Function-partitioned sulfur filler and preparation method thereof

Abstract

The invention discloses a functionally partitioned sulfur filler and a preparation method thereof. The functionally partitioned sulfur filler comprises a porous sulfur core and a polydopamine film, the surface of the porous sulfur core is coated with the polydopamine film; sulfur disproportionated bacteria are loaded in pores of the porous sulfur core; denitrifying bacteria are loaded on the surface of the polydopamine membrane, and a dissolved oxygen gradient is formed in the sulfur filler; an inner-layer anaerobic zone is arranged in the porous sulfur core and is used for performing sulfur disproportionation reaction; the surface of the polydopamine membrane is an outer-layer anoxic zone and is used for carrying out denitrification reaction. According to the present invention, the flora partition is constructed in the single filler, the sulfur disproportionation bacteria are separated from the external nitrate and the dissolved oxygen to a certain degree, the symbiosis and the cooperation of the sulfur disproportionation bacteria and the denitrifying bacteria are ensured, the sulfide and the polysulfide are produced through the internal sulfur disproportionation reaction, and the electrons in the sulfide and the polysulfide are supplied to the denitrifying bacteria for use so as to achieve the efficient and stable nitrogen removal.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment, and in particular to a functionally partitioned sulfur packing material and its preparation method. Background Technology

[0002] Nitrogen content is a key indicator of water quality. Efficient nitrogen removal in wastewater treatment plants (WWTPs) is crucial for addressing nitrogen pollution and maintaining aquatic ecosystem quality. Traditional wastewater denitrification methods utilize heterotrophic denitrification (HD), which, while efficient and practical, suffers from high costs and a large carbon footprint. For urban wastewater with a low carbon-to-nitrogen ratio, additional carbon sources are required, significantly increasing costs. Elemental sulfur autotrophic denitrification technology has attracted considerable attention due to its low cost and the fact that it requires no external carbon source. However, this technology is subject to S... 0 Its low bioavailability makes it difficult to promote its application.

[0003] The coupling of sulfur autotrophic denitrification and elemental sulfur disproportionation has been proven to offer advantages in low-cost, high-speed nitrogen removal. This method utilizes the sulfur disproportionation reaction occurring in the upper layer of the reactor to produce dissolved, highly reactive sulfides and polysulfides. A peristaltic pump creates a reflux, transporting these sulfides and polysulfides to the lower layer of the reactor, where they serve as electron donors for efficient nitrate reduction by denitrifying bacteria. However, the optimal growth environments for the two bacteria differ. Sulfur disproportionating bacteria require a sufficiently alkaline, anaerobic environment for growth and metabolism, while denitrifying bacteria require nitrates and thrive in an oxygen-deficient environment. In the aforementioned reaction system, sulfur disproportionating and denitrifying bacteria generally exhibit a stratified structure in the packed bed reactor. However, when nitrate levels surge, unreacted nitrate enters the upper layer, altering the metabolic pathways of sulfur disproportionating bacteria and thus affecting nitrogen removal efficiency. To address this, some studies have used a two-stage device to separate the sulfur disproportionating and denitrifying bacteria, but this significantly increases infrastructure and maintenance costs. Summary of the Invention

[0004] In order to overcome the above-mentioned shortcomings and deficiencies of the prior art, the present invention aims to provide a functionally partitioned sulfur packing and its preparation method. In the depth direction of the sulfur-based packing microenvironment, anaerobic (DO<0.1mg / L) and anoxic (DO<2mg / L) functional partitions are formed from the inside to the outside. The partitioned environment forms a dissolved oxygen gradient, which can provide a suitable growth environment for the two microorganisms. At the same time, the nitrate fluctuation is limited to the outer layer and does not interfere with the sulfur disproportionation in the inner layer, thus ensuring the symbiosis and cooperation of sulfur disproportionating bacteria and denitrifying bacteria.

