Method for fast start of dye-organic wastewater anaerobic co-metabolic system based on s-nzvi

Abstract

The present application relates to the technical field of water pollution control, and particularly relates to a method for rapidly starting a dye-organic wastewater anaerobic co-metabolic system based on S-nZVI, comprising the following steps: S1, preparing S-nZVI and S2, an anaerobic treatment method for optimizing dye-organic wastewater by S-nZVI; the present application applies sulfur-doped nano-iron to a dye-organic wastewater anaerobic co-metabolic system for the first time, improves the dispersibility of nano-iron through sulfur doping, inhibits the hydrogen evolution reaction and avoids the reduction damage of the cell membrane through sulfur doping; meanwhile, the formation of FeS endows nano-iron with stronger conductivity, which is conducive to the electron transfer pathway of abundant microorganisms and improves the electron transfer efficiency; the optimization method of the present application not only realizes the efficient degradation of dyes, but also effectively overcomes the acid inhibition of the anaerobic digestion process under dye stress, and realizes the rapid start of the reactor and the recovery of methane without sludge domestication.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of water pollution control, in particular to a method for rapidly starting a dye-organic wastewater anaerobic co-metabolic system based on S-nZVI. BACKGROUND

[0002] Textile, printing and dyeing, papermaking and other industries produce a large amount of dye wastewater, which accounts for about 20% of the total global industrial wastewater, among which the use of azo dyes accounts for 60-70% of the total amount of synthetic dyes, and azo dyes are one of the characteristic pollutants that must be concerned in dye wastewater. If not properly treated, it may cause serious environmental problems and harm human health. At present, the main treatment technologies of azo dyes include physical method, chemical method, biological method and their combined process. Anaerobic treatment is a green and economical pretreatment process, which can improve the biodegradability of refractory wastewater by converting macromolecular organic matter, and in this process, azo dyes are converted into aromatic amines, which are easily degraded by microorganisms under aerobic conditions.

[0003] However, the anaerobic treatment of dye wastewater has not achieved satisfactory results so far, the reasons are as follows: first, azo dyes have large molecular weight and strong polarity, which makes it difficult to enter the cell and be degraded by microorganisms, second, as a typical low carbon-nitrogen ratio wastewater, the lack of electron donor source and the competition of other electron acceptors lead to insufficient biodegradation efficiency of azo dyes. Therefore, dye wastewater is usually co-metabolized with high organic wastewater to provide sufficient electron source for dye degradation. However, this co-metabolic mode usually has an inhibitory effect on anaerobic digestion, which is worth noting. Due to the biological toxicity of azo dyes and their reduced products aromatic amines, the activity of acid-producing and methane-producing microorganisms is easily out of balance, leading to poor mutual nutritional metabolism and poor system stability. It is reported that compared with acid-producing bacteria, methanogens are more sensitive to adverse environments, which leads to the accumulation of volatile fatty acids (VFAs) (mainly acetic acid, propionic acid and butyric acid) due to the inhibition of conversion, and the reactor fails to start or collapses due to excessive acidification during operation. Therefore, it is of great practical significance to successfully start the reactor from potential failure and maintain the stability of the co-metabolic system, which not only ensures the efficient degradation of dyes, but also realizes efficient energy recovery.

[0004] In recent years, nano-iron materials have been applied to anaerobic digestion systems. Due to its strong reducing and conductive properties, nano-iron can act as an electron donor for CO2 reduction and enrich hydrogenotrophic methanogens, thereby reducing the hydrogen partial pressure in the anaerobic digestion process, which indirectly leads to easier transformation of VFAs in thermodynamics. On the other hand, a large number of studies have reported that conductive or semiconductive materials can enhance microbial extracellular electron transfer (EET), so the extracellular degradation of azo dyes may be enhanced, which not only saves the energy consumed by crossing the membrane into the cell and improves the efficiency of electron transfer, but also relieves the toxic effects of azo dyes on anaerobic microorganisms. In addition, methanogens can use extracellular electrons to establish interspecies direct electron transfer (DIET) mechanisms. DIET is achieved by conductive pili or cytochrome C for electron transfer between microorganisms, and this syntrophic metabolism is more energy-efficient than interspecies hydrogen transfer (IHT). Therefore, even under adverse conditions (dye stress) or high concentrations of VFAs, the thermodynamic bottleneck in the syntrophic metabolism process can be overcome, and the DIET pathway can be used to degrade VFAs and produce methane in a more energy-efficient way. It is worth mentioning that the establishment of DIET not only benefits CO2 reduction, but also enhances acetate-utilizing methanogenesis. However, nano-iron is prone to agglomeration due to the influence of surface forces such as van der Waals forces and magnetic forces, which reduces its reactivity. At the same time, a large number of studies have reported that the effect of nano-iron on microorganisms is dose-dependent, which is mainly due to the strong reducing property of nano-iron, which not only leads to the reduction and destruction of microbial cell membranes, but also easily causes hydrogen evolution reactions with protons in aqueous media, which not only leads to the waste of electrons, but also affects the thermodynamic equilibrium of the anaerobic digestion process.

