JP2015104712A - Sewage treatment system and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sewage treatment method that can reduce the air blowing amount and power consumption of a blower by improving removal ratios of organic matter, nitrogen, and phosphorus in a primary sedimentation basin to reduce an inflow load to a downstream side aeration tank.SOLUTION: A sewage treatment system comprises a primary sedimentation basin having an inflow water passage into which sewage flows, an aeration tank installed downstream of the primary sedimentation basin, and a final sedimentation basin installed downstream of the aeration tank. Surplus sludge of the final sedimentation basin is returned into the inflow water passage of the primary sedimentation basin to be supplied to the primary sedimentation basin. Aeration is carried out by a blower in the aeration tank. The sewage treatment system comprises a control device of the blower that supplies air to the aeration tank to determine dissolved oxygen in the aeration tank, and a control device for the surplus sludge supplied to the primary sedimentation basin. The control device for the surplus sludge determines the amount of the surplus sludge flowing into the primary sedimentation basin to control the flow rate of the surplus sludge returned from the final sedimentation basin to the primary sedimentation basin.

Description

  The present invention relates to a sewage treatment facility and a sewage treatment method for biologically treating sewage with activated sludge.

  As a conventional sewage treatment facility, for example, in the sewage treatment facility of Patent Document 1, a first sedimentation basin having an inflow channel into which sewage flows, an aeration tank provided downstream of the first sedimentation basin, and a final sedimentation basin downstream of the aeration tank It has. As a sewage treatment method for treating sewage with activated sludge, surplus sludge from the final sedimentation basin is introduced into the inflow channel of the first sedimentation basin.

  Patent Document 1 does not specifically disclose the equipment or control method for introducing surplus sludge from the final sedimentation basin into the inflow channel of the first sedimentation basin. It is described that an inflow water channel (return line) leading to a pond is provided with an on-off valve, and surplus sludge is charged batchwise. Further, in Patent Document 2, the organic matter concentration of raw water (sewage) is monitored, and when this exceeds a predetermined concentration, excess sludge is mixed and introduced at the first stage of the first sedimentation basin.

  In such a sewage treatment facility, organic matter, nitrogen and phosphorus in the sewage are biologically treated with an aggregate of microorganisms called activated sludge. Since activated sludge requires oxygen when treating sewage, oxygen is supplied by introducing sewage into an aeration tank, aeration with a blower, and dissolving oxygen in the air.

  Sewage containing organic matter is introduced into the aeration tank through the introduction pipe. Air is introduced into the aeration tank through a diffuser tube, and oxygen in the air is dissolved in sewage in the aeration tank. As one method of controlling biological treatment in such an aeration tank, a control method is known in which dissolved oxygen in the sewage of the aeration tank is measured and made constant.

  In this control method, the dissolved oxygen concentration measured by the dissolved oxygen concentration meter provided in the sewage is input to the control means, and the control means is preset in the control means by the input dissolved oxygen concentration and the set value input means. Compare the dissolved oxygen concentration setting values. When the input dissolved oxygen concentration is lower than the set value, a control command is output to the blowing means to increase the blowing amount, and when the dissolved oxygen concentration is higher than the set value, the blowing amount is reduced to the blowing means. A control command is output accordingly. For example, Patent Document 3 is an example of introducing such a control method.

  Further, Patent Document 4 pays attention to the BOD amount (biochemical oxygen demand amount), calculates the difference between the measured value and the target treated water BOD value as an index value of dirty water, and the index value and the flow rate. The target value of the aeration air volume depending on the product of the above is calculated, and the air volume of the blower is controlled according to this target value.

JP-A 63-139088 JP 2010-264424 A JP 2007-144277 A JP 2000-325980 A

  Regarding the treatment in the aeration tank, for example, in a sewage treatment plant that performs biological treatment on a large scale, the power cost of the blower accounts for a large proportion of the facility maintenance cost. If the power cost of the blower is reduced and the amount of aeration is reduced, the sewage treatment cannot be satisfied and the quality of the treated water is deteriorated. For this reason, it has been a challenge to reduce the power consumption of the blower while maintaining the quality.