[0005] Another objective of this invention is to provide a wastewater denitrification method based on sulfur disproportionation-sulfur autotrophic denitrification coupling, which utilizes the aforementioned functionally zoned sulfur packing material to achieve efficient and stable denitrification.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] The present invention provides a functionally partitioned sulfur packing material, comprising a porous sulfur core and a polydopamine membrane; the polydopamine membrane is wrapped around the surface of the porous sulfur core; sulfur dismutating bacteria are loaded in the pores of the porous sulfur core; and denitrifying bacteria are loaded on the surface of the polydopamine membrane.

[0008] Specifically, the sulfur packing material in the functional zones forms a dissolved oxygen gradient inside; the porous sulfur core is an inner anaerobic zone, which is conducive to sulfur disproportionation reaction; and the polydopamine membrane is an outer anoxic zone, which is conducive to denitrification reaction.

[0009] Specifically, the polydopamine membrane is a hydrophilic medium, which is conducive to the attachment of denitrifying bacteria, and at the same time adsorbs some of the products of the sulfur disproportionation reaction.

[0010] The present invention also provides a method for preparing the sulfur filler for the aforementioned functional zones, comprising the following steps:

[0011] Preparation of porous sulfur cores;

[0012] The sulfur dismutase solution was immersed into the pores of the porous sulfur core and stabilized under an anaerobic environment to obtain a porous sulfur core loaded with sulfur dismutase.

[0013] A polydopamine membrane was coated on the surface of a porous sulfur core loaded with sulfur dismutase to obtain a filler coated with a polydopamine membrane.

[0014] The filler coated with polydopamine membrane was placed in denitrifying bacteria solution and immobilized in an anaerobic environment to obtain sulfur biological filler with functional zones.

[0015] Preferably, the preparation of the porous sulfur core specifically involves: mixing sulfur with an additive containing a pore-forming agent, heating until the sulfur melts, and granulating to form porous spheres with a diameter of 5-10 mm.

[0016] Preferably, the stabilization under anaerobic conditions specifically refers to stabilization in an anaerobic environment at 20~40℃ for more than 48 hours.

[0017] Preferably, the coating of the porous sulfur core loaded with sulfur dismutase with a polydopamine membrane specifically involves:

[0018] The porous sulfur core loaded with sulfur superoxide dismutase was immersed in Tris-HCl buffer, and dopamine hydrochloride at a concentration of 1.8~2.2 mg / ml was added. The mixture was shaken for 3~6 h, and then removed and rinsed to remove any residual polydopamine from the surface.

[0019] Preferably, the immobilization in an oxygen-deficient environment specifically refers to immobilization in an oxygen-deficient environment at 20~40℃ for more than 48 hours.

[0020] This invention also provides a wastewater denitrification method based on sulfur disproportionation-sulfur autotrophic denitrification coupling, comprising the following steps:

[0021] Wastewater is injected into a reactor containing sulfur packing material with the aforementioned functional zones for denitrification treatment involving sulfur disproportionation and sulfur autotrophic denitrification coupled.

[0022] Preferably, during the denitrification process, the core of the sulfur packing in the functional zone undergoes a sulfur disproportionation reaction to generate sulfur disproportionation product S. n 2- and HS - Some of the products are adsorbed by the polydopamine membrane and react with the denitrifying bacteria loaded on the inner surface of the polydopamine membrane, consuming the sulfur disproportionation reaction products in the core; some of the products pass through the polydopamine membrane and react with the denitrifying bacteria loaded on the outer surface of the polydopamine membrane.

[0023] In this invention, the polydopamine membrane facilitates the attachment of denitrifying bacteria and provides suitable growth environments for both sulfur-disproportionating and denitrifying bacteria, promoting bacterial growth and thus accelerating the sulfur disproportionation and denitrification reactions to improve nitrogen removal efficiency. Furthermore, the polydopamine membrane can adsorb some sulfur disproportionation products, reducing mass transfer resistance and increasing the diffusion rate of these products, thereby accelerating the reaction and further improving nitrogen removal efficiency.

