KR101345642B1 - Method for removing nitrogen in waste water - Google Patents

Abstract

The present invention relates to a method for removing nitrogen in wastewater using a continuous batch reactor, and more particularly, to a method for removing short-circuit nitrogen in wastewater in which a nitrite nitrogen accumulation step and a denitrification step are continuously performed.

Description

How to remove nitrogen in waste water {Method for removing nitrogen in waste water}

The present invention relates to a method for removing nitrogen from wastewater using a continuous batch reactor, and more particularly, to a method for removing uniaxial nitrogen from wastewater in which a nitrite nitrogen accumulation step and a denitrification step are continuously performed.

Recently, due to excessive development policy and industrialization, most of the nutrients in the wastewater which have not been removed in the first and second treatments are discharged without being removed, causing problems in the appeal water quality environment. In particular, nitrogen and phosphorus are released, causing the eutrophication. Since 1996, Korea has introduced advanced treatment for nitrogen and phosphorus in sewage treatment plants by setting the standard of discharged water quality and mandatory removal of nitrogen and phosphorus with 60mg / L of nitrogen and 8mg / L of phosphorus. Korea's multi-purpose dams are used as important water sources, but due to the excessive development policy and industrialization, they are introduced into river lakes contaminated with various wastewaters. Recently, lake eutrophication has become a serious problem.

The eutrophication is caused by the increase of nutrients in the water bodies, which are considered to be the floating and organic substances, which are the representative pollutants that cause water pollution, and the effective removal of these substances has long been the goal of sewage treatment.

The activated sludge method has been used as a representative biological wastewater treatment method, which is a wastewater treatment method applied for the second treatment of the first treated wastewater or to treat the wastewater that has not been subjected to the first treatment. In general, the activated sludge method grows as microorganisms ingest and decompose organic matter in the wastewater and nitrate as the wastewater is injected into an aeration tank. The grown microorganisms are aggregated and precipitated in the settling tank, and some of the precipitate is returned to the aeration tank in the form of activated sludge, and some waste sludge is discarded, so that the amount of microorganisms in the aeration tank is maintained at an appropriate level to decompose organic matter in the wastewater and nitrogen, phosphorus, etc. Removal is done.

Activated sludge has an excellent effect in treating organic matter in wastewater, but it is not suitable for effective removal of organic matter and nitrogen from wastewater containing high concentrations of organic matter and nitrogen at the same time.

Therefore, various biological nitrogen and phosphorus removal methods have been developed to improve the problem of activated sludge method. Biological Nutrient Removal (BNR) is basically a technique that induces nitrification and denitrification by alternating anoxic-aerobic conditions. Biological nitrogen treatment technology can remove the phosphorous (phosphorous) component with a slight modification, so BNR is usually referred to the simultaneous removal of nitrogen and phosphorus. Existing BNR techniques include oxidative sphere method, activated sludge method, A / O (Anaerobic + Oxic) method, A ² O (Anaerobic + Anoxic + Oxic) method, Badenpho method, UCT (University of Cape Town) method, VIP (Virginia Initiative Plant) process and the like are well known, these techniques are evaluated as a technology that can be treated simultaneously with nitrogen and phosphorus without a significant cost compared to the conventional activated sludge method. However, the understanding of biochemical theory and process design of the biological nitrogen and phosphorus treatment technology is not yet complete, and there is still a great need for improvement in this respect.

Japanese Patent Publication 2006-122771 Japanese Patent Publication 2004-154700

The problem to be solved by the present invention while reducing the optimum, and the treatment site using a SBR with reduced nitrogen removal process for the waste water is relatively low nitrogen concentration, and the optimum NO ₂ -N accumulation condition in accordance with the properties of the waste water The dilution ratio and dissolved oxygen concentration can be easily adjusted to provide a partial nitrification process effectively, and to provide a method for shortening nitrogen of wastewater to reduce the amount of sulfur consumed in the denitrification step.

In order to achieve the first object, the present invention provides a method for removing nitrogen from wastewater using a continuous batch reactor,

1) introducing waste water;

2) nitrite nitrogen accumulation step of heterotrophic denitrification and partial nitrification of the introduced wastewater;

3) a denitrification step in which autotrophic denitrification occurs after the nitrite nitrogen accumulation step; And

4) after the denitrification step to discharge the nitrogen-removed effluent water provides a method for removing short-circuit nitrogen of the waste water, characterized in that is carried out continuously.

