A method for separating sulfur in a biological desulfurization process

Abstract

The present invention belongs to environmentally friendly purification technology and relates to a method suitable for separating sulfur in a biological desulfurization process. In response to the shortcomings of the existing technology, the present invention provides a method for separating biological sulfur by adding an immobilized complex enzyme preparation and a sulfur particle modifier and combining it with an electrode method. The effluent containing biological sulfur to be treated enters a pretreatment tank through a liquid inlet pipe, and the immobilized complex enzyme preparation is added to the pretreatment tank. The effluent containing biological sulfur is catalytically hydrolyzed and then flows into a flocculation tank. A voltage is applied and a sulfur particle modifier is added to obtain a flocculated precipitate containing biological sulfur, which flows into a sedimentation tank for separation. The present invention can quickly and efficiently separate biological sulfur from effluent and is suitable for sulfur recovery processing units in microbial desulfurization processes such as natural gas, biogas, coal-fired flue gas, and sulfur-containing wastewater. It is simple to operate, has low power consumption, requires a small amount of complex enzyme preparation and modifier, is environmentally friendly, and can achieve a biological sulfur recovery rate of 95-99% and a sulfur purity of 90%.

Description

Technical Field

[0001] The present invention belongs to environmentally friendly purification technology and relates to a method suitable for separating sulfur in a biological desulfurization process. The method is mainly used in a sulfur recovery processing unit in a microbial desulfurization process of natural gas, biogas, coal-fired flue gas, sulfur-containing wastewater, etc. The method can efficiently and quickly separate biological sulfur particles in the desulfurization solution to realize the recovery of sulfur resources. Background Art

[0002] Biological desulfurization technology, developed in the 1980s as an alternative to conventional desulfurization, offers numerous advantages, including the absence of catalysts and oxidants, chemical sludge treatment, minimal biofouling, low energy consumption, sulfur recovery, high efficiency, and odorlessness. However, its disadvantages include difficult process control and demanding operating conditions.

[0003] In bioreactors, elemental sulfur (biosulfur) produced through bioconversion differs significantly from naturally occurring chemical sulfur in several properties. By investigating the properties of this microbially converted biosulfur and observing its morphology, Lettinga et al. discovered that the surface of the biosulfur is very rough and uneven. The raised areas are composed of various biomacromolecules, which adhere to the surface of the biosulfur particles. This contrasts sharply with the smooth surface of chemical sulfur particles, which have regular geometric shapes. They also found that the long-chain polymers on the surface of these biosulfur particles carry a negative charge, significantly inhibiting the aggregation and precipitation of the sulfur particles. Consequently, the elemental sulfur produced through bioconversion exhibits a colloidal state that is less prone to sedimentation and aggregation, remaining suspended in water and difficult to separate.

[0004] Currently, the commonly used methods for separating particulate matter include gravity sedimentation, centrifugal sedimentation, flocculation sedimentation, flotation, etc. Regarding the separation methods of biosulfur, current research mainly focuses on the separation of biosulfur during the sulfide removal process.

[0005] Janssen et al. discovered that biosulfur particles have a negative surface charge. Therefore, they proposed using flocculation and sedimentation to separate biosulfur particles by adding a cationic flocculant to water containing the particles. Li Yaxin et al. believed that flocculation and sedimentation could separate biosulfur particles from water, but the flocculant would encapsulate the particles, making subsequent solvent extraction and crystallization purification difficult.

[0006] Li Yaxin et al. studied the recovery of elemental sulfur from effluent water after sulfide treatment in a colorless sulfur bacteria biooxidation reactor. They proposed a "slow sand filter-sand scraping-extraction-distillation" process for elemental sulfur recovery. By controlling the filtration rate in the slow sand filter, a sulfur recovery rate of 76.1% to 80.0% was achieved. While feasible, this process route remains to be tested for engineering applications due to the high cost and economic advantages of extraction and its high toxicity.

[0007] Shell-Paques of the Netherlands uses flotation to recover biogenic sulfur particles. The process primarily consists of a flotation tank, inclined plate sedimentation tank, vacuum drum filter, heat exchanger, and sulfur centrifuge. The principle is to use pressurized flotation or dissolved air flotation to lift biogenic sulfur particles to the surface of the water. A surface scraper then scrapes the particles away from the water, and further centrifugation is performed to separate the biogenic sulfur particles. However, this method is not only energy-intensive and costly, but also susceptible to air oxidation during the flotation process, making it unsuitable for large-scale use. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the present invention provides a method for separating biosulfur by adding an immobilized complex enzyme preparation and a sulfur particle modifier, combined with an electrode method. The goal is to fundamentally destabilize the biosulfur colloidal system, accelerate the sedimentation and aggregation of sulfur particles, and improve the recovery rate and purity of biosulfur.

