Sulfur-doped nano zero-valent iron material based on humic acid coating as well as preparation method and application of sulfur-doped nano zero-valent iron material

Abstract

The invention discloses a sulfur-doped nano zero-valent iron material based on humic acid coating and a preparation method and application thereof, and the method comprises the following steps: (1) dispersing dry nano zero-valent iron powder in deionized water, under the protection of nitrogen, dropwise adding a sodium sulfide solution, stirring, centrifuging, and removing a supernatant to obtain nano zero-valent iron powder; washing and drying to obtain sulfur-doped nano iron particles; and (2) adding the sulfur-doped nano iron particles into a humic acid solution, uniformly dispersing, stirring under the protection of nitrogen, and then washing and drying to obtain the sulfur-doped nano zero-valent iron material based on humic acid coating. According to the method, the nano zero-valent iron material is modified, so that the sludge activity in anaerobic treatment of the wastewater is enhanced, and the methane yield and the removal rate of organic indexes such as COD (Chemical Oxygen Demand) are increased.

Description

Technical Field

[0001] The present invention relates to the technical field of water pollution control and resource utilization, and in particular to a sulfur-doped nano zero-valent iron material coated with humic acid, and a preparation method and application thereof. Background Art

[0002] With the acceleration of industrialization, the massive discharge of organic wastewater and other pollutants poses a serious threat to the aquatic ecosystem. Anaerobic biological treatment technology is widely used in wastewater treatment, but due to the accumulation of toxic substances and insufficient electron donors, anaerobic sludge activity decreases and organic matter removal efficiency declines. Therefore, improving sludge activity during anaerobic wastewater treatment has become an urgent need.

[0003] In recent years, nano-zero-valent iron (nZVI) has been widely used in organic wastewater treatment and heavy metal remediation due to its strong reducing properties and high reactivity. Adding nZVI to anaerobic wastewater treatment systems can effectively enhance microbial metabolic activity, promote electron transfer, and accelerate the decomposition of organic pollutants. However, exposed nZVI is prone to agglomeration, resulting in a rapid decrease in activity, and its direct contact with microorganisms can cause certain toxicity, limiting the application of nZVI. Secondly, traditional nZVI and its modified products have defects such as easy agglomeration and surface oxidation, which easily lead to inactivation in anaerobic reaction systems. Sulfur doping often leads to problems such as poor material dispersion performance, insufficient electron transfer efficiency, and low material utilization.

[0004] In summary, existing technologies still face challenges such as poor material stability, low biocompatibility, and poor process economics. There is an urgent need to develop a new modification method to enhance the activity of anaerobic wastewater treatment sludge. Summary of the Invention

[0005] The purpose of the present invention is to provide a sulfur-doped nano zero-valent iron material coated with humic acid, a preparation method and application thereof. By modifying the nano zero-valent iron material, the activity of sludge in anaerobic wastewater treatment is enhanced, and the removal rate of organic indicators such as methane production and COD is improved.

[0006] In one aspect of the present invention, a method for preparing a sulfur-doped nano-zero-valent iron material coated with humic acid is provided. According to an embodiment of the present invention, the method comprises the following steps:

[0007] (1) Dispersing the dried nano-zero-valent iron powder in deionized water, adding sodium sulfide solution dropwise under nitrogen protection, stirring, centrifuging, removing the supernatant, washing, and drying to obtain sulfur-doped nano-iron particles;

[0008] (2) adding sulfur-doped nano-iron particles to a humic acid solution and dispersing the particles uniformly, stirring the particles under nitrogen protection, and then washing and drying the particles to obtain the humic acid-coated sulfur-doped nano-zero-valent iron material.

[0009] In addition, the method for preparing the sulfur-doped nano-zero-valent iron material based on humic acid coating according to the above embodiment of the present invention may also have the following additional technical features:

[0010] In some embodiments of the present invention, in step (1), the preparation method of the nano zero-valent iron powder is as follows: under a nitrogen atmosphere, the ferric chloride hexahydrate solution is deoxygenated and then ascorbic acid is added, the reaction process is stirred in an oil bath, after the reaction is completed, the supernatant is removed by centrifugation, and the nano zero-valent iron powder is obtained after washing and drying.

