Carbon source for sewage treatment and preparation method and application thereof

Abstract

The application relates to the technical field of sewage treatment, in particular to a carbon source for sewage treatment and a preparation method and application thereof. The preparation method of the carbon source for sewage treatment comprises the following steps: (1) crushing and drying wheat straw and reed straw, soaking in a calcium hydroxide solution, filtering, washing with deionized water until neutral, and drying to obtain plant materials; (2) stirring polyvinyl alcohol and modified chitosan in water, then adding the plant materials in step (1) to obtain a mixed solution, adding a glutaraldehyde aqueous solution for crosslinking to obtain solution A; (3) dispersing functional fillers in water to obtain solution B, adding the solution B into the solution A obtained in step (2), uniformly mixing, and freeze-drying to form, and the carbon source is obtained. The carbon source can continuously and stably provide carbon sources, has good denitrification effect and heavy metal ion removal effect in sewage treatment, has good compressive strength, and can meet the actual application requirements.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sewage treatment, in particular to a carbon source for sewage treatment and a preparation method and application thereof. BACKGROUND

[0002] The content of nitride in urban domestic sewage and industrial wastewater is seriously over-standard, if directly discharged without treatment, it will not only cause water eutrophication, but also pose a serious threat to human health. Therefore, domestic sewage and the like needs to be subjected to denitrification treatment before being discharged into the environment. At present, the biological nitrification-denitrification process is the mainstream sewage denitrification technology, which relies on the metabolism of microorganisms to degrade pollutants, and a large amount of carbon source is needed for microorganisms in the denitrification section to remove nitrate nitrogen. However, the actual carbon-nitrogen ratio (C / N) of urban sewage in China is low, and a part of the carbon source is also consumed in the nitrification section, which leads to the fact that the remaining carbon source is often difficult to meet the metabolic needs of denitrifying bacteria in the denitrification process, thereby seriously affecting the denitrification and phosphorus removal effect of the sewage.

[0003] The most direct and effective way to solve the above problems is to add external carbon source to the sewage. The external carbon source can be divided into three categories: one is liquid carbon source, mainly including hydrolysate after organic waste treatment and industrial waste residue leachate; two is gaseous carbon source, mainly methane and other gases; three is solid carbon source, mainly including natural plant cellulose, artificially synthesized biodegradable polymers and composite carbon source. Among them, the solid carbon source is most widely used in sewage treatment because of its convenience for storage and addition, but it also has some problems in practical application, such as too high initial carbon release rate and low compressive strength. Therefore, it is necessary to develop a carbon source for sewage treatment with stable carbon release rate and strong compressive strength. In addition, the content of heavy metal ions in domestic sewage and industrial wastewater is also seriously over-standard, and these heavy metal ions have biological accumulation and toxicity, which pose a potential threat to the ecological environment and human health. Therefore, it is necessary to simultaneously remove heavy metal ions in the process of sewage denitrification treatment. SUMMARY

[0004] In order to overcome the shortcomings of the prior art, one of the purposes of the present application is to provide a preparation method of a carbon source for sewage treatment, which is simple and efficient, and has strong feasibility, providing a new technical idea for the preparation of carbon source and being helpful to realize industrial production.

[0005] The second purpose of the present application is to provide a carbon source for sewage treatment prepared by the method. The carbon source can continuously and stably provide carbon source, has good denitrification effect, heavy metal ion removal effect in sewage treatment, and has good compressive strength, which can meet the actual application requirements.

[0006] The third purpose of the present application provides the application of the carbon source for sewage treatment in sewage treatment, which has a positive significance for sewage treatment.

[0007] The object of the present application is achieved by adopting the following technical solutions:

[0008] A preparation method of a carbon source for sewage treatment, comprising the following steps:

[0009] (1) Wheat straw and reed straw are crushed and dried, then soaked in a calcium hydroxide solution, filtered, washed with deionized water until neutral, and dried to obtain plant material;

[0010] (2) Polyvinyl alcohol and modified chitosan are added to water and stirred, then the plant material of step (1) is added to obtain a mixed solution, and glutaraldehyde aqueous solution is added for crosslinking to obtain solution A;

[0011] (3) Functional fillers are dispersed in water to obtain solution B, and solution B is added to solution A obtained in step (2) and uniformly mixed, and then freeze-dried to form.