[0005] Sulfur doping technology provides an opportunity to solve the above problems. In the preparation process of nano-iron, sulfurizing reagents are introduced to form FeS as the skeleton, which can effectively improve the dispersibility of nano-iron particles. FeS has certain hydrophobicity, which is conducive to regulating the hydrogen evolution reaction of nano-iron, thereby avoiding excessive hydrogen partial pressure. In addition, FeS has excellent conductivity and can act as an active site for nano-iron, which not only improves the conductivity of nano-iron, but also relieves the reduction and destruction of microbial cell membranes. Therefore, we speculate that in the co-metabolic system of dye wastewater and organic wastewater, sulfur doping will strengthen the improvement of nano-iron on anaerobic digestion in terms of thermodynamics, kinetics, etc., and provide a more suitable environment for microorganisms, while further optimizing the proton-electron transfer network and microbial community structure of pollutant degradation and methanogenesis process. Thus, an energy-saving, efficient and stable anaerobic metabolic system is constructed. SUMMARY

[0006] To solve the above problems, the present application provides a method for rapidly starting a dye-organic wastewater anaerobic co-metabolic system based on S-nZVI.

[0007] The technical scheme of the present application is: a method for rapidly starting a dye-organic wastewater anaerobic co-metabolic system based on S-nZVI, comprising the following steps:

[0008] S1, preparation of S-nZVI

[0009] In an inert atmosphere, sodium dithionite and ferrous sulfate heptahydrate with a concentration of 0.1-0.15 mol / L were dissolved in ultrapure water according to a molar ratio of S:Fe=(0.1-0.5):1, and stirred to obtain a mixed solution. Then, potassium borohydride with a concentration of 0.4-0.5 mol / L was added dropwise to the mixed solution at a dropwise rate of 8-12 mL / min by using a peristaltic pump, and the dropwise time was 18-22 min. After centrifugal treatment, the supernatant was removed and washed with ultrapure water and ethanol in sequence, and then vacuum dried to obtain sulfur-doped nano-iron particles, denoted as S-nZVI;

[0010] S2, S-nZVI optimizes anaerobic treatment of dye-organic wastewater

[0011] Anaerobic digestion sludge was added to a serum bottle to make the concentration of anaerobic digestion sludge 4-6 g TS / L, then S-nZVI obtained in step S1 was added to the anaerobic digestion sludge, the addition amount was 0.4-0.6 g / L, and 120-180 mL of dye-organic wastewater was introduced, then a pH regulator was used to adjust the pH to pH=6.8-7.2, and after nitrogen stripping for 25-35 min, it was put into a shaking bed for anaerobic biological treatment for 10-14 h; the pH regulator was 0.1 mol / L HCl solution or 0.1 mol / L NaOH solution; the above-mentioned addition amount of S-nZVI can have the ability to enrich functional microorganisms and provide exogenous electrons, so as to efficiently convert VFAs to methane under the adverse conditions of dye stress.

[0012] Further, in step S1, the purity of the inert atmosphere is 99-99.9%, the stirring speed is 180-220 rpm, and the stirring time is 25-40 min;

[0013] Note: The S-nZVI prepared under the above parameters has better performance, can effectively improve the dispersion of nano-iron, thereby inhibiting the hydrogen evolution reaction and further avoiding the destruction of nano-iron, thereby optimizing the performance of nano-iron.