  Incidentally, when the amount of organic matter in the sewage introduced into the aeration tank increases, aerobic microorganisms consume a large amount of dissolved oxygen to remove the organic matter. As a result, the dissolved oxygen concentration in the sewage is lowered, so in the conventional technical methods described in Patent Document 3 and Patent Document 4, the amount of air to be blown by the blowing means is increased, and the power consumed by the blower is increased. There was a fear.

  From the above, the object of the present invention is to improve the removal rate of organic matter, nitrogen and phosphorus in the first sedimentation basin, reduce the air flow by reducing the inflow load to the aeration tank in the subsequent stage, and the power consumption of the blower Is to provide a method for treating sewage.

  To achieve the above object, the present invention comprises a first settling basin having an inflow channel into which sewage flows, an aeration tank provided downstream of the first settling basin, and a final settling basin downstream of the aeration tank. It is configured so that excess sludge from the settling basin is returned to the inflow channel of the settling basin first, and the aeration tank is a sewage treatment facility that is aerated by a blower, and supplies air to the aeration tank. It has a blower control device that determines the amount of dissolved oxygen and a control device for excess sludge that is put into the first sedimentation basin. The surplus sludge control device determines the amount of surplus sludge that flows into the first sedimentation basin, and final sedimentation. It is characterized by controlling the flow rate of excess sludge that returns from the pond to the first settling basin.

  According to the present invention, by improving the removal rate of organic matter, nitrogen, and phosphorus in the first sedimentation basin, the amount of blown air can be reduced and the energy consumption can be reduced by reducing the sewage treatment load due to the activated sludge in the subsequent stage.

The block diagram of the sewage treatment apparatus which comprised the sewage treatment method of this invention. The flowchart which shows a sewage treatment method.

  Embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is an overall configuration diagram of a sewage treatment facility equipped with a sewage treatment method of the present invention.

  First, sewage flows into the settling basin 1 from the inflow channel 2, and the solid material of the sewage that has entered is settled and separated. The water to be treated after the solid substance is settled and separated flows into the downstream aeration tank 3. In the aeration tank 3, activated sludge composed of a plurality of microbial groups is inhabited.

  Usually, the activated sludge floats in the aeration tank 3 as a floc of microorganisms. The air diffuser 5 is connected to the tip of the blower 4, and the aeration tank 3 is aerated. Oxygen in the air is dissolved by aeration and supplied to the activated sludge as dissolved oxygen, and organic substances, nitrogen and phosphorus in the sewage are removed. Since the aeration amount of the blower 4 is proportional to the organic matter, nitrogen, and phosphorus in the sewage, the power consumed by the blower 4 can be reduced by changing the flow rate and concentration of the inflowing sewage. Further, a final sedimentation basin 6 is installed downstream of the aeration tank 3, where activated sludge is settled and separated, and the supernatant liquid is discharged as treated water.

  In addition, in the bottom of the first sedimentation basin 1, a sedimented solid substance generally called primary sedimentation sludge is accumulated, and is discharged outside the system by starting the primary sedimentation sludge pump 7. On the other hand, the component settled and separated at the bottom of the final settling basin 6 is activated sludge. This activated sludge is returned to the upstream portion of the aeration tank 3 by the return sludge pump 8 and reused for removing organic matter, nitrogen and phosphorus in the sewage.

  Activated sludge grows by treating sewage. For this reason, in order to maintain a predetermined amount of activated sludge, it is necessary to discard a part. The sludge to be discarded is generally called surplus sludge and is discarded by the surplus sludge pump 9 in the final sedimentation basin 6.

  A regulating valve 10 and a regulating valve 11 are installed on the downstream side of the excess sludge pump 9. When the regulating valve 10 is “open” and the regulating valve 11 is “closed”, excess sludge flows down to a sludge treatment system (not shown) and is disposed of. When the regulating valve 10 is “closed” and the regulating valve 11 is “open”, surplus sludge flows into the sludge treatment system by starting the first settling sludge pump 7 after the settling separation process in the first settling basin 1 and is disposed of. Is done.

