JP2014205104A - Water treatment apparatus and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water treatment apparatus and method which maintains both activity of DPAO and quality of treated water in the AN method.SOLUTION: A water treatment apparatus includes an anaerobic tank 1 into which raw water flows, a sludge separation tank 2 which separates an activated sludge mixed liquor flowing out from the anaerobic tank 1 into a supernatant liquid and concentrated sludge, a nitrification tank 3 which treats the supernatant liquid, an anoxic tank 4 into which the concentrated sludge and outflow water from the nitrification tank 3 flow, and an aerobic tank 5 into which outflow water from the anoxic tank 4 flows. The water treatment apparatus is provided with water quality measuring means 16, 18 which measure an index of the nitrate nitrogen concentration in the inflow water and the outflow water of the anoxic tank 4, and first air volume control means 19 which calculates the nitrate nitrogen concentrations in the inflow water and the outflow water of the anoxic tank 4 from the index measured by the water quality measuring means 16, 18 and controls the aeration air volume of the nitrification tank 3 using the calculated nitrate nitrogen concentrations.

Description

The present invention relates to a water treatment process by biological treatment using activated sludge.

In water treatment plants such as sewage treatment plants, advanced treatment has been introduced in various places to remove nitrogen and phosphorus with activated sludge (microorganism group) in addition to organic substances in order to improve the quality of treated water. General biological nitrogen removal in advanced treatment consists of a nitrification process and a denitrification process. The nitrification process is performed in an aerobic state, and ammonia nitrogen (NH ₄ -N) in sewage is oxidized to nitrate nitrogen (NO ₃ -N) by nitrifying bacteria. The denitrification process is performed in the absence of oxygen, and NO ₃ -N is reduced to N ₂ gas by denitrifying bacteria. Since N ₂ gas is released into the atmosphere, nitrogen is removed from the liquid phase. On the other hand, biological phosphorus removal uses the action of microorganisms called phosphorus accumulating bacteria (PAO). This PAO hydrolyzes the polyphosphate accumulated in the cells during the anaerobic process and acquires energy (ATP: adenosine triphosphate). Using this ATP, PAO ingests organic matter, but simultaneously decomposed polyphosphoric acid is released as phosphate phosphorus (PO ₄ -P), increasing the concentration of PO ₄ -P in the liquid phase. On the other hand, in the aerobic process, organic substances accumulated in the cells of PAO are oxidatively decomposed by oxygen to generate energy (ATP). PAO uses this ATP to capture more PO ₄ -P and releases it as polyphosphate. The activated sludge accumulated with PO ₄ -P is extracted in the sedimentation basin, and phosphorus is removed from the system.

An anaerobic-anoxic-aerobic method (A ₂ O method) is a process that achieves both nitrogen and phosphorus removal. In the A ₂ O method, nitrogen and phosphorus are removed by the combined use of nitrifying bacteria, denitrifying bacteria, and PAO. However, since denitrifying bacteria and PAO are both heterotrophic bacteria, there is a competitive relationship for organic matter between them. Therefore, especially when the concentration of organic matter in the inflowing sewage is low as in Japan, the organic matter may become a limiting factor and the removal of nitrogen and phosphorus may be insufficient. As a means of solving such problems, it is expected to utilize denitrifying phosphorus accumulating bacteria (DPAO) which has denitrification ability in addition to the phosphorus removal ability of PAO. All PAOs can use oxygen as an electron acceptor, but DPAO can use nitric acid in addition to oxygen. Since DPAO removes nitrogen and phosphorus independently, it can efficiently use organic substances.

The DPAO utilization process includes the single-sludge system and the two-sludge system. An example of a single-sludge system is an anaerobic-aerobic-anoxic activated sludge method (AOA method) (see [Patent Document 1]). Activated sludge in the AOA method is exposed to anaerobic, aerobic, and anoxic conditions. In the AOA method, it is said that organic substances must be added before the start of the aerobic process in order to suppress phosphorus intake by DPAO in the aerobic process and perform sufficient denitrification in the anaerobic process. On the other hand, as an example of the two-sludge system, there is an external nitrification anaerobic anoxic method (A ₂ N method or DEPHANOX method) (see [Non-patent Document 1]). In the A ₂ N method, a sludge separation tank is installed after the anaerobic tank. Activated sludge is settled in the sludge separation tank and separated into supernatant and concentrated concentrated sludge. The supernatant is transferred to the nitrification tank, and NH ₄ -N is nitrified to NO ₃ -N by nitrifying bacteria present in the nitrification tank. Then, the nitrification tank effluent and concentrated sludge are mixed in the anoxic tank. A final sedimentation basin is installed after the anaerobic tank, where activated sludge and supernatant liquid are settled and separated, and the supernatant liquid is discharged out of the system as treated water. The sedimented activated sludge is returned to the anaerobic tank by a return pump and used again for a series of biological treatments. Organic matter in sewage is ingested by DPAO in the anaerobic tank, nitrogen is nitrified in the nitrification tank, denitrified by DPAO or denitrifying bacteria in the anaerobic tank, and phosphorus is ingested by DPAO using nitric acid in the nitrification tank effluent. To be removed.

In the A ₂ N method, activated sludge used in the nitrification process and denitrification / phosphorus removal process is separated, and the latter activated sludge is not exposed to aerobic conditions. As a result, the activity of DPAO increases and DPAO accumulates highly. Utilizing the integrated DPAO makes it possible to remove phosphorus without supplying oxygen, reducing the power consumption of the blower. In addition, DPAO uses accumulated organic matter for both denitrification and phosphorus removal, so it is possible to remove nitrogen and phosphorus even when the inflowing organic matter load is low.