[0012] Further, the preparation process of the modified chitosan is as follows:

[0013] a. Chitosan is dissolved in solvent A to obtain a chitosan solution; L-cysteine is dissolved in solvent B to obtain an L-cysteine solution, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide are added to the L-cysteine solution for activation, and then the activated solution is added to the chitosan solution for reaction; after the reaction is completed, the product is dialyzed and dried to obtain intermediate 1;

[0014] b. Intermediate 1 and di(3-sulfopropyl) itaconic acid dipotassium salt are added to a solvent and uniformly mixed, then a photoinitiator is added, and the reaction is carried out under nitrogen protection and ultraviolet irradiation; after the reaction is completed, the product is washed, dialyzed, and dried to obtain modified chitosan.

[0015] Further, the mass ratio of chitosan, L-cysteine, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, and N-hydroxysuccinimide in step a is 1:(2.4-2.6):(1-1.2):(1-1.2); the concentration of the chitosan solution is 0.01-0.04 g / mL; the concentration of the L-cysteine solution is 0.024-0.05 g / mL; the solvent A is 1.5-2 wt% acetic acid solution, and the solvent B is 50-60% ethanol solution by volume fraction; the activation time is 2-3 h, and the reaction time is 25-30 h.

[0016] Further, the use amount ratio of the intermediate 1, di(3-sulfonic acid propyl) itaconic acid dipotassium salt, the photoinitiator and the solvent in step b is 1g:2.5-4.5g:0.02-0.03g:50-75mL; the solvent is dimethyl sulfoxide, the photoinitiator is 2,2-dimethoxy-2-phenylacetophenone, the reaction time is 8-12h, and the wavelength of the ultraviolet irradiation is 350-370nm.

[0017] Further, the functional filler is prepared according to the following process:

[0018] S1. The montmorillonite is dispersed in a solvent, 3-aminopropyl triethoxysilane is added, and stirring reaction is carried out, and then the product is filtered, washed and dried to obtain the aminated montmorillonite;

[0019] S2. The aminated montmorillonite is dispersed in a solvent, 4-hydroxy-2-oxo-2H-chromen-3-formaldehyde is added, and stirring reaction is carried out, and then the product is filtered, washed and dried to obtain the functional filler.

[0020] Further, the use amount ratio of the montmorillonite, 3-aminopropyl triethoxysilane and the solvent in step S1 is 5g:2.5-4g:30-50mL; the stirring reaction temperature is 70-90℃, and the stirring reaction time is 3-8h; and the solvent is an ethanol aqueous solution with a volume fraction of 60-70%.

[0021] Further, the use amount ratio of the aminated montmorillonite, 4-hydroxy-2-oxo-2H-chromen-3-formaldehyde and anhydrous ethanol in step S2 is 1g:0.8-1.2g:30-50mL, and the solvent is anhydrous ethanol; the stirring reaction temperature is 40-60℃, and the stirring reaction time is 2-5h.

[0022] Further, in step (1), the use amount ratio of the wheat straw, reed straw and calcium hydroxide solution is 1g:1-2g:5-10mL; the mass concentration of the sodium hydroxide solution is 2-4wt%; and the soaking time is 8-15h; in step (2), the mass ratio of the polyvinyl alcohol, modified chitosan, plant material and water is (5-15):(2-6):(20-40):(90-100); the volume ratio of the glutaraldehyde aqueous solution and the mixed solution is (0.8-1.5):100; the concentration of the glutaraldehyde aqueous solution is 10-20wt%; and in step (3), the mass ratio of the solution A and the solution B is 100:(10-20); and the concentration of the functional filler in the solution B is 20-30wt%.

[0023] The application provides a carbon source for sewage treatment prepared by the preparation method.

[0024] The application provides application of the carbon source for sewage treatment in sewage treatment.

