JP2017006894A - Method for controlling the amount of aeration in activated sludge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for appropriately controlling the amount of aeration, in activated sludge in which aeration treatment (ultra-low DO treatment) is performed with the DO of a mixed activated sludge solution inside an aeration tank being almost 0 mg/L.SOLUTION: (1-1) After increasing DO in an aeration tank by transiently intensifying aeration while performing ultra-low DO treatment, an aeration stopping operation is performed, (1-2) the equilibrium DO value C1 during strong aeration is calculated, on the basis of changes in DO value during strong aeration or when aeration is stopped, and (1-3) an aeration amount G2, which is appropriate when ultra-low DO treatment is being performed, is determined from equation (3) estimating from C1 and an aeration amount (G0) when the oxygen supply capacity due to aeration and the oxygen consumption rate of the mixed solution become equal, G0 being determined using the aeration amount G1, etc. when aeration is transiently intensified. G2=k((Cs-C1)/Cs)(Ea1/Ea2)G1... equation (3). In the equation, k is an experimentally set proportionality coefficient corresponding to device characteristics.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an aeration amount control method for activated sludge, and more particularly, to an aeration amount control method in a treatment apparatus that treats BOD components in wastewater with microorganisms or simultaneously treats BOD components and denitrification.

BOD removal in wastewater can be efficiently treated using activated sludge, but total nitrogen (hereinafter referred to as TN) in wastewater can only be removed by sludge growth, and about 5% of the total amount of BOD It is only removed. In order to remove more nitrogen using activated sludge, the nitrogen component in the wastewater is converted to ammonia nitrogen (hereinafter NH4-N) by activated sludge bacteria, and then nitrite nitrogen in an aerobic environment by nitrifying bacteria. Alternatively, after converting to nitrate nitrogen (hereinafter referred to as NO _x -N), an anaerobic environment is converted to nitrogen gas by the action of denitrifying bacteria.

The process that simultaneously removes BOD and nitrogen from wastewater is generally called biological denitrification, and specific equipment includes nitrifying-liquid denitrification, DC denitrification, and batch anaerobic. There are aerobic denitrification, etc., both of which treat BOD and nitrogen by combining the above-mentioned anaerobic / aerobic.
Furthermore, as in the case of carrier activated sludge and biofilm treatment methods, the aerobic environment is maintained in an aerobic environment without making the aeration tank clearly anaerobic, and the oxygen concentration gradient in the microorganism group held on the carrier or support is utilized. It is also possible to perform a BOD and nitrogen simultaneous treatment by aerobic treatment on the surface of the microorganism group and anaerobic treatment on the carrier or support side.

  Also in activated sludge, sludge is granulated to enlarge microbial flocs, and oxygen concentration gradients within the microbial community are used to aerobically treat the surface of the microbial community and anaerobically treat it internally. There has also been proposed a method for performing simultaneous processing. However, in order to granulate microorganisms, it is limited to operation under conditions where the BOD load is very large, and granulation itself is a general reason because it requires advanced technology. It is not processing.

  Even in normal activated sludge, floating sludge forms flocs, and as with carrier activated sludge and biofilm treatment methods, an oxygen concentration gradient that is aerobic on the surface of microbial flocs and anaerobic inside flocs should occur. It can be treated, and it is known that BOD can be removed and denitrification can be performed to some extent by actually operating the dissolved oxygen concentration (hereinafter referred to as DO) in the aeration tank at about 0.5 mg / l.

As described above, there are several methods for simultaneously treating BOD and denitrification with microorganisms, and there is a method using low DO operation using ordinary activated sludge. This method has the merit that it can be diverted as a BOD / nitrogen simultaneous treatment device with almost no modification of existing activated sludge. Low-DO operation is a highly advantageous method that can reduce the power cost of the aeration equipment, even when only aiming at BOD processing that is not conscious of nitrogen processing.
However, when the DO value of the aeration tank is approximately 0.5 mg / l or less, it is difficult to accurately grasp the oxygen consumption supply balance based on the DO value, and it becomes difficult to accurately maintain the dissolved oxygen state in the aeration tank. If the oxygen supply amount is too large, denitrification will be insufficient, and if it is too small, the treatment of BOD will be insufficient, or the nitrification activity will decrease, resulting in insufficient nitrogen removal.

In order to accurately perform simultaneous BOD and denitrification with low DO, not only the control method using the DO meter, but also control that accurately follows the oxygen supply amount due to aeration against changes in influent water and changes in operating conditions. Become important.
Since the denitrification reaction is a reduction reaction, an oxidation-reduction potential (hereinafter referred to as ORP) is widely used for managing the denitrification process. However, ORP is -100mV to -300mV in an anaerobic state, and + 200mV to + 300mV in an aerobic state. However, ORP is aerobic to the extent that aeration is performed but oxygen is insufficient. Since it is only reduced by about 50 mV from +200 mV to +300 mV of the state, it is difficult to distinguish from changes due to fluctuations in raw water or changes in the state of the activated sludge mixture, and it is difficult to control low DO operation.

In order to cope with this problem, Patent Document 1 discloses a method of controlling the DO in the aeration tank to a low DO based on the predicted value of the treated water BOD and the nitrate ion concentration based on the oxygen consumption rate of the treated water BOD and sludge. ing.
In Non-Patent Document 1, air volume control is performed using the coenzyme NADH (nicotinamide adenine dinucleotide) involved in the respiratory reaction of activated sludge microorganisms as an index, and DO in the aeration tank ranges from 0.2 mg / l to 0.6 mg / l. A case where about 75% of denitrification was performed on urban sewage was reported.
The NADH sensor is a relatively new sensor that can measure changes from an aerobic region to an anaerobic region that cannot be measured with a DO meter. However, the NADH sensor is affected by suspended substances in wastewater, and there is a problem that the measured value varies. 2 also presents a method for reducing control errors caused by variations in NAND sensors.

