JP3269957B2 - How to remove nitrogen from wastewater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing nitrogen from wastewater containing organic pollutants and compounds such as organic nitrogen and ammonia, which are reducing nitrogen compounds, such as municipal sewage, organic industrial wastewater, and sludge treatment water. The present invention relates to a method for removing nitrogen from wastewater for stably and efficiently removing compounds.

[0002]

2. Description of the Related Art Regarding a method for removing nitrogen in wastewater,
Although physical or chemical treatment methods have been studied for some time, biological treatment methods are currently the most popular treatment methods because of their cost advantages. Biological nitrogen removal is basically performed by reducing nitrogen by nitrifying bacteria under aerobic conditions, for example, ammonia nitrogen (hereinafter abbreviated as NH ₄ -N).
Reaction of nitrate nitrogen (hereinafter abbreviated as NO ₃ -N) by oxidation of nitrocellulose, ie, nitrification or nitrification reaction (see the following formula (1)), and facultative anaerobic bacteria under anaerobic conditions Is performed in combination with nitrogen gas generation by reduction of NO ₃ —N, that is, denitrification or a denitrification reaction (see the following formula (2)). The denitrification reaction is the respiration of facultative anaerobic bacteria under the condition that dissolved oxygen (hereinafter abbreviated as DO) does not exist, and requires an organic substance or the like as a carbon source (hydrogen donor).

[0003] _{NH 4 -N → NO 2 -N →} NO 3 -N ( _{nitrification) --- (1) NO 3 -N} → NO 2 -N → N 2 ( denitrification) --- (2)

[0004] Regarding the biological nitrogen removal process, reduction of equipment area, reduction of organic carbon source as hydrogen donor,
Various processes have been proposed for the purpose of reducing alkali agents such as sodium hydroxide. It can be broadly classified into a series system, a circulation system, or a combination thereof. In the series method, nitrification is first performed, and then denitrification is performed.
There is a case where a hydrogen donor necessary for denitrification is added from the outside, and a case where endogenous respiration of activated sludge is used without addition.

On the other hand, as a circulation system, as shown in FIG. 3, a nitrification solution circulation system in which denitrification is performed first and then nitrification is performed, that is, a modified activated sludge circulation method is widely studied. This method has the advantage that the alkali consumed by the nitrification can be recovered to some extent by denitrification by circulating the nitrification solution. However, in the activated sludge circulation modified method, a part of the nitrification liquid that is not returned in circulation flows out without passing through the denitrification tank,
There is a limit to the total nitrogen removal rate (hereinafter abbreviated as TN removal rate). In addition, as shown in FIG. 3, the aerobic tank in the conventional modified activated sludge circulation method is intended to remove organic substances and promote the nitrification reaction in the same tank.

[0006] Nitrifying bacteria used in the nitrification reaction have a slower growth rate than activated sludge that decomposes organic substances, and it is difficult to maintain a high concentration in a reaction tank. Therefore, various methods have been proposed in which various carriers are added to a reaction vessel, nitrifying bacteria are adhered to the carrier, the nitrifying bacteria are maintained at a high concentration in the reaction vessel, and the reaction efficiency is improved. For example, JP-A-5-100787 discloses that a polyurethane sponge is added to an aerobic tank of a reactor in which activated sludge is present so that a BOD (biological oxygen demand) / N ratio in city sewage is 4 to 20. Organic wastewater to its BOD / N
Biological methods of treating while maintaining are described.

[0007]

[Problems to be solved by the present invention]
In the process of biological nitrogen removal, urban sewage
Contains components that inhibit nitrification and denitrification reactions
And NH _Four-N is about 20 to 50 mg / l
It is. Therefore, the activated sludge circulation
NH in water_Four-N is NO_ThreeBiologically oxidized to -N
Reaction) and the generated NO_Three−N to nitrogen gas
Then, it can be denitrified. However, the rate of nitrification reaction
Is smaller than the decomposition rate of organic matter,
Hydraulic Retention Time (HRT)
(Abbreviated) becomes extremely long. example
If it is NH like city sewage_Four-N of 20 to 50 mg / l
Even in this case, the HRT is long, 12 to 16 hours, and the equipment is large.
It has to be typed.