[0025] Compared with the prior art, the present application has the beneficial effects that:

[0026] The present application provides a carbon source for sewage treatment, which is prepared by wrapping alkali-treated wheat straw and reed straw powder with a network structure formed by cross-linking polyvinyl alcohol and modified chitosan with glutaraldehyde, and compounding with functional fillers, i.e., organic modified montmorillonite. The carbon source can continuously and stably provide carbon source, has good denitrification effect and heavy metal ion removal effect in sewage treatment, and has good compressive strength, which can meet the actual application requirements.

[0027] 1. Continuous and stable carbon source and denitrification effect: The alkali-treated wheat and reed straw powder is rich in cellulose and hemicellulose, which can be decomposed by microorganisms to provide carbon source for the denitrification process; the three-dimensional network skeleton formed by cross-linking polyvinyl alcohol and modified chitosan with glutaraldehyde can not only inhibit the rapid dissolution of the initial carbon source, but also release carbon source stably for a long time, and can itself serve as a supplemental carbon source, thereby significantly improving the denitrification effect of sewage.

[0028] 2. Heavy metal ion removal effect: On the one hand, sulfhydryl groups are introduced by the reaction of the amino groups of chitosan and the carboxyl groups of L-cysteine, and further, sulfonic groups are introduced on the chitosan by the click chemistry reaction between the sulfhydryl groups and the double bonds of di(3-sulfopropyl)iconic acid dipotassium salt, which can combine with heavy metal ions in sewage through chelation to form a precipitate, thereby removing heavy metal ions in sewage; on the other hand, after the functional fillers are aminated with 3-aminopropyltriethoxysilane, a Schiff base structure is constructed by the reaction of the amino groups and the aldehyde groups of 4-hydroxy-2-oxo-2H-chromen-3-formaldehyde, and the Schiff base (C=N) double bond and the hydroxyl groups (-OH) and carbonyl groups (C=O) on the chromone ring together constitute multiple coordination sites, which can selectively capture heavy metal ions, further enhancing the removal effect of heavy metal ions.

[0029] 3. Compressive strength: The chromone-Schiff base is a rigid conjugated structure, which can significantly improve the chemical stability and mechanical strength of the functional fillers, preventing interlayer collapse; further, the reinforced functional fillers synergistically act with the polyvinyl alcohol-chitosan three-dimensional network skeleton through nano-enhancing effect, significantly improving the compressive strength of the carbon source, so that it can adapt to complex hydraulic impact conditions. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 The infrared curve of chitosan and modified chitosan in Example 1 of the present application;

[0031] Figure 2 The infrared curve of montmorillonite and functional fillers in Example 1 of the present application. DETAILED DESCRIPTION

[0032] The application will be further described below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the embodiments described below or technical features between the embodiments can be combined to form new embodiments without conflict. The specific conditions not mentioned in the embodiments are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are conventional products obtained through commercial channels, unless otherwise specified.

[0033] Embodiment 1

[0034] A preparation method of a carbon source for sewage treatment, comprising the following steps:

[0035] (1) The wheat straw and reed straw are washed, crushed, and dried to constant weight, and then 3wt% calcium hydroxide solution is added, and the amount ratio of the wheat straw, reed straw and calcium hydroxide solution is 1g:1.5g:8mL; After soaking for 12h, filter, wash with deionized water until neutral, and dry to constant weight to obtain plant material;

[0036] (2) Polyvinyl alcohol (average molecular weight 10000Da) and modified chitosan are added to deionized water, heated to 90℃ and stirred for 2.5h until the solution becomes transparent, then the plant material is added and mixed uniformly to obtain a mixed solution; The mass ratio of polyvinyl alcohol, modified chitosan, plant material and deionized water is 10:5:30:95; Then 15wt% glutaraldehyde aqueous solution is added and cross-linked for 40min, and the volume ratio of glutaraldehyde aqueous solution and mixed solution is 1:100; To obtain solution A;

[0037] (3) The functional filler is dispersed in deionized water to obtain solution B, and the concentration of the functional filler in solution B is 25wt%; Solution B is added to solution A obtained in step (2), and the mass ratio of solution A and solution B in step (3) is 100:15; Mix well, freeze-dry and shape.

