, Shandong Province, and other raw materials were all conventional commercially available products.

[0041] Example 1

[0042] A method for dewatering sludge and simultaneously removing antibiotic resistance genes from sludge:

[0043] (1) Using a solution containing 0.75 mol / L ammonium sulfate and 0.75 mol / L sulfuric acid as the electrolyte, electrolysis was carried out in an electrolytic cell with platinum as the anode and graphite as the cathode, at a current density of 1 A / m 2, the white ammonium persulfate crystal was obtained after being extracted and filtered, washed with ice water for 3 times, and dried at 55 DEG C under vacuum.

[0044] (2) 0.5 g of Fe(NO3)3·9H2O, 1 g of antibiotic residue, and 2 g of melamine were added into 60 mL of hydrochloric acid ethanol (containing 2 vol.% concentrated hydrochloric acid), and mechanically stirred at a stirring speed of 500 rpm for 6 h, then dried at 60 DEG C for 12 h, and then heated to 900 DEG C at a heating rate of 5 DEG C / min under an argon atmosphere and calcined for 2 h, and the calcined product was washed with a 6 mol / L hydrochloric acid solution and dried at 60 DEG C for 12 h, and then the product was ground and sieved through a 100 mesh sieve to obtain a composite catalyst.

[0045] (3) The pure ammonium persulfate crystal obtained in step (1) was dissolved in water to prepare a 0.75 mol / L ammonium persulfate solution.

[0046] (4) 1 g of the composite catalyst obtained in step (2) and 2 mL of the ammonium persulfate solution obtained in step (3) were added into 10 g of sludge, and the sludge was stirred at 200 rpm at room temperature for 40 min to complete the dewatering and removal of antibiotic resistance genes.

[0047] The water content of the sludge treated according to the method of Example 1 was determined, and the sludge before treatment was used as a control, and the results are shown in Figure 1 .

[0048] As can be seen from Figure 1 , the water content of the sludge is reduced by 29.95 wt.% after being treated according to the method of Example 1, indicating that the system can achieve rapid dewatering of the sludge.

[0049] The capillary suction time (CST) of the sludge treated according to the method of Example 1 was determined, and the sludge before treatment was used as a control, and the results are shown in Figure 2 .

[0050] As can be seen from Figure 2 , the capillary suction time of the sludge is reduced by 13 s after being treated by the composite catalyst activated ammonium persulfate, indicating that the method provided in the present application has good dewatering effect on the sludge.

[0051] The concentration of antibiotic resistance genes in the sludge treated according to the method of Example 1 was determined, and the sludge before treatment was used as a control, and the results are shown in Figure 3 .

[0052] As can be seen from Figure 3It can be seen that after the treatment according to the method of Example 1, the beta-lactam (blaTEM) resistance gene in the sludge is removed by more than 99%, the tetracycline (tet A) resistance gene is eliminated by 97.4%, the sulfonamide (sul1) resistance gene is eliminated by 85.9%, and the resistance gene genetic element (intI 1) is also removed by 67.3%. It shows that the method provided by the application can efficiently remove various antibiotic resistance genes in the sludge, and can effectively reduce the spread of the resistance genes.

[0053] Example 2

[0054] The difference from Example 1 is only that:

[0055] In step (3), the concentration of the ammonium persulfate aqueous solution is 0 mol / L, and the rest of the amount, operation and Example 1 are completely the same.

[0056] Example 3

[0057] The difference from Example 1 is only that:

[0058] In step (3), the concentration of the ammonium persulfate aqueous solution is 0.3 mol / L, and the rest of the amount, operation and Example 1 are completely the same.

[0059] Example 4

[0060] The difference from Example 1 is only that:

[0061] In step (3), the concentration of the ammonium persulfate aqueous solution is 1.25 mol / L, and the rest of the amount, operation and Example 1 are completely the same.

[0062] The capillary suction time of the sludge treated in Example 1, 2, 3 and 4 is determined, and the sludge before treatment is used as a control, and the results are shown in Figure 4 .

