JP2002346585A - Wastewater treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To subject treated water from a batchwise activated sludge treatment apparatus to membrane separation without providing a special storage tank. SOLUTION: Respective processes for wastewater charging-aeration- sedimentation-treated water discharge are successively performed as one cycle and the operation time of one cycle in batchwise reaction tanks 30A and 30B repeating this cycle is set to 5 hr or less and the reaction tanks 30A and 30B are operated so as to provide a time lag and the treated water discharged from the reaction tanks is directly guided to a common membrane separation tank 60 to be subjected to filtering treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wastewater treatment method, and more particularly to a wastewater treatment method mainly comprising a batch activated sludge treatment.

[0002]

2. Description of the Related Art Batch activated sludge treatment involves oxidizing the BOD components in wastewater by the action of activated sludge by pouring organic wastewater into a reaction tank containing activated sludge and then continuously or intermittently aerated for a predetermined time. Decompose. Thereafter, the aeration is stopped, the activated sludge is allowed to stand for a predetermined time, the activated sludge is settled at the bottom of the tank, and the supernatant water is discharged out of the tank as treated water. Each cycle of the wastewater charging, aeration, sedimentation, and treated water discharging is sequentially performed in one reaction tank, and this cycle is repeated. This eliminates the need for a sedimentation basin and sludge return system compared to ordinary continuous activated sludge treatment, and can save space and make the equipment compact, and is often used as a relatively small-scale wastewater treatment method. ing.

[0003] In the batch type activated sludge treatment, the sedimentation of the sludge may deteriorate depending on the properties of the wastewater to be treated and the operating conditions. When human waste is subjected to batch activated sludge treatment, the suspended sediment of the sludge is deteriorated due to the incorporation of floating suspended matter in the wastewater. For this reason, in the sedimentation step, the sedimentation and separation of the sludge become insufficient, and there is a problem that the sludge containing a suspended suspension in the treated water (supernatant water) leaks to lower the water quality.

[0004] In order to solve the above problems, it is conceivable to remove the leaked sludge by membrane-separating the treated water of the batch activated sludge treatment. However, in the batch type activated sludge treatment, a large amount of treated water is discharged in a short time in one cycle of the treated water discharging process. Since the capacity must be increased, and the treated water is not discharged in the steps other than the treated water discharging step of the batch activated sludge treatment, the membrane separation apparatus is idle during that time. In order to solve such a problem, a storage tank is provided between the batch activated sludge treatment device and the membrane separation device, and the storage water is temporarily stored in the storage tank from the batch activated sludge treatment device, A method of averaging the amount of treated water sent to the membrane separation device can be considered. However, this method requires a large storage tank separately. Moreover, it was difficult to maintain the concentration of the activated sludge in the reaction tank properly in the batch type activated sludge treatment apparatus.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, and to perform membrane separation of treated water from a batch type activated sludge treatment apparatus without providing a special storage tank. It is to provide a wastewater treatment device.
It is another object of the present invention to provide a wastewater treatment apparatus in which the concentration of activated sludge in a reaction tank in a batch activated sludge treatment apparatus can be easily controlled.

[0006]

A wastewater treatment method according to the present invention is a batch type activated sludge treatment apparatus in which the steps of wastewater input, aeration, sedimentation and treated water discharge are sequentially performed as one cycle, and this cycle is repeated. Operating time of one cycle of 5
In addition to setting the time to not more than the time, the treated water discharged from the batch-type activated sludge treatment device is directly guided to the membrane separation device and filtered.

That is, the present invention reduces the operation time of one cycle of the batch type activated sludge treatment apparatus to 5 hours or less, preferably 3 hours.
By setting the range to 4 hours, the amount of treated water in the treated water discharging step in one cycle is reduced, and the load on the membrane separation device is reduced. Therefore, there is no need to provide a special storage tank for adjusting the amount of treated water between the batch type activated sludge treatment device and the membrane separation device.

Further, in the wastewater treatment method according to the present invention, each cycle of the plurality of batch type activated sludge treatment devices is operated with a time difference, and the treatment is sequentially discharged from these batch type activated sludge treatment devices. It is characterized in that water is guided to a common membrane separation device. According to such a method, the membrane separation device can be operated efficiently.

