KR20000012818A - Waste water treatment method - Google Patents

Abstract

PURPOSE: A method for biological wastewater treatment is provided to remove effectively nitrogen contained in the wastewater and reduce the output of sludge. CONSTITUTION: The method is performed in a biological wastewater treatment apparatus comprising:an aeration tank(10) for decomposing organic materials in the wastewater with microorganisms; a sedimentation tank(30) for settling sludge produced in the aeration tank; and a denitrification tank(20) for denitrifying a wastewater returned from a wastewater feedback line for returning the wastewater processed at the aeration tank(10), wherein zeolite or diatom earth is introduced in the aeration tank(10).

Description

Waste water treatment method

The present invention relates to a wastewater treatment apparatus, and more particularly, to a new method for biological treatment of wastewater, which can effectively remove nitrogen in wastewater causing water eutrophication and reduce sludge generation.

In general, in the case of treating wastewater, the treated water is first discharged after removing solids, suspended solids, oils, and the like, and then physically, chemically or biologically treated according to the quality of the wastewater. Treated water purified through this process must satisfy the required water quality standards. In general water quality, the amount of BOD and COD is important, but the amount of nitrogen that acts as an important factor for water eutrophication is also important.

On the other hand, the nitrogen contained in the waste water is present in the form of NO ₂ ^-- N _, NO ₃ ^-- N, NH ₄ ⁺ -N or combined with organic substances, most of them in the form of NH ₄ -N. Nitrogen in these wastewaters is oxidized with NO ₃ and then denitrated with N ₂ to be removed. Therefore, in order to remove the nitrogen in the waste water, the above-mentioned types of nitrogen must be oxidized to NO ₃ .

However, the form of nitrogen or organic matter in NH ₄ -N form the wastewater is oxidized to NO ₃ by nitrogen oxide microorganisms, and the nitrification reaction by microorganisms is based on BOD / TKN (total kjeldahl nitrogen) It is greatly affected. In addition, according to the results of the present research, it is reported that nitrification by microorganisms is suppressed when BOD / TKN is 2.0 or more. Therefore, in order to promote nitrification by microorganisms, BOD should be lowered to create an environment in which nitrification by microorganisms can be effectively performed. However, at present, almost all sewage treatment plants in Korea are simply settled before biological treatment, so the BOD of influent water flowing into biological treatment process is not low. For this reason, the nitrogen in the waste water, in particular the NH ₄ -N type of nitrogen is not effectively oxidized, and thus the nitrogen contained in the waste water is not removed during the wastewater treatment and is discharged as it is.

On the other hand, sludge is generated in the treatment of waste water, and there is a problem in that the sludge generated at this time not only takes a separate cost but also a secondary environmental pollution caused by the sludge. Therefore, in recent years, various methods have been proposed to reduce the amount of sludge generated during the treatment of effluent, but have not been able to obtain satisfactory effects.

The present invention is to solve the above problems, an object of the present invention is to effectively remove the nitrogen in the waste water that causes the water quality can not only satisfy the water quality requirements for nitrogen but also the amount of sludge generated In addition, it is possible to reduce the volume of sludge generated together with the new method for biological treatment of wastewater, which can reduce the overall cost of sludge treatment.

1 is a schematic view showing a treatment process of waste water according to the present invention.

2 is a particle size distribution diagram of a floc produced by a conventional standard activated sludge method.

3 is a particle size distribution diagram of the flocs produced by the present invention

<Description of the symbols for the main parts of the drawings>

10. Aeration tank 20. Denitrification tank

30. Settling tank

According to the present invention, the aeration tank 10 for decomposing and removing the organic matter in the influent into microorganisms, the settling tank 30 for settling the sludge produced in the aeration tank 10, and the treated water is returned to the aeration tank 10 The treatment water transport line 50 is provided to be made in a biological treatment apparatus of waste water comprising a denitrification tank 20 to denitrify the treated water, the aeration tank 10, the waste water, characterized in that for injecting zeolite or diatomaceous earth A biological treatment method of is provided.

According to another feature of the present invention, by adding an inorganic coagulant such as alum (aluminum sulfate) or ferric chloride to the aeration tank 10, the biological treatment of wastewater, characterized in that the adsorption of phosphorus contained in the wastewater is removed. A method is provided.

