Calcium / magnesium carbonate modified sulfur microporous foaming material and preparation and application method thereof

Abstract

The application discloses a calcium / magnesium carbonate modified 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 combines the carbon dioxide foaming technology under high pressure or even supercritical state with the modified sulfur material foaming technology, dissolves carbon dioxide in a molten body of sulfur and calcium / magnesium carbonate, and obtains the modified sulfur microporous foaming material with micron-level small pore diameters and uniform bubble distribution, and the modified sulfur microporous foaming material has the characteristics of good compression resistance, self-regulation and control 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 the filler of a fluidized bed and a fixed bed reactor of sewage treatment, and has a good application prospect.

Description

TECHNICAL FIELD

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

[0002] According to different electron donors, the sulfur autotrophic denitrification technology can be divided into three categories: 1) sulfur autotrophic denitrification technology using elemental sulfur as substrate; 2) sulfur autotrophic denitrification technology using sulfide as substrate; and 3) sulfur autotrophic denitrification technology using reducing sulfur compounds as substrate. Among them, the sulfur-limestone autotrophic denitrification technology is widely concerned by domestic and foreign scholars due to its high-efficiency nitrogen removal.

[0003] The traditional sulfur-limestone autotrophic denitrification system (SLAD) usually simply mixes limestone and elemental sulfur particles in a certain proportion, and the limestone is continuously dissolved in the treatment process to achieve the effect of buffering pH. However, the SLAD has some drawbacks, such as high effluent hardness, high sulfate content, uneven mixing of materials, which leads to limited denitrification rate and unstable performance; in addition, the solubility of limestone is limited, and the stability of the provided inorganic carbon source is low. Therefore, it is urgent to seek a new sulfur-limestone autotrophic denitrification method to open up a new way for sewage treatment.

[0004] According to the search, the Chinese patent application for the invention entitled "Improving the effect of denitrification and phosphorus removal of tail water in sewage plant and avoiding biological clogging of subsurface wetland system", application number 201510067571.1, application date February 9, 2015, discloses a subsurface wetland system, which includes a water distribution area, a purification area and a water collection area arranged in sequence, wherein the purification area is placed with sulfur / limestone mixed substrate, gravel substrate and zeolite substrate from front to back in the water flow direction. The subsurface wetland is combined with sulfur autotrophic denitrification to remove nitrate in sewage, and to avoid clogging of the subsurface wetland system caused by the large reproduction of microorganisms. However, the sulfur and limestone used in the invention are both granular with large particle size and small specific surface area, which is not conducive to the adhesion and utilization of microorganisms, and the denitrification rate is only 0.875-1.45 mg NO3 - -N / (L·h).

[0005] In addition, the patent entitled "Preparation method and application method of calcium / magnesium carbonate modified sulfur light material", application number: 201910332916.X, application date: April 24, 2019, discloses a method of mixing sulfur and calcium / magnesium carbonate powder, then melting under high temperature conditions, and then foaming the molten mixture by mechanical stirring, cooling and forming to obtain a light material. The obtained light material not only helps to attach more biomass, but also can improve the utilization rate of microorganisms, thereby improving the removal rate of pollutants. However, the foamed product prepared by the invention has low gas solubility in the filler and uneven distribution, resulting in uneven pore structure of the material, large bubbles (millimeter level), and poor compression resistance of the material. SUMMARY

[0006] 1. Problems to be solved

[0007] In view of the problems of sulfur autotrophic denitrification filler in the prior art, such as not conducive to microbial attachment and utilization, poor compression resistance, and denitrification denitrification rate to be further improved, the present application provides a calcium / magnesium carbonate modified sulfur microporous foaming material and its preparation and application method. The present application first proposes to combine the carbon dioxide foaming technology under high pressure or even supercritical state with the modified sulfur material foaming technology, to dissolve carbon dioxide in the molten body of sulfur and calcium / magnesium carbonate, so as to obtain a modified sulfur microporous foaming material with micron-level small pore diameter and uniform bubble distribution, to ensure more biomass attachment in wastewater treatment application, to improve the denitrification denitrification rate, and to enhance the compression resistance.

[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 calcium / magnesium carbonate modified sulfur microporous foaming material of the present application comprises melting and mixing sulfur and calcium / magnesium carbonate at a temperature of 115-180℃ to obtain a molten body; then dissolving carbon dioxide in the molten body under a pressure of 0.5-15Mpa; releasing pressure, cooling and forming to obtain the calcium / magnesium carbonate modified sulfur microporous foaming material; wherein no nucleating agent is added in the molten body, and the calcium / magnesium carbonate is used as a nucleating agent.