  As mentioned above, even in normal activated sludge, the method of removing BOD alone or BOD and nitrogen at the same time by low DO operation is a very advantageous process if it can be properly controlled. In the case where there are fluctuations, it is difficult to stably maintain the BOD treatment and the denitrification treatment.

JP2011-005354 A JP2014-83524

Katsumi Moriyama et al. “Air volume control system that adds nitrogen removal function to the standard activated sludge process” Proceedings of Sewerage Research Presentation, Vol.

  In view of the above problems, the present invention provides a method for appropriately and stably controlling low DO operation in BOD treatment or simultaneous BOD / denitrification treatment.

As a result of earnest research, the present inventor has found a control method for appropriately and stably controlling the low DO operation.
(1) Aeration treatment (hereinafter referred to as extremely low DO treatment) is carried out with the dissolved oxygen concentration (hereinafter referred to as DO) in the activated sludge mixture in the aeration tank being almost 0 mg / l to remove BOD in wastewater or In activated sludge treatment equipment that removes BOD and nitrogen content simultaneously,
(1-1) During the ultra-low DO treatment operation, after temporarily increasing the aeration to raise the DO in the aeration tank, perform the operation to stop the aeration,
(1-2) When KLa is the overall mass transfer coefficient, Cs is the saturated dissolved oxygen concentration, and Rr is the oxygen consumption rate under the aerobic condition of the activated sludge mixture, the change in DO value over time (dC (t) / dt) is expressed by equation (1),
dC (t) / dt = K _L a (Cs−C (t)) − Rr (1)
(1-2-1) Obtain Rr based on the C (t) change in the DO reduction process when aeration is stopped,
(1-2-2) Equilibrium DO value C1 (dC (t) / dt = 0, C (t) = C1) when aeration is temporarily increased, and C in the DO increase process when aeration is increased (t) Obtained based on the change and the relationship of equation (2),
K _L a (Cs−C (t)) = Rr (2)
(1-3) When the amount of aeration when aeration is temporarily increased is G1, and the oxygen dissolution efficiency at that time is Ea1,
By analogizing that the aeration amount G0 when the oxygen supply capacity by aeration and the oxygen consumption rate of the liquid mixture are equal is obtained from the equation (3 '), the appropriate aeration amount G2 at the time of extremely low DO treatment operation is (3) Calculated by the formula
G0 = ((Cs-C1) / Cs) · (Ea1 / Ea0) · G1 (3 ')
G2 = k · ((Cs−C1) / Cs) · (Ea1 / Ea2) · G1 (3) (where Ea0 and Ea2 are the oxygen dissolution efficiency when the aeration amount is G0 and G2, respectively.
k is a proportionality coefficient determined experimentally according to the characteristics of the activated sludge)
(1-4) By appropriately performing an operation during the ultra-low DO treatment operation to set the aeration amount during the ultra-low DO treatment operation to G2 obtained by (1-3) (hereinafter referred to as aeration calibration operation). ,
A method of controlling the amount of aeration in activated sludge, characterized by maintaining an appropriate amount of aeration during ultra-low DO treatment operation.

(2) In the invention of (1), the proportionality coefficient k is set by the equation (4).
k = k1 · (Rr−k2 · R _NOX ) / Rr (4) where
R _NOX: Oxygen consumption rate by nitrification measured by sampling the activated sludge mixture in the aeration tank.
Rr _: Oxygen consumption rate Rr of the activated sludge mixture obtained by (1-2-2) above
k1 _: Correction coefficient determined experimentally.
k2 _: Percentage of oxygen used for BOD treatment out of the amount of oxygen required for nitrification.

  Hereinafter, the specific contents of the present invention will be described in more detail, including comparison with the prior art. In the following description, “waste water” is used as a general concept that collectively refers to polluted water that requires treatment. Further, “waste water” introduced into the treatment apparatus as a treatment target is referred to as “inflow water” (or raw water).

Normally, the oxygen supply amount in activated sludge is managed based on the DO value of the activated sludge mixture in the aeration tank. In the case of air aeration, the DO value is managed from 0.5 mg / l to 3 mg / l. . On the other hand, in the case of the BOD / nitrogen simultaneous treatment according to the present invention, it is necessary to manage at an extremely low DO value of about 0.1 mg / l or less in the most efficient operation state.
The DO measurement in the aeration tank is performed by immersing the DO meter electrode in the activated sludge mixed solution being aerated in the aeration tank. The measured DO value is a value determined by the balance between the oxygen consumption rate by microorganisms in the activated sludge mixed solution and the oxygen supply rate by aeration. When the DO value is approximately 0.5 mg / l or less, there are various factors such as DO meter electrode response speed, contact of fine bubbles on the electrode surface, oxygen consumption rate of the activated sludge mixture, locality of dissolved oxygen concentration, etc. The effect of the factor becomes relatively large, and the balance cannot be accurately reflected. In particular, for extremely low DO values of about 0.1 mg / l, the control of the oxygen supply amount by aeration becomes virtually impossible with the control by the DO instruction value by the DO meter.

<Relationship between aeration volume increase / decrease operation and KLa, Rr, C1>
The change (dC (t) / dt) of the DO value (C (t)) of the activated sludge mixture in the aeration tank when aeration is strengthened is: KLa is the overall mass transfer coefficient, Cs is the saturated dissolved oxygen concentration, and Rr is The oxygen consumption rate of the activated sludge mixed liquid is expressed by equation (1).
dC (t) / dt = K _L a (Cs−C (t)) − Rr (1)
Rr is considered to be constant when the aeration amount changes for a short time, and Cs can be treated as a constant because the temperature does not change during the aeration amount calibration operation. Therefore, when equation (1) is integrated, t is the elapsed time. The change in C (t) can be expressed by equation (5) with an initial value of 0.
C (t) ＝ C1−C1 ・ exp (−K _L a ・ t) (5)
Here, C1 is the DO value when the oxygen supply rate KLa (Cs−C (t)) and the oxygen consumption rate Rr of the activated sludge mixed solution are equal when t is sufficiently long, and the equation (2) It is expressed by the relationship.
K _L a (Cs−C1) = Rr (2)

In the equation (5), C1 becomes a substantially constant value by performing aeration for a sufficiently long time with a constant aeration amount. Therefore, the C1 value can be directly obtained using the equation. However, this method requires a long time.
For example, when calculating the KLa of the diffuser pipe generally used for aeration of activated sludge as 15 [1 / hr], the value of C (t) with the variation in the aeration tank is used. In order to obtain the C1 value directly from the above, it is necessary to measure until C (t) reaches about 98% of C1, and it takes about 16 minutes.

