Method for promoting simultaneous denitrification and nitrogen removal by biodegradation of n,n-dimethylformamide

Abstract

This invention discloses a method for promoting the biodegradation of N,N-dimethylformamide and simultaneous denitrification. The method constructs a zero-valent iron (ZFE)-coupled biological treatment system, which not only accelerates electron transfer efficiency but also significantly increases the activity of DMF-degrading enzymes and nitrate reductases, synergistically promoting electron transfer and microbial metabolic activity, thereby enhancing the removal of DMF and nitrate nitrogen. Compared to biological treatment systems that only add activated sludge without adding ZFE, adding ZFE significantly improves the removal efficiency of DMF and nitrate nitrogen, making it suitable for the treatment of large-scale polluted water bodies or industrial wastewater.

Description

Technical Field

[0001] This invention belongs to the field of biological treatment technology for organic pollutants, and relates to a method for promoting the biodegradation of N,N-dimethylformamide and simultaneous denitrification. Background Technology

[0002] N,N-Dimethylformamide (DMF) is a synthetically produced polar organic solvent with good water miscibility and the ability to dissolve various organic compounds. It is widely used in the chemical, pharmaceutical, and textile industries. DMF is structurally stable, but due to its thermal stability and low biodegradability, it is difficult to degrade naturally and readily accumulates and metastasizes in the environment, exhibiting biotoxicity, embryotoxicity, hepatotoxicity, teratogenicity, and carcinogenicity. Therefore, developing efficient and economical wastewater treatment technologies for DMF-containing industrial wastewater has become a crucial issue in environmental governance.

[0003] Currently, methods for removing DMF from wastewater mainly include advanced oxidation, physical adsorption, photocatalysis, and membrane separation. Among these, physicochemical methods such as advanced oxidation are costly and cause serious secondary pollution. Biological treatment technology is characterized by low cost and environmental friendliness. However, because wastewater containing DMF has poor biodegradability, its degradation rate is slow or difficult to achieve in traditional biological treatment systems, resulting in unsatisfactory conventional biological treatment processes. Zero-valent iron (ZVI) has advantages such as strong reducing power, large specific surface area, and environmental friendliness, and is widely used for the removal of organic pollutants in wastewater treatment. The coupling of ZVI with biotechnology allows ZVI to enhance pollutant degradation by lowering the redox potential of the reaction system, promoting the activity of functional enzymes, and facilitating direct / indirect electron transfer pathways between ZVI and microorganisms (Jia, YY, Wang, PD, Ou, YY, Y, et al., Insights into the microbial response mechanisms to ciprofloxacin during sulfur-mediated biological wastewater treatment using a metagenomics approach. Water Res. 2022, 223, 118995). It has been reported that under anaerobic or hypoxic conditions, ZVI acts as an electron donor in the reductive degradation of halogenated organic compounds such as polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and chlorinated hydrocarbons, and has been widely used in groundwater and soil remediation. However, research on ZVI-enhanced DMF biodegradation is currently lacking. Considering that industrial wastewater typically contains high concentrations of nitrates, achieving ZVI-enhanced biological denitrification simultaneously with DMF biodegradation would be significant for the low-cost and harmless treatment of industrial wastewater containing DMF and nitrate nitrogen. Summary of the Invention

[0004] The purpose of this invention is to provide a method for promoting the biodegradation of N,N-dimethylformamide and simultaneous denitrification. This method utilizes zero-valent iron to accelerate electron transfer efficiency, and ferrous and ferric ions can enhance the activity of functional enzymes, synergistically promoting electron transfer and microbial metabolic activity, thereby accelerating the decomposition and metabolism of pollutant DMF and the reduction of nitrate nitrogen.

[0005] The technical solution for achieving the objective of this invention is as follows:

[0006] The specific method for promoting simultaneous denitrification and nitrogen removal through the biodegradation of N,N-dimethylformamide is as follows:

[0007] In an anoxic reactor, acclimatized sludge for treating DMF wastewater is inoculated, zero-valent iron is added, and wastewater containing DMF and nitrate nitrogen is introduced for biodegradation. The amount of zero-valent iron added is 10-15 g / L.

[0008] Furthermore, the pH of the wastewater containing DMF and nitrate nitrogen is 6 to 8, preferably 6.0 to 6.5.

[0009] Furthermore, in the wastewater containing DMF and nitrate nitrogen, the concentration of nitrate nitrogen is 5 mM to 15 mM, preferably 12 to 15 mM, and the concentration of DMF is 4.1 to 27.4 mM, preferably 4.1 to 8.2 mM.

