JP2020099877A - Water treatment method and apparatus for wastewater containing nitrogen and organic matter - Google Patents

Abstract

To provide a technology to achieve a high T-N removal rate in a short treatment time for wastewater containing organic matter and Kjeldahl nitrogen while simultaneously treating the organic matter.SOLUTION: A water treatment method for simultaneously treating organic matter and Kjeldahl nitrogen in the water to be treated by passing water containing organic matter and Kjeldahl nitrogen through a treatment tank filled with a carrier under aerobic conditions, in which the ratio of the amount of BOD and Kjeldahl nitrogen flowing into the treatment tank (amount of BOD/Kjeldahl nitrogen) is maintained within a range of 8 or more.SELECTED DRAWING: Figure 1

Description

The present invention relates to wastewater treatment technology for biologically treating wastewater containing nitrogen and organic matter.

Conventionally, as a technique for performing a reaction that proceeds under aerobic conditions such as organic substance decomposition and nitrification in one treatment tank and a reaction that proceeds under anoxic conditions such as denitrification, there is a method of adjusting the aeration amount and aeration time. Widely known.

In Patent Document 1, by controlling the aeration time and performing intermittent aeration, an aerobic environment and an anoxic environment are alternately created, and organic matter decomposition, nitrification, and denitrification are performed in one tank to remove organic matter and nitrogen. The method is described.

In Patent Document 2, by controlling an aeration location and an aeration amount to simultaneously create an aerobic region and an anoxic region in the tank, organic matter decomposition, nitrification, and denitrification are performed in one tank to separate organic matter and nitrogen. The method of removal is described.

Patent Literature 3 discloses a method of removing organic matter and nitrogen by performing organic matter decomposition/nitrification/denitrification in a single tank by controlling the amount of aeration and performing operation management with extremely low DO (Dissolved Oxygen). Have been described.

Patent Document 4 describes a method of removing nitrogen by performing an nitrification/anammox reaction in a single tank by controlling the aeration amount and operating and controlling at an extremely low DO.

Japanese Patent Laid-Open No. 2015-009203 JP, 2013-103185, A JP, 2017-006894, A Japanese Unexamined Patent Publication No. 2017-077509

However, in the methods disclosed in Patent Documents 1 to 3, the processing time is low even if the TN (total nitrogen) removal rate is as low as 50 to 60%, or even if the TN removal rate is as high as 80 to 90%. The problem was that it was as long as 12 to 24 hours.
In addition, the method disclosed in Patent Document 4 has a problem that the organic matter contained in the water to be treated cannot be simultaneously removed.
In view of the above circumstances, the problem to be solved by the present invention is to provide a technique for simultaneously removing organic substances and nitrogen at a high rate in a short processing time.

The above problem is a water treatment method of simultaneously treating organic matter and Kjeldahl nitrogen in treated water by passing treated water containing organic matter and Kjeldahl nitrogen through a treatment tank under aerobic conditions filled with a carrier. The water treatment is characterized in that the ratio of the BOD (Biological Oxygen Demand) amount and the Kjeldahl nitrogen amount (BOD amount/Kjeldahl nitrogen amount) flowing into the treatment tank is kept in a range of 8 or more. Method or water to be treated containing organic matter and Kjeldahl nitrogen, by passing through a treatment tank under aerobic conditions filled with a carrier, a water treatment apparatus for simultaneously treating organic matter and Kjeldahl nitrogen in the water to be treated, The problem is solved by providing a water treatment device provided with means for keeping the ratio of the BOD amount flowing into the treatment tank and the Kjeldahl nitrogen amount (BOD amount/Kjeldahl nitrogen amount) within a range of 8 or more. The ratio of the BOD amount/Kjeldahl nitrogen amount indicates the mass ratio.

The BOD volume load applied to the treatment tank is preferably 5.5 kg/m ³ ·d or less.

As a means for keeping the BOD amount/Kjeldahl nitrogen amount in the range of 8 or more, it is preferable to add an organic substance to the treated water inflow line or the treatment tank.

Alternatively, as a means for keeping the BOD amount/Kjeldahl nitrogen amount in a range of 8 or more, it is preferable to provide a raw water adjusting tank in front of the treatment tank and add an organic substance into the raw water adjusting tank.

