JPH038839B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to a batch activated sludge treatment method for treating wastewater by repeating the steps of stirring, aeration, settling, and discharging in a single treatment tank, and in particular, stirring and aeration are repeated a predetermined number of times and a predetermined number of times. The present invention relates to a batch type activated sludge treatment method for effectively treating sewage by performing sedimentation and discharge after alternating cycles. Among the activated sludge treatment methods that have become mainstream in domestic wastewater treatment in recent years, as shown in Figure 1, each process of aeration, precipitation, and discharge is treated as one cycle in a single treatment tank 1 that receives wastewater. Batch-type activated sludge treatment methods are attracting attention. FIG. 2 shows a time chart of the treatment process according to the conventional batch type activated sludge treatment method shown in FIG. 1, and in this example, one cycle is set to 6 hours. Conventional activated sludge treatment begins with an aeration process in which sewage to be treated is charged into the treatment tank 1 at once and air is blown into the sewage contained in the tank from an aeration pipe 2. After this aeration process was carried out for about 3 hours, the air blowing was stopped, and from this point on, after the precipitation process for about 1 hour, the discharge process began for about 2 hours, and the supernatant liquid was discharged from the decanter 3. Evacuation takes place. This cycle of approximately 6 hours is repeated throughout the day. However, although these conventional treatment processes have higher removal rates for denitrification and dephosphorization than the general long-term activated sludge process or standard activated sludge process, they still only achieve a removal rate of about 60% for both. Ta. In other words, in the conventional treatment process described above, an aeration process is set first, and after the oxidation of organic matter in the inflowing wastewater is completed, the digestion of ammonia positive nitrogen is performed, so the stirring process that is provided next performs the aeration process, which is necessary for the denitrification reaction. The organic matter is inadvertently present, resulting in insufficient denitrification in the agitation step of the nitrate nitrogen produced in the initial aeration step, significantly reducing the overall nitrogen removal rate during the cycle. Furthermore, if the aeration step is set before the stirring step as described above, a long aeration time is required to complete the nitrification reaction. To explain in more detail, as mentioned above, in the aeration step that is set before the stirring step, the oxidation of organic matter in the inflowing sewage is completed first, and then the nitrification of ammonia nitrogen is carried out, so the first aeration step A long aeration time is required to nitrify ammonia nitrogen, and an even longer time is required in the next aeration step. In other words, since there is not enough organic matter in the tank to denitrify the nitrate nitrogen that has been nitrified in the aeration process, the nitrate nitrogen is not denitrified and remains until the organic matter flows in, resulting in complete denitrification. It takes a considerable amount of time to nitrate, and an even longer time is required to elute phosphorus. Furthermore, the elution of phosphorus was also insufficient, and the reason for this will be described below. In other words, in the aeration step that is set before the stirring step as mentioned above, the organic matter in the inflow water is oxidized first, and after this is completed, the ammonia nitrogen is nitrified, so in the next stirring step, the organic matter in the activated sludge is oxidized. Less organic matter is needed to elute the phosphorus. For this reason, in the next agitation step following the aeration step, the elution of phosphorus from the activated sludge using organic matter in the inflow water is insufficient, resulting in excessive phosphorus intake by the activated sludge in the next aeration step. is also insufficient, resulting in a significant reduction in the overall phosphorus removal rate. In addition, in the conventional sewage treatment method described above, sewage is charged into the treatment tank (aeration tank) at once, so a large capacity sewage storage tank is required in addition to the treatment tank. Therefore, the equipment cost increases greatly, which is uneconomical, and the processing time for one cycle also increases. In this way, conventional wastewater treatment methods do not require denitrification,
There were many problems such as the dephosphorization treatment efficiency was very low and the equipment was large-scale and extremely uneconomical. This invention was made in view of the above circumstances,
While the wastewater to be treated is continuously flowed into a single treatment tank, denitrification and dephosphorization can be carried out extremely efficiently in a significantly shorter time than in the past,
Moreover, it is an object of the present invention to provide a highly economical batch type activated sludge treatment method that eliminates the need for large-capacity storage tanks other than the upper single treatment tank. The batch activated sludge treatment method according to this invention includes:
A single treatment tank having a buttful that divides the inside of the tank into an inflow part and a main treatment part for sewage, and an opening provided at the bottom of the buttfull to communicate between the inflow part and the main treatment part. a stirring step in which the activated sludge in the main treatment section is first stirred while sewage is continuously flowing into the inflow section; an aeration step in which the liquid in the tank is aerated in the main treatment section after this stirring step; A stirring/aeration process in which the stirring/aeration process is repeated a predetermined number of times at a predetermined time interval, a precipitation process in which the sludge of the aerated mixture is precipitated after the stirring/aeration process, and a supernatant liquid is discharged after this precipitation process. This discharge process is repeated as one cycle. In the batch type activated sludge treatment method of the present invention, the activated sludge is first stirred in the main treatment section of the treatment tank while sewage is continuously introduced into the inflow section of the single treatment tank, and after the stirring, the activated sludge is stirred inside the tank. The liquid is aerated,
Next, after the above-mentioned stirring and aeration are repeated a predetermined number of times at predetermined intervals, the sludge of the aerated mixture is precipitated, and after the precipitation, the supernatant liquid in the tank is discharged. The treatment process is repeated as one cycle. . Here, the wastewater that continuously flows into the inflow section in the treatment tank is prevented from directly flowing into the main treatment section by the baffle. That is, there is sewage that has already accumulated below the inflow section, and this stagnant sewage is pushed out from the lower opening of the buffer to the main treatment section by the continuous flow of sewage into the inflow section. As a result, the water levels in the inflow section and the main treatment section rise. At this time,
The sewage that has flowed in during the aeration process is mixed with the sewage that has already accumulated, and the sewage that has accumulated is pushed out to the main treatment section as described above, but the amount of this extrusion is quite small compared to the amount of sewage that has accumulated. Moreover, the aeration process requires significantly less time than the stirring process for reasons explained later, so even if wastewater is continuously introduced into the inflow section of the treatment tank as described above, the treatment cycle including the aeration process is There is no risk of any problem. As mentioned above, the stirring process of the activated sludge in the tank is performed before the aeration process, so that the residual nitrate nitrogen is denitrified very efficiently using the organic matter in the inflow water, and the next process is carried out efficiently. The amount of organic matter to be oxidized decreases by the amount consumed for denitrification in the aeration process. For this reason, the more denitrification progresses in the stirring process that precedes the aeration process, the more effectively the inflowing organic matter is used, and the less organic matter is oxidized in the next aeration process, which reduces the aeration time. Even if the stirring time is shorter than the stirring time, the nitrification reaction is sufficiently satisfied. In addition, as mentioned above, by having a stirring process before the aeration process, the elution of phosphorus from the activated sludge is promoted using organic matter in the inflow water. Therefore, by drawing out the activated sludge with excessive phosphorus intake to the outside of the tank,
The dephosphorization effect is also significantly improved. In addition, by continuously flowing wastewater into the inlet of the treatment tank as described above, it is possible to eliminate the need for a storage tank other than the treatment tank, or even when such a storage tank is used, the volume of the storage tank is extremely large. You can get away with something small. Furthermore, the buffling in the treatment tank prevents short-circuit discharge of new inflowing sewage, especially sewage flowing in during the sedimentation/discharge process. Hereinafter, one embodiment of the present invention will be described based on the drawings. In FIG. 3, at the bottom of the single treatment tank 1,
An aeration device 5 is arranged to blow air from an aeration blower 4 into wastewater during the aeration process. This aeration device 5 uses, for example, a jet type aeration device in this embodiment, so that both the stirring step and the subsequent aeration step can be performed only by switching control of the aeration blower 4. A pipe 6 and a water supply pipe 7 are connected. Note that, without being limited to this embodiment, an independent stirring means for performing only the stirring step may be provided. Furthermore, a DO sensor 8 for measuring DO in wastewater is provided in the treatment tank 1, and based on this measured value, the rotation speed of the aeration blower 4 is controlled by a DO meter 9 and a computer 10. The decanter 3 for discharging the supernatant during the discharge process following the precipitation process includes a discharge pipe 12 rotatably connected to the shaft pipe 11, and a discharge pipe 12 attached to the free end of the discharge pipe 12 to prevent overflow. Outlet 13
It consists of an overflow pipe 13 with an opening a and a float 14 which also serves as a scum baffle. Therefore, when the overflow pipe 13 is at the water surface,
The supernatant liquid in the treatment tank 1 flows into the overflow pipe 1 from the overflow port 13a.