[0011] In some embodiments of the present invention, the molar ratio of iron to ascorbic acid in the ferric chloride hexahydrate is (0.3-0.5):1; the oil bath temperature is 65-75°C; the stirring speed is 400-500 rpm for 110-120 minutes; and the washing is sequentially performed with deionized water and anhydrous ethanol. The nano-zero-valent iron powder produced under these parameters exhibits improved performance, effectively reducing impurities and optimizing its properties. The centrifugation speed is 8000 rpm, and the centrifugation time is 8-10 minutes. These centrifugation conditions produce a more uniform nano-zero-valent iron powder, facilitating the subsequent preparation of modified materials with improved properties.

[0012] In some embodiments of the present invention, in step (1), the molar ratio of S:Fe in the sodium sulfide nonahydrate and ferric chloride hexahydrate is (0.2-0.6):1; the washing is sequentially performed with deionized water and anhydrous ethanol; the drying temperature is 55-65°C, and the drying time is 6-12 hours. The above method can ensure uniform sulfurization of the nano-zero-valent iron powder and facilitates volatilization and drying while effectively washing the sulfur-doped nano-zero-valent iron material.

[0013] In some embodiments of the present invention, in step (2), the concentration of the humic acid solution is 1.0-1.2 g / L; the mass ratio of the sulfur-doped nano-iron particles to the humic acid is (5-6):1; the sodium sulfide is added at a rate of 0.5-1.0 mL / min; the stirring speed is 300-350 rpm, and the stirring time is 5-6 hours; the washing is sequentially performed with deionized water and anhydrous ethanol; the drying temperature is 40-45°C, and the drying time is 6-10 hours. The above drying temperature can prevent the humic acid coating from failing at excessively high temperatures, ensuring that the humic acid layer is stably coated around the sulfur-doped nano-zero-valent iron material.

[0014] In another aspect of the present invention, the present invention provides a sulfur-doped nano-zero-valent iron material coated with humic acid prepared by the preparation method of the sulfur-doped nano-zero-valent iron material coated with humic acid.

[0015] In another aspect, the present invention provides a method for enhancing the activity of anaerobic sludge. According to an embodiment of the present invention, the sulfur-doped nano-zero-valent iron material coated with humic acid is added to the anaerobic activated sludge mixture.

[0016] In another aspect of the present invention, a method for enhancing the activity of anaerobic sludge in organic wastewater is proposed. According to an embodiment of the present invention, the method includes the following steps: adding the sulfur-doped nano zero-valent iron material coated with humic acid to wastewater containing anaerobic activated sludge for anaerobic biological treatment.

[0017] In addition, the method for enhancing the activity of anaerobic sludge in organic wastewater according to the above embodiment of the present invention may also have the following additional technical features:

[0018] In some embodiments of the present invention, the concentration of the anaerobic digestion sludge is 4–6 g / L, and the dosage of the humic acid-coated, sulfur-doped, nano-zero-valent iron material is 0.3–0.6 g / L. This dosage of the humic acid-coated, sulfur-doped, nano-zero-valent iron material can provide exogenous electrons, enriching the functional microbial capacity and thereby improving treatment efficiency.

[0019] In some embodiments of the present invention, the temperature of the anaerobic biological treatment is 34-36°C.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The present invention introduces a sulfurizing agent, and sulfur doping fundamentally enhances its performance by forming a layer of FeS shell with good conductivity outside the nano iron core. This FeS shell first replaces the traditional easily generated insulating oxide passivation layer, and can effectively and quickly transfer the electrons generated by the internal core to the surface of the material, thereby more easily transferring them to pollutants. At the same time, the microgalvanic effect formed by FeS and the iron core accelerates the release of electrons. These two together greatly enhance the electron donor reduction ability of the material. In addition, this iron sulfide surface itself is an excellent catalytic active site, which can efficiently activate peroxides to produce strong oxidizing free radicals or promote hydrogen evolution reactions, thereby giving the material excellent catalytic reaction ability.

