Sulfur autotrophic denitrification filter material for water treatment and preparation method and application thereof

Abstract

The present application relates to the technical field of water treatment, and particularly relates to a sulfur autotrophic denitrification filter material for water treatment and a preparation method and application thereof. Pyrite, siderite and sulfur are selected as a sulfur source, biological raw material starch is selected as a binder, and environment-friendly material halloysite nanotubes are selected as an adsorbent. The sulfur autotrophic denitrification filter material is prepared by mixing and granulating sodium silicate, silica ash and deionized water to obtain a sinter-free sulfur autotrophic denitrification filter material. Nano-FeS and ascorbic acid are co-precipitated on the halloysite nanotubes, and then a composite branched chitosan containing carboxyl groups is grafted to obtain modified halloysite nanotubes. The composite branched chitosan containing carboxyl groups is prepared by using sodium periodate to prepare aldehyde-based chitosan, then reacting with chitosan to obtain self-branched chitosan, and grafting a conjugated microporous polymer containing polycarboxyl groups. Corn starch is used as a raw material, and the composite branched chitosan containing carboxyl groups, itaconic acid and silica sol are used as grafting monomers to obtain a biomass binder.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, specifically to a sulfur autotrophic denitrification filter media for water treatment, its preparation method, and its application. Background Technology

[0002] With rapid industrialization and urbanization, pollution of water bodies by nitrogen, phosphorus, and other pollutants has become increasingly serious, leading to a series of environmental problems. Traditional biological nitrogen removal processes mainly involve heterotrophic denitrification, which often requires the addition of organic carbon sources, increasing operating costs and potentially posing a risk of secondary pollution. Compared to traditional heterotrophic denitrification, sulfur autotrophic denitrification has advantages such as no need for external organic carbon sources, low sludge production, and low operating costs. Therefore, the development of economical and environmentally friendly autotrophic denitrification filter media has become a research hotspot in the field of water treatment.

[0003] However, the practical application of existing sulfur autotrophic denitrification filter media still faces the following challenges: most filter media are mainly composed of sulfur, and their components are mostly simple, resulting in limited denitrification efficiency; some filter media need to be sintered at high temperature, which is costly; most sulfur autotrophic denitrification filter media cannot simultaneously meet the multi-functional requirements of complex working conditions such as denitrification, phosphorus removal, pH buffering, and durability. Summary of the Invention

[0004] The purpose of this invention is to provide a sulfur autotrophic denitrification filter media for water treatment, its preparation method, and its application, so as to solve the problems in the prior art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0006] A method for preparing a sulfur-autotrophic denitrification filter media for water treatment includes the following steps:

[0007] S1: Crush sulfur, pyrite powder, and siderite powder, mix them, and sieve them to obtain a mixed sulfur-containing powder.

[0008] S2: Mix sulfur-containing powder, composite starch, modified halloysite nanotubes, sodium silicate, silica fume, and deionized water, granulate, age, and cure to obtain a sulfur-autotrophic denitrification filter media for water treatment.

[0009] Furthermore, in the preparation of the mixed sulfur-containing powder, the mass ratio of sulfur, pyrite powder, and siderite powder is 7:2:1, and the particle size of the mixed sulfur-containing powder is 100 mesh.

[0010] Furthermore, the maintenance conditions are: humidity 88%, temperature 20-25℃, and time 7 days.

[0011] Furthermore, the aging conditions are: temperature 18-25℃, time 22-24h.

[0012] Furthermore, by mass, the raw material composition of the filter media is as follows: 24-33 parts of mixed sulfur-containing powder, 15-25 parts of composite starch, 8-11 parts of modified halloysite nanotubes, 1-4 parts of sodium silicate, 3-7 parts of silica fume, and 10-23 parts of deionized water.

[0013] Furthermore, the preparation of modified halloysite nanotubes includes the following steps:

[0014] 1) Under a nitrogen atmosphere, halloysite nanotubes and sodium sulfide solution were mixed and stirred for 1-2 hours. A mixture of ascorbic acid and deionized water was added, followed by ferrous sulfate. The mixture was ultrasonically treated for 8-10 minutes, filtered, washed, and freeze-dried to obtain pretreated halloysite nanotubes.

[0015] 2) Mix 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, N-hydroxysuccinimide, deionized water, and carboxyl-containing composite branched chitosan, add pretreated halloysite nanotubes, heat to 75-80℃ and keep warm for 4-5 hours to obtain modified halloysite nanotubes.