Further, various industrial wastewaters such as a leather industry, a textile industry, and a chemical industry, and sludge treated waters are used for biological oxygen demand (hereinafter abbreviated as BOD) and chemical oxygen demand (Chemical oxygen demand). Oxygen Demand: high concentration of organic material as represented by the following COD abbreviated), moreover, with include components, such as aromatic organic substances inhibit nitrification and denitrification, the NH ₄ -N It often contains 50 mg / l or more. Therefore, the rate of the nitrification reaction is further reduced, and the equipment must be further enlarged. Therefore, it is considerably difficult to efficiently remove nitrogen by a conventional activated sludge circulation method or the like. Hereinafter, the problems of a conventional biological nitrogen removal process will be described separately into a nitrification reaction and a denitrification reaction.

First, in the nitrification reaction, NH4 is contained in wastewater._Four
When -N is contained in an amount of 50 mg / l or more, NH_Four
-N to NO_Three-N is not complete and nitrite
Element (hereinafter NO_Two−N).
No. Nitrifying bacteria are NH_Four-N is NO_TwoOxidizes to -N
Bacterial groups such as Nitrozomonas (Nitrosomon
as) And NO_Two-N is NO_ThreeBacteria that oxidize to -N
Groups, such as Nitrobacter (Nitrobacto
r), But Nitrobacter is more
Because the growth rate is higher than that of Rozomonas, urban sewage
NO for elephants_Two-N is not accumulated. I
However, DO becomes insufficient or inhibits nitrification reaction in wastewater
If the substance is present, the Nitrobactor
Nitrobac is more susceptible to reaction inhibition than Zomonas.
The growth rate of the tar becomes extremely low. In such a case, N
O_Two−N easily accumulates.

[0010] NO accumulated in a large amount in the reaction tank_Two-N is Yes
Inhibits the function of microorganisms that degrade equipment and nitrifying bacteria themselves
There is a risk of doing. Furthermore, NO_Two1 mg of -N is COD
Is measured as 1.14 mg as NO_Two-N is
When accumulated in the treated water, the COD in the treated water may increase.
I have a mind. Such NO_Two-Nitration reaction to produce N
Prevent and NO_ThreeTo promote the nitrification reaction that produces -N
To the reactor _Four-N load reduction, organic load reduction
Control, aerobic control of the reaction tank, microorganism retention time (Sludge R
etention Time (hereinafter abbreviated as SRT)
It is necessary to take measures such as increasing the HRT of the tank. But,
An increase in SRT or HRT causes an increase in the size of the equipment.
This is described, for example, in "Wat.Res., 1990, Vol. 24, N.
o.3, pp.303-312 ".

The artificial wastewater containing 80 mg / l of NH ₄ —N was maintained at a DO of 0.5 mg / l, and the HRT of the reactor was 4 mg / l.
It was reported that when treated under day conditions, 60 mg / l of NO ₂ -N was accumulated, and it was concluded that the oxidation reaction for producing NO ₂ -N proceeds even when DO is low.
In addition, experiments in which the COD of the influent water was varied report that the organic matter load affects the generation and accumulation of NO ₂ -N. Thus, the concentration of organic matter is high and NH
_When treating wastewater containing a high concentration of _4- N by a biological nitrogen removal process using a conventional floating activated sludge such as a modified activated sludge circulation method, NO ₂ -N
However, there remains a problem that a nitrification reaction that accumulates easily proceeds.

Meanwhile, conventionally, in the above-mentioned modified activated sludge circulation method, there is a method in which a floating carrier such as a polyurethane sponge is added to an aerobic tank to efficiently perform a nitrification reaction. It is said that when a floating carrier is added to an aerobic tank, nitrifying bacteria can be maintained at a high concentration on the surface of the floating carrier, and as a result, the nitrification reaction speed is increased and the nitrification reaction is apt to occur. However, when the concentration of the organic matter in the wastewater is high, not only the nitrifying bacteria, but also the bacteria that decompose the organic matter on the surface of the floating carrier will be propagated at the same time. It is well known that the growth rate of bacteria that decompose organic matter is much higher than that of nitrifying bacteria, and the effect of accelerating the nitrification reaction by adding a floating carrier is significantly reduced when the concentration of organic matter in wastewater is high. Resulting in. In addition, wastewater is from the leather industry,
In the case of various industrial wastewater such as textile industry and chemical industry and sludge treated water, even if a suspended carrier is added, the function of nitrobacter is easily reduced due to the influence of inhibitory components, and NO ₂ -N is reduced. The problem of accumulation remains.

