JP2003126888A - Method and device for treating wastewater containing nitrogen and phosphorus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for easily removing nitrogen at a high removal rate and at a low cost while recovering a phosphoric resource at a high efficiency from a wastewater containing a high-concentration ammoniacal nitrogen and phosphor. SOLUTION: A method and a device for treating the wastewater containing nitrogen and phosphorus, wherein the wastewater containing the ammoniacal nitrogen and phosphorus is treated in a dephosphorization process that the crystal of magnesium ammonium phosphate is produced while the ammoniacal nitrogen and a magnesium ion are allowed to stay behind, in a first denitrification process that the ammoniacal nitrogen, nitrite nitrogen and/or nitrate nitrogen in an effluent of the dephosphorization process are partially denitrified as nitrogen gas, while the ammoniacal nitrogen is allowed to stay behind in the presence of independent nutritious nitrifying bacteria independent nutritious denitrifying bacteria under a slightly aerobic condition and/or an intermittent aeration condition, and in a second denitrification process that the ammoniacal nitrogen, the nitrite nitrogen and/or the nitrate nitrogen in the effluent of the first denitrification process are denitrified as nitrogen gas in the presence of the mycology of the independent nutritious denitrifying bacteria capable of utilizing a bound oxygen.

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 purifying sewage containing high concentrations of nitrogen and phosphorus, and in particular, phosphorus is recovered as a resource by using a physicochemical method, and nitrogen is used as a biological method. TECHNICAL FIELD The present invention relates to a method and a device for treating nitrogen- and phosphorus-containing wastewater, which removes nitrogen and phosphorus with high efficiency.

[0002]

2. Description of the Related Art Nitrogen and phosphorus contained in wastewater are contained in rivers,
It is a causative agent of eutrophication problems in the ocean, reservoirs, etc., and it is desired to be efficiently removed in the wastewater treatment process. Today, as a method of treating sludge generated from the sewage treatment process, a method of dewatering sludge and incinerating it for disposal, a method of anaerobically digesting sludge and then dehydrating it, and further disposing by drying, incineration, melting, etc. There is. The separated liquid (dehydrated separated liquid) discharged from these treatment methods is highly concentrated nitrogen (about 500 to 3000 mg / liter) and phosphorus (about 1
(00-600 mg / liter), and when these are returned to the sewage treatment system, the load of nitrogen and phosphorus becomes high and the treatment cannot be completed, which causes the concentration of nitrogen and phosphorus in the discharged water to be high. Therefore, a method for efficiently removing sewage containing high concentrations of nitrogen and phosphorus is desired.

Conventionally, as a method of removing phosphorus from wastewater containing phosphorus, a biological removal method, a coagulation sedimentation method,
Various methods such as crystallization method and adsorption method have been developed. Each treatment method has merits and demerits, but the crystallization method basically does not generate sludge, the removed phosphorus can be easily reused, and the phosphorus can be removed (recovered) in a stable state. The crystallization method is HAP that recovers phosphorus in the liquid as hydroxyapatite.
Method, M recovered as magnesium ammonium phosphate
The AP method has been developed. If phosphorus is to be removed from sewage containing a high concentration of ammonia nitrogen and phosphorus, particularly sewage containing carbonic acid in the liquid, MAP method or MAP
A method combining the method and the HAP method is suitable.

The MAP method uses ammonium ions in the liquid,
Phosphate ion, magnesium ion, and hydroxyl group have the formula (1)
It reacts in the form of and is generated. The generated MAP can be reused as a slow-release fertilizer (magnesium phosphorus-containing ammonium system). Mg ²⁺ ＋ NH ₄ ⁺ ＋ HPO ₄ ² ＋ OH ⁻ ＋ 6H ₂ O → MgNH ₄・ 6H ₂ O (MAP) ＋ H ₂ O ・ ・ (1) In order to generate MAP, phosphorus, ammonia, magnesium and hydroxyl concentration obtained by multiplying the molar concentration (as ion product _{^{[HPO 4 2-] [NH 4}} +] [Mg 2+] [OH -];. [] units mol / l in) is more than the solubility product of MAP To operate as follows. That is, the phosphorus concentration in the treated water is determined by the pH in the treated water, the concentration of ammonia nitrogen,
The magnesium concentration.

As an example, the pH of treated water is 8.5,
When the magnesium concentration is 30 mg / liter and the ammonia nitrogen concentration in the treated water is 50 mg / liter, the phosphorus concentration is 36 mg / liter. Furthermore, if it is desired to lower the phosphorus concentration in the treated water, the ammonia concentration, magnesium concentration, p,
Either H must be high. For example, in the above example, assuming that there is no change in the pH and magnesium concentration in the treated water, the ammonia concentration in the treated water is 100%.
When the concentration is increased to mg / liter, the phosphorus concentration of treated water is 1
When the ammonia nitrogen concentration is 200 mg / liter, the treated water phosphorus concentration is 9 mg / liter.
It drops to mg / l. Thus, in order to lower the phosphorus concentration by the MAP method, there is a problem that the concentration of ammonia nitrogen in the treated water must be increased.