[0016] Furthermore, the preparation of the compound starch includes the following steps:

[0017] Starch, carboxyl-containing composite branched chitosan, and hydrochloric acid solution are mixed and stirred in a water bath at 55-60℃ for 1-2 hours. The pH is adjusted to 3.9-4.1, and the temperature is raised to 68-70℃. Ammonium persulfate, sodium dodecyl sulfate, deionized water, and itaconic acid are added and kept at this temperature for 1-2 hours. Ammonium persulfate is added again and kept at this temperature for 1-2 hours. Silica sol and polyvinyl alcohol solution are added, and the temperature is raised to 80-85℃ and kept at this temperature for 20-40 minutes. The product is then discharged to obtain composite starch.

[0018] Furthermore, the mass ratio of starch, carboxyl-containing composite branched chitosan, itaconic acid, and silica sol is 35:5:1.1:1.5.

[0019] Furthermore, the preparation of carboxyl-containing complex branched chitosan includes the following steps:

[0020] (1) Under a nitrogen atmosphere, 1,3,5-triethynylbenzene, 2,5-dibromoterephthalic acid, bis(triphenylphosphine)palladium dichloride, cuprous iodide and triphenylphosphine were mixed, and toluene and triethylamine were added in sequence. The mixture was stirred, heated to 88-90℃ and kept in an oil bath for 23-24 hours, and then cooled to 18-25℃. The mixture was washed with chloroform, methanol and deionized water in sequence, filtered and dried to obtain a polycarboxyl conjugated microporous polymer.

[0021] (2) Under nitrogen protection, chitosan and sodium periodate solution are mixed, protected from light, and shaken at 28-32℃ for 1-2 hours. Ethylene glycol solution is added, and the mixture is allowed to stand for 20-30 minutes. After filtration, acetone is added, and the mixture is precipitated, filtered, washed, and dried to obtain aldehyde-modified chitosan. Chitosan and acetic acid solution are mixed, aldehyde-modified chitosan is added, and the mixture is stirred for 1-2 hours. Sodium borohydride acetate is added, and the mixture is stirred for another 3-4 hours. The mixture is then dialyzed for 46-48 hours to obtain branched chitosan.

[0022] (3) Mix 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, N-hydroxysuccinimide and potassium phosphate buffer, stir in an ice-water bath for 8-10 min, add the polycarboxyl conjugated microporous polymer, sonicate for 5-8 min, stir in an ice-water bath for 20-30 min, add potassium phosphate buffer and branched chitosan, shake for 11-12 h, filter, wash and dry to obtain carboxyl-containing composite branched chitosan.

[0023] A sulfur-autotrophic denitrification filter media for water treatment is applied to the nitrogen and phosphorus removal purification process in water treatment.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] This invention provides a sulfur autotrophic denitrification filter media for water treatment, its preparation method, and its application. By optimizing the composition ratio and process design of the filter media, a high-strength, non-burning sulfur autotrophic denitrification filter media that is green, environmentally friendly, recyclable, and has high efficiency in nitrogen and phosphorus removal and heavy metal adsorption is prepared. When used in water treatment, it can effectively improve water pollution and increase purification efficiency.

[0026] To meet the requirements of green production, this invention uses a mixture of inexpensive pyrite, siderite, and sulfur as the sulfur source, biological starch as the binder, and halloysite nanotubes as the adsorbent. These are mixed with sodium silicate, silica fume, and deionized water and granulated to prepare a non-fired autotrophic denitrification filter media. By optimizing the proportions of each component, the structural stability of the autotrophic denitrification filter media is improved, enabling it to achieve efficient nitrogen and phosphorus removal without the need for an external carbon source, and exhibiting a strong adsorption capacity for pollutants in water.

[0027] To improve the uniformity of halloysite nanotube dispersion in sulfur autotrophic denitrification filter media, pretreated halloysite nanotubes with multiple hydroxyl groups were prepared by co-precipitation of nano-FeS and ascorbic acid on the halloysite nanotubes. Then, composite branched chitosan containing carboxyl groups was grafted onto them, which significantly improved the adsorption and purification properties of the halloysite nanotubes. The introduction of nano-FeS further enhanced the iron-sulfur synergistic effect with the mixed sulfur-containing powder, thereby buffering the pH of the system, reducing the inhibitory effect of sulfate accumulation on microorganisms, and improving denitrification efficiency and stability.

