KR20210026556A - Denitrification apparatus for sewage supplied with carbon source using sewage sludge and method for reducing nitrous oxide using the same - Google Patents

Abstract

An embodiment of the present invention is a fermentation tank in which sewage sludge is introduced and anaerobic fermentation is performed to produce an organic acid; And a bioreactor in which the organic acid is introduced to remove biological nitrogen.

Description

[Denitrification apparatus for sewage supplied with carbon source using sewage sludge and method for reducing nitrous oxide using the same}

The present invention relates to a wastewater denitrification apparatus that reduces the generation of nitrous oxide (N ₂ O) in a wastewater treatment plant, and more specifically, improves the efficiency of a biological nitrogen removal process by using concentrated sludge obtained from its own sewage in a wastewater treatment plant. Thus, the present invention relates to a wastewater denitrification apparatus in which the generation of nitrous oxide is reduced, and a method of reducing the generation of nitrous oxide by using the same.

Nitrous oxide (N ₂ O) is one of the greenhouse gases, and its warming potential is _{310 times larger than that of carbon dioxide (CO 2} ), and it is known that its residence time in the atmosphere approaches 116 years. For this reason, it is estimated that nitrous oxide accounts for a small amount of about 0.03% of the total greenhouse gas, but accounts for 10% of the total greenhouse gas impact on the environment.

Of the nitrous oxide that makes up the atmosphere, about 3.4% of artificially generated nitrous oxide is generated in the wastewater treatment plant, and in order to reduce the amount of nitrous oxide in the atmosphere, such anthropogenic generation is suppressed or the amount of gas generated. Need to be reduced.

As a method of removing the amount of nitrous oxide generated as described above, a method of trapping gaseous nitrous oxide and removing it through joint metabolism in a biofilter is used. However, this method does not provide a method for reducing the amount of nitrous oxide generated during the denitrification process of the biological nitrogen removal process, so in most open sewage treatment plants, nitrous oxide is diffused into the atmosphere and trapped to reach a gas removal device. There is a problem that is difficult to do.

Meanwhile, it is known that the emission of nitrous oxide in the process of denitrification of wastewater is affected by the type and concentration of electron acceptors, the electron donor/electron acceptor (C/N) ratio, and the complexity of the electron donor. In particular, when the organic carbon source/nitrogen (C/N) ratio decreases, the nitrogen removal rate decreases, but the conversion rate to nitrous oxide is known to increase. Therefore, it is recommended to supply an external carbon source when the inflow carbon source is insufficient. However, when methanol is used as an external carbon source, the purchase cost is enormous, putting a burden on the operation of the sewage treatment facility.

Korean Patent Application Publication No. 10-2018-0085389

The present invention is to solve the above problem, and a wastewater denitrification device that reduces the amount of nitrous oxide by providing a carbon source necessary for a biological nitrogen removal process using concentrated sludge of wastewater, and a wastewater denitration device that occurs during the wastewater treatment process using the same. One problem is to provide a method for reducing the amount of nitrous oxide.

One aspect of the present invention is a fermentation tank in which sewage sludge is introduced and anaerobic fermentation is performed to produce an organic acid; And a bioreactor in which the organic acid is introduced to remove biological nitrogen.

According to an embodiment of the present invention, the wastewater denitration apparatus may further include a sedimentation tank, and the effluent water of the bioreactor is solid-liquid separated through the sedimentation tank, and residual sludge generated by the solid-liquid separation is recycled to the fermentation tank. Can be supplied.

According to an embodiment of the present invention, the wastewater denitration apparatus may further include a biogas generation tank.

According to an embodiment of the present invention, the sewage sludge may be concentrated sludge.

According to an embodiment of the present invention, the organic acid is acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, isovaleric acid. ) And may be any one selected from the group consisting of a combination thereof.

Another aspect of the present invention provides a sewage treatment facility including the nitrogen dioxide removal device.

Another aspect of the present invention is the step of producing an organic acid by supplying sewage sludge to a fermentation tank; And supplying the prepared organic acid to a bioreactor to remove biological nitrogen.

In the case of using the nitrous oxide reduction device according to an embodiment of the present invention, the fermentation broth of sewage sludge is used as an external carbon source in the denitrification process in the biological nitrogen removal process to reduce the amount of nitrous oxide generated in the bioreactor itself, while sewage It has the effect of promoting the denitrification process using sludge fermentation broth. .

