Method for Degrading Dimethyl Sulfide in Aqueous Phase by Mixed Microbial Flora and Enrichment Method Thereof

Abstract

The present invention provides a method for degrading dimethyl sulfide in aqueous phase by a mixed microbial flora, and the mixed microbial flora includes Thiobacillus, Bacteroides, Hyphomicrobium, Leadbetterella and Bacillus. The functional mixed microbial flora of the present invention can metabolize and grow using dimethyl sulfide as a carbon source, and dimethyl sulfide is effectively degraded as an electron acceptor. The addition of Mg<supgt;2+< / supgt; and saponin enables the mixed flora to have a better degradation effect, when the concentrations of Mg<supgt;2+< / supgt; and saponin are 10 mg / L and 100 mg / L respectively. The shake flask test in the laboratory shows that the mixed flora can efficiently degrade 35 mg / L of dimethyl sulfide in aqueous phase within 24 h, having a good repair effect.

Description

Technical Field

[0001] The present invention relates to a method for degrading dimethyl sulfide in an aqueous phase by a mixed microbial flora and an enrichment method thereof, belonging to the technical field of environmental biochemical remediation technology applications. Background Art

[0002] VOCs (volatile organic pollutants) are one of the important precursors for the formation of PM2.5 and O3. VOCs and their secondary pollutants formed not only have a great impact on air quality, but also have a negative impact on human health. In particular, components such as benzene series, aldehydes and halogenated hydrocarbons in VOCs have irritation, toxicity and carcinogenic effects, endangering human health. Therefore, the prevention and control of VOCs pollution has become a hot issue in current air pollution prevention and control. In fact, most malodorous substances are just a type of VOCs. It is often a mixture composed of multiple organic components and is also a typical atmospheric environmental pollution.

[0003] The malodorous smell around fertilizer factories is caused by the anaerobic microbial decomposition of livestock manure containing a large amount of organic matter, nutrients and other compounds in the compost fermentation tank. Most of the odors generated in the fermentation tank system are NH3 and VOSCS (volatile organic sulfur compounds) and some organic amine substances. Volatile organic sulfur compounds, such as carbon disulfide, methanethiol, dimethyl sulfide, ethanethiol, dimethyl disulfide, etc., although at low concentrations, are the key compounds behind most malodorous smell complaints. These substances can be detected even at very low concentration levels and diffuse relatively slowly in the atmosphere until reaching a concentration level far lower than the concentration corresponding to the harmful level.

[0004] Dimethyl sulfide (DMS) has been identified as the main contributor to the odor source among VOSCs. Although the mitigation strategies of fertilizer factory treatment facilities can control the rancid smell of fatty acids and the rotten egg smell of hydrogen sulfide, its "rotten cabbage" smell still exists. In addition to causing malodorous pollution and discomfort to human senses, dimethyl sulfide will also have an impact on the change of the earth's climate to a certain extent. Dimethyl sulfide (DMS) is the most abundant sulfur-containing compound emitted into the atmosphere. DMS is mainly released by some marine algae and phytoplankton in the upper layer of seawater. The oxidation of DMS in the upper atmosphere of the ocean will produce various sulfur-containing compounds, such as sulfur dioxide, dimethyl sulfoxide (DMSO), methanesulfonic acid, dimethyl sulfone and sulfuric acid. SO2 is the precursor of sulfate aerosol particles in the atmosphere. Sulfate aerosol particles, as cloud condensation nuclei (CCN), lead to the formation of new aerosols. CCN have a great impact on climate because they affect the radiative properties of the atmosphere and clouds by scattering solar radiation and influencing the microphysics and albedo of clouds. Therefore, the large amount of DMS emissions over the ocean may play an important role in the change of the earth's climate.

[0005] The existing treatment methods for sulfur-containing malodorous waste gas mainly include physical adsorption method, chemical oxidation method and biological treatment method. The physical adsorption method and chemical oxidation method are costly and prone to secondary pollution, making it difficult to be used on a large scale for the treatment of sulfur-containing malodorous gas. Among them, the technology of controlling malodorous pollution by biological method has existed for nearly half a century, and the process has been basically mature. The biological method mainly degrades organic matter through the metabolism of microorganisms, and is divided into three categories: biological scrubbing method, biological filter method and biological trickling filter method. At the same time, due to the unique ecological and economic advantages of the biological method, it has received more and more attention in the treatment of malodorous gas. The biological method stands out among various methods with its advantages such as good treatment effect, low operating cost and no secondary pollution, and has been proven to be an effective, eco-friendly and potentially cost-saving method in the treatment of VOCs and malodors, and is the most promising technology.