[0028] The carboxyl-containing composite branched chitosan is prepared by using sodium periodate to prepare aldehyde-modified chitosan, which is then reacted with chitosan to obtain self-branched chitosan. Based solely on chitosan segments without introducing other artificially synthesized blocks, it maintains excellent biocompatibility while improving performance. To enhance the stability of branched chitosan, its surface hydroxyl groups are grafted with conjugated microporous polymers containing multiple carboxyl groups. Utilizing the unique conjugated structure, high specific surface area, skeletal structure, and good chemical stability of the conjugated microporous polymers, the composite branched chitosan possesses excellent metal ion storage capacity. Simultaneously, as a biofilm carrier, it facilitates the attachment of microorganisms to the surface of the sulfur autotrophic denitrification filter media. During sulfur autotrophic denitrification, it synergistically increases the contact area between the water and microorganisms, thereby significantly improving the nitrogen and phosphorus removal efficiency of the sulfur autotrophic denitrification filter media.

[0029] In this invention, starch is selected as a binder and plant carbon source. To improve the bonding strength and water resistance of starch, corn starch is used as raw material, and carboxyl-containing composite branched chitosan, itaconic acid, and silica sol are used as grafting monomers to obtain a biomass binder. This binder has a composite effect on mixed sulfur-containing powder, modified halloysite nanotubes, sodium silicate, and silica fume, improving the bonding strength between filter media materials and reducing sludge volume. The multi-carboxyl conjugated microporous polymer in the carboxyl-containing composite branched chitosan serves as a framework, significantly improving the mechanical strength and carbon release stability of the filter media. As a microbial carrier, it increases the contact area between the water to be treated and the microorganisms, improving the adsorption capacity and nitrogen and phosphorus removal efficiency of the filter media. Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0031] It should be noted that if the embodiments of the present invention involve directional indicators such as up, down, left, right, front, and back, these directional indicators are only used to explain the relative positional relationship and movement of components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0032] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are only used to explain the present invention and are not intended to limit the present invention.

[0033] Example 1: A method for preparing a sulfur-autotrophic denitrification filter media for water treatment, comprising the following steps:

[0034] S1: Crush sulfur, pyrite powder, and siderite powder, mix them, and sieve them to obtain a mixed sulfur-containing powder.

[0035] In the preparation of the mixed sulfur-containing powder, the mass ratio of sulfur, pyrite powder and siderite powder is 7:2:1, and the particle size of the mixed sulfur-containing powder is 100 mesh.

[0036] S2: Mix sulfur-containing powder, composite starch, modified halloysite nanotubes, sodium silicate, silica fume, and deionized water, granulate, age, and cure to obtain a sulfur-autotrophic denitrification filter media for water treatment.

[0037] The working conditions for maintenance are: humidity 88%, temperature 20℃, and time 7 days;

[0038] The aging conditions are: temperature 18℃, time 22h;

[0039] The raw material composition of the filter media by mass is as follows: 24 parts of mixed sulfur-containing powder, 15 parts of composite starch, 8 parts of modified halloysite nanotubes, 1 part of sodium silicate, 3 parts of silica fume, and 10 parts of deionized water.

[0040] The preparation of the modified halloysite nanotubes includes the following steps:

[0041] 1) Under a nitrogen atmosphere, 4g halloysite nanotubes and 100mL of 2mol / L sodium sulfide solution were mixed and stirred for 1h. A mixture of 0.6g ascorbic acid and 500mL of deionized water was added, along with 200mL of 1mol / L ferrous sulfate solution. The mixture was sonicated for 8min, filtered, and freeze-dried to obtain pretreated halloysite nanotubes.

[0042] 2) Mix 2g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, 1g of N-hydroxysuccinimide, 120mL of deionized water, and 4.2g of carboxyl-containing composite branched chitosan. Add 9.3g of pretreated halloysite nanotubes and heat to 70℃ for 5h to obtain modified halloysite nanotubes.

[0043] The preparation of the composite starch includes the following steps:

[0044] Mix 35g starch, 5g carboxyl-containing composite branched chitosan, and 55mL 1mol / L hydrochloric acid solution. Stir in a water bath at 55℃ for 2h, adjust the pH to 3.9, raise the temperature to 68℃, add 0.3g ammonium persulfate, add a mixture of 0.6g sodium dodecyl sulfate, 15mL deionized water, and 1.1g itaconic acid, keep warm for 1h, add 0.2g ammonium persulfate, keep warm for 1h, add 1.5g silica sol and 20mL 10% polyvinyl alcohol solution, raise the temperature to 80℃ and keep warm for 40min, then discharge to obtain composite starch.

