WO2004031084A1

WO2004031084A1 - Method of removing nitrate nitrogen and device used for the method

Info

Publication number: WO2004031084A1
Application number: PCT/JP2002/010180
Authority: WO
Inventors: Toshiaki Miyanaga; Yasuhiro Hirato; Tetsuo Ichiguchi; Toru Oishi; Katsuhiro Yamada
Original assignee: Nippon Steel Chemical Co., Ltd.
Priority date: 2002-09-30
Filing date: 2002-09-30
Publication date: 2004-04-15

Abstract

A method of removing nitrate nitrogen in drain water by using sulfur-oxidizing bacteria under the presence of denitrifying material formed of sulfur and calcium components and a device used for the method, the method comprising the steps of passing the drain water containing the nitrate nitrogen through the denitrifying material-filled layer in a drain water processing chamber having the denitrifying material-filled layer and returning at least a part of the treated drain water passed through the filled layer to the inlet side of the filled layer or to the intermediate layer of the filled layer; the device comprising a circulating pump for circulating at least a part of the drain water passed through the filled layer in the drain water treating chamber to the inlet side of the filled layer or to the intermediate layer, wherein a denitrifying material formed of calcium carbonate and sulfur may be combined with iron oxide.

Description

Description Nitrate nitrogen removal method and equipment used for it

TECHNICAL FIELD The present invention relates to a method for removing nitrate nitrogen in wastewater using microorganisms, and a removal device used for the method. BACKGROUND ART In recent years, the problem of nitrate ion concentration in wastewater has become more serious, and various treatment systems using biological treatment methods have been devised. In particular, wastewater from agricultural lands such as upland fields, tea fields, orchards, pastures, etc. contains high concentrations of nitrate nitrogen due to excessive fertilization in recent years, which is a problem. In addition, nitrate nitrogen contained in domestic wastewater such as septic tanks has been taken up as one of the problems of eutrophication of lakes.

As this treatment method, there is known a heterotrophic denitrification technique in which an organic carbon source in methanol sludge is used as a hydrogen donor for denitrification. In addition to the low rate, after denitrification, excess hydrogen donors need to be removed separately so as not to be discharged outside, so many treatment facilities and equipment are required.

On the other hand, a nitrate nitrogen treatment system using sulfur oxidizing and denitrifying bacteria does not require the addition of a methanol / organic carbon source. It does not require secondary treatment facilities after denitrification, and is attracting attention.

In particular, W02000-8869, Japanese Patent Application Laid-Open No. 11-2857377, Japanese Patent Application Laid-Open No. 2001-10949, Japanese Patent Application Laid-Open No. In the system using solid-nutrition of a molten mixture of sulfur and calcium carbonate-based components as described in Japanese Patent Publication No. It is easy and has an excellent effect on the cost of denitrification.

However, since the above technology utilizes the action of microorganisms, it has been difficult to follow changes in the temperature, amount of water, concentration of contaminants, and the like of the wastewater. For example, sulfur-oxidizing bacteria generally have low activity at low temperatures below 15 ° C, and their processing capacity fluctuates depending on the season. In some cases, it was necessary to introduce more processing equipment. In addition, when denitrification was attempted until the concentration became extremely low, problems such as a reduction in the denitrification rate and the generation of hydrogen sulfide in some environments were found. DISCLOSURE OF THE INVENTION Accordingly, an object of the present invention was to use sulfur-oxidizing bacteria that always exhibit stable denitrification performance, and do not require a power source, etc., and are easy to maintain near a wastewater generation site. An object of the present invention is to provide an efficient removal apparatus that makes full use of the features of the apparatus. Another object of the present invention is to provide a method for removing nitric acid nitrogen which solves the above problems. The present invention uses a sulfur-oxidizing bacterium by passing a wastewater containing nitrate nitrogen through a denitrification material packed bed in a wastewater treatment tank having a denitrification packed bed composed of sulfur and calcium-based components. A nitrate nitrogen removal method that consists of removing nitrate nitrogen from the wastewater and returning at least part of the treated wastewater that has passed through the packed bed to the inlet side of the packed bed or to the middle layer of the packed bed. is there.

Further, the present invention relates to an apparatus for removing nitrate nitrogen using a sulfur-oxidizing bacterium in a wastewater treatment tank having a packed bed filled with a denitrifying agent comprising sulfur and calcium-based components. This is a nitrate nitrogen removal device having a circulation pump for circulating at least a part of the wastewater that has passed through the packed bed to the inlet side of the packed bed or to the intermediate bed.

Further, the present invention relates to a denitrification material used for denitrification of nitrate nitrogen in water using a sulfur-oxidizing bacterium, wherein the composition of the denitrification material is calcium carbonate and a coexistence of sulfur and iron oxide. It is a denitrifying material which has a content of coexisting iron oxide of 1 to 20 wt% and a specific surface area of 0.1 lm ² / g or more, and can suppress generation of hydrogen sulfide. Hereinafter, the present invention will be described in detail.

The wastewater containing nitrate nitrogen is wastewater containing at least one selected from nitrate ions and nitrite ions, and may be abbreviated as wastewater. Wastewater includes industrial wastewater, domestic wastewater, and agricultural wastewater. Further, the present invention is effective for wastewater whose temperature, amount, and contaminant concentration have large differences in time, season, and the like. For example, it is effective for wastewater that can be 10 ° C or less, and such wastewater includes domestic wastewater and agricultural wastewater in winter.

Denitrifying materials consisting of sulfur and calcium components are described in the above publication. Examples of such materials include a material in which calcium carbonate powder is dispersed in molten sulfur and a material in which inorganic fibers, a porous material, an ion-exchange substance, and the like are mixed.