At this time, it is preferable that the carrier is a gel carrier composed of polyvinyl alcohol.

According to the present invention, in the treatment of wastewater containing organic matter and nitrogen, it is possible to provide a wastewater treatment technology that removes organic matter and nitrogen at a high rate in a treatment time that is much shorter than existing methods.

As an embodiment of the present invention, it is a schematic diagram of a processing system when adding an organic substance directly into a processing tank. As an embodiment of the present invention, it is a schematic diagram of a treatment system when an organic substance is added to a treated water supply line. As an embodiment of the present invention, it is a schematic diagram of a treatment system when an organic substance is added to a raw water conditioning tank provided in a preceding stage of the treatment tank.

In the present invention, it is an object of the present invention to promote three reactions of BOD decomposition, nitrification, and denitrification with high efficiency under aerobic conditions. As is generally known, BOD decomposition and nitrification require molecular oxygen, and thus proceed under aerobic conditions, whereas denitrification proceeds under nitric acid using nitric acid as an oxygen source. Therefore, in the present invention, by using a carrier capable of supporting microorganisms to the inside, coexisting an aerobic environment and anoxic environment in the carrier, three reactions of BOD decomposition, nitrification, and denitrification can be performed in a single tank. It is possible to proceed.

Further, it is known that the denitrification reaction generally requires an organic substance (BOD) as a hydrogen donor. However, in a tank under aerobic conditions, BOD decomposition rapidly progresses, BOD required for denitrification reaction is consumed, and denitrification does not proceed sufficiently. Therefore, in the present invention, a sufficient amount of BOD required for denitrification is supplied by maintaining the ratio of the BOD amount flowing into the treatment tank and the Kjeldahl nitrogen amount (BOD amount/Kjeldahl nitrogen amount) within a range of 8 or more. However, even if the BOD amount/Kjeldahl nitrogen amount is set to 8 or more in the ordinary activated sludge method or the like, denitrification does not occur because the BOD decomposition proceeds further. Therefore, in the present invention, by using a carrier capable of supporting microorganisms inside, an aerobic environment in which BOD decomposition and nitrification reaction proceed and an anoxic environment in which denitrification reaction proceeds are formed in the carrier under aerobic conditions. Not only BOD decomposition and nitrification but also denitrification can be advanced in the lower tank with high efficiency, and a high TN removal rate can be achieved.

The present invention is characterized in that the ratio of the BOD amount flowing into the treatment tank and the Kjeldahl nitrogen amount (BOD amount/Kjeldahl nitrogen amount) is maintained in a range of 8 or more.

By maintaining the ratio of the BOD amount flowing into the treatment tank to the Kjeldahl nitrogen amount (BOD amount/Kjeldahl nitrogen amount) in a range of 8 or more, a high TN removal rate in the treatment tank can be achieved in a shorter treatment time than before. (For example, in the examples described later, a BOD amount/Kjeldahl nitrogen amount=8 and a TN removal rate of 80% or more is achieved at a treatment time of 2.4 hours). On the other hand, if the ratio of the amount of BOD flowing into the treatment tank and the amount of Kjeldahl nitrogen is less than 8, the TN removal rate in the treatment tank will decrease.

From the viewpoint of preventing the occurrence of problems such as the generation of filamentous fungi and the unprocessed BOD due to BOD overload, which hinders the operation, the ratio of the BOD amount flowing into the treatment tank and the Kjeldahl nitrogen amount (BOD amount/Kjeldahl nitrogen amount) is 20 or less is preferable, 15 or less is more preferable, and 11 or less is further preferable.

The BOD volume load in the treatment tank is preferably 5.5 kg/m ³ ·d or less. If the BOD volume load exceeds the preferable range, there is a possibility that problems such as the generation of filamentous fungi may occur due to BOD overload, which may impair operation. The BOD volume load is more preferably 5 kg/m ³ ·d or less.

