KR20210141826A - A denitrification catalyst, a manufacturing method thereof and a denitrification method using thereof - Google Patents

Abstract

The present invention relates to a denitrification catalyst, and relates to a denitrification catalyst for underground water. The denitrification catalyst for underground water comprises zero valent iron added with sulfur. According to the present invention, denitrification efficiency in underground water can be improved.

Description

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a denitration catalyst for groundwater using sulfur-added zero-valent iron, a method for preparing the same, and a denitration method according thereto, and relates to ferrous sulfate (FeSO ₄ ), thioacetamide (CH ₂ CSNH ₂ ) and sodium borohydride (NaBH ₄ ) It relates to a denitrification method of producing sulfur-added zero-valent iron using (NaBH 4 ) and denitrifying nitrates contained in groundwater by introducing denitrification bacteria into groundwater along with the denitration catalyst thus prepared.

According to the operation result of the Ministry of Environment's groundwater quality monitoring network, nitrate (NO ₃ ^- ), which causes cyanosis in infants and is closely related to the development of non-Hawkins lymphoma, is known as the main pollutant of groundwater. In particular, contamination of groundwater, which is the main water source for most rural residents, is an important issue that goes beyond the point of improving the environment of the water source and determines the basic water problem and the basis of life.

Therefore, for the safety of rural groundwater quality, it is urgently necessary to reuse groundwater through denitrification of nitrate, a major pollutant in rural groundwater.

Let's take a look at Korean Patent Registration No. 10-0922481, which is the first prior art disclosed in the technical characteristics for the denitrification of nitrates contained in groundwater.

The first prior art discloses a technical feature in which indigenous heterotrophic denitrification bacteria in soil use molasses eluted from a solid molasses purifying agent as a carbon source to convert nitrates in contaminated groundwater into nitrogen gas to remove nitrates.

Let's look at the second prior art, Republic of Korea Patent Registration No. 10-1323711, which discloses a technical feature for increasing the denitrification efficiency in a wastewater treatment device.

The second prior art discloses the technical characteristics of the denitrification process of a wastewater treatment device that uses alkaline water, which has a very high efficiency in increasing the pH level of the nitrification tank in the wastewater treatment device, to create a pH environment suitable for denitrification bacteria that cause nitrification reaction. are doing

Although the prior art discloses technical features for increasing the denitrification efficiency by denitrification bacteria, in order to increase the denitrification efficiency in the groundwater, the technical characteristics of the denitrification efficiency of the denitrification bacteria in a state where the denitrification catalyst is located in the groundwater are not disclosed at all. It is not disclosed, and there is no hint or suggestion.

Therefore, in order to increase the denitrification efficiency of the denitrification bacteria in the groundwater, there is an urgent need to study the denitrification efficiency of the denitrification bacteria in the state where the denitrification catalyst is placed in the groundwater, or the suspension efficiency in the groundwater in the state where only the denitrification catalyst is located. it is necessary.

In order to solve the problems of the prior art described above, it is intended to propose a technical feature capable of increasing the denitrification efficiency in groundwater using a denitration catalyst.

Specifically, it is intended to propose a technical feature capable of increasing the denitration efficiency of a denitration catalyst alone or in a state in which denitrification bacteria are located in groundwater.

In order to solve the problems of the prior art described above, the denitration catalyst for groundwater according to the present invention may include sulfur-added zero valent iron in the denitration catalyst.

In order to solve the problems of the prior art, the method for preparing a denitration catalyst for groundwater according to the present invention includes (a) hydrated form of ferrous sulfate (FeSO ₄ ) and thioacetamide (CH _{2 )} CSNH ₂ ) is dissolved in ultrapure water to produce a first mixture; And (b) sodium borohydride (NaBH ₄ ) is added to the first mixture in step (a) to produce a second mixture.

Preferably, step (a) may be carried out in an anaerobic state.

