KR100446577B1 - Method for Eliminating Nitrogen Using Granule of Nitrifying Microorganisms - Google Patents

Abstract

PURPOSE: To substantially reduce consumption of oxygen required for nitrification and amount of organic matter required for denitrification and reduce volume of biofilm reactor by eliminating nitrogen from sewage and wastewater using granule of nitrifying microorganisms predominantly containing ammonia oxidizing bacteria. CONSTITUTION: The method comprises a step (a) of preparing granule of nitrifying microorganisms in which ammonia oxidizing bacteria are predominantly distributed by checking the growth of nitrite oxidizing bacteria in a nitrifying microorganism granule reactor; a nitrifying step (b) of oxidizing ammonia nitrogen into nitrate-nitrogen by flowing the granule of the nitrifying microorganisms into a nitrifying tank; a denitrifying step (c) of converting nitrate-nitrogen into nitrogen gas (N2) using denitrifying microorganisms by flowing wastewater containing the nitrate-nitrogen obtained in the nitrifying step into a denitrifying tank; and a step of transferring a denitrified mixed solution to a secondary settling chamber so that the denitrified mixed solution is separated into treated water and microorganism sludge, returning some of the microorganism sludge to the nitrifying tank or the nitrifying microorganism granule reactor, and passing the other some of the microorganism sludge through thickening, digestion and dewatering processes so that the treated sludge is disused.

Description

Method for Eliminating Nitrogen Using Granule of Nitrifying Microorganisms}

The present invention relates to a method for removing nitrogen using nitrified microorganism granules, and more particularly, to prepare a nitrified microorganism granule based on ammonia oxidizing bacteria in a nitrified microorganism granule reactor, and then using the same to remove nitrogen from sewage and wastewater. It is about how to.

The eutrophication caused by excessive inflow of nitrogen and phosphorus in lakes, rivers, inland seas, etc. causes not only aquatic environment and health risks, but also lowers the social and economic value of water resources. In particular, the nitrogen component represented by ammonia (NH ₃ -N) is toxic to aquatic organisms due to its own toxicity, and is recognized as an important pollutant due to its characteristic of increasing in proportion to population growth and industrial development. Has been.

Therefore, the development of advanced wastewater treatment technology to remove nitrogen is essential for protecting the water environment and securing clean water resources. In general, the advanced wastewater treatment technology for removing nitrogen components is divided into biological treatment and physicochemical treatment, and biological treatment methods are mainly used to remove nitrogen components in wastewater due to technical and economic factors.

Biological nitrogen removal technology of wastewater generally involves the ammonia oxidation of oxidizing ammonia to nitrite in aerobic conditions, the nitrification of nitrite oxidation of nitrite to nitric acid, and the nitrite or nitrate oxidized in anoxic conditions. It can be divided into denitrification step, which is reduced to nitrogen (N ₂ ) with the help of donor organic material. Nitrification step is carried out by autotrophic microorganisms such as ammonia and nitrite, and denitrification step is carried out with various heterotrophic Proceed by. As autotrophic ammonia and nitrite oxidants are lower in yield and growth rate than denitrification bacteria, the concentration of nitrifying microorganisms in sludge is lowered and is likely to be washed out, which is sensitive to pH, temperature and inhibitors. This is known as the rate limiting step in most biological nitrogen removal processes. In addition, suspended nitrification microorganisms are limited in their growth in the predation relationship with rotifers, the higher organisms present in the sludge. In the prior art, to solve this characteristic of nitrifying microorganisms, a biofilm method in which microorganisms are attached to a carrier is attempted. However, the biofilm method has problems such as expensive carrier cost, limited use of the treatment process, heterogeneous mixing inside the bioreactor, and microorganism attachment and desorption despite its advantages.

As a method for removing nitrogen from conventional sewage and wastewater, the nitrogen in the wastewater is discharged by using the ammonia wastewater treatment unit connected to the nitrification reactor and the nitrification microorganism incubator in Korea Patent Publication No. 2002-0049328. A method of removal is disclosed. This method has the advantage that it can remove the ammonia which has not been treated in the existing wastewater treatment plant in a small space by using the growth characteristics of nitrifying bacteria. In addition, Korean Patent Laid-Open Publication No. 2003-0038137 discloses a method for removing nitrogen in sewage by generating and controlling two processes of nitrification and denitrification at the same time by controlling and controlling metabolic activity of nitrifying microorganisms in sewage. Doing.