When the BOD amount of raw water/Kjeldahl nitrogen amount is 8 or more, it may be allowed to flow into the treatment tank as treated water without adjustment. When the ratio of BOD amount of raw water to Kjeldahl nitrogen amount (BOD amount/Kjeldahl nitrogen amount) is not within the range of 8 or more, the ratio of BOD amount and Kjeldahl nitrogen amount flowing into the treatment tank is calculated by the following method. Keep (BOD amount/Kjeldahl nitrogen amount) in the range of 8 or more. Here, raw water refers to factory effluent or sewage itself that has not been adjusted by adding chemicals, and treated water refers to effluent that actually flows into the treatment tank.

Examples of the adjusting method include a method of adding an organic substance to the treated water inflow line or the treatment tank, and a method of providing a raw water adjusting tank in the front stage of the treatment tank and adding the organic substance to the raw water adjusting tank.

The organic substance added in the adjusting method may be any organic substance that does not inhibit the activity of microorganisms, and examples thereof include alcohols such as methanol, organic acids such as acetic acid, and sugars such as glucose.

The timing of adding the organic substance in the adjusting method is preferably such that the BOD concentration of the water to be treated flowing into the treatment tank is constant. When an organic substance is added to the treated water inflow line or the treatment tank, it is preferable to continuously add a necessary amount represented by the following formula at a constant ratio. Further, when a raw water adjusting tank is provided in the front stage of the treatment tank and an organic substance is added to the raw water adjusting tank, the required amount shown by the following formula is continuously added at a constant ratio, or it flows into the treatment tank. It is preferable to add intermittently at a time interval such that the BOD concentration of the water to be treated becomes constant.

The BOD concentration of the water to be treated flowing into the treatment tank is preferably 600 mg/L or less, and more preferably 550 mg/L or less, from the viewpoint of sufficiently promoting the BOD decomposition.

By the adjustment method described above, the BOD amount (C) added to maintain the ratio of the BOD amount flowing into the treatment tank and the Kjeldahl nitrogen amount (BOD amount/Kjeldahl nitrogen amount) in the range of 8 or more is represented by the following formula (I) and Calculated according to (II).

A: Required treated water BOD concentration (mg/L), B: Raw water Kjeldahl nitrogen concentration (mg/L), C: Required BOD addition amount (kg/d) D: Raw water BOD concentration (mg/L), E: Raw water flow rate (m ³ /d)

Preferably Kjeldahl nitrogen volume loading in the processing bath is not more than 0.69kg / ^{m 3} · d, more preferably not more than 0.63kg / ^{m 3} · d.

From the viewpoint of sufficiently promoting nitrification and denitrification, the Kjeldahl nitrogen concentration in the treatment tank is preferably 75 mg/L or less, more preferably 65 mg/L or less.

The treatment time (HRT: hydraulic retention time) in the treatment tank is preferably 5 hours or less, and more preferably 4 hours or less from the viewpoint of miniaturization of the treatment tank. Further, in order to proceed the treatment sufficiently, it is preferably 1 hour or longer, more preferably 2 hours or longer.

Raw water to which the present invention is applicable includes sewage and industrial wastewater containing both organic matter and Kjeldahl nitrogen.

Raw water to which the present invention is applied has a relatively large amount of Kjeldahl nitrogen relative to the amount of BOD, for example, raw water having a ratio of BOD to Kjeldahl nitrogen of raw water (BOD amount/Kjeldahl nitrogen amount) of less than 8. However, the application of the present invention is more effective because the TN removal rate is remarkably improved by promoting the denitrification reaction.

In the present invention, a carrier capable of supporting microorganisms is placed in the treatment tank.

Examples of the microorganisms carried on the carrier include Nitroactor and Nittosomonas as bacteria involved in nitrification reaction, and Pseudomonas and Paracoccus as bacteria involved in BOD decomposition and denitrification.

As the carrier, a carrier that can support microorganisms on the surface and inside can be appropriately used, such as a carrier composed of an organic polymer such as PVA or PEG or a carrier composed of an inorganic substance such as activated carbon or ceramics.

