Siderite modified sulfur microporous foaming material and preparation and application method thereof

Abstract

The application discloses a sintered modification sulfur microporous foaming material and a preparation and application method thereof, and belongs to the field of environmental protection materials and sewage treatment technologies.The application first applies the carbon dioxide foaming technology under the high pressure or even supercritical state to liquid sulfur to prepare the sintered modification sulfur microporous foaming material.The material has a large number of uniform microporous structures, can improve the carbon source utilization rate of sintered modification, can greatly increase the contact area of the filler and sewage, stably and efficiently removes pollutants, and provides technical support for the sulfur autotrophic denitrification technology in the field of sewage treatment.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of environmental protection materials and sewage treatment, and more particularly relates to a siderite modified sulfur microporous foaming material and a preparation and application method thereof. BACKGROUND

[0002] Nitrate and phosphate are the most common pollutants in water. High nitrate concentration in drinking water can pose a considerable risk to health. Higher concentrations of nitrate and phosphate in water can promote the growth of algae in water, leading to eutrophication and posing a serious threat to aquatic ecosystems. In order to control water eutrophication, the nitrogen and phosphorus discharge standards of sewage in China are becoming more and more stringent.

[0003] Sulfur autotrophic denitrification refers to the process in which sulfur autotrophic denitrifying bacteria use reduced sulfur as an electron donor and inorganic carbon source as a carbon source to reduce nitrate nitrogen in water into nitrogen. Due to the advantages of no need for external organic carbon source, less sludge production, and low treatment cost, sulfur autotrophic denitrification has gradually become a research hotspot in the field of denitrification and is increasingly becoming a technology for low-cost and efficient removal of nutrients in water. When elemental sulfur is used as an electron donor and siderite (FeCO3) is used as an inorganic carbon source in the process of sulfur autotrophic denitrification, a sulfur-siderite autotrophic denitrification (SSAD) system is formed. Siderite not only provides inorganic carbon source and buffers pH, but also uses released iron ions and their precipitates and other products to remove phosphorus, achieving the effect of simultaneous phosphorus removal.

[0004] After searching, it was found that a patent entitled "Denitrification and phosphorus removal material based on siderite and use method thereof" with the application number 201410063868.6 and the application date of February 25, 2014 discloses the use of iron-oxidizing bacteria to reduce nitrate to nitrogen gas using ferrous iron in siderite as an electron donor, and the conversion of ferrous ions to ferric ions. Iron and ferrous particles precipitate with phosphate to remove phosphorus, and siderite plays an important role as a carbon source. This patent application points out the value of siderite in the field of denitrification, but due to the low utilization rate of siderite, its effect in biological denitrification has certain limitations and can only be used for the treatment of slightly polluted wastewater.

[0005] In addition, it is found through retrieval that the Chinese invention patent application with the patent name of Siderite / sulfur biological filter and method for simultaneously removing nitrogen and phosphorus in water by using the same, application number 201710636553.X and application date July 31, 2017 discloses that sulfur and siderite particles are used as biological filter fillers to achieve the purpose of strengthening the wastewater denitrification process and improve the simultaneous nitrogen and phosphorus removal effect. In the method, the sulfur provides an electron donor for sulfur autotrophic denitrifying bacteria, the siderite acts as an inorganic carbon source to support the autotrophic denitrification reaction and release iron ions to chemically remove phosphorus, so that the simultaneous nitrogen and phosphorus removal is realized in the biological filter. The method has simple structure and is easy to start, and is suitable for the advanced treatment of sewage. However, the method also has some drawbacks, such as the large particle size and small specific surface area of the siderite and sulfur particles, the uneven distribution of the siderite and sulfur, the poor utilization of the electron donor and inorganic carbon source by microorganisms, the large density difference between the siderite particles and sulfur particles, the poor mass transfer of the formed fixed bed and the poor backwashing, which limit the further improvement of the nitrogen and phosphorus removal efficiency. In order to avoid these problems, the Chinese invention patent application with the patent name of Siderite modified sulfur light material and its preparation method and application, application number 201910326682.8 and application date April 23, 2019 discloses that the sulfur and siderite are melted, foamed and granulated to obtain a siderite modified sulfur light material. The material has uniform particles and a large specific surface area, and improves the simultaneous nitrogen and phosphorus removal performance of the SSAD system. However, the material is foamed under normal pressure, and the solubility of the bubbles in the liquid sulfur is very small. The bubbles are mainly dispersed in the liquid sulfur by physical dispersion, and the bubbles are easily broken during the preparation, resulting in large pore size (millimeter level) and uneven distribution, which affects the simultaneous autotrophic denitrification performance. SUMMARY