[0022] 2. This preparation method solves the problem of material instability by constructing a synergistic structure in steps. First, a FeS shell with stronger conductivity and corrosion resistance is generated outside the nZVI core through a sulfurization reaction, which initially improves the electron transfer efficiency and antioxidant capacity. Then, the HA coating is used to fundamentally solve the problem of particle agglomeration by utilizing electrostatic repulsion and steric hindrance effects. At the same time, HA acts as a physical barrier to completely prevent oxidative deactivation. Its unique quinone-based structure can also act as an electron shuttle, synergizing with the FeS shell to efficiently transfer electrons to pollutants, achieving the unity of stability and efficiency.

[0023] 3. The present invention solves the problem of microbial toxicity by coating with HA. The present invention puts a natural and non-toxic "biocompatible coat" on the highly active S-nZVI core. The HA coating not only physically isolates the direct contact between the nanoparticles and the microbial cells, avoiding physical damage, but also effectively complexes and buffers the iron ions that may leak, eliminating chemical toxicity, and transforming the material from having an inhibitory effect on microorganisms to a friendly material that can be safely integrated into biological systems such as anaerobic digestion.

[0024] 4. The method of the present invention significantly improves wastewater COD removal and anaerobic digestion methane production. Experimental data show that the material of the present invention significantly enhances sludge activity. The modified S-nZVI has excellent reducing ability, synergizing microbial metabolism, effectively promoting organic matter decomposition and methane production. The overall methane production is higher than that of traditional anaerobic reaction systems, and the reaction endpoint is more stable.

[0025] 5. The entire process of the present invention is carried out under mild aqueous conditions. The HA used is a natural organic compound that is environmentally friendly and non-toxic. The doping elements such as iron and sulfur used are widely available, resulting in a simple preparation process and convenient operation. The entire process has a mild reaction and does not require high temperature and high pressure conditions, significantly reducing operating energy consumption. This allows the preparation of high-performance, highly stable materials at a low cost and in an environmentally friendly manner, making them suitable for industrial-scale production and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a comparison chart of total methane production and yield when the materials prepared in Examples 1-3 and Comparative Examples 1-5 are used to enhance the activity of anaerobic sludge in Application Example 1 of the present invention;

[0027] Figure 2 This is a comparison chart of methane production during anaerobic digestion when the materials prepared in Examples 1-3 and Comparative Examples 1-5 are used to enhance the activity of anaerobic sludge in Application Example 1 of the present invention;

[0028] Figure 3 This is a comparison chart of the residual SCOD when the materials prepared in Examples 1-3 and Comparative Examples 1-5 are used to enhance the activity of anaerobic sludge in Application Example 1 of the present invention;

[0029] Figure 4 This is a comparison chart of VFAs accumulation during anaerobic digestion when the materials prepared in Examples 1-3 and Comparative Examples 1-5 are used to enhance the activity of anaerobic sludge in Application Example 1 of the present invention;

[0030] Figure 5 This is a comparison chart of pH changes during anaerobic digestion when the materials prepared in Examples 1-3 and Comparative Examples 1-5 are used to enhance the activity of anaerobic sludge in Application Example 1 of the present invention;

[0031] Figure 6 This is a comparison chart of COD removal rates when the materials prepared in Examples 1 and 4-13 of the present invention are used to enhance the activity of anaerobic sludge and when the materials prepared in Application Examples 2-4 are used to enhance the activity of anaerobic sludge. DETAILED DESCRIPTION

[0032] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0033] Example 1

[0034] A method for preparing a sulfur-doped nano-zero-valent iron material coated with humic acid comprises the following steps:

[0035] S1. Preparation of nZVI

[0036] A 0.1 mol / L ferric chloride hexahydrate solution was added to a three-necked flask, and 99.9% nitrogen was passed through for 30 minutes to completely deoxygenate. A 0.2 mol / L ascorbic acid solution was added dropwise at 1 mL / min using a constant pressure dropping funnel for 1 hour. The mixture was stirred in an oil bath at 70°C and 500 rpm for 2 hours. After the reaction was completed, the mixture was centrifuged at 8000 rpm for 10 minutes to remove the supernatant. The mixture was washed with deionized water and 95% anhydrous ethanol in sequence under the same centrifugal conditions, and then dried in vacuo at 60°C for 6 hours to obtain nano-iron particles, which were recorded as nZVI.