Since C (t) in equation (5) is a function of KLa, Rr, and t, KLa and C1 are set so that the value of C (t) for a given t agrees with the calculation result of the equation. It is also possible to obtain the matching KLa and C1 by repeatedly performing the calculation while changing. However, in order to obtain C1 with high accuracy, since there are two variables, a long time C (t) operation is required.
In order to obtain KLa and C1 accurately by repeated calculations, it is necessary to measure until C (t) reaches about 90% of C1 based on experience. When KLa is 15 [1 / hr], this is about It takes 9 minutes.
Furthermore, the time from stopping aeration until returning to the appropriate DO value of the present invention depends on the size of Rr. For example, when Rr = 12 mg / l / hr, aeration is performed at 90% of C1 = 3.0 mg / l. It takes about 14 minutes to stop. Therefore, the total time for the aeration calibration operation is 23 minutes.
On the other hand, when the fluctuation of the influent water is large, it is necessary to perform the aeration amount calibration operation in accordance with the fluctuation, but the calibration operation time zone is in an excessive oxygen state as compared with the appropriate DO value in the present invention. Therefore, it is necessary to complete the aeration amount calibration operation in the shortest possible time from the viewpoint of maintaining an appropriate DO value.

In order to solve the above problems, in the present invention, an appropriate aeration amount during the operation of the extremely low DO processing is determined according to the following steps.
<Acquisition of Rr and calculation of KLa and C1>
Referring to FIG. 2, when aeration is increased from the state of DO value L1 when the extremely low DO processing is being performed, DO follows L3 curve calculated by equation (5) as L2. To rise.
From equation (5), equation (6) is derived if the DO value C (t1) after t1 hours from the start of aeration increase and the DO value C (t2) after t2 hours.

When aeration is stopped, the DO value changes to L4 with KLa = 0 in equation (1). Therefore, the activated sludge mixture is measured by measuring the rate of decrease in the process in which aeration is stopped and DO decreases. Can be obtained (corresponding to the above (1-2-1)).
From the formula (2), C1 = Cs−Rr / KLa, so the formula (6) is

で表されるから、曝気停止時のDO低下速度測定により求めたRrを用いて、KLaを変化させて繰り返し演算を行い、（６ａ）式が成立するKLaを求めることができる。
求めたKLa とRrを用いて（２）式からC1を求めることができる（同（1-2-2）に対応）。
また（２）式から、KLa＝Rr/(Cs−C1)であるから、（６）式は、

Therefore, using Rr obtained by measuring the DO decrease rate at the time of aeration stop, KLa can be changed and repeated calculation can be performed to obtain KLa that satisfies Equation (6a).
Using the obtained KLa and Rr, C1 can be obtained from equation (2) (corresponding to (1-2-2)).
Also, from equation (2), KLa = Rr / (Cs−C1), so equation (6) is

とも表される。よって、C1を変化させて繰り返し演算を行うことにより、（６ｂ）式が成立するC1を求めることができる（同（1-2-2）に対応）。

It is also expressed. Therefore, C1 satisfying the equation (6b) can be obtained by repeatedly performing calculation while changing C1 (corresponding to (1-2-2)).

According to the method of the present invention, by obtaining Rr, since either one of the expressions (6a) and (6b) is used, there is one variable in the repetitive calculation. Compared to this, it is possible to obtain C1 much more quickly.
For example, in the same way as described above, with KLa set to 15 [1 / hr], to obtain the C1 value accurately from the formula (6a) or (6b), experience shows that C (t) reaches about 50% of C1. This takes about 3 minutes. Furthermore, when the aeration is stopped and the return to the appropriate DO value of the present invention is the same as described above, Rr = 12 mg / l / hr, and when aeration is stopped at 50% of C1 = 3.0 mg / l. It takes about 8 minutes, and the total aeration calibration time is 11 minutes, which can be reduced to about half.

<Appropriate aeration calculation during ultra-low DO processing operation>
The relationship between KLa, aeration amount G, and oxygen dissolution efficiency Ea is expressed by equation (7) based on the oxygen amount balance. This formula is based on the description of Japan Sewerage Association: “Sewage test method” and “Sewerage facility design plan / design guidelines and explanation”.

ここに、Vは曝気槽の有効容量、ρは空気中の酸素密度である。

Here, V is the effective capacity of the aeration tank, and ρ is the oxygen density in the air.

In the equation (7), when the aeration amount G1 and the oxygen dissolution efficiency Ea1 at that time, the equation (2) is rewritten as the equation (8).
Rr = γ ・ Ea1 ・ G1 ・ (Cs−C1) (8) where γ = ρ / (Cs ・ V × 10 ^-1 )
When the oxygen supply capacity by the aeration amount G is the same as the oxygen consumption rate of the activated sludge mixture, the DO value C (t) of the aeration tank is almost 0, so the aeration amount at that time is G0. When the oxygen dissolution efficiency is represented by Ea0, the equation (9) is obtained.
Rr = γ · Ea0 · G0 · Cs (9) From the equations (8) and (9),
G0 = ((Cs-C1) / Cs) · (Ea1 / Ea0) · G1 (3 ') Equation, and the aeration amount G0 where the oxygen supply capacity is the same as the oxygen consumption rate of the activated sludge mixture Can be sought.