  In addition, a tank 17 and a pump 16 are provided downstream of the regulating valve 11. After the excess sludge is accumulated in the tank 17, it is attracted by the pump 16 and flows down into the inflow water channel 2, and is mixed with sewage for the first precipitation. It flows into the pond 1. Here, a sufficient amount of excess sludge is accumulated in the tank 17. For this reason, the continuous supply of the excess sludge to the first sedimentation tank 1 is realized irrespective of the open / closed state of the regulating valve 10 and the regulating valve 11.

  Control in the sewage treatment facility having the above configuration is realized by two control devices. One of them is a control device CB for the blower 4 for supplying air to the aeration tank 3. Although several types of control devices CB for the blower 4 are conceivable, the techniques of Patent Document 3 and Patent Document 4 described above can be used. Both are controlled by the dissolved oxygen signal. If the dissolved oxygen amount is small, the supply oxygen amount is increased, and if the dissolved oxygen amount is large, the supply oxygen amount is decreased. When the amount of inflowing organic matter is small, the amount of dissolved oxygen is increased, so that the blower output is suppressed.

  Another control device is a control device 15 for surplus sludge that is initially introduced into the settling basin 1. A control device 15 for operating and controlling the sludge treatment facility shown in FIG. 1 is provided with a flow meter 13 for measuring the flow rate of the water to be treated and a water quality measuring device 14 for measuring the concentration of organic substances in the water to be treated. The measurement signal of the flow meter 13 and the measurement signal of the water quality measuring instrument 14 are input to the control means 15, and the control means 15 judges the processing load from the product of the flow rate and the organic substance concentration, and determines the input amount of surplus sludge and flocculant. Then, the adjustment valve 10, the adjustment valve 11, and the flocculant charging means 12 are adjusted. Instead of the water quality measuring device 14 for measuring the organic matter concentration in the water to be treated, a measuring device for measuring another water quality item correlated with the organic matter concentration is used as an alternative to the organic matter concentration input to the control means 15. Also good.

  FIG. 2 shows a schematic processing flow in the control device 15. In the processing procedure S1, the flow rate of the water to be treated and the organic substance concentration in the water to be treated are input as various process amounts necessary for the treatment in the present invention. In the processing procedure S2, the amount of organic matter (processing load) is calculated as the product of the flow rate of the water to be treated and the concentration of the organic matter.

  In the processing procedure S3, the surplus sludge input amount is determined from the relationship between the organic matter amount (processing load) of the water to be treated and the flow rate of the pump 16. When the amount of organic matter (treatment load) is large, the amount of surplus sludge input is increased to increase the amount of organic matter adsorbed in the sewage, and when the amount of organic matter (treatment load) is small, the amount of surplus sludge input is reduced to reduce the amount of organic matter in the sewage. Reduce the amount of adsorption. The pump 16 controls the pump 16 so that the determined amount of excess sludge is input (processing procedure S4).

  In processing procedure S5, the amount of flocculant charged is controlled in accordance with the determined inflow rate. Generally, the residence time in the first settling basin 1 depends on the inflow flow rate. If the inflow flow rate is large, the residence time becomes short, so that the sedimentation is difficult. If the inflow flow rate is small, the residence time becomes long. For this reason, when the inflow flow rate is large, the amount of flocculant input is increased to increase the coagulation effect, and when the inflow rate is small, control is performed to decrease the coagulant input amount to reduce the coagulation effect.

  In the processing procedure S6, the control valves 10 and 11 are controlled. If it is assumed that a sufficient amount of excess sludge is accumulated in the tank 17, the regulating valves 10 and 11 may be opened and closed at appropriate time intervals to intermittently supply the excess sludge to the tank 17. . Opening and closing may be repeated as appropriate while looking at the tank level.

  According to the present invention, by introducing a part or all of the excess sludge into the settling basin 1 first, it is possible to settle and separate organic matter in the sewage after adsorption, so that the inflow load of the aeration tank 3 can be reduced. For this reason, the power consumption of the blower 4 for processing sewage in the aeration tank 3 can be reduced. In addition, the amount of treatment with activated sludge in the aeration tank 3 is reduced, the amount of activated sludge is increased, and the amount of surplus sludge is also reduced, so that the treatment load of the sludge treatment system can be reduced.