[0045] The preparation of the carboxyl-containing composite branched chitosan includes the following steps:

[0046] (1) Under a nitrogen atmosphere, 3 mmol of 1,3,5-triethynylbenzene, 4.5 mmol of 2,5-dibromoterephthalic acid, 158 mg of bis(triphenylphosphine)palladium dichloride, 42.8 mg of cuprous iodide and 590 mg of triphenylphosphine were mixed, and 78 mL of toluene and 98 mL of triethylamine were added in sequence. The mixture was stirred, heated to 88 °C and kept in an oil bath for 24 h, and then cooled to 18 °C. The mixture was washed with chloroform, methanol and deionized water in sequence, filtered and dried to obtain a polycarboxyl conjugated microporous polymer.

[0047] (2) Under nitrogen protection, 3g of chitosan and 150mL of 0.3mol / L sodium periodate solution were mixed, protected from light, and shaken at 28℃ for 2h. 20mL of 0.1mol / L ethylene glycol solution was added, and the mixture was allowed to stand for 20min. After filtration, 100mL of acetone was added, and the mixture was precipitated, filtered, washed, and dried to obtain aldehyde-modified chitosan. 0.6g of chitosan and 50mL of 1% acetic acid solution were mixed, and 0.3g of aldehyde-modified chitosan was added. The mixture was stirred for 1h, and 0.5g of sodium borohydride acetate was added. The mixture was stirred for another 3h and dialyzed for 46h to obtain branched chitosan.

[0048] (3) Mix 0.32g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, 0.24g of N-hydroxysuccinimide, and 20mL of potassium phosphate buffer at pH 7. Stir in an ice-water bath for 8min. Add 0.1g of polycarboxyl conjugated microporous polymer and sonicate for 5min. Stir in an ice-water bath for 20min. Add 20mL of potassium phosphate buffer at pH 7 and 0.2g of branched chitosan. Seal and shake at 25℃ for 11h. Filter, wash, and dry to obtain a composite branched chitosan containing carboxyl groups.

[0049] Example 2: A method for preparing a sulfur-autotrophic denitrification filter media for water treatment, comprising the following steps:

[0050] S1: Crush sulfur, pyrite powder, and siderite powder, mix them, and sieve them to obtain a mixed sulfur-containing powder.

[0051] In the preparation of the mixed sulfur-containing powder, the mass ratio of sulfur, pyrite powder and siderite powder is 7:2:1, and the particle size of the mixed sulfur-containing powder is 100 mesh.

[0052] S2: Mix sulfur-containing powder, composite starch, modified halloysite nanotubes, sodium silicate, silica fume, and deionized water, granulate, age, and cure to obtain a sulfur-autotrophic denitrification filter media for water treatment.

[0053] The aging conditions are: temperature 20℃, time 23h;

[0054] The working conditions for maintenance are: humidity 88%, temperature 23℃, and time 7 days;

[0055] The raw material composition of the filter media by mass is as follows: 27 parts of mixed sulfur-containing powder, 20 parts of composite starch, 9 parts of modified halloysite nanotubes, 3 parts of sodium silicate, 5 parts of silica fume, and 18 parts of deionized water.

[0056] The preparation of the modified halloysite nanotubes includes the following steps:

[0057] 1) Under a nitrogen atmosphere, 4g halloysite nanotubes and 100mL of 2mol / L sodium sulfide solution were mixed and stirred for 1.5h. A mixture of 0.6g ascorbic acid and 500mL of deionized water was added, along with 200mL of 1mol / L ferrous sulfate solution. The mixture was sonicated for 9min, filtered, and freeze-dried to obtain pretreated halloysite nanotubes.

[0058] 2) Mix 2g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, 1g of N-hydroxysuccinimide, 120mL of deionized water, and 4.2g of carboxyl-containing composite branched chitosan. Add 9.3g of pretreated halloysite nanotubes and heat to 75℃ for 4.5h to obtain modified halloysite nanotubes.

[0059] The preparation of the composite starch includes the following steps:

[0060] Mix 35g starch, 5g carboxyl-containing composite branched chitosan, and 55mL 1mol / L hydrochloric acid solution. Stir in a water bath at 58℃ for 1.5h, adjust the pH to 4, raise the temperature to 69℃, add 0.3g ammonium persulfate, add a mixture of 0.6g sodium dodecyl sulfate, 15mL deionized water, and 1.1g itaconic acid, keep warm for 1.5h, add 0.2g ammonium persulfate, keep warm for 1.5h, add 1.5g silica sol and 20mL 10% polyvinyl alcohol solution, raise the temperature to 83℃ and keep warm for 30min, then discharge to obtain composite starch.