[0037] S2, nZVI vulcanization modification

[0038] The dried nZVI powder was ultrasonically dispersed in 100 mL of deionized water. In a nitrogen atmosphere with a purity of 99.9%, sodium sulfide heptahydrate solution was slowly added dropwise at 1 mL / min according to the target sulfur-iron ratio (S:Fe) of 0.4 (molar ratio). The mixture was stirred at room temperature for 2 h and centrifuged at 8000 rpm for 10 min. The supernatant was removed and the mixture was washed with deionized water and 95% anhydrous ethanol in sequence. After vacuum drying at 60°C for 6 h, sulfur-doped iron nanoparticles were obtained, which were recorded as S-nZVI.

[0039] S3, Humic acid modification

[0040] 0.2 g of HA powder was dissolved in 200 mL of deionized water and magnetically stirred for 2 hours. The pH was adjusted to 7.0 using 1 mol / L NaOH solution. Ultrasonic dispersion was performed for 30 minutes and the mixture was filtered. 0.2 g of the aforementioned S-nZVI powder was added to 200 mL of the HA solution and ultrasonically dispersed for 10 minutes. The mixture was magnetically stirred at 300 rpm for 6 hours in a 99.9% nitrogen atmosphere to allow for full adsorption of the HA. The mixture was then washed sequentially with deionized water and 95% anhydrous ethanol and dried under vacuum at 40°C for 6 hours to obtain HA-S-nZVI. This product was designated HS2-0.4.

[0041] Example 2

[0042] A method for preparing a humic acid-coated sulfur-doped nano-zero-valent iron material, which differs from Example 1 only in that: in step S2, sodium sulfate heptahydrate and ferric chloride hexahydrate are mixed in a molar ratio of S:Fe=0.2:1; the resulting humic acid-coated sulfur-doped nano-zero-valent iron material is named HS2-0.2.

[0043] Example 3

[0044] A method for preparing a humic acid-coated sulfur-doped nano-zero-valent iron material, which differs from Example 1 only in that: in step S2, sodium sulfate heptahydrate and ferric chloride hexahydrate are mixed in a molar ratio of S:Fe=0.6:1; the resulting humic acid-coated sulfur-doped nano-zero-valent iron material is named HS2-0.6.

[0045] Example 4

[0046] A method for preparing sulfur-doped nano-zero-valent iron material coated with humic acid, which differs from Example 1 only in that: in step S1, a 0.2 mol / L ascorbic acid solution is added to the mixed solution through a constant pressure funnel at a dropping rate of 2 mL / min for 42 minutes.

[0047] Example 5

[0048] A method for preparing sulfur-doped nano-zero-valent iron material coated with humic acid, which differs from Example 1 only in that: in step S1, a 0.4 mol / L ascorbic acid solution is added to the mixed solution through a constant pressure funnel at a dropping rate of 4 mL / min for 16 minutes.

[0049] Example 6

[0050] A method for preparing sulfur-doped nano-zero-valent iron material coated with humic acid is provided, which differs from Example 1 only in that: in step S1, the oil bath temperature is 65°C, the stirring speed is 320 rpm, and the stirring time is 48 min.

[0051] Example 7

[0052] A method for preparing sulfur-doped nano zero-valent iron material coated with humic acid is different from Example 1 only in that: in step S1, the oil bath temperature is 75°C, the stirring speed is 420 rpm, and the stirring time is 75 min.

[0053] Example 8

[0054] A method for preparing sulfur-doped nano-zero-valent iron material coated with humic acid is provided, which differs from Example 1 only in that: in step S2, the oil bath temperature is 30°C, the stirring speed is 320 rpm, and the stirring time is 48 min.

[0055] Example 9

[0056] A method for preparing sulfur-doped nano-zero-valent iron material coated with humic acid is provided, which differs from Example 1 only in that: in step S2, the oil bath temperature is 55°C, the stirring speed is 220 rpm, and the stirring time is 98 min.