When processing BOD without denitrification, it is necessary to increase the amount of oxygen supplied by aeration to be the same as or slightly higher than the oxygen consumption G0 of the activated sludge mixture so as not to run out of oxygen.
Further, in order to efficiently perform denitrification, it is necessary to operate with the oxygen supply amount by aeration being equal to or less than the oxygen consumption amount G0 of the activated sludge mixed solution. From this, if the amount of aerated air during the ultra-low DO treatment operation is G2, the oxygen dissolution efficiency at that time is Ea2, and k is a proportional coefficient of about 1 or less, G0 and Ea0 in equation (3 ') are By substituting with G2 (= k · G0) and Ea2, the appropriate aeration air amount G2 can be estimated by the equation (3).
G2 = k · ((Cs−C1) / Cs) · (Ea1 / Ea2) · G1 (3)
By setting the aeration volume in the aeration tank to this value immediately after obtaining G2, proper ultra-low DO processing operation becomes possible.

  The oxygen dissolution efficiency Ea is a characteristic that depends on the water depth of the aeration tank, the type and structure of the air diffuser, and is a value unique to each activated sludge device, but generally changes as shown in FIG. Within the proper use range, Ea is large when the aeration amount G is small, and Ea is small when it is large. Therefore, by calculating the relational expression of Ea and G in advance by experiment and inputting it to the computer, G2 is assumed when calculating (3), and Ea2 at that time is calculated from the relational expression of Ea and G. Obtaining G2 from Eq. (3) using Ea2 and calculating it repeatedly until it matches the assumed G2 makes it possible to obtain the correct G2.

<About proportionality constant k>
K in equation (3) is a coefficient that determines how much aeration amount is appropriate for the calculated aeration amount G0 where the oxygen supply amount and oxygen consumption amount by aeration match. Is 1 or more than 1 and close to 1.
In the case of simultaneous BOD and denitrification, the following considerations are necessary. In order to cause a denitrification reaction, it is necessary to create a dissolved oxygen-deficient environment in which microorganisms must acquire oxygen from NOx-N. Denitrification will not proceed.
On the other hand, in order to cause denitrification, it is necessary to nitrify ammonia nitrogen to nitrite nitrogen or nitrate nitrogen in advance. It is known that the nitrification reaction rate is large when DO is high and decreases when DO is low. In addition, excessive oxygen deficiency causes a rapid deterioration of the treated water BOD.

In the ultra-low DO treatment, the above three actions are realized by the oxygen concentration gradient from the surface of the activated sludge floc to the center. As an average of the whole aeration tank, even if the state is slightly oxygen excess, a floc having a large shape is in an oxygen-deficient state inside the center, and BOD / denitrification simultaneous processing becomes possible. When the oxygen consumption rate of BOD decomposition is large, even a relatively small floc can be in an oxygen-deficient environment inside the center, so k is a value from about 1 to about 1 or less.
Since the floc shape, the oxygen consumption rate for BOD decomposition, the relationship between DO and nitrification reaction rate, etc. are specific to each activated sludge, the optimum value of k is different. In addition, the overall configuration of the processing device also varies depending on the functions that the ultra-low DO processing is responsible for. For example, as in Example 3 described later, k is a numerical value of 1 or less in the first aeration tank and the second aeration tank exclusively for denitrification, and k is 3 in the third aeration tank exclusively for the treatment of BOD. A value of 1 or more is appropriate. Further, when there is a reoxidation tank after the apparatus of Example 3, the reoxidation tank takes charge of the treatment of BOD and maintenance of nitrification activity, and the third aeration tank also performs denitrification when denitrification has not been completed. It is also effective to make k slightly smaller than 1 so that it can be done.
As described above, the value of k is slightly different depending on various factors of each activated sludge. Therefore, it is practical to finally determine the value by experiment.

<Frequency of aeration calibration (1-4)>
In the laboratory, when testing with activated sludge treatment conditions being constant, it is sufficient to obtain G2 by a single aeration calibration procedure. However, in actual activated sludge treatment, Rr changes due to fluctuations in raw water and treatment conditions. Therefore, it is necessary to perform an aeration amount calibration operation every time the fluctuation occurs and always obtain an appropriate aeration amount. The frequency of aeration calibration is generally about once every few hours, although it varies depending on the fluctuations in the raw water and treatment conditions of each activated sludge. FIG. 3 conceptually shows the DO change when this operation is performed.

The DO value (C (t)) changes according to the equation (5) by aeration. For example, if the aeration intensity is such that C1 is about 3 mg / l or more, DO will rise to about 1.5 mg / l or more in a few minutes, and data measurement that can calculate C1 with sufficient accuracy is possible. is there. The rate of decrease of DO when aeration is stopped decreases at a substantially constant rate until DO reaches about 0.5 mg / l. Therefore, aeration should be stopped when DO reaches about 1.5 mg / l or more. Therefore, Rr can be measured accurately with a few minutes of measurement.
As described above, according to the present invention, it is possible to reduce the appropriate region departure time by one aeration amount calibration operation to about 10 minutes. Therefore, assuming that the aeration amount calibration operation is performed once every two hours, the time zone in which the balance is disturbed is within about 10% of the whole, so that even when the fluctuation of the raw water is large, it is possible to cope sufficiently.

<About Rr measurement (1-2-1)>
In the Rr measurement, since aeration is stopped for a short time of several minutes, there is a concern that the flow in the aeration tank disappears, the sludge begins to settle, MLSS changes, and an error occurs in the measured value of Rr. However, MLSS changes due to sludge sedimentation vary depending on the depth, such that MLSS gradually decreases near the surface, MLSS rapidly decreases if the sludge interface passes, and MLSS due to consolidation increases in the deep part. Therefore, a sludge sedimentation experiment is performed in advance, and a DO electrode is installed at a position where the MLSS change is small, thereby enabling measurement that is not affected by sludge sedimentation.
The DO meter can be measured without any problems if a DO electrode that does not require flow is selected on the electrode surface, or if a stirring blade or vibrator that moves the sludge on the electrode surface is equipped.