Although the calcium component is not particularly limited, calcium carbonate is preferred. Also, the ratio of sulfur and calcium-based components in the denitrification material is not particularly limited, but the sulfur content is preferably 30 to 90% by weight, more preferably 40 to 80% by weight. And more preferably 50 to 70% by weight. If the sulfur content in the denitrification material is less than 30% by weight, the material becomes brittle and easily friable, which is not practical. If it exceeds 90% by weight, the pH after water treatment becomes 5%. It can be: The method for producing the denitrification material is not limited, but preferably, a calcium-based component such as limestone powder and elemental sulfur are mixed at a ratio of about 1: 2 to 2: 1, and heated to melt the sulfur. After that, it is obtained by cooling, solidifying, integrating and pulverizing to a predetermined particle size. At this time, inorganic fibers, porous materials, and the like are blended as necessary. The ratio of sulfur to calcium carbonate-based components and other additives is determined by the fact that when these mixtures are melted, cooled, and solidified, an integrated product having a predetermined strength is obtained. However, the nutrient source of the denitrifying bacteria is biased, so it is within the above range. Therefore, when an inorganic fiber, a porous material, or the like is blended, it is preferred to blend such that a part of the calcium carbonate-based component is replaced with the inorganic fiber, the porous material, or the like. When a mineral fiber is blended, the ratio is preferably in the range of 1/10 to 1/2 of the calcium carbonate-based component. Examples of the mineral fiber include rock wool, slag wool, and glass wool.

When used in an environment where hydrogen sulfide is generated, the denitrification material is composed of a calcium-based component and a co-existing mixture of sulfur and iron oxide, and the content of co-existing iron oxide is low. It is preferable that the iron oxide has a specific surface area of 0.1 lm ² / g or more and that the generation of hydrogen sulfide can be suppressed.

Here, the calcium component and sulfur used may be the same as described above. Iron oxide coexists to prevent the generation of hydrogen sulfide, which is likely to be generated when nitric acid in wastewater is low in concentration and dissolved oxygen is low. As the iron oxide, there are ferrous iron and trivalent iron or a mixture thereof depending on the form. Specifically, although such _{_{F e OF e 2 0 3 F}} e 3 0 4 F e O OH ( iron oxide hydroxide), in order to use, Ya iron ore (F e ₂ 〇 ₃ present in natural F e ₃ 0 ₄ main components), crystalline or amorphous hydrous iron oxide such as red鲭generated from loess and mining waste water, red iron oxide (F e ₂ 0 _3), converter Dust generated from ironworks (Mainly Fe ₂ 〇 ₃ ). In this case, the iron oxide has a specific surface area in order to capture the hydrogen sulfide generated in real is required is 0. l MVG above, preferably be ^{1 1 0 0 m 2 / g} . The amount of coexisting iron oxide is 120 wt% in the denitrification material, preferably 2 to 15 wt%.

Since this iron oxide-containing denitrifying material is composed of a coexistent of carbonate, sulfur and iron oxide, each is present in the same processing apparatus and has an appropriate amount such that the denitrification reaction and the capture of hydrogen sulfide can be performed. As long as the contact is maintained, they need not be present in the same particle, and may be present separately. However, particles in which the respective components are integrated into the same particle are preferable in terms of the denitrification reaction and the efficiency of capturing hydrogen sulfide. When the denitrifying material is filled as a single particle of each component, it is preferable to use a single particle having a diameter of about 0.55 Oram. In the case of particles in which each component is integrated into the same particle, these are finely pulverized, mixed, integrated by melting or press molding, and further granulated to a diameter of 150. Good thing. Sulfur-oxidizing bacteria are microorganisms that denitrify under anaerobic conditions in the presence of the denitrifying agent. Propagation of denitrifying bacteria inside or around the surface of the denitrifying material is achieved by training with drainage or soil dispersion water containing nitrate nitrogen and denitrifying bacteria in the presence of the denitrifying material. However, when treating wastewater containing nitrate nitrogen and denitrifying bacteria, training is not necessary because denitrifying bacteria grow during treatment. Denitrifying bacteria grow using nitrate nitrogen and denitrifier as main nutrients, and nitrate nitrogen is decomposed into nitrogen gas.

The sulfur-oxidizing bacteria may be, for example, sulfur-oxidizing dechambered bacteria (Thiobacil lus deni trifi cans), which are autotrophic sulfur-oxidizing bacteria generally found in nature. Sulfur and carbon content in denitrification materials There is no restriction as long as it grows as a nutrient and can decompose nitrate nitrogen to nitrogen gas.

The activity of these naturally occurring sulfur-oxidizing bacteria at temperatures as low as 15 ° C or less is significantly reduced. To prevent this decrease, when the sulfur-oxidizing bacteria are established on the denitrifying agent, first contact the naturally occurring sulfur-oxidizing bacteria or soil containing the same with the denitrifying agent in a medium containing nitrate nitrogen. Then, it is preferable that the cells be cultured at a temperature of 1 to 10 ° C. for a predetermined period, and the bacteria be cultured, propagated, and fixed on the surface and voids of the denitrification material. Here, the cultivation method is a medium containing nitrate nitrogen, as long as it is maintained at the above temperature, and other trace components and the like may be present. The culture period at 1 to 10 ° C may be a period during which the bacteria can be established, but may be a culture period of 2 days or more, preferably 10 days or more, more preferably about 1 month. Good. If no denitrification material is used for wastewater treatment under low temperature conditions, a culture temperature of about 15 to 40 ° C can be adopted. During the cultivation, it is preferable that nitrate nitrogen is added each time the concentration of nitrate nitrogen in the culture medium decreases, and the condition of low dissolved oxygen is maintained. If dissolved oxygen is high, sulfur It is preferable to maintain an anaerobic state because oxidizing bacteria consume dissolved oxygen and do not perform denitrification.

The wastewater treatment tank is a tank filled with the above-mentioned denitrification material, and may be abbreviated as a treatment tank. There is no limitation on the shape of the treatment tank, but a type in which wastewater flows through the packed bed of denitrification material is advantageous. A plurality of treatment tanks may be provided, in which case they may be connected in series or arranged in parallel. Wastewater treatment equipment consists of one or more treatment tanks, pumps and other equipment.