  In particular, in the present invention, the amount of input sludge is continuously controlled, so that it can greatly contribute to the reduction of power consumption of the blower 4. In patent documents and the like, since the charging is performed in batches, the load of the blower is largely fluctuated and the power consumption is not stable. In the present invention, the fluctuation range of the power consumption can be reduced throughout the day, night, and season, which contributes to the reduction of the power consumption of the blower 4 through downsizing the motor for driving the blower.

  The inflow path 2 has a structure in which the flocculant can be input into the inflow path 2 by the flocculant charging means 12, so that the organic matter in the water to be treated is coagulated and settled in the first sedimentation basin and removed as initial sludge. Thus, the inflow load into the aeration tank 3 can be reduced.

  The effects of the present invention will be further described. It is known that activated sludge adsorbs organic matter in sewage when it comes into contact with sewage. In particular, surplus sludge is expected to have a large adsorption power since the decomposition of the adsorbed material has been completed and the adsorption power has recovered. Moreover, since the residence time of the first settling basin 1 is generally designed to be several hours, a time for adsorbing the activated sludge injected from the inflow water channel 2 can be secured. In addition, it is desirable for the inflow water channel 2 to have a structure in which surplus sludge that has passed through the regulating valve 11 and sewage are mixed.

1: First sedimentation tank 2: Inflow path 3: Aeration tank 4: Blower 5: Air diffuser 6: Final sedimentation tank 7: Initial sedimentation sludge pump 8: Return sludge pump 9: Surplus sludge pump 10, 11: Regulating valve 12: Flocculant charging means 13: flow meter 14: water quality measuring device 15: control means 16: surplus sludge tank 17: surplus sludge charging pump

Claims (6)

A first settling basin having an inflow channel into which sewage flows, an aeration tank provided downstream of the first settling basin, and a final settling basin downstream of the aeration tank, and surplus sludge in the final settling basin The sewage treatment facility is configured to return to the inflow water channel of the pond, and is aerated by a blower in the aeration tank,
A blower control device that determines the amount of dissolved oxygen in the aeration tank by supplying air to the aeration tank, and a surplus sludge control device that is put into the first settling basin,
The surplus sludge control device determines the amount of surplus sludge that flows into the first sedimentation basin, and controls the flow rate of surplus sludge that returns from the final sedimentation basin to the first sedimentation basin. . A sewage treatment facility according to claim 1,
The surplus sludge control device adjusts the flow rate of the flocculant to be introduced into the inflow water channel according to the inflow rate of the inflow water channel. A sewage treatment facility according to claim 1 or 2,
A tank for accumulating excess sludge in a flow path for returning surplus sludge from the final sedimentation basin to the inflow water channel of the first sedimentation basin, and a pump for continuously supplying the excess sludge in the tank; A sewage treatment facility for controlling the operation of the pump according to a signal of the amount. A first settling basin having an inflow channel into which sewage flows, an aeration tank provided downstream of the first settling basin, and a final settling basin downstream of the aeration tank, and surplus sludge in the final settling basin A sewage treatment method configured to return to the inflow water channel of the pond, and in the aeration tank, aeration is performed by a blower.
Determining the amount of dissolved oxygen in the aeration tank by supplying air to the aeration tank, and controlling the excess sludge to be put into the first settling tank;
In order to control the surplus sludge, the amount of surplus sludge that flows into the first sedimentation basin is determined, and the flow rate of surplus sludge that returns from the final sedimentation basin to the first sedimentation basin is controlled. Method. A sewage treatment method according to claim 4,
A sewage treatment method characterized in that an input amount of surplus sludge is determined based on a flow rate of the inflow channel and an organic substance concentration at the flow rate. In the sewage treatment method according to claim 4 or 5,
A sewage treatment method, wherein an input amount of an initial settling basin flocculant to be input to the first settling basin is determined based on a flow rate of the inflow water channel.

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