Next, the invention (2) will be described. The present invention is a particularly effective method in the case where simultaneous processing of BOD and denitrification is performed and NH4-N is present in the aeration tank and the nitrification reaction is performed.
When fluctuations in the BOD load or nitrogen load of the influent water are small, the BOD and denitrification can be appropriately treated as k: constant in the invention of (1). When the oxygen consumption rate due to the decomposition of BOD changes with time, it is necessary to control the aeration amount by changing the value of k corresponding to the fluctuation. The present invention finds that k has the following characteristics, and relates to aeration control using this.

  G0 calculated by the equation (3 ') uses Rr measured in an aerobic environment and is a value including oxygen consumption of nitrification. In the extremely low DO treatment, the amount of NOx-N that has been nitrified is quickly denitrified by consuming the BOD component, and as a result, part of the amount of oxygen required for nitrification was used for the treatment of the BOD component. Become.

  For example, the reaction formula for denitrifying methanol nitrogen as a hydrogen donor after oxidizing ammonia nitrogen to nitrite nitrogen or nitrate nitrogen is expressed by the following equations (11) to (14). When denitrifying with nitrite nitrogen (Equation (13)), 0.5 times the amount of oxygen required for nitrification, and when denitrifying with nitrate nitrogen (Equation (14)) 0.625 times the amount of oxygen required will be used for the BOD decomposition of methanol. This ratio is now k2.

The rate observed as Rr is the oxygen consumption rate (R _SS ) due to endogenous respiration of microorganisms under aerobic conditions, the oxygen consumption rate (R _BOD ) for decomposing and ingesting BOD components, and NH4-N _Is the sum of oxygen consumption rate (R _NOX ) for nitrifying NOx-N.
Assuming that the values of R _SS , R _BOD , and R _NOX do not change even in a low DO environment such as extremely low DO processing, the oxygen supply amount by the aeration amount G0 is Rr × t. On the other hand, part of the oxygen consumption required for the treatment of BOD is a portion of the amount of oxygen required for nitrification, which is k2, so the required oxygen supply by aeration in the extremely low DO treatment is (Rr × t −k2 × R _NOX × t).
Therefore, in the calculation, the aeration amount G2 is
G2 = G0 × (Rr−k2 × R _NOX ) / Rr (15) As a result, an oxygen supply amount that is not excessive or insufficient can be secured.
Substituting G0 in equation (3 ′) into equation (15),
G2 = (Rr−k2 × R _NOX ) / Rr ・ ((Cs-C1) / Cs) ・ (Ea1 / Ea0) ・ G1
It becomes. By comparing this with equation (3), k in equation (3) can be expressed by equation (4) using k1 as a correction coefficient.
k = k1 · (Rr−k2 · R _NOX ) / Rr (4) Here, as will be described later, the correction coefficient k1 is calculated based on the above assumptions to actual operating conditions, aeration tank characteristics, etc. It is a correction coefficient for making it correspond.

Since the value of Rr can be acquired as appropriate by aeration calibration, if the oxygen consumption rate R _NOX due to nitrification can be known, BOD and denitrification can be performed simultaneously using Eq. It is possible to maintain an appropriate aeration amount G2 for processing.
In the formula (4), k2 varies depending on the ratio of denitrification from nitrite nitrogen or denitrification from nitrate nitrogen. Moreover, it seems that it is influenced by the structure of the hydrogen donor, and the value is about 0.5 to 0.625. However, it is appropriate to finally determine the value based on experiments.

Acquisition of R _NOX is possible by: That is, the activated sludge mixed solution in the aeration tank is sampled, the ammonia nitrogen is measured, and then the ammonia nitrogen after the activated sludge mixed solution is aerated for a predetermined time is measured. Next, the value obtained by dividing the ammonia nitrogen reduction amount by the aeration time is converted into the oxygen consumption amount by the equations (11) and (12).
It is known that the nitrification rate is almost independent of the ammonia nitrogen concentration and is determined by the activity of the nitrifying bacteria in the activated sludge mixture, and even if the ammonia nitrogen concentration changes, the R _NOX does not change. Even a value measured by sampling at a location different from the calibration operation location can be used as the R _NOX value at the location of the aeration tank calibration operation.
R _{NOX also} has a nitrification rate that depends on the activity of nitrifying bacteria, and because nitrifying bacteria have a slow growth rate, measurement frequency is not as high as that of aeration calibration, and it also depends on fluctuations in influent and operating conditions. However, the purpose can often be achieved even with a measurement frequency of several times a day.

As described above, Equation (4) assumes that R _SS , R _BOD , and R _NOX do not change under aerobic conditions or extremely low DO conditions. However, in general, these values slightly decrease as the DO value decreases. The degree of decrease depends on the operating conditions such as the BOD component of the influent water and MLSS. It is also influenced by the idea of whether denitrification performance or BOD treatment should be emphasized with respect to inflow water fluctuation. Furthermore, it is also affected by the presence and capacity of the re-aeration tank after ultra-low DO treatment.
In the equation (4), k1 is a coefficient determined in consideration of these factors, and is a value in the vicinity of 1, but is finally determined based on experiments.

According to the extremely low DO treatment operation, treated water can be obtained that can be discharged as it is, but the DO value is low.
In addition, if the appropriate range for the extremely low DO treatment operation deviates in the direction of oxygen deficiency, BOD may deteriorate rapidly, or nitrification activity may decrease, resulting in denitrification failure. In order to prevent this and to increase the nitrification activity in a highly aerobic state of DO, it is more preferable to perform aeration after the extremely low DO treatment and perform the reoxidation treatment. Specifically, in the case of batch-type operation, after an extremely low DO treatment operation for inflow water, an air aeration process is performed such as standing and draining through an air aeration operation in which aeration is sufficiently performed. In the case of the continuous type, as shown in Fig. 1, a re-oxidation tank is provided after the ultra-low DO treatment tank, oxygen is further supplied to the activated sludge mixed liquid after the treatment, and aeration treatment is performed before precipitation. Transfer to tank.