[0061] The preparation of the carboxyl-containing composite branched chitosan includes the following steps:

[0062] (1) Under a nitrogen atmosphere, 3 mmol of 1,3,5-triethynylbenzene, 4.5 mmol of 2,5-dibromoterephthalic acid, 158 mg of bis(triphenylphosphine)palladium dichloride, 42.8 mg of cuprous iodide and 590 mg of triphenylphosphine were mixed, and 78 mL of toluene and 98 mL of triethylamine were added in sequence. The mixture was stirred, heated to 89 °C and kept in an oil bath for 23.5 h, cooled to 20 °C, and washed, filtered and dried with chloroform, methanol and deionized water in sequence to obtain a polycarboxyl conjugated microporous polymer.

[0063] (2) Under nitrogen protection, 3g of chitosan and 150mL of 0.3mol / L sodium periodate solution were mixed, protected from light, and shaken at 30℃ for 1.5h. 20mL of 0.1mol / L ethylene glycol solution was added, and the mixture was allowed to stand for 25min. After filtration, 100mL of acetone was added, and the mixture was precipitated, filtered, washed, and dried to obtain aldehyde-modified chitosan. 0.6g of chitosan and 50mL of 1% acetic acid solution were mixed, and 0.3g of aldehyde-modified chitosan was added. The mixture was stirred for 1.5h, and 0.5g of sodium borohydride acetate was added. The mixture was stirred for another 3.5h and dialyzed for 47h to obtain branched chitosan.

[0064] (3) Mix 0.32g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, 0.24g of N-hydroxysuccinimide, and 20mL of potassium phosphate buffer at pH 7. Stir in an ice-water bath for 9min. Add 0.1g of a polycarboxyl conjugated microporous polymer and sonicate for 7min. Stir in an ice-water bath for 25min. Add 20mL of potassium phosphate buffer at pH 7 and 0.2g of branched chitosan. Seal and shake at 25℃ for 11.5h. Filter, wash, and dry to obtain a composite branched chitosan containing carboxyl groups.

[0065] Example 3: A method for preparing a sulfur-autotrophic denitrification filter media for water treatment, comprising the following steps:

[0066] S1: Crush sulfur, pyrite powder, and siderite powder, mix them, and sieve them to obtain a mixed sulfur-containing powder.

[0067] In the preparation of the mixed sulfur-containing powder, the mass ratio of sulfur, pyrite powder and siderite powder is 7:2:1, and the particle size of the mixed sulfur-containing powder is 100 mesh.

[0068] S2: Mix sulfur-containing powder, composite starch, modified halloysite nanotubes, sodium silicate, silica fume, and deionized water, granulate, age, and cure to obtain a sulfur-autotrophic denitrification filter media for water treatment.

[0069] The aging conditions are: temperature 20℃, time 24h;

[0070] The working conditions for maintenance are: humidity 88%, temperature 25℃, and time 7 days;

[0071] The raw material composition of the filter media by mass is as follows: 33 parts of mixed sulfur-containing powder, 25 parts of composite starch, 11 parts of modified halloysite nanotubes, 4 parts of sodium silicate, 7 parts of silica fume, and 23 parts of deionized water.

[0072] The preparation of the modified halloysite nanotubes includes the following steps:

[0073] 1) Under a nitrogen atmosphere, 4g halloysite nanotubes and 100mL of 2mol / L sodium sulfide solution were mixed and stirred for 1-2h. A mixture of 0.6g ascorbic acid and 500mL of deionized water was added, along with 200mL of 1mol / L ferrous sulfate solution. The mixture was sonicated for 8-10min, filtered, and freeze-dried to obtain pretreated halloysite nanotubes.

[0074] 2) Mix 2g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, 1g of N-hydroxysuccinimide, 120mL of deionized water, and 4.2g of carboxyl-containing composite branched chitosan. Add 9.3g of pretreated halloysite nanotubes and heat to 70-80℃ for 4-5h to obtain modified halloysite nanotubes.