Next, in the case of a denitrification reaction, when organic matter or methanol in municipal sewage is used as a carbon source, NO ₃ -N to N ₂ as shown in the formula (2) is used in the reaction tank.
It is rare that the above reaction is completed and NO ₂ -N accumulates. However, also in the case of the denitrification reaction, when the wastewater is various industrial wastewater such as a leather industry, a textile industry, and a chemical industry or sludge treatment water, a phenomenon similar to the matter described in the nitrification reaction may occur. That is, denitrifying bacteria also convert NO ₃ -N to NO.
Until ₂ -N bacteria group and NO ₂ -N reducing considered to be divided into bacteria to reduced to N _2, but functions by inhibition of bacterial group include organic matter of reducing NO ₂ -N to N ₂ And the phenomenon that NO ₂ —N accumulates in the denitrification tank is often observed and poses a problem.

Furthermore, in controlling an aerobic tank in a biological nitrogen removal process using a conventional floating activated sludge such as a modified activated sludge circulation method, DO is generally used as a control index. Many. However, DO has little inhibitory component in wastewater, and it is hard to be an effective index in a situation where the activity of microorganisms tends to decrease. The nitrification reaction is DO
There are many reports on the correlation between the nitrification reaction and DO, such as progressing as the value increases. Certainly, DO is required for the nitrification reaction, which affects the nitrification reaction rate. But D
Just because O is high does not mean that nitrification is progressing. That is, for example, when the nitrifying bacteria are inhibited, DO increases because the oxygen consumption by the nitrifying bacteria decreases. Therefore, DO cannot be said to indicate the progress of the nitrification reaction. However, DO is a nitrification reaction rate,
That is, it is important from the viewpoint of maintaining the growth rate of nitrifying bacteria, and the DO of the reaction tank is at least 2-3 mg /
1 or more.

[0015] The present invention eliminates the above-mentioned problems when a conventional treatment method such as a modified activated sludge circulation method is applied to wastewater containing organic matter and high concentration of nitrogen as described above, and is stable. It is an object of the present invention to provide a method for efficiently and efficiently removing nitrogen in wastewater.

[0016]

In accordance with the present invention, in order to solve the problems] In the activated sludge circulation variant circulating process waste water containing organic substances and reducing nitrogen provided the anaerobic tank and the aerobic tank, a) the aerobic tank is good Divided into an air tank (1) and an aerobic tank (2) or in multi-stages; and b) the wastewater is denitrified in an anaerobic tank (3) and contains organic matter in the aerobic tank (1). Oxidized and nitrified in the aerobic tank (2) for reducing nitrogen, or, if the aerobic tank is divided into multiple stages, after the treatment in which the wastewater is oxidized for organic matter, Is treated for nitrification , and the treated water is subjected to final precipitation treatment.
After that, the reducing nitrogen in the treated water after the final precipitation
Exhausted after oxidation treatment by gas reactor (5)
A method for removing nitrogen from wastewater is provided. In the aerobic tank (1), organic substances indicated by BOD in the wastewater are sufficiently removed, and then, in the aerobic tank (2), the reducing nitrogen is nitrified. That is, according to the present invention, the organic matter oxidation and the nitrification are performed in independent and separate aerobic tanks (1) and (2), respectively, so that the organic matter oxidation and the nitrification are performed in the same aerobic tank. There is an advantage that the functional inhibition on the nitrification reaction due to the organic matter caused in the conventional treatment method, particularly the competition for ingestion of DO is reduced, and the nitrification reaction easily occurs. In addition, the effluent after the precipitation treatment is aerobic.
The oxidation treatment is performed by the reactor. As a result, nitrification
In the case of industrial wastewater containing a suitable inhibitory component, NO ₂ -N
Accumulation can be completely prevented.