  In the case of a continuous anaerobic / aerobic BOD / denitrification aeration tank, the denitrification tank operates in an anaerobic state, so it is necessary to completely separate the aerobic tank from the anaerobic tank. On the other hand, the aeration tank with ultra-low DO treatment and the re-aeration tank differ only in the intensity of aeration, so the aeration tank has a long and narrow structure in the flow direction from the inflow end to the outflow end. In the case of an aeration method with little stirring and mixing, it is possible to use an inflow side as an extremely low DO treatment operation and a reoxidation tank near the outflow end in one aeration tank.

  In case of batch type or continuous type, even if the aeration tank is a complete mixing tank, there is one device (hereinafter referred to as a control unit) that performs the aeration amount calibration operation and aeration amount control for ultra-low DO processing. However, if the aeration tank is a continuous structure that is elongated in the flow direction from the inflow end to the outflow end, Rr changes in the flow direction, so the entire control is performed as a single control. The unit may not be able to cover. In this case, as shown in FIG. 5, it is effective to provide a long and narrow aeration tank with a plurality of control units in the flow direction from the inflow end to the outflow end of the aeration tank and to control them independently. Also in this case, it is not always necessary to partition the aeration tank for each of the plurality of control units.

If R _NOX > 0, (Rr−k2 · R _NOX ) / Rr in equation (4) is 1 or less, so if k1 is 1, equation (4) is 1 or less. The activated sludge as a whole has nitrification activity, but in an aeration tank where NH4-N is small and R _NOX is not included in the aeration volume calibration operation, if k is changed by setting (4), It becomes less than the required oxygen amount in the aeration tank, resulting in insufficient oxygen. For example, in the final stage of the batch-type aeration process, or when controlled by a plurality of control units in a continuous manner as shown in FIG. 5, the denitrification process is substantially completed by the first aeration tank and the second aeration tank. In the third aeration tank, the case where only BOD processing is performed corresponds. In such a case, the 1st aeration tank and the 2nd aeration tank are set to change the k value in accordance with the fluctuation of the raw water using the formula (4) in the extremely low DO treatment, and the third aeration tank is operated with k fixed. It is appropriate to do.

Conventionally, there is no method that can appropriately follow fluctuations in the components of influent water (raw water) and the treatment is not stable, which is why BOD alone or simultaneous removal of BOD and denitrification by ultra-low DO treatment in activated sludge is not widespread. However, according to the present invention, proper control is possible even under conditions where the proper aeration amount range is narrow.
According to the present invention, there is an effect that BOD and denitrification can be performed and aeration power can be reduced without requiring a large modification of the activated sludge treatment apparatus.

It is a figure explaining the biological treatment apparatus 1 which concerns on one Embodiment of this invention. It is a figure explaining the change of DO at the time of aeration amount calibration operation It is a figure explaining the timing of the measurement of aeration amount calibration operation. It is a figure explaining the relationship between aeration amount and oxygen dissolution efficiency. It is a figure in the case of installing a plurality of extremely low DO treatments of the present invention when the aeration tank has an elongated structure.

  Hereinafter, with reference to FIG. 1, the measuring apparatus for the activated sludge oxygen consumption index acquisition which concerns on this invention, and its specific acquisition method are demonstrated in detail. It is needless to say that the scope of the present invention is described in the claims and is not limited to the following embodiments.

(Overall configuration of BOD / denitrification simultaneous processing equipment)
Referring to FIG. 1, a treatment apparatus 1 according to the present embodiment includes an aeration tank 2 that performs the ultra-low DO treatment of the present invention that removes BOD of influent water and denitrifies nitrogen, and an outflow from the aeration tank 2. The main components are a reoxidation tank 3 for aeration treatment of the liquid with a sufficient dissolved oxygen concentration, a precipitation tank 4, and a return sludge line 5 for returning sludge from the precipitation tank 4 to the aeration tank 2.
The re-oxidation tank 3 is not always necessary depending on the purpose of the treatment, but when better quality treated water is needed, when backup of extremely low DO treatment is needed, or when the nitrogen load is high and a large nitrification rate is needed Is preferably installed. The aeration tank 2 includes an aeration pipe 6, an aeration blower 7, an inverter 8 that automatically adjusts the aeration air volume of the aeration blower 7, an aeration air volume meter 9, and a temperature at which the temperature of the activated sludge mixture in the aeration tank and DO are measured. A total of 10 and a DO total 11 are attached. Furthermore, the control apparatus 12 which manages the measured value sent from each of these meters and has a computer as a main component for controlling the inverter 8 of the aeration blower 7 is provided.

Although not shown, the reoxidation tank 3 is provided with an independent aeration blower, an aeration air volume control device, an aeration tube, and an R _NOX measurement device 13 for responding to the invention of (2). The control device 12 is also configured to perform operations related to R _NOX measurement and acquisition of measurement values.
For aeration control, use another control method depending on the aeration method, such as the opening control of the aeration flow meter and the automatic valve that adjusts the aeration air volume, or in the case of the surface aeration method, such as motor rotation speed control. You can also.
The aeration tank 2 performs the ultra-low DO process by controlling the oxygen supply amount by aeration by the following ultra-low DO process control method. The re-aeration tank 3 is operated with a sufficient supply amount of oxygen while keeping the DO of the aeration tank at about 2 mg / l to 4 mg / l.
The computer of the control device contains in advance the k value related to the aeration amount calibration operation, the relationship between the aeration amount and the oxygen dissolution efficiency, the relationship between the temperature and the saturated dissolved oxygen concentration, the relationship between the inverter output and the aeration amount, R _NOX , k1, k2 Values are stored.