[0075] The preparation of the composite starch includes the following steps:

[0076] Mix 35g starch, 5g carboxyl-containing composite branched chitosan, and 55mL 1mol / L hydrochloric acid solution. Stir in a water bath at 55-60℃ for 1-2 hours, adjust the pH to 3.9-4.1, raise the temperature to 68-70℃, add 0.3g ammonium persulfate, add a mixture of 0.6g sodium dodecyl sulfate, 15mL deionized water, and 1.1g itaconic acid, keep warm for 1-2 hours, add 0.2g ammonium persulfate, keep warm for 1-2 hours, add 1.5g silica sol and 20mL 10% polyvinyl alcohol solution, raise the temperature to 80-85℃ and keep warm for 20-40 minutes, then discharge to obtain composite starch.

[0077] The preparation of the carboxyl-containing composite branched chitosan includes the following steps:

[0078] (1) Under a nitrogen atmosphere, 3 mmol of 1,3,5-triethynylbenzene, 4.5 mmol of 2,5-dibromoterephthalic acid, 158 mg of bis(triphenylphosphine)palladium dichloride, 42.8 mg of cuprous iodide and 590 mg of triphenylphosphine were mixed, and 78 mL of toluene and 98 mL of triethylamine were added in sequence. The mixture was stirred and heated to 88-90 °C and kept in an oil bath for 23-24 h. The mixture was then cooled to 18-25 °C and washed, filtered and dried with chloroform, methanol and deionized water in sequence to obtain a polycarboxyl conjugated microporous polymer.

[0079] (2) Under nitrogen protection, mix 3g of chitosan and 150mL of 0.3mol / L sodium periodate solution, protect from light, shake at 28-32℃ for 1-2h, add 20mL of 0.1mol / L ethylene glycol solution, let stand for 20-30min, filter, add 100mL of acetone, precipitate, filter, wash, and dry to obtain aldehyde-modified chitosan; mix 0.6g of chitosan and 50mL of 1% acetic acid solution, add 0.3g of aldehyde-modified chitosan, mix and stir for 1-2h, add 0.5g of sodium borohydride acetate, continue stirring for 3-4h, dialyze for 46-48h to obtain branched chitosan;

[0080] (3) Mix 0.32g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, 0.24g of N-hydroxysuccinimide, and 20mL of potassium phosphate buffer at pH 7. Stir in an ice-water bath for 8-10min. Add 0.1g of polycarboxyl conjugated microporous polymer and sonicate for 5-8min. Stir in an ice-water bath for 20-30min. Add 20mL of potassium phosphate buffer at pH 7 and 0.2g of branched chitosan. Seal and shake at 25℃ for 11-12h. Filter, wash, and dry to obtain a composite branched chitosan containing carboxyl groups.

[0081] Comparative Example 1: Using Example 1 as the control group, the modified halloysite nanotubes were replaced with halloysite nanotubes, and other processes were normal.

[0082] Comparative Example 2: Using Example 1 as the control group, corn starch was used to replace the compound starch, while other processes were normal.

[0083] Comparative Example 3: Using Example 1 as the control group, no carboxyl-containing composite branched chitosan was prepared, and other processes were normal.

[0084] Source of raw materials used (for illustrative purposes only):

[0085] Pyrite powder (by mass fraction, main elemental composition: iron 50.31%, sulfur 39.45%, oxygen 7.21%, silicon 1.02%, zinc 0.59%, aluminum 0.54%, magnesium 0.51%, potassium 0.09%); Siderite powder (main chemical component is FeCO3): commercially available; Silica fume A00918: Wuhan Jiyesheng Chemical Co., Ltd.; Silica sol (30%): Jiangmen Huihe Yongsheng Nanotechnology Co., Ltd.; Sulfur S106611, Halloysite nanotubes H431905, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride D303121, N-hydroxysuccinimide H109330, corn starch S116030, persulfate Ammonium, itaconic acid I106140, polyvinyl alcohol P139542, 1,3,5-triethynylbenzene T162680, 2,5-dibromoterephthalic acid D138185, bis(triphenylphosphine)palladium dichloride D196276, triphenylphosphine T104475, sodium borohydride acetate S106573, potassium phosphate buffer at pH 7 P406801, ascorbic acid A103533, ferrous sulfate F116338, chitosan C105802: Aladdin reagent; sodium silicate, sodium sulfide, hydrochloric acid, toluene, triethylamine, chloroform, methanol, sodium periodate, ethylene glycol, acetone, acetic acid, sodium dodecyl sulfate, cuprous iodide, analytical grade, commercially available.