Japanese Patent No. 4267860

T. Kuba, MCM Van Loosdrecht, JJ Heijnen: Phosphorus and nitrogen removal with minimal COD requirement by integration of denitrifying dephosphatation and nitrification in a two-sludge system.Water Research, Vol.30, No.7, pp.1702-1710, 1996. Yamanoi Ichiro, Takemoto Tsuyoshi, Tadokoro Hideyuki: Development of N2O suppression control system using redox potential (ORP), Journal of EICA, Vol.2 / 3, pp.28-37, 2011.

In the configuration of the A ₂ N method of Non-Patent Document 1, if nitrification in the nitrification process is insufficient, the amount of denitrification / phosphorus accumulation of DPAO and the amount of denitrification of denitrifying bacteria in the subsequent anaerobic process is reduced. There is a problem that the quality of treated water deteriorates. In addition, if the activity of DPAO and denitrifying bacteria is low in the anaerobic process, the removal of nitrogen and phosphorus in the anoxic process may be reduced and the quality of the treated water may be deteriorated. Accordingly, an object of the present invention is to provide a water treatment apparatus and method that ensure the nitrogen / phosphorus removal performance of DPAO in the A ₂ N method and maintain high treated water quality.

To achieve the above object, the present invention processes an anaerobic tank into which raw water flows, a sludge separation tank that separates an activated sludge mixed liquid flowing out from the anaerobic tank into a supernatant liquid and a concentrated sludge, and the supernatant liquid. In a water treatment apparatus comprising a nitrification tank, an oxygen-free tank into which the effluent from the concentrated sludge and the nitrification tank flows, and an aerobic tank into which the effluent from the oxygen-free tank flows.
Water quality measuring means for measuring an index of nitrate nitrogen concentration of the inflow water and effluent water of the anoxic tank is provided, and the nitrate nitrogen concentration of the inflow water and effluent water of the anoxic tank is calculated from the water quality measurement means. The first air volume control means for controlling the aeration air volume of the nitrification tank using the calculated nitrate nitrogen concentration is provided.

  Furthermore, the water treatment apparatus of the present invention is characterized in that a nitrate nitrogen concentration meter or a redox potential meter is installed as the water quality measuring means.

  Further, the water treatment apparatus of the present invention comprises a transfer sludge amount control means for controlling the flow rate of the concentrated sludge, calculates the nitrate nitrogen concentration of the effluent of the oxygen-free tank measured by the water quality measurement means, The flow rate of the concentrated sludge is controlled by the transferred sludge amount control means based on the calculated nitrate nitrogen concentration.

  Furthermore, the water treatment apparatus of the present invention comprises second air volume control means for controlling the aeration air volume of the aerobic tank, and phosphorus concentration measurement means for measuring the phosphorus concentration of the effluent of the anaerobic tank. The aeration air volume of the aerobic tank is controlled by the second air volume control unit based on the phosphorus concentration of the outflow water of the oxygen-free tank measured by the concentration measuring unit.

    Further, the water treatment apparatus of the present invention comprises second air volume control means for controlling the aeration air volume of the aerobic tank, and phosphorus concentration measurement means for measuring the phosphorus concentration of the effluent water of the oxygen-free tank. The aeration air volume of the second air volume control means is controlled based on the difference between the phosphorus concentration of the effluent of the oxygen tank and the phosphorus concentration of the target value.

To achieve the above object, the present invention comprises an anaerobic tank into which raw water flows, a sludge separation tank for separating an activated sludge mixed liquid flowing out of the anaerobic tank into a supernatant liquid and a concentrated sludge, and the supernatant liquid. A water treatment for treating the raw water, comprising a nitrification tank to be treated, an oxygen-free tank into which the effluent from the concentrated sludge and the nitrification tank flows, and an aerobic tank into which the effluent from the oxygen-free tank flows. In the method,
Measure the nitrate nitrogen concentration index of the inflow and effluent of the anoxic tank, calculate the nitrate nitrogen concentration of the inflow and effluent of the anoxic tank, and control the aeration air volume of the nitrification tank It is characterized by this.

  Furthermore, the water treatment method of the present invention is characterized in that a nitrate nitrogen concentration meter or an oxidation-reduction potentiometer is used for measuring the index of nitrate nitrogen concentration.

Furthermore, the water treatment method of the present invention is characterized in that the nitrate nitrogen concentration of the effluent of the oxygen-free tank is calculated, and the flow rate of the concentrated sludge is controlled based on the calculated nitrate nitrogen concentration. Is.
Furthermore, the water treatment method of the present invention is characterized in that the phosphorus concentration in the anaerobic tank effluent is measured and the aeration air volume in the aerobic tank is controlled based on the measured phosphorus concentration. .

Furthermore, the water treatment method of the present invention measures the phosphorus concentration of the effluent of the anaerobic tank, and controls the amount of aeration air in the aerobic tank based on the difference between the measured phosphorus concentration and the target phosphorus concentration. It is characterized by this.

  According to the present invention, stable nitrogen and phosphorus removal can be realized in water treatment using denitrifying phosphorus accumulating bacteria.

1 is a configuration diagram showing a configuration of a water treatment device S according to Embodiment 1. FIG. FIG. 3 is a control flow diagram of the aeration air volume of the first blower 9 and the transfer pump 7 in the first embodiment. It is a block diagram which shows the structure of the water treatment apparatus S which concerns on Example 2. FIG. FIG. 10 is a control flow diagram of the aeration air volume of the second blower 11 in the second embodiment. It is a block diagram which shows the structure of the water treatment apparatus S which concerns on the modification of Example 2. FIG. It is a control flow figure of the aeration air volume of the 2nd blower 11 in the modification of Example 2. FIG.

