JP2016013502A - N2o suppression type water treatment method and treatment device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for treating nitrogen-containing waste water reducing the total content of N2O generated in a treatment process while achieving a prescribed digestion rate.SOLUTION: Provided that the ratio of the volume of a treatment tank to the start point part of a pre-stage section and the boundary part to the volume of the whole of the treatment tank is defined as α, and the digestion rate (%) of ammonia nitrogen represented by the reduction value of ammoniac nitrogen concentration in the boundary part to the ammoniac nitrogen concentration in the start point part of the pre-stage section is defined as β, the α and/or β is selected so that the β/α reaches the optimum range of ammonia oxidation velocity per inflow load in the pre-stage section minimizing the nitrate nitrogen generation velocity and/or (1-β)/(1-α) reaches the optimum range of the ammonia oxidation velocity per inflow load in the post-stage section minimizing the nitrate nitrogen generation velocity, and the aeration quantity in the pre-stage section is controlled so that the nitrification ratio (%) of the ammoniac nitrogen reaches the selected β, and/or the aeration quantity in the post-stage section is controlled so that the concentration of the ammoniac nitrogen at an end point in the post-stage section reaches zero.

Description

The present invention relates to a treatment method that suppresses the generation of N ₂ O in the treatment of nitrogen-containing wastewater.

  Ammonia nitrogen contained in wastewater such as domestic wastewater and industrial wastewater causes a decrease in dissolved oxygen and eutrophication in closed water areas such as lakes and inner bays where the wastewater is discharged. Therefore, nitrification is generally performed in many wastewater treatment facilities. The nitrification treatment is a treatment for nitrifying ammonia nitrogen into nitrite nitrogen or nitrate nitrogen using microorganisms that have been introduced into the waste water in the reaction tank or microorganisms that are originally present in the waste water.

In such nitrification treatment, it is known that nitrous oxide (N ₂ O) gas is generated as a reaction by-product due to changes in microbial activity, reaction tank operating conditions, and the like. N ₂ O gas is a greenhouse gas, and its greenhouse effect is as high as about 310 times that of carbon dioxide gas. N ₂ O gas is also known as an ozone depleting gas that destroys the ozone layer in the stratosphere, similar to Freon gas. Therefore, from the viewpoint of protecting the global environment, there is an urgent need to suppress the diffusion of N ₂ O gas into the atmosphere.

In the nitrification process, ammonia is oxidized to nitrous acid by reaction formula (1) and reaction formula (2), and nitrous acid is oxidized to nitric acid by reaction formula (3). And a process. In addition, NH ₂ OH generated by the reaction formula (1) shown below is oxidized by the reaction formula (2) to become NO ²⁻ , but part of NH ₂ OH is oxidized by the reaction formula (4). To N ₂ O.

NH ₃ + O ₂ + 2e ⁻ + 2H ⁺ → NH ₂ OH + H ₂ O (1)
NH ₂ OH + H ₂ O → NO ₂ ⁻ + 5H ⁺ + 4e ⁻ (2)
NO ₂ ⁻ + 0.5O ₂ → NO ₃ ⁻ (3)
NH ₂ OH + 0.5O ₂ → 0.5N ₂ O + 1.5H ₂ O (4)

  In order to promote this nitrification reaction, it is necessary that about 1.5 mg / L of dissolved oxygen remains in the waste water. Therefore, in the nitrification treatment, a necessary amount of dissolved oxygen is secured by aeration with air from a blower.

In the conventional standard activated sludge method, in order to adjust the amount of dissolved oxygen in the treatment tank, a method of measuring the amount of dissolved oxygen at a predetermined position in the treatment tank with a DO meter and controlling the amount of aeration is common.
However, in this conventional method, the amount of aeration in the upstream portion of the DO meter is controlled based on the measured value of the DO meter, and there is no concept of managing the amount of aeration on the downstream side.
Also, the DO meter has poor sensitivity in the low concentration range. For example, when nitrification is suppressed at the front stage of the treatment tank, it is difficult to control the amount of air blown to the aeration means, and the progress of nitrification at the front stage is adjusted. Was close to impossible.
Furthermore, in DO control by the DO meter, the amount of dissolved oxygen at the end is secured to some extent, and the blast volume is controlled based on the degree of achievement of nitrification, so the DO value is set even after nitrification is completed. Since aeration was continued until the value reached, wasted air volume was generated.
N ₂ O discharged from the reaction tank is considered to be able to control the discharge amount by controlling the progress of nitrification, but it was difficult to suppress the generation of N ₂ O by DO control.

Therefore, in a multi-stage nitrification tank arranged along the flow direction of the nitrogen-containing wastewater, ammonia nitrogen contained in the nitrogen-containing wastewater is utilized using ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB). A wastewater treatment method including a nitrification step for nitrifying stepwise has been developed (see Patent Document 1). This nitrification step adjusts the amount of aeration in each nitrification tank so that the oxidation-reduction potential (ORP) of each nitrification tank changes the ammonia-oxidizing bacterial activity (AOB activity) in each nitrifying tank. And a control step for controlling the target oxidation-reduction potential to be equal to or less than (NOB activity). According to such a wastewater treatment method, generation of nitrogen nitrite (N ₂ O) when biologically treating nitrogen-containing wastewater can be suppressed.