According to another feature of the present invention, by mixing at least one or more of the zeolite or diatomaceous earth in the crayon glass or bentonite to the aeration tank 10 to increase the sedimentation of the microbial floc characterized in that the treatment method of waste water. This is provided.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. The present invention includes an aeration tank 10, a settling tank 30, as shown in Figure 1, a denitrification tank is formed in a front end portion of the aeration tank 10, the aeration tank between the settling tank 30 and the denitrification tank 20 The treated water treated in (10) is made in a biological treatment apparatus for wastewater in which a treated water conveying line 50 is returned to the denitrification tank 20.

The aeration tank 10 is the same as that used in a general biological treatment method, and is a reaction tank in which organic matter is decomposed by microorganisms. The inflow water flowing into the aeration tank 10 is removed from the primary settling tank 1 or the sedimentation basin or oil. In the present invention, zeolite or diatomaceous earth is added to the aeration tank 10. Since zeolite or diatomaceous earth introduced into the aeration tank 10 serves as a seed for microbial floc formation, a relatively large sized microbial floc is produced by the zeolite or diatomaceous earth.

The zeolite or diatomaceous earth is used having a particle diameter of 10 ~ 100㎛, when the particle size of the zeolite or diatomaceous earth is larger than 100㎛ seed of microbial flocs because the ion exchangeable inorganic material is less fluidity due to its specific gravity and settles at a rapid rate It does not perform its role effectively. If the particle size of the zeolite or diatomaceous earth is smaller than 10 μm, most of the zeolite or diatomaceous earth is suspended and flows out according to the inflow of the inflow, so even in this case, the zeolite or the diatomaceous earth does not effectively serve as a seed of the microbial flocs. Only results in increased turbidity.

The zeolite or diatomaceous earth is preferably added in such a manner that the concentration in the aeration tank 10 is maintained at 3500-4500 mg / l. When the concentration of zeolite or diatomaceous earth is higher than 4500 mg / l, the use of zeolite or diatomaceous earth is uneconomical, and when the concentration is lower than 3500 mg / l, the effect of zeolite or diatomaceous earth as described later is more than expected. Can't get it.

On the other hand, NH ₄ ⁺ -N is adsorbed on the microbial flocs produced by using zeolite or diatomaceous earth as seeds as described above by ion exchangeability of zeolite or diatomaceous earth. When NH ₄ ⁺ -N is coupled to the microbial flocs generated in the aeration tank 10 as described above, the TKN value around the microbial plaque increases, thereby reducing the BOD / TKN around the microbial plaque. Therefore, since the BOD / TKN which is actually encountered by microorganisms is reduced, the activity of nitrifying microorganisms becomes active, thereby promoting the oxidation reaction of NH ₄ ⁺ -N.

In this way, NO ₃ generated by nitrifying NH ₄ ⁺ -N is denitrified in the denitrification tank 20 to be removed by N ₂ . The denitrification tank 20 is formed by dividing a part of the front end of the aeration tank 10 and between the settling tank 30 and the degassing tank 20 so that the treated water treated in the aeration tank 10 can be returned to the denitrification tank 20. It consists of a circulating nitric oxide denitrification system in which the treatment water conveying line 50 is formed.

In addition, the microbial floes generated in the aeration tank 10 grow while oxidizing NH ₄ -N, and are precipitated in the precipitation tank 30. Of course, the microbial flocs oxidize not only NH ₄ ⁺ -N but also nitrogen bonded to organic matter.

On the other hand, in general, the dewatering property of the sludge is inversely proportional to the sludge specific resistance value α calculated as follows.

α =

(ε: porosity, S _P / V _P ; specific surface area, k: constant, ρ _P : density)

According to the above equation, if the porosity and density of the sludge is large, the specific resistance value of the sludge is lowered, so that the larger and denser the particles of the flocs produced in the aeration tank, the more dehydrated the sludge is. As described above, the microbial flocs generated in the aeration tank 10 according to the present invention are large and hard in overall by the seed role of zeolite and diatomaceous earth. Therefore, the sludge produced by the present invention is excellent in dehydration and thus excellent in concentration, thereby effectively reducing the volume of sludge discharged.

In general, solids retention time (SRT) is the time for sludge to stay in the aeration tank and sedimentation tank. In general, the longer the SRT, the less sludge is produced. However, if the SRT is long, the flocks are spattered and cracked to generate a small sized pin flop, which causes the pin flop to flow along the flow of the discharged water and does not effectively settle in the settling tank 30. Therefore, conventionally, the SRT cannot be made long enough.