[0006] 1. PROBLEMS TO BE SOLVED

[0007] In view of the low utilization rate of siderite as a carbon source, the limitations in the field of biological nitrogen removal, and the problems of large pore size and uneven distribution of the siderite modified sulfur light material, the present application provides a siderite modified sulfur microporous foaming material and its preparation and application method. The present application first proposes to use the carbon dioxide foaming technology under high pressure or even supercritical state for foaming liquid sulfur. The prepared siderite modified sulfur microporous foaming material has a large number of uniform pore structures, which not only improves the carbon source utilization rate of siderite, but also greatly increases the contact area of the filler and sewage, stably and efficiently removes pollutants, and provides technical support for the sulfur autotrophic denitrification technology in the field of sewage treatment.

[0008] 2. TECHNICAL SCHEME

[0009] In order to solve the above problems, the technical scheme adopted by the present application is as follows:

[0010] The preparation method of the sinter modified sulfur microporous foaming material of the present application comprises the following steps: melting and mixing sulfur and sinter in a reaction kettle under the temperature condition of 115-180 DEG C, to obtain the melting body of sulfur and sinter; pumping carbon dioxide into the reaction kettle under the pressure condition of 0.5-15 MPa, stirring, and dissolving carbon dioxide in the above-mentioned melting body of sulfur and sinter; pressure relief and cooling forming, to obtain the sinter modified sulfur microporous foaming material.

[0011] Preferably, the supercritical state carbon dioxide is pumped into the reaction kettle under the pressure condition of 7.5-15 MPa.

[0012] Preferably, the sinter acts as a nucleating agent in the preparation process of the microporous foaming material, and the particle size of the sinter is d≤0.15 mm.

[0013] Preferably, the mass ratio between the pumped carbon dioxide and sulfur is 0.0029-0.6400.

[0014] Preferably, the mass ratio between the sulfur and sinter is 10:1-1:3.

[0015] Preferably, the contact time of the carbon dioxide with the melting body is less than 60 min, and the time of pressure relief and cooling forming is less than 5 min.

[0016] Preferably, the cooling forming comprises steel belt granulation, wet granulation or post-solidification broken granulation.

[0017] The sinter modified sulfur microporous foaming material of the present application is prepared by the above-mentioned preparation method of the sinter modified sulfur microporous foaming material, wherein the density of the sinter modified sulfur microporous foaming material is 0.9-2.0 g / cm 3 , the porosity is 10%-70%, and the specific surface area is 30-200 cm 2 / g.

[0018] The sinter modified sulfur microporous foaming material is placed in a sewage treatment reactor or a constructed wetland, so that the sinter modified sulfur microporous foaming material surface is loaded with a biofilm, and the nitrogen, phosphorus and arsenic, antimony, chromium and cadmium pollutants in water are removed through the autotrophic denitrification, chemical precipitation and adsorption of microorganisms; or the sinter modified sulfur microporous foaming material loaded with a biofilm is mixed with soil polluted by sewage, to remove and immobilize the nitrogen, phosphorus and arsenic, antimony, chromium and cadmium pollutants in the soil.

[0019] Preferably, the biofilm contains sulfur autotrophic denitrifying bacteria, the sulfur autotrophic denitrifying bacteria include one or both of Thiobacillus denitrificans and Sulfur oxidizing bacteria; and the attached amount of the sulfur autotrophic denitrifying bacteria on the siderite modified sulfur microporous foaming material is 2.454*10 7 -4.909*10 7 cfu / mm 3 .

[0020] 3. Beneficial effects

[0021] Compared with the prior art, the beneficial effects of the present application are:

[0022] (1) The preparation method of the siderite modified sulfur microporous foaming material of the present application melts and mixes sulfur and siderite powder under high temperature conditions, and then foams the mixture in supercritical CO2 fluid to obtain a microporous lightweight modified material with a pore size of less than 100 μm. Not only is the high mixing of sulfur and siderite powder achieved, but also the material has small, uniformly distributed bubbles and controllable density through high-pressure or supercritical carbon dioxide foaming, which improves the physicochemical and biochemical properties of the material.