[0024] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0025] (1) The functionally partitioned sulfur packing of the present invention forms a polydopamine membrane layer on the surface of the porous sulfur core through the self-polymerization of dopamine, forming a microenvironmental stratification in the longitudinal direction of the sulfur-based packing. The interior is a porous packing with sulfur as the main component, mainly loaded with sulfur disproportionating bacteria, while the polydopamine membrane layer is loaded with denitrifying bacteria, realizing the separation of the internal and external environments of the packing. The polydopamine membrane prevents the sulfur disproportionating bacteria from directly contacting the high concentration of nitrate and dissolved oxygen in the solution, avoiding interference with their sulfur disproportionation function and ensuring the symbiosis and cooperation between sulfur disproportionating bacteria and denitrifying bacteria.

[0026] (2) The sulfur packing material of the functional partition of the present invention forms a dissolved oxygen gradient through the polydopamine membrane. The core is an anaerobic environment, which is conducive to the sulfur disproportionation reaction; the outer layer is an anaerobic environment, which is conducive to the denitrification reaction, providing a suitable growth environment for the two microorganisms.

[0027] (3) The sulfur filler in the functional partition of the present invention improves the hydrophilicity of sulfur by coating with a polydopamine membrane, thereby promoting the attachment and growth of denitrifying bacteria; the core undergoes a sulfur disproportionation reaction, and the product S is generated. n 2- and HS -Some of the products are adsorbed by the polydopamine membrane and react with denitrifying bacteria loaded on the inner surface of the membrane: the denitrifying bacteria accept electrons from the sulfur dismutation products and use nitrate in the solution as electron acceptors to reduce nitrate to nitrogen gas, while S n 2- / HS - The sulfur is converted into elemental sulfur or sulfate, further protecting the sulfur-disproportionating bacteria in the inner layer from interference. Some sulfur disproportionation products pass through the polydopamine membrane and react with the denitrifying bacteria loaded on the outer surface of the membrane, further consuming the sulfur disproportionation products and promoting sulfur disproportionation. At the same time, the polydopamine membrane can also adsorb some sulfur disproportionation products, reducing mass transfer resistance and increasing the diffusion rate of sulfur disproportionation products, thereby accelerating the reaction and further improving denitrification efficiency.

[0028] (4) The wastewater denitrification method based on the functional partition of the present invention has good anti-fluctuation properties because the nitrate fluctuation is restricted to the outer layer and does not interfere with the sulfur disproportionation of the inner layer.

[0029] (5) Based on the functional partition sulfur packing method of the present invention, the sulfur packing particles with millimeter-level functional partitions are used as an independent reaction system to achieve bacterial community separation, which reduces the infrastructure cost compared with the two-stage device.

[0030] (6) Based on the functional partitioning of the present invention, the wastewater denitrification method of sulfur packing has a closed-loop internal sulfur cycle and the sulfur disproportionation products are used in situ for sulfur autotrophic denitrification, thereby reducing the risk of secondary pollution. Attached Figure Description

[0031] Figure 1 The image shows the morphological appearance of porous sulfur balls loaded with sulfur dismutase bacteria prepared according to an embodiment of the present invention.

[0032] Figure 2 The image shows the morphology of the filler coated with polydopamine film prepared for an embodiment of the present invention.

[0033] Figure 3 The appearance morphology of the functional partition sulfur filler prepared for an embodiment of the present invention is shown in the figure.

[0034] Figure 4 A scanning electron microscope image of the surface of the sulfur packing material with functional partitions prepared for an embodiment of the present invention, wherein PDA refers to polydopamine and SOB refers to sulfur-oxidizing denitrifying bacteria.

[0035] Figure 5 The image shows a cross-sectional inner layer scanning electron microscope image of the functionally partitioned sulfur packing prepared for an embodiment of the present invention, where PDA refers to polydopamine and SDB refers to sulfur dismutating bacteria.

[0036] Figure 6The community structure of sulfur packing with functional partitions prepared for embodiments of the present invention and sulfur packing of comparative samples.

[0037] Figure 7 The relative content of functional microbial communities in the sulfur packing material with functional zones prepared for embodiments of the present invention and the sulfur packing material of the comparative sample.

[0038] Figure 8 A comparison of the active biomass of sulfur packing material with functional zones prepared for embodiments of the present invention and sulfur packing material of a comparative sample.

