JP2003245689A - Method and apparatus for treating wastewater - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently at a low cost treat wastewater containing suspended solid organic substances and ammoniacal nitrogen by reducing a nitrogen load on nitrification and denitrification. <P>SOLUTION: The wastewater containing suspended solid organic substances and ammoniacal nitrogen is separated into sludge and liquid in a precipitation tank 1, and the separated sludge is subjected to methane fermentation treatment in an anaerobic nitrification tank 2. The desorbed liquid of the nitrification tank 2 is subjected to nitrite type nitrification treatment in a nitrification tank 4, nitrification liquid is mixed with the separated liquid of the precipitation tank 1, and the mixture is denitrified by Anammox microorganisms in a denitrification tank 4. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for treating wastewater containing sewage, night soil, septic tank sludge, food wastewater and the like containing SS organic matter and ammonia nitrogen.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 2, wastewater containing SS organic matter and ammonia nitrogen is first removed from the wastewater by solid-liquid separation to remove the SS organic matter, and then subjected to a circulation denitrification method and a step denitrification method. Alternatively, it is treated by nitrifying and denitrifying by a usual nitrifying and denitrifying method. The separated sludge produced by the solid-liquid separation of SS organic matter from the wastewater is anaerobically digested together with the surplus sludge produced by the nitrification denitrification treatment, and the digested desorption solution is used to remove the SS organic matter from the wastewater in the above nitrification denitrification step. It is discharged with nitrification denitrification treatment together with the removed separated liquid, or after nitrification denitrification treatment separately outside the system.

By the way, generally, the ammoniacal nitrogen in the waste water is nitrified by oxidizing the ammoniacal nitrogen to nitrite nitrogen by the ammonia-oxidizing bacteria, and further oxidizing the nitrite nitrogen to nitrate nitrogen by the nitrite-oxidizing bacteria. The two-step biological reaction between the process and the denitrification process of decomposing these nitrite nitrogen and nitrate nitrogen into nitrogen gas by utilizing organic substances as electron donors by denitrifying bacteria which are heterotrophic bacteria After that, it is decomposed into nitrogen gas.

However, in such a conventional nitrification denitrification method, a large amount of an organic substance such as methanol is required as an electron donor in the denitrification step, and a large amount of oxygen is required in the nitrification step, so that the running cost is high. There is a drawback that.

On the other hand, in recent years, an autotrophic microorganism having ammonia nitrogen as an electron donor and nitrite nitrogen as an electron acceptor (hereinafter sometimes referred to as "ANAMMOX microorganism") has been used, A method of reacting ammoniacal nitrogen and nitrite nitrogen to denitrify has been proposed. This method does not require addition of organic matter, and thus can reduce the cost as compared with the method using heterotrophic denitrifying bacteria. Also, the yield of autotrophic microorganisms is low,
Since the amount of sludge generated is significantly smaller than that of the heterotrophic microorganisms, the amount of excess sludge generated can be suppressed. Furthermore, there is a feature that N ₂ O generated by the conventional nitrification denitrification method is not generated and the load on the environment can be reduced.

The biodenitrification process utilizing this ANAMMOX microorganism is described by Strous, M, et al., Appl. Microbio
l. Biotecnol., 50, p.589-596 (1998), it is considered that ammonia nitrogen and nitrite nitrogen react with each other in the following reaction to decompose into nitrogen gas. .

[0007]

[Chemical 1]

[0008]

As shown in FIG. 2, the digestion / desorption liquid obtained by the anaerobic digestion treatment of sludge is removed from wastewater by S
In the method of performing nitrification denitrification treatment with the separated liquid from which S-organic matter has been removed, the nitrogen load required for nitrification denitrification increases, so a large amount of oxygen is required for nitrification, and further a large amount of organic matter is required for denitrification. There is a drawback that

On the other hand, the method of separately treating nitrifying and denitrifying the digested desorbed liquid outside the system requires an apparatus for nitrifying and denitrifying the desorbed liquid, which is not preferable.

