Method for reinforcing denitrification of sulfur circulation microbial system by using siderophore

Abstract

The invention discloses a method for reinforcing denitrification of a sulfur circulation microbial system by using an iron carrier, and belongs to the technical field of nitrogen-containing wastewater treatment. The method comprises the following steps: inoculating sulfate reducing bacteria and thiobacillus denitrificans into a culture medium containing iron ions or ferrous ions for domestication; and applying the domesticated complex microbial inoculant to wastewater denitrification. In a sulfur circulating microorganism system, Fe < 2 + > can promote the activity of a biological denitrification key enzyme in a biological system by forming an iron carrier in a form of FeS, S < 2-> is fixed in the system and prevented from escaping, and when electron donors in the system are insufficient, the Fe < 2 + > can be used as a substitute electron donor for biological denitrification, so that the requirement on an external carbon source is reduced, and the energy consumption is reduced. And meanwhile, the impact load resistance of the system can be enhanced. Through sulfate reduction and sulfur autotrophic denitrification and iron coupling, sulfate in wastewater is converted into electron donors, a carbon-nitrogen-sulfur-iron biological co-reaction system is formed, the defects of a single-strain denitrification system are overcome, the denitrification effect is enhanced, and energy consumption and cost are reduced.

Description

Technical Field

[0001] The invention relates to the technical field of nitrogen-containing wastewater treatment, and in particular to a method for denitrification by using an iron carrier to strengthen a sulfur cycle microbial system. Background Art

[0002] Domestic sewage, industrial wastewater and other wastewaters contain a large amount of nitrogen. If they are directly discharged into the water body, it is easy to cause eutrophication of the water body. The pollutant discharge standard of urban sewage treatment plants requires TN≤15 mg / L (level A). Therefore, denitrification has always been the focus of sewage treatment. Among them, the removal of nitrate nitrogen in sewage is a big problem. For the removal of nitrate nitrogen, the most economical and efficient method is biological denitrification. The related process of heterotrophic biological denitrification is the most mature and widely used at home and abroad. Although heterotrophic denitrification has a good denitrification effect, the carbon source addition amount is large, the sludge output is large, and the operating cost is high. Especially for some low C / N wastewaters such as urban domestic sewage and industrial wastewater tail water, the denitrification effect is not ideal.

[0003] Compared with heterotrophic denitrification, biological autotrophic denitrification has the application advantage of low sludge production, which can reduce the operating costs caused by subsequent sludge disposal. Common autotrophic denitrification electron donors include hydrogen, iron and sulfur. Autotrophic denitrification can greatly reduce the cost of carbon source addition. Sulfur autotrophic denitrification (SAD) is the current mainstream autotrophic denitrification process. It refers to the biological process in which sulfur-oxidizing bacteria reduce nitrates by oxidizing reduced sulfur under anoxic or anaerobic conditions, using sulfur as an electron donor, so it has significant carbon reduction benefits. At the same time, SAD also has certain disadvantages, such as: S 2- Easy to lose in the system, etc. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention aims to provide a method for enhancing the denitrification efficiency of a sulfur cycle microbial system by using iron carriers. 2+ By forming an iron carrier in the form of FeS, sulfide can be effectively fixed in the system to prevent it from escaping. When the electron donor in the system is insufficient, it can serve as an alternative electron donor for biological denitrification to reduce the demand for external carbon sources. Sodium sulfate, as a sulfur source for sulfur autotrophic denitrification, converts sulfate pollutants in wastewater into electron donors through the combination of sulfate reduction and sulfur autotrophic denitrification, forming a carbon-nitrogen-sulfur biological co-reaction system, overcoming the defects of a single bacterial species denitrification system. Iron carriers in the form of FeS can also promote the activity of key enzymes in biological denitrification in the biological system, enhance the system's ability to resist shock loads, and thus enhance denitrification stability. The use of iron carriers to strengthen the sulfur cycle microbial system for denitrification of low-carbon wastewater can not only achieve low-carbon denitrification, but also reduce NO3 - The removal rate of -N is over 95%.

[0005] In order to achieve the above-mentioned purpose, the present invention provides a method for strengthening the denitrification of sulfur cycle microbial system by using iron carriers, wherein sulfate-reducing bacteria and denitrifying Thiobacillus are inoculated together into a culture medium containing iron ions or ferrous ions for domestication; and the domesticated composite bacterial agent is used for wastewater denitrification.