  However, in the wastewater treatment method described above, the target oxidation-reduction potential is such that the ammonia-oxidizing bacterial activity (AOB activity) is maintained equal to or less than the nitrite oxidizing bacterial activity (NOB activity) in each nitrification tank. In addition, it is set by accumulating experimental data in advance for each nitrification tank. Here, the magnitude relationship between AOB activity and NOB activity needs to be confirmed by measuring the oxidation rate of each bacterium.

That is, in setting the target oxidation-reduction potential, time-consuming and cumbersome work is required, and there is a problem that the effect of suppressing the generation of N ₂ O cannot be obtained efficiently.

JP 2011-104585 A

  The present invention has been made in view of the above problems, and its object is to obtain an air flow control that can efficiently obtain the effect of suppressing the generation of nitrous oxide and maintain the required water quality, in terms of time and labor. It is an object of the present invention to provide a wastewater treatment apparatus and a wastewater treatment method that can be easily performed without the need for a wastewater treatment.

In order to solve the above-mentioned problems, the present invention divides a treatment tank for flowing down nitrogen-containing waste water at a predetermined speed into a front section and a rear section, and a start point of the front section, a boundary between the front section and the rear section, and a rear section. An aeration control process is provided in which an ammonia meter is installed at each end point, and the operation control of the aeration means is performed independently for the front section and the rear section based on the measured values of the ammonia meters installed in each section. A sewage nitrification method,
Previously, the ammonia oxidation rate and nitrite nitrogen (N 2 _O) per inflow load in front section ammonia oxidation rate and nitrite nitrogen per inflow load in correlation and the subsequent sections of the production rate (N 2 _O) generated Calculate the correlation with speed,
The ratio (%) of the volume of the treatment tank up to the boundary and the start point of the previous section relative to the total volume of the treatment tank is α, and the decrease in the ammonia nitrogen concentration at the boundary relative to the ammonia nitrogen concentration at the start point of the previous section When the nitrification rate (%) of ammonia nitrogen represented by the value is β,
β / α is the optimum range of ammonia oxidation rate per inflow load in the preceding section that minimizes the nitrite production rate, and / or (100-β) / (100-α) is the nitrous acid Α and β are selected to be within the optimum range of the ammonia oxidation rate per inflow load in the latter section to minimize the nitrogen production rate,
The amount of aeration in the preceding stage is controlled so that the nitrification rate of ammonia nitrogen in the preceding stage becomes β, and the amount of aeration in the following stage is adjusted so that the concentration of ammonia nitrogen in the end point of the following stage becomes 0. It is characterized by controlling.

Further, in the sewage treatment apparatus of the present invention, the treatment tank for flowing down the nitrogen-containing waste water at a predetermined speed is divided into a front section and a rear section, and the start point of the front section, the boundary between the front section and the rear section, and the end point of the rear section Ammonia is installed in each part, and based on the measured value of ammonia nitrogen concentration by the ammonia meter installed in each part, the diffuser that performs the operation control of the aeration means independently in the former section and the latter section A sewage treatment apparatus having a control means,
Calculate the correlation between the ammonia oxidation rate per inflow load and the nitrite production rate in the preceding section, and the correlation between the ammonia oxidation rate per inflow load and the nitrite generation rate in the back section, And means for setting an optimum range of the ammonia oxidation rate per inflow load that minimizes the production rate of nitrogen nitrite in the latter section, the volume of the treatment tank up to the start point of the preceding section and the boundary with respect to the total volume of the treatment tank When the ratio (%) is α, and the nitrification rate (%) of ammonia nitrogen represented by the decrease value of the ammonia nitrogen concentration at the boundary with respect to the ammonia nitrogen concentration at the start point of the preceding section is β, β / α is The optimal range of ammonia oxidation rate per inflow load in the preceding section to minimize the nitrogen nitrite production rate, and Alternatively, means for selecting α and / or β so that (100−β) / (100−α) is in the optimum range of the ammonia oxidation rate per inflow load in the latter stage section that minimizes the nitrogen nitrite production rate. With
The aeration control means controls the amount of aeration in the preceding section so that the nitrification rate of ammonia nitrogen in the preceding section becomes the selected β, and / or ammonia nitrogen in the end point of the following section It is a means for controlling the amount of aeration in the latter section so that the concentration of the gas becomes zero.

  The means to set the optimal range of ammonia oxidation rate per inflow load that minimizes the nitrite production rate is the correlation between the ammonia oxidation rate per inflow load and the nitrite production rate in the front or rear stage From the program that automatically sets the optimum range based on the preset allowable value from the minimum value of the nitrite production rate, or the correlation between the ammonia oxidation rate per inflow load and the nitrite production rate Can be displayed on a monitor or the like, and an input / output device in which an optimum range value is manually input by an administrator of the device can be exemplified.

  Here, the correlation between the ammonia oxidation rate per inflow load and the nitrite production rate in the former section and the correlation between the ammonia oxidation rate per inflow load and the nitrite production rate in the latter section will be described later. And obtained by simulation.