[0006] However, the prerequisite for the biological method is to screen one or more strains of highly efficient methionine sulfide-tolerant and degradable strains. The number of microorganisms reported to have the function of degrading methionine sulfide is not large, and continuously screening methionine sulfide-degrading bacteria that can degrade methionine sulfide and have high degradation efficiency is of great significance in the purification of malodorous organic waste gas. Microbial mixed flora often has better performance than pure cultures. As a biological group with coexistence of multiple bacteria, the mixed flora can decompose organic matter during its growth process, and rely on the symbiotic proliferation and synergistic metabolism among various microorganisms to degrade organic matter in the environment, and can activate other microorganisms with purification functions, thus forming a complex and stable microecosystem. Compared with pure microbial cultures, the genes of microbial mixed flora enriched from natural environment are more diverse and the metabolic pathways are more abundant, which can enhance metabolic function cross-feeding, establish stable survival relationships and possess degradation performance, so it has more potential in the degradation of organic pollutants. At the same time, the mass transfer resistance between gas and liquid phases of hydrophobic VOCs is large, which limits its degradation and results in low removal efficiency of single biotechnology. At present, the main enhanced technologies for improving the degradation of hydrophobic organic waste gas at home and abroad are mainly in three aspects: surfactant enhancement, fungal microorganism enhancement and optimization of bioreactor enhancement. Under laboratory conditions, the above three enhancement pathways all have a certain enhancement effect on hydrophobic organic waste gas, and the removal efficiency is improved by enhancing the ability of the biological system to degrade organic matter. In view of the characteristics of green, simple and fast of surfactants, they have a relatively large application prospect in enhancing the biological system. Moreover, many studies have also shown that surfactants and metal ions have a good promoting effect on the removal of VOCs in polluted waste gas.

[0007] Therefore, whether a method can be provided to promote the efficient degradation of methionine sulfide by functional microbial flora is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0008] In view of the problems of treating waste gas containing dimethyl sulfide and sewage environment, and the fact that general pure microbial cultures often have weak colonization ability in the environment, the present invention provides a mixed microbial community with stable flora and good degradation performance, which is more suitable for repairing polluted sites, and thus proposes a method for degrading dimethyl sulfide in aqueous phase by a mixed microbial community and its enrichment method.

[0009] The technical solution of the present invention is realized as follows: A mixed microbial community for degrading dimethyl sulfide in aqueous phase, the mixed microbial community includes Thiobacillus, Bacteroides, Hyphomicrobium, Leadbetterella and Bacillus.

[0010] Furthermore, the mixed microbial community includes Thiobacillus with an abundance percentage (OTUs) of 30-40%, Bacteroides with an abundance percentage of 5-15%, Hyphomicrobium with an abundance percentage of 5-10%, Leadbetterella with an abundance percentage of 2-5%, and Bacillus with an abundance percentage of 0.1-0.2%.

[0011] Furthermore, the mixed microbial community includes Thiobacillus with an OTUs abundance percentage of 33-38%, Bacteroides with an abundance percentage of 8-12%, Hyphomicrobium with an abundance percentage of 7-9%, Leadbetterella with an abundance percentage of 3-4%, and Bacillus with an abundance percentage of 0.1-0.2%.

[0012] Furthermore, the mixed microbial community is mixed with an aqueous solution containing Mg2+ and saponin and then used to degrade dimethyl sulfide.

[0013] Furthermore, the concentration of Mg 2+ in the aqueous solution is 5-15 mg / L.

[0014] Furthermore, the concentration of saponin in the aqueous solution is 90-110 mg / L.