The present invention solves the above-mentioned conventional problems, and
An object of the present invention is to provide a method and an apparatus for reducing the nitrogen load on nitrification and denitrification and performing an efficient treatment at a low cost when treating a wastewater containing a volatile organic substance and ammonia nitrogen.

[0011]

A method for treating wastewater according to the present invention comprises a solid-liquid separation step of solid-liquid separating the wastewater in a method for treating the wastewater containing SS organic matter and ammonia nitrogen, and the solid-liquid separation step. An anaerobic digestion step of subjecting the sludge separated in the separation step to methane fermentation, and a nitrite-type nitrification step of nitrifying ammoniacal nitrogen in the desorbed liquid of the anaerobic digestion step into nitrite nitrogen, and the nitrite. And a biological denitrification step of mixing the treated water of the mold nitrification step and the separated liquid separated in the solid-liquid separation step to perform biological denitrification.

The wastewater treatment apparatus of the present invention is an apparatus for treating wastewater containing SS organic matter and ammonia nitrogen, and is separated by the solid-liquid separation means for solid-liquid separation of the wastewater and the solid-liquid separation means. Anaerobic digestion tank for methane fermentation treatment of sludge, nitrite type nitrification tank for nitrifying ammoniacal nitrogen in desorbed liquid of the anaerobic digestion tank to nitrite nitrogen, and treated water of the nitrite type nitrification tank And a separation liquid separated by the solid-liquid separation means, and a biological denitrification tank for performing biological denitrification treatment.

In the present invention, wastewater containing SS organic matter and ammonia nitrogen is first subjected to solid-liquid separation, and the desorbed liquid obtained by subjecting the separated sludge to methane fermentation treatment is subjected to nitrite type nitrification. Such nitrogen load can be significantly reduced. Moreover, since this nitrification treatment is nitrite type nitrification, the oxygen requirement is smaller than that in nitric acid type nitrification, and the aeration cost can be reduced.

Further, a nitrification solution containing nitrite nitrogen by nitrite type nitrification is mixed with a separation solution containing ammoniacal nitrogen obtained by solid-liquid separation of waste water to perform denitrification treatment, thereby producing an ANMMOX microorganism. Thus, denitrification can be performed at low cost.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a system diagram showing an embodiment of a wastewater treatment method and treatment equipment of the present invention.

Wastewater containing SS organic matter and ammonia nitrogen is first introduced into the settling tank 1 for solid-liquid separation. The solid-liquid separating means is not particularly limited, and a centrifugal separator, a flotation separator, a membrane separator, etc. can be used in addition to the precipitation tank. Further, in solid-liquid separation, a coagulant may be added to the waste water to perform coagulation separation. In this case, the aggregating agent used may be either an inorganic aggregating agent or an organic polymer aggregating agent, or a combination of these.

The sludge separated in the settling tank 1 is used as it is, or after being concentrated if necessary, it is introduced into the anaerobic digestion tank 2 alone or together with other sludge and the like, and subjected to methane fermentation treatment.

In the case of concentrating the separated sludge, as a concentrating method, a usual method such as gravity concentration, floating concentration, centrifugal concentration or the like can be adopted. When the separated sludge is subjected to methane fermentation treatment together with other sludge, other sludges include septic tank sludge,
In addition to biological sludge produced by biological treatment such as activated sludge, there are raw garbage, food waste, human waste, etc. In particular, when nitrogen-containing organic matter is added, not only the amount of methane gas generated increases, but also nitrogen. Since the concentration is increased, the ratio of ammoniacal nitrogen and nitrite nitrogen in the subsequent denitrification treatment is decreased, and the nitrogen removal rate is improved, which is more preferable.

In the anaerobic digestion tank 2, the sludge returned from the centrifugal separator 3 and the sludge containing the anaerobic microorganisms in the anaerobic digestion tank 2 and the separation sludge in the sedimentation tank 1 are gently stirred by the agitator 2A. Perform anaerobic digestion treatment while mixing with stirring.
Due to the anaerobic digestion process performed here, most of the organic substances in the raw water are decomposed by acid-producing bacteria and methanogenic bacteria.