The wastewater is supplied to the treatment tank and is denitrified by the action of sulfur-oxidizing bacteria when passing through the packed bed of denitrifying material and discharged. In this case, in order to improve the denitrification rate, in the method of the present invention, at least a part of the wastewater that has passed through the packed bed is circulated. Here, as a method of circulating, when there is one packed bed, at least a part of the passed wastewater is returned to the wastewater before passing through the packed bed, or when there are multiple treatment tanks or packed beds There is a method in which at least part of the downstream wastewater is returned to the upstream wastewater one or more times before the treatment tank or packed bed. Also, the wastewater to be treated may be mixed with the treated wastewater that has passed through the packed bed, and circulated to the inlet side of the packed bed. The amount of circulation varies depending on the properties of the wastewater, the amount of wastewater supplied, and the like, and is 2 to 500 times, preferably 10 to 100 times the amount of wastewater supplied. Further, it is 2 to 150 times / hr, preferably 2 to 150 times / hr of the packed bed volume (the total volume if there are a plurality). By circulating such an amount, the flow velocity of the wastewater passing through the packed bed increases, and the denitrification reaction proceeds inside the denitrification material without completing the denitrification reaction near the surface of the denitrification material. As a result, the denitrification reaction takes place over a wide range, and as a result, the processing speed increases. Furthermore, as the denitrification reaction progresses, air bubbles adhere to the surface of the denitrification material, causing poor contact between the wastewater and the denitrification material. Bubbles are more easily removed, resulting in increased processing speed. On the other hand, the amount of the denitrification material filled in the packed bed is gradually consumed and its amount decreases, so the circulation amount can be reduced if no denitrification material is added. If the packed bed is to be used for a long time without replacement, the initial circulation volume should be increased.

For this reason, the nitrate nitrogen removing apparatus of the present invention has a circulation pump for circulating the wastewater in the tank, and the circulation pump has a suction side located downstream of the flow of the wastewater (flow after passing through the packed bed). The discharge side is connected to the upstream side of the drainage flow (the flow before passing through the packed bed or the middle layer of the packed bed). BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 to 7 are schematic views of a nitrate nitrogen removing apparatus of the present invention. 1 to 4 show a nitrate nitrogen removal device having a circulation pump, FIG. 5 shows a nitrate nitrogen removal device having a preliminary tank, and FIG. 6 shows a nitrate nitrogen removal device provided with a deaeration means. Fig. 7 shows a nitrate nitrogen removal device provided with a dissolved oxygen means. BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described with reference to the drawings. In FIG. 1, a nitrate nitrogen removing device 1 is composed of a treatment tank 11, a denitrification material packed bed 2, a circulation pump 4, and the like. The treatment tank 11 has a denitrification material-filled layer 2 inside, and an upper aqueous phase 9 exists above the packed layer 2 and a lower aqueous phase 8 exists below. The wastewater is introduced into the treatment tank 11 from the inlet line 5, mixed with the upper aqueous phase 9, and sent to the lower aqueous phase ⁸ through the pipe 3 by the circulation pump 4 arranged in the inlet line 5. Can be The lower aqueous phase 8 thereby rises and passes through the filling tank 2 to reach the upper aqueous phase 9. Here, the wastewater that has reached the upper aqueous phase 9 near the outlet line 6 provided on the opposite side of the inlet line 5 is discharged from the outlet line 6 as treated water. On the other hand, the wastewater that has reached the upper aqueous phase 9 near the circulation pump 4 is again sent to the lower aqueous phase 8 by the circulation pump 4 and circulated. The lower part of the packed bed 2 has a perforated plate 7 that allows drainage to pass through but does not allow denitrification material to pass through.

FIG. 2 shows another embodiment, in which the inlet line 5 is located below the filling tank 2. Fig. 3 shows yet another embodiment, in which the inlet line 5 is located above the filling tank 2 but is provided with a partition plate 10, and the drainage charged from the inlet line 5 is the partition plate. It passes through the packed bed 2 separated by 10 and then passes through the packed bed 2 on the exit 6 line side to reach the upper aqueous phase 9. In FIGS. 2 and 3, other symbols have the same meaning as in FIG. These examples prevent the wastewater that does not pass through the filling tank 2 from mixing with the wastewater that has passed and being discharged from the outlet line 6.

FIG. 4 shows still another embodiment, in which two treatment tanks are connected. The wastewater introduced from the inlet line 5 of the first treatment tank 41 is

As in the case of the first example, the water is circulated by the pump 4, comes into contact with the packed bed, reaches the upper aqueous phase 9, flows out from the connection line 43, and is introduced into the second treatment tank 42. The wastewater introduced into the second treatment tank 42 is circulated by the pump 4 similarly to the first treatment tank 41, contacts the packed bed, reaches the upper aqueous phase 9, and is treated as treated water from the outlet line 6. Is discharged. 2 to 4, the same reference numerals as those in FIG. 1 indicate the same components.

Fig. 5 shows an example of a nitrate nitrogen removal device that is suitable when the wastewater to be charged is at low temperature. Is shown. The nitrate nitrogen removal device 1 has a configuration in which a treatment tank 11 is disposed in a preliminary tank 16. The wastewater is charged from the inlet line 5 into the preliminary tank 16, where it stays, and is charged into the treatment tank 11 by the metering pump 15. The treatment tank 11 has a packed bed 2 filled with a denitrifying agent inside, and is connected to the pump 15 at the bottom and to the outlet line 6 at the top. Here, at the upper part of the packed bed 2, a part of the drainage that has passed through the packed bed is circulated to the preliminary tank 16 by the pipe 3 and the circulation pump 4. Further, the treatment tank 11 is disposed inside the spare tank 16, and the wastewater 14 is stored in the spare tank 16. A band heater 13 is attached to the outside of the preliminary tank 16 so as to keep the temperature at a set value. The wastewater flows into the preparatory tank 16 from the inlet line 5, is heated to a predetermined temperature, is introduced from the bottom of the treatment tank 11 by the metering pump 15, and rises while contacting the denitrification material packed bed 2. The gas is denitrified by the action of the denitrifying bacteria, and the generated gas is discharged from the gas vent line 12 and the treated water flows out of the outlet line 6. In this device, the wastewater enters the preparatory tank 16 once, reaches a predetermined temperature sufficiently, and then enters the treatment tank 11, so that the activity of the denitrifying bacteria living inside or around the denitrification material in the treatment layer is reduced. There is no problem of extreme drop. Therefore, this device can maintain a high denitrification rate even if the wastewater to be charged is at a low temperature of less than 10 ° C, without the activity of the denitrifying bacteria dropping extremely.