[0006] The iron ion is selected from at least one of ferric sulfate, ferric nitrate and ferric chloride; the ferrous ion is selected from at least one of ferrous sulfate, ferrous chloride, ferrous sulfate and ferrous nitrate.

[0007] The culture medium containing ferrous ions is formulated as follows: 0.4-2 g / L C6H 12 O6, 0.4~4 g / L KNO3, 0.1~0.5 g / L Na2SO4, 0.04~0.1 g / L KH2PO4, 0.1~0.3 g / L FeSO4; the culture medium formula containing iron ions is obtained by replacing 0.1~0.3 g / L FeSO4 in the culture medium formula containing ferrous ions with 0.1~0.4 g / L Fe2(SO4)3.

[0008] The acclimation conditions are 15-40°C, 80-200 rpm, anaerobic darkness, and an acclimation time of 3-5 days; the pH in the culture medium is 6-9, and the pH is adjusted using a phosphoric acid solution and a sodium hydroxide solution. Preferably, a 1 mol / L phosphoric acid solution and a 1 mol / L sodium hydroxide solution are used.

[0009] Further,

[0010] The inoculation volume ratio of sulfate-reducing bacteria and denitrifying Thiobacillus during acclimation was 1-5; the concentration range of sulfate-reducing bacteria and denitrifying Thiobacillus in the inoculum after acclimation was 10 4 ~10 5 cfu / mL.

[0011] The domesticated composite bacterial agent is inoculated into nitrogen-containing wastewater, with the volume ratio of wastewater to composite bacterial agent being 0.5~5. Carbon source is added to a COD / N ratio of 3~5. Under anaerobic dark conditions, the culture is carried out at 15~40℃, 80~200 rpm, and pH 6~9 to remove nitrate nitrogen from the wastewater.

[0012] The denitrification time is 6~24 h.

[0013] NO3 in nitrogen-containing wastewater - -N concentration is controlled at 50~1000 mg / L.

[0014] The carbon source is selected from at least one of glucose, sucrose and xylose.

[0015] Sulfate reduction: Under anaerobic conditions, sulfate-reducing bacteria in the inoculant use the electrons provided by the organic carbon source to reduce sulfate to H2S and HS - and S 2- Sulfides such as sulfide provide electron donors for sulfur autotrophic denitrification.

[0016] Sulfur autotrophic denitrification: Under anaerobic conditions, the denitrifying Thiobacillus in the bacterial agent uses the sulfide generated by sulfate reduction as an electron donor to provide electrons to the nitrate nitrogen in the water sample, and the nitrate nitrogen is converted into nitrogen gas, and the sulfide is converted back into sulfate. Using sulfide as an electron donor solves the problem of poor mass transfer efficiency in traditional sulfur autotrophic denitrification.

[0017] Iron carrier strengthening: Fe 2+ By forming an iron carrier in the form of FeS, S 2- It is fixed in the system to prevent it from escaping, and when the electron donor in the system is insufficient, it can serve as an alternative electron donor for biological denitrification, reducing the demand for external carbon sources and enhancing the system's ability to resist shock loads. Iron carriers in the form of FeS can also promote the activity of key enzymes of biological denitrification in biological systems.

[0018] Compared with the prior art, the present invention provides a method for enhancing the denitrification efficiency of sulfur cycle microbial system by using iron carriers, which has the following effects:

[0019] (1) The present invention makes full use of the water quality characteristics of common low-carbon nitrogen-containing wastewater. This type of wastewater contains pollutants such as sulfate. The iron carrier-enhanced sulfur cycle biological denitrification agent uses sulfate-reducing bacteria to reduce sulfate to H2S and HS - and S 2- Sulfides such as ferrous iron can provide electron donors for sulfur autotrophic denitrification. Denitrifying Thiobacillus can use sulfides in water to achieve autotrophic denitrification and remove nitrates from water, while ferrous iron can react with S 2- Form FeS precipitates, effectively converting S 2- It is fixed in the system to prevent it from escaping. When trivalent iron is added to the system, it can also be converted into divalent iron. When the electron donor is insufficient in the system, it can be used as an alternative electron donor for biological denitrification. Iron carriers in the form of FeS can also promote the activity of key enzymes of biological denitrification in the biological system. At the same time, it can also enhance the flocculation effect of microorganisms and the system's ability to resist shock loads, thereby enhancing the system's denitrification stability.