[0038] The preparation process of the modified chitosan is as follows:

[0039]

[0040] a. Chitosan (average molecular weight 100 kDa) was dissolved in 2 wt% acetic acid solution, L-cysteine was dissolved in 55% (v / v) ethanol solution to obtain 0.01 g / mL chitosan solution and 0.024 g / mL L-cysteine solution, then 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide were added to the L-cysteine solution to activate for 2.5 h, the mass ratio of chitosan, L-cysteine, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide was 1:2.5:1.1:1.1; then the activated solution was added to the chitosan solution, and reacted for 28 h under nitrogen protection and away from light, after the reaction was completed, the product was dialyzed with deionized water and vacuum dried to obtain intermediate 1;

[0041] b. Intermediate 1 and di(3-sulfopropyl) itaconic acid dipotassium salt were mixed uniformly in dimethyl sulfoxide (DMSO), then a photoinitiator 2,2-dimethoxy-2-phenylacetophenone was added, the amount ratio of intermediate 1, di(3-sulfopropyl) itaconic acid dipotassium salt, 2,2-dimethoxy-2-phenylacetophenone and DMSO was 1 g:3.5 g:0.025 g:60 mL, after reaction for 10 h under nitrogen protection and 365 nm ultraviolet lamp irradiation, the product was precipitated with acetone, the obtained product was washed with acetone / DMSO (95:5, v / v) solution and pure acetone in turn, dialyzed with deionized water and vacuum dried to obtain modified chitosan.

[0042] The functional filler is an organically modified montmorillonite, which is prepared as follows:

[0043]

[0044] S1. Montmorillonite was ultrasonically dispersed in an aqueous ethanol solution (65%, v / v), and 3-aminopropyl triethoxysilane was added, the amount ratio of montmorillonite, 3-aminopropyl triethoxysilane and the aqueous ethanol solution was 5 g:3 g:40 mL; after stirring and reacting at 80°C for 5 h, filtration, anhydrous ethanol washing and vacuum drying were performed to obtain aminated montmorillonite;

[0045] S2. The aminated montmorillonite was dispersed in anhydrous ethanol, and 4-hydroxy-2-oxo-2H-chromen-3-formaldehyde was added, the amount ratio of the aminated montmorillonite, 4-hydroxy-2-oxo-2H-chromen-3-formaldehyde and anhydrous ethanol was 1 g:1 g:40 mL; after stirring and reacting at 50°C for 4 h, filtration, anhydrous ethanol washing and vacuum drying were performed to obtain the functional filler.

[0046] The embodiment also provides a carbon source for sewage treatment, which is prepared by the method.

[0047] Example 2

[0048] A method for preparing a carbon source for sewage treatment, comprising the following steps:

[0049] (1) The wheat straw and reed straw are cleaned, crushed, and dried to constant weight, then 2wt% calcium hydroxide solution is added, and the amount of wheat straw, reed straw, and calcium hydroxide solution is 1g:1g:5mL; After soaking for 8h, filter, wash with deionized water until neutral, and dry to constant weight to obtain plant material;

[0050] (2) Polyvinyl alcohol and modified chitosan are added to deionized water, heated to 80℃ and stirred for 3h until the solution becomes transparent, then the plant material is added and mixed uniformly to obtain a mixed solution; The mass ratio of polyvinyl alcohol, modified chitosan, plant material and deionized water is 5:2:20:90; Then 10wt% glutaraldehyde aqueous solution is added and crosslinked for 40min, and the volume ratio of glutaraldehyde aqueous solution and mixed solution is 0.8:100; To obtain solution A;

[0051] (3) The functional filler is dispersed in deionized water to obtain solution B, and the concentration of the functional filler in solution B is 20wt%; Solution B is added to solution A obtained in step (2), and the mass ratio of solution A and solution B in step (3) is 100:10; Mix well, freeze-dry and shape.