FIG. 1 is a configuration diagram illustrating a configuration of a water treatment device 500 according to the first embodiment. This water treatment device 500 removes nitrogen and phosphorus using DPAO.

(Configuration of water treatment equipment)
As shown in FIG. 1, the water treatment apparatus 500 has an anaerobic tank 1, a sludge separation tank 2, a nitrification tank 3, an oxygen-free tank 4, an aerobic tank 5 and a final sedimentation tank 6 as main components. Yes. The function of these components will be described below.

(Anaerobic tank)
The anaerobic tank 1 is a tank that removes organic substances by allowing PAO and DPAO in activated sludge to ingest organic substances in raw water (sewage 100).

(Sludge separation tank)
The sludge separation tank 2 is a tank that separates the supernatant liquid 101 and the concentrated sludge 102 obtained by sedimenting and concentrating the activated sludge. The supernatant liquid 101 is transferred to the nitrification tank 3, and the concentrated sludge 102 is transferred to the anoxic tank 4.

(Nitrification tank)
The supernatant liquid 101 separated in the sludge separation tank 2 is transferred to the nitrification tank 3, and NH ₄ -N is nitrified by nitrifying bacteria present in the nitrification tank 3 to make NO ₃ -N.

(Anoxic tank)
In the anoxic tank 4, DPAO and denitrifying bacteria remove and remove NO ₃ -N produced by nitrification in the nitrification tank 3, and DPAO ingests phosphorus using nitrate ions produced in the nitrification tank 3. It is a tank to do.

(Aerobic tank)
The aerobic tank 5 removes denitrification bubbles in the effluent of the anaerobic tank 4 by aeration, maintains the settleability of the activated sludge, and nitrifies NH ₄ -N remaining in the effluent of the anaerobic tank 4. , This tank performs complementary aerobic phosphorus removal with PAO and DPAO.

(Final sedimentation basin)
The final sedimentation basin 6 is a facility that separates and separates the supernatant and activated sludge. The supernatant liquid that has settled and separated is discharged out of the system as treated water 103. The activated sludge separated and separated is returned to the anaerobic tank 1 and used again for a series of biological treatments.

  Hereinafter, the water treatment apparatus 500 will be described in more detail.

  As shown in FIG. 1, the anaerobic tank 1 and the sludge separation tank 2 communicate with each other through a flow path. A nitrification tank 3 is installed downstream of the sludge separation tank 2, and the sludge separation tank 2 communicates with the anoxic tank 4 through the flow path 200 and the transfer pump 7. The nitrification tank 3 is provided with a first air diffuser 8 and a first blower 9 for supplying air thereto. An oxygen-free tank 4 is installed downstream of the nitrification tank 3. The oxygen-free tank 4 includes effluent water from the nitrification tank 3 and concentrated sludge 102 from the sludge separation tank 2 transferred by the transfer pump 7. Flows in. An aerobic tank 5 is installed downstream of the anaerobic tank 4, and a second air diffuser 10 and a second blower 11 for supplying air to the aerobic tank 5 are installed. A final sedimentation basin 6 is installed on the downstream side of the aerobic tank 5 and communicates with the anaerobic tank 1 through the flow path 800 and the return pump 12. An activated sludge carrier 13 is introduced into the nitrification tank 3, and a screen 14 is installed at the end of the nitrification tank 3 in order to capture the activated sludge carrier 13.

On the upstream side of the anaerobic tank 1, a flow meter 15 that measures the inflow amount of the sewage 100 is installed. In the flow path connecting the nitrification tank 3 and the anoxic tank 4, a first water quality meter 16, which is a water quality measuring means for measuring the NO ₃ -N concentration index, is installed. The NO ₃ -N concentration is calculated. Further, a second water quality meter 17 that is a water quality measuring means for measuring the NH ₄ -N concentration index of the inflow water of the oxygen-free tank 4 is installed in the flow path that connects the nitrification tank 3 and the oxygen-free tank 4. The NH ₄ -N concentration of the inflow water of the anoxic tank 4 is calculated. In addition, a third water quality meter 18 that is a water quality measuring means for measuring the NO ₃ -N concentration index is installed in the flow path that connects the anaerobic tank 4 and the aerobic tank 5. The NO ₃ -N concentration of the effluent from the water is calculated. In this embodiment, NO ₃ -N concentration meters are used as the first water quality meter 16 and the third water quality meter 18. In this embodiment, an NH ₄ -N concentration meter is used as the second water quality meter 17. First air volume control means 19 is connected to the first blower 9, and the aeration air volume of the first blower 9 is controlled by the first air volume control means 19. Further, a transfer sludge amount control means 20 is connected to the transfer pump 7, and the flow rate of the transfer pump 7 is controlled by the transfer sludge amount control means 20.

As described above, the water treatment apparatus 500 performs the A ₂ N method for separating the activated sludge used in the nitrification process and the activated sludge used in the denitrification / phosphorus removal process.

PAO in activated sludge includes PAO that can use only oxygen as an electron acceptor and PAO (DPAO) that can use both oxygen and nitric acid when phosphorus is taken up. In the A ₂ N method, the activated sludge used in the denitrification / phosphorus removal process does not pass through the nitrification tank 3 where a long-term aerobic condition exists, so DPAO compared to PAO which can use only oxygen as an electron acceptor. Activity increases and the level of DPAO accumulation increases.

The flow of treatment in the A ₂ N method by the water treatment apparatus 500 according to the first embodiment is as follows.