However, in order to remove nitrogen from sewage and wastewater, the disclosed documents use nitrification microorganisms under appropriate conditions to oxidize ammonia to nitrous acid under aerobic conditions, to nitrite to nitrate, and to nitrite oxidized under anoxic conditions. The efficiency of the denitrification step of reducing nitric acid to nitrogen is not seen as shortening the nitrification process itself as in the present invention.

Accordingly, the present inventors prepared the nitrification microorganism granules based on ammonia oxidizing bacteria under specific conditions, and then observed nitrification of wastewater using the same. As a result, most of the ammonia nitrogen was oxidized to nitrite nitrogen, and no nitrate nitrogen was produced. The present invention has been completed by confirming that no.

After all, the main object of the present invention is to provide a method for removing nitrogen using nitrified microorganism granules.

1 illustrates a denitrification process using nitrified microorganism granules according to the present invention.

Figure 2 shows the spatial distribution of ammonia oxidizing bacteria and nitrite oxidizing bacteria in nitrifying microorganism granules according to the present invention.

Figure 3 shows the concentration change of ammonia, nitrous acid and nitric acid during denitrification using nitrifying microorganism granules according to the present invention.

Figure 4 shows that the denitrification of nitrite accumulated during wastewater nitrification using nitrification microorganism granules.

Figure 5 shows the denitrification of the synthesized wastewater with a nitric acid concentration of 100mg / L to determine the amount of external carbon source consumed during the denitrification by a general complete nitrification.

In order to achieve the above object, the present invention comprises the steps of (a) to inhibit the growth of nitrite oxidizing bacteria in the nitrification microbial granule reactor to prepare a granule of nitrifying microorganisms mainly distributed ammonia oxidizing bacteria; (b) nitrification step of oxidizing the granule of nitrifying microorganism into nitrification tank to oxidize ammonia nitrogen to nitric acid; (c) a denitrification step of converting nitrate nitrogen into nitrogen gas (N ₂ ) using denitrification microorganisms by introducing wastewater containing nitrate nitrogen obtained in the nitrification step into a denitrification tank; And (d) transferring the denitrified mixed solution to the secondary settling tank to separate the treated water and the microbial sludge, and part of the microbial sludge is returned to the nitrification tank or the nitrification microbial granule reactor, and the sludge is concentrated, digested and dehydrated for disposal. It provides a method for removing nitrogen using nitrified microorganism granules comprising the step.

In the present invention, the step (a) of preparing a granule of nitrifying microorganisms comprises: (i) injecting wastewater containing a high concentration of ammonia into a culture substrate into a bioreactor containing nitrifying microorganisms in a continuous batch method; (ii) forming granules of nitrifying microorganisms while supplying oxygen for nitrification to a continuous batch reactor; (iii) stopping the oxygen supply to stop the reactor mixing, then settling the nitrified microorganism granules formed, and discharging the sludge that is not granulated; And (iv) withdrawing the precipitated nitrifying microbial granules.

According to the present invention, the granules of nitrifying microorganisms in which ammonia oxidizing bacteria are mainly distributed can be used, so that ammonia can be oxidized mainly to nitrous acid and prevented from being oxidized to nitric acid.

The present invention can also be characterized in that the aeration time is limited to the time when the ammonia oxidation is finished in the nitrification tank so that only ammonia is oxidized to nitrous acid, and the aeration time is preferably 2 to 4 hours.

In the present invention, the dissolved oxygen concentration of the nitrification microbial granule reactor is preferably about 2mg / L, the free ammonia concentration of the nitrification microbial granule reactor is preferably 0.1 ~ 2000mg / L. The free ammonia concentration can be obtained by appropriately adjusting the initial ammonia concentration, pH or water temperature.

Hereinafter, the present invention will be described in more detail with reference to Examples. These examples are only for illustrating the present invention, it will be apparent to those skilled in the art that the scope of the present invention is not to be construed as being limited by these examples.

Example 1: Preparation of Nitrified Microbial Granules

In addition to the reactors made of acrylic circular tubes, pumps for injecting wastewater containing pH regulators and ammonia, blowers for air supply, solenoid valves for supernatant and granule discharge, and automatic operation of the reactors A nitrified microbial granule can be prepared using a continuous batch reactor configured with a computer.