[0023] (2) The siderite modified sulfur microporous foaming material of the present application has a density of 0.9-2.0 g / cm 3 , a porosity of 10%-70%, and a specific surface area of 30-200 cm 2 / g. It has good compression resistance, light weight, can independently regulate water pH, has high reaction activity, is easy for microorganisms to adhere, can release electron donors for denitrification, and can effectively improve the utilization rate of carbon sources in siderite. It can be used as a filler for fluidized bed and fixed bed reactors for wastewater treatment.

[0024] (3) The siderite modified sulfur microporous foaming material of the present application is loaded into a fixed bed reactor inoculated with anaerobic sludge for denitrification simulation experiments. Under the condition of a hydraulic retention time of 0.5 h, simulated wastewater containing 40.0±0.5 mg / L NO3 - -N, 3±0.2 mg / L PO4 3- -P is treated, and the final effluent NO3 - -N and PO4 3- -P concentrations are 0.15±0.05 mg / L and 0.2±0.20 mg / L, respectively, which has good application prospects. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a schematic diagram of the device structure for preparing the siderite modified sulfur microporous foaming material of the present application;

[0026] Figure 2a is a diagram showing the microbial denitrification effect of the microporous foam material prepared in Example 1 of the present invention in a batch reactor; Figure 2 b is a SEM image of microorganisms attached to the surface of the microporous foam material prepared in Example 1 of the present invention;

[0027] In the picture:

[0028] 101. Carbon dioxide storage tank; 102. Plunger pump control panel; 103. Pressure monitoring instrument;

[0029] 104. Plunger pump; 201. High-pressure melting vessel; 202. High-pressure melting vessel rotor;

[0030] 203. High-pressure melting vessel venting valve; 300. Computer control system; 310. Computer data transmission pipeline;

[0031] 410. Carbon dioxide transmission pipeline. Detailed Implementation

[0032] The present invention will be further described below with reference to specific embodiments.

[0033] The following detailed description of exemplary embodiments of the invention is taken with reference to the accompanying drawings. Although these exemplary embodiments have been described in sufficient detail to enable those skilled in the art to practice the invention, it should be understood that other embodiments may be implemented and various changes may be made to the invention without departing from the spirit and scope thereof. The more detailed description of embodiments of the invention below is not intended to limit the scope of the claimed invention, but is merely illustrative and does not limit the description of the features and characteristics of the invention, in order to suggest the best mode for carrying out the invention and sufficient to enable those skilled in the art to practice the invention. Therefore, the scope of the invention is defined only by the appended claims.

[0034] like Figure 1 As shown, the preparation method of a siderite-modified sulfur microporous foaming material of the present invention includes the following steps: sulfur and siderite in a mass ratio of 10:1 to 1:3 are placed in a high-pressure melting kettle 201. Carbon dioxide fluid is pumped from a carbon dioxide storage tank 101 into the high-pressure melting kettle 201 through a carbon dioxide delivery pipeline 410 under a pressure of 0.5-15 MPa, preferably 7.5-15 MPa, by a plunger pump 104, so that the material in the kettle is in a high-pressure carbon dioxide or supercritical carbon dioxide fluid atmosphere. The plunger pump control panel 102 is used to adjust and control the plunger pump body, and the pressure monitor 103 is used to monitor the carbon dioxide pressure in the carbon dioxide delivery pipeline 410.

[0035] The computer control system 300 controls the high-pressure melting kettle 201 to melt and mix the material in the kettle at a temperature of 115-180℃ to obtain a melt, and the mixing time is 10-60 min; and the carbon dioxide is dissolved in the melt by stirring of the high-pressure melting kettle rotor 202. The mass ratio of the amount of the carbon dioxide to the sulfur is 0.0029-0.6400. The carbon dioxide is contacted with the melt for less than 60 min, and then depressurized via the high-pressure melting kettle gas release valve 203, and cooled and shaped to obtain the siderite modified sulfur microporous foaming material. The time for depressurizing and cooling and shaping is less than 5 min.