On the other hand, a biological method is used to remove nitrogen from wastewater. In general, ammoniacal nitrogen in wastewater is decomposed into nitrogen gas by a nitrification process and a denitrification process. Specifically, in the nitrification step, ammoniacal nitrogen is oxidized to nitrite nitrogen by an autotrophic bacterium, an ammonia-oxidizing bacterium, under the aerobic condition, and this nitrite nitrogen is also an autotrophic bacterium. It is oxidized to nitrate nitrogen by nitrate-oxidizing bacteria. In the denitrification step, nitrite nitrogen and nitrate nitrogen produced by the denitrifying bacterium, which is a heterotrophic bacterium, are decomposed to nitrogen gas by using organic matter as an electron donor under anaerobic conditions. In such a conventional biological denitrification method,
A large amount of oxygen (air) is required to oxidize ammoniacal nitrogen to nitrite nitrogen and nitrate nitrogen, and a large amount of methanol is used as an electron donor in the denitrification process, which reduces running costs. Was increasing.

[0007]

By the way, in recent years, a group of autotrophic microorganisms capable of producing nitrogen gas by reacting both ammonia nitrogen as an electron donor and nitrite nitrogen as an electron acceptor has recently been developed. Development of the new processing technology used is in progress. Japanese Patent Application Laid-Open No. 8-192185 shows an example of adding nitrite as nitrite nitrogen, but a method of partially nitrifying ammoniacal nitrogen is also suggested. Ammoniacal nitrogen and nitrite nitrogen are brought into contact with the above-mentioned microorganisms to react with each other, and are removed as nitrogen gas. As an example of this, in Japanese Patent Laid-Open No. 2001-104992, a part of wastewater is introduced into a nitrite tank, mixed with biological sludge containing ammonia-oxidizing bacteria in the tank, and aerated from an air diffuser to produce ammonia-oxidizing bacteria. To oxidize ammoniacal nitrogen to nitrite nitrogen. A method is disclosed in which the nitrite solution in the nitrite tank is mixed with biological sludge containing autotrophic denitrifying bacteria, and denitrification is performed under anaerobic conditions. However, even in this method, the reaction progresses up to nitrification, and as a result, denitrification by autotrophic denitrification is often insufficient under anaerobic conditions, and there is no stability in treatment and there is a problem in practicality. there were.

An object of the present invention is to contain nitrogen and phosphorus which can remove nitrogen resources from wastewater containing high concentration ammoniacal nitrogen and phosphorus with high efficiency and at low cost easily and with high removal rate. It is to provide a method for treating sewage. Further, the object of the present invention is to collect nitrogen resources and phosphorus-containing water capable of removing nitrogen at a low cost easily and at a high removal rate while efficiently recovering phosphorus resources from wastewater containing high-concentration ammonia nitrogen and phosphorus. It is to provide a processing device.

[0009]

The present invention was able to solve the above problems by using the following means. (1) In a method for purifying sewage containing ammoniacal nitrogen and phosphorus, a dephosphorization step of generating crystals of magnesium ammonium phosphate while leaving the ammoniacal nitrogen and magnesium ions in the sewage, and the dephosphorization step Of the effluent of A. niger under the presence of autotrophic nitrifying bacteria and autotrophic denitrifying bacteria under microaerobic conditions and / or intermittent aeration conditions, with ammonia nitrogen remaining and ammonia nitrogen and nitrite nitrogen And / or a first denitrification step of partially denitrifying with nitrate nitrogen as nitrogen gas;
The effluent of the step is denitrified in the presence of a group of autotrophic denitrifying bacteria capable of utilizing bound oxygen, by using ammonia nitrogen and nitrite nitrogen and / or nitrate nitrogen in the effluent as nitrogen gas. A method for treating nitrogen- and phosphorus-containing wastewater, which comprises treating in the second denitrification step. (2) The dephosphorization step comprises a reaction part for producing magnesium ammonium phosphate and a solid-liquid separation part for separating the produced magnesium ammonium phosphate from the liquid, and the pH of the reaction part is 7.5 to 9. 5. The nitrogen- and phosphorus-containing wastewater according to (1) above, wherein the concentration of ammonia nitrogen in the effluent of the dephosphorization step is 100 mg / liter or more and the concentration of magnesium ion is 3 mg / liter or more. Processing method. (3) The method for treating nitrogen- and phosphorus-containing wastewater according to (1) or (2) above, wherein the treated water after the second denitrification step is returned to the dephosphorization step or the wastewater supply pipe.

(4) In a device for purifying sewage containing ammoniacal nitrogen and phosphorus, a dephosphorization device for producing crystals of magnesium ammonium phosphate while leaving ammoniacal nitrogen and magnesium ions in the sewage, The effluent of the dephosphorization device is subjected to microaerobic conditions and / or intermittent aeration conditions in the presence of autotrophic nitrifying bacteria and autotrophic denitrifying bacteria, while further leaving ammoniacal nitrogen, And a nitrite nitrogen and / or nitrate nitrogen as a nitrogen gas to partially denitrify the first denitrification device, and the effluent of the first denitrification device is an autotrophic denitrification that can use combined oxygen A second denitrification device for denitrifying ammoniacal nitrogen and nitrite nitrogen and / or nitrate nitrogen in the effluent as nitrogen gas in the presence of bacterial groups;
A solid-liquid separation device that separates the effluent of the denitrification device into treated water and settling sludge, treated water circulation piping for a part of the treated water to the dephosphorization device, and sludge returned to the first denitrification device for the settling sludge An apparatus for treating nitrogen- and phosphorus-containing wastewater, which has a pipe. (5) The dephosphorization device comprises a reaction part for producing magnesium ammonium phosphate and a solid-liquid separation part for separating the produced magnesium ammonium phosphate from the liquid, and the pH of the reaction part is changed from 7.5 to 9.5. The treatment of nitrogen- and phosphorus-containing wastewater according to the above (4), characterized in that the concentration of ammonia nitrogen in the effluent of the dephosphorizer is adjusted to 100 mg / liter or more and the concentration of magnesium ion is kept to 3 mg / liter or more. apparatus.