Raw water (sewage 100) flows into the anaerobic tank 1, and organic matter in the sewage 100 is ingested by PAO and DPAO in the activated sludge. The activated sludge from the anaerobic tank 1 flows into the sludge separation tank 2 and is separated into the supernatant liquid 101 and the concentrated sludge 102 by gravity (sedimentation separation). The supernatant 101 flows into the nitrification tank 3, and NH ₄ -N in the supernatant 101 is nitrified to NO ₃ -N by the nitrifying bacteria immobilized in the activated sludge carrier 13. Outflow water from the nitrification tank 3 and concentrated sludge 102 transferred from the sludge separation tank 2 by the flow path 200 and the transfer pump 7 flow into the anoxic tank 4. In the anaerobic tank 4, denitrification and phosphorus removal by DPAO and denitrification by denitrifying bacteria are performed. In the aerobic tank 5, nitrification of remaining NH ₄ -N and aerobic phosphorus removal are performed. Further, the denitrification bubbles are removed by aeration in the aerobic tank 5, and the sedimentation property of the activated sludge in the final sedimentation basin 6 is maintained. In the final sedimentation basin 6, the activated sludge from the aerobic tank 5 is solid-liquid separated, and the supernatant liquid is discharged out of the system as treated water 103. On the other hand, the activated sludge separated in the final sedimentation basin 6 is returned to the anaerobic tank 1 by the flow path 800 and the return pump 12.

In the conventional A ₂ N method, the aeration air volume of the first blower 9 is kept constant or the ratio of the sewage 100 to the inflow water volume is controlled to be constant. Further, the flow rate of the transfer pump 7 is kept constant, or the ratio between the flow rate of the supernatant liquid 101 and the flow rate of the concentrated sludge 102 is controlled to be constant. Therefore, when the aeration air volume of the first blower 9 is small, nitrification in the nitrification tank 3 may be insufficient. When the amount of NO ₃ -N flowing into the anaerobic tank 4 decreases, anaerobic phosphorus intake by DPAO and denitrification by denitrifying bacteria are limited, and the nitrogen / phosphorus removal performance in the anoxic tank 4 decreases. Moreover, when the activity of DPAO in the anoxic tank 4 is low, the nitrogen removal performance in the anoxic tank 4 may be reduced, and the nitrogen concentration in the treated water 103 may be increased. Therefore, in this embodiment, the nitrification efficiency in the nitrification tank 3 and the denitrification efficiency in the anoxic tank 4 are evaluated, and the control for adjusting the aeration air volume of the first blower 9 and the flow rate of the transfer pump 7 from the evaluation results. The flow is shown. FIG. 2 is a control flow chart of the aeration air volume of the first blower 9 and the flow rate of the transfer pump 7. Hereinafter, the control flow in the first air volume control means 19 and the transferred sludge quantity control means 20 will be described in detail.

First, the aeration air volume (q ₁ ) of the first blower 9 is obtained by multiplying the inflow water volume (Q) of the sewage 100 measured by the flow meter 15 in step 101 (hereinafter referred to as S101) by the set air magnification (k ₁ ). ) Is calculated. At this stage, the aeration air volume (q ₁ ) of the first blower 9 may be constant regardless of the inflow water volume (Q) of the sewage 100. Next, in S102, taking measurements of the first water meter 16 and (C _NO3), the measured value of the second water meter 17 and (C _NH4), the measured value of the third water meter 18 and (C _'NO3) . In S103, the nitrification rate (R _N ) in the nitrification tank 3 and the NO ₃ -N concentration (C ′ _NO3 ) of the effluent of the anaerobic tank 4 are calculated as evaluation indexes. Here, the nitrification rate (R _N ) in the nitrification tank 3 is NO ₃ occupying the total amount of NH ₄ -N concentration (C _NH4 ) and NO ₃ -N concentration (C _NO3 ) of the inflow water of the anoxic tank 4. It represents the percentage of -N concentration (C _NO3 ) and is defined by equation (1).

If the nitrification rate (R _N ) in the nitrification tank 3 calculated by the first air volume control means 19 in S104 is equal to or greater than the target value (R _N-0 ), the aeration air volume (q ₁ ) of the first blower 9 in S105. Or decrease the nitrification rate (R _N ) so that it does not become smaller than the target value (R _N-0 ). On the other hand, if the nitrification rate (R _N ) in the nitrification tank 3 is less than the target value (R _N-0 ) in S104, the aeration air volume (q ₁ ) of the first blower 9 is increased in S106. Thereby, the nitrification rate (R _N ) in the nitrification tank 3 is improved, and a sufficient amount of NO ₃ -N can be flowed into the anoxic tank 4, so that the activity of DPAO can be maintained.

Next, if the NO ₃ -N concentration (C ′ _NO3 ) of the effluent of the anaerobic tank 4 measured by the third water quality meter 18 in S107 is less than or equal to the target value ( _C′NO3-0 ), the transfer pump in S108 The flow rate (q _S ) of 7 is constant. On the other hand, if the NO ₃ -N concentration (C ′ _NO3 ) of the effluent of the anaerobic tank 4 measured by the third water quality meter 18 in S107 is higher than the target value ( _C′NO3-0 ), the transfer pump 7 of S Increase the flow rate (q _S ). As a result, the amount of concentrated sludge 102 flowing directly into the anoxic tank 4 without passing through the nitrification tank 3 increases. Since DPAO ingests PO ₄ -P even in an aerobic state, if it passes through the aerobic state (nitrification tank 3) first, DPAO's PO ₄ -P intake in the subsequent anaerobic state (anoxic tank 4) The amount decreases, and the amount of denitrification by DPAO decreases accordingly. In addition, organic substances necessary for denitrification by denitrifying bacteria are reduced by oxidation in an aerobic state (nitrification tank 3). As described above, the denitrification performance in the oxygen-free tank 4 is improved by increasing the flow rate (q _S ) of the transfer pump 7 and allowing more DPAO and organic matter contained in the concentrated sludge 102 to flow directly into the oxygen-free tank 4. Can do. Moreover, since the contact with the aerobic state (nitrification tank 3) of DPAO can be reduced, the integration degree of DPAO can also be improved. However, when the flow rate (q _S ) of the transfer pump 7 is increased, the ratio between the flow rate of the supernatant 101 and the flow rate of the concentrated sludge 102 also changes, so the change amount (Δq _S ) of the flow rate (q _S ) of the transfer pump 7 The target value (R _N-0 ) of the nitrification rate in the nitrification tank 3 may be adjusted accordingly.