The ratio α (%) of the volume of the processing tank up to the boundary between the starting point of the preceding section and the total volume of the processing tank is, when the processing tank is a single tank, the starting point of the processing tank with respect to the total length in the flow direction of the processing tank. When the number of processing tanks is multiple tanks, it is expressed as the number of tanks from the first tank to the boundary with respect to the total number of processing tanks, and 0 at the starting point of the processing tank. %, And 100% at the end point of the treatment tank.
Further, the nitrification rate β (%) of ammonia nitrogen is β = (Nin−Nx) / Nin × 100, where ammonia nitrogen concentration Nin at the start point of the preceding section and ammonia nitrogen concentration Nx at the boundary are set. Β is 0% because Nin = Nx at the start point of the treatment tank.
Here, the ammonia meter was used under the condition that the dissolved oxygen concentration in the tank was about 0.1 mg / L, and the amount of change of the ammonia meter value can be grasped greatly, and it is used for air flow control. This is because it is considered suitable.

According to the wastewater treatment method of the present invention, it is possible to easily obtain the effect of suppressing the generation of nitrous oxide and to easily control the air volume without requiring time and labor so as to maintain the necessary water quality. it can.
Since the ammonia oxidation rate per inflow load used in the method of the present invention is a dimensionless number and does not depend on the processing conditions, the generation amount of N ₂ O under the processing conditions should be minimized under any processing conditions. In addition, the concentration of ammoniacal nitrogen discharged from the treatment tank can be made almost zero.

FIG. 1 is a schematic diagram showing the configuration of a wastewater treatment apparatus according to an embodiment of the prior art. FIG. 2 is a schematic diagram showing the configuration of the wastewater treatment apparatus according to the embodiment of the present invention. FIG. 3 is a graph showing the relationship between the DO value at the boundary and the N ₂ O generation rate at the preceding stage when the nitrification rate (%) at the boundary according to the embodiment of the prior art is changed. FIG. 4 is a graph showing the relationship between the ammonia nitrogen concentration at the boundary and the N ₂ O generation rate at the front stage when the nitrification rate (%) at the boundary according to the embodiment of the present invention is changed. FIG. 5 is a graph showing the relationship between the nitrification rate at the boundary and the N ₂ O production rate. FIG. 6 is a graph showing a relationship with the ammonia oxidation rate per inflow load in the front stage when the processing conditions in the front stage according to the embodiment of the present invention are changed. FIG. 7 is a graph showing the relationship between the ammonia oxidation rate per inflow load and the N ₂ O production rate in the front stage when the processing conditions in the rear stage are changed according to the embodiment of the present invention. FIG. 8 is an explanatory diagram of a production model of N ₂ O by ammonia oxidizing bacteria.

  FIG. 1 shows a prior art wastewater treatment apparatus. In this embodiment, the waste water treatment apparatus 1 includes first to n-th multiple stages, for example, six stages (n = 6) of nitrification tanks 2a, 2b, 2c, 2d, 2e, 2f, a solid-liquid separation tank 4, A sludge return path 5 and an information processing unit 10 are provided. Nitrogen-containing treated raw water (hereinafter, treated raw water) as nitrogen-containing wastewater flows into the nitrification tank 2a. The nitrification tanks 2a to 2f are arranged in series along the flow direction of the treated raw water. In each of the nitrification tanks 2a to 2f, the treated raw water that has flowed into the nitrification tank 2a is sequentially biologically treated as treated water. That is, in each nitrification tank 2a-2f, under aerobic conditions, ammonia nitrogen contained in the treated raw water is nitrified to nitrite nitrogen and nitrate nitrogen, and phosphorus contained in the treated raw water is active. Taken into sludge. The information processing unit 10 includes, for example, hardware such as a PC and software such as a program that causes the PC to execute predetermined information processing.

Corresponding to each of the respective nitrification tank 2a to 2f, nitrous oxide (N ₂ O) meter 3a, 3b, 3c, 3d, 3e, 3f and, diffuser portion 6a, 6b, 6c, 6d, 6e, 6f, oxidation-reduction potential (ORP) meters 7a, 7b, 7c, 7d, 7e, 7f and stirrers 11a, 11b, 11c, 11d, 11e, 11f are provided. Blowers 8a, 8b, 8c, 8d, 8e, which supply air, for example, as gas via the control valves 9a, 9b, 9c, 9d, 9e, 9f for controlling the amount of aeration, are respectively supplied to the air diffusers 6a-6f. 8f is connected. Each of the air diffusers 6a to 6f diffuses the activated sludge stored in each of the nitrification tanks 2a to 2f by using the air supplied from each of the blowers 8a to 8f. These N ₂ O totals 3 a to 3 f are not necessarily provided in the wastewater treatment apparatus 1. Moreover, also in the stirrers 11a-11f, it installs as needed and does not necessarily need to provide.

  The ORP meters 7a to 7f as the oxidation / reduction potential measuring means are devices for measuring the oxidation / reduction potential (ORP) in the nitrification tanks 2a to 2f, respectively. Each of the ORP meters 7 a to 7 f inputs the value of the measured oxidation-reduction potential to the information processing unit 10. That is, the ORP meter 7f constitutes the nth oxidation-reduction potential measuring means, and the upstream ORP meters 7a to 7e respectively include the first oxidation-reduction potential measurement means to the n-1th oxidation-reduction potential measurement means. Configure. Note that n is a natural number equal to or greater than 2, and in this first embodiment, n = 6.