The processing tank 11 may not be disposed in the preparatory tank 16 and may be provided independently. However, by disposing the processing tank 11 in the preparatory tank 16, it is easy to control the processing tank 11 to an optimum temperature. In addition, the wastewater in the preliminary tank can be used as a heat medium for heating the processing tank, and the entire processing tank can be uniformly heated, so that more efficient heating can be performed than using a band heater or the like. Conversely, high-temperature wastewater that can kill the denitrifying bacteria If the gas flows into the reserve tank 16, the reserve tank may have a cooling device.

In addition, since the reserve tank can be used as a stock tank for wastewater, for example, in wastewater treatment with intermittent flow characteristics, a constant volume pump is used to continuously discharge wastewater from the reserve layer to the treatment tank 11 filled with denitrification material. By controlling the flow of water, it is possible to continuously flow a constant amount of water into the treatment tank.

Since the amount of denitrification materials required for wastewater treatment depends on the amount of wastewater flow, for example, even if the amount of wastewater per day is the same, the amount of wastewater that is discharged continuously for one day and the amount of wastewater divided into several In the latter case, the flow rate per hour greatly changes, and a large amount of wastewater treatment must be performed at a certain time. And the disadvantage that the equipment becomes too large. Therefore, a method of flowing the treated wastewater into a tank filled with a denitrifying material composed of sulfur and calcium components with the above-mentioned reserve tank as a stock tank and a constant amount of continuous water flow from the reserve tank with a constant amount pump is used. It is very effective in terms of compacting equipment.

By the way, the growth environment of the denitrifying bacteria varies depending on the type, origin, etc. of the denitrifying bacteria, but it is generally said that the optimum temperature is around 30 ° C. Therefore, the temperature of the wastewater charged into the treatment tank is preferably from 10 to 50 ° C, more preferably from 15 to 40 ° C, and still more preferably from 20 to 40 ° C. In particular, when the wastewater flowing into the preliminary tank 16 is lower than 15 ° C, the heater is set to a temperature higher than that by 10 ° C or more and a predetermined temperature between 15 ° C and 40 ° C. It is preferable to adjust at 13. The shapes of the treatment tank and the preliminary tank are not particularly limited, but a cylindrical shape or a rectangular parallelepiped shape is preferable from a practical shape. The number of these tanks does not need to be one, but two or more depending on the processing purpose, required processing capacity, installation space, etc. It is also possible to combine tanks. For example, installing multiple treatment tanks in one spare tank is also an efficient method. The size of the spare tank is

The amount is 0.5 to 5 times, preferably 1 to 3 times.

Also, circulating the wastewater by the circulation pump 4 is effective for keeping the water temperature in the preparatory tank and the wastewater treatment tank constant.

Fig. 6 shows a device suitable for recovering from a decrease in the denitrification rate during use.Inlet line 5 leads to the lower part of treatment tank 11 and outlet line 6 at the upper part. The tank has a bed of denitrification material. From the inlet line 5, the wastewater introduced into the lower part of the packed bed passes through the packed bed and reaches the upper part, part of which is discharged as treated water from the outlet line 6, and part of which is pipe 3 and pump 4. And is circulated to the lower part of the treatment layer via the The treatment tank 11 and a storage tank 21 for temporarily storing wastewater are connected by a pipe 22.The monitoring device 23 provided at the wastewater outlet line 6 measures the concentration of nitrate nitrogen in the treated water. When the denitrification rate calculated from the measured nitrate nitrogen concentration falls below a predetermined value, the valves 24 and 25 are opened and closed and the operation of the pump 26 is controlled.

In the treatment tank 11, nitrate ions are constantly converted to nitrogen gas, and bubbles generated by the generated nitrogen gas gradually accumulate between the particles of the denitrifying material. Such accumulation of air bubbles prevents the contact between the wastewater and the denitrification material, and the denitrification efficiency gradually decreases. The monitoring device 23 measures the nitrate nitrogen concentration of the treated wastewater discharged from the treatment tank 1, and when the denitrification rate of the treated water falls below the set value, the switching system built into the monitoring device 23 (Not shown) are configured to operate. In this switching system, the valve 24 is closed to stop the inflow of wastewater, and then the valve 25 is opened, and the pump 26 is driven to drive the wastewater in the treatment tank 11 to the storage tank 21. Move it temporarily to empty the processing tank 1 1. This operation breaks bubbles existing between the particles of the denitrifying agent and releases nitrogen gas.

The switching system operates not only when the nitrate nitrogen concentration exceeds the regulation value, but also when the denitrification rate at the start of the denitrification treatment (initial value) is lower than the denitrification rate at the time of measurement.

(Measured value) drops by 5 to 30%, and it is also possible to remove bubbles. Here, the circulation by the circulation pump 4 increases the flow velocity of the drainage passing through the packed bed, and also serves to prevent bubbles from flowing out and accumulating bubbles.

After the air bubble removal processing is completed, the pump 26 is driven to return the wastewater from the storage tank 21 to the processing tank 11, and then the valve 25 is closed and the valve 24 is opened to restart the denitrification processing. By this operation, it is considered that the wastewater is sent to the treatment tank 11 once emptied, and the remaining air bubbles are pushed away. In addition, removal of sludge and the like attached to the surface of the denitrification material can be expected.