The preferred embodiments of the present invention are as described above. (6) Treatment of nitrogen- and phosphorus-containing wastewater according to the above (4) or (5), characterized by having a treated-water circulation pipe for returning the treated water after the second denitrification device to the dephosphorization device or the wastewater supply pipe. apparatus.

The sewage targeted by the present invention is sewage containing high concentrations of ammonia nitrogen and phosphorus, and may contain organic substances, carbonates, nitrite nitrogen, and other substances. When calcium is dissolved in the wastewater, calcium carbonate and calcium phosphate are produced when the pH is raised in the dephosphorization process, but if the calcium concentration drops to approximately 25% of the magnesium concentration, MAP will be given priority. It begins to crystallize. When the organic nitrogen is present, it may be put into the apparatus of the present invention as it is, but the organic nitrogen may be converted into ammoniacal nitrogen in advance by anaerobic treatment or aerobic treatment. Further, even in the case of waste water having a BOD of 3 times or more that of ammonia nitrogen, the waste water may be directly put into the apparatus of the present invention, but it should be biologically treated in advance so that it becomes 1/2 of ammonia nitrogen. It is even better to lower it. Examples of target sewage include human waste, sewage, dehydrated filtrate from anaerobic digestion, leachate from waste, and wastewater from fertilizer factories.

The treatment of nitrogen- and phosphorus-containing wastewater of the present invention comprises
A dephosphorization step of producing MAP crystals while leaving ammoniacal nitrogen and magnesium ions in the sewage;
The effluent of the dephosphorization step under microaerobic conditions and / or intermittent aeration conditions, in the presence of autotrophic nitrifying bacteria and autotrophic denitrifying bacteria, while further leaving ammoniacal nitrogen,
A first denitrification step of partially denitrifying ammoniacal nitrogen and nitrite nitrogen and / or nitrate nitrogen as nitrogen gas, and an effluent of the first denitrification step autologous nutrient that can use combined oxygen In the presence of a group of oxidative denitrifying bacteria, the effluent is treated with a second denitrification step of denitrifying ammoniacal nitrogen and nitrite nitrogen and / or nitrate nitrogen as nitrogen gas, It is a method and an apparatus that enable more effective treatment by using a physicochemical method and a biological method.

Sewage containing nitrogen and phosphorus first flows into the dephosphorization process. In the dephosphorization step, the reaction of the formula (1) enables the phosphorus compound to be recovered in a reusable state while reducing the phosphorus concentration in the liquid, that is, while reducing the phosphorus concentration in the treated water. However, if the phosphorus concentration in the treated water is to be made lower, the ammonia nitrogen and / or magnesium concentration in the treated water must be made higher. Alternatively, the pH must be higher.

A suitable pH for producing MAP is 7.5.
˜9.5, preferably 8.0 to 8.5. When the pH is 7.5 or less, the solubility of MAP is large and the amount produced is small. Therefore, the phosphorus concentration of the treated water becomes high. Also, the pH
When it is 9.5 or more, the concentration of free ammonia becomes high,
It diffuses in the air. This pH range needs to be maintained in the first denitrification step and the second denitrification step, which will be described later, and it is important to combine the dephosphorization step with the first denitrification step and the second denitrification step. It greatly contributes to cost reduction.

Usually, the sewage containing a high concentration of nitrogen and phosphorus has a low magnesium concentration of about several mg / liter at most. To generate MAP from such sewage, magnesium ion or a magnesium compound is added. Must. Examples of the magnesium source to be added include magnesium hydroxide, magnesium chloride, magnesium oxide, seawater, dolomite and the like. Magnesium has a molar ratio of 1 to 1.2 with respect to the phosphorus concentration in the liquid.
Is economical. However, the concentration of magnesium in the liquid is low, specifically 20 mg / liter or less, especially 3 mg.
When it is less than 1 liter / liter, the reaction rate is significantly reduced. Further, if magnesium is extremely deficient in the subsequent biological process, biological treatment will be significantly hindered.

Magnesium is an element constituting microbial cells, and its physiological function plays an important role in binding an enzyme and a substrate in the cell. The dehydrated filtrate of anaerobic digestion
Ammoniacal nitrogen is 500 to 3000 mg / liter,
Phosphorus is dissolved in 100 to 600 mg / liter, p
When H is high, it rises to around 8, and in this case, dissolved magnesium has a very low concentration of 0.5 mg / liter or less. It is important for the present invention to reduce the ammonia nitrogen concentration and the phosphorus concentration and increase the dissolved magnesium concentration by generating MAP to which magnesium is added to such a liquid, in consideration of the biological treatment step in the latter stage. It is a component. Approximately, the concentration of dissolved magnesium should be 3 mg / liter or more, which is equivalent to city water.