Further, the wastewater treatment method according to the present invention provides a method for treating wastewater in one cycle of the batch type activated sludge treatment apparatus in one cycle so that the wastewater treatment amount in one cycle of the batch type activated sludge treatment apparatus becomes substantially constant according to the fluctuation of the amount of wastewater to be treated. The operation time is set. According to such a method, the processing can be stabilized.

Further, in the wastewater treatment method according to the present invention, the respective steps of wastewater input, aeration, sedimentation and treated water discharge are sequentially performed as one cycle, and the excess activated sludge treatment equipment generated in a batch type activated sludge treatment apparatus which repeats this cycle is used. The method is characterized in that the entire amount of sludge is brought into the membrane separation device together with the treated water, and the sludge separated by the membrane separation device is extracted as surplus sludge. According to such a method, in the batch type activated sludge treatment apparatus, the sludge in the reaction tank can be maintained at a high concentration, and the operation management becomes easy.

[0011]

FIG. 1 is an apparatus system diagram showing an embodiment of the present invention. This apparatus mainly includes a raw water storage tank 10, two reaction tanks 30A and 30B provided in parallel, and a membrane separation tank 60.
And a piping system for connecting these devices. Line 12
The wastewater that has flowed into the raw water storage tank 10 is temporarily stored in the raw water storage tank 10, and then is pumped by a pump 16 provided in a pipeline 14.
It is charged into the reaction tank 30A via the switching valve 20 provided in the pipe 18, or is charged into the reaction tank 30B via the switching valve 24 provided in the pipe 22.

A stirrer 32A is disposed at the bottom of the reaction tank 30A. When air from the blower 34 flows into the stirrer 32A through a switching valve 38 provided in a pipe 36, the stirrer 32A is turned on.
A functions as an aerator to aerate the inside of the reaction tank 30A. In addition, when the stirrer 32A is operated in a state in which the inflow of air from the blower 34 is stopped, the wastewater in the reaction tank 30A is stirred and shifts to an anaerobic state. Activated sludge is previously held at a high concentration in the reaction tank 30A, and when aeration is performed in a state where the wastewater and activated sludge are mixed, B in the wastewater is removed.
The OD component is oxidatively decomposed and purified by the action of the activated sludge. Activated sludge is an aggregate of various bacteria such as nitrifying bacteria and denitrifying bacteria in addition to bacteria that degrade BOD components. For this reason, when the wastewater contains ammonia, in the aeration step, the ammonia is nitrified by the action of nitrifying bacteria and becomes nitrate nitrogen. Thereafter, when the operation of the stirrer 32A is continued in a state where the air inflow from the blower 34 is stopped, the wastewater in the reaction tank 30A is stirred and shifts to an anaerobic state. It is reduced to nitrogen gas by the action of nitrifying bacteria. Therefore, when treating wastewater containing ammonia such as animal husbandry waste, it is preferable to perform intermittent aeration in which the aeration step and the stirring step are alternately repeated in one cycle.

After the reaction in the aeration step and / or the stirring step is completed, the process proceeds to the precipitation step. That is, by stopping the flow of air from the blower 34 and stopping the operation of the stirrer 32A, the activated sludge settles in the lower part of the reaction tank 30A in the reaction tank 30A. After the precipitation step is completed, the process proceeds to a treated water discharging step, and the supernatant water of the reaction tank 30A is discharged from the discharger 44A as treated water while containing some sludge. This treated water is supplied to a subsequent membrane separation tank 60 via a pump 48 and a switching valve 50 provided in a pipeline 46. In the reaction tank 30A, the cycle of sequentially performing the above-described steps of wastewater charging, aeration (stirring), precipitation, and treated water discharge is defined as one cycle, and this cycle is repeated. The same cycle is repeated in the reaction tank 30B, but the operation time of each cycle is shifted from each other in the reaction tank 30A and the reaction tank 30B so that each step is not duplicated. Further, by setting the operation time of one cycle to 5 hours or less, preferably in the range of 3 to 4 hours, the amount of treated water in the treated water discharging step in one cycle is reduced, and the burden on the membrane separation tank 60 in the subsequent stage is reduced. To reduce Since the treated water discharged from the reaction tanks 30A and 30B is supplied to the membrane separation tank 60 with a time difference, the membrane separation tank 6
0 can reduce the burden. For this reason, the reaction vessels 30A, 3
There is no need to provide a special storage tank for adjusting the amount of treated water between OB and the membrane separation tank 60.