[0015] An enrichment method for a mixed microbial community for degrading dimethyl sulfide in aqueous phase, comprising the following steps: Step 1, culturing in a basic inorganic salt medium: Take the biofilm on the surface of the packing of a biotrickling filter for treating dimethyl sulfide waste gas that has been operating for a long time, add it to pure water to make a suspension, inoculate the suspension into an inorganic salt medium, add dimethyl sulfide, and culture it in a constant temperature shaking incubator. Take the culture solution and re-transfer it to a fresh inorganic salt medium, add dimethyl sulfide, and culture it under the same conditions;

[0016] Step 2, enrichment and domestication: Regularly detect the concentration of residual methylethyl sulfide in the culture medium. After its concentration significantly decreases, re-inoculate it into a fresh inorganic salt medium and add the same concentration of methylethyl sulfide. Continuously enrich and domesticate in this way, and maintain the concentration of this pollutant to continue domesticating multiple times to obtain the final enriched solution of the microbial mixed flora.

[0017] Furthermore, the inorganic salt medium is prepared according to the following ratio: Na2HPO4 1.8 g / L, KH2PO4 1.0 g / L, NH4Cl 1.0 g / L, MgCl2 0.2 g / L, CaCl2 0.024 g / L, FeCl2 1.0 g / L, H3BO3 0.014 g / L, MnCl2 0.10 g / L, ZnCl2 0.10 g / L, Na2MoO4·2H2O 0.02 g / L, CoCl2·6H2O 0.02 g / L, with a pH of 7.2, and sterilized at 121 °C for 20 min.

[0018] The beneficial effects of the present invention are as follows: The functional microbial mixed flora of the present invention can metabolize and grow using methylethyl sulfide as a carbon source, and methylethyl sulfide is effectively degraded as an electron acceptor. Mg 2+ and the addition of saponin enable the mixed flora to have a better degradation effect. When Mg 2+ and the saponin concentrations are 10 mg / L and 100 mg / L respectively. The shake flask test in the laboratory shows that this mixed flora can efficiently degrade 35 mg / L of methylethyl sulfide in the aqueous phase within 24 h, having a good repair effect. Description of the Drawings

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0020] Figure 1 It is the genus-level composition diagram of the amplicon sequencing results of the microbial mixed flora in Example 1;

[0021] Figure 2 It is the degradation effect diagram of the microbial mixed flora in Example 1 on methylethyl sulfide under different Mg 2+ concentrations;

[0022] Figure 3 It is the degradation effect diagram of the microbial mixed flora on 35 mg / L of methylethyl sulfide under different saponin concentration conditions. Detailed Embodiments

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0024] Example 1

[0025] A method for enriching a microbial mixed flora for degrading methyl mercaptan, comprising the following steps:

[0026] (1) Cultivation in a basic inorganic salt medium: The microorganisms are from the biofilm collected from the surface of the packing of a biotrickling filter tower for treating methyl mercaptan waste gas with long-term operation. Take 5 g of the biofilm and add it to 50 ml of pure water to make a suspension. Take 5 ml of the suspension and inoculate it into 100 mL of the inorganic salt medium. Add methyl mercaptan to make its final concentration 35 mg / L, and culture it in a constant temperature shaking incubator at 30 °C and 170 r / min for 72 h. Then take 10% (v / v) of the culture solution and re-transfer it to fresh 100 mL of the inorganic salt medium, add methyl mercaptan to make its final concentration 35 mg / L, and culture it under the same conditions.

[0027] (2) Enrichment and domestication: Regularly detect the concentration of the remaining methyl mercaptan in the medium. After its concentration significantly decreases, re-transfer it to fresh inorganic salt medium and add the same concentration of methyl mercaptan. Continuously enrich and domesticate in this way, and maintain the concentration of this pollutant and continue to domesticate multiple times to obtain the final functional microbial enrichment solution.

[0028] The above inorganic salt medium is prepared according to the following ratio: Na2HPO4 1.8 g / L, KH2PO4 1.0 g / L, NH4Cl 1.0 g / L, MgCl2 0.2 g / L, CaCl2 0.024 g / L, FeCl2 1.0 g / L, H3BO3 0.014 g / L, MnCl2 0.10 g / L, ZnCl2 0.10 g / L, Na2MoO4·2H2O 0.02 g / L, CoCl2·6H2O 0.02 g / L, pH 7.2, sterilize at 121 °C for 20 min.