Mg in the treated water having a pH of 9.5 in the treated water
When the amount is 3 mg / liter, the phosphorus concentration in the treated water is 60
To reduce the amount to less than mg / liter, it is necessary to leave at least 50 mg / liter of ammonia nitrogen. Further, in order to reduce the phosphorus concentration to 30 mg / liter or less, ammoniacal nitrogen must be 100 mg / liter or more. Ammoniacal nitrogen 100 to treated water
Remaining more than mg / l becomes a necessary factor in the first denitrification step as a post step. As will be described later, sewage having an ammoniacal nitrogen concentration of 100 mg / liter or more in the first denitrification step promotes nitrite and partial denitrification. Considering this, the dephosphorization process effluent, that is, the first denitrification process influent is 100 m of ammonia nitrogen.
It is preferable to use a liquid in which g / liter or more and magnesium concentration of 3 mg / liter or more remain.

The reaction system of the dephosphorization process includes a fluidized bed system, a complete mixing system, a seed crystal circulation system and the like. In any of the reaction methods, the crystallization phenomenon consists of a crystal nucleus generation phenomenon and a crystal growth phenomenon based on ion diffusion. In general, the reaction crystallization phenomenon has a high reaction rate, and the generation phenomenon of crystal nuclei is predominant in many cases. The crystal nuclei generated here are fine and do not have a sufficient sedimentation rate. In such a case, first, the degree of supersaturation needs to be reduced in order to reduce the phenomenon of crystal nucleus generation. Therefore, it is advisable to circulate the treated water or the supernatant of the first denitrification step and / or the second denitrification step to reduce the concentration of each ion in the wastewater. For example, in the case of the fluidized bed dephosphorization process, sewage flows in from the bottom of the reaction tower in an upward flow. In this case, when the phosphorus inflow is diluted to a concentration of 100 mg / liter or less, fine crystals are formed. And the solid-liquid separation becomes easy. Next, in order to increase the growth of crystals retained in the reaction tank, it is necessary to increase the effective reaction surface area in the reaction tank. Further, the reaction part and the solid-liquid separation part may be integrated. The integrated unit is, for example, a fluidized bed type dephosphorization apparatus, in which the reaction is carried out on the surface of the flowing MAP particles, and the grown MAP particles are descended and separated to allow the reaction and the solid-liquid reaction. A method of performing separation together can be mentioned. It is necessary to adjust the pH to 7.5 to 9.5 in the dephosphorization step, and circulating the alkaline component generated in the second denitrification step to the dephosphorization step contributes to the reduction of chemical cost.

Next, the liquid that has flowed out of the dephosphorization process flows into the first denitrification process. In the first denitrification step, about 1/3 to 1/2 amount of the ammonia nitrogen in the wastewater is oxidized to nitrite nitrogen or nitrate nitrogen, and at the same time, the nitrite nitrogen generated by the residual ammonia nitrogen or Denitrifying nitrate nitrogen. The reaction formulas are as shown in formulas (2) to (5). 1) Generation of nitrite nitrogen NH ₄ ⁺ + 3 / 2O ₂ → NO ₂ ⁻ + 2H ⁺ + H ₂ O (2) 2) Generation of nitrate nitrogen NO ₂ ⁻ + 1 / 2O ₂ → NO ₃ ^- ............. (3) 3) denitrification with ammonia nitrogen and autotrophic denitrification bacteria group using nitrous acid bound oxygen NH ₄ ^{+ +} NO ₂ ^- → _{N 2 + ············ (4) 4} ) denitrified by ammonia nitrogen and nitrate bound oxygen autotrophic denitrifying bacteria group using the reaction ^{_{NH 4 + + 2 / 3NO 3}} - → 5 / 6N ₂ + ・ ・ ・ ・ ・ ・ (5)

In the first denitrification step of the present invention, the reactions (2) and (4) are predominantly predominant, and the reactions (3) and (5) are extremely unlikely to occur. Furthermore, the trigger for the reactions of (2) and (4) is approximately 1 m in the first denitrification step.
The presence of g / l or more of free ammonia. In order to allow free ammonia to exist, it is preferable to control the water temperature and / or pH depending on the inflowing ammoniacal nitrogen. Equations (6) and (7) show the calculation formulas that serve as a guide. [NH3-N] = {[NH4 ⁺ -N] [10 ^pH ]} / {(Kb / Kw) +10 ^pH } ... (6) (Kb / Kw) = exp (6334 / (273 + T))・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ (7)

Here, [NH ₃ -N] is the concentration of free ammonia (mg-N / liter), [NH ₄ ⁺ -N] is the concentration of ammonia nitrogen (mg-N / liter), and T is the temperature (° C. ). In biological treatment, it is general to stabilize the treatment by dilution, and even when several thousand mg / liter of ammonia nitrogen is introduced, the concentration of ammonia nitrogen in the reaction tank is at most several tens mg / liter. ing. However, if the concentration is 100 mg / liter or less at the stage of inflowing ammoniacal nitrogen, the concentration of ammoniacal nitrogen in the reaction tank is more than 10 mg / liter, and in this case, nitrification nitrogen is easily nitrified. Therefore, the ammonia nitrogen in the first denitrification process inflow water (dephosphorization process effluent) is preferably 100 mg / liter or more,
Further, the water temperature and / or p is more than the value obtained by the equation (6).
It is preferable to set H to be slightly higher. In addition, the pH of 7.
The reaction in the first denitrification step is also promoted by adding the autotrophic denitrifying bacteria group, which has been subjected to increased culture under the conditions of 3 or more.