[0052] The preparation process of the modified chitosan is as follows:

[0053] a. Chitosan is dissolved in 1.5wt% acetic acid solution, and L-cysteine is dissolved in 50%(v / v) ethanol solution to obtain 0.01g / mL chitosan solution and 0.024g / mL L-cysteine solution, then 1-(3-dimethylaminopropyl)-3-ethyl carbodiimide hydrochloride and N-hydroxysuccinimide are added to the L-cysteine solution and activated for 2h, and the mass ratio of chitosan, L-cysteine, 1-(3-dimethylaminopropyl)-3-ethyl carbodiimide hydrochloride and N-hydroxysuccinimide is 1:2.4:1:1; Then the activated solution is added to the chitosan solution, and the reaction is carried out under nitrogen protection for 25h in the dark, after the reaction is completed, the product is dialyzed with deionized water and vacuum dried to obtain intermediate 1;

[0054] b. Intermediate 1 and di (3-sulfonic propyl) itaconic acid dipotassium salt were mixed uniformly in DMSO, and then a photoinitiator 2,2-dimethoxy-2-phenylacetophenone was added. The amount ratio of Intermediate 1, di (3-sulfonic propyl) itaconic acid dipotassium salt, 2,2-dimethoxy-2-phenylacetophenone and DMSO was 1 g:2.5 g:0.02 g:50 mL. After reaction for 8 h under nitrogen protection and 365 nm ultraviolet lamp irradiation, the product was precipitated with acetone, and then the obtained product was washed with acetone / DMSO (95:5, v / v) solution and pure acetone successively, deionized water dialysis and vacuum drying to obtain the modified chitosan.

[0055] The functional filler is an organically modified montmorillonite, which is prepared as follows:

[0056] S1. The montmorillonite was ultrasonically dispersed in an aqueous ethanol solution (60%, v / v), and 3-aminopropyl triethoxysilane was added. The amount ratio of the montmorillonite, 3-aminopropyl triethoxysilane and the aqueous ethanol solution was 5 g:2.5 g:30 mL. After stirring at 70 °C for 8 h, filtration, anhydrous ethanol washing and vacuum drying, the amino montmorillonite was obtained.

[0057] S2. The amino montmorillonite was dispersed in anhydrous ethanol, and 4-hydroxy-2-oxo-2H-chromen-3-formaldehyde was added. The amount ratio of the amino montmorillonite, 4-hydroxy-2-oxo-2H-chromen-3-formaldehyde and anhydrous ethanol was 1 g:0.8 g:30 mL. After stirring at 40 °C for 5 h, filtration, anhydrous ethanol washing and vacuum drying, the functional filler was obtained.

[0058] The embodiment also provides a carbon source for sewage treatment, which is prepared by the method.

[0059] Example 3

[0060] A method for preparing a carbon source for sewage treatment comprises the following steps:

[0061] (1) The wheat straw and reed straw were washed, crushed and dried to constant weight, and then 4 wt% of a calcium hydroxide solution was added. The amount ratio of the wheat straw, reed straw and calcium hydroxide solution was 1 g:2 g:10 mL. After soaking for 15 h, filtration, deionized water washing until neutral and drying to constant weight, the plant material was obtained.

[0062] (2) Polyvinyl alcohol and modified chitosan were added to deionized water, and the solution was stirred at 95 °C for 2 h until it became transparent. The plant material was added and mixed uniformly to obtain a mixed solution. The mass ratio of polyvinyl alcohol, modified chitosan, plant material and deionized water was 15:6:40:100. Then 20 wt% of a glutaraldehyde aqueous solution was added for crosslinking for 30 min. The volume ratio of the glutaraldehyde aqueous solution and the mixed solution was 1.5:100. Solution A was obtained.

[0063] (3) dispersing the functional filler in deionized water to obtain solution B, the concentration of the functional filler in solution B is 30wt%; adding solution B into solution A obtained in step (2), the mass ratio of solution A and solution B in step (3) is 100:20; uniformly mixing, and freeze-drying to form, thus obtaining.

[0064] The preparation process of the modified chitosan is as follows:

[0065] a. dissolving chitosan in 2wt% acetic acid solution, dissolving L-cysteine in 60% (v / v) ethanol solution to obtain 0.01g / mL chitosan solution and 0.024g / mL L-cysteine solution, then adding 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide into the L-cysteine solution for activation for 3h, the mass ratio of the chitosan, L-cysteine, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide is 1:2.6:1.2:1.2; then adding the activated solution into the chitosan solution, and reacting for 30h under nitrogen protection and away from light; after the reaction, the product is dialyzed with deionized water and vacuum dried to obtain intermediate 1;