The carrier may have any shape such as a sphere, a quadrangle, and a cylinder. A carrier having a fine structure on the surface and inside of the carrier and capable of supporting microorganisms on the surface and inside of the carrier is preferable. By supporting microorganisms on the surface and inside the carrier, a region near the surface of the carrier to which oxygen is easily supplied and a region inside the carrier that is low in oxygen or oxygen-free are formed, and organic matter decomposition proceeds under aerobic conditions. -This is because it is easy to simultaneously promote the nitrification reaction and the denitrification reaction that proceeds under anoxic conditions.

The equivalent spherical diameter of the carrier is preferably 1 to 10 mm. If the equivalent-sphere diameter is small, it is necessary to reduce the mesh size of the screen when a screen for preventing the carrier from flowing out is installed in the processing tank, which may cause clogging. Therefore, the equivalent spherical diameter is more preferably 2 mm or more. On the other hand, if the equivalent-sphere diameter exceeds 10 mm, the fluidity of the carrier may decrease. Therefore, the equivalent spherical diameter is more preferably 6 mm or less. Here, the equivalent sphere diameter is the diameter of a sphere having a volume equal to the volume of particles.

The specific gravity of the carrier is slightly larger than that of water, and it is preferable that the carrier can be swung in the treatment tank so that the carrier is not washed away. In the treatment method of the present invention, by using a carrier having a specific gravity slightly higher than that of water, wastewater can be treated more stably without causing the carrier to flow out. From this viewpoint, the specific gravity of the carrier is preferably 1.001 or more, more preferably 1.005 or more. On the other hand, the specific gravity is preferably 1.2 or less, more preferably 1.1 or less, and further preferably 1.05 or less.

The DO concentration in the communication hole changes depending on the distance from the surface of the carrier. Therefore, nitrifying bacteria are carried on the surface of the carrier under aerobic conditions, and denitrifying bacteria are carried inside the carrier under anoxic conditions. The pore size of the communication pores is preferably such that only bacteria can live inside the carrier. The pore diameter near the surface of the carrier is preferably 0.1 to 100 μm. If the pore size is less than 0.1 μm, bacteria may not be able to enter the carrier. The pore diameter near the surface is more preferably 0.5 μm or more. On the other hand, when the pore diameter near the surface exceeds 100 μm, large organisms other than bacteria may invade and the nitrification rate and denitrification rate may decrease. More preferably, the pore size is 50 μm or less. The diameter of the communication hole can be measured by a method such as observation using an electron microscope.

The volume ratio (filling rate) of the carrier to the tank volume can be appropriately determined according to the Kjeldahl nitrogen concentration of the waste water and the flow rate. The higher the packing rate of the carrier, the more efficiently the nitrification reaction and the denitrification reaction can proceed, but if the packing rate is too high, the fluidity of the carrier may decrease and the reaction efficiency may decrease. The filling rate is preferably 30% or less, and more preferably 25% or less. On the other hand, from the viewpoint of performing stable wastewater treatment in the treatment tank, the filling rate is preferably 5% or more.

As a method for supporting the microorganisms on the carrier, any method may be used as long as it can be immobilized on the carrier without impairing the biological activity of the microorganisms, and contains organic matter and Kjeldahl nitrogen in the acclimatization tank filled with the carrier and adjusted to aerobic conditions. The method of continuously injecting treated water to be treated, the method of entrapping separately cultivated BOD-decomposing bacteria, nitrification-related bacteria, and denitrifying-related bacteria in a carrier during entrapping To be

The pH in the treatment tank is preferably 5.0 to 9.0. When the pH is within this range, bacteria are likely to grow and the nitrification rate and denitrification rate tend to be maintained at an appropriate level. The pH is more preferably 5.5 or higher, and further preferably 6.0 or higher. On the other hand, the pH is more preferably 8.7 or less, further preferably 8.3 or less.

The temperature in the processing tank is preferably 10 to 40°C. When the temperature is within this range, bacteria are likely to grow and the nitrification rate and denitrification rate tend to be maintained at an appropriate level. The temperature is more preferably 20° C. or higher. On the other hand, the temperature is more preferably 35°C or lower.

The DO in the treatment tank is preferably 0.5 to 9.0 mg/L. If the DO is less than 0.5 mg/L, the nitrification rate may decrease. DO is more preferably 1.0 mg/L or more, further preferably 2.0 mg/L or more. On the other hand, if the DO exceeds 9.0 mg/L, the denitrification rate may decrease. DO is more preferably 8.0 mg/L or less, and further preferably 7.0 mg/L or less. The DO can be measured by a method such as a diaphragm electrode method.