[0010] Furthermore, the acclimation method for acclimated sludge used to treat DMF wastewater includes the following steps: A sample is taken from a reaction tank that has been used for treating DMF wastewater for a long time, and added to simulated wastewater containing DMF and sodium nitrate. The concentrations of DMF and sodium nitrate in the simulated wastewater are gradually increased to acclimate and cultivate the sludge. The simulated wastewater containing DMF and sodium nitrate has a composition of 1.53 g / L. -1 NaHPO4·12H2O, 0.38g L -1 KH2PO4, 0.1g L -1 MgSO4·7H2O, 0.05 g L -1 CaCl2, 10 mL -1 Trace element solution SL-4, 5mM~12mM sodium nitrate, 4.1~8.2mM DMF; wherein the composition of trace element solution SL-4 is: 0.5g L -1 EDTA, 0.2g / L -1 FeSO4·7H2O, 100mL -1 Trace element SL-6, wherein the composition of trace element SL-6 is: 0.01 g L -1 ZnSO4·7H2O, 0.03g L -1 MnCl2·4H2O, 0.3g L -1 H3BO4, 0.2g L -1 CoCl2·6H2O, 0.01g L -1 CuCl2·2H2O, 0.02g L -1 NiCl2·6H2O, 0.03g L -1 Na2MoO4·2H2O.

[0011] Furthermore, the nitrate nitrogen is selected from nitrate nitrogen in nitrate chemical raw materials such as sodium nitrate, ammonium nitrate, and calcium nitrate.

[0012] Furthermore, the inoculation concentration (MLSS) of the acclimated sludge is 2.0–5.0 g / L, preferably 4.0 g / L.

[0013] Furthermore, the particle size of zero-valent iron is 100–150 μm.

[0014] Furthermore, the temperature of the biodegradation system is 28–32°C.

[0015] The basic principle of this invention for promoting DMF degradation using zero-valent iron is as follows: ZVI and the dissolved ferrous and ferric ions can promote the enrichment of DMF-degrading microorganisms, denitrifying microorganisms, and electron transport microorganisms, and promote the activity of functional enzymes that regulate microbial metabolism, such as DMF hydrolase, nitrate reductase (NAR), and electron transport system (ETS), thereby accelerating the hydrolysis of DMF to generate dimethylamine. Subsequently, under the action of dimethylamine dehydrogenase and formic acid dehydrogenase, it is converted into formic acid, and finally mineralized into carbon dioxide and water.

[0016] Compared with the prior art, the advantages of this invention are as follows:

[0017] Compared to biological treatment systems without the addition of zero-valent iron (ZVFe), this invention utilizes the strong reducing properties of ZVFe and its ability to enhance microbial metabolic activity. By employing a ZVFe-coupled biological treatment system, the removal efficiency of DMF and nitrate nitrogen in wastewater can be significantly improved. The time required for complete DMF degradation is reduced from 36 hours to 24 hours, and the nitrate nitrogen removal rate is increased from 70.46% to 85.93%. Compared to other traditional biological treatment technologies, this invention is simple, easy to implement, and low in cost, making it suitable for treating large quantities of polluted water. Attached Figure Description

[0018] Figure 1 This is a diagram of the DMF degradation pathway in a zero-valent iron coupled biological treatment system.

[0019] Figure 2 This is a diagram showing the degradation effect of DMF in the zero-valent iron coupled biological treatment system in Example 1.

[0020] Figure 3 This is a diagram showing the removal effect of nitrate nitrogen in the zero-valent iron coupled biological treatment system in Example 1.

[0021] Figure 4 This is a diagram showing the degradation effect of DMF in the zero-valent iron coupled biological treatment system in Example 2.

[0022] Figure 5 This is a diagram showing the removal effect of nitrate nitrogen in the zero-valent iron coupled biological treatment system in Example 2.

[0023] Figure 6 This is a diagram showing the degradation effect of DMF in the zero-valent iron coupled biological treatment system in Example 3.

[0024] Figure 7 This is a diagram showing the degradation effect of DMF in the zero-valent iron coupled biological treatment system in Example 4.

[0025] Figure 8 This is a diagram showing the DMF removal effect in the cyclic experiment of the zero-valent iron coupled biological treatment system in Example 5.