[0057] Example 10

[0058] A preparation method of sulfur-doped nano zero-valent iron material coated with humic acid is provided, which differs from Example 1 only in that: in step S1, the vacuum drying method is to place the washed material in a vacuum drying oven at a temperature of 45°C and dry it for 12 hours.

[0059] Example 11

[0060] A preparation method of sulfur-doped nano zero-valent iron material coated with humic acid is provided, which differs from Example 1 only in that: in step S1, the vacuum drying method is to place the washed material in a vacuum drying oven at a temperature of 65°C and dry it for 3 hours.

[0061] Example 12

[0062] A method for preparing sulfur-doped nano zero-valent iron material coated with humic acid, which differs from Example 1 only in that: in step S2, the vacuum drying method is to place the washed material in a vacuum drying oven at a temperature of 45°C and dry it for 12 hours.

[0063] Example 13

[0064] A preparation method of sulfur-doped nano zero-valent iron material coated with humic acid is provided, which differs from Example 1 only in that: in step S3, the vacuum drying method is to place the washed material in a vacuum drying oven at a temperature of 45°C and dry it for 10 hours.

[0065] Comparative Example 1

[0066] A nano iron particle, whose preparation method is exactly the same as step S1 in Example 1, is denoted as nZVI.

[0067] Comparative Example 2

[0068] A sulfur-doped nano-iron particle, whose preparation method is exactly the same as steps S1 and S2 in Example 1, is denoted as S-nZVI.

[0069] Comparative Example 3

[0070] A method for preparing sulfur-doped nano-iron particles, which differs from that of Example 1 in that S-nZVI is synthesized by a one-step method. The specific method is as follows: 100 mL of 0.1 mol / L ferric chloride hexahydrate solution is added to a three-necked flask under a nitrogen atmosphere with a purity of 99.9%, and magnetic stirring is performed at 500 rpm. After slowly adding 0.02 mol / L sodium sulfide heptahydrate solution at a rate of 1 mL / min for 45 minutes, 0.2 mol / L ascorbic acid solution is added dropwise at a rate of 1 mL / min. The oil bath temperature is maintained at 50±1°C and stirring is continued for 1 hour. The solution gradually changes from brown-red to a black suspension. The solution is then centrifuged at 8000 rpm for 10 minutes, the supernatant is discarded, and the solution is washed three times with 10 mL of 95% anhydrous ethanol to remove unreacted substances. The solution is then vacuum-dried at 60°C for 6 hours to obtain black S-nZVI powder, which is then coated with HA and named HS1-0.4.

[0071] Comparative Example 4

[0072] A method for preparing sulfur-doped nano-iron particles, which is different from Comparative Example 3 only in that ferric chloride hexahydrate and sodium sulfate heptahydrate are prepared in a molar ratio of S:Fe=0.2:1, and is named HS1-0.2.

[0073] Comparative Example 5

[0074] A method for preparing sulfur-doped nano-iron particles, which is different from Comparative Example 3 only in that ferric chloride hexahydrate and sodium sulfate heptahydrate are prepared in a molar ratio of S:Fe=0.6:1, and is named HS1-0.6.

[0075] Application Example 1

[0076] A method for enhancing the activity of anaerobic sludge in organic wastewater comprises the following steps:

[0077] (1) Preparation of anaerobic activated sludge mixed liquor

[0078] Anaerobic activated sludge mixed liquor includes anaerobic activated sludge and organic wastewater. In this application example, the organic wastewater is artificially synthesized, and the raw materials are as follows: sucrose (C 12 H 22 O 11 ) provides the carbon source, ammonium chloride (NH4Cl) provides the nitrogen source, potassium dihydrogen phosphate (KH2PO4) provides the phosphorus source, and C:N:P=200:5:1 (mass ratio). Trace elements include the following raw materials: (NH4)6Mo6O 24 ·4H2O 1.5mg / L, H3BO40.5mg / L, NiCl2·6H2O 0.5mg / L, AlCl3 0.25mg / L, MnCl2·4H2O 0.5mg / L, COCl2·6H2O 0.5mg / L, MgCl2·6H2O 10mg / L, FeCl2 2.5mg / L, ZnCl2 0.5mg / L, CaCl2 5mg / L, CuCl2·5H2O 0.5mg / L, NaCl 1.0mg / L, EDTA 2.5mg / L.