Here, the amount of change (Δq ₁ ) in the aeration air volume (q ₁ ) of the first blower 9 is the amount of nitrification necessary for the nitrification rate (R _N ) in the nitrification tank 3 to reach the target value (R _N-0 ), In other words, this is a function of the total concentration of nitrogen components flowing into the anaerobic tank 4 and the difference between the nitrification rate (R _N ) and the target value (R _N-0 ). Further, when the aeration air volume (q ₁ ) of the first blower 9 is reduced in S105, the reduction quantity (Δq ₁ ) follows equation (1). Formula (2) shows the formula for calculating Δq ₁ . The amount of change (Δq _S ) in the flow rate (q _S ) of the transfer pump 7 is the difference between the NO ₃ -N concentration (C ' _NO3 ) and the target value (C' _NO3-0 ) It is expressed by the function of Formula (3) shows the formula for calculating Δq _S.

By controlling the aeration air volume of the first blower 9 and the flow rate of the transfer pump 7, the stabilization of the processing performance of the A ₂ N method and the maintenance of DPAO activity can be achieved at the same time. That is, when the nitrification efficiency in the nitrification tank 3 is insufficient, the aeration rate of the first blower 9 is increased to improve the nitrification rate, thereby improving the nitrogen removal rate and further maintaining or improving the activity of DPAO. Can do. Further, when the nitrification rate in the nitrification tank 3 is sufficient, but the denitrification efficiency in the anoxic tank 4 is low, the flow rate of the transfer pump 7 is increased so that the nitrification tank 3 can be transferred to the anoxic tank 4 without passing through the nitrification tank 3. Denitrification performance can be improved because the amount of inflowing organic matter and DPAO increase.

  In this embodiment, the activated sludge carrier 13 is introduced into the nitrification tank 3, but floating activated sludge may be introduced instead of the activated sludge carrier 13. In that case, a sedimentation basin and activated sludge return equipment are installed at the subsequent stage of the nitrification tank 3, the activated sludge mixed liquid from the nitrification tank 3 is solid-liquid separated by gravity, and the precipitated activated sludge is returned to the nitrification tank 3.

In the present embodiment, the first water quality meter 16 is installed in the flow path that connects the nitrification tank 3 and the anoxic tank 4, but the NO ₃ -N concentration index of the inflow water of the anoxic tank 4 can be measured. If present, it may be installed inside the nitrification tank 3 or inside the anoxic tank 4. Similarly, the third water quality meter 18 is installed in the anoxic tank 4 or the aerobic tank 5 if it can measure the NO ₃ -N concentration index of the effluent of the anoxic tank 4. Also good.

In this embodiment, an NH ₄ -N concentration meter was installed as a second water quality meter in the flow path connecting the nitrification tank 3 and the anoxic tank 4, but the second water quality meter was installed upstream of the nitrification tank 3. Then, the NH ₄ -N concentration of the inflow water of the anaerobic tank 4 may be calculated from the measured value. In addition, the maximum NH ₄ -N concentration (C _NH4 ) of the inflow water in the anaerobic tank 4 can be estimated based on a database that records changes in the NH ₄ -N concentration of the sewage 100, and the estimated value can be used. good.

  For the aeration air volume of the blower 9, an upper limit value may be provided so that the aeration air volume does not increase more than necessary.

In this embodiment, the target value (R _N-0 ) of the nitrification rate in the nitrification tank 3 is set, but the nitrogen concentration of the sewage 100 or the sewage is set so that the quality of the treated water 103 satisfies the sewage effluent quality standard value. You may adjust according to the flow volume of 100. Moreover, the removal of NH ₄ -N in the sewage 100 cannot be realized unless it is denitrified through nitrification. Therefore, the nitrogen removal performance of the water treatment device 500 affects the ratio of the effluent water of the sludge separation tank 2 flowing into the nitrification tank 3, that is, the ratio of the flow rate of the supernatant liquid 101 and the flow rate of the concentrated sludge 102. receive. Therefore, the target value (R _N-0 ) of the nitrification rate in the nitrification tank 3 is the flow rate of the supernatant liquid 101 and the flow rate of the concentrated sludge 102 so that the quality of the treated water 103 satisfies the sewage effluent quality standard value. You may adjust according to the ratio.

In the present embodiment has been set nitrification rate in the nitrification tank 3 target value (R _N) the (R _N-0), it is not necessary to set a target value, the nitrification rate of the nitrification tank 3 (R _N) Accordingly, the aeration air volume (q ₁ ) of the blower 9 may be controlled.

In this embodiment, the target value (C ' _NO3-0 ) of the effluent of the anaerobic tank 4 is set. However, it is not always necessary to set the target value, and the NO ₃ -N concentration ( The flow rate (q _S ) of the transfer pump 7 may be controlled according to C ′ _NO3 ).