[0026] Figure 9 The relative activities of DMFase, NAR, and ETS in the zero-valent iron-coupled biological treatment system and the biological control system in Example 5 are shown. Detailed Implementation

[0027] The acclimation method for treating DMF wastewater in this invention specifically includes the following steps:

[0028] (1) Take 200 mL of sludge from the reaction tank that has been used to treat DMF wastewater for a long time, and add it to 3000 mL of simulated wastewater containing DMF and sodium nitrate. Gradually increase the concentration of DMF in the simulated wastewater from 4.1 mM to 8.2 mM and the concentration of sodium nitrate from 5 mM to 12 mM to acclimate and cultivate the sludge.

[0029] The simulated wastewater composition is: 1.53g L -1 NaHPO4·12H2O, 0.38g L -1 KH2PO4, 0.1g L -1 MgSO4·7H2O, 0.05 g L -1 CaCl2, 10 mL -1 Add trace element solution SL-4, sodium nitrate and DMF as needed for the experiment.

[0030] Composition of trace element SL-4: 0.5g L -1 EDTA, 0.2g / L -1 FeSO4·7H2O, 100mL -1 Trace element SL-6.

[0031] Composition of trace element SL-6: 0.01g L -1 ZnSO4·7H2O, 0.03g L -1 MnCl2·4H2O, 0.3g L -1 H3BO4, 0.2g L -1 CoCl2·6H2O, 0.01g L -1 CuCl2·2H2O, 0.02g L -1 NiCl2·6H2O, 0.03g L -1Na2MoO4·2H2O.

[0032] This invention uses 250 mL serum bottles as sequencing batch reactors and acclimatized sludge, which has been used in the laboratory for long-term treatment of DMF wastewater, as inoculum. The sludge concentration (MLSS) is 4.0 g / L, and the ZVI particle size is selected as 150 μm. DMF is used as the carbon source and sodium nitrate is used as the nitrogen source to construct a zero-valent iron coupled biological treatment system. A biological treatment system without ZVI is set up as a control. The serum bottles are sealed with rubber stoppers, and the sequencing batch reactor is cultured in a constant temperature shaker (32℃, 180 r / min).

[0033] The present invention will now be further described with reference to specific embodiments and accompanying drawings.

[0034] Example 1

[0035] Application of zero-valent iron coupled biological treatment system in the treatment of wastewater containing DMF and nitrate nitrogen under different zero-valent iron dosage conditions.

[0036] 250 mL of simulated wastewater containing an initial DMF concentration of 8.2 mM and an initial nitrate nitrogen concentration of 12.0 mM was prepared. Initial ZVI dosages of 0.5 g / L, 1.0 g / L, 3.0 g / L, 5.0 g / L, 10.0 g / L, and 15.0 g / L were added to 250 mL serum bottles. High-purity helium gas was continuously purged to remove dissolved oxygen from the serum bottles and wastewater, thus constructing a zero-valent iron-coupled biological treatment system. The initial influent pH was set to 7.2, and the MLSS concentration of the activated sludge inoculated was 4.0 g / L. Changes in the concentrations of DMF and nitrate nitrogen in the wastewater were monitored. A biological treatment system without ZVI was set up as a control. Serum bottles were sealed with rubber stoppers, and the sequencing batch reactor was incubated in a constant-temperature shaker (32℃, 180 r / min).

[0037] Experimental results are as follows Figure 2 and 3 As shown, when the ZVI dosage is 0.5 g / L, the DMF concentration in the effluent after 36 hours is 0.269 ± 0.126 mM. The DMF degradation efficiency is poor at ZVI dosages of 3.0 g / L and 5.0 g / L. The best DMF removal effect is achieved when the ZVI dosage increases to 10.0 g / L, with complete degradation within 24 hours and a nitrate nitrogen removal rate of 83.40 ± 2.04%. While the nitrate nitrogen removal capacity increases when the ZVI dosage is 15.0 g / L, the DMF removal rate decreases. This example illustrates that in a zero-valent iron coupled biological treatment system, the optimal zero-valent iron dosage is 10.0 g / L; increasing or decreasing the zero-valent iron dosage significantly reduces the removal capacity of DMF or nitrate nitrogen.

[0038] Example 2

[0039] Application of zero-valent iron coupled biological treatment system in the treatment of wastewater containing DMF and nitrate nitrogen under different influent pH conditions.