[0086] Performance testing: The filter media prepared in the examples and comparative examples were tested:

[0087] The filter media was filled into the reactor, with a bulk density of 0.8 g / cm³. 3 A peristaltic pump was used to stabilize the influent, with a hRT of 9.6 h, simulating wastewater influent. The influent concentration was configured as follows: nitrate nitrogen concentration of 130 mg / L and total phosphorus concentration of 5 mg / L. The system was run continuously for 5 days to test the removal rates of nitrate nitrogen and total phosphorus in the wastewater. The filter media was then subjected to a 6-cycle experiment with wastewater, with one cycle lasting 1 day. The adsorption capacity for chromium ions was then tested using 80 mL of a 80 mg / L filter media. 6+ The test solution was used as wastewater; the removal rate was (X0-X1) / X0×100%; (X0 is the concentration of nitrate nitrogen, total phosphorus, and metal ions in the initial wastewater, and X1 is the concentration of nitrate nitrogen, total phosphorus, and metal ions in the treated wastewater); the results are shown in Table 1.

[0088] Table 1

[0089]

[0090] This invention provides a sulfur autotrophic denitrification filter media for water treatment, its preparation method, and its application. By optimizing the composition ratio and process design of the filter media, a high-strength, non-burning sulfur autotrophic denitrification filter media that is green, environmentally friendly, recyclable, and has high efficiency in nitrogen and phosphorus removal and heavy metal adsorption is prepared. When used in water treatment, it can effectively improve water pollution and increase purification efficiency.

[0091] Comparing Example 1 with Comparative Examples 1 and 3, it can be seen that in order to improve the uniformity of halloysite nanotube dispersion in sulfur autotrophic denitrification filter media, pretreated halloysite nanotubes with multiple hydroxyl groups were prepared by co-precipitating nano-FeS and ascorbic acid on halloysite nanotubes, and then grafting carboxyl-containing composite branched chitosan, which significantly improved the adsorption and purification performance of halloysite nanotubes. The introduction of nano-FeS further achieved an iron-sulfur synergistic effect with the mixed sulfur-containing powder, thereby buffering the pH of the system, reducing the effect of sulfate accumulation on microbial inhibition, and improving denitrification efficiency and stability.

[0092] The carboxyl-containing composite branched chitosan is prepared by using sodium periodate to prepare aldehyde-modified chitosan, which is then reacted with chitosan to obtain self-branched chitosan. Based solely on chitosan segments without introducing other artificially synthesized blocks, it maintains excellent biocompatibility while improving performance. To enhance the stability of branched chitosan, its surface hydroxyl groups are grafted with conjugated microporous polymers containing multiple carboxyl groups. Utilizing the unique conjugated structure, high specific surface area, skeletal structure, and good chemical stability of the conjugated microporous polymers, the composite branched chitosan possesses excellent metal ion storage capacity. Simultaneously, as a biofilm carrier, it facilitates the attachment of microorganisms to the surface of the sulfur autotrophic denitrification filter media. During sulfur autotrophic denitrification, it synergistically increases the contact area between the water and microorganisms, thereby significantly improving the nitrogen and phosphorus removal efficiency of the sulfur autotrophic denitrification filter media.

[0093] Comparing Example 1 with Comparative Examples 2 and 3, it can be seen that in this invention, starch is selected as a binder and plant carbon source. To improve the bonding strength and water resistance of starch, corn starch is used as raw material, and carboxyl-containing composite branched chitosan, itaconic acid, and silica sol are used as grafting monomers to obtain a biomass binder. This binder has a composite effect on the mixed sulfur-containing powder, modified halloysite nanotubes, sodium silicate, and silica fume, improving the bonding strength between filter media materials and reducing the amount of sediment. The multi-carboxyl conjugated microporous polymer in the carboxyl-containing composite branched chitosan is used as a framework to significantly improve the mechanical strength and carbon release stability of the filter media. As a microbial carrier, it increases the contact area between the water to be treated and the microorganisms, improving the adsorption and nitrogen and phosphorus removal efficiency of the filter media.