According to the results of long-term experiments conducted by the present inventors, the water temperature is 10 ° C to 80 ° C, preferably 20 ° C to 60 ° C, and the pH is 7.3 to 10.5, preferably 7.5 to 9. ．
By setting to 5, free ammonia is about 1 mg /
Since the amount was 1 liter or more, the reactions (1) and (3) predominantly proceeded in the first denitrification step. This pH range is the same as the pH range of the dephosphorization step, and according to the present invention, no pH adjustment is required to allow the effluent of the dephosphorization step to flow into the biological denitrification step.

Further, it was revealed in a long-term experiment that the DO (dissolved oxygen) concentration in the process is an important operating condition in the first denitrification process. That is, as shown in formulas (2) and (3), do not convert all of the ammoniacal nitrogen into nitrite nitrogen as well as nitrate nitrogen, and supply DO for denitrification of the converted nitrite nitrogen. It has been revealed that the restriction of γ is an important factor for stabilizing the treatment. Therefore, in this partial denitrification step, the oxygen-containing gas is aerated so that the dissolved oxygen concentration is constantly less than 1 mg / liter and the conditions are set to aerobic conditions, or when the dissolved oxygen concentration is 1 mg / liter or more. 0.2 mg / liter or less, preferably 0 mg
It is important to perform intermittent aeration so that there is a time zone of 1 / liter. In the case of intermittent aeration, it is preferable to take the time when the DO concentration is 0.2 mg / liter or less longer than the time when the DO concentration is 0.2 mg / liter or more.

In the present invention, the activated sludge (suspended microorganisms) alone can grow the autotrophic denitrifying bacteria group and the autotrophic nitrifying bacteria, and the reaction in the first denitrification step is possible. When a microbial carrier is added to the nitrogen step, biofilms of autotrophic denitrifying bacteria and autotrophic nitrifying bacteria are formed on this surface to accelerate the reaction. Since the number of bacteria on the surface of activated sludge and that on the surface of the microbial carrier are slightly different, the mutual effects exert each other, so that not only the reaction time of the first denitrification step is shortened, but also fluctuation of ammonia nitrogen in the wastewater It can be handled and the processing is extremely stable. Further, by making the inside of the first denitrification step multistage, it is possible to select an appropriate pH and sludge concentration according to the concentration of ammonia nitrogen in the wastewater, and more stable partial denitrification becomes possible. Specifically, it is possible to set a lower pH on the inflow end side of sewage, lower the MLSS to increase the nitrogen load, and set a higher pH on the outflow side of the process to raise the MLSS. .

The liquid flowing out of the first denitrification step flows into the second denitrification step. In the second denitrification step, the presence of a group of autotrophic denitrifying bacteria capable of utilizing the combined oxygen between ammoniacal nitrogen and nitrite nitrogen and / or nitrate nitrogen in the effluent of the preceding first denitrification step It is the step of denitrifying as nitrogen gas below. In this step, under anaerobic conditions, the DO concentration is preferably 0.2 mg / liter or less, whereby the denitrification reaction proceeds efficiently and the inflowing ammoniacal nitrogen is almost completely denitrified. Here, when the ratio of ammonia nitrogen to nitrite nitrogen and / or nitrate nitrogen is poor, particularly when the amount of ammonia nitrogen is small, a part of the liquid flowing out from the dephosphorization step is put into the second denitrification step. May be.

In the present invention, since DO is controlled in the first denitrification step of the preceding stage as described above, it is possible to easily carry out anaerobic conditions without using a special method. . Also, the BOD is 50 m in the first denitrification step.
Since it is less than or equal to g / liter, the environment is suitable for the growth of autotrophic denitrifying bacteria. Since the alkalinity increases during the denitrification process, it is possible to circulate this alkalinity in the first denitrification step or the dephosphorization step in the preceding stage. Further, by making the inside of the second denitrification step multistage, an appropriate pH and sludge concentration can be selected according to the ammonia and nitrite / nitric acid concentrations of the inflow water as in the case of the first denitrification step. The denitrification process can be performed. When a microbial carrier is added to the second denitrification step, biofilms of autotrophic denitrifying bacteria and autotrophic nitrifying bacteria are formed on this surface,
The reaction is accelerated. Since the number of bacteria on the surface of activated sludge and that on the surface of the microorganism carrier are subtly different, mutual effects exert each other, so not only the reaction time of this process is shortened, but also fluctuations of ammonia nitrogen in the wastewater can be handled. Is extremely stable.

The dephosphorization apparatus constituting the nitrogen and phosphorus processing apparatus of the present invention is processed by the fluidized bed method, complete mixing method, seed crystal circulation method, etc., as described above. In any case, the reaction pH is 7.5 to 9.5, the ammonia nitrogen in the treated water is 100 mg / liter or more, and the magnesium concentration in the treated water is 3 mg / liter or more, so that the phosphorus concentration in the treated water is 30 mg / liter. It can be less than or equal to liter. Further, lowering the concentration of ammonia nitrogen and phosphorus in the wastewater using the effluent of the second step is an important operating factor for favorably growing MAP crystals. The dephosphorization step consists of an apparatus that reduces the phosphorus concentration in the treated water while recovering phosphorus resources by operating in this way.