[0036] It should be noted that no nucleating agent is additionally added in the melt of the present application, and the siderite itself can be used as a nucleating agent. The particle size of the siderite is ≤0.15 mm. In addition, the cooling and shaping of the present application includes wet granulation, steel belt granulation or post-solidification crushing granulation; wherein the wet granulation is to drop the foamed microporous melt into water to cool and shape the melt mixture in water; the steel belt granulation is to drop the foamed microporous melt on a steel belt, and the melt is cooled and shaped on the surface of the steel belt by running of the steel belt and contacting with air, so as to realize granulation and shaping; and the post-solidification crushing granulation is to cool and solidify the foamed microporous melt, and crush the melt into particles. The modified microporous foaming material obtained by the preparation method of the present application has controllable density, and the density is 0.7-2.0 g / cm 3 , the porosity is 10%-70%, and the specific surface area is 30-200 cm 2 / g. Compared with the product obtained by high-temperature melting and stirring foaming, the modified microporous foaming material has the characteristics of large specific surface area, light mass, high reactivity, easy microbial adhesion, slow-release electron donor denitrification and iron ion phosphorus removal, etc.

[0037] Under the condition of normal pressure, the gas bubbles are dispersed in the melt by physical stirring, and the solubility of the gas in the melt is low and the distribution is uneven, resulting in uneven pore structure of the obtained material and large bubble pore size (millimeter level), which cannot fully play the advantages of the foaming material. Under high pressure or supercritical state, CO2 has high density similar to liquid and low viscosity close to gas, and has very strong diffusion and permeation capacity, and the foaming material prepared has small pore size and high compressive strength, which can effectively improve the mechanical properties of the material.

[0038] The modified sulfur microporous foaming material of siderite is used for sewage treatment, and the specific treatment method is as follows: the prepared modified sulfur microporous foaming material is filled into a reactor after screening, and anaerobic sludge is inoculated to treat wastewater; specifically, the modified sulfur microporous foaming material of siderite is placed in a sewage treatment reactor or a constructed wetland, and then microorganisms are inoculated, so that the surface of the modified sulfur microporous foaming material of siderite is loaded with a biofilm, nitrogen and phosphorus in water are removed through autotrophic denitrification and chemical precipitation of microorganisms; at the same time, through adsorption, part of arsenic, antimony, chromium and cadmium pollutants can be removed; wherein the sewage treatment reactor comprises a fluidized bed or a fixed bed reactor, the biofilm comprises sulfur autotrophic denitrifying bacteria, the sulfur autotrophic denitrifying bacteria comprise one or both of denitrifying sulfur-oxidizing bacteria and sulfur-oxidizing bacteria, and the amount of sulfur autotrophic denitrifying bacteria attached to the modified sulfur microporous foaming material of siderite is 2.454*10 7 -4.909*10 7 cfu / mm 3 .

[0039] The present application uses sinter as an inorganic carbon source and sulfur as an electron donor to complete the denitrification process, and at the same time, Fe 2+ released by sinter reacts with phosphate to achieve phosphorus removal effect. The specific reaction formula is as follows:

[0040] 5S 0 +6NO3-+2H2O→5SO4 2- +3N2↑+4H +

[0041] H + +FeCO3→Fe 2+ +HCO3 -

[0042] 3Fe 2+ +NO3 - +4H + →3Fe 3+ +NO↑+2H2O

[0043] 3Fe 2+ +2PO4 3- →Fe3(PO4)2↓

[0044] Fe 3+ +PO4 3- →FePO4↓

[0045] The microporous foaming material prepared by the method has the characteristics of small pore size (micron level), large specific surface area, good compression resistance, light mass, self-regulation of water quality pH, high reaction activity, easy microbial adhesion, slow-release electron donor denitrification, and effective improvement of carbon source utilization rate in inorganic minerals, and can be used as a filler for fluidized bed and fixed bed reactors of sewage treatment. Under the denitrification of microorganisms, the filler has good purification effect on pollutants in water, especially total nitrogen. In addition, the preparation method is simple and low in cost.