[0014] Further, the method of vacuum drying is to place the washed material into a vacuum drying oven with a temperature of 45-55°C and dry for 22-26 h;

[0015] Note: Drying at the above temperature can ensure drying efficiency while avoiding damage to S-nZVI caused by high temperature, thereby effectively ensuring the optimization of S-nZVI to nano-iron.

[0016] Further, in step S1, the centrifugal speed is 5900-6100 rpm, and the centrifugal time is 6-10 min.

[0017] Description: The sulfur-doped nano-iron particles obtained under the above centrifugal conditions are more uniform, and the optimization effect on the dye-organic wastewater anaerobic co-metabolic system is better.

[0018] Further, in step S1, the mass concentration of ethanol is 93-97%.

[0019] Description: The ethanol with the above mass concentration is easy to evaporate and dry on the basis of meeting the effective washing of sulfur-doped nano-iron.

[0020] Further, in step S2, the composition of the dye-organic wastewater is: methyl orange (MO): 200 mg / L, glucose: 2000 mg / L, KH2PO4: 25 mg / L, NH4Cl: 100 mg / L, MgCl2: 20 mg / L, CaCl2: 30 mg / L, EDTA: 5 mg / L, FeSO4·7H2O: 2 mg / L, ZnSO4·7H2O: 1 mg / L, MnCl2·4H2O: 3 mg / L, H3BO4: 30 mg / L, CoCl2·6H2O: 20 mg / L, CuCl2·2H2O: 1 mg / L, NiCl2·6H2O: 2 mg / L, Na2MoO4·2H2O: 3 mg / L.

[0021] Description: The main reason for adding glucose in the dye-organic wastewater treatment is to provide additional carbon source, enhance the biodegradation ability of microorganisms, promote the growth and metabolic activity of microorganisms, and thus improve the efficiency and stability of the entire wastewater treatment system.

[0022] Further, in step S2, the rotation speed of the shaking table is 140-160 rpm, and the temperature is 36-38℃.

[0023] Description: Proper low-speed shaking helps to maintain anaerobic conditions and promote the metabolic activity of anaerobic microorganisms, thereby improving the anaerobic biological treatment effect of the sample after nitrogen stripping.

[0024] Compared with the existing dye-organic wastewater anaerobic co-metabolic system, the beneficial effects of the present application are:

[0025] (1) The application first applies sulfur-doped nano-iron to the dye-organic wastewater anaerobic co-metabolic system, improves the dispersibility of nano-iron through sulfur doping, inhibits the hydrogen evolution reaction through sulfur doping, avoids the reduction damage of the cell membrane caused by the direct contact between nano-iron and microorganisms, and improves the biological adaptability of nano-iron; meanwhile, the formation of FeS endows nano-iron with stronger conductivity, which is conducive to enriching the electron transfer pathway of microorganisms and improving the electron transfer efficiency, not only realizing efficient degradation of dyes, but also effectively overcoming the acid inhibition of the anaerobic digestion process under dye stress, and realizing the rapid start-up of the reactor and methane recovery without sludge acclimation.

[0026] (2) For dye degradation, the formation of the conductive layer FeS is conducive to improving the extracellular electron transfer capacity of microorganisms, and the degradation of dyes is transferred from intracellular to extracellular, which not only avoids the limitation of dye transmembrane transport, but also relieves the toxic effect caused by the entry of pollutants into cells.

[0027] (3) For the anaerobic digestion process, S-nZVI is conducive to enriching functional microorganisms, providing external electrons to reduce CO2 to methane, and establishing a direct interspecies electron transfer mechanism, so that even under adverse conditions (dye stress), VFA can be efficiently converted to methane. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is a comparison chart of the removal of methyl orange (MO) in the application;

[0029] Figure 2 is a comparison chart of the accumulation of VFAs in the anaerobic digestion process in the application;

[0030] Figure 3 is a comparison chart of the removal of COD in the application;

[0031] Figure 4 is a comparison chart of the methane production in the anaerobic digestion process in the application. DETAILED DESCRIPTION

[0032] To further illustrate the methods adopted by the application and the effects achieved, the technical solutions of the application will be described in detail below in combination with experiments.