<Example 1>
Biological treatment was performed using the following treated water and treatment equipment.
(Water to be treated) Sewage drainage BOD 250 mg/L, Kjeldahl Nitrogen 50 mg/L, BOD amount/Kjeldahl Nitrogen amount=8, methanol is added to the raw water adjusting tank to adjust BOD 400 mg/L, Kjeldahl nitrogen 50 mg/L. did. The inflow rate is 0.42 L/hr. At this time, the BOD volume load is 4 kg/m ³ ·d and the Kjeldahl nitrogen volume load is 0.5 kg/m ³ ·d.
At the time of the above adjustment, the calculation was performed as follows using the formulas (I) and (II) for the added BOD amount.

Target treated water BOD concentration (A)=Kjeldahl nitrogen concentration 50 mg/L (B)×8=400 mg/L
Required BOD addition amount (C)={(A)-raw water BOD concentration (D)}/1000×raw water flow rate (E) (m ³ /d)
= (400-250)/1000 x (0.42 x 24/1000)
= 0.0015 kg/d
=1.5 g/d

(Processing device) 0.2 L of carrier (filling rate 20%) was put into 1 L of the processing tank. The carrier used here is a spherical gel carrier made of polyvinyl alcohol. The equivalent sphere diameter of this carrier is 4 mm, the specific gravity is 1.025, and the diameter of the communication holes in the carrier is 0.5 to 20 μm.
An air diffuser is installed at the bottom of the treatment tank, and the water to be treated is aerated by the air sent from the blower connected to the air diffuser. A screen is installed at the outlet of the processing tank to prevent the carrier from flowing out.
The inside of the treatment tank is controlled at a temperature of 30±2° C., a pH of 7.5 to 8.3, and a DO of 4 to 7 mg/L.
The inflow rate of the water to be treated is 0.42 L/hr and the HRT is 2.4 hr.

The results of the biological treatment performed using the above-mentioned treated water and treatment equipment are as follows.
(Results) When the water quality of the treated water obtained from the outlet of the treatment tank was analyzed, BOD 9 mg/L, T-N 10 mg/L, NH4-N (ammonia nitrogen) 0.5 mg/L, NOx-N (nitric acid/nitrous acid) Nitrate nitrogen) became 5 mg/L. The BOD removal rate was 98% and the TN removal rate was 80%.

<Example 2>
Biological treatment was performed using the following treated water and the same treatment equipment as in Example 1.
(Water to be treated) Sewage drainage BOD 250 mg/L, Kjeldahl nitrogen 50 mg/L, BOD amount/Kjeldahl nitrogen amount=10, so that the required BOD amount is calculated by the above formulas (I) and (II) as in Example 1. After calculation, 2.5 g/d of methanol was added to the raw water adjusting tank to adjust the BOD to 500 mg/L and the Kjeldahl nitrogen to 50 mg/L. The inflow is 0.42 L/hr and the HRT is 2.4 hr. At this time, the BOD volume load was 5 kg/m ³ ·d and the Kjeldahl nitrogen volume load was 0.5 kg/m ³ ·d. (Results) When the water quality of the treated water obtained from the outlet of the treatment tank was analyzed, it was BOD 9 mg/L, T-N 8 mg/L, NH4-N 0.4 mg/L, NOx-N 4 mg/L. The BOD removal rate was 98% and the TN removal rate was 84%.

<Example 3>
Biological treatment was carried out using the following treated water and the same treatment equipment as in the examples.
(Water to be treated) To obtain BOD amount/Kjeldahl nitrogen amount=12 for sewage drainage BOD 250 mg/L and Kjeldahl nitrogen 50 mg/L, the required BOD amount is calculated by the above formulas (I) and (II) in the same manner as in Example 1. After calculation, 3.5 g/d of methanol was added to the raw water adjusting tank to adjust the BOD to 600 mg/L and the Kjeldahl nitrogen to 50 mg/L. The inflow is 0.42 L/hr and the HRT is 2.4 hr. At this time, the BOD volume load is 6 kg/m ³ ·d and the Kjeldahl nitrogen volume load is 0.5 kg/m ³ ·d.
(Result) When the water quality of the treated water obtained from the outlet of the treatment tank was analyzed, it was BOD 10 mg/L, T-N 15 mg/L, NH4-N 9 mg/L, NOx-N 0.4 mg/L. The BOD removal rate was 98% and the TN removal rate was 70%. Under this condition, although the TN removal rate was improved to 70%, a large amount of filamentous fungi was generated in the treatment tank due to the high load of BOD.