[0009] The technical solution of the present invention is achieved as follows: a method for separating sulfur in a biological desulfurization process, characterized in that: 0.0001% to 0.005% of an immobilized complex enzyme preparation is added to the bio-sulfur-containing effluent to be treated to obtain a hydrolyzed bio-sulfur-containing effluent; the hydrolyzed bio-sulfur-containing effluent enters a flocculation tank with an applied voltage, and 10 to 50 ppm of a sulfur particle modifier is added simultaneously to obtain a bio-sulfur-containing flocculent precipitate; the bio-sulfur-containing flocculent precipitate is rapidly precipitated by gravity sedimentation to obtain a precipitate and a supernatant.

[0010] The biosulfur-containing effluent from the biodesulfurization process first enters a pretreatment tank, where an immobilized enzyme complex is added. Under the catalytic action of the enzyme complex, macromolecular polymers attached to the surface of the biosulfur particles are hydrolyzed into small biomolecules, which then leave the sulfur particle surface. As the absolute value of the zeta potential of the biosulfur particles decreases, the system's settling performance improves. The hydrolyzed biosulfur-containing effluent then enters a flocculation tank, where an external voltage is applied for electrolysis, promoting the directional aggregation of the biosulfur particles in the system. Simultaneously, a sulfur particle modifier is added to rapidly increase the particle size of the sulfur particles, further promoting agglomeration and sedimentation of the biosulfur particles, achieving rapid flocculation and separation of the biosulfur. The biosulfur-containing flocculated precipitate flows into a sedimentation tank, where gravity sedimentation allows for effective coagulation and high separation from the water. The precipitate exits the system through the outlet. The supernatant, rich in small biomolecules, provides nutrients for microbial growth and is pumped back into the bioreactor for recycling.

[0011] Generally, the immobilized complex enzyme preparation is composed of proteolytic enzyme, cellulolytic enzyme, lipase, nuclease, and lysozyme, and the mass ratio thereof is (6~8):(3~5):(1~2):(1~2):(3~5).

[0012] A voltage of 5 to 15 V is applied to the flocculation tank to form an electrolytic cell.

[0013] The sulfur particle modifier is composed of 10-30% of biological flocculant, 2-10% of biological surfactant, 5-15% of stabilizer, and the rest is water.

[0014] The proteolytic enzyme is at least one of cathepsin, trypsin and subtilisin, and the enzyme activity is 500-5000 U / g.

[0015] The cellulose hydrolyzing enzyme is at least one of beta-glucanase, xylanase and beta-glucosidase, and the enzyme activity is 100-2000 U / g.

[0016] The lipase is at least one of phosphatase, sterolase and carboxylesterase, and the enzyme activity is 100-1000 U / g.

[0017] The biological flocculant is a composite biological flocculant containing cellulose fermentation residues, flocculent bacterial cells and high-molecular flocculation active substances secreted by them.

[0018] The biosurfactant is any one or two of rhamnolipid, sophorolipid and surfactin.

[0019] The stabilizer is any one or two of sorbitol, sucrose and lauric acid.

[0020] The biological sulfur separation method of the present invention can be used for the sulfur recovery processing unit in the microbial desulfurization process of natural gas, biogas, coal-fired flue gas, sulfur-containing wastewater and the like.

[0021] Beneficial effects

[0022] The biosulfur separation method of the present invention can decompose the macromolecular polymers attached to the surface of biosulfur particles into biomicromolecules, which can be used as a nutrient source for microorganisms. At the same time, the negatively charged attachments on the surface of the biosulfur are reduced, the absolute value of the Zeta potential is reduced to below 10mV, and the sedimentation performance is improved. The use of an external voltage and a sulfur particle modifier can promote the coagulation and polymerization of biosulfur particles to form particle clusters, so that the sulfur particle size is rapidly increased to 40μm. The biosulfur particles are rapidly settled under the action of gravity and separated. The present invention can quickly and efficiently separate biosulfur from effluent, and the clear liquid can be recycled. It is simple to operate, has low power consumption, requires a small amount of complex enzyme preparation and modifier, is environmentally friendly, and can achieve a biosulfur recovery rate of 95-99% and a sulfur purity of 90%. DETAILED DESCRIPTION

[0023] The present invention will be further described below by way of examples, the purpose of which is to provide a better understanding of the present invention. Therefore, the examples given do not limit the scope of protection of the present invention.

