JP4218565B2 - Sewage treatment method, sewage treatment control system, and sewage treatment facility - Google Patents

Description

  The present invention relates to a sewage treatment method, a sewage treatment control system, and a sewage treatment facility.

  Sewage treatment facilities are required to remove nitrogen and phosphorus in addition to organic matter. In order to remove nitrogen and phosphorus stably, in addition to the organic matter contained in the inflowing sewage, it is necessary to further supply organic materials from outside or separately. As this organic matter source, there is a method in which the initial sedimentation sludge extracted from the initial sedimentation basin is used directly or after pretreatment such as solubilization. Patent Document 1 discloses a method in which initial settling sludge is introduced into a biological reaction tank in which return water from the sludge treatment process is mixed. Patent Document 2 discloses a method in which when the oxidation-reduction potential (ORP) of a denitrification tank is 0 mV, a part of the initial settling sludge is introduced into a denitrification tank or an anaerobic tank into which post-settling water flows.

Japanese Patent Laid-Open No. 11-104693 Japanese Patent Laid-Open No. 10-323893

  When using the biological properties of activated sludge to remove the nitrogen and phosphorus by introducing the initial settling sludge, it is desirable to prevent excessive addition in order to maintain the bacterial activity of the activated sludge. In addition, when the initial settling sludge is added, the load on organic matter increases, and the oxygen consumption accompanying the metabolism of organic matter in the process of removing nitrogen and phosphorus by the activated sludge microbial cells increases, so it is necessary to increase the blast volume. However, there is an upper limit on the BOD (biochemical oxygen demand) load that can be tolerated due to the oxygen supply capacity determined by the equipment specifications of the processing facility blower and diffuser. If sufficient oxygen is not supplied to the cells with respect to the amount of organic matter that has flowed in, unused organic matter may remain and the BOD concentration of the treated water may increase.

  However, in Patent Documents 1 and 2 listed in the previous section, neither of the upper limits of the input amount of initial sludge is taken into consideration, the input amount exceeds the allowable range of the sewage treatment facility, and the quality of the treated water deteriorates. There is a fear. It is desired that the initial sludge input amount be set to an upper limit value based on the SRT and the amount of air that can be supplied to improve the removal of nitrogen and phosphorus by activated sludge.

  An object of the present invention is to provide a sewage treatment method, a sewage treatment control system, and a sewage treatment facility capable of maintaining the bacterial cell composition of activated sludge required for removing nitrogen and phosphorus and reducing the amount of generated sludge.

Average Sludge residence time of activated sludge, or based on the oxygen supply, and controls the input of Hatsu沈 sludge.

  According to the present invention, it is possible to provide a sewage treatment method, a sewage treatment control system, and a sewage treatment facility capable of maintaining the bacterial cell composition of activated sludge required for removing nitrogen and phosphorus and reducing the amount of generated sludge.

  In the embodiment of the present invention, the initial settling sludge is charged in the biological reaction based on the average sludge residence time of the activated sludge or the oxygen supply amount.

  Removal of nitrogen and phosphorus requires an average sludge retention time (SRT: Sludge Retention Time) of activated sludge that is longer than the growth time of bacterial cells that contribute to the removal of nitrifying bacteria, denitrifying bacteria, and phosphorus accumulating bacteria. This SRT is obtained by the following (Equation 1) from MLSS (Mixed Liquor Suspended Solids) which is the suspended solid concentration of activated sludge and the amount of suspended sludge (SS: Suspended Solids).