However, since the microbial flocs produced in the present invention are large in size and hard due to the seed role of zeolite or diatomaceous earth as described above, pin flops are not generated even when the SRT is sufficiently long, and the precipitation is excellent. Therefore, in the method for treating wastewater according to the present invention, the SRT can be sufficiently long, and as a result, the amount of sludge generated is reduced.

In the general biological treatment method, the produced sludge is transported to the aeration tank 10 and reused. In the present invention, when the sludge is transported and used by the sludge conveying line 40, it is economical to obtain the effect of reusing zeolite or diatomaceous earth.

On the other hand, when the zeolite or diatomaceous earth is added to the aeration tank 10, an inorganic coagulant may be further added. As the inorganic coagulant, alum (aluminum sulfate) or ferric chloride is used, and it is preferable to add about 10 mg to 80 mg per 1 L of influent. When the inorganic coagulant is added in addition to zeolite or diatomaceous earth, phosphorus contained in the wastewater is adsorbed and removed from the inorganic coagulant. That is, while increasing the nitrification rate by the zeolite and diatomaceous earth, phosphorus can be effectively removed by the inorganic coagulant.

In addition, when zeolite or diatomaceous earth is thrown into the aeration tank 10, you may mix and throw in crayon glass or bentonite. The crana glass or bentonite is an ion-exchangeable material even though it is an inorganic material such as zeolite or diatomaceous earth, and when introduced into the aeration tank 10, the SRT can be set sufficiently long by increasing the settability of the microbial flocs. Preferably, crana glass or bentonite is mixed in a weight ratio of 1: 1 to 3: 1 based on the amount of zeolite or diatomaceous earth. That is, 1000-2000 mg / L of either crana glass or bentonite is thrown into 2000-3000 mg / L of zeolite or diatomaceous earth. If necessary, one or more of crana glass or bentonite may be mixed and added. When zeolite or diatomaceous earth is added to the aeration tank 10 in this way, when mixed with crana glass or bentonite, the amount of zeolite or diatomaceous earth, which is relatively expensive, can be relatively reduced, and the SRT can be set long enough to provide wastewater economically. Can be processed.

Comparative Example 1

Artificial wastewater was treated by a standard activated sludge process consisting of aeration tank and sedimentation tank. At this time, the residence time (HRT) in the aeration tank was 6 hours and the SRT was 10 days. As a result of analyzing the water quality of the treated water thus treated, it was as shown in Table 1 and Table 2.

Organic matter treatment rate Influent Concentration [mg / L] Treated water concentration [mg / L] Throughput [%] BOD ₅ COD _Cr BOD ₅ COD _Cr BOD ₅ COD _Cr Standard activated sludge method 169 25 30 43 82 83

Nitrification efficiency Influent Concentration [mg / L] Treated water concentration [mg / L] Nitrification Efficiency [%] T-N NO ₃ ^-- N T-N NO ₃ ^-- N Standard activated sludge method 68 0 64 14 22

Example 1

The artificial wastewater used in Comparative Example 1 was treated in a treatment device consisting of an aeration tank and a precipitation tank. At this time, zeolite and diatomaceous earth were injected into the aeration tank so as to have a concentration of 4000 mg / l, each having a different particle size. As a result of analyzing the water quality of the treated water thus treated, it was as shown in <Table 3> and <Table 4>.

Organic matter treatment rate Zeolite addition Particle Range [μm] Influent Concentration [mg / L] Treated water concentration [mg / L] Throughput [%] BOD ₅ COD _Cr BOD ₅ COD _Cr BOD ₅ COD _Cr 10 to 100 152 235 2.2 8.0 99 98 100-400 169 252 3.4 8.5 98 97 500 to 1000 165 243 5.2 12 96 95 Diatomaceous Earth Addition 10 to 100 152 235 2.5 14 98 97 100-400 169 252 2.8 9.4 98 96 500 to 1000 165 243 6.3 8.0 96 94

Nitrification efficiency Particle Range [μm] Influent Concentration [mg / L] Treated water concentration [mg / L] Nitrification Efficiency [%] T-N NO ₃ ^-- N T-N NO ₃ ^-- N Zeolite addition 10 to 100 68 0 61 61 100 100-400 60 0 52 49 94 500 to 1000 62 0 52 45 86 Diatomaceous Earth Addition 10 to 100 68 0 62 60 97 100-400 60 0 50 48 96 500 to 1000 62 0 51 84 97

Comparing the results of Comparative Example 1 and Example 1, it can be seen that the method according to the present invention is significantly superior in nitrification efficiency compared to the conventional standard activated sludge method. In addition, the method according to the present invention can be seen that the treatment efficiency of BOD _5, COD _Cr is also superior to the conventional standard activated sludge method.