The monitoring device 23 may be a device that can easily measure nitrate nitrogen, such as nitrate ion sensor measurement, colorimeter measurement, and GPC analysis by automatic drainage sampling.

Further, the method of removing bubbles is not limited to the above-described embodiment, but includes various embodiments as follows.

For example, pumps are provided at the drain inlet and drain outlet, and when the denitrification rate measured by the monitoring device exceeds a predetermined value, both valves are closed and the circulation pump 4 is driven to circulate the entire amount. By this operation, the wastewater in the treatment tank is circulated, and the air bubbles accumulated between the particles of the denitrification material are removed. Effluent can be removed efficiently by increasing the flow velocity in the same direction as the flow of wastewater during denitrification or by making it flow backward (opposite to the flow of wastewater during denitrification). In addition, air bubbles may be removed by reducing the pressure in the processing tank, applying vibration to the processing tank by ultrasonic waves, or blowing air or the like into the processing tank.

In addition, instead of the monitoring device, a timer device that activates / stops the bubble removal processing at a predetermined interval can be used. The predetermined interval is usually in the range of 7 days to 6 months, and should be short if the concentration of nitrate in the wastewater to be charged is high, and long if it is low.

In order to more efficiently denitrify wastewater with high dissolved oxygen, it is preferable to provide a means for reducing dissolved oxygen in the vicinity of the inflow part of wastewater with high dissolved oxygen, and more preferably, to reduce the amount of treated water in the device. It is preferable to provide a means for reducing dissolved oxygen at the part in contact with the atmosphere.

Means for reducing dissolved oxygen include heating, deaeration with an oxygen-free gas, addition of a reducing agent, treatment with aerobic microorganisms, such as treatment with aerobic sulfur-oxidizing bacteria.

Means for reducing dissolved oxygen include heating, aeration with gas that does not contain oxygen gas such as nitrogen gas, addition of a reducing agent such as sulfite that reacts with dissolved oxygen, and treatment with aerobic microorganisms. As treatment with aerobic microorganisms, it is advantageous to use a dissolved oxygen-lowering material provided with aerobic sulfur-oxidizing bacteria, elemental sulfur, a carbon source for sulfur-oxidizing bacteria, and a wastewater neutralizer.

FIG. 7 shows an example of an apparatus suitable for treating wastewater containing a large amount of dissolved oxygen. The apparatus has a dissolved oxygen removal tank 62 and a treatment tank 11. Drainage enters the dissolved oxygen removal tank 62 from the inlet line 5 and passes through the packed bed 62 filled with denitrification material. The denitrification material of the packed layer 62 may be the same as the denitrification material filled in the treatment tank 11, but it is preferable that aerobic sulfur-oxidizing bacteria adhere. Therefore, this charge The dissolved oxygen in the wastewater that has passed through the bed 62 decreases. The wastewater that has passed through the packed bed 62 enters the lower part of the treatment tank 11 from the upper part of the dissolved oxygen removal tank 61 via the connecting pipe 63, passes through the packed bed 2 filled with denitrification material, and undergoes humid sulfur oxidation. Denitrification is performed by bacteria. The wastewater that has passed through the packed bed 2 is discharged from the outlet line 6, but part of the wastewater is circulated to the lower part of the treatment tank 11 via the pump 4 and the pipe 3.

The nitrate nitrogen removal equipment of Figs. 1 to 7 can be used even in situations where hydrogen sulfide may be generated. In this case, the denitrifying agent is composed of a coexistent of calcium carbonate, sulfuric acid and iron oxide. The content of the coexisting iron oxide is 1 to 20 wt% _s and the specific surface area of the iron oxide is 0.1 lm Vg. As described above, it is preferable to use a material capable of suppressing the generation of hydrogen sulfide. Further, a denitrification material using a denitrification material in which an effective amount of iron oxide for suppressing the generation of hydrogen sulfide in addition to sulfur and calcium-based components is used is described in JP-A-2002-159993. It is also advantageous to use processing equipment. That is, a method of applying a denitrification method using autotrophic sulfur oxidizing and denitrifying bacteria is applied.A filter medium bed made of granular or massive sulfur-containing filter medium is provided in the tank, and a water supply piping system for feeding the water to be treated into the tank is provided with a filter medium. A drainage pipe system is installed in the lower part of the tank below the floor, and the drainage pipe system that sends out the treated water from the filter medium bed to the outside of the tank is installed in the upper part of the tank above the filter medium bed, and the water to be treated is raised from below the filter medium bed to above. It is configured as a water treatment tank of the upward flow type that flows toward the water, and the denitrifying agent coexists with an effective amount of iron oxide to suppress the generation of hydrogen sulfide in addition to sulfur and calcium components. Preferably, it is made of a denitrifying material. Example Using the nitrate nitrogen removal device 1 shown in Fig. 1, nitrate nitrogen was treated while circulating waste water. First, the wastewater that has flowed into the device from the inlet line 5 is filled up to the specified liquid level (the height of the outlet 6). Thereafter, the circulation pump 4 is operated, and the upper water 9 is circulated from above to below through the pipe 3, and flows out from the lower four-way outlet. The drained water uniformly penetrates into the denitrification material-filled layer 2 filled on the bottom plate having an opening and is subjected to denitrification. The amount of denitrified treated water corresponding to the flow rate is discharged from the outlet line 6 to the wastewater flowing from the inlet line 5.

In the present example, a rectangular parallelepiped treatment tank having a capacity of 100 L was filled with a sulfur-calcium carbonate mixed composition 4 O kg (bulk density 1.2) having a particle diameter of 5 to 20 mm as a denitrifying agent. Then, treated water (nutrient solution cultivation wastewater) 9 containing about 200 mg ZL of nitrate nitrogen was treated. The denitrification material was obtained by melting and mixing sulfur and limestone in a ratio of 1: 1 (weight ratio), and then pulverized, and obtained by fixing sulfur oxidizing and denitrifying bacteria at room temperature. The wastewater was passed through the inlet line 5 at a flow rate of 6 L / hr and circulated at a circulation rate of 1200 L / hr. Water temperature was maintained at 25 ° C.