[0020] (2) The iron carrier enhanced sulfur cycle microbial system has high-efficiency low-carbon denitrification performance and is suitable for the denitrification treatment of low-carbon wastewater. Under the conditions of 15~40℃ and COD / N of 3~5, the nitrate nitrogen removal rate can reach more than 95%, which has good application prospects for removing nitrate nitrogen from low-carbon wastewater. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The diagram is a denitrification mechanism diagram of the iron carrier enhanced sulfur cycle microbial denitrification agent of the present invention;

[0022] Figure 2 This is a diagram showing the denitrification effect of the iron carrier enhanced sulfur cycle microbial denitrification agent under different carbon-nitrogen ratio conditions in Example 2;

[0023] Figure 3 This is a diagram showing the denitrification effect of the sulfur cycle microbial denitrification agent under different carbon-nitrogen ratios in Example 2;

[0024] Figure 4 A comparison of the NAR / NIR enzyme activity of the iron carrier-enhanced sulfur cycle microbial denitrification agent and the sulfur cycle microbial denitrification agent in Example 5;

[0025] Figure 5 This is a scanning electron micrograph of the iron carrier enhanced sulfur cycle microbial denitrification agent in Example 6;

[0026] Figure 6 A scanning electron micrograph of the sulfur cycle microbial denitrification agent in Example 6;

[0027] Figure 7 This is a comparison chart of X-ray diffraction analysis (XRD) of the iron carrier enhanced sulfur cycle microbial denitrification agent and the sulfur cycle microbial denitrification agent in Example 7. DETAILED DESCRIPTION

[0028] Example 1: Domestication of iron carrier-enhanced sulfur cycle composite bacterial agent

[0029] The sulfate-reducing bacteria and denitrifying Thiobacillus in this example were purchased from the "China Microbial Strain Query Network" platform. The platform number of the sulfate-reducing bacteria is bio-00232, and the platform number of the denitrifying Thiobacillus is bio-72703.

[0030] The iron carrier enhanced sulfur cycle composite bacterial agent of the present invention is domesticated by inoculating sulfate-reducing bacteria and denitrifying Thiobacillus in a culture medium at a volume of 1:1 to obtain an iron carrier enhanced sulfur cycle composite bacterial agent, wherein the culture medium contains 1 g / L C6H 12 O6, 1g / L KNO3, 0.1 g / L Na2SO4, 0.06 g / L KH2PO4, 0.1 g / L FeSO4;

[0031] The acclimation conditions were 30°C, 130 rpm, anaerobic darkness, and acclimation time of 7 days. The pH of the culture medium was 7, and the pH was adjusted by 1 mol / L phosphoric acid solution and 1 mol / L sodium hydroxide solution. The concentration range of sulfate-reducing bacteria and denitrifying Thiobacillus in the inoculum after acclimation was 10 4~10 5 cfu / mL.

[0032] At the same time, a sulfur cycle composite bacterial agent was prepared as a control. The difference between the preparation of this bacterial agent and the preparation of the iron carrier enhanced sulfur cycle composite bacterial agent is that FeSO4 is not added to the culture medium, and the other culture and acclimatization steps are the same.

[0033] Example 2: Improvement of denitrification capacity of iron carrier enhanced sulfur cycle composite bacterial agent compared with sulfur cycle composite bacterial agent under different carbon-nitrogen ratio conditions

[0034] The iron carrier enhanced sulfur cycle composite bacterial agent and the sulfur cycle composite bacterial agent prepared in Example 1 were added to the simulated nitrogen-containing wastewater, respectively, and the volume ratio of wastewater to composite bacterial agent was 3:1, and NO3 - -N concentration was 60±3 mg / L, and the carbon source added to the simulated nitrogen-containing wastewater was C6H 12 O6, the sulfur source is Na2SO4, the nitrogen source is KNO3 (i.e. nitrate nitrogen), and the carbon source and nitrogen source are added until the COD / N is 2.6, 3.2, 3.9, 4.4, and 5, respectively. The reaction is carried out under anaerobic darkness, 30 ℃, 120 rpm, and pH 7. The removal capacity of the iron carrier enhanced sulfur cycle composite bacterial agent and the sulfur cycle composite bacterial agent on nitrate after 6 hours of reaction is determined. The results are as follows Figure 2 and Figure 3 As shown in the data, the iron carrier enhanced sulfur cycle composite bacteria agent can achieve a nitrate removal rate of more than 90% when the COD / N is above 2, and a nitrate removal rate of more than 95% when the COD / N is between 3-5, while the sulfur cycle composite bacteria agent can only achieve a nitrate removal rate of more than 90% when the COD / N is 5. This indicates that the iron carrier enhanced sulfur cycle composite bacteria agent has higher denitrification efficiency under low carbon-nitrogen ratio conditions than the sulfur cycle composite bacteria agent, can reduce the use of carbon source, and has better economic benefits.