[0039] Figure 9 A comparison of sulfide concentrations in the functional zone sulfur packing prepared for embodiments of the present invention and in the sulfur packing of a comparative sample under the same water exchange cycle.

[0040] Figure 10 A comparison of nitrate removal in the sulfur packing of the functional zones prepared for embodiments of the present invention and the sulfur packing of the comparative sample.

[0041] Figure 11 The denitrification rates of sulfur packing materials in functional zones prepared according to the embodiments of the present invention and sulfur packing materials in comparative samples are compared under the same water exchange cycle. Detailed Implementation

[0042] The present invention is further described below through specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0043] Example 1

[0044] The sulfur filler for the functional zones in this embodiment is prepared as follows:

[0045] Preparation of porous sulfur spheres: First, mix the materials according to the ratio of sulfur: concrete: gypsum: sodium bicarbonate = 27:4:3:2, heat to 140-160℃ until the sulfur melts, and granulate to form porous spheres with a diameter of 5-10 mm.

[0046] Sulfur-modifying bacteria were loaded: A solution of sulfur-modifying bacteria was injected into porous sulfur balls and stabilized at 30°C under anaerobic conditions for 72 hours to obtain the desired result. Figure 1 The porous sulfur spheres loaded with sulfur-disproportionating bacteria are shown.

[0047] Polydopamine-coated membrane: Porous sulfur beads loaded with superoxide dismutase were immersed in 0.01M Tris-HCl buffer, and 2 mg / ml dopamine hydrochloride was slowly added. The mixture was shaken for 6 hours, then removed and rinsed to remove any residual polydopamine, resulting in a polydopamine-coated packing material. Figure 2 As shown, the surface of the filler has turned noticeably black at this point;

[0048] Loading with denitrifying bacteria: The packing material coated with polydopamine membrane was placed in a denitrifying bacteria solution and fixed at 25°C under an anaerobic environment for 72 h to obtain sulfur packing material with functional zones, such as... Figure 3 As shown.

[0049] The functionally partitioned sulfur packing material prepared in this embodiment was observed by scanning electron microscopy (SEM). The bacterial adhesion was observed on the surface and inside of the packing material. The results are as follows: Figure 4 and Figure 5 As shown. The electron micrograph of the packing surface can be seen (see...) Figure 4 The packing material is covered with a PDA film, on which microorganisms are loaded and grown. After removing approximately 2 mm of the surface layer of the packing material, it can be observed that a large number of microorganisms are also attached to the inside of the packing material. Figure 5 This indicates that the functional bacteria have been successfully loaded into the packing material.

[0050] Example 2

[0051] The preparation of the sulfur filler for the functional zones in this embodiment is the same as in Example 1. To better illustrate the effects of the present invention, a comparative sample was also prepared in this embodiment. The preparation process of the comparative sample was the same as that of the sulfur filler for the functional zones in this embodiment (hereinafter referred to as the sample of this embodiment) except that the polydopamine film coating step was not performed.

[0052] After loading functional bacteria onto the samples and control samples of this embodiment for the same period, the inner and outer layers of microorganisms in the packing material were separated, and the bacterial species were identified by high-throughput sequencing. Both packing materials were loaded with a large number of sulfur-oxidizing denitrifying bacteria and sulfur superoxide dismutase bacteria, which became the dominant bacterial groups. There was no significant difference in the relative abundance of sulfur bacteria between the samples and control samples of this embodiment. Figure 6 This indicates that PDA has no negative impact on the attachment and growth of sulfur-oxidizing bacteria.

[0053] In the outer layer of the packing material, the total relative abundance of sulfur-disproportionating bacteria (Dissulfurimicrobium and Sulfurimonas) in the control sample was 3.50%, while the relative abundance in the outer layer of the sample in this embodiment was 4.75%. Figure 7 In the inner layer of the packing material, the total relative abundance of sulfur disproportionating microorganisms was 5.68% and 2.61% in the sample and control sample of this embodiment, respectively, indicating that after PDA treatment, the microenvironment inside the packing material became more anaerobic and more suitable for the growth of SDB bacteria.

