A method for improving the biological removal performance of VOCs using nano / micro Fe3O4 particles

Abstract

The application provides a method for improving the biological removal performance of VOCs by using nano / micron Fe3O4 particles, wherein the particle size of the Fe3O4 particles is not greater than 100 nm and / or the particle size of the Fe3O4 particles is not less than 10 microns, so that the removal capacity of VOCs is improved as a whole. By screening the Fe3O4 particles with a suitable particle size and mixing the Fe3O4 particles with a biological system used in biological filtration, the Fe3O4 particles have a significant effect on the microorganisms in the biological system, can significantly improve the activity of some microorganisms in the microorganism system, and the nano / micron Fe3O4 particles also enhance the cooperation and synergistic effect among the microorganisms.

Description

Technical Field

[0001] This invention relates to the field of biofiltration technology, and in particular to a method for improving the biological removal performance of VOCs using nano / micro Fe3O4 particles. Background Technology

[0002] Emissions of volatile organic compounds (VOCs) cause various forms of pollution in the atmospheric environment, with methane emissions being a major contributor to the global greenhouse effect. Aerobic biofiltration for VOC removal is a VOC control technology already applied in industry. Its principle involves microorganisms attached to the biofiltration system removing VOCs from the intake air through anabolism and decomposition. However, due to limitations such as the strong hydrophobicity and poor mass transfer efficiency of some VOCs, restricted growth of core microorganisms, and competition for resources among microorganisms within the system, biofiltration systems often encounter unsatisfactory operating results when treating hydrophobic or recalcitrant VOCs. For example, methane, a hydrophobic and recalcitrant VOC, is currently poorly removed using biofiltration methods. Summary of the Invention

[0003] This invention aims to at least partially address one of the technical problems in the prior art. Therefore, one object of this invention is to provide a method for improving the biological removal performance of VOCs using nano / micro Fe3O4 particles.

[0004] This invention proposes a method for improving the biological removal performance of VOCs using nano / micro Fe3O4 particles, wherein the particle size of the Fe3O4 particles is not greater than 100 nm and / or the particle size of the Fe3O4 particles is not less than 10 μm.

[0005] The inventors discovered that adding Fe3O4 particles during biofiltration, while controlling the particle size of Fe3O4 particles to be no greater than 100 nm and / or no less than 10 μm, can significantly improve the removal efficiency of VOCs. Nano / micron Fe3O4 particles can act as microcarriers for microbial attachment, providing a favorable microenvironment for microbial growth and enhancing VOC uptake; they can also accelerate the utilization of VOCs by driving the antioxidant defense system of microorganisms and increasing their metabolic energy requirements. For example, effective removal of methane from VOCs can be achieved. This may be because nano-Fe3O4 particles induce the generation of reactive oxygen species (ROS) within microbial cells and physically disrupt cell structure, creating stress on the microbial system. However, many aerobic methane-oxidizing bacteria in the microbial system gain a competitive advantage due to their faster growth rate, stronger metabolic flexibility, and more sophisticated antioxidant defense system. Under the stimulation of nano-Fe3O4 particles, the relative abundance of these aerobic methane-oxidizing bacteria significantly increases, thereby enhancing the overall aerobic methane oxidation capacity of the microbial system.

[0006] Furthermore, micron-sized Fe3O4 particles, acting as microcarriers for microbial attachment, can adsorb and bind with microorganisms, providing a suitable microenvironment for microbial growth. For example, under the stimulation of nano-Fe3O4 particles, the overall metabolic rate of the microbial system accelerates. Some aerobic methane-oxidizing bacteria continuously degrade methane and secrete extracellular secretions such as polysaccharides and proteins to nourish the overall microbial system, enhancing cooperation among microorganisms and thus increasing the rate of VOCs degradation.

[0007] Preferably, the Fe3O4 particles have a particle size of 20nm-100nm. For example, particle sizes of 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, etc., or any range between any two of the above values.

[0008] Preferably, the Fe3O4 particles have a particle size of 10μm-1000μm. For example, particle sizes of 10μm, 20μm, 50μm, 100μm, 200μm, 300μm, 400μm, 500μm, 800μm, 1000μm, etc., or any range between any two of the above values.

[0009] In some embodiments of the present invention, the mass ratio of the microbial system to the nano / micro Fe3O4 particles in the biofiltration tower of the biofiltration device is no greater than 100. Controlling the amount of nano / micro Fe3O4 particles added can better improve the VOCs removal rate.

[0010] Those skilled in the art will understand that when using a biofilter for treatment, Fe3O4 particles can be pre-modified onto the packing material of the biofilter before adding activated sludge or other microbial active systems for subsequent aeration to remove VOCs. Alternatively, the microbial active system can be mixed with Fe3O4 particles and loaded together onto the packing material of the biofilter. Furthermore, Fe3O4 particles can be added after the biofilter has been loaded with the microbial active system and operated for a period of time. Regardless of the method used, the VOCs removal capability of this invention can be achieved.