[0011] Preferably, the mass ratio between the sulfur and the calcium / magnesium carbonate is 10:1-1:5.

[0012] Preferably, the mass ratio between the amount of carbon dioxide and sulfur is 0.0029-0.6400.

[0013] The particle size d of the calcium / magnesium carbonate is ≤0.15mm.

[0014] Preferably, the carbon dioxide is dissolved in the melt under a pressure of 7.5-15 MPa, and the carbon dioxide is in a supercritical state.

[0015] Preferably, the mass ratio between the supercritical carbon dioxide and the sulfur is 0.244-0.640.

[0016] Preferably, the calcium / magnesium carbonate includes limestone, magnesite, dolomite, and shells.

[0017] Preferably, the time for which the carbon dioxide is in contact with the melt is less than 60 min, and the time for pressure release and cooling is less than 5 min.

[0018] Preferably, the forming includes steel belt granulation forming, wet cooling forming, or post-solidification crushing granulation forming.

[0019] A calcium / magnesium carbonate modified sulfur microporous foaming material is prepared by the method described above, wherein the pore size of the calcium / magnesium carbonate modified sulfur microporous foaming material is less than 100 μm.

[0020] Preferably, the density of the calcium / magnesium carbonate modified sulfur microporous foaming material is 0.7-2.0 g / cm 3 , the porosity is 10%-70%, and the specific surface area is 30-200 cm 2 / g.

[0021] A method for treating sewage using the calcium / magnesium carbonate modified sulfur microporous foaming material described above includes placing the calcium / magnesium carbonate modified sulfur microporous foaming material in a sewage treatment reactor or a constructed wetland, allowing the calcium / magnesium carbonate modified sulfur microporous foaming material to load a biofilm on its surface, and removing nitrogen, phosphorus, and arsenic, antimony, chromium, and cadmium pollutants in water through autotrophic denitrification, chemical precipitation, and adsorption of microorganisms.

[0022] Preferably, the biofilm contains sulfur autotrophic denitrifying bacteria, and the sulfur autotrophic denitrifying bacteria include one or both of Thiobacillus denitrificans and Sulfuroximans.

[0023] Preferably, the amount of the sulfur autotrophic denitrifying bacteria attached to the calcium / magnesium carbonate modified sulfur microporous foaming material is 2.454×10 7 -4.909×10 7 cfu / mm 3 .

[0024] 3. Beneficial effects

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] (1) The present invention provides a method for preparing a calcium / magnesium carbonate modified sulfur microporous foam material. It proposes for the first time to combine high-pressure carbon dioxide foaming technology with modified sulfur material foaming technology. No additional nucleating agent is required. By dissolving carbon dioxide in the melt of sulfur and calcium / magnesium carbonate, a microporous lightweight modified material with a pore size of less than 100 μm is obtained. This not only achieves a high degree of mixing between sulfur and calcium / magnesium carbonate, but also makes the medium bubbles in the material small, uniformly distributed, and controllable in density, thereby improving the physical, chemical and biochemical properties of the material.

[0027] (2) A calcium / magnesium carbonate modified sulfur microporous foaming material of the present invention has a density of 0.7–2.0 g / cm³. 3 Porosity is 10%–70%, and specific surface area is 30–200 cm². 2 / g, and has the characteristics of good pressure resistance, light weight, autonomous water pH control, high reactivity, easy microbial attachment, slow release electron donor denitrification, and effective improvement of carbon source utilization in inorganic minerals. It can be used as packing material for fluidized bed and fixed bed reactors in sewage treatment.

[0028] (3) The calcium / magnesium carbonate modified sulfur microporous foaming material of the present invention ensures the generation of micropores with suitable pore size and number by controlling the solubility of carbon dioxide in the melt of sulfur and calcium / magnesium carbonate. In wastewater treatment applications, the amount of microbial attachment can reach up to 2.454 × 10⁻⁶. 7 -4.909×10 7 cfu / mm 3 This further improves the denitrification rate and has good application prospects. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the apparatus used to prepare a calcium / magnesium carbonate modified sulfur microporous foaming material according to the present invention.