[0054] Equal masses of the two types of packing materials were taken, and ATP was extracted from the packing materials to characterize the content of active microorganisms. The results showed that the ATP content of the sample in this embodiment was 2.69 μmol / g packing material (…). Figure 8The ATP content of the PDA-coated packing material was significantly higher than that of the control sample (1.27 μmol / g packing material), indicating that the active biomass in the sulfur-based packing material was significantly higher after PDA coating than that in the uncoated packing material. This suggests that PDA coating improves the hydrophilicity of sulfur, allowing more microorganisms to attach and grow in the packing material, thus greatly increasing the biomass of the packing material. Simultaneously, it reduces mass transfer resistance, increases the diffusion rate of sulfur disproportionation products, and promotes sulfur disproportionation and denitrification reactions, thereby enhancing the process's sulfur production and denitrification capabilities.

[0055] Example 3

[0056] The preparation of the sulfur filler for the functional zones in this embodiment is the same as in Example 1. To better illustrate the effects of the present invention, a comparative sample was also prepared in this embodiment. The preparation process of the comparative sample was the same as that of the sulfur filler for the functional zones in this embodiment (hereinafter referred to as the sample of this embodiment) except that the polydopamine film coating step was not performed.

[0057] Samples of the same mass from this embodiment and the control sample were taken, added with nutrients, and anaerobically cultured. The difference in sulfide production by sulfur-dissipating bacteria (SDB) in the packing material was measured. The experiment was performed in three cycles, with the nutrient solution changed daily. The results showed that the longer the culture time, the more the sulfide production of SDB in the sulfur-based biological packing material gradually increased, indicating that the metabolic activity of SDB gradually improved. Figure 9 In this embodiment, the sulfide production of the sample increased by 32.625 mg / L from 5.475 mg / L in the first cycle (third cycle), while the sulfide production of the control sample only increased from 2.575 mg / L in the first cycle to 18.300 mg / L in the third cycle. This indicates that the sulfur-producing capacity of the sulfur-dissipating bacteria in the sample of this embodiment is higher than that of the control sample, which may be due to the increased number and metabolic activity of sulfur-dissipating bacteria in the PDA-coated packing material.

[0058] Example 4

[0059] The preparation of the sulfur filler for the functional zones in this embodiment is the same as in Example 1. To better illustrate the effects of the present invention, a comparative sample was also prepared in this embodiment. The preparation process of the comparative sample was the same as that of the sulfur filler for the functional zones in this embodiment (hereinafter referred to as the sample of this embodiment) except that the polydopamine film coating step was not performed.

[0060] Equal masses of the sample from this embodiment and the control sample were placed in 100 ml anaerobic flasks, and the same nutrients and 30 mg N / L nitrate were added. The solution in the flasks was then deoxygenated. The anaerobic flasks were then sealed, and the reaction was carried out for 4 hours. The denitrification rate was monitored during the reaction, and the experiment was performed four times. During the four water exchange cycles, it was observed that both the sample from this embodiment and the control sample effectively reduced nitrate (…). Figure 10 The denitrification rate was calculated based on the denitrification data at the first three time points. The average denitrification rate of the sample in this embodiment was 6.42 mg N / (L·h). Figure 11 The average denitrification rate of the packing material in the control sample was 4.91 mg N / (L·h), indicating that the PDA-coated packing material had a higher denitrification rate. This is because the PDA-coated packing material promoted the growth and attachment of sulfur-dissipating and denitrifying bacteria, and under this environment, the sulfur-dissipating bacteria produced sulfur (S). n 2- / HS - It is easier for them to come into contact with denitrifying bacteria, thus accelerating the denitrification process.

[0061] The functionally partitioned sulfur packing material of the present invention can be applied to a wastewater denitrification method through the following methods:

[0062] Nitrogenous wastewater is injected into a reactor containing sulfur-based biological packing material with functional zones as described in this invention. Highly efficient nitrogen removal is achieved through the coupling of sulfur disproportionation and sulfur autotrophic denitrification biochemical reactions within the packing material's micro-universe. This system is particularly suitable for water with low carbon-to-nitrogen ratios, including secondary effluent from municipal wastewater treatment plants, industrial wastewater, and groundwater, for efficient nitrogen removal.