SRT = (MLSS × reaction tank capacity) / (excess sludge SS amount) (Equation 1)
In a sewage treatment facility that separates activated sludge and treated water by gravity in the final sedimentation basin, if the MLSS is high, the interface position of the sedimentation sludge in the final sedimentation basin becomes high, and there is a risk of sludge outflow. For example, according to an advanced treatment facility design manual (Japan Sewerage Association, 1994), MLSS is generally around 3000 mg / l in an advanced treatment facility that removes nitrogen and phosphorus. When primary sludge is introduced, MLSS increases for two reasons: 1) microorganisms in activated sludge decompose and propagate organic matter in primary sludge, and 2) primary sediment sludge has a high SS. If the amount of initial sludge input becomes excessive, MLSS is restricted from the facility side, so it is necessary to increase excess sludge in order to reduce MLSS. As a result, SRT is shortened, and in particular, a long time is required for growth. Nitrifying bacteria to be reduced are likely to decrease, and the nitrogen removal rate may deteriorate.

  The embodiment of the present invention focuses on the average sludge residence time of activated sludge or the oxygen supply amount of the oxygen supply device, and optimizes the input amount of the first settling sludge.

  In FIG. 1, the block diagram of the sewage treatment apparatus and its control system in a present Example is shown. The sewage treatment apparatus includes a first sedimentation basin 2, a biological reaction tank 1, a final sedimentation basin 3, and a control means 7, and is installed in a sewage treatment facility or the like.

  The biological reaction tank 1 is a biological reaction means for biologically treating and decomposing organic matter, nitrogen, phosphorus, etc. in the supernatant liquid (hereinafter referred to as post-sedimentation water) flowing out from the settling basin 2 by activated sludge inhabited by microorganisms. It is a facility. The biological reaction tank 1 includes a plurality of reaction tanks, and includes anaerobic tanks 1-A and 2-A, and aerobic tanks 1-B and 2-B. An oxygen-containing gas supply means 4 made of a blower or the like is connected to the bottom of the aerobic tank 1-B. Air is supplied from the oxygen-containing gas supply means 4 to the aerobic tank 1-B. Reaction tank measurement means 9 is installed in any reaction tank of the biological reaction tank 1, and MLSS of the reaction tank is measured. In this embodiment, it is provided in the anaerobic tank 1-A. Moreover, the DO measurement means 11 is installed in the aerobic tank 1-B, and DO is measured.

  In the final sedimentation basin 3, surplus sludge measuring means 10 is installed, and surplus sludge extraction flow rate and surplus sludge MLSS are measured. Information on these measuring means is sent to the control means 7.

  The first settling basin 2 is provided with a first settling sludge transfer means 5 equipped with a pump or the like. Between the initial settling sludge transfer means 5 and the initial settling sludge supply port 13, an initial settling sludge measuring means 8 and a valve 14 for measuring the SS concentration of the initial settling sludge are installed. Information of the initial settling sludge measuring means 8 is sent to the control means 7. The control means 7 controls the amount of initial sludge input by means of the initial sludge transfer means 5 and the valve 14. The calculation conditions used for control by the control means 7 are set by the target value input means 6 and the device specification input means 12. In this embodiment, the initial settling sludge supply port 13 is provided in the anaerobic tank 2-A.

  Next, the process of inflow raw water in the sewage treatment facility in the present embodiment will be described.

  Inflow raw water supplied from the outside of the sewage treatment facility is supplied to the first sedimentation basin 2. In the first settling basin 2, the first settling sludge is generated by the settling and separation of the incoming raw water. Part of the generated initial settling sludge is supplied to the biological reaction tank 1 by the initial settling sludge transfer means 5. The organic matter, nitrogen and phosphorus in the post-water are removed by the biological reaction of the activated sludge in the biological reaction tank 1.

  The initial sedimentation sludge supplied to the biological reaction tank 1 is utilized as an organic matter source necessary for removal. The reaction liquid in the biological reaction tank 1 is supplied to the final sedimentation basin 3 and separated into activated sludge and a supernatant liquid, and the supernatant liquid is discharged as treated water. The surplus sludge that has passed through the surplus sludge measuring means 10 and the initial sedimentation sludge that is not put into the biological reaction tank 1 are treated as discharged sludge outside the system of the water treatment facility.

  Next, the operation method in the present embodiment will be described using steps S1 to S7 in the flowcharts of FIGS.