[0033] Example 1: A method for rapidly starting a dye-organic wastewater anaerobic co-metabolic system based on S-nZVI, comprising the following steps:

[0034] S1, preparing S-nZVI

[0035] In an inert atmosphere with a purity of 99.5%, sodium dithionite and ferrous sulfate heptahydrate with a concentration of 0.13 mol / L were dissolved in 50 L of ultrapure water according to a molar ratio of S:Fe = 0.3:1, and stirred at 200 rpm to obtain a mixed solution, then potassium borohydride with a concentration of 0.45 mol / L was added dropwise to the mixed solution at a rate of 10 mL / min, the dropwise time was 20 min, the reduction reaction was carried out, and the supernatant was removed under the condition of centrifugal speed of 6000 rpm for 8 min, and then washed with ultrapure water and 95% ethanol with mass concentration, and dried in a vacuum drying oven at a temperature of 50℃ for 24h to obtain sulfur-doped nano iron particles, denoted as S-nZVI, named S1-0.3.

[0036] S2, S-nZVI optimizes anaerobic treatment of dye-organic wastewater

[0037] Anaerobic sludge was added to a serum bottle with a capacity of 250 mL and an effective reaction volume of 200 mL, and the concentration of anaerobic sludge was adjusted to 5 gTS / L, then S-nZVI obtained in step S1 was added to the anaerobic sludge at a dosage of 0.5 g / L, and 150 mL of dye-organic wastewater was introduced, and then the pH was adjusted to pH = 7 by 0.1 mol / L HCl solution, and then nitrogen was blown off for 30 min, and then placed in a shaking bed, and the shaking speed was adjusted to 150 rpm, and the temperature was 37℃, and the anaerobic biological treatment was carried out for 12 h.

[0038] In step S2, the composition of the dye-organic wastewater was as follows: methyl orange (MO): 200 mg / L, glucose: 2000 mg / L, KH2PO4: 25 mg / L, NH4Cl: 100 mg / L, MgCl2: 20 mg / L, CaCl2: 30 mg / L, EDTA: 5 mg / L, FeSO4·7H2O: 2 mg / L, ZnSO4·7H2O: 1 mg / L, MnCl2·4H2O: 3 mg / L, H3BO4: 30 mg / L, CoCl2·6H2O: 20 mg / L, CuCl2·2H2O: 1 mg / L, NiCl2·6H2O: 2 mg / L, Na2MoO4·2H2O: 3 mg / L.

[0039] Example 2: Different from example 1, in step S1, sodium dithionite and ferrous sulfate heptahydrate were according to a molar ratio of S:Fe = 0.1:1, named S1-0.1.

[0040] Example 3: Different from example 1, in step S1, sodium dithionite and ferrous sulfate heptahydrate were according to a molar ratio of S:Fe = 0.5:1, named S1-0.5.

[0041] Example 4: Different from Example 1, in step S1, the potassium borohydride with a concentration of 0.4 mol / L was added dropwise into the mixed solution by a peristaltic pump at a dropwise rate of 8 mL / min, and the dropwise time was 18 min. After centrifugal treatment, the supernatant was removed and sequentially washed with ultrapure water and ethanol with a mass concentration of 93%, and then vacuum dried to obtain the sulfur-doped nano iron particles.

[0042] Example 5: Different from Example 1, in step S1, the potassium borohydride with a concentration of 0.5 mol / L was added dropwise into the mixed solution by a peristaltic pump at a dropwise rate of 12 mL / min, and the dropwise time was 22 min. After centrifugal treatment, the supernatant was removed and sequentially washed with ultrapure water and ethanol with a mass concentration of 97%, and then vacuum dried to obtain the sulfur-doped nano iron particles.

[0043] Example 6: Different from Example 1, in step S1, the purity of the inert atmosphere was 99%, the stirring speed was 180 rpm, and the stirring time was 25 min.

[0044] Example 7: Different from Example 1, in step S1, the purity of the inert atmosphere was 99.9%, the stirring speed was 220 rpm, and the stirring time was 40 min.

[0045] Example 8: Different from Example 1, in step S1, the method of vacuum drying was that the washed substance was placed in a vacuum drying box with a temperature of 45 °C for drying for 22 h.

[0046] Example 9: Different from Example 1, in step S1, the method of vacuum drying was that the washed substance was placed in a vacuum drying box with a temperature of 55 °C for drying for 26 h.