(Extremely low DO processing control method)
Hereinafter, an extremely low DO processing control method in the processing apparatus 1 will be described.
In the aeration tank 2, when it is time to perform the aeration amount calibration operation during the ultra-low DO processing operation, if the invention of (2) is included, check that the R _NOX measurement has been performed. Update the value of k and save it on your computer.
Next, the aeration amount is temporarily increased by operating the inverter 8 from the control device 12, and the activated sludge that rises with time from the thermometer 10 and the aeration amount G1 from the aeration airflow meter 9 at that time. The DO value (C (t)) of the mixed solution is obtained from the DO meter 10 respectively. When the value of C (t) rises to about 1.5 mg / l or more, aeration is stopped and Rr is calculated based on the rate of decrease of C (t). Based on the value of Rr and the data of the process of increasing C (t), KLa is calculated by equation (6a).
Furthermore, C1 is calculated from Eq. (2) from KLa and Rr, and is set based on Eq. (3) using Ea1 at G1, Cs at temperature T, k, and Ea2 at G2. Calculate the aeration amount G2. Next, based on the relationship between the inverter output and the aeration amount, the inverter 8 is controlled so that the aeration air amount by the aeration blower becomes the set aeration amount G2.
When the invention (2) is added, the R _NOX measurement device 13 is used to measure the R _NOX value at a timing different from the aeration amount calibration operation, and the measurement result is stored in the control device 12.
At the time of the aeration calibration operation, k is obtained by the equation (4) using the stored measurement value and each coefficient, and the inverter 8 is controlled so that the set aeration amount G2 obtained by the equation (3) is obtained.

(R _NOX measurement method)
R _NOX is measured by sampling the activated sludge mixture in the aeration tank, measuring ammonia nitrogen, measuring the ammonia nitrogen after aeration of the activated sludge mixture for a certain period of time, and measuring the decrease in ammonia nitrogen. This can be done by converting the value divided by the aeration time into oxygen consumption by the equations (11) and (12). Ammonia nitrogen can be measured by a commercially available ammonium ion measuring device or a method described in JIS K0102.
Furthermore, according to the method disclosed in JP 2001-235462 A by the inventors of the present application, the activated sludge mixed solution after the ultra-low DO treatment is sampled to be in an endogenous breathing state and ammonia nitrogen is removed. After that, it is also possible to quantitatively add ammonium ion and measure the time and oxygen consumption.

Hereinafter, an example in which the simultaneous treatment of BOD and denitrification is performed by the extremely low DO treatment control in the activated sludge treatment apparatus according to the present invention will be shown.
<Example 1>
The present example is an example of a test using test wastewater (test run A).
Table 1 shows the composition of raw water (influent water). As a treatment method, an aeration tank was used in a semi-batch operation. In addition, as a treatment cycle, after adding raw water and ultra-low DO treatment for 300 minutes (Step 1), let stand for 30 minutes to settle and separate sludge (Step 2), and discharge the supernatant for 30 minutes ( Step 3) was repeated.
The aeration tank was operated at a starting sludge volume of 1.1 liters, MLSS of 3,200 mg / l, raw water addition of 88 cc / hr, and a temperature of about 24 ° C. Table 2 shows the aeration conditions, and Table 3 shows the processing results after 150 minutes of step 1.
For comparison, the test No. 0 was carried out along with the normal activated sludge treatment in which aeration was performed so that DO was 0.5 mg / l or more in Step 1.
Table 2 also includes k calculated backward based on the relationship of equation (1) using each numerical value and aeration amount G2 during the aeration amount calibration operation. The relationship between the amount of aerated air and the oxygen dissolution efficiency Ea was obtained in advance by experiments on the change in DO increase with aeration time.
From Table 3, it can be seen that Test No. 2 is an appropriate condition for simultaneous BOD / denitrification treatment, and the k value at that time is 0.89 from Table 2. No. 1 has a k value of 1.10, which is larger than 0.89, and NO3-N remains in an excessive oxygen state, resulting in insufficient denitrification. No.3 and No.4 have k values smaller than 0.64, 0.48, and 0.89, respectively, and oxygen is in excess or deficiency, so the treated water TOC deteriorates and nitrification does not progress, and much NH4-N remains. I understand.
This example demonstrates that BOD and denitrification simultaneous processing can be optimally performed by setting k to 0.89, setting the aeration amount G2 obtained from equation (1), and performing the aeration amount calibration operation. It was.

<Example 2>
This example corresponds to the invention of (2), and in the processing test in which the composition of the BOD component of the raw water and the TN concentration were changed so that Rr and _RNOX differed as a result, extremely low DO processing was actually performed. This is a comparison between the case where the appropriate k value is obtained and the case where the k value is calculated by the equation (4).
As a treatment method, the aeration tank was used in a semi-batch operation as in Example 1. As a treatment cycle, after adding raw water and ultra-low DO treatment for 300 minutes (step 1), let stand for 30 minutes to settle and separate sludge (step 2), and discharge the supernatant for 30 minutes (step 3) The process of repeating the operation was performed. The amount of sludge at the start is 1.1 liters, and the amount of raw water added in process 1 is 88 cc / hr.
The aeration tank conditions are the same as in Example 1 for test run A ′. Test run B was operated at MLSS = 3,400 mg / l, temperatures of about 24.4 ° C. and 24.5 ° C., and test run C was operated at MLSS = 3,060 mg / l, temperatures of 25.2 ° C. and 23.2 ° C. The measurement was performed after 150 minutes of step 1.

Table 4 shows the raw water composition of each test run. The test run A ′ is the same as Table 1 in the first embodiment.
Table 5 shows the aeration amount conditions for each test run. The test run A ′ is the same as Table 2 in the first embodiment. Note that k1 and k2 were 1.0 and 0.56, respectively.
Table 6 shows the processing results of each test run.

From the processing results in Table 6, in test run A ′, test No. 2 has the best nitrogen removal rate and is the appropriate condition, and the k value calculated back from the test conditions is 0.89 (see Table 2, No. 2). On the other hand, the k value calculated by the equation (4) from Rr and R _NOX is 0.87, and they are almost the same.
Similarly, in test run B, test No. 7 has the best nitrogen removal rate and is an appropriate condition, and the k value calculated backward from the aeration amount condition in Table 5 is 0.90. On the other hand, from the processing results in Table 6, the k value calculated from Rr and R _NOX by the equation (4) is 0.90, and they are in agreement.
Similarly, in test run C, test No. 10 has NOx-N remaining slightly denitrified and aeration is excessive, and test No. 12 is NH4N increased and slightly aerated. The k values calculated from the aeration amount conditions in Table 5 are 0.86 for No. 10 and 0.73 for No. 11. On the other hand, from the processing results in Table 6, the k value calculated from Eq. (4) from Rr and R _NOX is 0.79, and the above No. 10 is slightly over-aerated and No. 11 is slightly under-aerated. It matches. .
From the above results, it was proved that the appropriate value of the aeration amount changes corresponding to the fluctuation of the influent composition, but it can be controlled appropriately by using k calculated by the equation (4).

