JP2007296499A - Waste water treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a fluidized bed-type nitrogen-containing waste water treatment process. <P>SOLUTION: An embodiment of the method for treating nitrogen-containing waste water comprises a nitration step of oxidizing an ammonia form of nitrogen and an organic nitrogen contained in nitrogen-containing waste water with nitrifying bacteria to a nitric acid form of nitrogen or a nitrous acid form of nitrogen, a denitration step of adding a hydrogen donor to treatment water in the nitration step and exposing the treatment water to anaerobic conditions to reduce the nitric acid form of nitrogen and the like with denitrifying bacteria to nitrogen and thus to remove nitrogen, and a reaeration step of decomposing a hydrogen donor, which has remained in the denitration step, with aerobic microorganisms. In the denitration step, a first fluidization carrier formed of a porous material having a first pore is fluidized in the treatment water. In the reaeration step, a second fluidization carrier formed of a porous material having a second pore larger than the first pore is fluidized in the treatment water. The first pore is constructed so that denitrifying bacteria can live and cannot deeply enter the first fluidization carrier. The second pore is constructed so that protozoa which can eat the nitrifying bacteria can live. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to treatment of wastewater containing nitrogen, and more particularly, to nitrification denitrification treatment using nitrogen as a microorganism.

  Conventionally, biological nitrogen removal has been used as a method for removing nitrogen in wastewater. Biological denitrification is a process that removes nitrogen by utilizing nitrate respiration in anoxic conditions of anaerobic bacteria, denitrifying bacteria. In biological denitrification, effluent is first nitrified under aerobic conditions, and ammonia nitrogen in the effluent is converted into nitrite nitrogen or nitrate nitrogen. (Nitrite nitrogen and nitrate nitrogen may be simply called nitrate nitrogen or nitric acid.) Subsequently, a hydrogen donor such as methanol is added to the nitrified treated water to make it oxygen-free. Thus, a denitrification process is performed. In biological treatment such as biological denitrification treatment, a floating activated sludge method that performs treatment in a state in which microorganisms are suspended, or a microorganism holding filler filled and fixed in a tank is used. There is a fixed bed type and a fluidized bed type using a fluid carrier having a size of about 3 to 10 mm which flows in a tank and flows.

  In the fluidized bed type, nitrification and denitrification are performed while microorganisms grow on the surface of the fluid carrier, and microorganisms are appropriately detached from the surface of the fluid carrier, so that the processing capacity is stably maintained for a long period of time. In addition, the amount of sludge in the treated water is generally stable. The fluidized bed type does not require a large sedimentation basin, unlike the floating type, and does not require backwashing to discharge sludge excessively attached to the filler, unlike the fixed type. And it can be said that it is an excellent system in terms of processing capability.

  In paragraphs 0006, 0017 and FIG. 1 of Japanese Patent No. 3019127, denitrification and nitrification are performed in this order, and a fluid carrier made of polyvinyl formal is introduced into the denitrification tank and the nitrification tank, and suspended matter in the nitrification water. Describes a nitrogen removal device that settles and removes using a sedimentation basin.

The summary of JP-A-2001-259683 is a nitrogen removal apparatus comprising a fluidized bed type nitrification tank and a denitrification tank, and an inorganic flocculant and a polymer flocculant are added to the waste water of the nitrogen removal apparatus, A nitrogen removal device is described that removes phosphorus by agglomeration and precipitation.
Japanese Patent No. 3019127 JP 2001-259683 A

  When the denitrification step is performed by a fluidized bed type, if a carrier having a relatively large pore size is employed in the denitrification tank, such as a pore size of 50 to 2000 μm, the denitrifying microorganisms enter deep into the pores and oxidize in the treated water. Since the nitrogen and hydrogen donating states are also likely to diffuse into the inside of the carrier, as a result, nitrogen gas is likely to be generated inside the carrier. As described above, when nitrogen gas is generated inside the carrier, the carrier floats to the surface of the water, resulting in poor flow, and the processing performance is significantly reduced. Excessive energy is required to suck the carrier once floated into the liquid and cause it to flow again. In order to solve this problem, a method of rotating a large draft tube to form a water flow by centrifugal force and degassing the gas inside the carrier may be considered, but the required energy may be increased.