[0035] Example 3: Improvement of denitrification capacity of the iron carrier-enhanced sulfur cycle composite bacterial agent acclimated with ferrous iron compared with the sulfur cycle composite bacterial agent with ferrous iron added

[0036] The difference between Example 3 and Example 2 is that the COD / N is 5, the inlet nitrate nitrogen concentration is 200±5 mg / L, and 1 mM ferrous ions are added to the sulfur cycle composite bacteria wastewater. It can be seen from Table 1 that compared with the sulfur cycle composite bacteria with added ferrous ions, the iron carrier enhanced sulfur cycle composite bacteria after long-term ferrous acclimation has a higher nitrate nitrogen degradation efficiency, reducing the nitrate concentration from 199.31 mg / L to 0 mg / L within 24 hours, and the degradation efficiency reaches 100%. The nitrate removal rate of the sulfur cycle composite bacteria in 24 hours is 85.76%, indicating that the iron carrier enhanced sulfur cycle composite bacteria has a better denitrification effect after long-term acclimation.

[0037]

[0038] Example 4: Improvement of denitrification capacity of iron carrier enhanced sulfur cycle composite bacterial agent compared with sulfur cycle composite bacterial agent under high concentration nitrate wastewater load

[0039] The difference between Example 4 and Example 2 is that the COD / N is 5, and the influent nitrate nitrogen concentration is 180-220 mg / L. It can be seen from Tables 2 and 3 that compared with the sulfur cycle composite bacterial agent, the iron carrier enhanced sulfur cycle composite bacterial agent has a nitrate residual concentration of 0 mg / L after reacting for 24 hours under different nitrate wastewater loads, and the nitrate removal rate is 100%, while the sulfur cycle composite bacterial agent still has nitrate accumulation after reacting for 24 hours under different nitrate loads. As the nitrate concentration increases, the nitrate removal rate gradually decreases. This shows that the iron carrier enhanced sulfur cycle composite bacterial agent can enhance the shock load resistance to water quality fluctuations and improve the denitrification efficiency under different nitrate wastewater loads.

[0040]

[0041]

[0042] Example 5: Improvement of the activity of key denitrification enzymes by using iron carrier-enhanced sulfur cycle composite bacterial agent compared with sulfur cycle composite bacterial agent

[0043] The sulfur cycle composite bacterial agent (Iron-0) and the iron carrier enhanced sulfur cycle composite bacterial agent (Iron-1) were centrifuged at 4000 rpm, 4°C, 10 min, and then washed twice with 0.1 M PBS buffer. This step was repeated three times, and the last time they were resuspended with 0.1 M PBS buffer, followed by ultrasonic disruption at 20 kHz, 5 min, 4°C, and centrifuged at 10000 g, 4°C, 10 min to extract the supernatant, which was the crude enzyme solution. The crude enzyme solution was used to determine the activity of key denitrification enzymes. The activities of nitrate reductase (NAR) and nitrite reductase (NIR) in the crude enzyme solutions of different groups were determined. Figure 4 As shown, compared with the sulfur cycle composite bacterial agent, the sulfur cycle composite bacterial agent enhanced by iron carrier increased the activities of two key enzymes under the condition of COD / N of 3.2, indicating that the iron carrier enhanced sulfur cycle composite bacterial agent accelerated the nitrate removal rate by enhancing the activity of key denitrification enzymes.

[0044] Example 6: Comparison of SEM and EDS of iron carrier enhanced sulfur cycle composite bacterial agent and sulfur cycle composite bacterial agent

[0045] SEM images of iron carrier enhanced sulfur cycle composite bacterial agent and sulfur cycle composite bacterial agent Figure 5 and Figure 6 As shown. Figure 6It can be seen that the surface of the sulfur cycle composite bacterial agent is smooth and there are certain gaps between the bacteria. Figure 5 Dense and fine block-like precipitates appeared on the outside of the iron carrier enhanced sulfur cycle composite agent, and these precipitates almost filled the gaps between the bacteria, making the flocculation effect of the microorganisms better. It can be seen from Tables 4 and 5 that the iron carrier enhanced sulfur cycle composite agent has an increased mass of Fe compared to the sulfur cycle composite agent, generating precipitate FeS, and this iron carrier in the form of FeS can effectively transfer S 2- It is fixed in the system to prevent it from escaping, and when the electron donor is insufficient in the system, it can serve as an alternative electron donor for biological denitrification, reducing the demand for external carbon sources and enhancing the denitrification stability of the system.