The effects of the present invention are not limited to the above effects, and should be understood to include all effects that can be inferred from the configuration of the invention described in the detailed description or claims of the present invention.

1 shows the configuration of a wastewater denitration apparatus according to an embodiment of the present invention.
2 is a diagram showing changes in properties and COD over time in a fermentation tank among devices according to an embodiment of the present invention.
3 shows the detection amount of nitrogen oxides dissolved in sewage over time in the apparatus according to the comparative example (a) and the example (b) of the present invention.
4 shows the detection amounts of nitrogen oxides and nitrous oxide gases dissolved in sewage over time in the apparatus according to Comparative Example (a) and Example (b) of the present invention.

Hereinafter, the present invention will be described with reference to the accompanying drawings. However, the present invention may be implemented in various different forms, and therefore is not limited to the embodiments described herein.

The terms used in the present specification are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the present specification, terms such as "include" or "have" are intended to designate the presence of features, numbers, steps, actions, components, parts, or a combination thereof described in the specification unless otherwise specified. However, it is to be understood that the possibility of the presence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof, is not precluded.

Hereinafter, a membrane strip sensor according to an embodiment of the present invention will be described with reference to the accompanying drawings.

1 shows the configuration of a wastewater denitration apparatus according to an embodiment of the present invention.

Referring to FIG. 1, an aspect of the present invention provides a wastewater denitration apparatus 1 including a fermentation tank 10, a bioreactor 20, a settling tank 30, and a biogas generation tank 40.

In the fermentation tank 10, sewage sludge is introduced and anaerobic fermentation is performed to produce an organic acid.

Sewage sludge is raw sludge generated after sedimentation in the primary sedimentation basin of a wastewater treatment facility (primary sludge), excess sludge sedimented in the secondary sedimentation basin after a water treatment process (secondary sludge), raw sludge and excess sludge in the distribution tank It may be mixed mixed sludge, or raw sludge, excess sludge, or concentrated sludge obtained by reducing the mixed sludge in a concentration tank, and preferably concentrated sludge.

Meanwhile, the sewage sludge may additionally include residual sludge generated in the settling tank 30.

Particulate organic substances in the sewage sludge are hydrolyzed to soluble organic substances, and the soluble organic substances can be converted to organic acids by acid fermentation bacteria. In anaerobic conditions, a relatively slow methane fermentation reaction and a relatively fast acid fermentation reaction occur competitively for chemical oxygen demand (COD), but increase the concentration of volatile fatty acids (VFA) that can be used as an alternative carbon source for the denitrification process. For this purpose, wastewater treatment can be performed while maintaining high temperature and low hydraulic residence time.

The hydrolysis, conversion to organic acids, and methane fermentation are performed by different microorganisms, such as fermenting bacteria and methanogenic bacteria, respectively, and their activities are organically linked to each other.

The fermentation tank 10 may be operated under a temperature of, for example, 45° C. to 60° C., for example, 55° C. to perform fermentation.

The hydraulic retention time (HRT) in the fermentor 10 may be, for example, 1 to 5 days, for example, 1.5 days.

The organic acid is selected from the group consisting of acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, isovaleric acid, and combinations thereof. It can be any one.

The fermentation tank 10 may further include a sample extractor for analyzing gas components in the fermentation tank 10 in real time, a temperature controller capable of automatically/manually adjusting the temperature in the fermentation tank 10, and a combination thereof.

The organic acid may be used as a carbon source in the denitrification process performed in the bioreactor 20 in the future.

The bioreactor 20 includes a denitrification tank and a nitrification tank, and in the bioreactor 20, some or all of the organic acid produced in the fermentation tank 10 is introduced and may be used to remove biological nitrogen by a denitrification process.