[0030] Figure 2 a 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;

[0031] In the picture:

[0032] 101. Carbon dioxide storage tank; 102. Plunger pump control panel; 103. Pressure monitoring instrument;

[0033] 104, plunger pump; 201, high pressure melting kettle; 202, high pressure melting kettle rotor;

[0034] 203, high pressure melting kettle gas release valve; 300, computer control system; 310, computer data transmission pipeline;

[0035] 410, carbon dioxide delivery pipeline. DETAILED DESCRIPTION

[0036] The application will be further described below in conjunction with specific examples.

[0037] The following detailed description of the exemplary embodiments of the present application refers to the accompanying drawings, which are meant to exemplify and do not limit the present application. Although these exemplary embodiments are described in sufficient detail to enable those skilled in the art to practice the application, it is understood that other embodiments can be employed and that changes can be made without departing from the spirit and scope of the present application. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present application is defined only by the appended claims.

[0038] As Figure 1 shown, the preparation method of the calcium / magnesium carbonate modified sulfur microporous foaming material of the present application, the specific steps are: the sulfur and calcium / magnesium carbonate with a mass ratio of 10:1-1:5 are put into the high pressure melting kettle 201, the carbon dioxide fluid is pumped into the high pressure melting kettle 201 from the carbon dioxide storage tank 101 via the carbon dioxide delivery pipeline 410 under the pressure condition of 0.5-15 Mpa by the plunger pump 104, the material in the kettle is in the 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.

[0039] 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. Preferably, the carbon dioxide is dissolved in the melt at a pressure of 7.5-15 MPa, and the carbon dioxide is in a supercritical state, and the mass ratio of the amount of the supercritical carbon dioxide to the sulfur is 0.244-0.640. The carbon dioxide is contacted with the melt for less than 60 min, and then depressurization is performed through the high-pressure melting kettle gas valve 203, and cooling and molding are performed to obtain a calcium / magnesium carbonate modified sulfur microporous foaming material. The time for depressurization and cooling is less than 5 min.

[0040] It should be noted that no nucleating agent is additionally added in the melt of the present application, and the calcium / magnesium carbonate itself can be used as a nucleating agent. The particle size of the calcium / magnesium carbonate is d≤0.15 mm, and the calcium / magnesium carbonate includes limestone, magnesite, dolomite, shells, etc. In addition, the cooling and molding 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 mold 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 molded on the surface of the steel belt by running of the steel belt and contacting with air, so that granulation molding is realized; and the post-solidification crushing granulation is to cool and solidify the foamed microporous melt, and then crush the melt to form 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. The bubble pore size in the modified microporous foaming material is <100 μm.

[0041] The calcium / magnesium carbonate modified sulfur microporous foaming material of the present application is used for sewage treatment, and the specific treatment method is as follows: the prepared modified sulfur microporous foaming material is sieved and filled into a reactor, and anaerobic sludge is inoculated to treat wastewater; specifically, the calcium / magnesium carbonate modified sulfur microporous foaming material is placed in a sewage treatment reactor or a constructed wetland, and then microorganisms are inoculated, so that the calcium / magnesium carbonate modified sulfur microporous foaming material is loaded with a biofilm, and the biofilm contains sulfur autotrophic denitrifying bacteria, and the sulfur autotrophic denitrifying bacteria include one or both of Thiobacillus denitrificans and Sulfuroximans. The amount of the sulfur autotrophic denitrifying bacteria attached to the calcium / magnesium carbonate modified sulfur microporous foaming material can reach 2.454×10 7 -4.909×10 7 cfu / mm.3 The nitrogen in water is removed by autotrophic denitrification of microorganisms, wherein the sewage treatment reactor comprises a fluidized bed or a fixed bed reactor.

[0042] The present application completes the denitrification process by taking calcium / magnesium carbonate powder as inorganic carbon source and taking sulfur as electron donor.