Further, in a preferred embodiment of the present invention, a floating carrier having a section of 5 to 100 mm is placed in the aerobic tank (2) for 5 minutes.
Add ~ 40% by volume. Thereby, the nitrification treatment is performed more efficiently. In the embodiment of the present invention, preferably, the oxidation-reduction potential of the wastewater in the anaerobic tank (Ag / AgCl
Standard) is set to -100 to -200 mV, and preferably, the oxidation-reduction potential (Ag / AgClCl) of the wastewater in the aerobic tank (2).
Criterion) is maintained at +100 to +200 mV.
Details, the filling carrier aerobic reactor and saddle ceramics blast furnace slag as a main raw material, also, preferably, the redox potential of the treated water in the aerobic reactor (Ag / AgCl reference) + 100 Maintain at +200 mV.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. FIG. 1 shows the flow of the method for removing nitrogen from wastewater according to the present invention. As shown in FIG. 1, organic wastewater containing organic matter such as sewage and wastewater is supplied to an anaerobic tank (3), an aerobic tank (1),
It is processed in the order of the aerobic tank (2), separated into solid and liquid by the final sedimentation tank (4), and discharged. In the anaerobic tank (3), NO ₃ -N in the nitrification liquid circulated from the aerobic tank (2)
The denitrification to N _2. The aerobic tank (1) promotes oxidation (removal) of organic substances, and the aerobic tank (2) promotes nitrification. Further, the aerobic reactor (5) downstream of the final sedimentation basin (4) is for completely preventing the remaining NO ₂ -N in the treated water by promoting the NO ₃ -N generating type nitrification reaction. .

First, the reason why the processing is performed by dividing the aerobic tank into the aerobic tank (1) and the aerobic tank (2) will be described. Aerobic tank (1)
If the organic matter decomposing bacteria almost completely decompose the organic matter in the wastewater, the nitrification reaction by the nitrifying bacteria in the aerobic tank (2)
It is rarely suppressed by DO consumption due to organic matter decomposition. In the case of wastewater containing an inhibitory component for nitrifying bacteria,
Since the inhibitory component does not flow directly into the aerobic tank (2) that causes nitrification, the adverse effect on nitrification can be reduced. Therefore, by dividing the aerobic tank into the aerobic tank (1) and the aerobic tank (2), the efficiency of the nitrification reaction can be remarkably improved. The aerobic tank is not limited to two tanks, and may be divided into multiple stages.

After the final sedimentation basin (4),
It is preferable to install the aerobic reactor (5) shown in FIG.
Good. In other words, wastewater is used in the leather, textile, and chemical industries.
NH as in the treated water of various industrial wastewater and sludge, such as work ₄
When the concentration of -N is high, the aerobic tank (2)
Completely complete the reaction from NH ₄ -N to NO ₃ -N
Instead, NO ₂ -N may remain. Such a place
If the aerobic reactor (5) is installed,
Immobilization of nitrifying bacteria such as slow nitrobacter at high concentration
The reaction from NO ₂ -N to NO ₃ -N is efficient
You can proceed to. As a result, NO ₂ −
N hardly remains. Furthermore, by adding a floating carrier to the aerobic tank (2), the aerobic tank (2)
The nitrification efficiency can be dramatically improved. In the wastewater flowing into the aerobic tank (2), since the organic matter has already been decomposed by the aerobic tank (1), almost no organic matter remains. Therefore, nitrifying bacteria are preferentially grown on the surface of the floating carrier. This is because you can do it. As shown in FIG. 2, the floating carrier (9) to be added to the aerobic tank (2) of the present invention may have a specific gravity of less than 1, and includes a hollow body, a porous body, and a foam. And a foam having a large specific surface area. In addition, as a material, an organic material such as a synthetic resin such as a polyether-based polyurethane and a polyester-based polyurethane, or an inorganic material such as a ceramic can be used. In addition, from the viewpoint of the affinity of microorganisms, it is preferable that the carrier such as polyurethane used has a water absorption of 3% or more as a water-permeable carrier.

Further, a foam of a hydrophilic synthetic polymer such as polyvinyl alcohol or polyacrylamide or a hydrophilic photocurable resin such as polyethylene glycol may be used as the floating carrier. The smaller the diameter of the carrier is, the larger the surface area is, and the reaction speed is improved. However, the smaller the diameter, the more easily it flows out of the aerobic tank (2), and the more easily it disappears due to wear. Therefore, the size is desirably about 5 to 100 mm. If the section is 5 mm or less, it easily flows out due to wear.
This is because if the size is more than 00 mm, the flow becomes difficult when bacteria adhere.