3 and is discharged to the outside through the shaft pipe 11. Further, in a state where the overflow pipe 13 is rotated by a rotation means (not shown) so as to be at a position higher than the liquid level, the liquid in the processing tank 1 is not discharged. Further, inside the treatment tank 1, there is a bath 1 that divides the inside of the tank into an inflow section 1a of sewage and a main treatment section 1b.
5 is arranged vertically, and an opening 1c is provided at the bottom of the baffle 15, which communicates circularly with the inflow section 1a and the main processing section 1b. The baffle 15 is for preventing new inflow sewage, especially sewage flowing into the sedimentation/discharge process, from being short-circuited and discharged. Therefore, in the treatment tank 1 according to the present invention, wastewater to be treated continuously flows into the inflow portion 1a. In such a continuous inflow state of sewage, first, the activated sludge is stirred in the main processing section 1b, and after the stirring step, the liquid in the tank is transferred to the main processing section 1.
In step b, an aeration process is carried out, and at the same time, a stirring and aeration process is carried out in which these stirring and aeration processes are repeated at predetermined intervals.
The aeration process and the discharge process of discharging the supernatant liquid after the stirring/aeration process are repeated as one cycle. Furthermore, excess sludge in the treatment tank 1 is drawn out through the drawing pipe 16 at an appropriate time. FIG. 4 shows a time chart when one cycle is 6 hours. In this example, a 45-minute stirring process and a 15-minute aeration process are repeated four times, followed by precipitation and discharge. As shown in the table below, the experimental results showed that the removal rate of denitrification and dephosphorization was extremely effective compared to the conventional treatment method, with both removal rates of over 90% being achieved.

[Table] Note that the repetition cycle of each of the above steps for a predetermined number of times and for a predetermined time is electrically controlled, for example, by a control means such as a counter (not shown). Further, the number of repetitions, time, etc. of the stirring/aeration process are not limited to the embodiment shown in FIG. 4, but are determined depending on the properties of the wastewater. According to the above configuration, the stirring and aeration steps are alternately repeated a predetermined number of times and for a predetermined time in the treatment tank 1, and then sedimentation and discharge are performed, as described above.
Denitrification and dephosphorization effects are dramatically improved. In addition, even if the dissolved oxygen concentration (hereinafter referred to as DO) in the aeration process is too high, it will take a long time for the DO to decrease in the next stirring process, so denitrification and
Conversely, if dephosphorization is performed, even if the DO is too low, the ammonia nitrogen in the wastewater will not be nitrified, so the nitrogen removal rate will decrease, so the DO in the wastewater should be appropriately controlled to, for example, 2.0mg/ It was essential to do so. In this regard, in the present invention, a DO sensor 8, a DO meter 9, etc. are provided to control the rotational speed of the aeration blower 4, and the DO in the treatment tank 1 can always be maintained at an optimum level, so that extremely effective treatment can be performed. Furthermore, if a jet type aeration device is used as the aeration device 5 as shown in FIG. 3, both stirring and aeration processes can be performed by the same aeration device 5 by simply opening and closing the aeration blower 4. There is no need to provide a separate stirring step, and costs can be reduced. Incidentally, the batch type activated sludge treatment method of the present invention may be applied to the aeration of a general continuous type activated sludge treatment apparatus, and the operation may be performed so that stirring and aeration of the aeration tank are repeated at predetermined intervals. As described above, according to the present invention, while the wastewater to be folded is continuously flowed into a single treatment tank, the activated sludge in the tank is first stirred and then aerated.