The conditions for methane fermentation in the anaerobic digester 2 include both mesophilic methanogens having an optimum temperature near 35 ° C. and high temperature methanogens having an optimum temperature near 55 ° C. Can be adopted. Since the mesophilic methanogen grows slowly, it is necessary to lengthen the residence time (SRT) of the anaerobic digester 2, that is, to increase the capacity of the anaerobic digester 2, but the treatment at a relatively low temperature is possible. Therefore, the equipment for heating and keeping warm becomes simple. On the other hand, in the case of a high temperature methanogen, a heating and heat-retaining facility is required, but since the growth is fast, the residence time may be short, and there is an advantage that the capacity of the anaerobic digester 2 can be reduced. .

When the mesophilic methanogen is mainly used, the residence time of sludge in the anaerobic digestion tank 2 is 10 days or more, preferably about 15 to 30 days. On the other hand, when the high temperature methanogen is mainly used, the residence time (for example, 2 days or more) shorter than the above range can be set.

The organic matter load of the anaerobic digester 2 is 0.5 to
2.0 kg-VSS / m ³ · day, M in anaerobic digester 2
The LSS concentration is preferably 5,000 to 100,000 mg / L, preferably 20,000 to 60,000 mg / L, and the temperature is preferably 30 to 38 ° C or 45 to 60 ° C.

In the methane fermentation in the anaerobic digestion tank 2, heat treatment, crushing by a mill, ozone treatment, other pretreatment such as physical or chemical treatment, or sludge extraction in the anaerobic digestion tank 2 It is preferable to carry out a circulation treatment or the like, in which the treatment is returned to the anaerobic digestion tank 2 after the treatment of
By combining such reforming treatments, not only the sludge decomposition rate is improved, but also the concentration of organic substances in the desorbed liquid is reduced, and as a result, the nitrite type nitrification of the next step can be carried out efficiently. Will be able to.

The anaerobic digestion sludge in the anaerobic digestion tank 2 is subjected to solid-liquid separation by the centrifugal separator 3, and the separated desorbed liquid is sent to the nitrification tank 4. On the other hand, a part of the separated concentrated sludge is withdrawn to the outside of the system as excess sludge, and the rest is circulated to the anaerobic digestion tank 2 as return sludge. By doing so, the outflow of solids from the system can be suppressed and the sludge holding amount in the anaerobic digestion tank 2 can be kept high, so that the sludge weight reduction effect can be enhanced. For solid-liquid separation of anaerobic digested sludge, in addition to the centrifugal separator 3 shown in FIG.
A solid-liquid separator such as a membrane separator, a precipitation tank, or a dehydrator can be used.

In the solid-liquid separation of the digested sludge, by adding a coagulant to coagulate the digested sludge, good solid-liquid separation is performed and a clear desorbed liquid is obtained.
It is possible to suppress the outflow of solids from the system and enhance the volume reduction effect of sludge. As the aggregating agent, either an organic type or an inorganic type may be used, but an organic polymer aggregating agent, particularly an amphoteric organic polymer aggregating agent is preferable because the addition amount may be small.

The desorbed liquid separated by the centrifugal separator 3 is subjected to nitrite type nitrification in the nitrification tank 4 under aeration by the air diffuser 4A, and the ammoniacal nitrogen in the liquid is oxidized to nitrite nitrogen. It

In this nitrification tank 4, in order to carry out nitrite-type nitrification by stopping the oxidation with nitrite nitrogen without oxidizing ammonia nitrogen to nitrate nitrogen, the dissolved oxygen in the nitrification tank 4 ( DO) concentration is 0.5 mg /
Keep below L. Shorten the SRT of the nitrification tank 4. The nitrite nitrogen concentration in the nitrification tank 4 is increased. The above conditions may be appropriately adopted. When the nitrification tank 4 is operated at a low DO, a fluidized bed, a floating simplex method, a nitrification method using granulating microorganisms and the like are preferable, and when operating the SRT for a short time, the floating method is preferable.