[0079] Anaerobic activated sludge was prepared as follows: Sludge seeded into the glass reactor was obtained from an internal circulation anaerobic reactor at a sewage treatment plant in Hefei. The sludge had a moisture content of 88.95%, a total suspended solids concentration of 191.44 g / L, and a volatile solids concentration of 265.32 g / L. Prior to inoculation, the anaerobic sludge was cultured for one week in a 5-L laboratory UASB reactor with a C:N:P ratio of 200:5:1 (mass ratio) and a hydraulic retention time of 48 hours to maintain activity.

[0080] (2) 400 mL of the anaerobic activated sludge mixture was added to a 500 mL glass reactor. The anaerobic digestion sludge concentration was 5 g / L, and the sludge load F / M was 0.93 kg COD / (kg VSS). Then, the materials prepared in Examples 1-3 and Comparative Examples 1-5 were added to the mixture at a dosage of 0.5 g / L. The pH was adjusted to 8.0 using NaHCO3. After nitrogen stripping for 30 minutes, the mixture was placed in a shaker. The shaker speed was adjusted to 200 rpm and the temperature was adjusted to 35°C for anaerobic biological treatment.

[0081] A blank control group was set up. The difference between it and Application Example 1 is that no optimized HA-S-nZVI was added. Then the following tests were performed:

[0082] (1) Total methane production and yield

[0083] Gas produced by the glass reactor was collected using a Beekman aluminum foil sampling bag. A 1 mL syringe was used to extract the gas and analyze its composition in a gas chromatograph, primarily measuring the CH4 content. The gas volume was determined using the water-displacement gas collection method. The methane yield was calculated by dividing the actual methane production by the theoretical methane production.

[0084] like Figure 1 As shown in the results, the addition of materials can effectively improve the methane yield during the anaerobic digestion of wastewater. The HS2-0.4, HS2-0.2 and HS1-0.4 obtained in Example 1, Example 2 and Comparative Example 3 increased by 11.89%, 9.41% and 7.34% respectively compared with the blank control group. Figure 2 As shown, except for the blank control group, the cumulative methane production in each group gradually increased. However, the acid accumulation in the blank control group was irreversible, affecting COD degradation and methane production, indicating that the addition of nZVI material enabled the anaerobic digestion process of organic wastewater to proceed smoothly. As can be seen from the comparison of Comparative Example 1 and Comparative Examples 2-5, sulfur doping further promoted methane production, and the HS2-0.4, HS2-0.2, and HS1-0.4 obtained in Example 1, Example 2, and Comparative Example 3 increased by 18.21%, 9.56%, and 4.72%, respectively, compared with the nZVI group in Comparative Example 1. Therefore, in the sludge anaerobic metabolism system, the HA-S-nZVI prepared by the two-step synthesis and the S / Fe molar ratio of 0.4, that is, Example 1, has absolute advantages in promoting anaerobic digestion of organic wastewater, alleviating acid inhibition, and increasing methane production and yield.

[0085] (2) Remaining SCOD situation

[0086] Take the water sample after the reaction in the glass reactor, filter it with a 0.45um water filter membrane, add it to the COD digestion tube, shake it evenly, and then place it in the COD digester for digestion at 165℃ for 15 minutes. After the digestion is completed, let it stand and cool to about 60℃, shake it again, let it stand until it is completely cooled, and then test it in the COD detector.

[0087] like Figure 3 As shown, in the first 72 hours after the start of the reaction, the residual SCOD of each group was below 1500 mg / L, among which the residual SCOD of HS2-0.4 was lower than that of the other groups, below 800 mg / L. During the 200-hour operation, the residual COD of Comparative Examples 1 to 5 and Examples 1 to 3 was less than 200 mg / L.