In the denitrification process, _{nitrate nitrogen (NO 3} ^-- _{N) formed by nitrification of ammonia (NH 3} ) by autotrophic microalgae and nitrifying bacteria is converted to nitrogen (N ₂ ) gas through nitrite nitrogen (NO _{2 -N).} It refers to the process of reduction, and the reaction route is as described in Equation 1 below:

[Equation 1]

_{NO 3 - (aq) → NO} 2 - (aq) → NO (g) → N 2 O (g) → N 2 (g)

In each of the above steps, a reductase that promotes electron transfer to nitrogen participates in the reaction. Denitrification step is NO ₃ ^- or NO ₂ ^-, and the electron donor is available, and proceeds by heterotrophic microorganisms in the anoxic conditions that are oxygen-deficient. _{Heterotrophic microorganisms use NO 3} ^- or NO ₂ ^- as an electron acceptor instead of oxygen during the denitrification reaction and use a carbon source, for example, organic substances such as acetic acid and methanol as the electron donor. At this time, when the carbon source is limited, the equation 1 is not completed with _{N 2} , and the reaction is stopped in the _{NO or N 2 O state, thereby causing the N 2} O to be discharged.

According to an embodiment of the present invention, heterotrophic microorganisms participating in the denitrification process are Achromobacter, Acinetobacter, Agrobacterium, Alcaligenes, and Asrobacter ( Arthrobacter), Bacillus, Corynebacterium, Flavobacterium, Hypomicrobium, Moraxella, Meisseria, Paracoccus, Profi Propionibacterium, Pseudomonas, Rhizobium, Rhodopseudomonas, Spirillum, and combinations thereof.

The settling tank 30 may be provided in succession to the bioreactor 20. The sedimentation tank 30 may separate the liquid and solid residual sludge from the effluent water flowing out of the bioreactor 20 and from which nitrogen has been removed from the bioreactor 20 using gravity or centrifugal force. The residual sludge may be resupplied to the fermentation tank 10 through a transfer pipe.

The biogas generating tank 40 may be provided by being connected to the fermentation tank 10.

In the biogas generation tank 40, the remainder of the organic acids supplied to the bioreactor 20 among the organic acids produced in the fermentation tank 10 are introduced, and may be used to generate biogas, for example, methane.

In the biogas generation tank 40, methane may be produced by an anaerobic digestion process in which organic acids are decomposed into anaerobic microorganisms, but the present invention is not limited thereto.

As described above, the wastewater denitration apparatus 1 according to an embodiment of the present invention enables an efficient denitrification process by using an organic acid produced by itself from sewage sludge as an additional external carbon source, thereby generating NO _x ^-n and N in the denitrification process. _{The amount of 2} O can be significantly reduced. In addition, it is possible to additionally generate biogas renewable energy including methane gas by using sewage sludge that is discarded at the same time.

In addition, the fermentation tank 10 of the wastewater denitration device 1 according to an embodiment of the present invention is provided in the previous step of the bioreactor 20 in which nitrous oxide is generated, and can be applied to an existing open sewage treatment plant without limitation. have.

Another aspect of the present invention provides a wastewater treatment facility including a wastewater denitration apparatus according to an embodiment of the present invention.

The sewage treatment facility may include a sewage denitrification device including a sedimentation tank in which the physical separation of foreign substances contained in the wastewater occurs, a concentration tank in which sludge obtained from the settling tank is reduced, a fermentation tank, and a bioreactor, as known in the art. , But is not limited thereto.

Another aspect of the present invention is the step of producing an organic acid by supplying sewage sludge to a fermentation tank; And It provides a method for reducing nitrous oxide comprising the step of performing biological nitrogen removal by supplying the prepared organic acid to a bioreactor.

In the method for reducing nitrous oxide according to an embodiment of the present invention, first, an organic acid may be prepared by supplying sewage sludge to a fermentation tank.

At this time, the sewage sludge may be raw sludge (primary sludge), excess sludge (secondary sludge), mixed sludge or concentrated sludge, preferably concentrated sludge. Sewage sludge contains a sufficient amount of dissolved organic substances, and also contains sufficient nutrients such as nitrogen sources.

Nutrients in sewage sludge can be fermented by anaerobic microorganisms to produce organic acids.

The organic acid may be any one selected from the group consisting of acetic acid, propionic acid, butyric acid, valeric acid, and combinations thereof.

Next, as a method for reducing nitrous oxide, biological nitrogen may be removed by supplying an organic acid prepared in a fermentation tank to a bioreactor.

2 is a diagram showing changes in properties and COD over time in a fermentation tank among devices according to an embodiment of the present invention.