[0011] It should be noted that the biofiltration device is a conventional device in the field. For example, a biofiltration device includes an air inlet mechanism, a biofiltration tower, and a spray mechanism. The air inlet mechanism is used to introduce the gas to be removed into the biofiltration tower, which contains a microbial system loaded on packing materials such as polyurethane. The gas passes through the biofiltration tower to achieve component removal. The spray mechanism is used to continuously inject spray liquid into the biofiltration tower to maintain the living environment of the microorganisms.

[0012] In some embodiments of the present invention, the mass ratio of the microbial system to the nano / micro Fe3O4 particles is (0.5-100):1, preferably (1-50):1. For example, the mass ratio is 0.5:1, 1:1, 5:1, 10:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, 100:1, etc., or any range between any two of the above values.

[0013] In some embodiments of the present invention, the microbial system is selected from activated sludge.

[0014] It should be noted that the activated sludge comes from municipal wastewater treatment plants, primarily from the anaerobic tanks of the A2 / O process. During wastewater treatment, microorganisms decompose organic matter in the wastewater through metabolism, forming flocculent microbial communities, i.e., activated sludge.

[0015] In some embodiments of the present invention, the volume concentration of VOCs entering the biofiltration tower of the biofiltration device is not less than 0.01%. Maintaining a certain concentration of VOCs in the gas entering the biofiltration tower is beneficial to improving the VOCs removal rate. Theoretically, the higher the concentration of VOCs, the easier they are to remove.

[0016] In some embodiments of the present invention, the volume concentration of oxygen in the gas entering the biofiltration tower of the biofiltration device is 10%-30%. Controlling a certain oxygen concentration is beneficial to the biodecomposition of microorganisms, thereby improving the removal rate of VOCs.

[0017] In some embodiments of the present invention, the gas flow rate entering the biofiltration tower of the biofiltration device is 0.1 L / min to 5 L / min. Maintaining a certain gas flow rate into the biofiltration tower allows VOCs to come into full contact with the microbial system, thereby achieving thorough decomposition and improving the VOCs removal rate.

[0018] In some embodiments of the present invention, the VOCs include one or more of methane, ethanol, and chlorobenzene, and preferably the methane in the VOCs is removed.

[0019] The present invention has at least the following beneficial effects: This invention is the first to discover that nano / micro Fe3O4 particles can enhance the VOCs degradation process. By screening Fe3O4 particles of suitable size and mixing them with the biological system used in biofiltration, it has a better promoting effect on the microbial system. For example, it has a significant effect on aerobic methanotrophs in the microbial system, which can significantly increase the relative abundance and metabolic activity of these aerobic methanotrophs in the microbial system. Secondly, it enhances the cooperation and synergy among microorganisms, thereby improving the overall VOCs removal capacity. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0021] Figure 1 This is a graph showing the methane removal rate of the continuous flow reactors in Examples 1-3 and Comparative Example 1 of the present invention; Figure 2 This is a graph showing the methane removal rate results after adding Fe3O4 particles of different sizes in Example 6 of the present invention; Figure 3 This is a graph showing the chlorobenzene removal rate results after adding Fe3O4 particles of different sizes in Example 7 of the present invention. Detailed Implementation

[0022] Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention. The invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the invention in any way.

[0023] The activated sludge used in this embodiment of the invention was collected from the anaerobic tank of the A2 / O process section of the Shahe Reclaimed Water Plant in Beijing. The retrieved activated sludge was washed with PBS buffer, centrifuged, and resuspended three times, and then washed with deionized water, centrifuged, and resuspended once before being used in the experiment.

[0024] Example 1 The biofiltration device used in Example 1 mainly consists of three parts: an air intake mechanism, a spray mechanism, and a biofiltration tower. The specific components of the biofiltration device are as follows: (1) The gas inlet mechanism consists of a mass flow controller, a mixing tank, an air pump, a methane cylinder (volume concentration of 60%), an ethanol cylinder (volume concentration of 20%), and a chlorobenzene cylinder (volume concentration of 20%). The methane, ethanol, and chlorobenzene cylinders provide the mixed gas. The mass flow controller regulates the VOCs mixed gas provided by the methane, ethanol, and chlorobenzene cylinders and the output flow of the air pump (the air pump is used to transport air). The four gas streams are mixed evenly in the mixing tank to form a mixed gas. The output mixed gas flows evenly into the three biofilters through the air inlet at the bottom of the biofilter. The volume concentration of methane in the mixed gas is 0.05%, the volume concentration of ethanol is 0.005%, the volume concentration of chlorobenzene is 0.005%, and the volume concentration of oxygen is 20%. The gas flow rate of the mixed gas entering the biofilter is approximately 0.5 L / min.