[0046]

[0047]

[0048] Example 7: XRD comparison between iron carrier enhanced sulfur cycle composite bacterial agent and sulfur cycle composite bacterial agent

[0049] X-ray diffraction analysis (XRD) revealed the crystal structure changes of the iron carrier enhanced sulfur cycle composite agent and the sulfur cycle composite agent. Iron-0 and iron-1 represent the XRD analysis diagrams of the sulfur cycle composite agent and the iron carrier enhanced sulfur cycle composite agent, respectively. Figure 7 As shown. No characteristic peaks appeared in the sulfur cycle composite bacterial agent without iron acclimation, while the iron carrier enhanced sulfur cycle composite bacterial agent showed peaks at 12.2°, 28.3°, 35.4°, 46.3° and 59.8°, respectively. By comparing the PDF#49-1632 card, it was determined that the substance was ferrous sulfide (FeS), which was consistent with the previous SEM and EDS analysis. Therefore, it can be determined that the precipitate formed on the sludge surface is FeS. Ferrous sulfide, as the main component of natural pyrrhotite, has a flaky structure similar to graphite and belongs to the hexagonal crystal system. Thiobacillus can use it for denitrification reaction, and the Fe and S in it can be used as electron donors for denitrification. The FeS produced can improve the denitrification performance of the biological system and enhance the denitrification stability of the system.

[0050] Therefore, the present invention adopts the above-mentioned method of using iron carriers to enhance the denitrification efficiency of the sulfur cycle microbial system, which can not only achieve the removal of nitrate nitrogen under low-carbon conditions, but also adapt to the complex wastewater that occurs in actual process operation. This method has good application prospects for removing nitrate nitrogen from low-carbon wastewater.

[0051] The above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for enhancing denitrification of sulfur cycle microbial system by using iron carrier, characterized in that: The method comprises the following steps: inoculating sulfate reducing bacteria and denitrifying Thiobacillus together into a culture medium containing iron ions or ferrous ions for domestication; and using the domesticated composite bacterial agent for wastewater denitrification.

2. The method according to claim 1, characterized in that The iron ion is selected from at least one of ferric sulfate, ferric nitrate and ferric chloride; the ferrous ion is selected from at least one of ferrous sulfate, ferrous chloride, ferrous sulfate and ferrous nitrate.

3. The method according to claim 1 or 2, characterized in that: The culture medium containing ferrous ions is formulated as follows: 0.4-2 g / L C6H 12 O6, 0.4~4 g / L KNO3, 0.1~0.5 g / L Na2SO4, 0.04~ 0.1g / L KH2PO4, 0.1~0.3g / L FeSO4; the culture medium formula containing iron ions is obtained by replacing 0.1~0.3 g / LFeSO4 in the culture medium formula containing ferrous ions with 0.1~0.4 g / L Fe2(SO4) 3。 4. The method according to claim 1 or 2, characterized in that: The acclimation conditions are 15-40°C, 80-200rpm, anaerobic darkness, and an acclimation time of 3-5 days; the pH in the culture medium is 6-9, and the pH is adjusted by using a phosphoric acid solution and a sodium hydroxide solution.

5. The method according to claim 1, characterized in that The inoculation volume ratio of sulfate-reducing bacteria and denitrifying Thiobacillus during acclimation was 1-5, and the concentration range of sulfate-reducing bacteria and denitrifying Thiobacillus in the inoculum after acclimation was 10 4 ~10 5 cfu / mL.

6. The method according to claim 1, characterized in that The composite bacterial agent acclimated with iron ions or ferrous ions is inoculated into nitrogen-containing wastewater, the volume ratio of wastewater to composite bacterial agent is 0.5~5, and the carbon source is added to COD / N of 3~5. Under anaerobic dark conditions, the culture is carried out at 15~40℃, 80~200 rpm, and pH 6~9 to remove nitrate nitrogen in the wastewater.

7. The method according to claim 1 or 6, characterized in that: The denitrification time is 6~24 h.

8. The method according to claim 1 or 6, characterized in that: The nitrate nitrogen concentration in nitrogen-containing wastewater is controlled at 50~1000 mg / L.

9. The method according to claim 1 or 6, characterized in that: The carbon source is selected from at least one of glucose, sucrose and xylose.

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