[0088] (3) VFAs accumulation

[0089] Water samples were collected from a glass reactor and filtered through a 0.45 μm water filter membrane. The samples were acidified with 3.3% formic acid and analyzed using a gas chromatograph (imported) equipped with a flame ionization detector and a 30 m × 0.25 m × 0.25 μm DB-FFAP column. The column oven temperature was initially set at 100°C for 3 minutes, then increased at 20°C / minute, held for 4 minutes, and finally held at 180°C for 3 minutes. The injector and detector temperatures were 220°C and 230°C, respectively. Nitrogen was used as the carrier gas at a flow rate of 5 mL / min. The acidified samples were placed in an autosampler for analysis. Standard solutions of the corresponding VFA acids were prepared to calculate the VFA concentrations in the effluent water.

[0090] For the anaerobic digestion process of wastewater, during the 200h operation, the blank control group showed obvious acid accumulation and was irreversible, which also led to significant inhibition of COD degradation and methane production, thus making the anaerobic digestion process unable to proceed smoothly. However, the addition of materials in Comparative Examples 1 to 5 and Examples 1 to 3 effectively alleviated the acid inhibition, such as Figure 4 As shown in the figure, after the anaerobic digestion, the VFAs in all material groups were below 30 mg / L.

[0091] (4) pH changes

[0092] The pH of the water sample in the glass reactor was tested using a pH meter.

[0093] For the anaerobic digestion process of wastewater, during the 200h operation, the blank control group showed obvious acidification and could not be restored, so that the anaerobic digestion process could not proceed smoothly, while the reaction could proceed normally after adding materials in Comparative Examples 1 to 5 and Examples 1 to 3. Figure 5As shown, the pH value of the water sample in the blank group was always maintained below 6.5, while the pH value of the material group fluctuated within the normal range of 7.0-7.5.

[0094] (5) COD removal rate

[0095] The COD removal content is obtained by subtracting the residual SCOD value from the initial COD value, and then the COD removal rate is calculated by dividing it by the initial COD value.

[0096] like Figure 6 As shown, in the first 72 hours after the start of the reaction, the COD removal rate of each group reached more than 50%, among which the COD removal rate of HS2-0.4 was higher than that of other groups, reaching 78.16%. During the 200-hour operation process, the COD removal rates of Comparative Examples 1 to 5 and Examples 1 to 3 were all greater than 90%.

[0097] Application Example 2

[0098] A method for enhancing the activity of anaerobic sludge, which differs from Application Example 1 only in that: the dosage of HA-S-nZVI prepared in Example 1 is 0.4 g / L, the concentration of anaerobic digestion sludge is 4 g / L, and the sludge load F / M is 0.74 kg COD / (kg VSS).

[0099] Application Example 3

[0100] A method for enhancing the activity of anaerobic sludge, which differs from Application Example 1 only in that: the dosage of HA-S-nZVI prepared in Example 1 is 0.6 g / L, the concentration of anaerobic digestion sludge is 6 g / L, and the sludge load F / M is 1.11 kg COD / (kg VSS).

[0101] Application Example 4

[0102] A method for enhancing the activity of anaerobic sludge, which differs from Application Example 1 only in that the rotation speed of the shaker is 160 rpm and the temperature is 38°C.

[0103] The materials prepared in Examples 1 and 4-13 were used to enhance the activity of anaerobic sludge according to the method of Application Example 1. Then, the above groups and Application Examples 2-3 were subjected to performance tests, including COD removal rate and methane production. The test results are shown in the following table:

[0104] Group Example 1 Example 4 Example 5 Example 6 Example 7 Example 8 Example 9 COD removal rate% 97.07 96.24 96.03 96.59 96.35 96.86 97.01 Methane production mL 306.9 298.6 295.5 300.2 296.7 302.4 305.7 Group Example 10 Example 11 Example 12 Example 13 Application Example 2 Application Example 3 Application Example 4 COD removal rate% 96.66 95.24 96.68 96.74 96.09 96.32 96.75 Methane production mL 301.1 291.1 301.7 302.3 295.6 298.3 299.3

[0105] As can be seen from the above table, the COD removal effect and methane generation efficiency achieved by anaerobic treatment of organic wastewater under 200h operation state with ascorbic acid addition parameters, stirring parameters, drying temperature and centrifugation parameters that are too low or too high within the specified range of this application are small compared with those in Example 1. Therefore, from an economic point of view, Example 1 is selected as the optimal solution.