<Comparative Example 1>
Biological treatment was performed using the following treated water and the same treatment equipment as in Example 1.
(Water to be treated) Sewage drainage BOD 250 mg/L and Kjeldahl nitrogen 50 mg/L were used as they were. The inflow is 0.42 L/hr and the HRT is 2.4 hr. The BOD volume load at this time is 2.5 kg/m ³ ·d, and the Kjeldahl nitrogen volume load is 0.5 kg/m ³ ·d.
(Results) When the water quality of the treated water obtained from the outlet of the treatment tank was analyzed, it was BOD 9 mg/L, T-N 26 mg/L, NH4-N 0.5 mg/L, NOx-N 24 mg/L. The BOD removal rate was 96% and the TN removal rate was 48%.

<Discussion>
From the results of the above Examples and Comparative Examples, by maintaining the ratio of the BOD concentration of the water to be treated and the Kjeldahl nitrogen concentration at 8 or more, a high TN removal rate could be achieved in a short treatment time. Further, comparing Examples 1 and 2 with Example 3, in Examples 1 and 2, generation of filamentous fungi is suppressed, and more stable operation is possible.

1 Treatment Tank 2 Raw Water Conditioning Tank 3 Treated Water and Treated Water Line 4 Treated Water and Treated Water Line 5 Addition BOD and BOD Addition Line 6 Carrier 7 Screen 8 Diffuser 9 Blower 10 Raw Water Pump

Claims (9)

A water treatment method for simultaneously treating organic matter and Kjeldahl nitrogen in treated water by passing water to be treated containing organic matter and Kjeldahl nitrogen through a treatment tank filled with a carrier under aerobic conditions, wherein the treatment A water treatment method characterized in that the ratio of the BOD amount flowing into the tank to the Kjeldahl nitrogen amount (BOD amount/Kjeldahl nitrogen amount) is kept in a range of 8 or more. The water treatment method according to claim 1, wherein the BOD volume load applied to the treatment tank is 5.5 kg/m ³ ·d or less. The water treatment method according to claim 1 or 2, wherein an organic substance is added to a treated water inflow line or a treatment tank as a means for maintaining the BOD amount/Kjeldahl nitrogen amount in a range of 8 or more. The water treatment method according to claim 1, wherein a raw water adjusting tank is provided in front of the treatment tank, and an organic substance is added to the raw water adjusting tank as a means for keeping the BOD amount/Kjeldahl nitrogen amount in a range of 8 or more. The water treatment method according to claim 1, wherein the carrier is a gel carrier composed of polyvinyl alcohol. A water treatment device for simultaneously treating organic matter and Kjeldahl nitrogen in water to be treated by passing water to be treated containing organic matter and Kjeldahl nitrogen through a treatment tank filled with a carrier under aerobic conditions. A water treatment device comprising means for keeping the ratio of the BOD amount flowing into the tank to the Kjeldahl nitrogen amount (BOD amount/Kjeldahl nitrogen amount) within a range of 8 or more. The water treatment apparatus according to claim 6, wherein the BOD volume load applied to the treatment tank is 5.5 kg/m ³ ·d or less. As a means for maintaining the BOD amount/Kjeldahl nitrogen amount in the range of 8 or more, a means for adding organic substances to the treated water inflow line or the treatment tank or a raw water adjusting tank provided in the preceding stage of the treatment tank is provided in the raw water adjusting tank. The water treatment device according to claim 6 or 7, further comprising means for adding an organic substance. The water treatment device according to claim 6, wherein the carrier is a gel carrier composed of polyvinyl alcohol.