Further, each of the N ₂ O meter 3a~3f as nitrous oxide measuring means is a device for measuring the nitrous oxide content in the nitrification tank 2a to 2f. These N ₂ O meters 3 a to 3 f are installed when it is necessary to measure the discharge amount of N ₂ O gas in the wastewater treatment apparatus 1.

  Further, the control valves 9a to 9f respectively connected to the air diffusers 6a to 6f are configured by, for example, air flow rate control valves and the like, and individually control the aeration amount of each nitrification tank according to a control signal from the information processing unit 10. To do. That is, the information processing unit 10 has a program in software constituting the aeration amount control unit as a part of the aeration amount control means. The aeration amount control unit individually controls the blowers 8a to 8f and the control valves 9a to 9f corresponding to the blowers 8a to 8f as a part of the aeration amount control means. Thereby, an aeration amount control part controls the aeration amount by each aeration part 6a-6f each independently. The stirrers 11a to 11f are for stirring the air from the air diffusers 6a to 6f and the internal activated sludge in the nitrification tanks 2a to 2f, respectively.

  To-be-treated water flowing out from the most downstream nitrification tank 2f along the flow of the to-be-treated water flows into the solid-liquid separation tank 4. In the solid-liquid separation tank 4, the water to be treated is separated into the separation liquid 4a and the activated sludge 4b, and the activated sludge 4b is stirred by the stirrer 4c. Further, a pipe (not shown) is connected to the side wall of the solid-liquid separation tank 4, and the sterilized separation liquid 4a is discharged out of the system through this pipe. Moreover, the sludge return path 5 provided with the pump 5a is connected to the bottom part of the solid-liquid separation tank 4, and the activated sludge 4b deposited on the bottom part of the solid-liquid separation tank 4 is returned to the nitrification tank 2a, for example. Thereby, the biomass in the nitrification tank 2a can be maintained at a predetermined amount.

(Embodiment)
Next, an embodiment of the present invention will be described. FIG. 2 is a schematic view showing a wastewater treatment apparatus according to this embodiment.

  As shown in FIG. 2, the wastewater treatment apparatus 21 according to the present embodiment is provided with ammonia meters 12a, 12b, and 12c as ammonia concentration measuring means. The ammonia meter 12a is configured to be able to measure the ammonia concentration or ammonia nitrogen concentration contained in the treated raw water. The ammonia meter 12b is installed at a substantially intermediate position as a midway position among the nitrification tanks 2a to 2f, and the upstream side of the ammonia meter 12b is a preceding section of the nitrification region. The ammonia meter 12b is configured to be able to measure, for example, the ammonia concentration or ammonia nitrogen concentration contained in the water to be treated in the nitrification tank 2c. The ammonia meter 12c is installed at a downstream position as the end point position in the nitrification tanks 2a to 2f, and the upstream side of the ammonia meter 12c and the downstream side of the ammonia meter 12b constitute a rear stage section of the nitrification region. The ammonia meter 12c measures, for example, the ammonia concentration or ammonia nitrogen concentration contained in the water to be treated in the nitrification tank 2f. The ammonia meter 12b can be installed in any of the nitrification tanks in the nitrification tanks 2a to 2f, but is preferably installed in 2b to 2e excluding the nitrification tanks 2a and 2f from the viewpoint of controlling the amount of aeration.

Further, the information processing unit 10 is configured to be able to control each unit according to software that constitutes the aeration amount control unit as a part of the aeration amount control means. And an aeration amount control part controls each control valve 9a-9f corresponding to each blower 8a-8f and each blower 8a-8f which comprises a part of aeration amount control means, respectively. Thereby, the aeration amount by each of the air diffusers 6a to 6f is independently controlled. The information processing unit 10 is configured to be able to execute various simulations, and is also used as a control unit in which various experimental data in the wastewater treatment apparatus 21 are stored so as to be read and written in a table shape. Furthermore, the information processing unit 10 includes a control unit that controls the amount of aeration in the former stage and the latter stage according to the measurement value of each ammonia meter. And the information processing part 10 processes information based on the information in the processing apparatus 21 with the software which comprises these each part, or controls each part. Since other configurations are the same as those of the embodiment of the prior art, description thereof is omitted.
As described above, the processing tank is divided into six tanks. However, the processing tank is a single tank, the ammonia meter 12b is provided in the middle of the processing tank, and the ammonia meter 12c is provided in the terminal portion of the processing tank. It is good. In this case, the aeration amount from the aeration means in the upstream part of the treatment tank upstream from the ammonia meter 12b and the aeration amount from the aeration means in the downstream part of the treatment tank downstream from the ammonia meter 12b can be controlled separately. .

FIG. 3 is a graph showing an example of the dependence of the production rate of N ₂ O on the nitrification rate in the previous stage obtained by experiments and simulations conducted by the present inventors. The measured value by the DO meter in the apparatus is also shown.

FIG. 4 is a graph showing an example of the dependence of the production rate of N ₂ O on the previous stage nitrification rate obtained by experiments and simulations conducted by the present inventors, corresponding to the nitrification rate (%). 2 is a graph showing ammonia nitrogen concentration values measured by the ammonia meter of the embodiment of the present invention shown in FIG.