In the nitrification tank 4, the nitrification solution subjected to nitrite type nitrification is mixed with the separation solution in the precipitation tank 1 and is denitrified in the denitrification tank 4 under anaerobic conditions.

In the denitrification tank 5, the nitric acid-type nitrification in the nitrification tank 4 oxidizes the ammoniacal nitrogen in the desorbed liquid to nitrifying nitrogen, and the nitrifying liquid containing nitrifying nitrogen and the nitrifying nitrogen in the wastewater to be treated. Since the separated liquid of the precipitation tank 1 containing ammoniacal nitrogen is introduced, the biodenitrification by the ANAMMOX microorganism using ammoniacal nitrogen as an electron donor and nitrite nitrogen as an electron acceptor is performed.

The ratio of the ammoniacal nitrogen and the nitrite nitrogen in the mixed solution of the nitrification solution and the separation solution introduced into the denitrification tank 5 is such that the molar ratio of ammoniacal nitrogen to nitrite nitrogen is 0.5. It is preferable to be 2 to 2, especially 1 to 1.5. The concentrations of ammoniacal nitrogen and nitrite nitrogen in the raw water are preferably 5 to 1000 mg / L and 5 to 200 mg / L, respectively, but the treated water is circulated or other wastewater is mixed to dilute it. This is not the case.

The biological denitrification conditions in the denitrification tank 5 are as follows:
For example, the temperature of the liquid in the denitrification tank is 10 to 40 ° C, especially 20 to 3
5 ° C., pH 5-9, especially 6-8, DO concentration 0-2.
5 mg / L, especially 0-0.2 mg / L, BOD concentration 0
-50 mg / L, especially 0-20 mg / L, nitrogen load 0.1-10 kg-N / m ³ · day, especially 1-5 kg-N
/ M ³ · day is preferable.

The form of the denitrification tank is not particularly limited, and (1) the ANAMMOX microorganisms are grown in a suspended state in the tank, and the ANAMMO discharged from the denitrification tank in the subsequent stage.
The X microorganisms are separated from the treated water by a sedimentation tank, a flotation separator, a centrifugal separator, and other solid-liquid separation means, and the concentrated ANAMMOX sludge is returned to the denitrification tank. (2) A denitrification tank using an ANAMMOX microorganism, which is filled with a carrier to which microorganisms adhere, and which grows as a biofilm on the surface of the carrier. In this case, a fixed bed in which the carrier is held in a substantially denitrified state in the denitrification tank, a fluidized bed in which the carrier slowly flows by gas or a stirrer, and a microorganism mainly composed of bacterial cells are used. A so-called USB denitrification tank, a biological filtration system in which the carrier is densely packed with a relatively uniform particle size, and has an SS filtration function, or the like may be used. (3) A denitrification tank in which an ANAMMOX microorganism that grows in a floating state and an ANAMMOX microorganism that grows on the surface of a carrier are used together. Any of the above may be adopted.

The separated liquid in the precipitation tank 1 may be subjected to aerobic treatment prior to the denitrification treatment in the denitrification tank 5 to remove soluble organic substances in advance. Excess sludge generated by the aerobic treatment in this case and excess sludge generated in other systems are preferably charged into the anaerobic digestion tank 2 for treatment.

[0035]

EXAMPLES The present invention will be described in more detail with reference to the following examples.

Example 1 According to the present invention, sewage (SS:
250 mg / L, BOD: 190 mg / L, NH ₄ −
N: 22 mg / L). First, 1 mg / L of anionic polymer flocculant was added to this sewage, and the sedimentation tank 1
The mixture was allowed to stand for 30 minutes and the supernatant was collected. This supernatant is S
S: 12 mg / L, BOD: 35 mg / L, NH ₄ −
N: It was 22 mg / L.

The sludge precipitated was collected, mixed with sewage methane fermentation sludge in a ratio of 1: 1 and stirred slowly at 35 ° C. for 30 days in an anaerobic digestion tank 2 without contact with air, and then centrifuged. Solid-liquid separation was performed by the separation device 3, and the desorbed liquid was collected. The organic matter load of the anaerobic digester 2 is 2.5 kg-VS.
S / m ³ · day, MLSS concentration was 5,400 mg / L. This desorbed liquid was SS: 88 mg / L, NH ₄ −.
It was N: 775 mg / L and BOD: 197 mg / L.