The apparatus for carrying out the first denitrification step is controlled so that the activity of the ammonia-oxidizing bacteria is high and the activity of the nitrite-oxidizing bacteria is low, and the ammonia-nitrogen is removed by the autotrophic denitrifying bacteria group. Used to denitrify. In addition, it is a device that does not convert all ammoniacal nitrogen into nitrite nitrogen as well as nitrate nitrogen. That is, the water temperature is 10 ° C to 80 ° C, preferably 20 ° C to 60 ° C,
The pH is set to 7.3 to 10.5, preferably 7.5 to 9.5. This is because nitrite-oxidizing bacteria become dominant at a pH of less than 7.3. Furthermore, the dissolved oxygen concentration is always 1 mg.
Aeration of oxygen-containing gas to less than 1 liter / liter is performed under microaerobic conditions, or when the concentration is 1 mg / liter or more, the dissolved oxygen concentration is 0.2 mg / liter or less, preferably 0 mg / liter It is important to intermittently aerate as there are. In the case of intermittent aeration, it is preferable to take the time when the DO concentration is 0.2 mg / liter or less longer than the time when the DO concentration is 0.2 mg / liter or more. The nitrogen load is controlled so as to be ³ kg-N / m ³ · day or less.

The apparatus for carrying out the second denitrification process is the first stage of the first stage.
Ammoniacal nitrogen and nitrite nitrogen and / or nitrate nitrogen in the effluent of the denitrification step are denitrified as nitrogen gas in the presence of a group of autotrophic denitrifying bacteria capable of utilizing combined oxygen. In this device, the denitrification reaction proceeds efficiently under anaerobic conditions, and the inflowing ammoniacal nitrogen is almost completely denitrified. That is, the water temperature is 10 ° C to 80 ° C, preferably 2 ° C.
The temperature is 0 ° C to 60 ° C, and the pH is set to 7.3 to 10.5, preferably 7.5 to 9.5. Below pH 7.3,
This is because the nitrite-oxidizing bacteria become dominant. Nitrogen load is 1
It is controlled so as to be not more than kg-N / m ³ · day.

[0031]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail with reference to the drawings. In all the drawings for explaining the embodiments and examples, constituent elements having the same functions are designated by the same reference numerals.

FIG. 1 shows an example of a flow sheet according to the processing method of the present invention. The structure of the processing apparatus of the present invention comprises a dephosphorization apparatus 1, a first denitrification apparatus 2, a second denitrification apparatus 3, and a solid-liquid separation apparatus 4. The dephosphorization apparatus 1 has a structure including an apparatus part for performing a reaction and an apparatus part for performing solid-liquid separation.

The entire amount of waste water 5 is supplied to the dephosphorization device 1. Here, the pH is adjusted to 7.5 to 9.5 by aeration or addition of an alkali component 6, and by adding magnesium ion or its compound 7, ammonia nitrogen and phosphorus in the wastewater 5 are removed. React to produce MAP. To lower the phosphorus concentration, the concentration of ammonia nitrogen in the water to be treated should be 100 mg /
A magnesium concentration of 3 mg / liter or more is left in order to accelerate the crystallization reaction and for the reason described above. At this time, if the concentrations of ammoniacal nitrogen and phosphorus in the wastewater are too high, the degree of supersaturation becomes too large and the crystals tend to become finer. Therefore, the concentration of ammoniacal nitrogen is 500 mg / liter or more and the phosphorus concentration is 100 m.
In the case of g / liter or more, treated water 8 of the solid-liquid separation device 4
Is used via the treated water circulation pipe 9 to dilute the wastewater 5. The treated water thus dephosphorized has a pH of 7.5 to 9.
5. Ammonia nitrogen of 100 mg / liter or more and magnesium concentration of 3 mg / liter or more are left to flow into the first denitrification step.

The first denitrification device 2 is also supplied with the return sludge 10 which has been solid-liquid separated by the solid-liquid separation device 4. The amount of sewage 5 input is controlled so that the nitrogen load is 3 kg-N / m ³ · d or less. The first denitrification device 2 uses an aeration device (not shown) and is intermittently aerated. The aeration timing is 0.2 when the DO is 0.2 mg / liter or less.
Longer than the time of mg / liter or more, and 0m
It is controlled so that the time of g / l is present. The pH of the liquid is adjusted to 7.5 to 9.5 in the dephosphorization step. In the first denitrification device 2, 1/3 to 1/2 of ammonia nitrogen in sewage is oxidized to nitrite nitrogen and some is oxidized to nitrate nitrogen. Nitrous nitrogen and nitrate nitrogen react with nitrogen to denitrify as nitrogen gas.

All of the effluent of the first denitrification unit flows into the second denitrification unit 3, and the remaining ammoniacal nitrogen reacts with the nitrite nitrogen and nitrate nitrogen to denitrify as nitrogen gas. . The nitrogen load is controlled to be 1 kg-N / m ³ · d or less. Here, when the ratio of ammoniacal nitrogen to nitrite nitrogen and nitrate nitrogen is poor and the ammoniacal nitrogen concentration is lower than that of nitrite nitrogen and nitrate nitrogen, a part of the effluent of the dephosphorization step 1 It is good to let in.