Preferably, the ultrapure water in step (a) may be ultrapure water in a state from which oxygen is removed.

Preferably, the hydrated form of ferrous sulfate (FeSO ₄ ) may be ferrous sulfate heptahydrate (FeSO ₄ ·7H ₂ O).

_{Preferably, the amount of the thioacetamide (CH 2} CSNH ₂ ) may be 5 to 15 parts by weight based on 100 parts by weight of the ferrous sulfate heptahydrate (FeSO ₄ ·7H _{2 O).}

Preferably, in the first mixture, 3 to 8 mg of the ferrous sulfate heptahydrate (FeSO ₄ ·7H ₂ O) per 100 mL of the ultrapure water may be dissolved.

Preferably, in the second mixture, 0.4 to 0.8 mg of the thioacetamide (CH ₂ CSNH ₂ ) per 100 mL of the ultrapure water may be dissolved.

In order to solve the problems of the prior art described above, the method of denitrification in groundwater according to the present invention includes the step of (c) adding sulfur-added zero valent iron to the groundwater in the method of denitration in groundwater. can do.

Preferably, in step (c), denitrifying bacteria may be introduced into the groundwater.

Preferably, the denitrification bacteria may be hydrogen-oxidizing denitrification bacteria.

Preferably, in step (c), the pH of the groundwater may be 5.5 to 8.5.

Preferably, in step (c), the pH of the groundwater may be 7.5 to 8.5.

Preferably, the concentration of nitrate (NO ₃ ⁻ ) in the groundwater may be 25 to 100 mg/L.

Preferably, the concentration of nitrate (NO ₃ ⁻ ) in the groundwater may be 25 to 50 mg/L.

Preferably, the sulfur-added zero valent iron may be added to the groundwater so that the concentration of the sulfur-added zero valent iron in the groundwater is 0.02 to 0.06 mg/L. .

Preferably, the sulfur-added zero valent iron may be added to the groundwater so that the concentration of the sulfur-added zero valent iron in the groundwater is 0.035 to 0.045 mg/L. .

Due to the above-described problem solving means, it is possible to increase the denitrification effect in the groundwater.

1 is a diagram schematically illustrating a method for synthesizing sulfur-added zero-valent iron (S-nZVI).
2A to 6 are diagrams showing experimental data on the denitrification effect.

Hereinafter, preferred embodiments of the method according to the present invention will be described with reference to the accompanying drawings. In this process, the thickness of the lines or the size of the components shown in the drawings may be exaggerated for clarity and convenience of explanation. In addition, the terms to be described later are terms defined in consideration of functions in the present invention, which may vary according to the intention or custom of the user or operator. Therefore, definitions of these terms should be made based on the content throughout this specification.

Zero valent iron (hereinafter nZVI) has been widely used in groundwater treatment because of its ability to remove organic or inorganic contaminants. However, nZVI tends to have low nitrogen gas selectivity through abiotic denitrification process, reducing reaction with contaminants as it has a property of being easily agglomerated.

In the present invention, the denitrification efficiency of nZVI and sulfur-added zero-valent iron (hereinafter, S-nZVI) in groundwater in the presence of denitrification bacteria or in groundwater in the absence of denitrification bacteria is to be examined.

1. Synthesis method of sulfur-added zero-valent iron (S-nZVI)

A method of synthesizing sulfur-added zero-valent iron (S-nZVI) will be described with reference to FIG. 1 .

_{Ferrous sulfate (FeSO 4} ) and thioacetamide (CH ₂ CSNH ₂ ) in the form of hydrates are dissolved in ultrapure water from which oxygen has been removed to form a first mixture. Generation of the first mixture may be performed in an anaerobic state, and the synthesis process may proceed while maintaining an anaerobic state by purging nitrogen gas during the synthesis process for generating the first mixture.