<Variation 1 of the first embodiment>
In the first embodiment described above, in the nitrification tank 3 using the measured value of the NO ₃ -N concentration meter as the first water quality meter 16 and the measured value of the NH ₄ -N concentration meter as the second water quality meter 17. The nitrification rate (R _N ) was calculated, but using the redox potential (ORP) meter as the first water quality meter 16, the ORP of the effluent of the anoxic tank 4 was measured, and the nitrification rate (R _N ) in the nitrification tank 3 was measured. May be calculated.

ORP is defined by the Nernst equation shown in equation (4), and is calculated based on the concentrations of oxidant and reductant. Here, Ox is an oxidant, Red is a reductant, and m and n are coefficients in an equilibrium equation. E _h [V]: Electrode potential, E ₀ [V]: Standard electrode potential, R [J / (K ・ mol)]: Gas constant, T [K]: Absolute temperature, n [mol]: Redox The number of electrons exchanged in the reaction, F [C / mol]: Faraday constant. Among redox substances contained in the activated sludge mixed liquor in the reaction is the main reaction of NO ₃ -N is oxidized to NH ₄ -N in nitrification, the concentration of other materials assuming a constant, ORP value Is known to be approximated by a linear expression of log ([NO ₃ -N] / [NH ₄ -N]) as shown in Equation (4) (Non-patent Document 2). Here, a and b are coefficients. When the nitrification rate is expressed using ORP, the shape is as shown in Equation (6). Therefore, if the coefficients A and B in Equation (6) are estimated in advance based on the actual measurement data of the sewage treatment plant, the nitrification rate (R in the nitrification tank 3 is measured by measuring the ORP of the inflow water in the anoxic tank 4. _N ) can be derived. Further, the NO ₃ -N concentration (C _NO3 ) of the inflow water of the anoxic tank 4 can be derived by using the measured value of the second water quality meter 17.

From the above, even when an ORP meter is installed as the first water quality meter 16, the aeration air volume (q ₁ ) of the first blower 9 and the flow rate (q _S ) of the transfer pump 7 through the control flow shown in FIG. Can be controlled. By using the ORP meter as the first water quality meter, in addition to the effects of the first embodiment described above, the configuration of the measuring instrument is simplified and the maintenance frequency can be reduced.

<Modification 2 of the first embodiment>
In the first embodiment, the NO ₃ -N concentration meter is used as the third water quality meter 18, and the NO ₃ -N concentration (C ′ _{NO 3} ) of the effluent of the anoxic tank 4 is measured. Alternatively, the ORP meter may be used to measure the ORP of the effluent of the anaerobic tank 4 to calculate the NO ₃ -N concentration (C ′ _NO3 ) of the effluent of the anoxic tank 4.

Assuming that the redox substances contained in the activated sludge mixture in the anaerobic tank 4 are only NO ₃ -N and NH ₄ -N, the ORP of the effluent of the anaerobic tank 4 is given by equation (5): As shown, it is represented by the ratio of the NH ₄ -N concentration and the NO ₃ -N concentration (C ' _NO3 ) of the effluent of the anaerobic tank 4. Assuming that there is no change in the NH ₄ -N concentration in the anoxic tank 4, the NH ₄ -N concentration (C _NH4 ) of the inflow water of the anoxic tank 4 measured by the second water quality meter 17 and the third water quality meter 18 The NO ₃ -N concentration (C ′ _{NO 3} ) of the effluent of the anaerobic tank 4 can be calculated from the ORP of the effluent of the anaerobic tank 4 measured by the above.

From the above, even when the ORP is installed as the third water quality meter 18, the aeration air volume (q ₁ ) of the first blower 9 and the flow rate (q _S ) of the transfer pump 7 are controlled through the control flow shown in FIG. Can be controlled. When both the first water quality meter 16 and the third water quality meter 18 are ORP meters, in addition to the effect of the first modification of the first embodiment described above, the configuration of the measuring instrument is further simplified and the maintenance frequency can be reduced.

FIG. 3 is a configuration diagram showing the configuration of the water treatment device 500 according to the second embodiment. In the second embodiment, in addition to the configuration of the first embodiment, a phosphorus concentration meter 21 which is a phosphorus concentration measuring means for the outflow water of the anoxic tank 4 is connected to the anaerobic tank 4 and the aerobic tank 5. It is installed on the road. Moreover, the 2nd air volume control means 22 which controls the aeration air volume of the 2nd blower 11 is installed.

In the conventional A ₂ N method, similarly to the first blower 9, the aeration air volume of the second blower 11 is maintained constant or the ratio of the sewage 100 to the inflow water volume is controlled to be constant. Therefore, there is a limit to the phosphorus removal ability in the aerobic tank 5, and when high concentration phosphorus flows into the aerobic tank 5, the water quality of the treated water 103 may be deteriorated. Therefore, in this embodiment, a control flow was devised that adjusts the aeration air volume of the second blower 11 in accordance with the phosphorus concentration of the outflow water of the anoxic tank 4 measured by the phosphorus concentration meter 21. FIG. 4 is a control flow of the aeration air volume of the second blower 11. Hereinafter, the control flow of the aeration air volume of the second blower 11 by the second air volume control means 22 will be described in detail.