In addition, when the particle size of the zeolite and the diatomaceous earth introduced into the aeration tank is 10-100㎛ it can be seen that the treatment effect and nitrification rate of the organic material is the best.

Example 2

The experiment was carried out under the same conditions as in Example 1, wherein the aeration tank was injected with zeolite and diatomaceous earth having a particle size of 10-100 μm, and the SRT was adjusted to 40 days for 10 days and 20 days, and the treatment efficiency according to the change of the SRT was tested. . As a result of analyzing the water quality of the treated water thus treated, it was as shown in Tables 5 and 6.

Organic matter treatment rate SRT [d] Influent Concentration [mg / L] Treated water concentration [mg / L] Throughput [%] BOD ₅ COD _Cr BOD ₅ COD _Cr BOD ₅ COD _Cr Zeolite 10 162 235 5.2 12 97 95 20 179 252 3.4 8.5 98 97 40 165 243 2.2 8.0 95 97 Add diatomaceous earth 10 162 235 6.3 14 96 91 20 179 252 2.8 9.4 98 96 40 165 243 2.5 8.0 98 97

Nitrification efficiency SRT [d] Influent Concentration [mg / L] Treated water concentration [mg / L] Nitrification Efficiency [%] T-N NO ₃ ^-- N T-N NO ₃ ^-- N Zeolite 10 68 0 61 58 95 20 60 0 52 52 100 40 102 0 93 91 98 Diatomaceous Earth Addition 10 68 0 62 54 88 20 60 0 50 48 96 40 102 0 92 89 97

In addition, in general, the standard activated sludge method can not treat the waste water by setting the SRT to 20 days or more, but by using the method according to the present invention it was possible to treat the waste water by setting the SRT long enough to more than 40 days.

Comparative Example 2

As a result of measuring the particle size distribution of the flocs produced in the aeration tank of Comparative Example 1 was as shown in FIG.

Example 3

As a result of measuring the particle size distribution of the flocks produced as a result of Example 2, the results were the same as those shown in FIGS.

As can be seen in Figures 2 and 3, which are the results of Comparative Example 2 and Example 3, the particle size of the sludge produced by the method according to the present invention is generally larger than the particle size of the sludge produced by the standard activated sludge method. And the particle size of the sludge produced in the present invention increases as the SRT increases.

Therefore, it can be seen from the results of Comparative Example 2 and Example 3 that the precipitation and dehydration properties of the sludge produced by the present invention are relatively excellent from the particle size distribution of the sludge produced by the method of the present invention.

Example 4

The sedimentation of sludge obtained in the experiments of Comparative Example 1 and Example 2 was evaluated by measuring the sludge sedimentation rate and SVI (Sludge Volume Index, sludge capacity index) for the initial 5 minutes. The results are shown in <Table 7>.

Sedimentation Rate and SVI According to SRT SRT Zeolite input Standard Activated Sludge Sedimentation rate SVI Sedimentation rate SVI [mm / s] [mL / g] [mm / s] [mL / g] 10 0.34 50-80 0.12 80-100 20 0.3 50-100 * 40 0.1 50-80 *

From the results of <Table 7>, it can be seen that the sludge settling rate of the sludge produced as a result of the treatment of wastewater by the addition of zeolite was significantly increased compared to the sludge settling rate produced by the standard activated sludge method. In general, when the SVI is 100 or less, the sludge settling property is excellent, and when the SVI is 200 or more, the sludge settling property is inferior. Able to know.

Example 5

The resistivity values of the sludges obtained as a result of Comparative Example 1 and Example 2 were calculated, and the results were as shown in <Table 8>.