  On the other hand, when a carrier with a pore size of 50 μm or less and a relatively small pore size is used, the denitrifying bacteria do not enter deep into the carrier, so the above problem does not occur, and the carrier is not in the denitrification tank. Good fluidity can be maintained. However, if the pore size is small, protozoa that prey on denitrifying bacteria (the size is approximately 50 μm or more) cannot live in the pores. As a result, the effect of reducing the amount of sludge generated by predation of protozoa cannot be obtained, and the amount of microorganism-derived SS (Suspended Solids, particulate matter having a diameter of 2 mm or less suspended or suspended in water) is increased. Proliferated microorganisms are difficult to flock, become cloudy, and flow into the treated water in a dispersed state, making it difficult to remove SS in the subsequent SS removal equipment, which may increase the amount of coagulant required.

As a result of intensive studies by the inventors to solve such problems, in the denitrification process, denitrification is performed using the first fluid carrier made of a porous material having pores having relatively small pore diameters, and after the denitrification process. In the step of decomposing the residual hydrogen donor by an aerobic microorganism, the above-mentioned problem is solved by allowing the second fluid carrier made of a porous material having a relatively large pore size to flow into the re-aeration tank. I found that I can do it.
Here, the pores of the first fluid carrier are preferably formed to have a size that allows denitrifying bacteria to inhabit but cannot penetrate deep into the carrier. In addition, the pores of the second fluid carrier are preferably formed in a size that allows protozoa that prey on denitrifying bacteria to live.

  According to the present invention, by adopting a fluid carrier having a small pore diameter in the denitrification step, it becomes difficult for denitrifying bacteria to penetrate deep into the carrier, and the diffusion of oxidized nitrogen and hydrogen donor state into the inside of the carrier is prevented. It becomes difficult to happen. For this reason, it is difficult for the carrier to float or flow poorly due to gas generation, and good carrier flow can be ensured even with low stirring power. As a result, the denitrification ability can be stably maintained. In consideration of the size of the denitrifying bacteria, the pore size of the carrier used in the denitrification step is preferably 50 μm or less, and more preferably 1 to 50 μm.

  Furthermore, according to the present invention, in the step after the denitrification step, the second fluid carrier made of a porous material having pores having a size that allows the protozoa that prey on the denitrification bacteria to inhabit is flowed to the re-aeration tank. Such a protozoan can be inhabited by a carrier. Then, since the protozoa prey on the denitrifying bacteria that have flowed out of the denitrification tank and dispersed, the amount of sludge generated from the denitrifying bacteria is greatly reduced. Furthermore, since the floc peeled off from the second fluid carrier is relatively coarse, the condensability and sedimentation of sludge are greatly improved. Therefore, the amount of the flocculant in the SS removal equipment can be reduced, and the size of the sedimentation tank can be kept small. In consideration of the size of the protozoa, the pore size of the carrier used in the step is preferably 50 μm or more, more preferably 50 to 500 μm.

Therefore, when the present invention is combined with a known SS removing device, the overall size of the device can be reduced, the quality of treated water can be improved, and the running cost can be reduced due to the reduction in the amount of chemicals and sludge generated.
The SS removal device combined with the present invention is not particularly limited to a sedimentation type or pressurized flotation type, but the present invention is most suitable for combination with SS removal by an ultra high speed coagulation precipitation method.
In the ultra-high speed coagulation sedimentation method, the flocs settling speed is increased by mixing the coagulant and the settling accelerator in the water to be treated in the mixing tank, and SS is precipitated and separated at high speed in the settling tank. The precipitated sludge is separated into a settling accelerator and sludge by centrifugal separation with a cyclone, and the separated sludge is re-concentrated in the concentration tank.
In the ultra-high speed coagulation sedimentation method, the sedimentation rate of the separated sludge is often small, and if the amount of SS contained in the water to be treated is large, a large concentration tank may be required for the concentration of the separated sludge. In such a case, flocculation and precipitation can be performed at a high speed, and the features of the ultrafast flocculation and precipitation method that the apparatus can be miniaturized cannot be sufficiently exhibited. Therefore, when the ultrafast coagulation sedimentation method is applied after biological treatment, the SS concentration is 500 mg / l or less, preferably 300 mg / l or less, more preferably 50 to 100 mg / l. Is particularly effective.

  However, according to the present invention, the SS of the wastewater after the treatment is in a coarse floc form, and since the SS concentration can be reduced, it is well suited to the ultra high speed coagulation precipitation method as a method for removing SS. The advantage of high-speed coagulation and precipitation, which is a feature of the high-speed coagulation and precipitation method, can be enjoyed.