[0040] 250 mL of simulated wastewater containing an initial DMF concentration of 8.2 mM, an initial nitrate nitrogen concentration of 12.0 mM, and initial pH values ​​of 6.0, 6.5, 7.0, 7.5, and 8.0 was prepared. ZVI was added at a dosage of 10.0 g / L to a 250 mL serum bottle. High-purity helium gas was continuously purged to remove dissolved oxygen from the serum bottle and wastewater. Activated sludge was inoculated with MLSS at a concentration of 4.0 g / L, and the concentration changes of DMF and nitrate nitrogen in the wastewater were monitored. A biological treatment system without ZVI was set up as a control. The serum bottles were sealed with rubber stoppers, and the sequencing batch reactor was incubated in a constant-temperature shaker (32℃, 180 r / min).

[0041] Experimental results are as follows Figure 4 and 5 As shown, when the influent pH is 6.0 and 6.5, DMF is completely degraded within 20 hours, and the nitrate nitrogen removal rate is above 90%. When the influent pH is above 6.5, the effluent DMF concentration gradually increases. When the influent pH increases to 8.0, the DMF removal rate is below 80%, and the nitrate nitrogen removal rate decreases to about 65%. This may be because alkaline conditions inhibit the activity of denitrifying microorganisms. This example illustrates that in a zero-valent iron coupled biological treatment system, the suitable pH range is slightly acidic; an alkaline environment significantly reduces the removal capacity of DMF and nitrate nitrogen.

[0042] Example 3

[0043] Application of zero-valent iron coupled biological treatment system in the treatment of wastewater containing DMF and nitrate nitrogen under different influent nitrate nitrogen concentrations.

[0044] 250 mL of simulated wastewater with an initial DMF concentration of 8.2 mM, initial nitrate nitrogen concentrations of 5.0 mM, 8.0 mM, 10.0 mM, 12.0 mM, and 15.0 mM, and an initial pH of 6.5 was prepared. ZVI was added at a dosage of 10.0 g / L to a 250 mL serum bottle. High-purity helium gas was continuously purged to remove dissolved oxygen from the serum bottle and wastewater. Activated sludge was inoculated with MLSS at a concentration of 4.0 g / L, and the concentration changes of DMF and nitrate nitrogen in the wastewater were monitored. A biological treatment system without ZVI was set up as a control. The serum bottles were sealed with rubber stoppers, and the sequencing batch reactor was incubated in a constant-temperature shaker (32℃, 180 r / min).

[0045] Experimental results are as follows Figure 6As shown, DMF can be completely degraded within 20 hours when the influent nitrate nitrogen concentration is 12 mM and 15 mM. Since an influent nitrate nitrogen concentration of 15 mM may lead to an excess of nitrate nitrogen, and a nitrate nitrogen concentration below 12 mM will result in insufficient electron acceptors, which is detrimental to DMF degradation, the optimal influent nitrate nitrogen concentration is 12 mM.

[0046] Example 4

[0047] Application of zero-valent iron coupled biological treatment system in the treatment of wastewater containing DMF and nitrate nitrogen under different influent DMF concentration conditions.

[0048] 250 mL of simulated wastewater containing initial DMF concentrations of 4.1 mM, 8.2 mM, 13.7 mM, 20.5 mM, and 27.4 mM, initial nitrate nitrogen concentration of 12.0 mM, and initial pH of 6.5 was prepared. ZVI was added at a dosage of 10.0 g / L to 250 mL serum bottles. High-purity helium gas was continuously purged to remove dissolved oxygen from the serum bottles and wastewater. Activated sludge was inoculated with MLSS at a concentration of 4.0 g / L, and the concentration changes of DMF and nitrate nitrogen in the wastewater were monitored. A biological treatment system without ZVI was set up as a control. Serum bottles were sealed with rubber stoppers, and the sequencing batch reactor was incubated in a constant-temperature shaker (32℃, 180 r / min).

[0049] Experimental results are as follows Figure 7 As shown, DMF can be completely degraded within 24 hours when the influent nitrate nitrogen concentration is 4.1 mM and 8.2 mM. As the influent DMF concentration increases, the degradation efficiency of DMF gradually decreases, which may be because high concentrations of DMF have a certain inhibitory effect on the activity of microorganisms. Therefore, the optimal initial DMF concentration should be 8.2 mM.

[0050] Example 5

[0051] Long-term cyclical application of zero-valent iron coupled biological treatment system in the treatment of wastewater containing DMF and nitrate nitrogen.