According to one embodiment of the invention, the step 1) nitrite nitrogen accumulation step is

i) an anaerobic step of denitrifying by changing the nitrous nitrogen into a gas using an organic material in the influent as an electron donor;

Ii) an aeration step of oxidizing ammonia after the anoxic step;

Iii) settling the microorganisms under aerobic conditions after the aeration step; And

Iii) drawing only a certain flow rate in a state in which sludge and supernatant in the influent water are separated after the precipitation step;

Also, according to one embodiment of the invention, the 2) sulfur denitrification step is 1) H ₂ S, HS the nitrite generated in the step of as an electron acceptor, and present in the inlet water ^- as an electron donor ^-, Fe ² It is characteristic that denitrification takes place by using.

In addition, the method for removing short-circuit nitrogen of waste water according to the present invention may further include the step of replenishing dissolved oxygen (DO) in the effluent by placing an aeration tank after the denitrification step.

Nitrogen removal method according to the present invention is most suitable as a uniaxial nitrogen removal process for wastewater having a relatively low nitrogen concentration, and since the reactors occur sequentially in one reactor during SBR operation, the area of the site can be reduced, which is advantageous in small facilities such as small and medium sized enterprises. Do.

In addition, H ₂ S, which can be adjusted to facilitate dilution and the concentration of dissolved oxygen in accordance with the optimum NO ₂ -N accumulation condition in accordance with the properties of the waste water can be achieved at the best part of the nitrification process, present in the influent HS ^-, Since Fe ^{2 -} and the like are used as electron donors, it is useful to reduce the amount of sulfur consumed in the denitrification step.

1 is a process flowchart of a nitrogen removal method of wastewater according to an embodiment of the present invention.
2 is a schematic diagram of a denitrification reactor used in Example 2 of the present invention.
3 is a graph showing the water quality for each unit process according to Example 3 of the present invention.

Hereinafter, the present invention will be described in detail.

Ammonia nitrogen in sewage water is generally treated by biological treatment by a two-step process of nitrification-denitrification. That is, in the nitrification step, ammonium nitrite (NO ₂ ⁻ ) → nitric acid (NO ₃ ⁻ ) is converted by aerobic nitrification bacteria. Nitric acid nitrogen is reduced by denitrifying microorganisms using organic substances such as methyl alcohol or inorganic substances such as sulfur as electron donors and released into the atmosphere as nitrogen gas. However, in the conventional nitrogen treatment, a large amount of oxygen and organic matter required in the nitrification-denitrification process cause an increase in treatment cost.

In the present invention, in order to solve the problem of excessive oxygen and carbon source pointed out in the conventional BNR technology, a method of oxidizing ammonia nitrogen to nitrite nitrogen rather than nitrous nitrogen is introduced and then denitrification using an organic material as an electron donor. . Using this process requires about 25% less oxygen and about 40% less organic matter required for denitrification.

In addition, in order to overcome the necessity of warming and short SRT, which is pointed out as a problem of the conventional SHARON technology in the partial nitrification process, a selective inhibition by free ammonia and a selective growth restriction method by low DO concentration are used.

By using a selective growth inhibition technique with low DO concentration, it is distinguished from other partial nitrification techniques using only selective inhibition by preammonia, which can lower the ammonia concentration in the treated water. In addition, in the biofilm process, partial nitrification is possible, and thus the nitrification rate can be enhanced.

In addition, in the present invention, in order to solve the problem of supply of expensive organic carbon source remaining in the existing partial nitrification, denitrification technology, a combination of autotrophic denitrification using sulfur. By linking the denitrification technology to the partial nitrification process, the problems of excessive alkalinity consumption and sulfate generation pointed out in the existing denitrification technology are alleviated.

Ultimately, the present invention combines the advantages of partial nitrification with the advantages of denitrification, which can reduce energy costs required for oxygen supply by about 25% and organic carbon sources by more than 40% compared to conventional nitrogen treatment technologies.

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. It will be apparent to those skilled in the art, however, that these examples are provided to further illustrate the present invention, and the scope of the present invention is not limited thereto.

Example  One: Nitrite  Nitrogen accumulation stage

Conventionally, a continuous flow reactor was used mainly for partial nitrification, but the embodiment according to the present invention used a sequencing batch reactor (SBR). SBR has an advantage that the concentration of free ammonia (FA) is also increased since the initial ammonia concentration is maintained higher than that of the continuous flow reactor, and thus it is easy to implement partial nitrification using FA in low concentration ammonia wastewater. In addition, it is easy to find the end point where nitrous oxidation is terminated and nitrification starts, so that partial nitrification rate can be improved.

A specific continuous batch reactor is shown in FIG. 1. As shown in FIG. 1, first, when wastewater is introduced into a reactor (S1), a nitrite nitrogen accumulation step (S2) in which heterotrophic denitrification and partial nitrification of the introduced wastewater is performed is performed.