As apparent from FIGS. 3 and 4, in the region where the nitrification rate is 20 to 30%, the production rate of N ₂ O is the smallest, but as shown in FIG. 3, the DO value in this region is However, it is difficult to control the nitrification rate with high accuracy using a conventional apparatus using a DO meter.
On the other hand, as shown in FIG. 4, the nitrification rate and the ammoniacal nitrogen concentration are in a proportional relationship, and therefore the apparatus of the present invention equipped with an ammonia meter can accurately control the nitrification rate in the previous stage. is there.

Hereinafter, how to obtain the relationship between the nitrification rate and the N ₂ O production rate in FIGS. 3 and 4 will be described.
The present inventors variously change the nitrification rate (%) of the preceding stage calculated based on the measurement of the boundary portion by the above-described ammonia meter 12b, and ammonia nitrogen at the end point portion that is the measurement position of the ammonia meter 12c. Concentration was measured. In the embodiment of FIG. 2, the nitrification rate (%) is obtained from the following equation (5).

{(Ammonia nitrogen concentration at the inflow position (nitrification tank 2a) −Ammonia nitrogen concentration measured by the ammonia meter 12b) / (Ammonia nitrogen concentration at the inflow position)} × 100 (%) (5)

Here, the ammonia nitrogen concentration at the inflow position is an ammonia nitrogen concentration considering the inflow of the return water returned together with the return sludge with respect to the ammonia nitrogen concentration of the treated raw water measured by the ammonia meter 12a. is there. As a specific example, the ammonia nitrogen concentration at the inflow position (nitrification tank 2a) with respect to the inflow amount Q ₁ of the treated raw water and the return amount Q ₂ of the return water is the Q of the ammonia nitrogen concentration of the treated raw water. ₁ / (Q ₁ + Q ₂ ) times.

  Then, the inventors set the nitrification rate of the previous section (previous section nitrification rate) measured at the installation position (intermediate position) of the ammonia meter 12b as various nitrification rates, and the downstream nitrification tank 2f (terminal tank). The ammonia nitrogen concentration was measured and the ammonia nitrogen concentration in the nitrification tank 2f was found to decrease monotonously.

Here, in the generation path where N ₂ O is generated, NO ₂ ⁻ is reduced to N ₂ O as shown in the following reaction formulas (6) and (7). That is, N ₂ O is produced mainly by reduction of nitrite by ammonia oxidizing bacteria (AOB).

NH ₂ OH + NO ₂ ⁻ → N ₂ O + H ₂ O + OH ⁻ (6)
H ₂ + NO ₂ ⁻ → 0.5N ₂ O + 0.5H ₂ O + OH ⁻ (7)

The production of N ₂ O is assumed only by AOB, and denitrification of nitrous acid is the main production route as the N ₂ O production route by AOB, and a conversion rate model (FIG. 8 (b)) is adopted as the expression method. That is, the N ₂ O production rate is expressed by multiplying the ammonia oxidation rate by the conversion rate. Up to now, it seems that there are many examples of modeling as a so-called sequential reaction (FIG. 8 (a)), but it was judged that it is simple and highly practical because it is not necessary to determine a constant related to NO.
In addition, the present inventors tried to derive the N ₂ O production rate in the nitrification tanks 2a to 2f by setting the nitrification rate in the previous section (previous section nitrification rate) to various nitrification rates. As described above, N ₂ O is generated along with the ammonia oxidation of AOB. As will be described in detail later, as a result of extensive studies by the present inventors based on simulations and experiments, it has been found that the N ₂ O production rate can be derived from the following equation (8).

N ₂ O production rate = ammonia oxidation rate × N ₂ O conversion rate (8)

And according to the knowledge obtained by the present inventors based on experiments and simulations regarding the formula (8), the ammonia oxidation rate is based on the biological constant of AOB, and the ammonia concentration and dissolved oxygen (DO). Depending on the concentration, the N ₂ O conversion depends on the nitrite concentration and the DO concentration. That is, it was found that the reaction formulas (6) and (7) described above have an influence on the N ₂ O production rate of the formula (8).

Further, as described above, the increase in N ₂ O is suppressed under conditions where AOB activity is lower than NOB activity (AOB activity ≦ NOB activity), particularly under moderate conditions where NOB activity is almost equal to AOB activity. The On the other hand, in general, the doubling rate of microorganisms is about twice as large for AOB as compared to NOB. From these points, the present inventors focused on AOB activity and focused on distinguishing microorganisms contained in AOB in order to suppress N ₂ O. AOB includes various microorganisms, and specifically includes the genus Nitrosospira and the genus Nitorosomonas. According to the knowledge of the present inventors, regarding the ammonia oxidation activity, the ammonia oxidation activity of the genus Nitorosomonas is larger than the ammonia oxidation activity of the genus Nitrosospira.