Further, the amount of the suspended carrier to be added to the aerobic tank (2) can be determined by measuring the nitrification rate per unit volume of the suspended carrier in advance, and determining the amount of NH ₄ —N in the wastewater flowing into the tank. The size may be determined in consideration of the size of the air tank (2). For example, in the case of a polyurethane foam, the nitrification rate per unit volume is about 100 mgN / carrier · l · hr on average. Therefore, 5-20% by volume in the aerobic tank (2)
By addition, 5 to 20 mg N /
A nitrification rate of 1 tank · l · hr is obtained. In the case of the modified activated sludge circulation method according to the conventional method, the nitrification rate per unit volume of the tank is MLSS (Mixed Liquor Suspended Solids).
Even at 00 mg / l, the nitrification rate is increased by a factor of 5 to 10 since it is about 2 to 4 mg N / tank · l · hr. However, as the added amount of the floating carrier increases, the cost of the floating carrier increases, and the circulation of the carrier in the aerobic tank (2) becomes difficult. Therefore, the addition of 40% by volume is limited. Further, it is difficult to obtain a remarkable effect by adding 5% by volume or less. Therefore, the addition amount of the floating carrier is most preferably about 10 to 20% by volume.

Next, a method of determining the volume ratio between the aerobic tank (1) and the aerobic tank (2) in the aerobic tank will be described. Basically, the volume of the aerobic tank (1) is determined from the BOD removal rate per unit MLSS, and the volume of the aerobic tank (2) is determined from the nitrification rate per unit MLSS or the nitrification rate per unit carrier. It is determined by estimating the speed per unit volume of the tank.
For example, when the MLSS of the aerobic tank (1) is 2000 mg / l, the BOD volume load for removing organic substances is usually about 0.4 kgBOD / kgMLSS.day. Therefore, BOD per aerobic tank (1) per unit time
The removal rate is 33 mg BOD / tank · l · hr. on the other hand,
When 10% by volume of polyurethane is added to the aerobic tank (2), the nitrification rate per unit volume of the aerobic tank (2) is 10 mg.
N / tank · l · hr.

From this result and the BOD / N ratio of the waste water, the volume ratio between the aerobic tank (1) and the aerobic tank (2) is calculated. For example,
In the case of wastewater with a BOD / N ratio of 5, the BRT is 200 mg / l and the TN is 40 mg / l wastewater, the HRT of the aerobic tank (1) is 6 hours, aerobic. H in tank (2)
The RT is 4 hours, the total HRT is 10 hours, and the volume ratio between the aerobic tank (1) and the aerobic tank (2) is 1.5. More precisely, taking into account that BOD is decomposed in the anaerobic tank preceding the aerobic tank (1), the volume ratio of the aerobic tank (1) and the aerobic tank (2) flows into the aerobic tank. It may be determined by the BOD / N ratio of the wastewater. In the case of such wastewater, in the conventional activated sludge circulation modified method, it is considered that the total HRT is required about 20 hours, so that the volume of the reaction tank can be reduced by 50%.

In the vicinity of the outlet of the aerobic tank (2), for example, FIG.
A holding device (8) for a floating carrier (9) such as a basket made of stainless steel as shown in (1) may be provided, and a carrier such as polyurethane may be added to the inside thereof. As a carrier separation device, a wedge wire screen is often installed inside an aerobic tank and only treated water is taken out.However, in this method, it is difficult to exchange floating carriers when polyurethane is degraded, etc. When a pump or the like is installed, there is a problem that the strainer of the circulation pump is easily clogged. If the carrier holding device (8) is installed instead of the carrier separation device, there is an advantage that such a problem does not occur and the addition amount of the suspended carrier can be easily controlled. Therefore, it is desirable to install a carrier holding device near the outlet inside the aerobic tank (2).