The reactor had a height of 200 cm and an outer diameter of 15 cm, and a solenoid valve for discharge of the supernatant and granules after precipitation was installed at the center height of the reactor and 100 cm, respectively. Air volume was controlled in the range 0.005 ~ 0.2m / s using a control valve, the pH in the reactor was kept constant in the range 7.0 ~ 8.0.

The operation was started by inoculating wastewater sludge containing nitrification microorganisms into the reactor and injecting wastewater containing ammonia into the reactor. The operation sequence of the continuous batch reactor was repeated in the order of ammonia wastewater injection, nitrification, precipitation, supernatant discharge, and in some cases, the granule of the reactor may be withdrawn after the supernatant discharged. The ammonia concentration of the influent wastewater can be operated up to 2000mg / L above 100mgN / L, and can be diluted when the ammonia concentration is above. Inorganic carbon source for the cell structure of the nitrification microorganisms with ammonia _{^{(HCO 3 -, CO 3 2-}} ) requires this, and supplies the NaHCO ₃ or Na ₂ CO ₃ as the inorganic carbon source. The concentration of these inorganic carbon sources should be at least 500 mg / L, and additional inorganic carbon sources multiplied by ammonia concentration of 7.13 (based on CaCO ₃ ) should provide sufficient carbon sources for the prevention of pH reduction and cell synthesis by nitrification. can do. Other inorganic materials were used in the composition ranges shown in Table 1 below.

Composition of Wastewater for Preparation of Nitrified Microbial Granules ingredient density ingredient density CaCl ₂ · 2H ₂ O 7-70 mg / L NaHPO ₄ · 12H ₂ O 20-200 mg / L FeCl ₃ · 6H ₂ O 5-50 mg / L MgSO ₄ H ₂ O 5-100 mg / L KCl 5-50 mg / L KH ₂ PO ₄ 10-100 mg / L

While maintaining the sedimentation time of the continuous batch reactor at 10 ~ 60m / h was operated to selectively accumulate granules of good nitrifying microorganisms, the precipitated nitrifying microorganism granules were taken out. The withdrawn nitrifying microbial granules can be transferred directly to another bioreactor where nitrification occurs or can be stored elsewhere and used as needed.

Example 2: Characterization of Nitrification and Nitrite Accumulation in Wastewater in a Batch Bioreactor by Nitrifying Microbial Granules

The nitrification experiment of wastewater in a continuous batch bioreactor was carried out using the nitrification microorganism granules prepared in Example 1 above. The continuous batch bioreactor was made of a 3 L cylinder, with ammonia inflow (5 minutes)-aeration and nitrification (2 hours 40 minutes)-sedimentation (1-3 minutes)-treated water discharge (5 minutes)-sludge withdrawal And atmosphere (7-9 minutes) and one cycle was 3 hours. The treated water discharged 1.5L, which is 1/2 of the total reactor volume, so that the overall hydraulic retention time of the wastewater was maintained at 6 hours. The ammonia nitrogen concentration of the wastewater used in the experiment was 200 mg / L, NaHCO ₃ 1.2 g / L, MgSO ₄ · H ₂ O 5 mg / L, KCl 7 mg / L, NaHPO ₄ · 12H ₂ O 29 mg / L, CaCl ₂ 2H ₂ O 7mg / L, KH ₂ PO ₄ 11mg / L, FeCl ₃ · 6H ₂ O 1mg / L, pH and temperature of the reactor were maintained at 7.3 ~ 7.5 and 28 ± 1.0 ° C, respectively. Oxygen required for nitrification flowed air to the diffuser and dissolved oxygen was maintained at about 2mg / L, the nitrification microorganism granules of the reactor is about 2g / L nitrified microorganism granules prepared by the method of Example 1 based on dry weight Experiments were carried out while maintaining (FIG.

The concentration changes of ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen with reaction time in one cycle in the nitrification tank are shown in FIG. 3. First, it was confirmed that the ammonia oxidizing bacteria of the nitrification granules oxidized the ammonia nitrogen and converted to nitrite nitrogen, and the activity of the nitrite oxidizing bacteria was low at about 5 mg until most of the ammonia nitrogen was oxidized to the nitrite nitrogen. It was confirmed that nitrate nitrogen of about / L was produced.