[0024] Example 1

[0025] (1) Experimental conditions: The treated biosulfur-containing effluent with a biosulfur content of 845 ng / L was passed into a pretreatment tank, to which 0.0005% of an immobilized composite enzyme preparation was added, wherein the mass ratio of cathepsin, β-glucanase, phosphatase, nuclease, and lysozyme was 6:4:1:1:3. The hydrolyzed biosulfur-containing effluent was then passed into a flocculation tank, where a voltage of 10 V was applied and 30 ppm of a sulfur particle modifier was added, consisting of 25% composite bioflocculant, 7% surfactant, 12% sorbitol, and the remainder water.

[0026] (2) Experimental results: After pretreatment, the absolute value of the Zeta potential of the biosulfur particles decreased from 43mV to 8mV, and the particle size of the biosulfur particles in the flocculation tank increased from 7μm to 48μm. They flowed into the sedimentation tank for rapid separation, and the biosulfur recovery rate reached 98%, and the sulfur purity reached 92%.

[0027] Example 2

[0028] (1) Experimental conditions: The treated biosulfur-containing effluent with a biosulfur content of 845 ng / L was passed into a pretreatment tank, to which 0.0005% of an immobilized composite enzyme preparation was added, wherein the mass ratio of cathepsin, β-glucanase, phosphatase, nuclease, and lysozyme was 6:4:1:1:3. The hydrolyzed biosulfur-containing effluent was then passed into a flocculation tank, where a voltage of 5 V was applied and 20 ppm of a sulfur particle modifier was added, consisting of 25% composite bioflocculant, 7% surfactant, 12% sorbitol, and the remainder water.

[0029] (2) Experimental results: After pretreatment, the absolute value of the Zeta potential of the biosulfur particles decreased from 43mV to 8mV, and the particle size of the biosulfur particles in the flocculation tank increased from 7μm to 40μm. They flowed into the sedimentation tank for rapid separation, and the biosulfur recovery rate reached 96%, and the sulfur purity reached 90%.

[0030] Example 3

[0031] (1) Experimental conditions: The treated biosulfur-containing effluent with a biosulfur content of 845 ng / L was passed into a pretreatment tank, to which 0.001% immobilized composite enzyme preparation was added, wherein the mass ratio of cathepsin, β-glucanase, phosphatase, nuclease, and lysozyme was 6:4:1:1:3. The hydrolyzed biosulfur-containing effluent was then passed into a flocculation tank, where a voltage of 10 V was applied and 30 ppm of a sulfur particle modifier was added, consisting of 25% composite bioflocculant, 7% surfactant, 12% sorbitol, and the remainder water.

[0032] (2) Experimental results: After pretreatment, the absolute value of the Zeta potential of the biosulfur particles decreased from 43mV to 5mV, and the particle size of the biosulfur particles in the flocculation tank increased from 7μm to 52μm. They flowed into the sedimentation tank for rapid separation, and the biosulfur recovery rate reached 99%, and the sulfur purity reached 93%.

[0033] Example 4

[0034] (1) Experimental conditions: The treated biosulfur-containing effluent with a biosulfur content of 845 ng / L was passed into a pretreatment tank, to which 0.001% immobilized composite enzyme preparation was added, wherein the mass ratio of cathepsin, β-glucanase, phosphatase, nuclease, and lysozyme was 6:4:1:1:3. The hydrolyzed biosulfur-containing effluent was then passed into a flocculation tank, where a voltage of 5 V was applied and 20 ppm of a sulfur particle modifier was added, consisting of 25% composite bioflocculant, 7% surfactant, 12% sorbitol, and the remainder water.

[0035] (2) Experimental results: After pretreatment, the absolute value of the Zeta potential of the biosulfur particles decreased from 43mV to 5mV, and the particle size of the biosulfur particles in the flocculation tank increased from 7μm to 50μm. They flowed into the sedimentation tank for rapid separation, and the biosulfur recovery rate reached 97%, and the sulfur purity reached 91%.

[0036] Example 5

[0037] (1) Experimental conditions: The treated biosulfur-containing effluent with a biosulfur content of 1407 ng / L was passed into a pretreatment tank, to which 0.002% immobilized composite enzyme preparation was added, with the mass ratio of trypsin, xylanase, carboxylesterase, nuclease, and lysozyme being 8:3:1:1:4. The hydrolyzed biosulfur-containing effluent was then passed into a flocculation tank, where a voltage of 15 V was applied and 50 ppm of a sulfur particle modifier was added, consisting of 20% composite bioflocculant, 10% rhamnolipid, 8% lauric acid, and the remainder water.