A separation membrane 62 is provided in the membrane separation tank 60, and a suction pump 66 is connected to a secondary side of the separation membrane 62 through a pipe 64. The treated water in the membrane separation tank 60 is filtered by the separation membrane 62 by the suction force of the suction pump 66, and the clear permeated water is discharged from the line 64 to the outside of the apparatus.
A diffuser 68 is provided below the separation membrane 62,
The air from the blower 34 is diffused by the diffusing means 68, and the sludge attached to the primary side of the separation membrane 62 is washed away. Separation membrane 6
These sludges separated in 2 settle at the bottom of the membrane separation tank 60 and are appropriately extracted from the pipeline 70.

[0015] In the batch type activated sludge treatment apparatus according to the prior art, since the membrane separation tank according to the present invention is not provided at the subsequent stage of the reaction tank, it is necessary to appropriately control the concentration of the activated sludge in the reaction tank. Careful consideration is needed. That is, the activated sludge multiplies in the reaction tank using the BOD component or the like in the wastewater as a nutrient source, and the activated sludge concentration in the reaction tank increases. For this reason, the sludge interface at the time of sedimentation rises, and the activated sludge accompanies the treated water (supernatant water), resulting in a decrease in water quality. Therefore,
Excessive activated sludge needs to be periodically pulled out from the bottom of the reaction tank or the like so that the concentration of the activated sludge in the reaction tank does not exceed a predetermined value. If the amount of sludge withdrawn is too large, the activated sludge concentration in the reaction tank will decrease, and it will not be possible to achieve a desired treatment result. If the amount of withdrawal is too small, treated water (supernatant water)
There remains a problem that activated sludge accompanies it and lowers water quality.
Further, the settling property of the activated sludge varies depending on the properties of the wastewater to be treated, seasonal factors, and the like, so that the appropriate value of the activated sludge concentration in the reaction tank also slightly changes. As described above, in order to properly maintain the activated sludge concentration in the reaction tank, meticulous management is required, which involves considerable difficulty.

On the other hand, in the present embodiment, the reaction vessels 30A, 30A
It is possible to operate the process without managing the concentration of sludge in OB. That is, without extracting the excess sludge from the reaction tanks 30A and 30B at all, the entire amount of the excess sludge is brought into the membrane separation tank 60 together with the treated water, and the sludge separated in the membrane separation tank 60 is converted into the excess sludge. Can be pulled out as According to such a method, the reaction tank 30A,
In 30B, the activated sludge can always be autonomously maintained at a high concentration, so that it is possible to improve the treatment efficiency and simplify the operation management.

FIG. 2 is a time lapse diagram showing an example of an operation state of the apparatus shown in FIG. The horizontal axis indicates the elapsed time, and the vertical axis indicates the respective steps of the reaction tanks 30A and 30B and the membrane separation tank 60. Further, the bars in the figure indicate the operation times of these steps, and the thick bars indicate the flow of wastewater charged into the reaction tank A through a series of steps until the treatment is completed. This example shows a case where the time of one cycle of batch processing is 3 hours and intermittent aeration is performed, but the present invention is not limited to this.

In the reaction tank A, stirring (30 minutes) is performed in parallel with the introduction of wastewater (20 minutes), and the denitrification reaction proceeds. Subsequently, by intermittent aeration (30 minutes), stirring (30 minutes), and aeration (30 minutes), the decomposition reaction, nitrification reaction, and denitrification reaction of the BOD component in the wastewater proceed, and the wastewater is purified. Next, after the precipitation step (40 minutes), the treated water (supernatant water) is discharged (20 minutes), and one cycle of processing in the reaction tank A is completed in 3 hours in total, and thereafter, this cycle is repeated. . The treated water discharged from the reaction tank A contains excess activated sludge and fine suspended solids, and is slowly filtered over 1 hour while being stored in the upper part of the membrane separation tank 60.
It is discharged outside the device as clarified water. In the membrane separation tank 60, after the filtration is completed, the air diffusion of the air diffuser 68 is stopped, and the separated sludge is allowed to settle to the bottom of the tank (for 20 minutes), and then the settled sludge is extracted as surplus sludge. After this series of operations is completed, the process in the membrane separation tank 60 is subsequently shifted to the filtration of the treated water discharged from the reaction tank B.