In the oxygen supply amount calculation step of step S 1, the oxygen supply amount calculation means in the control means 7 provides information on the maximum air flow F _max of the oxygen-containing gas supply means 4 from the equipment specification input means 12 and DO measurement from the DO measurement means 11. A value is obtained, and the maximum value of the oxygen supply amount is calculated using the overall oxygen transfer capacity coefficient _KLA . For the calculation, for example, the following (Equation 2) and (Equation 3) are used. Where ΔD is the amount of oxygen supplied by the oxygen-containing gas supply means 4, K _LA is the overall oxygen transfer capacity coefficient,
DOS is the saturation level of dissolved oxygen, and DO is dissolved oxygen at present.

ΔD = K _LA (DO _S −DO) (Formula 2)
K _LA = f (F _max ) (Formula 3)
Where ΔD is the amount of oxygen supplied by the oxygen-containing gas supply means 4, K _LA is the overall oxygen transfer capacity coefficient,
DO _S is the degree of saturation of dissolved oxygen, and DO is currently dissolved oxygen. The supplied oxygen amount may be calculated from the relationship between the blown amount created in advance and DO. The value obtained by multiplying the maximum value of the oxygen supply amount obtained here by the constant γ previously set by the target value input means 6 is the biological oxygen demand BOD.
(biochemical oxygen demand) The upper limit of load. γ may be set based on the volume of the biological reaction tank 1. Furthermore, the BOD load upper limit value described above may be reduced in consideration of the BOD load due to the inflow of post-sinking water.

In the calculation and setting step of the maximum input flow rate of the initial settling sludge flow rate in step S2, the control means 7 obtains the BOD value of the initial settling sludge from the equipment specification input means 12, and based on the information of the BOD load upper limit value calculated in the previous stage. Calculate the initial sludge flow rate. This initial sedimentation sludge flow rate represents the maximum input flow rate. This value is Q _Omax . The BOD value may be set from the actual value. Alternatively, a BOD meter may be provided in the initial settling sludge transfer means 5 and the measured value may be used. When there is no BOD meter, there is a method of calculating using the correlation between SS and BOD of the first settling sludge. The calculated Q _Omax is _compared with the current initial settling sludge input amount Q. When Q _Omax <Q, Q = Q _Omax is set, and when Q _Omax ≧ Q, the _{process proceeds to the} next step. In this manner, Q _Omax is calculated and set by the maximum input flow rate calculation setting means.

  In the SRT calculation step of step S3, the control means 7 receives the MLSS of the reaction tank measurement means 9, the flow rate of the excess sludge measurement means 10, and the measurement information of MLSS. The control means 7 calculates the amount of extracted SS of excess sludge from the flow rate of the excess sludge measuring means 10 and MLSS. The control means 7 has a function of recording these measurement information. From the accumulated measurement information, the MLSS of the reaction tank measurement means 9 and the excess sludge extraction SS amount are set for a predetermined period set in advance by the target value input means 6. The average value of is calculated. Using this value, the current SRT is calculated from (Equation 1). Thus, the SRT is calculated by the SRT calculation means.

In step S4, the control means 7 obtains the values of SRT _S and δ _L from the target value input means 6.
SRT _S may be set based on the growth rate of nitrifying bacteria. [delta] _L is a lower tolerance, may the value of which 20% or less of the value of the SRTS. Next, the control unit 7 and SRT calculated in step S3, by comparing the difference between the SRTS and [delta] _L, in the case who SRT is large to step S6, if it is smaller proceeds to step S5.

In step S5, the control means 7 sets the current input amount Q of the first settling sludge to a value reduced by ΔQ _L and ends the flow. ΔQ _L of the initial settling amount of sludge is appropriately set based on past data.

In step S6, the control means 7 obtains the value of δ _U from the target value input means 6. δ _U is an upper tolerance, and its value is preferably 20% or less of SRTS. Next, the control means 7 compares the SRT calculated in step S3 with the difference between SRTS and δ _U obtained in step S4.
If the SRT is larger, the process proceeds to step S7, and if smaller, the process ends.