[0046] Example 1

[0047] The preparation method of the siderite modified sulfur microporous foaming material in this embodiment specifically comprises the following steps:

[0048] Sulfur and siderite are uniformly mixed at a mass ratio of 5:1, high-temperature melting is performed on the mixture at a high temperature of 160 DEG C, a molten body is obtained, CO2 is introduced into the molten body under a pressure of 0.5 MPa, and the CO2 bubbles are uniformly dispersed and dissolved in the molten body after 20 minutes of mixing. Finally, the microporous foaming material is obtained after crushing and granulating the cooled and shaped product. The density of the microporous foaming material is about 1.8 g / cm 3 , the porosity is 26.8%, and the specific surface area is about 45.3 cm 2 / g.

[0049] After the microporous foaming material prepared in this embodiment is crushed, the above-mentioned microporous foaming material 5 cm 3 is placed in a batch reaction container, 50 mL of simulated wastewater containing 28 mg / L of NO3 - -N and 12 mg / L of PO4 3- -P is added to the batch reaction container. Then, 3.5 mL of sulfur autotrophic denitrification bacteria liquid (the volume of the bacteria liquid accounts for 7% of the volume of the wastewater) is added to the batch reaction container, the above-mentioned mixed solution is deoxygenated by nitrogen blowing, and then the denitrification reaction process is carried out after being sealed with a cover. The denitrification reaction is carried out at a constant temperature of 28 DEG C in the dark for 7 days. The adhesion of microorganisms on the surface of the carrier on the 7th day is observed by SEM, and the concentrations of NO3 - -N and PO4 3- -P in the wastewater are detected. The detection conditions are shown in Figs. Figure 2 a and Figure 2 b.

[0050] Example 2

[0051] The basic content of this embodiment is the same as that of Example 1, except that the preparation method of the siderite modified sulfur microporous foaming material in this embodiment specifically comprises the following steps:

[0052] Sulfur and siderite are mixed uniformly at a mass ratio of 5:1, high-temperature melting is performed on the mixture at a high temperature of 160°C to obtain a molten body; then supercritical CO2 fluid is introduced into the molten body at a pressure of 7.5 MPa, and mixed sufficiently for 30 min, so that CO2 bubbles are uniformly dispersed and dissolved in the molten body; finally, the target microporous foaming material is obtained after cooling, shaping, and crushing and granulating. Measurement shows that the density of the microporous foaming material is about 1.5 g / cm 3 , the porosity is 43.6%, and the specific surface area is about 95.9 cm 2 / g.

[0053] The microporous foaming light pyrite material of the present embodiment is loaded into a fixed bed reactor, inoculated with anaerobic sludge, and subjected to denitrification simulation experiment. Under the condition of a hydraulic retention time of 1 h, simulated wastewater containing 45.5±0.5 mg / L NO3 - -N and 12.4±0.2 mg / L PO4 3- -P is treated, and the concentrations of NO3 - -N and PO4 3- -P in the final effluent are 1.23±0.04 mg / L and 0.49±0.13 mg / L, respectively.

[0054] Example 3

[0055] The basic content of the present embodiment is the same as that of Example 1, except that the preparation method of the microporous foaming material of the present embodiment is different. Specifically, the preparation method of the microporous foaming material of the present embodiment comprises the following steps:

[0056] Sulfur and siderite are mixed uniformly at a mass ratio of 5:1, high-temperature melting is performed on the mixture at a high temperature of 160°C to obtain a molten body; then supercritical CO2 fluid is introduced into the molten body at a pressure of 15 MPa, and mixed sufficiently for 40 min, so that CO2 bubbles are uniformly dispersed and dissolved in the molten body; finally, the target microporous foaming material is obtained after cooling, shaping, and crushing and granulating. Measurement shows that the density of the microporous foaming material is about 1.1 g / cm 3 , the porosity is 68.6%, and the specific surface area is about 196.8 cm 2 / g.

[0057] The microporous foaming light pyrite material of the present embodiment is loaded into a fixed bed reactor, inoculated with anaerobic sludge, and subjected to denitrification simulation experiment. Under the condition of a hydraulic retention time of 1 h, simulated wastewater containing 45.5±0.5 mg / L NO3 - -N and 12.4±0.2 mg / L PO4 3- -P is treated, and the concentrations of NO3 - -N and PO4 3- -P in the final effluent are 0.75±0.05 mg / L and 0.54±0.10 mg / L, respectively.