[0066] b. adding intermediate 1 and di(3-sulfopropyl) itaconic acid dipotassium salt into DMSO and uniformly mixing, then adding photoinitiator 2,2-dimethoxy-2-phenylacetophenone, the dosage ratio of intermediate 1, di(3-sulfopropyl) itaconic acid dipotassium salt, 2,2-dimethoxy-2-phenylacetophenone and DMSO is 1g:4.5g:0.03g:75mL; after reacting for 12h under nitrogen protection and 365nm ultraviolet lamp irradiation, the product is precipitated with acetone, and then washed with acetone / DMSO (95:5, v / v) solution and pure acetone successively, dialyzed with deionized water and vacuum dried to obtain the modified chitosan.

[0067] The functional filler is an organic modified montmorillonite, and the preparation process is as follows:

[0068] S1. dispersing montmorillonite in ethanol aqueous solution (70%, v / v) under ultrasonic, adding 3-aminopropyl triethoxysilane, the dosage ratio of the montmorillonite, 3-aminopropyl triethoxysilane and ethanol aqueous solution is 5g:4g:50mL; after stirring and reacting for 3h at 90℃, filtering, washing with anhydrous ethanol and vacuum drying, the amino montmorillonite is obtained;

[0069] S2. Aminated montmorillonite was dispersed in anhydrous ethanol, and 4-hydroxy-2-oxo-2H-chromone-3-carboxaldehyde was added. The ratio of aminated montmorillonite, 4-hydroxy-2-oxo-2H-chromone-3-carboxaldehyde and anhydrous ethanol was 1 g: 1.2 g: 50 mL. After stirring and reacting at 60 °C for 2 h, the mixture was filtered, washed with anhydrous ethanol, and dried under vacuum to obtain the functional filler.

[0070] This embodiment also provides a carbon source for wastewater treatment, which is prepared by the method described above.

[0071] Comparative Example 1

[0072] Comparative Example 1 is basically the same as Example 1, except that modified chitosan is replaced with chitosan.

[0073] Comparative Example 2

[0074] Comparative Example 2 is basically the same as Example 1, except that the functional filler is replaced with montmorillonite.

[0075] Experimental Example 1

[0076] The infrared spectra of chitosan and modified chitosan obtained in Example 1, the filler obtained in Example 1, and the functional filler were tested using an infrared spectrometer. Figure 1 Infrared curves of chitosan and modified chitosan. Figure 2 Infrared curves of montmorillonite and functional fillers.

[0077] Depend on Figure 1 It can be seen that, compared to chitosan, modified chitosan has a lower content of 1750 cm⁻¹. -1 1033cm -1 The presence of characteristic peaks for ester and sulfonic acid groups indicates the successful synthesis of modified chitosan.

[0078] Depend on Figure 2 It can be seen that, compared to montmorillonite, the functional filler at 2940cm³... -1 2885cm -1 Symmetric and asymmetric stretching vibration peaks of the methylene group on 3-aminopropyltriethoxysilane appear at 1750 cm⁻¹; -1 The presence of a stretching vibration peak on the ester group of 4-hydroxy-2-oxo-2H-chromone-3-carboxaldehyde indicates that the functional filler was successfully prepared.

[0079] Experimental Example 2

[0080] In order to explore the carbon release capacity of the carbon sources obtained in Examples 1-3 and Comparative Examples 1-2, the following test was carried out: the carbon sources obtained in Examples 1-3 and Comparative Examples 1-2 were respectively placed in a conical flask containing 400 mL of deionized water, 10 g for each group, sealed and oscillated at 120 rpm at room temperature, and samples were taken at 12 h, 48 h and 120 h respectively, the collected water samples were filtered through 45 μm filter paper, and then the COD of each group of samples was determined according to the standard heavy chromate method specified in HJ / T 828-2017 cr The results are shown in Table 1.

[0081] Table 1

[0082]

[0083] As can be seen from the experimental results in Table 1, the carbon source obtained in the present application can be decomposed by microorganisms to provide a carbon source for the denitrification process; the plant material (wheat straw and reed straw) is wrapped in a three-dimensional network skeleton formed by cross-linking polyvinyl alcohol and modified chitosan to obtain a carbon source, which can not only avoid excessive carbon release at the initial stage of the experiment, but also stably release carbon source for a long time, and itself can serve as a supplemental carbon source to improve the denitrification effect of wastewater.