As a result of confirming the change over time in the nitrate nitrogen removal treatment status, there was no significant stagnation of nitrogen gas between the particles of the denitrification material, and the nitric acid remaining in the treated water even after 300 days from the start of the denitrification treatment. The nitrogen concentration remained below 1 Omg / L and maintained an excellent denitrification effect.

Example 2

The treatment tank was filled with 3 kg of a denitrifier made of an inorganic material obtained by granulating a sulfur molten mixture composed of 50 parts by weight of sulfur and 50 parts by weight of calcium carbonate into particles having a diameter of 5 to 20 mm. This denitrifying material was cultured for three weeks with denitrifying bacteria contained in soil collected from a leek field. The nitrate nitrogen removal device shown in Fig. 5 was used. The treatment tank is a cylinder with a diameter of 10 cm and a length of 70 cm, the capacity of the spare tank 16 is about 20 L, the capacity of the treatment tank is about 5 L, and the capacity of the spare tank and the treatment tank is 30 L. ° C setting. As the wastewater, artificial wastewater adjusted to a nitrate nitrogen concentration of 200 mg / L by mixing Otsuka Chemical's OK_F-2 into tap water was used. The concentration of nitrate nitrogen (N0 ₃ value) changes in the treated wastewater discharged from the outlet of the treatment tank through continuous water flow for 3 times at a wastewater temperature of 100 ° C at a temperature of 100 ° C / 100 ° C. Was examined over time. The amount of circulation was 100 L / hr or 0. When the circulating amount was 0, the lower limit of the concentration was 3 mg / L and the upper limit was 7 mg ZL. At 100 L / hr, the lower limit of the concentration was 1 mg / L and the upper limit was 3 mg ZL.

On the other hand, if the treatment is performed under similar conditions using a nitrate nitrogen removal device without a preparatory tank, the wastewater with a wastewater temperature of 10 ° C will be charged to the inlet of the processing tank at the same temperature, and will be discharged from the outlet. The nitrate nitrogen concentration of the treated wastewater was a lower limit of 25 mg ZL and an upper limit of 42 mg / L. In this case, the circulation amount was set to zero.

Example 3

The nitrate nitrogen removal device shown in Fig. 5 was used. Otsuka Chemical's OK—F—2 is mixed with tap water to make human wastewater adjusted to a nitrate nitrogen concentration of 50 mg ZL for 12 hours at a wastewater temperature of 5 ° C and a drainage rate of 1 L / hr. The nitrate nitrogen concentration at the outlet of the treatment tank was examined 12 hours later when the water was passed and the circulation rate was set to 10 L / hr or 0.When the circulation rate was 0, it was 5 mg ZL. In the case of L / hr, it was 2 mg / L.

Example 4

The same experiment as in Example 3 was performed. Adjust the nitrate nitrogen concentration to 5 O mg / L. The artificial wastewater was drained at a drain temperature of 5 ° C and a drainage rate of 50 mL / _min , with 1 hour of continuous water flow and 1 hour of stop time alternately repeated three times, and the outlet of each tank after the third drainage The nitrate nitrogen concentration was examined. At this time, the feed rate of the drainage metering pump leading to the treatment tank was set to be 400 mLZhr. As a result, the nitrate nitrogen concentration of the wastewater discharged from the treatment tank after the third drainage was 3 mgZL (circulation volume 0) and lmg / L (circulation volume 40 L / hr).

Example 5 '

Sulfur and limestone powder were melt-mixed at a ratio of 1: 1 (weight ratio) and crushed to obtain a denitrifying material. A denitrification material in which sulfur oxidizing and denitrifying bacteria were established at room temperature was obtained by a conventional method. An equal amount of the denitrifying material on which the sulfur oxidizing and denitrifying bacteria are fixed and the denitrifying material before fixing are mixed and added to the culture medium adjusted to a nitrate nitrogen concentration of 200 mg / L with a nitric acid reamer. , Culture, and colonization. The culture medium was maintained at a water temperature of 5 ° C, and when the nitrate nitrogen concentration reached 1 Otng / L or less, a nitrate rim was added so that the nitrate nitrogen concentration became 200 mg / L. After culturing for months, a low-temperature denitrifying material was obtained.

In this example, a rectangular parallelepiped treatment tank having a capacity of 100 L was filled with 40 kg of a low-temperature denitrifying agent, and wastewater of about 100 mg L of nitrate nitrogen was treated. The wastewater is passed through the inlet line 5 at a flow rate of 6 L / hr, circulated at a circulation rate of 120 L / hr or 0, and maintained at a water temperature of 5 ° C or 30 ° C. And the denitrification performance at high temperature was measured.

Table 1 shows the results of measurement of the nitrate nitrogen concentration of the wastewater and treated water from the start of the test to the 10th day, and Table 1 shows the average values for the 10th day.

Note that a 20 ° C-denitrification material was obtained in the same manner except that the medium was maintained at a water temperature of 20 ° C. The denitrification performance of this denitrification material at low and high temperatures was measured in the same manner as above. Table 1 shows the average values for 10 days. 20 ° C- Use denitrification material At 30 ° C, it is possible to treat the treated water with a nitrate nitrogen concentration as low as 0.4 mg / L on average, and the denitrification rate is 99.6 ° / ₀ . However, when the water temperature was 5 ° C, the nitrate nitrogen concentration of the treated water could only be treated to an average of 63.9 rag / L, and the denitrification rate was 41.4%. there were.

table 1

Example 6

Using the processing apparatus shown in Fig. 6, two denitrifying materials (autotrophic sulfur oxidative denitrification; bacteria attached to a molten mixture of sulfur and limestone) were placed in a processing tank 11 (capacity: 200 L). 100 kg of artificial wastewater filled with solution fertilizer for solution cultivation (OK-F1 manufactured by Otsuka Chemical Co., Ltd.) and adjusted to a nitrate ion concentration of about 200 mg / L, at a temperature of 20 ° C and a flow rate of 70 ° C A denitrification treatment was performed by pouring at 0 L / S. The circulation volume was set at 700 000 L / day or 0.