[0026]

The aerobic reactor generally comprises a packed bed (28) filled with a packed carrier and an air diffuser (29) for supplying air to the packed bed. Packing carriers for the aerobic reactor (5) include floating carriers, saddle-type ceramics mainly made of granulated blast furnace slag, silica-alumina ceramics, plastics, anthracite, sand, activated carbon, granulated blast furnace slag, etc. There is. In particular,
An aerobic fixed-bed reactor using a saddle-type ceramic as a carrier, which is mainly made of granulated blast-furnace slag as disclosed in No. 6589, has a large ceramic surface area and a large surface area, and nitrifying bacteria are easily immobilized. Because of its saddle shape, it has excellent gas-liquid mixing performance in the reactor, and is most desirable as an aerobic reactor (5) installed after the final sedimentation basin (4). Nitrifying bacteria are susceptible to the effect of water temperature, and if the water temperature decreases, the processing capacity tends to decrease. However, this aerobic fixed-bed reactor has a capacity of 10 mg · N / tank · l even under conditions where the water temperature is 5 to 10 ° C.
・ Has nitrification capacity of hr or more. Further, there is no need for sludge pull-out management, SRT management, sludge return, etc., and this is the most desirable as an aerobic reactor (5) for finishing.

The oxidation-reduction potential (based on Ag / AgCl) of the aerobic tank (2) for oxidizing the reducing nitrogen compound and the aerobic reactor (5) is +100 to +200 mV.
By controlling the blowing rate of air and / or oxygen-enriched air and / or oxygen from the air diffuser (29) to the aerobic tank (2) and the aerobic reactor (5) so that In addition, the nitrification reaction can be stably promoted. The oxidation-reduction potential is lowered by the organic matter of the wastewater or a reducing nitrogen compound such as NH ₄ —N, and
O ₃ —N and DO tend to increase. As described above, the progress of the nitrification reaction is closely related to the value of the oxidation-reduction potential. When the oxidation-reduction potential increases to +100 to +200 mV, nitrogen is not NH ₄ —N, but NO ₂ —N or NO ₃ −
N form. Furthermore, using DO management together, D
O may be controlled so as to be maintained at 3 mg / l or more. If the DO management is used together, it becomes clear that when the nitrification performance is lowered, it is not the performance deterioration due to the shortage of DO, and the investigation of the cause and the subsequent measures are facilitated.

In order to completely remove nitrogen from the treated water, an anaerobic reactor to which a hydrogen donor such as methanol is added and a re-aeration tank for decomposing the remaining hydrogen donor are provided downstream of the aerobic reactor. It is more preferable to install them. The nitrified liquid nitrified in the aerobic tank (2) is supplied to the anaerobic tank (3).
Returned to and circulated. The anaerobic tank (3) has a function of biologically and efficiently reducing NO ₂ -N and NO ₃ -N contained in the nitrification liquid of the aerobic tank (2) to nitrogen gas.

Usually, no carrier is added to the anaerobic tank (3), but for the purpose of improving efficiency, any one of a floating carrier, plastics, anthracite, sand, activated carbon, granulated blast furnace slag, etc. is added, or Any of saddle-type ceramics mainly made of granulated blast furnace slag and ceramics mainly made of silica-alumina clay as disclosed in Japanese Patent Publication No. 2-006589 may be filled. By maintaining a high concentration of denitrifying bacteria in such a carrier, the denitrification reaction can proceed efficiently. In order to keep the activity of the denitrifying bacteria in the anaerobic tank (3) good, the oxidation-reduction potential of the anaerobic tank (3) should be -100 to -200 mV (Ag /
(AgCl standard) is important.

The oxidation-reduction potential depends on the organic matter and NH ₄ −
It tends to be reduced by reducing nitrogen compounds such as N, and conversely, increased by NO ₃ —N and DO. For this reason, the oxidation-reduction potential management of the anaerobic tank is performed by the following method. First, when the oxidation-reduction potential is -100 mV or more, the denitrification rate decreases, and the processing performance tends to deteriorate. Conversely, if the oxidation-reduction potential of the anaerobic tank is too low, methane gas, hydrogen sulfide gas, and the like are likely to be generated, and the function of the denitrifying bacteria may be hindered. Therefore, it is desirable to maintain the oxidation-reduction potential of the anaerobic tank at -100 to -200 mV (based on Ag / AgCl).

In order to control the oxidation-reduction potential of the anaerobic tank, when the oxidation-reduction potential becomes -200 mV or less, air is supplied by a blower, and when it becomes -100 mV or more, a hydrogen donor such as methanol, isopropyl alcohol or acetic acid is added. It is desirable to install equipment. A waste liquid containing no nitrogen may be used. In general, in the case of municipal sewage, the oxidation-reduction potential of the anaerobic tank tends to increase due to inflow of rainwater and the like, and in the case of industrial wastewater containing a large amount of organic substances, the oxidation-reduction potential of the anaerobic tank tends to decrease. .