In step S7, the control means 7 sets the current input amount Q of initial sludge to a value obtained by adding ΔQ _U and ends the flow. ΔQ _U of the initial settling sludge input amount is appropriately set based on past data and the like.

  The cycle of this control is performed at least at SRT or less, and may be set according to the variation in the BOD concentration or SS concentration of the post-sinking water and the initial sludge to be added or the measurement cycle.

  According to the above-described steps S1 to S7, in this embodiment, oxygen for decomposing the BOD of the initial settling sludge can be supplied in order to control the input amount of the initial settling sludge from the air flow rate and the SRT. Therefore, it is possible to maintain the bacterial composition of activated sludge necessary for nitrogen and phosphorus removal.

  According to the present embodiment, the amount of initial settling sludge can be optimized, and the nitrogen / phosphorus removal rate by activated sludge can be improved. Moreover, since the initial settling sludge is decomposed with activated sludge, the amount of discharged sludge can be reduced.

  The flow of another embodiment of the present invention will be described with reference to the flowchart of FIG. The difference between the present embodiment and the flow of embodiment 1 is after step S4. Hereinafter, it demonstrates from step S11.

In step S11, the control means 7 obtains the SRTS value from the target value input means 6. SRT _S should be set based on the growth rate of nitrifying bacteria. Next, the control means 7 compares the SRT calculated in step S3 with SRT _S. If the SRT is larger, the process proceeds to step S12, and if smaller, the process proceeds to step S13.

In step S12, the control means 7 sets the input amount Q of the first settling sludge to a value obtained by subtracting ΔQ _SL and ends the flow. The setting method of ΔQ _SL is as follows. Calculating the excess sludge SS weight than from the reactor MLSS and SRT _S (Equation 1), compared with the excess sludge SS of current obtained from the values and excess sludge measuring means 10, and the excess sludge reduction the difference To do. The amount of the first settling sludge SS is calculated from (Equation 4) from this excess sludge reduction amount and the sludge conversion rate α described later. The amount of the initial sedimentation sludge SS is converted into ΔQ _SL using the primary sedimentation sludge SS concentration obtained from the primary sedimentation sludge measuring means 8.

In step S13, the control means 7 calculates ΔQ _SU in the same manner as in step S12. Next, the input amount Q of the first settling sludge is set to a value obtained by adding ΔQ _SU , and the flow is finished.

  From (Equation 1), SRT is determined by the amount of excess sludge. When the initial settling sludge is added, the surplus sludge increases due to the growth of the cells due to the decomposition of the initial settling sludge and the partial remaining of the initial settling sludge. The amount of surplus sludge has a correlation with the amount of initial sludge input. For example, assuming a proportional relationship, the amount of initial sludge SS input is expressed as (Equation 4) using the sludge conversion rate α. .

SS amount = (increase in excess sludge SS due to initial settling sludge) / α (Formula 4)
Since the value of α varies depending on the SRT or the like, it is desirable to set it for each processing place. For example, when the SRT is around 15th, it may be set to 0.35.

  According to the present embodiment, the amount of initial settling sludge input is calculated based on the sludge conversion rate α, so that the initial settling sludge input amount at which the SRT becomes the target value can be set. Thereby, the amount of initial sludge input can be optimized, and the nitrogen / phosphorus removal rate by activated sludge can be improved. Moreover, since the initial settling sludge is decomposed with activated sludge, the amount of generated sludge can be reduced.

  The operation method in the present embodiment will be described with reference to the flowchart of FIG.

In steps S1 and S2, as in the first embodiment, the upper limit value of the initial sludge input amount is calculated from the oxygen supply amount. This value is Q _Omax .

  In step S21, the control means 7 calculates the surplus sludge SS amount from (Equation 1) using the MLSS and SRT set values obtained from the target value input means 6.

  In step S22, the control means 7 performs the following 1) to 3).