Using a nitrate ion sensor and a personal computer as the monitoring device 23, air bubble removal means (opening / closing the valves 24 and 25 and stopping the operation of the pump 26) according to the denitrification rate of nitrate nitrogen in the treated wastewater. Is configured to be controlled.

The nitrate nitrogen concentration of monitoring device 23 was set to 10 mg / L (denitrification rate 95%). The denitrification treatment was continued while continuously measuring the change in the concentration of nitrate nitrogen in the treated water. The nitrate nitrogen concentration of the treated water was 5 mg / L or less (denitrification rate 97.5%), but started to increase gradually from about 2 weeks after the start of treatment, and on the 23rd day (circulation volume 0) On the 50th and 50th days (circulation volume of 700 L /), the air bubble removal means was activated. At this time, the wastewater in the treatment tank 11 moves to the storage tank 21 and the treatment tank 11 is emptied. After that, the wastewater in the storage tank 21 returns to the treatment tank 11 and the wastewater is continuously introduced into the treatment tank 11 to be removed. It was confirmed that the nitrogen treatment was restarted.

Example 7

Using the apparatus shown in FIG. 7, a wastewater nitrate removal test of 4.5 rag of dissolved oxygen and 104.1 mg / l of nitrate nitrogen was conducted.

Drainage enters the dissolved oxygen removal tank 61 from the inlet line 5 and passes through the packed bed 62 filled with denitrification material. The denitrification material in the packed layer 62 is the same as the denitrification material to be filled in the treatment tank 11, but has aerobic sulfur-oxidizing bacteria attached thereto. The wastewater that has passed through the dissolved oxygen removal tank 61 enters the treatment tank 11 ', passes through the denitrification material packed bed 2, and is denitrified by aerobic sulfur-oxidizing bacteria. The wastewater that has passed through the packed bed 2 is discharged from the outlet line, but part of it is circulated through the pump 4 and the pipe 3.

As the denitrifying material, a granular material obtained by mixing 100 parts by weight of limestone powder and 120 parts by weight of sulfur powder and compression-molding the mixture at 65 kg / cm ² was used. For the denitrification material in packed beds 2 and 62, a new SC material without sulfur-oxidizing bacteria was added to 10 parts by weight of denitrifying material with Thiobacillus denitrificans, which is a facultative anaerobic sulfur-oxidizing bacterium. The denitrification material in the dissolved oxygen removal tank 61, which was filled with a mixture of 90 parts by weight, was subjected to aerobic treatment in advance to convert sulfur-oxidizing bacteria into aerobic sulfur-oxidizing bacteria, and denitrification of the treated layer 11. The material is of facultative anaerobic sulfur oxidizing bacteria Used as is.

Set the temperature to 25 ° C, pump 5 L / day of artificial drainage by pump, and

When 500 L / day or 0 was set, the final treated water was 0.3 rag / 1 of dissolved oxygen, 0.4 mg / l of nitrate nitrogen (circulation amount 0) or 0.2 rag 8 (circulation amount 5 00 L / day), and the denitrification rate was 99.6% or 99.8%.

If the denitrification material in the dissolved oxygen removal tank 61 and the denitrification material in the treatment layer 11 were both used as facultative anaerobic sulfur-oxidizing bacteria, the final treated water had a denitrification rate of 9 4.

It was 6% (circulation volume 0).

Examples 8 to 10, Comparative Examples 1 to 3

Pour 400 ml of artificial wastewater with a nitrate ion concentration of 100 mg / 1 into a 200 ml glass sealed container, adjust the pH to 4.5 with dilute sulfuric acid, and then use commercially available sulfur-oxidizing bacteria. (DSM807) Inoculated with Nikko Co., Ltd. Sulfuric carbonate-based denitrifying material (SC material, average particle size 5 to 20 mm) 400 g, and various oxidations shown in Table 2 Iron, iron sulfide, and iron powder were added, and a denitrification test was performed by a batch test. The values in the table are% by weight of additives with respect to the whole. The denitrification test was performed while keeping the container at an average water temperature of 20 ° C. with the container sealed.

Table 2 shows the results of measuring the nitrate ion concentration in the artificial wastewater and the hydrogen sulfide gas concentration in the closed vessel on the 5th day after the start of the test.

It was found that iron oxide suppressed the generation of hydrogen sulfide without reducing the denitrification performance. On the other hand, the additive-free, iron sulfide and iron powder-added ones did not show any reduction in the denitrification performance, but did not show the effect of preventing hydrogen sulfide generation, and on the contrary, the addition increased.

Table 2 Example Example Example Comparative example Comparative example Comparative example

6 7 8 1 2 3 Hydrous iron oxide 2

Mac, netite 5

Hematite 8

Iron sulfide 1 0

Iron 10 Nitrate ion concentration 1.8 2 .1 2 .2 2 .0 2 .6 2 .2 degree (mg / 1)

Amount of hydrogen sulfide generated <0.2.2.6.3.5 1 2 0 3 9 0 3 5 0

(ppm)