  In the re-aeration tank, it is necessary to perform aeration in order to supply oxygen to the aerobic microorganisms. At this time, carbon dioxide in the water to be treated is released into the atmosphere. Then, although the pH of to-be-processed water will rise gradually, when calcium ion is contained in to-be-processed water, the raise of pH may produce the following problems. That is, when the pH rises, calcium ions of water to be treated and carbonate ions generated by decomposition of the hydrogen donor are combined to generate calcium carbonate, which adheres to the surface of the fluid carrier in the re-aeration tank. Since the specific gravity of the carrier is increased, the fluidity is remarkably deteriorated and the processing performance is lowered. Furthermore, the adhesion of calcium carbonate to the surface of the fluid carrier makes it difficult for protozoa to live on the fluid carrier, resulting in a decrease in the predation amount of denitrifying bacteria by the protozoa and an increase in the SS concentration in the treated water. There is a possibility of inviting.

  Therefore, when calcium ions are contained in the wastewater to be treated, the pH of the treated water is monitored in the re-aeration tank. If the pH rises above a predetermined value, an acid is added to the treated water. It is preferable to lower the pH.

The present invention includes, in one of its specific embodiments, the following method for treating nitrogen-containing wastewater. This method
A nitrification step of oxidizing ammonia nitrogen and / or organic nitrogen contained in the nitrogen-containing wastewater into nitrate nitrogen and / or nitrite nitrogen by nitrifying bacteria;
・ By adding a hydrogen donor to the treated water of the nitrification process, the treated water of the nitrification process is put under anaerobic conditions, and the nitrate nitrogen and / or the nitrite nitrogen is reduced to nitrogen by denitrifying bacteria. A denitrification step of removing the nitrogen,
A re-aeration step in which the hydrogen donor remaining in the denitrification step is decomposed by an aerobic microorganism;
Have
In the denitrification step, the first fluid carrier made of a porous material having the first pores is caused to flow into the treated water,
In the re-aeration step, a second fluid carrier made of a porous material having a second hole larger than the first hole is caused to flow into the water to be treated.
The first hole is formed so that the denitrifying bacteria can live and the denitrifying bacteria do not penetrate deep into the first fluid carrier;
The second hole is formed so that a protozoa that prey on the denitrifying bacteria can inhabit,
It is characterized by that.

One of the specific embodiments of the present invention includes the following nitrogen-containing wastewater treatment apparatus. This processor is
A nitrification tank that oxidizes ammonia nitrogen and / or organic nitrogen contained in the nitrogen-containing wastewater into nitrate nitrogen and / or nitrite nitrogen by nitrifying bacteria;
-By adding a hydrogen donor to the treated water in the nitrification tank, the treated water in the nitrification step is put under anaerobic conditions, and the nitrate nitrogen and / or the nitrite nitrogen is reduced to nitrogen by denitrifying bacteria. A denitrification tank for removing the nitrogen,
A re-aeration tank for decomposing the hydrogen donor remaining in the denitrification step with an aerobic microorganism,
-Flowing the first fluid carrier made of a porous material having the first pores into the denitrification tank;
Flowing a second fluid carrier made of a porous material having a second pore larger than the first pore into the re-aeration tank;
The first hole is formed so that the denitrifying bacteria can live and the denitrifying bacteria do not penetrate deep into the first fluid carrier;
The second hole is formed so that a protozoa that prey on the denitrifying bacteria can inhabit,
Nitrogen-containing wastewater treatment equipment.
It is characterized by that.

  Hereinafter, in order to help understanding of the present invention, an example of an embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a diagram illustrating an outline of a wastewater treatment facility 10 which is an example of a wastewater treatment facility to which the present invention is applied.

  The wastewater treatment facility 10 includes a nitrification tank 101, a denitrification tank 111, a re-aeration tank 121 for removing residual methanol, an SS removal device 131, and the like. Waste water to be treated in the waste water treatment facility 10 is first introduced into the nitrification tank 101. In the nitrification tank 101, ammonia nitrogen and organic nitrogen contained in the waste water are oxidized into nitrate nitrogen and / or nitrite nitrogen by nitrifying bacteria. The nitrification tank 101 is a fluidized bed type, and a large number of fluid carriers 103 on which nitrifying bacteria adhere and grow are flowing in the tank by the water flow generated by the aeration apparatus 125. The material of the fluid carrier 103 is not particularly limited, and examples thereof include a porous body made of cellulose, polyethylene, polypropylene, polyurethane and the like, a gel-like body made of polyvinyl alcohol, polyethylene glycol and the like.

  In the nitrification tank 101, the pH is lowered by nitrification of ammonia nitrogen or the like. However, since the activity of nitrifying bacteria is inhibited when the pH decreases, an alkaline agent such as sodium hydroxide is added as necessary to maintain the pH in the tank near neutrality. For this purpose, the nitrification tank 101 is provided with a pH sensor 107 for measuring the pH in the tank, and when a decrease in pH is detected, the alkaline agent is transferred from the alkaline agent storage tank to the nitrification tank 101 by an alkaline pump. It is configured to supply.