The hydrated form of ferrous sulfate (FeSO ₄ ) may be ferrous sulfate heptahydrate (FeSO ₄ ·7H ₂ O), and further, based on 100 parts by weight of _{ferrous sulfate heptahydrate (FeSO 4} ·7H _{2 O).} The weight part of thioacetamide (CH ₂ CSNH ₂ ) may be 5 to 15.

Furthermore, in producing the first mixture, _{3 to 8 mg of ferrous sulfate heptahydrate (FeSO 4} ·7H ₂ O) may be dissolved per 100 mL of ultrapure water, and thioacetamide (CH ₂ CSNH ₂ ) per 100 mL of ultrapure water It may be 0.4 to 0.8 mg.

Then, sodium borohydride (NaBH ₄ ) is added to the resulting first mixture to produce a second mixture. The suspended S-nZVI is filtered off with constant stirring, washed, and stored in ethanol to prevent further oxidation.

As a specific example, _{22.12 g of ferrous sulfate heptahydrate (FeSO 4} ·7H ₂ O) and 2.52 g of thioacetamide (CH ₂ CSNH ₂ ) were added to 400 mL of ultrapure water from which oxygen was removed and stirred at 150 rpm for 15 minutes. A first mixture was formed. At this time, nitrogen gas was purged and the synthesis process was performed in an anaerobic state.

Then, sodium borohydride (NaBH ₄ ) 0.4M solution was slowly added dropwise to the first mixture and stirred at 150 rpm to produce a second mixture.

S-nZVI suspended in the second mixture was filtered and washed several times with ethanol. It is then stored in ethanol to prevent oxidation of S-nZVI.

2. Batch experiment

Fill a number of 125mL serum bottles with 50mL of 25mg/L, 50mg/L, and 100mg/L of nitrate (NO ₃ ^- ) depending on the experimental conditions, respectively. To keep each serum bottle filled with nitrate (NO ₃ ⁻ ) solution anaerobic, nitrogen gas was purged into the serum bottle for 10 minutes. Afterwards, S-nZVI, n-ZVI, denitrifying bacteria, etc. are added to the serum bottle according to each experimental condition, or _{the pH of the nitrate (NO 3} ^- ) solution is adjusted. Depending on the experimental conditions, the concentration or number of denitrification bacteria added to the serum bottle is 500 to 900 ATP.

Then, each serum bottle was shaken at 150 rpm for 3 days at 35° C. in an incubator shaker. Samples were taken from each serum bottle at intervals of 15 minutes to 3 days.

Concentrations of nitrate (NO ₃ ⁻ ) and nitrite (NO ₂ ⁻ ) in the collected samples were measured with an ion chromatograph, and ammonia (NH ₃ ⁺ ) concentrations were measured with an ammonia test kit (nessler method).

The number of denitrifying bacteria obtained in the active form as a medium plate from the Center for Biological Resources (KCTC) was measured by the ATP test kit. Cupriavidus necator (ATCC17699) was used as the denitrification bacteria in the present invention as hydrogen-oxidizing denitrification bacteria. The denitrifying bacteria were converted into a solution on a medium plate and stored in a refrigerator below 4°C.

The pH of the nitrate (NO ₃ ⁻ ) solution was adjusted with diluted 0.1 M hydrochloric acid (HCl) and 0.1 M sodium hydroxide (NaOH).

3. Comparison of denitrification effect of nZVI and S-nZVI

After each 50 mL of 25 mg/L nitrate (NO ₃ ⁻ ) solution was filled in a 125 mL serum bottle, 0.04 g/L of nZVI and S-nZVI were added to the serum bottles in the state in which the denitrification bacteria were added and in the state in which the denitrification bacteria were not added. . The pH of the nitrate (NO ₃ ⁻ ) solution was adjusted to 7, and each serum bottle was shaken at 35° C. for 3 days at 150 rpm in an incubator shaker.