[0084] Compared with Example 1, in Comparative Example 1, the modified chitosan is replaced by chitosan, and the cross-linking effect between chitosan and polyvinyl alcohol is poor, resulting in rapid release of carbon source at the initial stage and decreased carbon release at the later stage, indicating that the modified chitosan has poor durability in slow-release performance.

[0085] Test Example 3

[0086] In order to explore the compressive strength of the carbon sources obtained in Examples 1-3 and Comparative Examples 1-2, the carbon sources obtained in Examples 1-3 and Comparative Examples 1-2 were selected, and the samples were prepared into a shape of 1.5 cm x 1.5 cm x 1.5 cm, a push-pull force meter was vertically and uniformly applied to the stress surface to press the material, and the value at which the material was broken was recorded, which was the compressive strength of the sample. The results are shown in Table 2.

[0087] Table 2

[0088]

[0089]

[0090] As can be seen from the experimental results in Table 2, the compressive strength of Examples 1-3 is higher than that of Comparative Examples 1 and 2, and both have high compressive strength, which can meet the requirements of solid carbon source. Among them, in Comparative Example 1, the modified chitosan is replaced by chitosan; in Comparative Example 2, the functional filler is replaced by montmorillonite; the compressive strength of both is poorer than that of Example 1. The above results show that the functional filler can synergistically act with polyvinyl alcohol-modified chitosan to improve the compressive strength of the carbon source, so that it has stronger impact resistance and can adapt to complex hydraulic impact conditions.

[0091] Test Example 4

[0092] In order to explore the heavy metal ion removal effect of the carbon sources of Examples 1-3 and Comparative Examples 1-2, the following experiments were performed: Cu-containing nitrate solution and Zn-containing nitrate solution simulating wastewater with a concentration of 50 mg / L were prepared, and randomly divided into Example 1 group, Example 2 group, Example 3 group, Comparative Example 1 group and Comparative Example 2 group; the carbon sources corresponding to Examples 1-3 and Comparative Examples 1-2 were added to the wastewater in each group, and the concentration of the carbon source in the wastewater was 5 g / L, and stirring was performed at a speed of 300 rpm, after 5 days, the above solution was centrifuged, the supernatant was taken, and the atomic flame absorption spectrometer was used to determine the heavy metal ion removal rate, and the test results are shown in Table 3.

[0093] Table 3

[0094] Group Cu heavy metal ion removal rate (%) Zn heavy metal ion removal rate (%) Example 1 99.3 98.5 Example 2 98.4 97.3 Example 3 98.6 97.8 Comparative Example 1 76.8 79.5 Comparative Example 2 81.9 83.4

[0095] As can be seen from the test results in Table 3, the heavy metal ion removal rates of Examples 1-3 all maintain above 90%, which is obviously improved compared with Comparative Examples 1 and 2. By comparing Comparative Example 1 with Example 1, it can be seen that the metal ion removal rate decreases when the modified chitosan is replaced by chitosan in Comparative Example 1, which is due to the introduction of sulfonate groups in the modified chitosan, which can combine with heavy metal ions in wastewater through chelation to achieve the removal of heavy metal ions. By comparing Comparative Example 2 with Example 1, it can be seen that the metal ion removal rate decreases when the functional filler is replaced by montmorillonite in Comparative Example 2, which is due to the fact that the hydroxyl (-OH) and carbonyl (C=O) on the Schiff base structure and chromone ring in the functional filler together form multiple coordination sites, which can effectively capture heavy metal ions and enhance the removal effect of heavy metal ions.

[0096] The above embodiments are only preferred embodiments of the present application, and cannot be used to limit the scope of protection of the present application, and any non-essential changes and replacements made by those skilled in the art on the basis of the present application are within the scope of protection of the present application.