The effluent of the second denitrification device is the solid-liquid separation device 4
And is separated into sludge and treated water 8. The separated sludge is returned to the first denitrification device 2 as return sludge 10. A part of the treated water 8 is returned to the dephosphorization device 1. The remaining treated water 8 is discharged outside the system. In addition, a part of the sludge that has been solid-liquid separated is discharged outside the system as excess sludge.

The first denitrification device 2 and the second denitrification device 3 of the present invention are not limited to the above-mentioned activated sludge system, a system in which activated sludge + a microbial carrier is added, and a biofilm filtration system (floating filter medium or immersion filter). Any material including a filter medium can be used. Further, by making the insides of the first denitrification device 2 and the second denitrification device 3 multi-staged, an appropriate pH and sludge concentration according to the ammonia nitrogen concentration in the sewage 5 can be selected, and more stable denitrification can be performed. Processing becomes possible. As the solid-liquid separator 4, not only a sedimentation tank but also a membrane separator for hollow fiber membranes and a dynamic filtration device can be adopted.

[0038]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

Example 1 In this example, dehydrated filtrate from anaerobic digestion was treated using the treatment flow shown in FIG. The treatment apparatus comprises a dephosphorizer reaction section 11, a dephosphorizer precipitation section 12, a first denitrification apparatus 2, a second denitrification apparatus 3, and a solid-liquid separation apparatus 4. The reaction part of the dephosphorization device had a capacity of 10 liters, and the first denitrification device 2 and the second denitrification device 3 each had a capacity of 20 liters. Table 1 shows the operating conditions of the dephosphorizer, Table 2 shows the operating conditions of the first denitrification device 2 and the second denitrification device 3, and Table 3 shows the water quality of the sewage 5 and the treated water 8. In each table, ammoniacal nitrogen is represented by NH ₄ —N and nitrite nitrogen is represented by NO ₂
Expressed in -N, it represents a nitrate nitrogen in NO ₃ -N, indicating phosphorous Santai phosphorus PO ₄ -P. Waste water 5 is the dephosphorizer reaction section 1
1 and magnesium 7 and NaOH 6 were added. Magnesium 7 has a molar ratio of Mg / PO ₄ -P = 1.
The pH was adjusted to 8.5 so as to be 1.
Further, the treated water 8 of the solid-liquid separation section 4 is treated with the dephosphorization reaction section 11
6 liter / d was supplied as the treated water circulation 9.

The liquid flowing out of the dephosphorizer precipitation section 12 is the first
It flowed into the denitrification device 2. The returned sludge 10 concentrated in the solid-liquid separation device 4 was returned to the first denitrification device 2 at 6 liter / d. All the first denitrification equipment effluent was introduced into the second denitrification equipment 3. 5 mm x 5 mm x for the second denitrification device 3
A 5 mm sponge carrier was added at 10 v / v% of the device volume, and continuous stirring was performed using a stirrer. Aeration with air was not performed, and DO was always 0.2 mg / liter or less. No particular pH adjustment was performed. Sewage ammonia nitrogen = 1000 mg / liter, phosphoric acid phosphorus = 300
Ammonia nitrogen in the effluent of the dephosphorizer 1 = 430 mg / liter, and phosphate phosphorus is 11 mg / liter
mg / liter, the phosphorus removal rate was 96%,
Ammonia nitrogen of the 1st denitrification apparatus 2 effluent = 30 mg
/ Liter, nitrite nitrogen = 19 mg / liter, nitrate nitrogen = 5 mg / liter, and the second denitrification equipment effluent (treated water) is ammonia nitrogen, nitrite nitrogen, nitrate nitrate 1 mg / liter It was below. According to the method and apparatus for treating nitrogen- and phosphorus-containing wastewater of the present invention, the phosphorus removal rate was 96% and the nitrogen removal rate was 99% or more.

[0041]

[Table 1]

[0042]

[Table 2]

[0043]

[Table 3]

Comparative Example 1 Biological nitrogen was removed by a conventional nitrification reaction and denitrification reaction using an organic substance as a hydrogen donor. The size and arrangement of the tank were the same as in Example 1, the first denitrification device was continuously aerated, and the pH was adjusted to around 7 with sulfuric acid 13. In addition, methanol 14 was added to the second denitrification device. The operating conditions such as the flow rate of sewage and the circulation rate were the same as in Example 1. Table 4 shows the quality of sewage and treated water. Wastewater ammonia nitrogen = 1000 mg / liter, phosphoric acid phosphorus = 300 mg
/ L, the dephosphorizer effluent is ammonia nitrogen = 420 mg / L, and phosphate phosphorus is 10 mg / L.
It was 1 liter and the phosphorus removal rate was 96%. In the first denitrification device, ammoniacal nitrogen = 1 mg / liter or less, nitrite nitrogen = 10 mg / liter, nitrate nitrogen =
It was 350 mg / liter, and the treated water had ammoniacal nitrogen = 1 mg / liter or less, nitrite nitrogen = 1 mg / liter or less, and nitrate nitrogen = 30 mg / liter. Denitrification proceeded by adding methanol, and nitrate nitrogen was removed by 90%. PH in the first denitrification equipment
The amount of sulfuric acid used for adjustment was 8.4 g / d, and the amount of methanol used was 6.0 g / d. Compared with Example 1, the quality of treated water was low, despite the increase in chemical cost.