Therefore, the present inventors conducted various experiments and simulations focusing on these microorganisms belonging to the genus Nitrosospira and Nitrorosomonas. Here, from the conventional knowledge of the present inventors, it is found that the following formulas (9), (10) and (11) are established for the growth rate of the microorganisms in the respective nitrification tanks 2a to 2f. ing. In the formulas (9) to (11), dX _SPR / dt is the growth rate of Nitrosospira genus of AOB, dX _MNS / dt is the growth rate of Nitrorosomonas genus of AOB, and dX _NOB / dt is the growth rate of NOB. S _O2 is a dissolved oxygen concentration (DO concentration), for example, 2.0 mg in the nitrification tank 2 f and various values from 0 to 2.0 mg / L in the nitrification tank 2 c, and according to these values, The DO concentration S _O2 in the nitrification tanks 2b, 2d, and 2e is also set to various values. Further, S _NH4 is the ammonia concentration, and is, for example, the ammonia concentration S _NH4 in each nitrification tank 2a to 2f corresponding to each DO concentration S _O2 when the DO concentration S _{O2 is set} to various values. _SNO2 is the nitrous acid concentration. Furthermore, X _SPR microorganisms concentration Nitrosospira genus, X _MNS is microorganism concentration, the concentration of microorganisms X _NOB is NOB of Nitorosomonas ^{_{genus, K SPR O2, K SPR NH4}} , μ SPR max, K MNS O2, K MNS NH4, μ ^MNS _max , μ ^NOB _max , K ^NOB _O2 , and K ^NOB _NO2 are constants shown in Table 1 below. These constants are not necessarily limited to these constants, and constants based on various definitions can be adopted. Further, b ^SPR , b ^MNS , and b ^NOB are kill coefficients of Nitrosospira genus, Nitorosomonas genus, and NOB, respectively.

表１参考文献
1) Taylor, A.E., Bottomley, P.J., : Nitrite production by Nitrosomonas europaea and Nitrosospira sp. AV in soils at different solution concentrations of ammonium. Soil Biol. Biochem.38 (4), p.828-836. (2006)
2) Sin, G., Kaelin, D., Kampschreur, M.J., Taka´ cs, I., Wett, B., Gernaey, K.V., Rieger, L., Siegrist, H., van Loosdrecht, M. : Modelling nitrite in wastewater treatment systems: a discussion of different modelling concepts. Water Science and Technology 58 (6), p.1155-1171 (2008)

Table 1 References
1) Taylor, AE, Bottomley, PJ,: Nitrite production by Nitrosomonas europaea and Nitrosospira sp.AV in soils at different solution concentrations of ammonium.Soil Biol. Biochem. 38 (4), p.828-836. (2006)
2) Sin, G., Kaelin, D., Kampschreur, MJ, Taka´ cs, I., Wett, B., Gernaey, KV, Rieger, L., Siegrist, H., van Loosdrecht, M.: Modeling nitrite in wastewater treatment systems: a discussion of different modeling concepts.Water Science and Technology 58 (6), p.1155-1171 (2008)

Further, according to the knowledge of the present inventor, it is known that the following equations (12) and (13) are established for ammonia oxidation rates γ ^SPR _NH4 and γ ^MNS _NH4 by the genera Nitrosospira and Nitrorosomonas. . Further, it is known that the following equation (14) holds for the nitrite oxidation rate γ ^NOB _NO2 by ^NOB . In the formulas (12) to (14), Y _SPR , Y _MNS , and Y _NOB are yields.

However, it has been extremely difficult to derive the N ₂ O production rate in each of the nitrification tanks 2a to 2f by simulation only with the above-described microorganism growth rate, ammonia oxidation rate, and nitrite oxidation rate. The present inventors have conducted further experiments and intensive studies, in each of the nitrification tank 2a to 2f, it recalled deriving the N ₂ O conversion based on the DO concentration and the nitrite concentration.

As a result of various experiments and simulations by the present inventor, the present inventor found that the N ₂ O conversion rates η ^SPR and η ^{MNS of} each of the genus Nitrosospira and Nitrorosomonas were expressed by the following formula (15): And it was devised that it can be derived by the equation (16). Note that η ^SPR _max is a constant that is the maximum N ₂ O conversion rate by the genus Nitrosospira, the value obtained from our experiments is 40, and η ^MNS _max is the maximum N ₂ O by the genus Nitrorosomonas. The constant, which is the conversion rate, was 11 as determined from our experiments. K ^SPR _{η_O2} is a saturation constant with respect to the oxygen concentration derived from the _batch test result by Nitrosospira genus, and K ^MSN _{η_O2} is a saturation constant with respect to the oxygen concentration derived from the batch test result by Nitrorosomonas genus. The values obtained from these experiments were all 0.07.

As shown in the equation (15), the N ₂ O conversion rate by the Nitrosospira genus is derived based on the DO concentration S _O2 and the nitrite concentration S _NO2 , and as shown in the equation (16), the N ₂ O by the Nitrorosomonas genus. The conversion rate is derived based on the DO concentration S _O2 .

The N ₂ O production rate in the equation (8) is a total value of N ₂ O production rates by the genus Nitrosospira and Nitrorosomonas, and is derived from the following equation (17).

N ₂ O formation rate = Nitrosospira genus by N ₂ O formation rate + Nitorosomonas genus by _{N 2} O formation rate ^{_{= (γ SPR NH4 · η SPR}} ) + (γ MNS NH4 · η MNS) ...... (17)

And by setting the boundary conditions which are the operating conditions as an example shown in Table 2 based on the above-described equations (8) to (17), the dependence of the N ₂ O production rate on the nitrification rate in the previous stage can be derived. . Thus, the present inventors have found that in the relationship between the N 2 _O formation rate and front section nitrification rate, 3, as shown in FIG. 4, derives the front section nitrification rate dependent trend in N 2 _O production rate I found it possible.