[0063] During the denitrification process, the core of the sulfur packing microcosm in the functional zone undergoes a sulfur disproportionation reaction, generating product S. n 2- and HS - Some of the products are adsorbed by the polydopamine membrane and react with the denitrifying bacteria loaded on the inner surface of the polydopamine membrane, consuming the sulfur disproportionation reaction products in the core; some of the products pass through the polydopamine membrane and react with the denitrifying bacteria loaded on the outer surface of the polydopamine membrane.

[0064] Those skilled in the art will readily understand that the above description is merely an embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A functionally partitioned sulfur filler, characterized in that, It includes a porous sulfur core and a polydopamine membrane; the polydopamine membrane is wrapped around the surface of the porous sulfur core; sulfur dismutating bacteria are loaded in the pores of the porous sulfur core; and denitrifying bacteria are loaded on the surface of the polydopamine membrane.

2. The sulfur packing for functional partitioning according to claim 1, characterized in that, An oxygen gradient is formed inside; the porous sulfur core is an inner anaerobic zone, which is conducive to sulfur disproportionation; the polydopamine membrane is an outer anoxic zone, which is conducive to denitrification.

3. The sulfur filler for functional partitioning according to claim 2, characterized in that, The polydopamine membrane is a hydrophilic medium, which is conducive to the attachment of denitrifying bacteria, and at the same time adsorbs some of the products of the sulfur disproportionation reaction.

4. The method for preparing the sulfur filler for functional partitioning according to any one of claims 1 to 3, characterized in that, Includes the following steps: Preparation of porous sulfur cores; The sulfur dismutase solution was immersed into the pores of the porous sulfur core and stabilized under an anaerobic environment to obtain a porous sulfur core loaded with sulfur dismutase. A polydopamine membrane was coated on the surface of a porous sulfur core loaded with sulfur dismutase to obtain a filler coated with a polydopamine membrane. The filler coated with polydopamine membrane was placed in denitrifying bacteria solution and immobilized in an anaerobic environment to obtain sulfur biological filler with functional zones.

5. The preparation method according to claim 4, characterized in that, The preparation of the porous sulfur core specifically involves mixing sulfur with an additive containing a pore-forming agent, heating the mixture until the sulfur melts, and granulating it to form porous spheres with a diameter of 5-10 mm.

6. The preparation method according to claim 4, characterized in that, The stabilization under anaerobic conditions specifically refers to stabilization at 20-40°C in an anaerobic environment for more than 48 hours.

7. The preparation method according to claim 4, characterized in that, The process of coating the porous sulfur core loaded with sulfur dismutase with a polydopamine membrane specifically involves: The porous sulfur core loaded with sulfur superoxide dismutase was immersed in Tris-HCl buffer, and dopamine hydrochloride at a concentration of 1.8~2.2 mg / ml was added. The mixture was shaken for 3~6 h, and then removed and rinsed to remove any residual polydopamine from the surface.

8. The preparation method according to claim 4, characterized in that, The immobilization under hypoxic conditions specifically refers to immobilization at 20~40℃ in a hypoxic environment for more than 48 hours.

9. A wastewater denitrification method based on sulfur disproportionation-sulfur autotrophic denitrification coupling, characterized in that, Includes the following steps: Wastewater is injected into a reactor containing sulfur packing material with functional zones as described in any one of claims 1 to 3 for denitrification treatment involving sulfur disproportionation and sulfur autotrophic denitrification coupled.

10. The wastewater denitrification method based on sulfur disproportionation-sulfur autotrophic denitrification coupling according to claim 9, characterized in that, During the denitrification process, the core of the sulfur packing in the functional zone undergoes a sulfur disproportionation reaction, generating sulfur disproportionation product S. n 2- and HS - Some of the products are adsorbed by the polydopamine membrane and react with the denitrifying bacteria loaded on the inner surface of the polydopamine membrane, consuming the sulfur dismutation reaction products in the core. Some of the product passes through the polydopamine membrane and reacts with denitrifying bacteria loaded on the outer surface of the polydopamine membrane.

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