Meanwhile, Partial nitrification of ammonia to nitrous acid alone provides about 25% more oxygen savings than nitric acid. In FIG. 1, about 90% of ammonia is accumulated as nitrite by nitrification granules, and only about 10% is completely nitrified to nitric acid. Therefore, by the chemical reaction equations of Tables 1 and 2, the net oxygen consumption is reduced by 22.5%, which is 90% of 25%.

Oxygen consumption at full nitrification ^{_{Energy reaction stoichiometry 100 NH 4 + +150}} O 2 → 200 H + +100 H 2 O + 100 NO 2 - (ammonia oxidizers) 100 NO 2 - +50 O 2 → 100 NO 3 - (nitrite oxidizers) ------ (One) ------ (2) NH ₄ ⁺ + O ₂ 200 100 200 → H ⁺ H ₂ O + 100 +100 NO ₃ ^- ------ (3)

Nitrification to Nitrite and Nitric Acid by Nitrification Granules ^{_{Energy reaction stoichiometry 100 NH 4 + +150}} O 2 → 200 H + +100 H 2 O + 90 NO 2 - (ammonia oxidizers) 10 NO 2 - + 5 O 2 → 10 NO 3 - (nitrite oxidizers) ------ (One') ------ (2') NH ₄ ⁺ + O ₂ 155 100 200 → H ⁺ H ₂ O +90 +200 NO ₂ ^- + NO ₃ 10 ^- ------ (3 ')

Deactivation of nitrite oxidizing bacteria in the nitrifying microorganism granules can be explained in three ways. First, the number of nitrite oxidizing bacteria is smaller than that of ammonia oxidizing bacteria, so the activity of nitrite oxidizing bacteria is relatively low. This is because only a part of the nitrite is oxidized from the reactor for producing granules, there is a lack of an energy source for the production of nitrite oxidizing bacteria, and thus the growth of the nitrite oxidizing bacteria itself is limited, thereby reducing the number of individuals. Second, most of the ammonia nitrogen in the waste water is in the form of NH ₄ ⁺ ions, but is in equilibrium with free ammonia (NH ₃ ) depending on pH and temperature conditions. Some existing NH ₃ inhibits the activity of ammonia oxidizing bacteria and nitrite oxidizing bacteria. In particular, nitrite oxidizing bacteria are inhibited even at low concentrations of 0.1 mgN / L, making them more unfavorable than ammonia oxidizing bacteria at the same concentration conditions. . For reference, free ammonia may be represented by Equation 1 as a function of ammonia ion, pH, and temperature.

(One)

K _a = equilibrium ionization constant of ammonia and nitric acid

K _w = ionization constant of water

K _a / K _w = e ^{(6334 / (273+ ??))}

Third, the distribution of nitrifying microorganisms in the granules shows that nitrite oxidizing bacteria are more predominantly distributed inside the granules than ammonia oxidizing bacteria, and the opportunity to use oxygen supplied from the outside of the granules is lower than that of the ammonia oxidizing bacteria. In addition, the substrate affinity (K _s ) for oxygen is also lower than that of ammonia oxidizing bacteria, which is in an unfavorable position than ammonia oxidizing bacteria in competition for using oxygen under the same conditions. This nitrite accumulation can be confirmed when the dissolved oxygen concentration of the bulk liquid is maintained at about 2 mg / L. For this reason, ammonia is first oxidized to nitrous acid and nitrous acid is oxidized to nitrate nitrogen after the ammonia oxidation is completed. Therefore, if the aeration time is limited to the end of ammonia oxidation in a continuous batch reactor, ammonia is mostly denitrified after being oxidized to nitrite nitrogen.

Example 3: Experiment on reduced oxygen consumption and organic matter

If the aerobic nitrification operation time of the continuous batch reactor is adjusted to the nitrite accumulation time, the ammonia can be operated to convert only to nitrous acid. 3 shows that nitrite is accumulated and converted to nitric acid during wastewater nitrification using nitrification microorganism granules. As shown in FIG. 3, when the continuous batch reactor is operated for 3 hours and terminated, nitrification close to 100% is achieved, about 90% of nitrite is accumulated, and about 10% of nitric acid is formed. If this is immediately introduced into the denitrification reactor with acetic acid, an external carbon source, denitrification by nitrous acid proceeds.