Specifically, as shown in FIG. 3, the N ₂ O production rate decreases as the nitrification rate increases in the range where the nitrification rate in the previous stage is 0 to a predetermined first nitrification rate, for example, about 25%. . On the other hand, in the range where the preceding section nitrification rate exceeds the first nitrification rate and the second nitrification rate, for example, up to about 80%, the N ₂ O production rate monotonously increases as the nitrification rate increases. When the preceding section nitrification rate exceeds the second nitrification rate, the N ₂ O production rate also monotonously decreases as the nitrification rate increases.

That is, the N ₂ O production rate is minimal (the enclosed portion in FIGS. 3 and 4) when the preceding section nitrification rate is 50% or less, and is maximized when it is about 50% to 70%. It has been found. As a result of various experiments and examinations by the present inventors, it has been found that this tendency is a tendency to occur in a general waste water treatment apparatus using a nitrification tank.

Furthermore, the present inventors performed similar simulations and experiments by changing the treatment conditions such as the load of the water to be treated and the treatment amount. The result is shown in FIG.
As is apparent from FIG. 5, it has been found that when the processing conditions are changed, the optimum nitrification rate region where the N ₂ O production rate in the preceding section is minimized also varies.

The present inventors further examined the influence of the processing conditions, and adopted the ammonia oxidation rate (dimensionless) per inflow load obtained by the following equation instead of the nitrification rate as a variable of the N ₂ O production rate. As a result, it has been found that the optimum region where the N ₂ O generation rate in the preceding section is minimized is substantially constant as shown in FIG. 6 regardless of the processing conditions.

Ammonia oxidation rate per inflow load [-]
= Ammonia oxidation rate [mgN / L · h] / Inflow load [mgN / L · h] ·· (18)

Inflow load [mgN / L · h]
= Inflow ammonia concentration [mgN / L] / Residence time [h] (19)

According to the result of FIG. 6, if the ammonia oxidation rate per inflow load is controlled to be in an appropriate region, the N ₂ O production rate can always be minimized under the conditions even if the processing conditions are changed. it can.

In addition, the present inventors have examined the nitrification rate of the latter stage, which is the average ammonia oxidation rate between the nitrification tank 2c as the nitrification tank at the intermediate position and the nitrification tank 2f as the terminal tank, N ₂ O verify nitrification rate dependence of the stepped portion of the waste water treatment apparatus in the production rate of, for the subsequent zones, N 2 _O formation rate was ascertained that there is an optimum region is minimized.
Then, the present inventors also adopted the ammonia oxidation rate per inflow load (dimensionless) instead of the ammonia oxidation rate as a variable of the N ₂ O production rate for the rear zone, regardless of the processing conditions. As shown in FIG. 7, it has been found that the optimum region where the N ₂ O generation rate in the preceding section is minimized is substantially constant.

6, the graph of FIG. 7, as a variable of N 2 _O formation rate, ammonia oxidation rate per inflow load (dimensionless) adopted, in front section and the rear stage section, N _{2 O} formation rate is minimized, respectively If the ammonia oxidation rate per inflow load, which is an optimal region, is controlled, the amount of N ₂ O generated as a whole can be minimized.

The inventors further examined the conditions under which ammonia nitrogen can be treated while minimizing the amount of N ₂ O produced as a whole facility.
The ratio (%) of the volume of the treatment tank up to the boundary and the start point of the previous section relative to the total volume of the treatment tank is α, and the decrease in the ammonia nitrogen concentration at the boundary relative to the ammonia nitrogen concentration at the start point of the previous section When the nitrification rate (%) of ammonia nitrogen represented by the value is β, the ammonia oxidation rate in the former section is a value obtained by dividing the decrease in the ammonia nitrogen concentration in the former section by the residence time in the former stage ( β × ammonia inflow concentration × inflow amount per unit time) / (α × treatment tank capacity).

Therefore, the ammonia oxidation rate per inflow load in the preceding section is β / α from the equations (18) and (19).
On the other hand, the ammonia oxidation rate in the latter section is the target of 0 in the last stage of the latter section, so the decrease in the ammonia concentration in the latter section becomes the ammonia concentration in the last stage of the former section. It is a value divided by the residence time at (100−β) × ammonia inflow concentration × inflow per unit time / ((100−α) × treatment tank capacity).
Therefore, the ammonia oxidation rate per inflow load in the latter section is (100−β) / (100−α) from the equations (18) and (19).

According to the above, the relationship between the ammonia oxidation rate per inflow load and the N ₂ O production rate in each of the preceding stage and the subsequent stage is graphed by simulation to determine the optimum region where the N ₂ O production rate is minimized, β / α is the optimum area of the preceding section, (100−β) / (100−α) satisfies the optimum area of the succeeding section, α and / or β is selected, and the setting value of the ammonia meter installed at the boundary Is set so that the nitrification rate in the preceding section is β and the aeration amount in the preceding section is controlled, and the aeration amount in the succeeding section is controlled so that the measured value of the ammonia meter installed at the final end of the following section becomes 0 As a result, the content of ammonia nitrogen in the treated wastewater discharged from the facility can be brought close to 0 while minimizing the amount of N ₂ O produced as a whole facility.