A in Figure 2a is experimental data comparing the denitrification effect of nZVI and S-nZVI in the absence of denitrifying bacteria, and B in Figure 2a is the denitrification effect of nZVI and S-nZVI in the presence of denitrifying bacteria. are experimental data comparing In FIGS. 2A and 2B , Fe ₀ refers to nZVI, and S-Fe ₀ refers to S-nZVI.

Nitrate (NO ₃ ⁻ ) may be directly converted into ammonia by S-nZVI while passing through the abiotic reduction pathway shown in Formula 1 below. Moreover, when zero ferrous iron is dissolved, it causes the generation of hydrogen gas, which can act as an electron contributor in the related biological denitrification process (refer to Formula 2 below).

As can be seen from A in FIG. 2a, when denitrification bacteria were not present, nitrate (NO ₃ ^- ) was almost removed in 1 day, and when denitrification bacteria were present, nitrate (NO ₃ ^- ) was almost removed in 2 days did. This may mean that the reduction rate of _{nitrate (NO 3} ⁻ ) is reduced in the state in which the denitrification bacteria are present than in the state in which the denitrification bacteria are not present.

Both nZVI and S-nZVI show high total nitrogen removal efficiency in the presence of denitrifying bacteria. This means that denitrification bacteria are contributing to the denitrification process.

Cupriavidus necator, known as a denitrification bacterium using hydrogen, uses hydrogen generated from S-nZVI corrosion. This hydrogen acts as an electron contributor in the process of reducing _{nitrate (NO 3} ^- ) to nitrogen (N _{2 ) gas.} It shows high total nitrogen removal efficiency (refer to Formula 3 below)

Formula 1

NO ₃ ^- + 4Fe ⁰ + 10H ⁺ --> NH ₄ ⁺ + 4Fe ²⁺ + 3H ₂ O

Formula 2

NO ₃ ^- + 2H ₂ O --> H ₂ + Fe ²⁺ + 2OH ^-

Formula 3

2NO ₃ ^- + 5H ₂ -->N ₂ + 4H ₂ O + 2OH ^-

C in Figure 2b is experimental data showing the total nitrogen removal efficiency of nZVI and S-nZVI in the presence and absence of denitrification bacteria, and D in Figure 2b is the denitrification effect when only denitrification bacteria are present. Experimental data on the denitrification effect and the denitrification effect of sulfur in the presence of denitrification bacteria.

In FIG. 2B C, S-ZVI refers to S-nZVI, M+SZVI refers to S-nZVI introduced in the presence of denitrifying bacteria, ZVI refers to nZVI, and M+ZVI refers to nZVI introduced in the presence of denitrifying bacteria. refers to In FIG. 2B , Microbial refers to denitrifying bacteria, and S-Microbial refers to denitrifying bacteria coexisting with sulfur.

As can be seen from C in FIG. 2B , S-nZVI exhibits higher total nitrogen removal efficiency than nZVI in the presence of denitrification bacteria and in the absence of denitrification bacteria. It can be seen that the presence of sulfur contributes to the denitrification process. Sulfur-doped nZVI increases the electron transfer to contaminants while decreasing the solubility of nZVI with corrosion due to the low solubility of FeS.

D in Figure 2b shows the denitrification effect of the denitrification bacteria in the presence of sulfur. As can be seen in D in FIG. 2b, in the presence of sulfur, nitrate (NO ₃ ^- ) was removed on the second day, whereas nitrite (NO ₂ ^- ) and ammonia production were increased. Thus, it can be seen that the sulfur in S-nZVI acts as an electron donor to which electrons contribute to the denitrification bacteria to enhance the denitrification effect.

3 is a view showing the states of nZVI and S-nZVI after 3 days of denitrification.

S-nZVI shows higher nitrate (NO ₃ ⁻ ) reduction efficiency than nZVI under the same reducing conditions. As can be seen in FIG. 3 , this is because sulfur reduces the magnetic attraction between particles and prevents the aggregation of nZVI. Aggregation of nZVI reduces the total surface area the liquid can come into contact with, which changes the reaction and efficiency.