As in the case of the conventional method of aerating wastewater immediately after inflow,
BOD removal precedes the nitrification reaction, which does not become rate-limiting, and denitrification is promoted. In other words, in the repeated process of the batch activated sludge treatment cycle, the nitrate nitrogen remaining from the previous cycle process is quickly denitrified using organic matter in the influent water during the stirring process at the beginning of the next cycle. be exposed. As described above, in the present invention in which the stirring step of activated sludge in the tank is performed before the aeration step, the denitrification efficiency is significantly improved compared to the case where the stirring step is set after the aeration step. Further, if the aeration step is performed before the stirring step as described above, a long aeration time is required to complete the nitrification reaction, but in the present invention, a sufficient nitrification reaction can be obtained with a short aeration time. That is, in this invention, since the activated sludge in the tank is first stirred, residual nitrate nitrogen is denitrified using organic matter in the inflow water, and the remaining nitrate nitrogen is consumed in the next aeration process. Therefore, there are fewer organic substances to oxidize. Therefore, the more denitrification progresses in the previous stirring step, the more effectively the inflowing organic matter is utilized, and the less organic matter is oxidized in the next aeration step, resulting in the aeration time being longer than the stirring time. Even though the period is shorter than that of the previous period, the redemption response is sufficiently satisfactory. In addition, regarding dephosphorization, as in the case of denitrification, first a stirring step is provided to sufficiently elute phosphorus from the activated sludge using organic matter in the inflow water, and then an aeration step is provided. , the dephosphorization effect is further improved by ingesting it in excess into activated sludge. In short, in this invention, as mentioned above, there is a stirring process before the aeration process, so phosphorus in the activated sludge is sufficiently eluted using organic matter in the inflow water, so the aeration process that follows takes a short aeration time. However, it is possible to make the activated sludge contain a sufficient amount of phosphorus, and by drawing this activated sludge that has taken in too much phosphorus out of the tank, the dephosphorization effect becomes significant. In this way, in the present invention, by first stirring the activated sludge in the tank, the aeration time in the next step can be shortened compared to the stirring time, and furthermore, by repeating stirring and aeration many times, desorption can be achieved. Nitrogen and dephosphorization effects can be increased compared to conventional methods. That is, as mentioned above, the aeration time can be significantly shortened compared to the stirring time, so the processing time for one cycle can be shortened, and this cycle is typically repeated 4 times a day.
This process can be repeated several times, and therefore the denitrification and dephosphorization effects can be greatly increased compared to conventional methods. In addition, since the present invention allows wastewater to continuously flow in,
The above-mentioned storage tank is advantageous in that it is unnecessary or its volume can be significantly reduced.

[Brief explanation of the drawing]

FIG. 1 is a schematic vertical cross-sectional view showing a conventional batch type activated sludge treatment apparatus, FIG. 2 is a time chart of the treatment process by the batch type activated sludge treatment apparatus shown in FIG. FIG. 4 is a schematic longitudinal sectional view of a batch type activated sludge treatment apparatus to which an embodiment is applied, and a time chart of the treatment process. 1... Processing tank, 1a... Inflow section, 1b... Main processing section,
1c...opening, 3...decanter, 4...aeration blower,
5... Diffuser, 8... DO sensor, 9... DP meter, 10
...Computer, 15...Batsuful.

Claims (1)

[Claims] 1. In a batch activated sludge treatment method in which sewage is treated by repeating the steps of stirring, aeration, precipitation, and discharge in a single treatment tank, the inside of the tank is divided into a sewage inflow section and a main treatment section. The treatment tank has a buttful that is divided into two parts, and an opening that communicates between the inflow part and the main treatment part is provided in the lower part of the treatment tank. There is a stirring process in which the activated sludge in the main treatment section is first stirred, an aeration process in which the liquid in the tank is aerated in the main treatment part after this stirring process, and a stirring and aeration process in which these stirring and aeration processes are repeated a predetermined number of times at predetermined intervals. It is characterized by repeating the aeration process, the precipitation process of precipitating the sewage of the aerated mixture after the stirring/aeration process, and the discharge process of discharging the supernatant liquid after the precipitation process, as one cycle. Batch-type activated sludge treatment method. 2. In the aeration step, a DO sensor measures the dissolved oxygen concentration in the treatment tank, and an aeration amount automatic control device automatically controls the aeration amount to control the dissolved oxygen concentration to a predetermined concentration based on the measured value of the DO sensor. The batch type activated sludge treatment method according to claim 1, further comprising a control means.