[0047] Example 10: Different from Example 1, in step S1, the centrifugal speed was 5900 rpm, and the centrifugal time was 6 min.

[0048] Example 11: Different from Example 1, in step S1, the centrifugal speed was 6100 rpm, and the centrifugal time was 10 min.

[0049] Example 12: Different from Example 1, in step S2, the dosage of S-nZVI was 0.4 g / L, and the concentration of anaerobic digestion sludge was 4 gTS / L.

[0050] Example 13: Different from Example 1, in step S2, the dosage of S-nZVI was 0.6 g / L, and the concentration of anaerobic digestion sludge was 6 gTS / L.

[0051] Example 14: Different from Example 1, in step S2, the rotation speed of the shaking table was 140 rpm, and the temperature was 36 °C.

[0052] Example 15: Different from Example 1, in step S2, the rotation speed of the shaker was 160 rpm, and the temperature was 38℃.

[0053] Experimental Example: The description of this experimental example is based on the description of Example 1, and is intended to illustrate the practical application effect of the present application.

[0054] 1. To explore the influence of the composition of the optimized material and the synthesis method of the optimized material on the rapid start-up of the dye-organic wastewater anaerobic co-metabolic system:

[0055] Blank group: Different from Example 1, no optimized material was added.

[0056] Control group 1: Different from Example 1, 0.5 g / L of sulfur-doped nanoscale iron particles was replaced by nanoscale iron particles, and was named nZVI. The synthesis of nanoscale iron was the same as the one-step method S-nZVI, except that no sodium hydrosulfite was added.

[0057] Control group 2: Different from Example 1, S-nZVI was synthesized by a two-step method. The synthesis method was as follows: under the conditions of 99.99% nitrogen atmosphere and 200 rpm stirring, 0.13 mol / L ferrous sulfate heptahydrate was dissolved in 50 L ultrapure water, 0.45 mol / L potassium borohydride was slowly added at a speed of 10 mL / min by peristaltic pump, the dropping time was 20 min, then sodium hydrosulfite was added and reacted for 30 min, the molar ratio of sodium hydrosulfite to ferrous sulfate heptahydrate was S:Fe=0.3:1, centrifugation was carried out at 6000 rpm for 8 min to remove the supernatant, and then ultrapure water and 95% concentrated ethanol were used for washing, and the sulfur-doped nanoscale iron particles were dried in a vacuum drying oven at 50℃ for 24 h, and were named S2-0.3.

[0058] Control group 3: Different from control group 2, the molar ratio of sodium hydrosulfite to ferrous sulfate heptahydrate was S:Fe=0.1:1, and was named S2-0.1.

[0059] Control group 4: Different from control group 2, the molar ratio of sodium hydrosulfite to ferrous sulfate heptahydrate was S:Fe=0.5:1, and was named S2-0.5.

[0060] Conclusion: The test results are shown in the accompanying drawings. As shown in the accompanying drawings, at the 12th hour after the start of the reaction, the dye removal rate of each group reached more than 80%, among which the dye removal rate of S1-0.3 was higher than that of other groups, reaching 93.82%; Figure 1

[0061] ​For the anaerobic digestion process, during the 184h operation process, the blank group showed obvious acid accumulation and was not recoverable due to the stress of the dye, and also led to significant inhibition of COD degradation and methane production, so that the anaerobic digestion process could not proceed smoothly, while the control groups 1-4 and the materials added in examples 1-3 effectively alleviated the acid inhibition, as shown in Figure 2 As shown in Figure 3 It can be seen that the COD removal rates of the control groups 1-4 and examples 1-3 are all greater than 80%;

[0062] As shown in Figure 4 It can be seen that, except for the blank group, the cumulative methane production of each group gradually increased, while the acid accumulation and non-recoverable of the blank group affected the COD degradation and methane production, indicating that the addition of nano iron material realized the smooth start of the methane production process; and by comparing the control examples 1, 2-4, it can be seen that the sulfur doping further promoted the production of methane, and S1-0.3, S1-0.5 and S2-0.3 obtained from examples 1, 3 and control group 1 were improved by 35.07%, 17.72% and 8.52% respectively compared with the nZVI group. Therefore, in the anaerobic co-metabolic system of dye-organic wastewater, S-nZVI prepared by one-step synthesis and S / Fe of 0.3, i.e. example 1, has absolute advantages in promoting dye degradation, alleviating acid inhibition and improving methane production efficiency.