The nitrite nitrogen accumulation step (S2) is an anaerobic step (S201) of denitrifying by changing the nitrite nitrogen into a gas using the organic material in the influent as an electron donor (S201); An aeration step (S202) of oxidizing ammonia after the anoxic step; Settling the microorganisms under aerobic conditions after the aeration step (S203); And a step (S204) of drawing only a predetermined flow rate in a state in which the sludge and the supernatant in the influent water are separated after the precipitation step.

According to the present invention, there is no need to separately install an organic reaction tank (dissolved oxygen removal tank) before and after partial nitrification, and the throughput can be determined according to the amount of electron donors in the influent, thereby providing a smooth operation for fluctuations in quantity and water quality. The advantage is that it is possible.

The reactor was operated in a wastewater treatment plant of a factory producing semiconductors. Most of the nitrogen from the influent was ammonia nitrogen and the concentration was about 100 ~ 150 mg / L. Organic matter concentration was less than 50 mg / L, C / N ratio was low, about 0.3 ~ 0.5, and suspended solids concentration of influent was low, below 10 mg / L.

The total volume of the SBR reactor was operated at 2 m ³ . The operation cycle was operated in the inflow stage (30 minutes), the anaerobic stage (2-5 hours), the aeration stage (1-6 hours), the precipitation stage (1 hour) and the outflow stage (30 minutes). The anoxic stage time is changed in operation time in consideration of denitrification when organic matter is present in the influent. The aeration phase time is an important driving factor for the accumulation of nitrous nitrogen. Therefore, the operation time of the aeration step was operated by changing the operation time in consideration of the accumulation rate of nitrite nitrogen according to the oxidation time of ammonia nitrogen.

In the outflow step of the SBR reactor, 1/2 of the supernatant of the reactor was discharged and introduced in consideration of the loss of microorganisms. Therefore, the concentration of influent water is 50% diluted since it is combined with the quantity remaining in the reactor after completion of the inflow stage. In order to adjust the pH of the influent water, it is adjusted to pH 8.5 by using 33% NaOH and 10% H ₂ SO ₄ in the inflow stage and the anoxic stage so that the FA concentration can be started at about 10 mg / L. Drive. Since the alkalinity required for nitrification of the ammonia nitrogen concentration contained in the raw water was not sufficient, NaHCO ₃ stock solution was supplied with the influent water at the inflow stage. The amount of alkalinity was injected to allow CaCO ₃ of 360-500 mg / L concentration, considering that the average ammonia nitrogen concentration was about 50-70 mg N / L after the end of the inflow.

The inoculated sludge was inoculated with the return sludge of the activated sludge tank of the nearby sewage treatment plant. During the operation period, no sludge disposal was made to control the SRT. The temperature was maintained at 28 ℃ using a heater installed in the SBR reactor and dissolved oxygen concentration was maintained at 1.5 ~ 2 mg / L in the aeration step.

Example  2: Desulfurization  step

When the nitrite nitrogen accumulation step is completed in Example 1, the denitrification process proceeds while passing through the sulfur particle column through a reservoir. As shown in FIG. 1, in the denitrification step S3, autotrophic denitrification is performed, and the nitrogen removal process of the wastewater is performed while the step S4 of discharging the effluent removed from nitrogen after the denitrification step is performed continuously. Is completed.

In this embodiment, after the nitrogen in the wastewater oxidation with nitric acid to the wastewater advanced treatment method using a sulfur denitrifying autotrophic microorganisms sulfur compounds as an electron donor for the denitrification ^{(S 2 -, S, S} 2 O 3 2 -, S 4 O 6 ^{2 -,} SO ₃ ^{2 -} a technique using a) is used. Sulfur compounds (particularly sulfur particles) are inexpensive compared to organic carbon sources, thus enabling economic denitrification.

As such, since H ₂ S or the like is used as an electron donor for denitrification, the present invention does not require an intermittent aeration to control H ₂ S.

In addition, by disposing the aeration tank (S4) after the denitrification tank and immediately before the discharge, it is possible to exclude the possibility of dissolved oxygen depletion and anaerobic odor occurrence in the inflow stream, and the storage tank (S301) for stable operation of the denitrification reactor. ) Is preferable.