[0033]

[0034]

[0035]

[0036]

[0037]

<Example> An on-site experimental treatment was performed using leather factory wastewater. The wastewater from the leather factory, which was the subject of the experimental treatment,
Is removed. BOD averaged 600mg / l, C
OD _Mn average 400 mg / l, TN average 150 mg / l
Met. Further, the water temperature was maintained at 12 ° C. or higher even in winter. FIG. 2 shows an outline of the method. In the aerobic tank (2),
Since the TN is considerably high, 20% by volume of 20 mm square polyurethane was added as an attachment carrier for nitrifying bacteria. The polyurethane was flowed in a 5 mm mesh stainless steel carrier holding device (8). The amount of circulation from the aerobic tank (2) to the anaerobic tank (3) was 250% based on the wastewater, and the amount of sludge returned from the final sedimentation tank (4) to the anaerobic tank (3) was 50% based on the wastewater. The MLSS control value of the aerobic tank (1) and the anaerobic tank (3) was 5000 mg / l.

The capacities of the aerobic tanks (1) and (2) were determined by the following method. When the MLSS control value is 5000 mg / l, the BOD removal rate is 83 mg · BOD / tank · l · hr.
Since the nitrification rate is about 20 mg · N / tank · l · hr, the BOD removal rate / nitrification rate ratio is 4. Furthermore, since the sewage BOD / TN ratio is 4, the capacity ratio of the aerobic tank (1) / aerobic tank (2) is 4/4 =
It becomes 1. Specifically, the HRT of the aerobic tank (1) was set to 7.2 hours, and the HRT of the aerobic tank (2) was set to 7.2 hours. Further, since the denitrification rate is about 1 mgN / g · MLSS · hr, the denitrification rate per capacity of the anaerobic tank (3) is 5 mgN / g.
The tank is lhr. The total circulation amount R including the returned sludge amount is
Since it is 300%, (NO ₂ -N
+ NO ₃ -N) concentration is 150 mg × 1 / (1+
It is estimated by the formula of 3), and it is about 37.5 mg / l. Therefore, the HRT of the anaerobic tank (3) was set to 7.5 hours. Therefore, the total HRT of the anaerobic tank (3), the aerobic tank (1), and the aerobic tank (2) in this experiment is 22 hours. Further, since the HRT of the aerobic reactor (5) was maintained at 12 ° C. or higher at the water temperature, the nitrification rate was 1
0 mg · N / tank · l · hr, and the (NO ₂ −N + NO ₃ −N) concentration at the outlet of the aerobic tank (2) was 37.5 mg /
It was set to 4 hours because it is estimated to be about l.

Since the oxidation-reduction potential of the anaerobic tank (3) tends to decrease, the oxidation-reduction potential control device is used to supply air from the blower (18) into the tank via the air diffuser (29). Was controlled to -200 mV by the method of supplying.
The oxidation-reduction potential of the aerobic tank (1) was controlled to +50 mV by supplying oxygen from the blower (19) by the oxidation-reduction potential controller (13). Further, the oxidation-reduction potential of the aerobic tank (2) and the aerobic reactor (5) is increased from the blowers (20) and (21) by the oxidation-reduction potential control devices (15) and (17). ) Was supplied to the inside of the tank to control to +150 mV. 1-3
Table 2 shows the experimental results of the lunar winter season. From the results in Table 2, the treated water (26) of this method has a BOD of 10 mg / l.
Hereinafter, COD _Mn is 50 mg / l or less, and TN is 40 mg / l.
Hereinafter, NO ₂ -N was not detected, and good results were obtained.

From the results of this experiment, the present method can be applied to low water temperature in winter.
The total treatment time is about 26 hours, and leather wastewater
Organic substances and nitrogen compounds can be efficiently removed, and
NO _Two-N does not accumulate, so treated water quality is stable
Was revealed.