Figure 4 shows that the denitrification of nitrite accumulated during wastewater nitrification using nitrification microorganism granules. As shown in FIG. 4, when denitrifying nitrite accumulated by nitrifying microbial granules by injecting an external carbon source (acetic acid), the SCOD consumption / NO ₂ ^-- N removal ratio was 2.67 mgSCOD / mgNO ₂ ^-- N, and NO ₂ ^- higher than -N ^- -N removed during SCOD somobi of 2.295 mgSCOD / mgNO ₂ Considering the cell synthesis. This is because ammonia does not accumulate to 100% nitrous acid, some of which is completely nitrified to nitric acid and nitric acid consumes a lot of external carbon sources involved in denitrification.

Figure 5 shows the results of performing the denitrification test by artificially producing the nitrate wastewater to determine the amount of external carbon source consumed during the denitrification by the normal complete nitrification. When denitrification of 100 mg / L of nitric acid was injected with an external carbon source (acetic aicd), the SCOD consumption / NO ₃ ⁻ -N removal ratio was 4.05 mg SCOD / mgNO ₃ ⁻ -N. This value is almost similar to the SCOD consumption ratio of 3.75 ~ 4.05 mgSCOD / mgNO ₃ ^-- N in consideration of cell synthesis in NO ₃ ^-- N removal.

Comparing the results of FIGS. 4 and 5, the amount of SCOD consumed in nitrous acid denitrification was about 34% less than the amount of SCOD consumed in nitric acid denitrification. Although theoretically 40% carbon source can be saved, ammonia accumulates as 90% nitrite by nitrification and 6% error occurs due to denitrification in nitric acid form, but denitrification from nitrous acid is very economical in terms of saving carbon source. It can be seen that.

Having described the specific part of the present invention in detail, it is obvious to those skilled in the art that such a specific description is only a preferred embodiment, thereby not limiting the scope of the present invention. something to do. Thus, the substantial scope of the present invention will be defined by the appended claims and their equivalents.

As described in detail above, the nitrogen removal technology of the sewage and wastewater using the nitrification microorganism granules based on the ammonia oxidizing bacterium of the present invention oxidizes ammonia only to nitrous acid so that it can be directly denitrated, which is necessary for oxygen consumption and denitrification. The amount of organic matter can be significantly reduced. In addition, according to the present invention, since the nitrification and denitrification rates can be significantly faster than those via nitric acid, there is also an effect of reducing the volume of the bioreactor.

Claims (5)

Nitrogen removal method using nitrified microorganism granule comprising the following steps: (a) inhibiting the growth of nitrite oxidizing bacteria in the nitrifying microorganism granule reactor to prepare granules of nitrifying microorganisms mainly containing ammonia oxidizing bacteria; (b) nitrification step of oxidizing the granule of nitrifying microorganism into nitrification tank to oxidize ammonia nitrogen to nitric acid; (c) a denitrification step of converting nitrate nitrogen into nitrogen gas (N ₂ ) using denitrification microorganisms by introducing wastewater containing nitrate nitrogen obtained in the nitrification step into a denitrification tank; And (d) transferring the denitrified mixed liquor to the secondary settling tank to separate the treated water and the microbial sludge, and returning part of the microbial sludge to the nitrification tank or nitrification microbial granule reactor and partially disposing the sludge by concentration, digestion and dehydration. . The method of claim 1, wherein the step (a) of preparing the granules of nitrifying microorganisms comprises the following steps: (i) injecting wastewater containing a high concentration of ammonia into the culture substrate in a continuous batch method into a bioreactor containing nitrifying microorganisms; (ii) forming granules of nitrifying microorganisms while supplying oxygen for nitrification to a continuous batch reactor; (iii) stopping the oxygen supply to stop the reactor mixing, then settling the nitrified microorganism granules formed, and discharging the sludge that is not granulated; And (iv) withdrawing the precipitated nitrifying microbial granules. The method of claim 1, wherein the ammonia is mainly oxidized to nitrous acid and prevented from being oxidized to nitric acid so as to denitrate directly from nitrous acid to nitrogen. The method of claim 1, wherein the aeration time is limited to the time at which the ammonia oxidation ends in the nitrification tank so that the ammonia is oxidized to nitrous acid only. The method of claim 1 wherein the free ammonia concentration of the nitrifying microbial granule reactor is 0.1-2000 mg / L and the dissolved oxygen concentration is about 2 mg / L.