<Example 3>
This embodiment corresponds to the inventions of (1) and (2), and in the treatment tank in which three independent ultra-low DO control units are arranged in the three aeration tanks shown in FIG. Is an example of
The raw water was added under the conditions of 264 cc / hr, MLSS = 3,300 mg / l, temperature 24.4 ° C. The raw water composition, the k value setting condition, and the aeration amount condition are shown in Tables 7-1 to 7.3, respectively.
R _NOX was measured with sludge in the third aeration tank. Note that k1 was 1.0 and k2 was 0.56.
The processing results are shown in Tables 7 and 4. In the same table, the removal rates of the first and second aeration tanks are blank, because new NOx-N is generated in the third aeration tank and decreases due to denitrification. This is because N of the treated water is in the middle of the reaction in the tank.

  Each aeration tank has different oxygen consumption rate due to decomposition of raw water BOD, oxygen consumption due to nitrification, and simultaneous denitrification amount.Therefore, the appropriate aeration amount in each aeration tank is also different. In the first aeration tank and the second aeration tank, the k value was set based on the equation (4), and in the third aeration tank, the k value was fixed, and aeration was performed with the aeration amount G2 according to the equation (3). As a result, good treatment was achieved as shown in Tables 7 and 4.

The necessary denitrification has been completed up to the second aeration tank, and the third aeration tank aims to remove BOD alone. In the third aeration tank, NH4-N is insufficient for the nitrification capacity, and when the k value is controlled by the equation (4), the oxygen amount for BOD treatment is insufficient, so the k value was fixed.
As shown in Tables 7 and 3, whether or not NH4-N is deficient in nitrification capacity depends on the fact that Rr in the third aeration tank is significantly lower than Rr in the second aeration tank, and oxygen due to endogenous respiration. It is a value close to consumption, and it can be easily judged from the assumption that R _NOX is not included.

The present invention can be widely applied to control the amount of reducing agent added to the denitrification process of various types of biological denitrification methods such as the single tank sludge system, nitrification liquid circulation system, batch denitrification system of FIG. is there.
Furthermore, it goes without saying that the present invention can also be applied to an operation for reducing the aeration air volume of a normal activated sludge that does not aim at denitrification but only aims at energy saving.

DESCRIPTION OF SYMBOLS 1 ... Very low DO processing device 2 ... Aeration tank 3 ... Reoxidation tank 4 ... Precipitation tank 5 ... Return sludge line 6 ... Aeration device 7 ... Aeration blower 8 ... Inverter 9 ... Aeration air flow meter 10 ... Thermometer 11 ... DO meter 12 ... Control device 13 ... R _NOX measurement device

Claims (2)

BOD removal or BOD and nitrogen in wastewater by performing aeration treatment (hereinafter referred to as extremely low DO treatment) with the dissolved oxygen concentration (hereinafter referred to as DO) in the activated sludge mixture in the aeration tank being almost 0 mg / l In the activated sludge treatment equipment that removes
(1-1) During the ultra-low DO treatment operation, after temporarily increasing the aeration to raise the DO in the aeration tank, perform the operation to stop the aeration,
(1-2) When KLa is the overall mass transfer coefficient, Cs is the saturated dissolved oxygen concentration, and Rr is the oxygen consumption rate under the aerobic condition of the activated sludge mixture, the change in DO value over time (dC (t) / dt) is expressed by equation (1),
dC (t) / dt = K _L a (Cs−C (t)) − Rr (1)
(1-2-1) Obtain Rr based on the C (t) change in the DO reduction process when aeration is stopped,
(1-2-2) Equilibrium DO value C1 (dC (t) / dt = 0, C (t) = C1) when aeration is temporarily increased, and C in the DO increase process when aeration is increased (t) Obtained based on the change and the relationship of equation (2),
K _L a (Cs−C (t)) = Rr (2)
(1-3) When the aeration volume when the aeration is temporarily strengthened is G1 and the oxygen dissolution efficiency at that time is Ea1, the aeration volume when the oxygen supply capacity by aeration and the oxygen consumption rate of the mixture are equal By analogy with the fact that G0 is obtained from the equation (3 ′), the appropriate aeration amount G2 at the time of extremely low DO processing operation is obtained from the equation (3).
G0 = ((Cs-C1) / Cs) · (Ea1 / Ea0) · G1 (3 ')
G2 = k · ((Cs−C1) / Cs) · (Ea1 / Ea2) · G1 (3) (where Ea0 and Ea2 are the oxygen dissolution efficiency when the aeration amount is G0 and G2, respectively.
k is a proportionality coefficient determined experimentally according to the characteristics of the activated sludge)
(1-4) By appropriately performing the operation to set the amount of aeration during the ultra-low DO treatment operation to G2 obtained in (1-3) during the ultra-low DO treatment operation,
A method of controlling the amount of aeration in activated sludge, characterized by maintaining an appropriate amount of aeration during ultra-low DO treatment operation. The aeration amount control method in activated sludge according to claim 1, wherein the proportional coefficient k is set by the equation (4).
k = k1 · (Rr−k2 · R _NOX ) / Rr (4) where
R _NOX: Oxygen consumption rate by nitrification measured by sampling the activated sludge mixture in the aeration tank.
Rr _: Oxygen consumption rate of the activated sludge mixture obtained by (1-2-2) above.
k1 _: Correction coefficient determined experimentally.
k2 _: Percentage of oxygen used for BOD treatment out of the amount of oxygen required for nitrification.

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