[0052] A simulated wastewater containing 8.2 mM DMF, 12.0 mM nitrate nitrogen, and 6.5 at an initial pH was prepared in 250 mL of serum. A ZVI dosage of 10.0 g / L was added to the 250 mL serum bottle. High-purity helium gas was continuously purged to remove dissolved oxygen from the serum bottle and the wastewater. A zero-valent iron coupled biological treatment system was constructed. Activated sludge with an MLSS concentration of 4.0 g / L was inoculated. A biological treatment system without ZVI was set up as a control. The system was cultured on a shaker at 32℃ and 180 r / min, and the concentration changes of DMF and nitrate nitrogen in the wastewater were monitored.

[0053] like Figure 8As shown, DMF in the ZVI-coupled biological treatment system was completely degraded within 24 hours, while in the biological control system, it took 36 hours for DMF to be completely degraded. Even after 96 hours of cyclic experiments, DMF in the ZVI-coupled biological treatment system was still able to be completely degraded within 24 hours. Figure 9 As shown, sludge samples were collected from both systems to determine the activities of DMFase and NAR. The results showed that compared with the biological control system, the relative activities of DMFase (120%) and nitrate reductase (140%) were significantly increased in the ZVI-coupled biological treatment system, and the ETS activity was increased by more than 50%. This example illustrates that in the ZVI-coupled biological treatment system, ZVI can act as a medium for interspecies electron transfer among microorganisms, accelerating electron transfer efficiency, promoting microbial metabolic activity and DMF biodegradation. Secondly, ferrous and ferric ions can enhance the interaction of functional enzymes, synergistically promoting electron transfer and microbial metabolism, ultimately accelerating the removal of nitrate nitrogen and DMF.

Claims

1. A method for promoting the biodegradation of N,N-dimethylformamide and simultaneous denitrification, characterized in that, Specifically as follows: In an anoxic reactor, acclimated sludge used for treating DMF wastewater was inoculated, zero-valent iron was added, and wastewater containing DMF and nitrate nitrogen was introduced for biodegradation. The amount of zero-valent iron added was 10-15 g / L. The acclimation method for the acclimated sludge used for treating DMF wastewater involved the following steps: samples were taken from a reaction tank that had been used for treating DMF wastewater for a long time, and added to simulated wastewater containing DMF and sodium nitrate. The concentrations of DMF and sodium nitrate in the simulated wastewater were gradually increased to acclimate the sludge. The simulated wastewater containing DMF and sodium nitrate had a composition of 1.53 g / L. -1 NaHPO4·12H2O, 0.38 g L -1 KH2PO4, 0.1 g L -1 MgSO4·7H2O, 0.05 g L -1 CaCl2, 10 mL L -1 Trace element solution SL-4, 5 mM ~12 mM sodium nitrate, 4.1~8.2 mM DMF; wherein the composition of trace element solution SL-4 is: 0.5 g L -1 EDTA, 0.2 g / L -1 FeSO4·7H2O, 100 mL L -1 Trace element SL-6, wherein the composition of trace element SL-6 is: 0.01 g L -1 ZnSO4·7H2O, 0.03 g L -1 MnCl2·4H2O, 0.3 g L -1 H3BO4, 0.2 g L -1 CoCl2·6H2O, 0.01 g L -1 CuCl2·2H2O, 0.02 g L -1 NiCl2·6H2O, 0.03 g L -1 Na2MoO4·2H2O.

2. The method according to claim 1, characterized in that, The pH of the wastewater containing DMF and nitrate nitrogen is 6-8.

3. The method according to claim 1, characterized in that, The pH of the wastewater containing DMF and nitrate nitrogen is 6.0~6.

5.

4. The method according to claim 1, characterized in that, The wastewater containing DMF and nitrate nitrogen has a nitrate nitrogen concentration of 5 mM to 15 mM and a DMF concentration of 4.1 to 27.4 mM.

5. The method according to claim 1, characterized in that, The wastewater containing DMF and nitrate nitrogen has a nitrate nitrogen concentration of 12-15 mM and a DMF concentration of 4.1-8.2 mM.

6. The method according to claim 1, characterized in that, The nitrate nitrogen is selected from sodium nitrate, ammonium nitrate, or calcium nitrate.

7. The method according to claim 1, characterized in that, The inoculation concentration (MLSS) of the acclimated sludge was 2.0–5.0 g / L.

8. The method according to claim 1, characterized in that, The inoculation concentration (MLSS) for acclimation sludge was 4.0 g / L.

9. The method according to claim 1, characterized in that, The particle size of zero-valent iron is 100~150 μm, and the temperature of the biodegradation system is 28~32 ℃.

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