The denitrification reactor was made in column form and the total volume was made in 50 liters. The yellow carrier was filled with a carrier purchased from Jeon Tech. The carrier is a molten CaCO ₃ with sulfur in the carrier synthesis step, there is a feature that does not need to separately inject the alkalinity required for denitrification. The size of the carrier was 20-40 mm and about 80% was charged to the reactor in the apparent volume. Inflow was operated according to the change of residence time using a metering pump. It was operated in a bottom-up manner that flowed in from the bottom of the reactor and exited to the top. A perforated plate was installed at a height of 10 cm below the denitrification reactor, and a yellow carrier was charged thereon. The position of the inlet valve serves to install the lower portion of the porous plate so that the inflow water can be uniformly transferred from the lower portion of the porous plate to the upper portion. In addition, the outlet valves were installed at regular intervals from the bottom to enable water quality analysis by height. The whole reactor was wrapped with a heating wire and insulation, and a temperature controller was installed on the heating wire to maintain 25 to 28 ° C.

Experimental Example  1: Measurement result of nitrogen removal rate of waste water

FIG. 3 shows the results of water quality analysis for each unit process as a result of a combination of short-nitrogen nitrogen and denitrification for real wastewater generated in a semiconductor production process.

SBR _in is the result of water quality analysis _in the aeration stage. As described above, the total nitrogen of the influent water is mostly present as ammonia nitrogen, and there is no separate organic nitrogen. The influent is diluted in half because it is combined with the remaining water in the entire cycle as it enters the SBR.

The total concentration of nitrogen _in SBR _in at the start of the aeration step was 100 mg / L, which was 70 mg / L for ammonia nitrogen and 30 mg / L for nitrous nitrogen, with trace amounts of nitrate nitrogen. . The average concentration of total nitrogen in SBR _out after the aeration step was almost the same as _in SBR _in , but the average concentration of ammonia nitrogen decreased to about 35 mg / L, which showed 50% nitrification efficiency and about 70 nitrite nitrogen. Increasing to mg / L, the accumulation rate was more than 95%.

The reason that the total N concentrations are the same _in SBR _in and SBR _out means that heterotrophic denitrification with organics did not occur in the anaerobic phase because the organic concentration of the influent was very low. Assuming that 100% denitrification occurs, the nitrite nitrogen concentration _in SBR _in is close to zero and the total nitrogen concentration and ammonia nitrogen concentration are the same because nitrite nitrogen is excluded from the total nitrogen.

On the other hand, the ammonia nitrogen of SBR _in was nitrified in the aeration stage and converted to nitrite nitrogen in SBR _out . Nitrous acid nitrogen remains at an average concentration of 30 mg / L _in SBR _in because it is diluted 1/2 of the influent in the next cycle and there is no denitrification in the anoxic stage.

Nitrite nitrogen accumulated in SBR _out was denitrified from sulfur oxidation denitrification (SOD), resulting in more than 90% treatment efficiency, and total nitrogen concentration was decreased by denitrified nitrite nitrogen. There was no treatment of ammonia nitrogen introduced in the shear.

The effluent quality criteria of the wastewater treatment plant where this experiment was conducted was 60 mg / L of total nitrogen concentration, and the average total concentration of nitrogen in the final effluent that passed through the denitrification process was 35 mg / L or less, and the standard deviation was 60 mg / L. Stable treatment water quality was maintained below L. As a result of processing only as much as necessary within the standard value, it was operated with the minimum economic loss required for overtreatment. If lower effluent standards are desired, this can be achieved by adjusting the reaction time (Aeration stage of SBR), and desulfurization reactors can also be designed accordingly.

Claims (5)

In the method of removing the nitrogen of the waste water by using a continuous batch reactor,
1) introducing waste water;
2) nitrite nitrogen accumulation step of heterotrophic denitrification and partial nitrification of the introduced wastewater;
3) a denitrification step in which autotrophic denitrification occurs after the nitrite nitrogen accumulation step; And
4) characterized in that the step of discharging the nitrogen-free effluent after the denitrification step is carried out continuously,
The nitrite nitrogen accumulation step is
i) an anaerobic step of denitrifying by changing the nitrous nitrogen into a gas using an organic material in the influent as an electron donor;
Ii) an aeration step of oxidizing ammonia after the anoxic step;
Iii) settling the microorganisms under aerobic conditions after the aeration step; And
And iii) drawing only a certain flow rate in a state in which sludge and supernatant in the influent water are separated after the precipitation step. delete The method of claim 1,
In the step 2) denitrification, nitrite nitrogen produced in step 1) is used as an electron acceptor, and denitrification is performed using H ₂ S, HS ^- and Fe ^{2 -} present in the influent as an electron donor. Nitrogen removal method. The method of claim 1,
3) The method for removing uniaxial nitrogen of waste water, characterized in that the storage tank is installed in the denitrification reactor. The method of claim 1,
The method of claim 1, further comprising replenishing the dissolved oxygen (DO) of the effluent by placing the aeration tank after the denitrification step.

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