  1) The amount of sludge generated due to the decomposition of the water after settling is obtained from the BOD load and the bacterial cell yield or the amount of sludge generated from the target value input means 6. The value of this sludge generation amount is obtained from past data in which the initial settling sludge has not been introduced.

  2) The amount of sludge generated due to the decomposition of the post-sink water is compared with the amount of excess sludge SS obtained in step S21, and the difference is set as the amount of excess sludge by the initial settling sludge input.

3) From the surplus sludge amount resulting from the initial sludge input and the sludge conversion rate α used in step S12, the initial sludge input amount Q _Smax is obtained.

In step S23, Q _Omax and Q _Smax are compared. If Q _Omax <Q _Smax , the _{process proceeds} to step S24, the initial sludge input Q is set to Q _Omax , and the flow ends. If Q _Omax ≧ Q _Smax, the _{process proceeds} to step S25, the initial settling sludge input amount Q is set to Q _Smax , and the flow ends.

  In this embodiment, the initial settling sludge amount can be set to the maximum amount obtained from the oxygen supply amount and the SRT. Thereby, the reduction amount of generated sludge can be maximized. In addition, the amount of initial sludge can be optimized and the nitrogen / phosphorus removal rate by activated sludge can be improved.

  As described above, in this embodiment, since the amount of the initial settling sludge is controlled from the air flow rate and the SRT, oxygen for decomposing the BOD of the initial settling sludge can be supplied, and the SRT can be used as a nitrifying bacterium having a slow growth rate. Since it can be set together, the bacterial composition of activated sludge required for nitrogen and phosphorus removal can be maintained. Moreover, since the initial settling sludge is decomposed with activated sludge, the amount of generated sludge can be reduced.

  It is possible to provide a sewage treatment method, a sewage treatment control system, and a sewage treatment facility that can maintain the bacterial cell composition of activated sludge required for removing nitrogen and phosphorus and reduce the amount of generated sludge.

The block diagram of the sewage treatment equipment in Example 1 and its control system is shown. The flowchart of the operation control method of the sewage treatment apparatus and its control system in Example 1 is shown. The flowchart of the operation control method of the sewage treatment apparatus and its control system in Example 2 is shown. The flowchart of the operation control method of the sewage treatment apparatus and its control system in Example 3 is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Biological reaction tank, 2 ... First sedimentation tank, 3 ... Final sedimentation tank, 4 ... Oxygen containing gas supply means, 5 ... Initial sedimentation sludge transfer means, 6 ... Target value input means, 7 ... Control means, 8 ... Initial sedimentation Sludge measuring means, 9 ... reaction tank measuring means, 10 ... excess sludge measuring means, 11 ... DO measuring means, 12 ... equipment specification input means, 13, 14 ... valve.

Claims (9)