[0106] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in similar ways. As long as they do not deviate from the structure of the present invention or exceed the scope defined by the claims, they shall fall within the scope of protection of the present invention.

Claims

1. A method for preparing sulfur-doped nano zero-valent iron material coated with humic acid, characterized in that: The following steps are involved: (1) Dispersing the dried nano-zero-valent iron powder in deionized water, adding sodium sulfide solution dropwise under nitrogen protection, stirring, centrifuging, removing the supernatant, washing, and drying to obtain sulfur-doped nano-iron particles; (2) adding sulfur-doped nano-iron particles to a humic acid solution and dispersing the particles uniformly, stirring the particles under nitrogen protection, and then washing and drying the particles to obtain the humic acid-coated sulfur-doped nano-zero-valent iron material.

2. The method for preparing a sulfur-doped nano-zero-valent iron material coated with humic acid according to claim 1, characterized in that: In step (1), the preparation method of the nano zero-valent iron powder is as follows: under a nitrogen atmosphere, the ferric chloride hexahydrate solution is deoxygenated and then ascorbic acid is added, the reaction process is stirred in an oil bath, after the reaction is completed, the supernatant is removed by centrifugation, and the nano zero-valent iron powder is obtained after washing and drying.

3. The method for preparing a sulfur-doped nano-zero-valent iron material coated with humic acid according to claim 2, characterized in that: The molar ratio of iron to ascorbic acid in the ferric chloride hexahydrate is (0.3-0.5):1; the temperature of the oil bath is 65-75°C; the stirring speed is 400-500 rpm, and the stirring time is 110-120 minutes; and the washing is carried out sequentially with deionized water and anhydrous ethanol.

4. The method for preparing a sulfur-doped nano-zero-valent iron material coated with humic acid according to claim 1, characterized in that: In step (1), the molar ratio of S: to Fe in the sodium sulfide nonahydrate and ferric chloride hexahydrate is (0.2-0.6):1; the washing is carried out sequentially with deionized water and anhydrous ethanol; the drying temperature is 55-65° C., and the drying time is 6-12 h.

5. The method for preparing a sulfur-doped nano-zero-valent iron material coated with humic acid according to claim 1, characterized in that: In step (2), the concentration of the humic acid solution is 1.0-1.2 g / L; the mass ratio of the sulfur-doped nano-iron particles to the humic acid is (5-6):1; the dripping rate of the sodium sulfide is 0.5-1.0 mL / min; the stirring speed is 300-350 rpm, and the stirring time is 5-6 hours; the washing is carried out sequentially with deionized water and anhydrous ethanol; the drying temperature is 40-45° C., and the drying time is 6-10 hours.

6. A humic acid-coated sulfur-doped nano-zero-valent iron material prepared by the method for preparing a humic acid-coated sulfur-doped nano-zero-valent iron material according to any one of claims 1 to 5.

7. A method for enhancing the activity of anaerobic sludge, characterized in that: The humic acid-coated sulfur-doped nano zero-valent iron material according to claim 6 is added to the anaerobic activated sludge.

8. A method for enhancing the activity of anaerobic sludge in organic wastewater, characterized in that: The method comprises the following steps: adding the humic acid-coated sulfur-doped nano zero-valent iron material according to claim 6 into wastewater containing anaerobic activated sludge to perform anaerobic biological treatment.

9. The method for enhancing the activity of anaerobic sludge in organic wastewater according to claim 8, characterized in that: The concentration of the anaerobic digestion sludge is 4-6 g / L; the dosage of the humic acid-coated sulfur-doped nano zero-valent iron material is 0.3-0.6 g / L.

10. The method for enhancing the activity of anaerobic sludge in organic wastewater according to claim 8, characterized in that: The temperature of the anaerobic biological treatment is 34-36°C.

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