  The treated water treated in the nitrification tank 101 is then introduced into the denitrification tank 111 as treated water. In the denitrification tank 111, by supplying methanol to the treated water, the treated water is put under anaerobic conditions, and nitrate nitrogen and nitrite nitrogen in the treated water are reduced to nitrogen gas by the denitrifying bacteria. To remove nitrogen in the water to be treated. Along with this reduction reaction, methanol is also consumed. The denitrification tank 111 is also a fluidized bed type like the nitrification tank 101, and a large number of fluid carriers 113 are flowing in the tank by the water flow generated by the stirring device 115. A large number of holes are formed on the surface of the fluid carrier 113, and denitrifying bacteria can be inhabited in the holes. However, the pores of the flow carrier 113 are formed in such a size that the denitrifying bacteria cannot penetrate deep into the carrier. For this reason, the generation of nitrogen gas does not occur deep in the fluid carrier 113, and the nitrogen gas does not easily accumulate inside the carrier. Therefore, gas hardly accumulates inside the carrier and the carrier floats on the surface of the water, so that there is almost no flow failure. For this reason, the flow carrier 113 can always maintain a good flow, and the denitrification tank 111 can maintain a stable denitrification ability over a long period of time. The fluid carrier 113 is preferably a polyvinyl alcohol gel carrier having a pore diameter of 1 to 20 μm.

  In the denitrification tank 111, the pH increases with the denitrification reaction, but when the pH rises, the activity of the denitrifying bacteria is inhibited. Therefore, if necessary, an acid such as hydrochloric acid is added to adjust the pH in the tank. I try to keep it near neutral. For this purpose, the denitrification tank 111 is provided with a pH sensor 117 for measuring the pH in the tank, and when an increase in pH is detected, hydrochloric acid is supplied from the hydrochloric acid storage tank to the denitrification tank 111 by a pump. It is configured.

  The treated water treated in the denitrification tank 111 is then introduced into the re-aeration tank 121 as treated water. In the treated water of the denitrification tank 111, excess methanol remains in the denitrification reaction, and denitrifying bacteria that have proliferated with the denitrification reaction are dispersed and mixed in a cloudy state. Residual methanol is removed from the water to be treated by aerobic microorganisms. Furthermore, the residual methanol removal tank 121 is loaded with a porous fluid carrier 123 having pores of a size that allows protozoa that prey on denitrifying bacteria to inhabit, and the water flow generated by the aeration apparatus 125 allows the inside of the tank to be moved. It is flowing. Since these protozoa prey on denitrifying bacteria drifting in the treated water while flowing in the tank together with the fluid carrier 123, the denitrifying bacteria are removed from the treated water, and the amount of sludge generated from the denitrifying bacteria is greatly reduced. Can do. Furthermore, since the protozoan-derived floc that is peeled off from the fluid carrier 123 is coarse, the condensability and sedimentation of sludge are greatly improved. The fluid carrier 123 is preferably a polyurethane sponge carrier having a pore diameter of 100 to 200 μm so that a predator can be inhabited in the pore diameter.

  In the re-aeration tank 121, carbon dioxide contained in the water to be treated is released into the atmosphere by aeration for supplying oxygen to the aerobic microorganisms. Then, although the pH of to-be-processed water will rise gradually, when calcium ion is contained in to-be-processed water, the raise of pH may produce the following problems. That is, when the pH rises, calcium ions of water to be treated and carbonate ions generated by the decomposition of methanol are combined to generate calcium carbonate, which adheres to the surface of the fluid carrier 123 and can inhabit protozoa. It will disappear. Then, the predation amount of denitrifying bacteria by the protozoa also decreases, and the SS concentration in the treated water increases. Specific gravity increases and fluidity deteriorates.

  Therefore, the residual methanol removal tank 121 is provided with a pH sensor 127 for measuring the pH in the tank. When an increase in pH is detected, hydrochloric acid is supplied from the hydrochloric acid storage tank to the residual methanol removal tank 121 by a pump. , Configured to suppress an increase in pH.

  The treated water treated in the re-aeration tank 121 is introduced into the SS removing device 131. The SS remover is an ultrafast coagulation sedimentation type SS remover. The ultra-high speed coagulation sedimentation type SS removal device has the advantage of high-speed solid-liquid separation and a small installation area, but has the disadvantage that it cannot be used for waste water with high SS concentration. However, the SS in the treated water in the re-aeration tank 121 has a coarse floc form, and the SS is greatly reduced due to the predator's predatory action. Can be done.