[0045]

[Table 4]

[0046]

INDUSTRIAL APPLICABILITY According to the present invention, phosphorus resources are recovered from sewage containing high concentrations of ammonia nitrogen and phosphorus by using a physicochemical method, and nitrogen is highly efficiently used by using a biological method. It has been possible to provide a method and an apparatus for treating nitrogen- and phosphorus-containing wastewater, which can be removed in particular, and in which the recovery amount of phosphorus resources is high, and running costs such as chemical costs and aeration power costs can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a schematic explanatory diagram of a method for treating nitrogen- and phosphorus-containing wastewater of the present invention.

FIG. 2 is a flow sheet of a processing apparatus used in an example of the present invention.

FIG. 3 is a flow sheet illustrating a processing method of Comparative Example 1.

[Explanation of symbols]

1 Phosphorus removal equipment 2 First denitrification equipment 3 Second denitrification equipment 4 Solid-liquid separator 5 dirty water 6 Alkaline component (NaOH) 7 McNesium source 8 treated water 9 Treated water circulation (piping) 10 Return sludge (piping) 11 Reaction part 12 Precipitation part 13 Sulfuric acid 14 Methanol

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B01D 9/02 615 B01D 9/02 615Z C02F 1/58 C02F 1/58 J P ZAB ZABS C12M 1/00 C12M 1/00 H C12N 1/20 C12N 1/20 D (72) Inventor Kiyomi Arakawa 11-1 Haneda Asahi-cho, Ota-ku, Tokyo Inside the EBARA CORPORATION (72) Inventor Yukiko Miura Asahi-cho, Ota-ku, Tokyo 11th No. 1 in EBARA CORPORATION (72) Inventor Katsuyuki Kataoka No. 11-1 Haneda Asahi-cho, Ota-ku, Tokyo F-term inside EBARA CORPORATION (reference) 4B029 AA01 BB01 CC01 CC02 CC03 DA03 4B065 AA01X AC20 BA22 CA54 4D038 AA08 AB29 AB49 AB54 AB59 BA04 BB13 BB18 BB19 4D040 BB02 BB12 BB33 BB52 BB66 BB73

Claims (5)

[Claims] 1. A method for purifying sewage containing ammoniacal nitrogen and phosphorus, wherein a dephosphorization step of producing crystals of magnesium ammonium phosphate while leaving ammoniacal nitrogen and magnesium ions in the sewage,
In the presence of autotrophic nitrifying bacteria and autotrophic denitrifying bacteria under microaerobic conditions and / or intermittent aeration conditions, the effluent of the dephosphorization step is treated with ammonia nitrogen while further leaving ammoniacal nitrogen. A first denitrification step of partially denitrifying nitrite nitrogen and / or nitrate nitrogen as nitrogen gas;
The effluent of the first step in the presence of a group of autotrophic denitrifying bacteria capable of utilizing bound oxygen, ammonia nitrogen and nitrite nitrogen and / or nitrate nitrogen in the effluent as nitrogen gas A method for treating nitrogen- and phosphorus-containing wastewater, which comprises treating in a second denitrification step of denitrifying. 2. The dephosphorization step comprises a reaction part for producing magnesium ammonium ammonia and a solid-liquid separation part for separating the produced magnesium ammonium phosphate from the liquid, and the pH of the reaction part is adjusted to 7.5 or less. Adjust to 9.5 and adjust the ammonia nitrogen concentration of the dephosphorization process effluent to 100.
More than mg / liter, and magnesium ion concentration 3
The method for treating nitrogen- and phosphorus-containing wastewater according to claim 1, wherein the residual amount is at least mg / liter. 3. The treated water after the second denitrification step is returned to the dephosphorization step or the sewage supply pipe.
Alternatively, the method for treating nitrogen- and phosphorus-containing wastewater according to claim 2. 4. An apparatus for purifying sewage containing ammoniacal nitrogen and phosphorus, which is a dephosphorization apparatus for producing crystals of magnesium ammonium phosphate while leaving ammoniacal nitrogen and magnesium ions in the sewage,
The effluent of the dephosphorization device under microaerobic conditions and / or intermittent aeration conditions, in the presence of autotrophic nitrifying bacteria and autotrophic denitrifying bacteria, while further leaving ammoniacal nitrogen,
A first denitrification device for partially denitrifying ammoniacal nitrogen and nitrite nitrogen and / or nitrate nitrogen as nitrogen gas, and an effluent of the first denitrification device, an autotrophic nutrient that can use combined oxygen A denitrification device for denitrifying ammoniacal nitrogen and nitrite nitrogen and / or nitrate nitrogen in the effluent as nitrogen gas in the presence of a group of denitrifying bacteria, and A solid-liquid separator that separates the effluent into treated water and settled sludge, a treated water circulation pipe for a part of the treated water to a dephosphorization unit, and a sludge pipe for returning the settled sludge to the first denitrification unit. An apparatus for treating nitrogen- and phosphorus-containing wastewater, comprising: 5. The dephosphorization device comprises a reaction part for producing magnesium ammonium phosphate and a solid-liquid separation part for separating the produced magnesium ammonium phosphate from the liquid, and the pH of the reaction part is 7.5 to 9. 5 and adjust the ammonia nitrogen concentration of the dephosphorizer effluent to 100 m.
g / liter or more, and magnesium ion concentration of 3 m
5. Remaining g / liter or more.
The nitrogen and phosphorus-containing wastewater treatment device described.