On the other hand, S-nZVI provides more surface area while exhibiting a low level of aggregation. More surface area results in a higher reduction rate.

4. Initial nitrate (NO ₃ ^- ) effect of concentration

After filling each 125ml serum bottle with 50mL of 25mg/L, 50mg/L, and 100mg/L nitrate (NO ₃ ^- ) solutions, 0.04g/L into the serum bottles with and without denitrification bacteria added. of S-nZVI was added. The pH of the nitrate (NO ₃ ⁻ ) solution was adjusted to 7, and each serum bottle was shaken at 35° C. at 150 rpm for 3 days in an incubator shaker.

(a) and (b) in FIG. 4a and (c) in FIG. 4b _{are experimental data for the denitrification effect at the initial nitrate (NO 3} ^- ) concentration of 25 mg/L, 50 mg/L, and 100 mg/L, respectively, (d) in FIG. 4B is experimental data for nitrogen gas generation. 4A and 4B, M refers to denitrifying bacteria, Z refers to S-nZVI, and MZ refers to S-nSVI introduced in the presence of denitrifying bacteria.

As can be seen in FIGS. 4A and 4B , the initial high concentration of nitrate (NO ₃ ⁻ ) causes high nitrite (NO ₂ ⁻ ) and ammonia production, while exhibiting low total nitrogen removal.

In denitrification using S-nZVI in the presence of denitrification bacteria and in the absence of denitrification bacteria, the selectivity of ammonia or nitrogen gas is lowered _{at a high initial concentration of nitrate (NO 3} ^{− ).} It can be seen that the initial nitrate (NO ₃ ⁻ ) concentration affects the reduction of nitrate (NO ₃ ⁻ ) and the by-product selectivity of the intermediate step.

5. Nitrate (NO ₃ ^- ) Effect of the pH of the solution

After each 125 ml serum bottle was filled with 50 mL of a 25 mg/L nitrate (NO ₃ ⁻ ) solution, 0.04 g/L of S-nZVI was added to each of the serum bottles in which denitrification bacteria were added and in which they were not. The pH of the nitrate (NO ₃ ⁻ ) solution was adjusted to 6, 7, and 8, respectively, and each serum bottle was shaken at 35° C. for 3 days at 150 rpm in an incubator shaker.

(a) and (b) in FIG. 5a and (c) in FIG. 5b are experimental data on the denitrification effect at pH 6, 7, and 8, and (d) in FIG. 5b is an experiment on nitrogen gas generation is data. 5A and 5B, M refers to denitrifying bacteria, SZ refers to S-nZVI, and MSZ refers to S-nSVI introduced in the presence of denitrifying bacteria.

As can be seen in (a) of FIG. 5A , when the denitrification bacteria were used, the highest denitrification effect was exhibited at pH 6 on the 3rd day. As can be seen in (b) of Figure 5a, when S-nZVI is used, the selectivity of ammonia and nitrogen gas is lowered as the pH is increased, and the most nitrite (NO ₂ ^- ) is generated.

However, as can be seen in (c) of Figure 5b, when S-nZVI was used in the presence of denitrifying bacteria, it can be seen that the selectivity of ammonia and nitrogen gas at pH 8 is increased.

As can be seen in (b) and (c) of Figure 5b, when S-nZVI was used, nitrate (NO ₃ ⁻ ) was almost removed on day 1, and when S-nZVI was used with denitrifying bacteria, nitrate (NO _{3 ) on day 2} ^- ) is almost eliminated. It can be seen that the denitrification rate is reduced when S-nZVI is used together with denitrifying bacteria.

Therefore, it can be seen that the pH of the initial solution _{has a strong effect on the reduction of nitrate (NO 3} ⁻ ) and the selectivity of the intermediate by-product.