In this regard, as a result of performing an unpaired two sample t-test (p <0.05), the concentration of dissolved COD (sCOD) and volatile fatty acids (VFAs) in sewage sludge increased as a result of anaerobic fermentation, and the total COD (tCOD ) There was no change in phase, but it was confirmed that the fraction of volatile fatty acids (VFAs) with respect to total COD (tCOD) increased (see Table 1 below). Through this, it was confirmed that various fatty acids, which are organic acids, are produced from sewage sludge through fermentation in a fermentation tank.

division value Before fermentation After fermentation tCOD (mg/L) 60.0 ± 8.8 58.0 ± 6.3 sCOD (mg/L) 6.3 ± 2.5 14.3 ± 1.7 VFAs (mgCOD/L) 4.3 ± 2.1 7.0 ± 1.2 VFAs/tCOD (%) 7.5 ± 3.7 12.2 ± 2.1

3 and 4 show the detection amounts of nitrogen oxides dissolved in sewage and the detection amounts of nitrogen oxides and nitrous oxide gas dissolved in sewage over time in the comparative example and the apparatus according to an embodiment of the present invention, respectively.

FIG. 3 is a diagram showing the detection amount of nitrogen oxides dissolved in sewage over time in the apparatus according to Comparative Example (a) and an Example (b) of the present invention, and a control without using a fermentation broth of sewage sludge (a ), _{compared to that the total amount of NO x} -N (aq) added in was not removed, in an embodiment (b) of the present invention using the sewage sludge fermentation broth, _{the total amount of added NO x} -N (aq) was removed. I could confirm. In addition, it was confirmed that the dissolved form of nitrous oxide (N ₂ O) was removed in both cases of Comparative Examples and Examples, but was removed at a faster rate in the case of Examples.

In addition, Figure 4 shows the detection amount of nitrogen oxide and nitrous oxide gas dissolved in sewage over time in the apparatus according to Comparative Example (a) and an Example (b) of the present invention, and the fermentation liquid of sewage sludge is not used. _{While the total amount of N 2} O (l) in the dissolved state added in the control group (a) _{was generated as N 2} O (g) in the gas phase, in an embodiment (b) of the present invention using the fermented sewage sludge It was confirmed that only about 51% of the added N _{2 O(l) was generated as N 2} O(g). _{Through this, it was experimentally confirmed that potential N 2} O (g) emission can be reduced by 49% through the use of an alternative external carbon source.

The above description of the present invention is for illustrative purposes only, and those of ordinary skill in the art to which the present invention pertains will be able to understand that other specific forms can be easily modified without changing the technical spirit or essential features of the present invention. will be. Therefore, it should be understood that the embodiments described above are illustrative and non-limiting in all respects. For example, each component described as a single type may be implemented in a distributed manner, and similarly, components described as being distributed may also be implemented in a combined form.

The scope of the present invention is indicated by the claims to be described later, and all changes or modified forms derived from the meaning and scope of the claims and their equivalent concepts should be construed as being included in the scope of the present invention.

1: wastewater denitrification device 10: fermentation tank
20: bioreactor 30: settling tank
40: biogas generation tank

Claims (7)

A fermentation tank in which sewage sludge is introduced and anaerobic fermentation is performed to produce an organic acid; And
Bioreactor in which the organic acid is introduced to remove biological nitrogen
Wastewater denitrification device comprising a. The method of claim 1,
The wastewater denitration apparatus further includes a sedimentation tank, wherein the effluent water from the bioreactor is separated into a solid-liquid through the sedimentation tank, and the residual sludge generated by the solid-liquid separation is resupplied to the fermentation tank. The method of claim 2,
The wastewater denitrification apparatus further comprises a biogas generation tank. The method of claim 1,
The sewage sludge is a wastewater denitration apparatus, characterized in that the concentrated sludge. The method of claim 1,
The organic acid is from the group consisting of acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, isovaleric acid, and combinations thereof. Wastewater denitrification apparatus, characterized in that any one selected. A wastewater treatment facility comprising the wastewater denitrification device of any one of claims 1 to 5. Supplying sewage sludge to a fermentation tank to produce an organic acid; And
Supplying the prepared organic acid to a bioreactor to perform biological nitrogen removal
Method for reducing nitrous oxide during wastewater treatment comprising a.

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