[0058] Example 4

[0059] The basic content of this example is the same as that of Example 1, except that the preparation method of the siderite modified sulfur microporous foaming material of this example specifically comprises the following steps:

[0060] Sulfur and siderite are uniformly mixed at a mass ratio of 1:3, and the mixture is subjected to high-temperature melting at a high temperature of 160°C. Then, CO2 is introduced into the molten body under a pressure of 0.5 MPa, and mixed for 30 min to make the CO2 bubbles uniformly dispersed and dissolved in the molten body. Finally, the molten body is cooled and shaped, and then broken and granulated to obtain the target microporous foaming material. The density of the microporous foaming material is about 1.9 g / cm 3 , the porosity is 24.8%, and the specific surface area is about 42.3 cm 2 / g.

[0061] The microporous foaming pyrite material of this example is loaded into a fixed bed reactor, inoculated with anaerobic sludge, and subjected to denitrification simulation experiment. Under the condition of a hydraulic retention time of 3 h, simulated wastewater containing 28±0.5 mg / L NO3 - -N, 12.4±0.2 mg / L PO4 3- -P is treated, and the final effluent NO3 - -N can reach 1.83±0.05 mg / L, and the effluent PO4 3- -P is lower than the detection limit.

Claims

1. A method for preparing siderite modified sulfur microcellular foamed material, characterized by: The method comprises the following steps: melting and mixing sulfur and siderite in a reaction kettle at a temperature of 115-180 DEG C to obtain a molten mixture of sulfur and siderite, wherein the mass ratio of the sulfur to the siderite is 10:1-1:3; pumping carbon dioxide into the reaction kettle under a pressure of 0.5-15 MPa and stirring to dissolve the carbon dioxide in the molten mixture of sulfur and siderite, wherein the mass ratio of the pumped carbon dioxide to the sulfur is 0.0029-0.6400; releasing pressure and cooling and forming to obtain siderite-modified sulfur microporous foaming material, wherein the contact time of the carbon dioxide with the molten mixture is less than 60 min, and the time for releasing pressure and cooling and forming is less than 5 min.

2. A method of preparing a siderite modified sulfur microcellular foamed material according to claim 1, characterized in that: The carbon dioxide in a supercritical state is pumped into the reaction kettle under a pressure of 7.5-15 MPa.

3. A method of preparing a siderite modified sulfur microcellular foamed material according to claim 1, characterized in that: The siderite acts as a nucleating agent in the preparation of the microporous foaming material, and the particle size of the siderite is d≤0.15 mm.

4. The method of claim 1, wherein the method is characterized by: The cooling and forming comprises steel belt granulation, wet granulation or post-solidification crushing granulation.

5. A siderite modified sulfur microcellular foamed material characterized by: A method for preparing a siderite modified sulfur microporous foaming material according to any one of claims 1-4, wherein the density of the siderite modified sulfur microporous foaming material is 0.9-2.0 g / cm 3 , the porosity is 10%-70%, and the specific surface area is 30-200 cm 2 / g.

6. A method for sewage treatment using the siderite modified sulfur microcellular foamed material according to claim 5, characterized in that: The siderite-modified sulfur microporous foaming material is placed in a sewage treatment reactor or a constructed wetland to load a biofilm on the surface of the siderite-modified sulfur microporous foaming material, and the nitrogen, phosphorus and arsenic, antimony, chromium and cadmium pollutants in water are removed through autotrophic denitrification, chemical precipitation and adsorption of microorganisms; or the siderite-modified sulfur microporous foaming material loaded with the biofilm is mixed with soil polluted by sewage to remove and immobilize the nitrogen, phosphorus and arsenic, antimony, chromium and cadmium pollutants in the soil.

7. The method of sewage treatment according to claim 6, characterized in that: The biological membrane comprises sulfur autotrophic denitrifying bacteria, the sulfur autotrophic denitrifying bacteria include one or both of denitrifying sulfur bacteria and sulfur-oxidizing bacteria; and the attached amount of the sulfur autotrophic denitrifying bacteria on the modified-siderite sulfur microporous foaming material is 2.454*10 7 -4.909*10 7 cfu / mm 3 .

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