[0063] As shown in Figure 4 , the capillary suction time of the sludge increases first and then decreases with the increase of the concentration of ammonium persulfate. This is because a lower concentration of ammonium persulfate will destroy the stability of the original sludge floc, produce more fine particles, increase the viscosity and filtration resistance of the filtrate, and cause the CST to rise. While a higher concentration of ammonium persulfate will cause the hydrophobicity of the sludge to increase, and it is easier to aggregate to form dense flocs, which improves the dewatering performance.

[0064] Example 5

[0065] The difference from Example 1 is only that:

[0066] In step (4), the amount of the composite catalyst added is 0 g, and the rest of the amount, operation and Example 1 are completely the same.

[0067] Example 6

[0068] The only difference from Example 1 is that:

[0069] In step (4), the amount of composite catalyst added is 0.4g, and the remaining amounts and operations are exactly the same as in Example 1.

[0070] Example 7

[0071] The only difference from Example 1 is that:

[0072] In step (4), the amount of composite catalyst added is 0.8g, and the remaining amounts and operations are exactly the same as in Example 1.

[0073] Example 8

[0074] The only difference from Example 1 is that:

[0075] In step (4), the amount of composite catalyst added is 1.2g, and the remaining amounts and operations are exactly the same as in Example 1.

[0076] The capillary suction time of the sludge after treatment in Examples 1, 5, 6, 7, and 8 was measured, with the sludge before treatment serving as a control. The results are shown in the figure. Figure 5 .

[0077] like Figure 5 As shown, the capillary suction time of sludge initially decreases and then increases with the increase of the composite catalyst mass. This is because excessive catalytic material can lead to over-hardening of the sludge, clogging the filter paper pores and causing the CST to rise.

[0078] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a composite catalyst, characterized by, The method comprises the following steps: Iron nitrate nonahydrate, antibiotic bacteria residue and melamine are added into hydrochloric acid alcohol, and then mechanically stirred, dried, calcined at 700-1100 DEG C under inert atmosphere, acid washed, dried and ground to obtain the composite catalyst.

2. The method of claim 1, wherein the composite catalyst is prepared by the steps of: The volume fraction of concentrated hydrochloric acid in the hydrochloric acid alcohol is 2%, and the ratio of the iron nitrate nonahydrate, antibiotic bacteria residue, melamine and hydrochloric acid alcohol is 0.1-1 g:0.5-2 g:1-3 g:50-70 mL.

3. The method of claim 1, wherein the composite catalyst is prepared by the steps of: The stirring speed of the mechanical stirring is 500-700 rpm, and the stirring time is 3-8 h; and / or, the drying temperature after the mechanical stirring is 60 DEG C, and the drying time is 12-24 h; and / or, the heating rate of the high-temperature calcination is 2.5-8 DEG C / min, and the holding time is 2 h.

4. The method of claim 1, wherein the composite catalyst is prepared by the steps of: The acid used in the acid washing is 6 mol / L hydrochloric acid; and / or, the drying temperature after the acid washing is 60 DEG C, and the drying time is 12 h; and / or, the grinding is to pass through a 100-mesh sieve. 5.A composite catalyst prepared by the method according to any one of claims 1-4.

6. Use of the composite catalyst according to claim 5 for sludge treatment, characterized in that, The method comprises the following steps: The composite catalyst and ammonium persulfate solution are added into sludge, and then stirred and reacted to realize sludge dewatering and simultaneous removal of antibiotic resistance genes in the sludge.

7. Use according to claim 6, characterized in that, The adding amount of the composite catalyst is 8-12% of the mass of the sludge; the concentration of the ammonium persulfate solution is 0.75-1.25 mol / L; and the adding amount of the ammonium persulfate solution is 0.1-0.3 mL / g of the sludge.

8. Use according to claim 6, characterized in that, The stirring rate of the stirring reaction is 100-300 rpm, and the stirring time is 20-60 min.

9. Use according to claim 6, characterized in that, The ammonium persulfate in the ammonium persulfate solution is obtained by electrolysis of an electrolyte containing ammonium sulfate and sulfuric acid.

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