  An initial sedimentation sludge separation step for separating the incoming raw water into primary sedimentation sludge and a supernatant liquid, a treatment step for biologically treating the supernatant liquid with activated sludge in a biological reaction tank, and the biological reaction of the primary sedimentation sludge A sewage treatment method including an initial settling sludge charging step for charging into a tank, wherein the initial settling sludge in the initial settling sludge charging step is charged based on an average residence time of the activated sludge. Processing method.   The sewage treatment method according to claim 1, wherein the activated sludge concentration grasping step for grasping the concentration of activated sludge in the biological reaction tank, the surplus sludge amount grasping step for grasping the amount of excess sludge withdrawn for a predetermined period, and the activity From the information of the sludge concentration grasping step and the excess sludge amount grasping step, including an average residence time calculating step for calculating the average residence time of the activated sludge, and an average residence time setting step for setting the average residence time of the activated sludge, A sewage treatment method characterized by setting an input amount of the initial settling sludge input step from information on an average residence time calculation step and the average residence time setting step.   The amount of surplus sludge calculation which calculates the amount of surplus sludge from the set value of the density | concentration of the said activated sludge, the set value of the average residence time of the said activated sludge, and the volume of this biological reaction tank in the sewage treatment method of Claim 1. A sewage treatment method characterized by setting an input amount of the first settling sludge input step based on a process and information on the surplus sludge amount calculating step. An initial settling sludge separation step for settling and separating the influent raw water into an initial settling sludge and a supernatant, a treatment step for biologically treating the supernatant with activated sludge, and an initial introduction of the first settling sludge into a biological reaction tank. a sewage treatment process which includes a沈汚mud adding step comprises to that oxygen supply amount calculation step calculates the supply amount of oxygen from the air amount of the blower, the information before hexane containing feed amount calculation step, the Hatsu沈A sewage treatment method characterized by setting an input amount of a sludge input step. In sewage treatment method according to any one of claims 1 to 3, the to that oxygen supply amount calculation step calculates the supply amount of oxygen from the air amount of the blower is provided, the input of the primary sludge adding step, sewage treatment method is compared with the input amount calculated from the information of the previous hexane containing feed amount calculation step, lesser the input of, characterized in that the input of該初沈汚mud adding step. A sewage treatment control system that settles and separates inflow raw water into primary sludge and supernatant liquid, and biologically treats the supernatant liquid with activated sludge in a biological reaction tank, based on the average residence time of the activated sludge sewage treatment control system characterized by comprising a control means for introducing said Hatsu沈 sludge organism reactor. A sewage treatment control system that separates inflow raw water into primary sedimentation sludge and supernatant liquid, and biologically treats the supernatant liquid with activated sludge in a biological reaction tank, and supplies an oxygen-containing gas to the biological reaction tank A sewage treatment control system comprising control means for introducing the first settling sludge into the biological reaction tank based on the amount of air flow . An initial sedimentation basin that separates the influent raw water into primary sludge and supernatant liquid, a biological reaction tank that biologically treats the supernatant liquid with activated sludge, and a first reaction tank that introduces the initial sedimentation sludge into the biological reaction tank. surplus沈汚and mud inserting equipment, the control device for controlling the input of primary sludge of primary sludge inserting equipment, a settling tank for settling a reaction solution from the bioreactor to the activated sludge and treated water A wastewater treatment facility including surplus sludge discharge means for discharging active activated sludge and input means for setting a set value of the average residence time of activated sludge in the control device, wherein the biological reaction tank has a concentration of activated sludge and activated sludge concentration measuring means for measuring, withdrawal flow rate of excess sludge in the excess sludge discharge means, and excess sludge measuring means for measuring the concentration of excess sludge, Hatsu沈measuring the primary sludge concentration of the primary sludge inserting equipment Sludge concentration measuring means Only, the control device, the withdrawal rate of the excess sludge, measured in excess sludge measuring means, calculates the withdrawal SS amount of excess sludge from the concentration of excess sludge, accumulating a history of the information, the activated sludge concentration Calculate the average residence time of activated sludge based on the activated sludge concentration measured by the measuring means, and use the initial sludge concentration measured by the first settled sludge concentration measuring means to obtain the surplus sludge amount obtained from the input means. sewage treatment facility, wherein the benzalkonium to calculate the amount of the primary sludge to the value. An initial sedimentation basin that separates the influent raw water into primary sludge and supernatant liquid, a biological reaction tank that biologically treats the supernatant liquid with activated sludge, and a first reaction tank that introduces the initial sedimentation sludge into the biological reaction tank. A sewage treatment facility comprising a settling sludge input facility, a control device for controlling the input amount of the initial settling sludge of the initial settling sludge input facility, and an input means for setting a set value of the blower amount of the blower of the control device. Te, wherein the primary sludge concentration measuring means for measuring the concentration of the primary sludge to primary sludge inserting equipment, the control device calculates the supply amount of oxygen from the air volume set values of the blower, the calculated oxygen feed sewage treatment facility, wherein the benzalkonium to calculate the dosage of the primary sludge inserting equipment based on the concentration of primary sludge, which is measured by the amount and the primary sludge concentration measuring means.

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