First, in step 201 (hereinafter referred to as S201), the amount of aeration air (q2) of the second blower 11 is calculated by multiplying the inflow water amount (Q) of the sewage 100 measured by the flow meter 15 by the set air magnification (k ₂ ). ₂ ) is calculated. At this stage, the aeration volume (q ₂ ) of the second blower 11 may be constant regardless of the inflow volume (Q) of the sewage 100. Next, the phosphorus concentration (C _P ) of the effluent of the anoxic tank 4 is calculated by the phosphorus concentration meter 21 in S202. If the phosphorus concentration (C _P ) of the effluent water from the anaerobic tank 4 is equal to or less than the target value (C _P-0 ) in S203, the aeration air volume (q ₂ ) of the second blower 11 is made constant in S204. On the other hand, if the phosphorus concentration (C _P ) of the effluent of the oxygen tank 4 is higher than the target value (C _P-0 ) in S203, the aeration air volume (q ₂ ) of the second blower 11 is increased in S205. By increasing the aeration air volume (q ₂ ) of the blower 11, aerobic phosphorus intake by PAO or DPAO is promoted in the aerobic tank 5, and the phosphorus removal performance is improved.

Here, the amount of change (Δq ₂ ) in the aeration air volume (q ₂ ) of the second blower 11 is a function of the difference between the phosphorus concentration (C _P ) of the effluent of the anaerobic tank 4 and the target value (C _P-0 ). It is represented by In Equation (7) shows a calculation formula of [Delta] q _2.

By controlling the amount of aeration air of the second blower 11 described above, the phosphorus removal capability of the water treatment device 500 can be maintained. When phosphorus removal in the anoxic tank 4 is insufficient due to low DPAO activity, etc., the aeration air volume of the blower 11 is controlled to be constant or the flow rate ratio to the sewage 100 is controlled. There is a limit and it may not be possible to achieve residual phosphorus treatment. On the other hand, in this embodiment, since the amount of aeration air of the blower 11 is controlled so as to satisfy the treatment water standard according to the phosphorus concentration of the effluent of the anoxic tank 4, it is possible to maintain the treatment performance.

In this embodiment, the target value (C _P-0 ) of the phosphorus concentration of the effluent of the anaerobic tank 4 is set, but the target value (C _P-0 ) of the phosphorus concentration of the effluent of the anoxic tank 4 is set. May be adjusted according to the phosphorus concentration of the sewage 100 or the flow rate of the sewage 100 so that the quality of the treated water 103 satisfies the sewage effluent quality standard value.

In this embodiment, the target value (C _P-0 ) of the phosphorus concentration of the effluent of the anaerobic tank 4 is set, but it is not always necessary to set the target value. The aeration volume (q ₂ ) of the blower 11 may be controlled according to _P ).

In the present embodiment, the phosphorus concentration meter 21 is installed in the flow path connecting the anoxic tank 4 and the aerobic tank 5, but it may be installed downstream of the aerobic tank 5. For example, it is possible to install a phosphorus concentration meter 21 on the downstream side of the final sedimentation basin 6 and control the amount of aeration air of the blower 11 according to the phosphorus concentration of the treated water 103.

<Modification of Second Embodiment>
FIG. 5 is a configuration diagram showing a configuration of a water treatment device 500 according to a modification of the second embodiment. In the second embodiment described above, the aeration air volume (q ₂ ) of the second blower 11 is controlled using the phosphorus concentration (C _P ) of the effluent of the anoxic tank 4 measured by the phosphorus concentration meter 21. The amount of aeration air (q ₂ ) of the second blower 11 may be controlled from the amount of decrease in phosphorus concentration (ΔP) in the oxygen-free tank 4 calculated from the measured values of the 1 water quality meter 16 and the third water quality meter 18. FIG. 6 is a control flow diagram of the aeration air volume of the second blower 11 in a modification of the second embodiment.

  A method for calculating the decrease (ΔP) of the phosphorus concentration in the anoxic tank 4 from the measured values of the first water quality meter 16 and the third water quality meter 18 will be described in detail.

In the anoxic state, both NO ₃ -N concentration and phosphorus concentration decrease because phosphorus intake by DPAO and denitrification by DPAO and denitrifying bacteria progress. Therefore, if the ratio of the decrease amount of phosphorus concentration per decrease amount of NO ₃ -N concentration in the anaerobic tank 4 is set in advance from the measured data of the sewage treatment plant, the first water quality meter 16 and the third water quality meter are set. The amount of decrease in phosphorus concentration (ΔP) in the oxygen-free tank 4 can be calculated from the amount of decrease in NO ₃ -N concentration in the oxygen-free tank 4 calculated from the 18 measured values.

  The control flow of the aeration air volume of the second blower 11 in the modification of the second embodiment will be described in detail.

First, in step 301 (hereinafter referred to as S301), the aeration air volume (q ₂ ) of the second blower 11 is obtained by multiplying the inflow water volume (Q) of the sewage 100 measured by the flow meter 15 by the set air magnification (k ₂ ). ₂ ) is calculated. At this stage, the aeration volume (q ₂ ) of the second blower 11 may be constant regardless of the inflow volume (Q) of the sewage 100. Next, the measured value of the 1st water quality meter 16 and the 3rd water quality meter 18 is taken in by S302. Next, in S303, from the decrease in NO ₃ -N concentration in the anaerobic tank 4 calculated from the measured values of the first water quality meter 16 and the third water quality meter 18, the decrease in phosphorus concentration in the anaerobic tank 4 (ΔP ) Is calculated. If the amount of decrease in phosphorus concentration (ΔP) in the anaerobic tank 4 is equal to or greater than the target value (ΔP ₋₀ ) in S304, the aeration air volume (q ₂ ) of the second blower 11 is made constant in S305. On the other hand, if the decrease amount (ΔP) of the phosphorus concentration in the oxygen-free tank 4 is higher than the target value (ΔP ₋₀ ) in S304, the aeration air volume (q ₂ ) of the second blower 11 is increased in S306. By increasing the aeration air volume (q ₂ ) of the blower 11, aerobic phosphorus intake by PAO or DPAO is promoted in the aerobic tank 5 and the phosphorus removal performance is improved.