Claims

1. A method for producing a carbon source for sewage treatment, characterized by, The method comprises the following steps: (1) crushing and drying wheat straw and reed straw, adding calcium hydroxide solution to soak, filtering, washing with deionized water until neutral, drying to obtain plant material; (2) adding polyvinyl alcohol and modified chitosan into water to stir, then adding the plant material of step (1) to obtain a mixed solution, adding glutaraldehyde aqueous solution to crosslink to obtain solution A; (3) dispersing the functional filler in water to obtain solution B, adding solution B into solution A obtained in step (2) to mix uniformly, and freeze-drying to form, thereby obtaining the product; The preparation process of the modified chitosan is as follows: a. dissolving chitosan in solvent A to obtain a chitosan solution, dissolving L-cysteine in solvent B to obtain an L-cysteine solution, adding 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide to the L-cysteine solution to activate, then adding the activated solution into the chitosan solution to react, after the reaction is completed, dialyzing the product, drying to obtain intermediate 1; b. adding intermediate 1 and di(3-sulfopropyl) itaconic acid dipotassium salt into a solvent to mix uniformly, then adding a photoinitiator, and performing reaction under nitrogen protection and ultraviolet irradiation, after the reaction is completed, washing, dialyzing and drying the product to obtain the modified chitosan; The preparation process of the functional filler is as follows: S1. dispersing montmorillonite in a solvent, adding 3-aminopropyl triethoxysilane to stir and react, filtering, washing and drying the product to obtain amino montmorillonite; S2. dispersing the amino montmorillonite in a solvent, adding 4-hydroxy-2-oxo-2H-chromen-3-formaldehyde to stir and react, filtering, washing and drying the product to obtain the functional filler.

2. The method for producing a carbon source for sewage treatment according to claim 1, characterized by, The mass ratio of chitosan, L-cysteine, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide in step a is 1:(2.4-2.6):(1-1.2):(1-1.2); the concentration of the chitosan solution is 0.01-0.04 g / mL; the concentration of the L-cysteine solution is 0.024-0.05 g / mL; the solvent A is 1.5-2 wt% acetic acid solution, and the solvent B is 50-60% ethanol solution by volume fraction; the activation time is 2-3 h, and the reaction time is 25-30 h.

3. The method for producing a carbon source for sewage treatment according to claim 1, characterized by, The dosage ratio of intermediate 1, di(3-sulfopropyl) itaconic acid dipotassium salt, photoinitiator and solvent in step b is 1 g:2.5-4.5 g:0.02-0.03 g:50-75 mL; the solvent is dimethyl sulfoxide, the photoinitiator is 2,2-dimethoxy-2-phenylacetophenone, the reaction time is 8-12 h, and the wavelength of the ultraviolet irradiation is 350-370 nm.

4. The method for producing a carbon source for sewage treatment according to claim 1, characterized by, The dosage ratio of montmorillonite, 3-aminopropyl triethoxysilane and solvent in step S1 is 5 g:2.5-4 g:30-50 mL; the stirring and reaction temperature is 70-90℃, and the time is 3-8 h; and the solvent is 60-70% ethanol aqueous solution by volume fraction.

5. The method for preparing a carbon source for wastewater treatment according to claim 1, characterized in that, The amino montmorillonite, 4-hydroxy-2-oxo-2H-chromen-3-carboxaldehyde and solvent in step S2 are used in a ratio of 1g:0.8-1.2g:30-50mL, and the solvent is anhydrous ethanol; the stirring reaction is carried out at a temperature of 40-60℃ for 2-5h.

6. The method for preparing a carbon source for wastewater treatment according to claim 1, characterized in that, In step (1), the wheat straw, reed straw and calcium hydroxide solution are used in a ratio of 1g:1-2g:5-10mL; the mass concentration of the calcium hydroxide solution is 2-4wt%; the soaking time is 8-15h; In step (2), the polyvinyl alcohol, modified chitosan, plant material and water are used in a ratio of (5-15):(2-6):(20-40):(90-100); the volume ratio of the glutaraldehyde aqueous solution and the mixed solution is (0.8-1.5):100; the concentration of the glutaraldehyde aqueous solution is 10-20wt%; In step (3), the mass ratio of solution A and solution B is 100:(10-20); the concentration of the functional filler in solution B is 20-30wt%.

7. A carbon source for sewage treatment, characterized by, The preparation method of any one of claims 1-6.

8. The carbon source for sewage treatment according to claim 7 is applied in sewage treatment.

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