This desorbed solution was continuously added to a nitrification tank (aeration tank) 4 in which nitrite type nitrification was carried out in advance so that the residence time was 24 hours, the temperature was 30 ° C., the pH was 7.5, and the DO concentration was 0.3-.
The treatment was performed at 0.5 mg / L and a nitrogen load of 0.8 kg-N / m ³ · day. No settling tank was provided. This nitrification solution is S
S: 221 mg / L, BOD: 76 mg / L, NH ₄ −
_{N: 13mg / L, NO 2} -N: was 770 mg / L.

This nitrification solution was mixed with the supernatant obtained by the coagulation separation of the sewage in the settling tank 1, and the nitrification solution: supernatant solution = 1: 40.
The mixture was mixed at a ratio of (volume ratio), continuously added to the denitrification tank 5 containing a microorganism having ANAMMOX activity so as to have a residence time of 12 hours, and anaerobically treated. This ANAMMOX microorganism was prepared by adding ammonia nitrogen and nitrite nitrogen at a ratio of 1: 1 in a reaction vessel using a non-woven fabric as a carrier and culturing for about 1 year. The temperature of the denitrification tank was 25 ° C., the pH was 7.4, and the nitrogen load was 0.1 kg-N / m ³ · day.

As a result, from this denitrification tank 5, BOD: 16
_{mg / L, SS: 26mg /} L, NH 4 -N: 8mg /
_{L, NO 2 -N: 0.1mg /} L or _less, NO 3 -N:
0.7 mg / L of treated water could be obtained.

[0041]

As described above in detail, according to the wastewater treatment method and treatment apparatus of the present invention, the nitrogen load on nitrification and denitrification can be reduced in the treatment of wastewater containing SS organic matter and ammonia nitrogen. Therefore, efficient processing can be performed at low cost.

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of a wastewater treatment method and treatment equipment of the present invention.

FIG. 2 is a system diagram showing a conventional method.

[Explanation of symbols]

1 settling tank 2 Anaerobic digester 3 Centrifuge 4 Nitrification tank 5 denitrification tank

Claims (4)

[Claims] 1. A method for treating wastewater containing SS organic matter and ammonia nitrogen, comprising a solid-liquid separation step of solid-liquid separation of the wastewater, and anaerobic digestion of sludge separated in the solid-liquid separation step with methane. In the anaerobic digestion step, a nitrite type nitrification step of nitrifying ammoniacal nitrogen in the desorbed liquid of the anaerobic digestion step to nitrite nitrogen, and treated water in the nitrite type nitrification step and the solid-liquid separation step. A biological denitrification step of mixing the separated liquid with the separated liquid to perform a biological denitrification process. 2. The biological denitrification step according to claim 1,
A method for treating wastewater, which comprises a step of performing biological denitrification treatment with an autotrophic denitrifying microorganism using ammoniacal nitrogen as an electron donor and nitrite nitrogen as an electron acceptor. 3. An apparatus for treating wastewater containing SS organic matter and ammonia nitrogen, wherein solid-liquid separation means for solid-liquid separating the wastewater and anaerobic methane fermentation treatment for sludge separated by the solid-liquid separation means. Oxidative digestion tank, a nitrite type nitrification tank for nitrifying ammoniacal nitrogen in the desorbed liquid of the anaerobic digestion tank to nitrite nitrogen, treated water of the nitrite type nitrification tank and the solid-liquid separation means. An apparatus for treating wastewater, comprising: a biological denitrification tank that mixes the separated liquid separated to perform a biological denitrification process. 4. The biological denitrification tank according to claim 3, wherein the biological denitrification treatment is performed by an autotrophic denitrifying microorganism having ammonia nitrogen as an electron donor and nitrite nitrogen as an electron acceptor. A wastewater treatment device characterized in that