[0029] The microbial mixed flora obtained by the above method, the taxonomic classification at the genus level of the amplicon sequencing results is as Figure 1As shown. The bacteria include OTUs abundance percentages including 31% of Thiobacillus, 10.21% of Bacteroides, 5.85% of Hyphomicrobium, 4.2% of Leadbetterella, and 0.18% of Bacillus.

[0030] Example 2

[0031] The mixed bacterial community was inoculated into an inorganic salt medium containing 35 mg / L of methyl sulfide at an inoculation amount of 10% (v / v). The Mg concentration in the medium was set at 2 mg / L, 5 mg / L, 10 mg / L, 25 mg / L, and 50 mg / L respectively. It was cultured in a constant temperature shaking incubator at 30 °C and 170 r / min for 96 h. Samples were taken regularly to measure the concentration of methyl sulfide in the medium, and the degradation effect of the mixed bacterial community on methyl sulfide was investigated. The results are as 2+ shown. The mixed bacterial community can effectively degrade methyl sulfide in the medium. It can be found that when the Mg concentration is 10 mg / L, the bacterial community can degrade 35 mg / L of methyl sulfide within 72 h, while the other concentration groups are still not completely degraded after 96 h. Therefore, when the Mg concentration in the medium is 10 mg / L, it has a higher degradation rate. Figure 2 As shown. The mixed bacterial community can effectively degrade methyl sulfide in the medium. It can be found that when the Mg 2+ concentration is 10 mg / L, the bacterial community can degrade 35 mg / L of methyl sulfide within 72 h, while the other concentration groups are still not completely degraded after 96 h. Therefore, when the Mg 2+ concentration in the medium is 10 mg / L, it has a higher degradation rate.

[0032] Example 3

[0033] To obtain the optimal promoting concentration of saponin, different concentration groups were set to explore their effects on the degradation performance of the mixed bacterial community. The saponin concentration in the medium was set at 0 mg / L, 50 mg / L, 100 mg / L, 150 mg / L, and 300 mg / L respectively. The mixed bacterial community was inoculated into an inorganic salt medium containing 35 mg / L of methyl sulfide at an inoculation amount of 10% (v / v). It was cultured in an incubator at 30 °C and 170 r / min for 72 h. Samples were taken regularly to measure the concentration of methyl sulfide in the medium. The results are as Figure 3 shown. The mixed bacterial community has a good degradation effect in the range of saponin concentration from 100 to 300 mg / L. It can be seen from the figure that when the saponin concentration is 100 mg / L, the degradation rate of methyl sulfide is close to 100% at 24 h, while the degradation rate of the control group without saponin is only 11.82% at 24 h. Obviously, the addition of saponin has greatly improved the rate of the bacterial community degrading methyl sulfide, and 100 mg / L is the optimal concentration.

[0034] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for degrading dimethyl sulfide in an aqueous phase by a microbial mixed flora, characterized in that: The microbial mixed flora includes Thiobacillus, Bacteroides, Hyphomicrobium, Leadbetterella, and Bacillus; Among them, the microbial mixed flora includes Thiobacillus with an abundance percentage of 30-40%, Bacteroides with an abundance percentage of 5-15%, Hyphomicrobium with an abundance percentage of 5-10%, Leadbetterella with an abundance percentage of 2-5%, and Bacillus with an abundance percentage of 0.1-0.2%; Among them, the method for the microbial mixed flora to degrade dimethyl sulfide in the aqueous phase includes: mixing the microbial mixed flora with an aqueous solution containing Mg 2+ and saponin, and then degrading dimethyl sulfide.

2. The method for degrading methyl sulfide in an aqueous phase according to claim 1, characterized in that: The microbial mixed flora includes Thiobacillus with an abundance percentage of 33-38%, Bacteroides with an abundance percentage of 8-12%, Hyphomicrobium with an abundance percentage of 7-9%, Leadbetterella with an abundance percentage of 3-4%, and Bacillus with an abundance percentage of 0.1-0.2%.

3. The method for degrading methyl sulfide in an aqueous phase according to claim 1, characterized in that: The concentration of Mg in the aqueous solution 2+ is 5 - 15 mg / L.

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