[0038] (2) Experimental results: After pretreatment, the absolute value of the Zeta potential of the biosulfur particles decreased from 48mV to 10mV, and the particle size of the biosulfur particles in the flocculation tank increased from 5μm to 45μm. They flowed into the sedimentation tank for rapid separation, and the biosulfur recovery rate reached 98%, and the sulfur purity reached 93%.

[0039] Example 6

[0040] (1) Experimental conditions: The treated biosulfur-containing effluent with a biosulfur content of 1407 ng / L was passed into a pretreatment tank, to which 0.002% immobilized composite enzyme preparation was added, wherein the mass ratio of trypsin, xylanase, carboxylesterase, nuclease, and lysozyme was 8:3:1:1:4. The hydrolyzed biosulfur-containing effluent was then passed into a flocculation tank, where a voltage of 10 V was applied and 40 ppm of a sulfur particle modifier was added, consisting of 20% composite bioflocculant, 10% rhamnolipid, 8% lauric acid, and the remainder water.

[0041] (2) Experimental results: After pretreatment, the absolute value of the Zeta potential of the biosulfur particles decreased from 48mV to 10mV, and the particle size of the biosulfur particles in the flocculation tank increased from 5μm to 42μm. They flowed into the sedimentation tank for rapid separation, and the biosulfur recovery rate reached 97%, and the sulfur purity reached 91%.

[0042] Example 7

[0043] (1) Experimental conditions: The treated biosulfur-containing effluent with a biosulfur content of 1407 ng / L was passed into a pretreatment tank, to which 0.003% immobilized composite enzyme preparation was added, with the mass ratio of trypsin, xylanase, carboxylesterase, nuclease, and lysozyme being 8:4:1:1:3. The hydrolyzed biosulfur-containing effluent was then passed into a flocculation tank, where a voltage of 15 V was applied and 50 ppm of a sulfur particle modifier was added, consisting of 20% composite bioflocculant, 10% rhamnolipid, 8% lauric acid, and the remainder water.

[0044] (2) Experimental results: After pretreatment, the absolute value of the Zeta potential of the biosulfur particles decreased from 48mV to 5mV, and the particle size of the biosulfur particles in the flocculation tank increased from 5μm to 50μm. They flowed into the sedimentation tank for rapid separation, and the biosulfur recovery rate reached 99%, and the sulfur purity reached 94%.

[0045] Example 8

[0046] (1) Experimental conditions: The treated biosulfur-containing effluent with a biosulfur content of 1407 ng / L was passed into a pretreatment tank, to which 0.003% immobilized composite enzyme preparation was added, with the mass ratio of trypsin, xylanase, carboxylesterase, nuclease, and lysozyme being 8:4:1:1:3. The hydrolyzed biosulfur-containing effluent was then passed into a flocculation tank, where a voltage of 10 V was applied and 40 ppm of a sulfur particle modifier was added, consisting of 20% composite bioflocculant, 10% rhamnolipid, 8% lauric acid, and the remainder water.

[0047] (2) Experimental results: After pretreatment, the absolute value of the Zeta potential of the biosulfur particles decreased from 48mV to 5mV, and the particle size of the biosulfur particles in the flocculation tank increased from 5μm to 45μm. They flowed into the sedimentation tank for rapid separation, and the biosulfur recovery rate reached 98%, and the sulfur purity reached 92%.

[0048] Blank example

[0049] (1) Experimental conditions: The treated biosulfur effluent with a biosulfur content of 845 ng / L was passed into the pretreatment tank and then into the flocculation tank and sedimentation tank. No immobilized enzyme preparation or sulfur particle modifier was added, and no external voltage was applied. The biosulfur particles relied solely on their own gravity for flocculation and sedimentation.

[0050] (2) Experimental results: After half an hour, there was no obvious flocculation of the biosulfur particles, the absolute value of the Zeta potential was still 42mV, the particle size of the biosulfur particles was within 10μm, the biosulfur recovery rate was less than 20%, and the sulfur purity was less than 40%.

[0051] Comparative Example 1

[0052] (1) Experimental conditions: The treated biosulfur-containing effluent with a biosulfur content of 845 ng / L was passed into a pretreatment tank, to which 0.005% immobilized complex enzyme preparation was added, with the mass ratio of cathepsin, β-glucanase, phosphatase, nuclease, and lysozyme being 6:4:1:1:3. The hydrolyzed biosulfur-containing effluent was then passed into a flocculation tank without the application of voltage or sulfur particle modifier.