[0025] (2) The spraying mechanism consists of an outlet at the top of the biological filter tower, an inlet at the bottom of the biological filter tower, a water storage tank, and a peristaltic pump. The spray water is pumped from the water storage tank to the outlet by the peristaltic pump. After passing through the biological filter tower, the water flows into the water storage tank from the bottom inlet. The spraying frequency is 2 minutes / 2 hours, the spraying flow rate is 80 mL / min, and the spraying liquid in the tank is replaced every 10 days.

[0026] (3) The diameter of the biological filter tower is 7 cm and the effective filling volume is about 2.5 L. The tower is filled with 2 cm*2 cm*2 cm polyurethane packing material to provide an inoculation carrier for microorganisms. The tower is equipped with three layers of partitions with evenly spaced round holes to support the polyurethane packing material.

[0027] The operation process is as follows: Activated sludge from a municipal wastewater treatment plant was collected. 2g of activated sludge, 1g of Fe3O4 with a particle size of 20nm and 2L of spray liquid were placed in a water storage tank and stirred evenly to obtain a mixed liquid. The mixed liquid was then continuously sprayed into the biological filter tower through a spraying mechanism to achieve microbial inoculation. This process lasted for two days.

[0028] After inoculation is completed, the mixed gas is introduced into the biofilter tower from the bottom air inlet at a flow rate of 0.5 L / min using the air inlet mechanism of step (1) above. During this process, the spraying mechanism continuously feeds spray liquid into the biofilter tower in the manner of step (2) above.

[0029] During the continuous operation of the biofiltration device, the gas discharged from the biofiltration tower is extracted daily, and the volume content of methane in the gas is measured.

[0030] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is as follows: During the operation of the biofiltration device in Comparative Example 1, Fe3O4 was never added to the biofiltration tower.

[0031] The removal rates of methane, ethanol, and chlorobenzene in Example 1 and Comparative Example 1 are shown in Table 1. Pollutant removal rate = (Content of pollutants in the gas entering the biofilter - Content of pollutants in the gas discharged from the biofilter) / Content of pollutants in the gas entering the biofilter × 100%.

[0032] As shown in Table 1, the addition of Fe3O4 particles with nano-sized particles can effectively enhance the removal of various VOCs such as methane, ethanol, and chlorobenzene by the biofiltration tower.

[0033] Table 1

[0034] Example 2 After the biological filtration device of Example 1 had been running for 75 days, 1g of Fe3O4 with a particle size of 20nm was added to the water storage tank, and a stirrer was used for continuous stirring and a spraying mechanism for continuous spraying to achieve the secondary addition of nano Fe3O4.

[0035] To ensure the continuous operation of the biofiltration device, the gas discharged from the biofiltration tower is extracted daily, and the volumetric methane content in the gas is measured.

[0036] Example 3 The difference between Example 3 and Example 1 is as follows: In Example 3, no Fe3O4 was added to the biofiltration tower before the biofiltration device had been in operation for 75 days. Starting from the 75th day, 1g of Fe3O4 with a particle size of 20nm was added to the water storage tank, and a stirrer was used for continuous stirring and a spraying mechanism for continuous spraying to achieve the addition of nano Fe3O4.

[0037] To ensure the continuous operation of the biofiltration device, the gas discharged from the biofiltration tower is extracted daily, and the volumetric methane content in the gas is measured.

[0038] The methane removal rates of Examples 1-3 and Comparative Example 1 are shown in the figure. Figure 1 .from Figure 1 It can be seen that Comparative Example 1's methane degradation efficiency gradually increased to 35.7% during 110 days of operation. Example 3's operating efficiency was similar to Comparative Example 1 for the first 75 days, and the degradation efficiency gradually increased to 62.7% after the addition of nano-Fe3O4 particles on day 75. In Example 1, the addition of nano-Fe3O4 particles at startup resulted in a gradual increase in methane degradation efficiency to over 65% before leveling off. Compared to Example 1, Example 2, in addition to the addition of nano-Fe3O4 particles at startup, also added them on day 75, and its degradation efficiency gradually increased to 84.8% by day 110.

[0039] Example 4 The difference between Example 4 and Example 1 is as follows: Example 4 uses 2g of activated sludge and 0.05g of Fe3O4 with a particle size of 20nm.

[0040] Example 5 The difference between Example 5 and Example 1 is as follows: Example 5 uses 2g of activated sludge and 2g of Fe3O4 with a particle size of 20nm.