SRT [d] Zeolite input Standard Activated Sludge Resistivity [m / kg] 10 2.2 × 10 ⁸ to 1.2 × 10 ⁹ 3.0 × 10 ¹¹ to 5.2 × 10 ¹¹ 20 7.2 × 10 ⁸ to 2.4 × 10 ⁹ * 40 5.1 × 10 ⁹ to 3.4 × 10 ¹¹ *

From the results of Table 8, comparing the specific resistance values of the sludge produced by the general activated sludge method and the method according to the present invention showed that the specific resistance value of the sludge produced by the method according to the present invention in which zeolite was added to the aeration tank was considerably low. . Therefore, it can be seen that the dewatering property of the sludge produced in the method according to the present invention is considerably superior to that of the sludge produced by the standard activated sludge method.

Zeolite and diatomaceous earth were injected into the activated sludge aeration tank to confirm the increase in nitrification efficiency and then applied to the cyclic nitrification denitrification process.

Example 6

An aeration tank and a sedimentation tank were formed, and a denitrification tank was formed at the front end of the aeration tank, thereby treating the same artificial wastewater as in Example 1 in a treatment apparatus equipped with a circulating nitric oxide denitrification system. At this time, a zeolite having a particle size of 10-100 μm was injected into the aeration tank, and the HRT in the denitrification tank and the nitrification tank was 2 hours, 4 hours, and the SRT was 40 days. In addition, when the amount of influent was set to 1Q, the sludge conveyed amount was 1Q and the internal conveyed amount was 3Q. The nitrogen removal rate of the treated water thus treated and the nitrogen removal rate obtained in Comparative Example 1 were as shown in <Table 9>.

Influent Concentration [mg / L] Treated water concentration [mg / L] Nitrogen removal rate [%] T-N T-N Circulation Nitrification Denitrification Method 62 15 75 Comparative Example 1 (Standard Activated Sludge Method) 68 64 6

As a result of Example 6, the zeolite was injected as in the present invention and applied to the cyclic nitrification denitrification process. As a result, a high removal rate of 75% was obtained with a short HRT of 6 hours. These results can be seen that the removal efficiency is significantly superior to the nitrogen removal rate of 6% by the conventional standard activated sludge method.

The method according to the present invention as described above is to increase the nitrification rate by the microorganism by adding zeolite or diatomaceous earth to the aeration tank during the biological treatment of the waste water to effectively remove the nitrogen contained in the waste water.

As described above, according to the present invention, by promoting the nitrification reaction by nitrifying microorganisms can effectively remove the nitrogen in the waste water and can reduce the amount of sludge generated to satisfy the water quality requirements for nitrogen as well as sludge The overall cost of removal can be reduced, providing a new economical biological treatment method for wastewater.

The wastewater treatment method according to the present invention increases the removal efficiency of nitrogen by activating the activity of nitrogen oxide microorganisms by injecting particulate inorganic matter in the conventional biological treatment process.

In addition, the microbial flocs produced in the present invention are produced by using the particulate inorganic material as a seed, and thus are relatively large in size and hard, and have a specific gravity. Therefore, the SRT can be set long enough to reduce the amount of sludge generated. In addition, since the microbial flocs produced in the present invention have a high specific gravity, the microbial flocs are precipitated at a higher speed than sludge produced in comparison with the conventional method, so that high-speed treatment of wastewater is possible without the need for additional treatment facilities. And the sludge produced in the present invention can be reduced to a minimum volume of the sludge generated because the particles are large, dehydration and excellent concentration. Therefore, the overall costs for sludge treatment can be reduced. Moreover, when conveying sludge and using it, the effect of reusing a zeolite can be acquired and it is economical.

Claims (3)

Aeration tank 10 for decomposing and removing organic matter in the influent into microorganisms, sedimentation tank 30 for settling sludge generated in the aeration tank 10, and a treated water conveying line to which the treated water treated in the aeration tank 10 is returned. (50) is provided in the biological treatment apparatus of waste water comprising a denitrification tank 20 is provided to denitrify the treated water, the aeration tank 10 biological treatment method of waste water, characterized in that the injection of zeolite or diatomaceous earth The biological treatment method of wastewater according to claim 1, wherein an inorganic coagulant such as alum (aluminum sulfate) or ferric chloride is additionally added to the aeration tank 10 to adsorb and remove phosphorus contained in the wastewater. According to another feature of the present invention, by mixing at least one or more of crana glass or bentonite in zeolite or diatomaceous earth to the aeration tank 10 characterized in that to increase the settling of the microbial floc The wastewater treatment method is provided.