Since this configuration eliminates the need for a phosphorus concentration meter, in addition to the effects of the first and second embodiments described above, the cost required for the measuring instrument can be reduced.

In this embodiment, the target value (ΔP ₋₀ ) of the decrease amount of phosphorus concentration in the anaerobic tank 4 is set, but the target value (ΔP ₋₀ ) of phosphorus concentration in the effluent water of the anoxic tank 4 is You may adjust according to the phosphorus density | concentration of the sewage 100, or the flow volume of the sewage 100 so that the water quality of the treated water 103 may satisfy the sewage effluent quality standard value.

In this embodiment, the target value (ΔP ₋₀ ) of the phosphorus concentration in the anaerobic tank 4 is set. However, it is not always necessary to set the target value, and it depends on the amount of decrease in the phosphorus concentration (ΔP) in the anoxic tank 4. Thus, the aeration air volume (q ₂ ) of the blower 11 may be controlled.

1… Anaerobic tank
2… Sludge separation tank
3 ... Nitrification tank
4… Anoxic tank
5 ... Aerobic tank
6 ... Final sedimentation basin
7 ... Transfer pump
8… First diffuser
9 ... 1st blower
10 ... Second diffuser
11 ... Second blower
12 ... Return pump
13 ... Activated sludge carrier
14 ... Screen
15 ... Flow meter
16 ... 1st water quality meter
17 ... Second water quality meter
18 ... 3rd water quality meter
19: First air volume control means
20… Transfer sludge volume control means
21 ... Phosphor concentration meter
22 ... Second air volume control means
100 ... Sewage
101 ... Supernatant liquid
102 ... Concentrated sludge
103 ... treated water
200: Concentrated sludge transfer channel to nitrification tank 3
500 ... Water treatment equipment
800… Transfer flow path for return sludge

Claims (10)

An anaerobic tank into which raw water flows, a sludge separation tank for separating the activated sludge mixed liquid flowing out from the anaerobic tank into a supernatant liquid and a concentrated sludge, a nitrification tank for treating the supernatant liquid, the concentrated sludge and the nitrification tank In a water treatment apparatus comprising an anaerobic tank into which effluent water flows from and an aerobic tank into which effluent water from the anoxic tank flows,
Water quality measuring means for measuring an index of nitrate nitrogen concentration of the inflow water and the outflow water of the anoxic tank,
First air volume control means for calculating the nitrate nitrogen concentration of the inflow water and effluent water of the anoxic tank from the water quality measuring means and controlling the aeration air volume of the nitrification tank using the calculated nitrate nitrogen concentration. A water treatment apparatus characterized by comprising. The water treatment device of claim 1,
A water treatment apparatus comprising a nitrate nitrogen concentration meter or an oxidation-reduction potentiometer as the water quality measuring means. In the water treatment device according to claim 1 or 2,
A transfer sludge amount control means for controlling the flow rate of the concentrated sludge,
Calculate the nitrate nitrogen concentration of the effluent of the anoxic tank measured by the water quality measuring means, and control the flow rate of the concentrated sludge by the transfer sludge amount control means based on the calculated nitrate nitrogen concentration. Water treatment device characterized by. In one water treatment apparatus in any one of Claims 1-3,
A second air volume control means for controlling the aeration air volume of the aerobic tank; and a phosphorus concentration measuring means for measuring the phosphorus concentration of the effluent of the anoxic tank,
The water treatment apparatus, wherein the aeration air volume of the aerobic tank by the second air volume control means is controlled based on the phosphorus concentration of the outflow water of the anoxic tank measured by the phosphorus concentration measuring means. In one water treatment apparatus in any one of Claims 1-3,
Second air volume control means for controlling the aeration volume of the aerobic tank;
Phosphorus concentration measuring means for measuring the phosphorus concentration of the effluent of the oxygen-free tank,
A water treatment apparatus, wherein the aeration air volume of the second air volume control means is controlled based on a difference between a phosphorus concentration of effluent water of the anoxic tank and a phosphorus concentration of a target value.
An anaerobic tank into which raw water flows,
A sludge separation tank for separating the activated sludge mixed liquid flowing out of the anaerobic tank into a supernatant liquid and a concentrated sludge;
A nitrification tank for treating the supernatant;
An oxygen-free tank into which the concentrated sludge and effluent water from the nitrification tank flow,
An aerobic tank into which effluent water from the anoxic tank flows, and a water treatment method for treating the raw water,
Measure the index of nitrate nitrogen concentration of the inflow and effluent of the anoxic tank,
A water treatment method characterized in that the nitrate nitrogen concentration of inflow water and outflow water of the anoxic tank is calculated to control the amount of aeration air in the nitrification tank.
The water treatment method according to claim 6,
A water treatment method using a nitrate nitrogen concentration meter or an oxidation-reduction potentiometer to measure the index of nitrate nitrogen concentration.
In the water treatment method of Claim 6, or Claim 7,
A water treatment method characterized in that the nitrate nitrogen concentration of the effluent of the anoxic tank is calculated, and the flow rate of the concentrated sludge is controlled based on the calculated nitrate nitrogen concentration.
The water treatment method according to any one of claims 6 to 8,
Measure the phosphorus concentration of the effluent of the anaerobic tank,
A water treatment method characterized by controlling the aeration volume of the aerobic tank based on the measured phosphorus concentration.
The water treatment method according to any one of claims 6 to 8,
Measure the phosphorus concentration of the effluent of the anaerobic tank,
A water treatment method characterized by controlling the aeration air volume in the aerobic tank based on the difference between the measured phosphorus concentration and the target phosphorus concentration.