Overall judgment 〇〇〇 X X X

Examples 11 to 13 and Comparative Examples 4 to 6 Sulfur Z calcium carbonate / iron oxide was integrated by the heating and quenching method with the composition shown in Table 2, and the mixture was crushed to obtain 5 to 10 mm φ. A commercially available sulfur-oxidizing bacterium (DSM807) was inoculated into 200 g of the nitriding material, and then made into glass containing 200 ml of artificial drainage adjusted to a nitric acid concentration of 50 mg / 1. It was stored in a closed container (400 Oml) and a denitrification test was performed by a batch test. The denitrification test was carried out by keeping the container sealed and maintaining the average water temperature at 20 ° C. Table 3 shows the results of measuring the concentration of ion nitrate in the wastewater and the concentration of hydrogen sulfide gas in the sealed container on the 5th day after the start of the test. It was confirmed that iron oxide coexisting in the same particle suppressed the generation of hydrogen sulfide without lowering the denitrification performance in the specific surface area and the coexistence ratio. On the other hand, a large amount of hydrogen sulfide was generated in the case of no addition. Even if iron oxide has a small specific surface area, the prevention of hydrogen sulfide generation is not sufficient, and if the amount of iron oxide added is large, hydrogen sulfide generation can be prevented, but it is good in terms of denitrification efficiency. I could not tell. Table 3

The properties of the iron oxide and the like used are shown below.

Hydrous iron oxide: loess, specific surface area: 4 O mVg

Magunetai DOO: Fe ₃ 0 _4, the specific surface area; 8 0 m ² / g

To Matthew bets: α - Fe ₂ 0 _3, a specific surface area; 5 m ² / g

. To Matthew preparative B: - Fe ₂ 0 ₃ specific surface area; 0 0 1 m ² / g

Iron sulfide: F e S, specific surface area: 8 m ² / g

Iron: Fe, specific surface area; 1 raVg Industrial applicability According to the present invention, stable nitric oxide performance is always exhibited, and efficient nitric acid utilizing the characteristics of the removal method using sulfur-oxidizing bacteria to the maximum. A nitrogen removal is performed. The nitrate-nitrogen denitrification material of the present invention is excellent when low-nitrate nitrogen in water has a low concentration. However, it can prevent the outflow and death of sulfur-oxidizing bacteria, and can prevent the generation of hydrogen sulfide, which is likely to be generated at low concentrations of nitrate nitrogen and dissolved oxygen in water.

Claims

The scope of the claims

(1) In a wastewater treatment tank having a bed of denitrification material composed of sulfur and calcium components, wastewater containing nitrate nitrogen is passed through the bed of denitrification material and drained using sulfur-oxidizing bacteria. Removal of nitrate nitrogen by removing nitrate nitrogen from inside, and circulating at least a part of treated wastewater that has passed through the packed bed to the entrance side of the packed bed or to the middle layer of the packed bed Method.

(2) A preliminary tank equipped with temperature control means is placed in front of the wastewater treatment tank.If the temperature of the wastewater to be introduced into the preliminary tank is outside the specified temperature range, keep it at 10 to 50 ° C. 2. The method for removing nitrate nitrogen according to claim 1, wherein the temperature is adjusted in the preliminary tank to a predetermined temperature range suitable for the growth of sulfur-oxidizing bacteria living inside or around the denitrification material.

(3) The method for removing nitrate nitrogen in wastewater according to claim 1, wherein wastewater is introduced into a wastewater treatment tank after a dissolved oxygen reduction treatment.

(4) The method for removing nitrate nitrogen according to claim 1, wherein the sulfur-oxidizing bacteria are cultured on the denitrifying material at a temperature of 1 to 1 ° C for 23 or more times and allowed to settle.

(5) The method for removing nitrate nitrogen according to claim 1, wherein when the predetermined interval or the denitrification rate decreases, the denitrification material is subjected to a treatment for removing bubbles attached to the surface of the denitrification material to restore the denitrification activity.

(6) The air bubbles are removed by discharging the wastewater in the treatment tank and emptying it, then re-introducing the wastewater, reducing the pressure in the treatment tank, and applying vibration to the treatment tank by ultrasonic waves or the like. 6. The method for removing nitric acid and nitric acid according to claim 5, wherein the method is a method of giving, a method of increasing the flow rate of wastewater, a method of recirculating wastewater, a method of blowing air into a treatment tank, or a combination thereof.

(7) It has a packed bed filled with a denitrifying material consisting of sulfur and calcium components. In a device that removes nitrate nitrogen using sulfur-oxidizing bacteria in a wastewater treatment tank, at least a part of the wastewater that has passed through the packed bed in this wastewater treatment tank is at the inlet side or in the middle of the packed bed. A nitrate nitrogen removal device characterized by having a circulation pump for circulating through the bed.

(8) The apparatus for removing nitrate nitrogen according to claim 7, further comprising a temperature control means, and a preliminary tank for introducing wastewater containing nitrate nitrogen, before the wastewater treatment tank.

(9) The nitric acid according to claim 7, wherein the wastewater treatment tank filled with the denitrification material is arranged inside the reserve tank, and at least a part is immersed in the wastewater in the reserve tank. Nitrogen removal equipment.

(10) The apparatus for removing nitrate nitrogen according to claim 7, wherein the wastewater treatment tank includes a temperature adjusting means.

(11) The nitrate nitrogen removing apparatus according to claim 7, further comprising a dissolved oxygen reducing means in front of the wastewater treatment tank.

(12) The nitric acid according to claim 11, wherein the dissolved oxygen lowering means is at least one means selected from treatment with an aerobic oxidizing bacterium, addition of a reducing agent, heat treatment and aeration with a gas containing no oxygen gas. Nitrogen removal equipment.

(13) The apparatus for removing nitrate nitrogen according to claim 7, wherein the denitrifying material is made of a coexistent of calcium carbonate, sulfur and iron oxide, and can suppress generation of hydrogen sulfide.

(14) A denitrification material used for denitrification of nitrate nitrogen in water using sulfur oxidizing bacteria, wherein the composition of the denitrification material is composed of a calcium carbonate salt and a coexistence of sulfur and iron oxide. A content of coexisting iron oxide of 1 to 20 wt%, a specific surface area of the iron oxide is 0.1 lm ² Zg or more, and generation of hydrogen sulfide can be suppressed; Processing materials.