[0094] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the present invention's specification under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for preparing a sulfur-autotrophic denitrification filter media for water treatment, characterized in that, Includes the following steps: S1: Crush sulfur, pyrite powder, and siderite powder, mix them, and sieve them to obtain a mixed sulfur-containing powder. S2: Mix sulfur-containing powder, composite starch, modified halloysite nanotubes, sodium silicate, silica fume, and deionized water, granulate, age, and cure to obtain a sulfur-autotrophic denitrification filter media for water treatment. The preparation of modified halloysite nanotubes includes the following steps: 1) Under a nitrogen atmosphere, halloysite nanotubes and sodium sulfide solution were mixed and stirred for 1-2 hours. A mixture of ascorbic acid and deionized water was added, followed by ferrous sulfate. The mixture was ultrasonically treated for 8-10 minutes, filtered, washed, and freeze-dried to obtain pretreated halloysite nanotubes. 2) Mix 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, N-hydroxysuccinimide, deionized water, and carboxyl-containing composite branched chitosan, add pretreated halloysite nanotubes, heat to 75-80℃ and keep warm for 4-5 hours to obtain modified halloysite nanotubes. The preparation of compound starch includes the following steps: Starch, carboxyl-containing composite branched chitosan, and hydrochloric acid solution are mixed and stirred in a water bath at 55-60℃ for 1-2 hours. The pH is adjusted to 3.9-4.1, and the temperature is raised to 68-70℃. Ammonium persulfate, sodium dodecyl sulfate, deionized water, and itaconic acid are added and kept at this temperature for 1-2 hours. Ammonium persulfate is added again and kept at this temperature for 1-2 hours. Silica sol and polyvinyl alcohol solution are added, and the temperature is raised to 80-85℃ and kept at this temperature for 20-40 minutes. The product is then discharged to obtain composite starch. The preparation of carboxyl-containing complex branched chitosan includes the following steps: (1) Under a nitrogen atmosphere, 1,3,5-triethynylbenzene, 2,5-dibromoterephthalic acid, bis(triphenylphosphine)palladium dichloride, cuprous iodide and triphenylphosphine were mixed, and toluene and triethylamine were added in sequence. The mixture was stirred, heated to 88-90℃ and kept in an oil bath for 23-24 hours, and then cooled to 18-25℃. The mixture was washed in sequence with chloroform, methanol and deionized water, filtered and dried to obtain a polycarboxyl conjugated microporous polymer. (2) Under nitrogen protection, chitosan and sodium periodate solution are mixed, protected from light, and shaken at 28-32℃ for 1-2 hours. Ethylene glycol solution is added, and the mixture is allowed to stand for 20-30 minutes. After filtration, acetone is added, and the mixture is precipitated, filtered, washed, and dried to obtain aldehyde-modified chitosan. Chitosan and acetic acid solution are mixed, aldehyde-modified chitosan is added, and the mixture is stirred for 1-2 hours. Sodium borohydride acetate is added, and the mixture is stirred for another 3-4 hours. The mixture is then dialyzed for 46-48 hours to obtain branched chitosan. (3) Mix 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, N-hydroxysuccinimide and potassium phosphate buffer, stir in an ice-water bath for 8-10 min, add the polycarboxyl conjugated microporous polymer, sonicate for 5-8 min, stir in an ice-water bath for 20-30 min, add potassium phosphate buffer and branched chitosan, shake for 11-12 h, filter, wash and dry to obtain carboxyl-containing composite branched chitosan.

2. The method for preparing a sulfur-autotrophic denitrification filter media for water treatment according to claim 1, characterized in that, In the preparation of the mixed sulfur-containing powder, the mass ratio of sulfur, pyrite powder and siderite powder is 7:2:1, and the particle size of the mixed sulfur-containing powder is 100 mesh.

3. The method for preparing a sulfur-autotrophic denitrification filter media for water treatment according to claim 1, characterized in that, The working conditions for maintenance are: humidity 88%, temperature 20-25℃, and time 7 days.

4. The method for preparing a sulfur-autotrophic denitrification filter media for water treatment according to claim 1, characterized in that, The raw material composition of the filter media by mass is as follows: 24-33 parts of mixed sulfur-containing powder, 15-25 parts of composite starch, 8-11 parts of modified halloysite nanotubes, 1-4 parts of sodium silicate, 3-7 parts of silica fume, and 10-23 parts of deionized water.

5. The method for preparing a sulfur-autotrophic denitrification filter media for water treatment according to claim 1, characterized in that, In the preparation of the composite starch, the mass ratio of starch, carboxyl-containing composite branched chitosan, itaconic acid, and silica sol is 35:5:1.1:1.

5.

6. A sulfur-autotrophic denitrification filter media for water treatment, characterized in that, It is prepared by the preparation method according to any one of claims 1-5.

7. The application of the sulfur-autotrophic denitrification filter media for water treatment according to claim 6, characterized in that, It is used in the denitrification and phosphorus removal purification process in water treatment.

Images