[0053] (2) Experimental results: After pretreatment, the absolute value of the Zeta potential of the biosulfur particles decreased from 43mV to 5mV, and the particle size of the biosulfur particles in the flocculation tank increased from 7μm to 25μm. They flowed into the sedimentation tank for separation. The biosulfur recovery rate was 82% and the sulfur purity was 90%.

[0054] Comparative Example 2

[0055] (1) Experimental conditions: The biosulfur-containing effluent to be treated with a biosulfur content of 845 ng / L was passed into the pretreatment tank without adding any immobilized complex enzyme preparation. The biosulfur-containing effluent flowed into the flocculation tank, and a voltage of 30 V was applied, but no sulfur particle modifier was added.

[0056] (2) Experimental results: The absolute value of the Zeta potential of the biosulfur particles in the flocculation tank decreased from 45mV to 28mV, and the particle size increased from 7μm to 18μm. They flowed into the sedimentation tank for separation. The biosulfur recovery rate was 75% and the sulfur purity was 68%.

[0057] Comparative Example 3

[0058] (1) Experimental conditions: The treated biosulfur effluent with a biosulfur content of 845 ng / L was passed into the pretreatment tank without the addition of any immobilized composite enzyme preparation. The biosulfur effluent flowed into the flocculation tank without the application of external voltage. 100 ppm of sulfur granule modifier was added, consisting of 25% composite bioflocculant, 7% surfactant, 12% sorbitol, and the remainder water.

[0059] (2) Experimental results: The absolute value of the Zeta potential of the biosulfur particles in the flocculation tank decreased from 45mV to 35mV, and the particle size increased from 7μm to 20μm. They flowed into the sedimentation tank for separation. The biosulfur recovery rate was 65% and the sulfur purity was 70%.

[0060] Comparing the results of Examples 1-3, it can be seen that under the same conditions, the use of the immobilized composite enzyme preparation alone for hydrolysis of biosulfur-containing effluent significantly reduced the absolute value of the zeta potential of the biosulfur particles and increased the particle size. The biosulfur recovery rate and sulfur purity increased to 82% and 90%, respectively, which is worse than the results achieved by applying voltage or using a sulfur particle modifier alone. However, the results were significantly inferior to those achieved by the Examples. Furthermore, the addition of the composite enzyme preparation and modifier in the Examples was small, resulting in lower power consumption.

[0061] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for separating sulfur in a biological desulfurization process, characterized in that: 0.0001% to 0.005% of an immobilized complex enzyme preparation is added to the biosulfur-containing effluent to be treated to obtain hydrolyzed biosulfur-containing effluent; the hydrolyzed biosulfur-containing effluent enters a flocculation tank with an external voltage, and 10 to 50 ppm of a sulfur particle modifier is added to obtain a biosulfur-containing flocculent precipitate; the biosulfur-containing flocculent precipitate is rapidly precipitated by gravity sedimentation to obtain a precipitate and a supernatant; the immobilized complex enzyme preparation consists of proteolytic enzyme, cellulose hydrolytic enzyme, lipase, nuclease, and lysozyme, and the mass ratio thereof is (6 to 8):(3 to 5):(1 to 2):(1 to 2):(3 to 5).

2. The method according to claim 1, wherein: A voltage of 5~15V is applied to the flocculation tank to form an electrolytic cell.

3. The method according to claim 1, wherein: The sulfur particle modifier is composed of 10-30% bioflocculant, 2-10% biosurfactant, 5-15% stabilizer, and the rest is water.

4. The method according to claim 1, wherein: The proteolytic enzyme is at least one of cathepsin, trypsin and subtilisin, and the enzyme activity is 500-5000 U / g.

5. The method according to claim 1, wherein: The cellulose hydrolyzing enzyme is at least one of beta-glucanase, xylanase and beta-glucosidase, and the enzyme activity is 100-2000 U / g.

6. The method according to claim 1, wherein: The lipase is at least one of phosphatase, sterolase and carboxylesterase, and the enzyme activity is 100-1000 U / g.

7. The method according to claim 3, wherein: The biological flocculant is a composite biological flocculant containing cellulose fermentation residues, flocculent bacterial cells and high-molecular flocculation active substances secreted by them.

8. The method according to claim 3, wherein: The biosurfactant is any one or two of rhamnolipid, sophorolipid and surfactin; and the stabilizer is any one or two of sorbitol, sucrose and lauric acid.

9. The method according to claim 1, wherein: It is suitable for sulfur recovery treatment units in the microbial desulfurization process of natural gas, biogas, coal-fired flue gas and sulfur-containing wastewater.