On the other hand, the same cycle as the reaction tank A is repeated in the reaction tank B with a time difference of one and a half hours from the reaction tank A. In the reaction tank A and the reaction tank B, the aeration process is operated so as not to overlap at the same time as illustrated. For this reason, by switching and supplying the air for aeration from the blower 34 to the reaction tank A and the reaction tank B, the blower can be shared, which contributes to a reduction in equipment cost. Also, in the membrane separation tank 60, the treated water discharged from the reaction tank A and the reaction tank B is alternately filtered.
Efficient operation with a common membrane separation device can be realized. The switching between the input of the waste water, the discharge of the treated water, and the aeration is performed by opening and closing the switching valves 20, 24, 38, 42, 50, and the like.

In this type of wastewater treatment, the amount of wastewater to be treated generally varies greatly depending on the day and season. In the present invention, it is preferable to set the operation time of one cycle so that the wastewater treatment amount in one cycle of the batch type activated sludge treatment apparatus becomes substantially constant according to the fluctuation of the wastewater amount.
For example, when the design processing amount per day is 100%, the operation time of one cycle is set to 3 hours, and the actual processing amount is 7 hours.
If the operating time of one cycle is set to 4 hours at 5% and the operating time of one cycle is set to 5 hours at 60% of the actual throughput, the amount of wastewater treated per cycle is the same in each case. Thus, the processing can be stabilized.

[0021]

According to the wastewater treatment method of the present invention, the treated water from the batch activated sludge treatment apparatus can be subjected to membrane separation without providing a special storage tank. Further, according to the wastewater treatment method of the present invention, it is easy to control the concentration of activated sludge in the reaction tank in the batch activated sludge treatment apparatus.

[Brief description of the drawings]

FIG. 1 is an apparatus system diagram showing an embodiment of the present invention.

FIG. 2 is a time lapse diagram illustrating an example of an operation state of the device illustrated in FIG. 1;

[Explanation of symbols]

 10 Raw water storage tanks 30A, 30B Reaction tanks 32A, 32B Stirrer 34 Blower 60 Membrane separation tank 62 Separation membrane 66 Suction pump 68 Aeration means

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Katsumi Shida 1-1-1-14 Uchikanda, Chiyoda-ku, Tokyo Inside Hitachi Plant Construction Co., Ltd. (72) Masayuki Matsuura 1-1-1 Uchikanda, Chiyoda-ku, Tokyo No. 14 F-term in Hitachi Plant Construction Co., Ltd. (reference) 4D006 GA02 HA93 KA12 KC14 MB02 PA01 PB15 PB24 PC63 4D028 AA02 BB01 BC17 BC24 BC26 BD08 BD10 BD17 CB08 4D040 BB08 BB24 BB67

Claims (4)

[Claims] 1. One cycle of sequentially performing the steps of wastewater input, aeration, sedimentation, and treated water discharge is defined as one cycle, and the operation time of one cycle of the batch type activated sludge treatment apparatus that repeats this cycle is set to 5 hours or less. A wastewater treatment method, wherein treated water discharged from a batch-type activated sludge treatment device is directly guided to a membrane separation device and subjected to a filtration treatment. 2. Each of the plurality of batch activated sludge treatment apparatuses is operated with a time difference between the cycles, and the treated water sequentially discharged from these batch activated sludge treatment apparatuses is led to a common membrane separation apparatus. The wastewater treatment method according to claim 1, wherein: 3. The operation time of one cycle of the batch type activated sludge treatment apparatus is set such that the amount of wastewater treatment in one cycle of the batch type activated sludge treatment apparatus becomes substantially constant according to the fluctuation of the amount of wastewater to be treated. The wastewater treatment method according to claim 1 or 2, wherein 4. A cycle in which the steps of wastewater input, aeration, sedimentation and treated water discharge are sequentially performed as one cycle, and the entire amount of excess sludge generated in the batch type activated sludge treatment apparatus which repeats this cycle is entrained in the treated water. A wastewater treatment method, wherein the sludge separated by the membrane separation device is drawn out as excess sludge.