[0043] 5S 0 +6NO3-+2H2O→5SO4 2- +3N2↑+4H +

[0044] H + +CaCO3→Ca 2+ +HCO3-

[0045] (H + +MgCO3→Mg 2+ +HCO3-,2H + +CaMg(CO3)2→Ca 2+ +Mg 2+ +2HCO3-)。

[0046] The microporous foaming material prepared by the present application has the characteristics of small pore size (micron level), large specific surface area, good compression resistance, light weight, self-regulation of water quality pH, high reaction activity, easy microbial adhesion, slow release of electron donor for denitrification, and effective improvement of carbon source utilization rate in inorganic minerals, and can be used as the filler of the fluidized bed and fixed bed reactor for sewage treatment. Under the denitrification of microorganisms, the filler has good purification effect on the pollutants in water, especially total nitrogen. In the case of a hydraulic retention time of 0.5 h, the simulated sewage containing 50±0.5 mg / L of NO3 - -N is treated, and the concentration of NO3 - -N in the final effluent is 0.15±0.05 mg / L. In addition, the preparation method of the present application is simple and low in cost.

[0047] Embodiment 1

[0048] The preparation method of the calcium / magnesium carbonate modified sulfur microporous foaming material of the present embodiment specifically comprises the following steps:

[0049] Sulfur and light calcium carbonate are uniformly mixed at a mass ratio of 3:1, high-temperature melting is performed on the mixture under high-temperature conditions of 160℃, and a molten body is obtained. Then, CO2 is introduced into the molten body under a pressure of 0.5 MPa, and the carbon dioxide is dissolved in the molten body after 20 min of sufficient mixing. Finally, the target microporous foaming material is obtained after cooling, shaping, and crushing. The density of the microporous foaming material is about 1.7 g / cm 3, porosity is 25.7%, and specific surface area is about 45.7 cm 2 / g.

[0050] After the microporous foamed material prepared in this example is crushed, 5 cm 3 of the microporous foamed material is placed in a batch reaction container, 50 mL of simulated sewage containing 28 mg / L of NO3 - -N is added to the batch reaction container. Then, 3.5 mL of the self- nourishing denitrifying bacteria solution (the volume of the bacteria solution accounts for 7% of the volume of the sewage) is added to the batch reaction container, and the mixed solution is deoxygenated by nitrogen blowing. Then, the batch reaction container is sealed and cultured at 28°C for 7 days in the dark. The adhesion of the microorganisms on the surface of the carrier is observed by SEM on the 7th day, and the concentration of NO3 - -N in the sewage is detected. The denitrification effect of the microorganisms is shown in Figure 2 a, and the adhesion of the microorganisms on the surface of the microporous foamed material is shown in Figure 2 b.

[0051] Example 2

[0052] The basic content of this example is the same as that of Example 1, except that the preparation method of the calcium / magnesium carbonate modified sulfur microporous foamed material in this example includes the following steps:

[0053] Sulfur and light calcium carbonate are uniformly mixed at a mass ratio of 6:1, and the mixture is high-temperature melted at 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 the mixture is fully mixed for 30 min to dissolve carbon dioxide in the molten body. Finally, the molten body is cooled and formed, and then crushed and granulated to obtain the target microporous foamed material. The density of the microporous foamed material is about 1.5 g / cm 3 , the porosity is 45.3%, and the specific surface area is about 96.5 cm 2 / g.

[0054] The calcium / magnesium carbonate modified sulfur microporous foamed material in this example is loaded into a fixed bed reactor and inoculated with anaerobic sludge to perform a denitrification simulation experiment. Under the condition of a hydraulic retention time of 1 h, simulated sewage containing 40±0.5 mg / L of NO3 - -N is treated, and the concentration of NO3 - -N in the effluent is 0.3±0.05 mg / L.

[0055] Example 3

[0056] The basic content of this example is the same as that of Example 1, except that the preparation method of the calcium / magnesium carbonate modified sulfur microporous foamed material in this example includes the following steps:

[0057] Sulfur and light calcium carbonate were mixed uniformly at a mass ratio of 10:1, and the mixture was subjected to high-temperature melting at a high temperature of 180°C to obtain a melt. Then, supercritical CO2 fluid was introduced into the melt at a pressure of 15 MPa, and mixed sufficiently for 40 min, so that carbon dioxide was dissolved in the melt. Finally, the melt was cooled and shaped, and then broken and granulated to obtain the target microporous foaming material. It was measured that the density of the microporous foaming material was about 0.9 g / cm 3 , the porosity was 69.5%, and the specific surface area was about 198.3 cm 2 / g.

[0058] The calcium / magnesium carbonate modified sulfur microporous foaming material of the present example was inoculated with anaerobic sludge in a fixed bed reactor to perform a denitrification simulation experiment. Under the condition of a hydraulic retention time of 0.5 h, simulated sewage containing 50±0.5 mg / L of NO3 - -N was treated, and the final effluent NO3 - -N concentration was 0.15±0.05 mg / L.