[0041] The methane removal rates at different times in Examples 1, 4, 5 and Comparative Example 1 are shown in Table 2.

[0042] Table 2

[0043] Table 2 shows that the addition of nano-sized Fe3O4 particles effectively enhances the start-up and strengthening of the biofilter's removal function for various VOCs such as methane, ethanol, and chlorobenzene, and this strengthening effect increases with the increase of the concentration of nano-Fe3O4 particles. During the 60-day start-up period, the methane removal efficiency of Comparative Example 1 was approximately 27.4%, while the methane removal efficiencies of Examples 4, 1, and 5 reached 39.%, 60.3%, and 77.7%, respectively.

[0044] Example 6 The effect of different Fe3O4 particle sizes on methane removal rate was studied using a closed shake flask method.

[0045] Experimental group: 50 mL of liquid culture medium, 1 g of activated sludge, and 0.1 g of Fe3O4 particles were added to a 300 mL sealed shake flask. The gas at the top of the shake flask was replaced with 10% methane and 10% oxygen by volume, with the remainder being air components excluding oxygen. Ten groups of experiments were conducted. The particle size of Fe3O4 in group 1 was 20 nm, in group 2 it was 50 nm, in group 3 it was 100 nm, in group 4 it was 200 nm, in group 5 it was 500 nm, in group 6 it was 1 μm, in group 7 it was 10 μm, in group 8 it was 50 μm, in group 9 it was 100 μm, and in group 10 it was 500 μm.

[0046] Control group: Add 50 mL of liquid culture medium and 1 g of activated sludge to a 300 mL sealed shake flask. Replace the gas at the top of the shake flask with 10% methane and 10% oxygen by volume, and the rest is air components other than oxygen.

[0047] The shake flasks for both the experimental and control groups were placed in a shaker and shaken continuously for 12 hours. The methane content in the gas at the top of the flasks was measured, and the methane removal rate was calculated. Detailed results can be found... Figure 2 ,from Figure 2 It was found that the enhancement effect on microbial methane removal efficiency first increased and then decreased with the increase of Fe3O4 particle size. The addition of Fe3O4 particles with diameters of 20-100 nm and 50-500 μm significantly increased the methane removal efficiency of the microbial system. The control group without added material removed 39.1 ± 2.2% of methane within 12 hours, while the experimental groups with 20-100 nm and 10-500 μm Fe3O4 particles removed over 71.9% and 63.5% of methane, respectively, within the same timeframe. The inventors also discovered that repeating the experiment with 10 nm Fe3O4 particles was not feasible, as 10 nm Fe3O4 exhibited a certain toxic effect on microorganisms. Specifically, excessively small magnetic materials may induce excessive generation of reactive oxygen species (ROS) within microbial cells, excessively damaging cell structure and leading to strong nanotoxicity, thus affecting the normal metabolic capacity of microorganisms.

[0048] Example 7 The difference between Example 7 and Example 1 is as follows: In Example 7, the gas at the top of the shake flask was 10% chlorobenzene and 10% oxygen by volume.

[0049] The control group without added materials removed 45.2 ± 0.9% of chlorobenzene within 12 hours. The removal efficiency of Fe3O4 particles with different particle sizes is shown in [reference needed]. Figure 3 ,from Figure 3 It can be seen that the experimental groups with 20-100nm and 10-500μm Fe3O4 particles added can remove more than 75.8% and 77.1% of chlorobenzene, respectively, within the same time period.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for improving the biological removal performance of VOCs using nano / micro Fe3O4 particles, characterized in that, The Fe3O4 particles have a particle size of 20nm-100nm and / or a particle size of 10μm-1000μm; the Fe3O4 particles are mixed with a microbial system and then contacted with the gas to be removed; wherein, the microbial system is selected from activated sludge containing aerobic methanogenic bacteria; the volume concentration of VOCs in the gas entering the biofiltration tower of the biofiltration device is not less than 0.01%; the volume concentration of oxygen in the gas entering the biofiltration tower of the biofiltration device is 10%-30%.

2. The method according to claim 1, characterized in that, The mass ratio of the microbial system in the biofiltration tower of the biofiltration device to the mass of the nano / micro Fe3O4 particles is no greater than 100.

3. The method according to claim 2, characterized in that, The mass ratio of the microbial system to the nano / micro Fe3O4 particles is (0.5-100):

1.

4. The method according to claim 3, characterized in that, The mass ratio of the microbial system to the nano / micro Fe3O4 particles is (1-50):

1.

5. The method according to claim 1, characterized in that, The gas flow rate entering the biofiltration tower of the biofiltration device is 0.1L / min-5L / min.

6. The method according to claim 1, characterized in that, The VOCs include one or more of methane, ethanol, and chlorobenzene.

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