[0042]

[Table 2]

[0043]

According to the conventional activated sludge circulation modification method, there is a problem that the nitrification rate is slow and the equipment becomes excessively large in the treatment of wastewater containing organic substances and reducing nitrogen compounds such as ammoniacal compounds. Further, in the case of industrial wastewater, since components that inhibit nitrification and denitrification may be contained, the size of the equipment is further increased, and NO ₂ -N, which is a COD source, easily accumulates in the treated water. Becomes In the present invention, the aerobic tank comprises an aerobic tank (1) for removing organic substances and an aerobic tank (2) for nitrification, and a floating carrier is added to the aerobic tank (2) to control the oxidation-reduction potential. As compared with the conventional activated sludge circulation modified method, the nitrification rate is large, and it is possible to efficiently remove reducing nitrogen compounds such as ammonia nitrogen.
Facilities can in miniaturization, established the aerobic reactor (5),
As a result of NO ₂ -N being almost completely oxidized, the quality of treated water is improved.

[0044]

[Brief description of the drawings]

FIG. 1 is a diagram showing a flow of a method for removing nitrogen from wastewater according to the present invention.

FIG. 2 is a diagram showing an embodiment of the present invention.

FIG. 3 is a diagram showing a flow of wastewater treatment by a conventional activated sludge circulation modified method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Aerobic tank (1) 2 ... Aerobic tank (2) (nitrification tank) 3 ... Anaerobic tank 4 ... Final sedimentation tank 5 ... Aerobic reactor 6 ... Sludge return pump 7 ... Nitrification liquid circulation pump 8 ... Floating carrier holding Device 9: Floating carrier 10: Redox potential sensor 11: Redox potential control device 12: Redox potential sensor 13: Redox potential control device 14: Redox potential sensor 15: Redox potential control device 16: Redox potential sensor 17 ... Redox potential control device 18 ... Blower 19 ... Blower 20 ... Blower 21 ... Blower 22 ... Underwater stirrer 23 ... Methanol addition pump 24 ... Methanol tank 25 ... Municipal sewage or industrial wastewater 26 ... Treated water 27 ... Treated water 28 ... Filling Layer 29: diffuser

Continuation of front page (56) References JP-A-2-139094 (JP, A) JP-A-60-54792 (JP, A) JP-A-64-51197 (JP, A) JP-A-6-31297 (JP, A) , A) JP-A-7-39899 (JP, A) JP-A-7-100485 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C02F 3/34 101 C02F 3/30

Claims (7)

(57) [Claims] 1. An activated sludge circulating method in which an anaerobic tank and an aerobic tank are provided to circulate wastewater containing organic matter and reducing nitrogen. A) The aerobic tank comprises an aerobic tank (1) and an aerobic tank. B) the wastewater is denitrified in an anaerobic tank (3), oxidized for organic matter in the aerobic tank (1), and the aerobic tank (2) In the case where the reducing nitrogen is nitrified in the above or the aerobic tank is divided into multiple stages, after the above-mentioned treatment in which the wastewater is oxidized with respect to the organic matter, the treatment in which the reducing nitrogen is nitrified is performed. , The final treatment of the treated water
After that, the reducing nitrogen in the treated water after the final precipitation
Exhausted after oxidation treatment by gas reactor (5)
A method for removing nitrogen from wastewater. 2. The method according to claim 1, wherein 5 to 40% by volume of a floating carrier having a section of 5 to 100 mm is added to the aerobic tank (2) or the aerobic tank in which nitrification is performed. . 3. The method according to claim 2, wherein the floating carrier is a polyurethane foam. 4. The oxidation-reduction potential (based on Ag / AgCl) of wastewater in the aerobic tank (2) or the aerobic tank where nitrification is performed is increased by +1.
2. The method according to claim 1, wherein the voltage is maintained at 00 to +200 mV.
The method according to any one of claims 1 to 3. 5. The method according to claim 1, wherein the oxidation-reduction potential (based on Ag / AgCl) of the wastewater in the anaerobic tank (3) is maintained at -100 to -200 mV. . 6. The packed carrier of the aerobic reactor (5),
The method according to any one of claims 1 to 5, wherein the blast furnace granulated slag is a saddle-shaped ceramic mainly used as a raw material. 7. The oxidation-reduction potential (based on Ag / AgCl) of treated water in the aerobic reactor (5) is set to +100 to +2.
7. The method according to claim 1, wherein the voltage is maintained at 00 mV.
The method according to claim 1 .