  In this way, the wastewater treatment facility 10 is worried about an increase in the SS concentration derived from denitrifying bacteria in the treated water by introducing into the residual methanol removal tank 121 a fluid carrier that can be inhabited by protozoa that prey on the denitrifying bacteria. In addition, it is possible to use a fluid carrier with an optimal pore size in the denitrification tank 111 in order to maintain a stable denitrification capacity for a long period of time. It is also possible to use an SS remover of the type.

  As mentioned above, although an example of the embodiment of the present invention has been described, it is obvious that the embodiment of the present invention is not limited to the above example, and the present invention can be implemented in various ways without departing from the scope thereof. It is possible to take aspects. For example, the nitrification tank 101 in the wastewater treatment facility 10 may be a fixed bed type instead of a fluidized bed type, and the SS removing device 131 is not an ultra-high speed coagulating sedimentation device, but a pressurized floating type or a normal sedimentation type. It is good also as SS removal apparatus.

It is the figure on which the outline of the waste water treatment facility 10 which is an example of the waste water treatment facility to which this invention is applied was drawn.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Wastewater treatment facility 101 Nitrification tank 103 Fluid carrier 107 pH sensor 111 Denitrification tank 113 Fluid carrier 115 Stirrer 117 pH sensor 121 Residual methanol removal tank 123 Fluid carrier 125 Aeration device 127 pH sensor 131 SS remover

Claims (8)

A method for treating nitrogen-containing wastewater,
A nitrification step of oxidizing ammonia nitrogen and / or organic nitrogen contained in the nitrogen-containing wastewater into nitrate nitrogen and / or nitrite nitrogen by nitrifying bacteria;
-By adding a hydrogen donor to the treated water of the nitrification process, the treated water of the nitrification process is put under anaerobic conditions, and the nitrate nitrogen and / or the nitrite nitrogen is reduced to nitrogen by denitrifying bacteria. A denitrification step of removing the nitrogen,
A re-aeration step in which the hydrogen donor remaining in the denitrification step is decomposed by an aerobic microorganism;
Have
In the denitrification step, the first fluid carrier made of a porous material having the first pores is caused to flow into the treated water,
In the re-aeration step, a second fluid carrier made of a porous material having a second hole larger than the first hole is caused to flow into the water to be treated.
The first hole is formed so that the denitrifying bacteria can live and the denitrifying bacteria do not penetrate deep into the first fluid carrier;
The second hole is formed so that a protozoa that prey on the denitrifying bacteria can inhabit,
Nitrogen-containing wastewater treatment method.   The method according to claim 1, wherein the first hole has a hole diameter of 50 μm or less, and the second hole has a hole diameter of 50 μm or more.   When the nitrogen-containing wastewater contains calcium ions, in the re-aeration step, the pH of the treated water in the re-aeration step is monitored, and when the pH rises above a predetermined value, the removal step The method according to claim 1 or 2, wherein an acid is added to the treated water.   4. The method according to claim 1, further comprising a step of removing SS (Suspended Solids) contained in the treated water of the re-aeration step by an ultrafast coagulation precipitation method. 5. A treatment device for treating nitrogen-containing wastewater,
A nitrification tank that oxidizes ammonia nitrogen and / or organic nitrogen contained in the nitrogen-containing wastewater into nitrate nitrogen and / or nitrite nitrogen by nitrifying bacteria;
-By adding a hydrogen donor to the treated water in the nitrification tank, the treated water in the nitrification step is put under anaerobic conditions, and the nitrate nitrogen and / or the nitrite nitrogen is reduced to nitrogen by denitrifying bacteria. A denitrification tank for removing the nitrogen,
A re-aeration tank for decomposing the hydrogen donor remaining in the denitrification step with an aerobic microorganism,
-Flowing the first fluid carrier made of a porous material having the first pores into the denitrification tank;
Flowing a second fluid carrier made of a porous material having a second pore larger than the first pore into the re-aeration tank;
The first hole is formed so that the denitrifying bacteria can live and the denitrifying bacteria do not penetrate deep into the first fluid carrier;
The second hole is formed so that a protozoa that prey on the denitrifying bacteria can inhabit,
Nitrogen-containing wastewater treatment equipment.   6. The apparatus according to claim 5, wherein the first hole has a hole diameter of 50 μm or less, and the second hole has a hole diameter of 50 μm or more.   The apparatus according to claim 5 or 6, further comprising a pH meter for monitoring the pH of treated water in the re-aeration tank, and means for adding an acid to the removal tank. 8. The apparatus according to claim 5, further comprising an ultrafast coagulation sedimentation device for removing SS (Suspended Solids) contained in the treated water of the re-aeration process by ultrafast coagulation sedimentation. The device described.

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