[0063] 2. Explore the preparation of S-nZVI and the influence of S-nZVI on the COD removal rate and methane production in the anaerobic treatment process of dye-organic wastewater under the operation of 184h

[0064] Table 1 Influence of treatment method of examples 1, 4-15 on COD removal rate and methane production rate

[0065]

[0066] Conclusion: From the comparison of examples 1, 4-15, it can be seen that within the scope of the present application, too low or too high potassium borohydride dropping parameters, inert atmosphere purity, stirring parameters, drying temperature and centrifugation parameters for the anaerobic treatment of dye-organic wastewater under the operation of 184h have little difference in COD removal effect and methane efficiency compared with example 1, therefore, from the economic point of view, example 1 is the optimal scheme.

Claims

1. A method for rapidly starting a dye-organic wastewater anaerobic co-metabolism system based on S-nZVI, characterized in that, Includes the following steps: S1, Preparation of S-nZVI In an inert atmosphere, sodium dithionite and ferrous sulfate heptahydrate (0.1–0.15 mol / L) were dissolved in ultrapure water at a molar ratio of S:Fe = (0.1–0.5):

1. The mixture was stirred to obtain a homogeneous solution. Then, potassium borohydride (0.4–0.5 mol / L) was added dropwise to the solution at a dropping rate of 8–12 mL / min using a peristaltic pump for 18–22 min. After centrifugation, the supernatant was removed, and the solution was washed sequentially with ultrapure water and ethanol. After vacuum drying, sulfur-doped iron nanoparticles, denoted as S-nZVI, were obtained. S2 and S-nZVI optimized anaerobic treatment method for dye-organic wastewater Anaerobic digested sludge was added to a serum bottle to achieve a concentration of 4–6 gTS / L. Then, the S-nZVI obtained in step S1 was added to the anaerobic digested sludge at a dosage of 0.4–0.6 g / L. 120–180 mL of dye-organic wastewater was introduced, and the pH was adjusted to 6.8–7.2 using a pH adjuster. After nitrogen stripping for 25–35 min, the mixture was placed in a shaker for anaerobic biological treatment for 10–14 h. In step S2, the composition of the dye-organic wastewater is as follows: Methyl orange (MO): 200 mg / L, glucose: 2000 mg / L, KH2PO4: 25 mg / L, NH4Cl: 100 mg / L, MgCl2: 20 mg / L, CaCl2: 30 mg / L, EDTA: 5 mg / L, FeSO4·7H2O: 2 mg / L, ZnSO4·7H2O: 1 mg / L, MnCl2·4H2O: 3 mg / L, H3BO4: 30 mg / L, CoCl2·6H2O: 20 mg / L, CuCl2·2H2O: 1 mg / L, NiCl2·6H2O: 2 mg / L, Na2MoO4·2H2O: 3 mg / L.

2. The method for rapidly starting a dye-organic wastewater anaerobic co-metabolism system based on S-nZVI as described in claim 1, characterized in that, In step S1, the purity of the inert atmosphere is 99-99.9%, the stirring speed is 180-220 rpm, and the stirring time is 25-40 min.

3. The method for rapidly starting a dye-organic wastewater anaerobic co-metabolism system based on S-nZVI as described in claim 1, characterized in that, The vacuum drying method is as follows: the washed material is placed in a vacuum drying oven at a temperature of 45-55℃ and dried for 22-26 hours.

4. The method for rapidly starting a dye-organic wastewater anaerobic co-metabolism system based on S-nZVI as described in claim 1, characterized in that, In step S1, the centrifugation rate is 5900-6100 rpm and the centrifugation time is 6-10 min.

5. The method for rapidly starting a dye-organic wastewater anaerobic co-metabolism system based on S-nZVI as described in claim 1, characterized in that, In step S1, the mass concentration of the ethanol is 93-97%.

6. The method for rapidly starting a dye-organic wastewater anaerobic co-metabolism system based on S-nZVI as described in claim 1, characterized in that, In step S2, the shaking table rotates at a speed of 140–160 rpm and is heated at a temperature of 36–38°C.

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