[0059] Example 4

[0060] The basic content of the present example was the same as that of Example 1, except that the preparation method of a calcium / magnesium carbonate modified sulfur microporous foaming material of the present example specifically included the following steps:

[0061] Sulfur and light calcium carbonate were mixed uniformly at a mass ratio of 1:4, and the mixture was subjected to high-temperature melting at a high temperature of 180°C to obtain a melt. Then, supercritical CO2 fluid was introduced into the melt at a pressure of 0.5 MPa, and mixed sufficiently for 30 min, so that carbon dioxide was dissolved in the melt. Finally, the melt was cooled and shaped, and then broken and granulated to obtain the target microporous foaming material. It was measured that the density of the microporous foaming material was about 1.9 g / cm 3 , the porosity was 24.6%, and the specific surface area was about 42.3 cm 2 / g.

[0062] The calcium / magnesium carbonate modified sulfur microporous foaming material of the present example was inoculated with anaerobic sludge in a fixed bed reactor to perform a denitrification simulation experiment. Under the condition of a hydraulic retention time of 3 h, simulated sewage containing 30±0.5 mg / L of NO3 - -N was treated, and the final effluent NO3 - -N concentration was 0.50±0.05 mg / L.

Claims

1. A method for preparing calcium / magnesium carbonate modified sulfur microcellular foamed material, characterized in that: The method comprises melting and mixing sulfur and calcium / magnesium carbonate at a temperature of 115-180 DEG C to obtain a melt, the mass ratio between the sulfur and the calcium / magnesium carbonate being 10:1-1:5; then dissolving carbon dioxide in the melt under a pressure of 0.5-15 MPa, the mass ratio between the amount of the carbon dioxide and the sulfur being 0.0029-0.6400; releasing pressure, cooling and shaping to obtain calcium / magnesium carbonate modified sulfur microcellular foam material; wherein no nucleating agent is added in the melt, the calcium / magnesium carbonate is used as a nucleating agent, the contact time of the carbon dioxide with the melt is less than 60 min, and the time for releasing pressure and cooling is less than 5 min.

2. The method for preparing calcium / magnesium carbonate modified sulfur microcellular foaming material according to claim 1, characterized in that: The particle size of the calcium / magnesium carbonate is ≤0.15 mm.

3. A calcium / magnesium carbonate modified sulfur microcellular foamed material characterized by: The calcium / magnesium carbonate modified sulfur microcellular foam material is prepared by the method according to any one of claims 1-2, wherein the bubble pore size of the calcium / magnesium carbonate modified sulfur microcellular foam material is less than 100 μm.

4. The calcium / magnesium carbonate-modified sulfur microcellular foamed material according to claim 3, characterized in that: The density of the calcium / magnesium carbonate modified sulfur microporous foaming material is 0.7-2.0 g / cm 3 , the porosity is 10%-70%, and the specific surface area is 30-200 cm 2 / g.

5. A method for sewage treatment using the calcium / magnesium carbonate modified sulfur microporous foamed material prepared by the preparation method according to any one of claims 1-2 or the calcium / magnesium carbonate modified sulfur microporous foamed material according to any one of claims 3-4, characterized in that: The method comprises placing the calcium / magnesium carbonate modified sulfur microcellular foam material in a sewage treatment reactor or a constructed wetland, so that the calcium / magnesium carbonate modified sulfur microcellular foam material is loaded with a biofilm on the surface, and nitrogen, phosphorus and arsenic, antimony, chromium and cadmium pollutants in water are removed through autotrophic denitrification, chemical precipitation and adsorption of microorganisms.

6. The method of sewage treatment according to claim 5, characterized in that: The biofilm comprises sulfur autotrophic denitrifying bacteria, and the sulfur autotrophic denitrifying bacteria comprise one or both of Thiobacillus denitrificans and Sulfuroximans. The biofilm comprises sulfur autotrophic denitrifying bacteria, and the sulfur autotrophic denitrifying bacteria comprise one or both of Thiobacillus denitrificans and Sulfuroximans.

7. The method of sewage treatment according to claim 6, characterized in that: The attached amount of the sulfur autotrophic denitrifying bacteria on the calcium / magnesium carbonate modified sulfur microporous foaming material is 2.454 x 10 7 -4.909 x 10 7 cfu / mm 3 .

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