6. Actual groundwater treatment experiment

6 is data on the denitrification effect obtained by adding 0.2 g/L of S-nZVI and nZVI to 60 mL of each actual groundwater.

In FIG. 6 , Fe ₀ refers to nZVI, and S-Fe ₀ refers to S-nZVI.

Compared to nZVI, S-nZVI exhibits nitrogen gas selectivity and high nitrate ((NO ₃ ⁻ ) removal efficiency, while showing low ammonia production.

In the above, the present specification has been described with reference to the embodiments shown in the drawings so that those skilled in the art can easily understand and reproduce the present invention, but these are merely exemplary, and those skilled in the art may make various modifications and equivalent other modifications from the embodiments of the present invention. It will be appreciated that embodiments are possible. Therefore, the protection scope of the present invention should be defined by the claims.

Claims (17)

In the denitration catalyst for groundwater,
A denitration catalyst for groundwater containing sulfur-added zero valent iron.
In the method for producing a denitration catalyst for groundwater,
(a) hydrated form of ferrous sulfate (FeSO ₄ ) and thioacetamide (CH ₂ CSNH ₂ ) are dissolved in ultrapure water to form a first mixture; and
(b) sodium borohydride (NaBH ₄ ) is added to the first mixture in step (a) to produce a second mixture.
3. The method of claim 2,
The step (a) is a method for producing a denitration catalyst for groundwater that is carried out in an anaerobic state.
3. The method of claim 2,
The method for producing a denitration catalyst for groundwater, wherein the ultrapure water in step (a) is ultrapure water in a state from which oxygen has been removed.
3. The method of claim 2,
The hydrated form of ferrous sulfate (FeSO ₄ ) is ferrous sulfate heptahydrate (FeSO ₄ ·7H ₂ O).
6. The method of claim 5,
The method for preparing a denitration catalyst for groundwater is 5 to 15 parts by weight of _{the thioacetamide (CH 2} CSNH ₂ ) based on 100 parts by weight of the ferrous sulfate heptahydrate (FeSO ₄ ·7H _{2 O).}
6. The method of claim 5,
A method for producing a denitration catalyst for groundwater in which 3 to 8 mg of the ferrous sulfate heptahydrate (FeSO ₄ ·7H _{2 O) is dissolved per 100 mL of the ultrapure water in the first mixture.}
6. The method of claim 5,
A method for preparing a denitration catalyst for groundwater in which _{0.4 to 0.8 mg of the thioacetamide (CH 2} CSNH ₂ ) is dissolved in the second mixture per 100 mL of the ultrapure water.
In the method of denitrification in groundwater,
(c) a method of denitrification in groundwater comprising the step of adding sulfur-added zero valent iron to the groundwater.
10. The method of claim 9,
In the step (c), the denitrification method in the groundwater in which the denitrification bacteria are introduced into the groundwater.
11. The method of claim 10,
The denitrification method in groundwater, wherein the denitrification bacteria are hydrogen-oxidizing denitrification bacteria.
11. The method of claim 10,
In step (c), the pH of the groundwater is 5.5 to 8.5.
13. The method of claim 12,
In step (c), the pH of the groundwater is 7.5 to 8.5 denitrification method in groundwater
11. The method of claim 10,
The concentration of nitrate (NO ₃ ⁻ ) in the groundwater is 25 to 100 mg/L.
15. The method of claim 14,
The concentration of nitrate (NO ₃ ⁻ ) in the groundwater is 25 to 50 mg/L.
11. The method of claim 10,
A denitrification method in which the sulfur-added zero valent iron is added to the groundwater so that the concentration of the sulfur-added zero valent iron in the groundwater is 0.02 to 0.06 mg/L.
17. The method of claim 16,
A denitration method in which the sulfur-added zero valent iron is added to the groundwater so that the concentration of the sulfur-added zero valent iron in the groundwater is 0.035 to 0.045 mg/L.

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