As shown in FIG. 6, the ammonia oxidation rate per inflow load is 0.30 to 0.65 in the region where the N ₂ O production rate in the preceding section is minimized, and the N ₂ O production rate in the latter section is minimized from FIG. Assuming that the region has an ammonia oxidation rate per inflow load of 1.2 to 1.5, from the above results,
0.30 ≦ β / α ≦ 0.65 (20)
In the latter section,
1.2 ≦ (100−β) / (100−α) ≦ 1.5 (21)
Therefore, if α and β satisfying these equations (20) and (21) are selected, it is possible to minimize the amount of N ₂ O generated as a whole facility, but depending on the conditions of the facility, only one of the equations can be used. Although conceivable is not satisfied, even in this case, if the interval satisfying the above formula, it is possible to minimize the N 2 _O production amount.
For example, in the embodiment of FIG. 2, the boundary is an intermediate point in the flow direction of the treatment tank, so α = 50%, and β satisfying equations (20) and (21) is 25% to 33%. If the value is set to a value within the range, it is possible to minimize the amount of N ₂ O generated as a whole equipment.

1, 21 Treatment device 2, 2a, 2b, 2c, 2d, 2e, 2f Nitrification tank 3a, 3b, 3c, 3d, 3e, 3f N ₂ O meter 4 Solid-liquid separation tank 4a Separation liquid 4b Activated sludge 4c, 11a, 11b, 11c, 11d, 11e, 11f Stirrer 5 Sludge return path 5a Pump 6a, 6b, 6c, 6d, 6e, 6f Air diffuser 7a, 7b, 7c, 7d, 7e, 7f ORP meters 8a, 8b, 8c, 8d , 8e, 8f Blower 9a, 9b, 9c, 9d, 9e, 9f Control valve 10 Controller 12a, 12b, 12c Ammonia meter

Claims (3)

The treatment tank for flowing down nitrogen-containing wastewater at a predetermined speed is divided into a front section and a rear section, and ammonia meters are installed at the start point of the front section, the boundary between the front section and the rear section, and the end point of the rear section. A sewage treatment method including an aeration control process for performing an operation control of the aeration means independently on the front stage and the rear stage on the basis of a measured value of ammonia nitrogen concentration by an ammonia meter installed in each part,
In advance, the correlation between the ammonia oxidation rate per inflow load and the nitrite production rate per inflow load in the preceding section and the correlation between the ammonia oxidation rate per inflow load and the nitrite production rate in the rear section are calculated,
The ratio (%) of the volume of the treatment tank up to the boundary and the start point of the previous section relative to the total volume of the treatment tank is α, and the decrease in the ammonia nitrogen concentration at the boundary relative to the ammonia nitrogen concentration at the start point of the previous section When the nitrification rate (%) of ammonia nitrogen represented by the value is β,
β / α is the optimum range of ammonia oxidation rate per inflow load in the preceding section that minimizes the nitrogen nitrite production rate, and / or (100-β) / (100-α) is the nitrogen nitrite production Α and / or β is selected so that the optimum range of ammonia oxidation rate per inflow load in the latter section to minimize the speed,
Control the amount of aeration in the preceding section so that the nitrification rate of ammonia nitrogen in the preceding section becomes the selected β and / or the concentration of ammonia nitrogen in the end point of the following section becomes zero A sewage treatment method for controlling the amount of aeration in the latter section.   The optimum range of the ammonia oxidation rate per inflow load in the preceding section that minimizes the nitrogen nitrite production rate is 0.30 to 0.65, and / or the nitrogen nitrite production rate is minimized. The sewage treatment method according to claim 1, wherein the optimum range of the ammonia oxidation rate per inflow load in the latter section is 1.2 to 1.5. A treatment tank that allows nitrogen-containing wastewater to flow down at a predetermined speed is divided into a front section and a rear section, and ammonia meters are installed at the start point of the front section, the boundary between the front section and the rear section, and the end point of the rear section. In the sewage treatment apparatus having an aeration control means for independently controlling the operation of the aeration means in the front stage and the rear stage based on the measured value of the ammonia nitrogen concentration by an ammonia meter installed in each part,
Calculate the correlation between the ammonia oxidation rate per inflow load and the nitrite production rate in the preceding section, and the correlation between the ammonia oxidation rate per inflow load and the nitrite generation rate in the back section, And means for setting an optimal range of ammonia oxidation rate per inflow load that minimizes the production rate of nitrous nitrite in the latter section,
The ratio (%) of the volume of the treatment tank up to the boundary and the start point of the previous section relative to the total volume of the treatment tank is α, and the decrease in the ammonia nitrogen concentration at the boundary relative to the ammonia nitrogen concentration at the start point of the previous section When the nitrification rate (%) of ammonia nitrogen represented by the value is β, β / α is the optimum range of the ammonia oxidation rate per inflow load in the preceding section that minimizes the nitrogen nitrite production rate, and / Alternatively, means for selecting α and / or β so that (100−β) / (100−α) is in the optimum range of the ammonia oxidation rate per inflow load in the latter stage section that minimizes the nitrogen nitrite production rate. With
The aeration control means controls the amount of aeration in the preceding section so that the nitrification rate of ammonia nitrogen in the preceding section becomes the selected β, and / or ammonia nitrogen in the end point of the following section A sewage treatment apparatus, which is means for controlling the amount of aeration in the latter section so that the concentration of water becomes zero.

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