JP2841131B2 - Activated sludge treatment method for sewage - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating activated sludge in treating sewage such as sewage and industrial wastewater. [0002] Purification of sewage by an activated sludge treatment method is a process in which activated sludge takes up organic matter in sewage as a nutrient source and grows under appropriate dissolved oxygen in a reaction tank. It is carried out by adsorbing and oxidizing the organic substances in it. For this reason, it is important for the design and operation management of the activated sludge treatment method to maintain the equilibrium of the reaction in which the activated sludge in the reaction tank adsorbs and oxidizes the organic matter which is a polluting source and proliferates. [0003] The rate of this reaction depends on various factors such as aeration time, activated sludge amount, and amount of inflowing organic matter. Among these factors, the amount of inflowing organic matter (BO) is a basic factor.
D amount) and the ratio of the activated sludge amount in the reaction tank to “BOD-SS
It is expressed as "load", and each processing method is determined according to the range of this value, and is set as an important parameter in operation management. For example, in the standard activated sludge method, the value of the BOD-SS load is set to 0.1.
2 to 0.4 kg / kg-SS / day, and 0.03 to 0.05 kg / kg-SS / day in the long-time aeration method.
And so on. Therefore, BOD-
We consider it important to keep the SS load constant, and set an appropriate sludge concentration in the reaction tank for this purpose, and manage it by the excess sludge withdrawal amount. The method of managing the sludge concentration in the reaction tank based on the excess sludge withdrawal amount is as follows. The sludge concentration in the tank to be managed is determined by determining an appropriate sludge amount in the tank with respect to the inflow load, and the calculated sludge concentration is calculated. A method of extracting an appropriate amount of excess sludge from the sedimentation basin is used, but the excess sludge concentration is the same as the sludge returned from the sedimentation basin, so it is strongly affected by fluctuations in the amount of inflow water and sludge settling speed, and therefore fluctuations in concentration Is big. The amount of the extracted sludge is a product of the excess sludge concentration and the amount of the extracted sludge (flow rate). In the sewage treatment, the fluctuation of the inflow amount is large, so that the excess sludge concentration fluctuates greatly, and the extracted sludge for securing the predetermined sludge concentration in the tank. Adjusting the volume is extremely difficult. On the other hand, according to recent research results on water treatment, activated sludge treatment is defined as sludge residence time (normal expression), ie, residence time of solid matter (activated sludge) in a reaction tank, rather than BOD-SS load. SRT (Solids
Retention time is considered to be a more fundamental factor, and it has become clear that maintaining this SRT properly is more important. SRT is the ratio of the amount of activated sludge in the reaction tank to the amount of sludge flowing out of the treatment system (the sum of the amount of excess sludge and the amount of treated water SS, which can be approximated by the amount of excess sludge). In the method of pulling out excess sludge from the pond, it is extremely difficult to properly maintain the SRT because the sludge concentration in the pulling-out fluctuates significantly due to fluctuations in the inflow load. Then, in order to solve the above-mentioned drawbacks, the activated sludge treatment method of Japanese Patent Application No. 2-293126 has been proposed as a means for facilitating the adjustment of the SRT. That is, according to the present invention, a pump is installed in a reaction tank for quantitatively feeding a sludge mixture, and the sludge mixture in the reaction tank is quantitatively withdrawn and discharged as sludge out of the treatment system. Is constantly controlled to the set value, and by quantitatively extracting sludge directly from the reaction tank, regardless of the amount of influent wastewater, water quality, and changes in the sludge concentration in the reaction tank and the return sludge concentration This is to keep the SRT constant. [0007] However, the above method is extremely effective when the load fluctuation of the amount of inflowing water and water quality is small, but when the fluctuation of the inflow load is large, for example,
If the load is greatly affected by the tourist population, such as a sewage treatment plant located in a tourist area, and if it is significantly different between weekends and weekdays, the MLSS concentration will fluctuate if the SRT is kept constant, responding to load fluctuations It turns out there is a limit to what you can do. [0008] This is because activated sludge method is, in principle, BOD
Maintaining a constant load per sludge amount, as indicated by -SS load, is the basis for stabilizing the treatment. In general, the design of a treatment facility is designed based on the point of high inflow load, but when the inflow load fluctuation is large and the actual load is small, as in the example of the sightseeing spot mentioned earlier, the SRT is set by the above means. When the operation is performed at a constant level, the MLSS concentration decreases. On the other hand, when the MLSS concentration is constant, the SRT
Changes greatly. Under both of these operating conditions, when the load is extremely reduced on weekdays, the effect on processing is small directly, but when a heavy load is applied on the next weekend, the processing function often does not recover. This tendency is particularly remarkable in a biological denitrification method in which nitrification and denitrification are performed by repeating anaerobic and aerobic. Nitrifying bacteria in the activated sludge maintain their activity under the condition that the amount of cells corresponding to the loading condition is maintained, but it is extremely difficult to maintain the activity corresponding to a large variation in the loading. For example, in a single tank method in which an underwater aerator is installed in a reaction tank and anaerobic and aerobic are repeated, when sludge is extracted in accordance with the inflow load and the operation is performed with the MLSS concentration kept constant, the inflow on weekdays is performed. sewage quantity is small, _NH 4 -N
Under the condition where the load is kept small, the anaerobic / aerobic operation time ratio is set to the same mode as the weekend with a high load, and the SR
Nitrogen bacteria in sludge are killed because T or ASRT becomes too long. The activity decreases. If the load suddenly rises from such a state, the change cannot be followed, and the processing function is reduced and the water quality is deteriorated. In a processing plant having such a large load fluctuation, it is difficult to maintain the activity and maintain the processing function for a long time. Accordingly, the present invention is to provide a method for treating wastewater with activated sludge which can exhibit a sufficient function even when such a load fluctuation is large. Means for Solving the Problems The inventor of the present invention has conducted intensive studies to solve the above-mentioned problems, and as a result, the sludge mixture is directly extracted from the reaction tank as excess sludge. Withdraw the amount corresponding to the inflow load. As a result, when the inflow load changes greatly, the SRT changes. However, by adjusting the substantial ratio of the aerobic processing time to the anaerobic processing time in accordance with the inflow load, the aerobic condition is adjusted. Residence time of the solids in the reactor below (Aerobi
It has been found that good processing performance can be exhibited by controlling the ASRT defined as c Solids Retention Time) at a constant level, and the present invention has been accomplished. In other words, according to the activated sludge treatment method of the present invention, a drawing tank for directly discharging a part of the sludge mixture directly out of the system is provided in a reaction tank for performing activated sludge treatment by repeating anaerobic and aerobic treatments. The ASRT is controlled to be constant by adjusting the amount of excess sludge withdrawal according to the load and adjusting the substantial ratio of the aerobic treatment time to the anaerobic treatment time according to the inflow load. It is characterized by having done. [0014] The type of the reaction tank to be used in the present invention is a single tank method in which anaerobic and aerobic are repeated in a single reaction tank, and an anaerobic aerobic circulation in which a plurality of reaction tanks capable of performing anaerobic and aerobic are arranged in tandem. A variant is preferred. Also, the present invention can be applied to a multistage anaerobic aerobic method in which an anaerobic tank and an aerobic tank are alternately arranged in multiple stages. As a means for extracting the sludge mixed liquid from the reaction tank, generally, the mixed liquid is extracted from the bottom of the reaction tank by a pump. In the modified anaerobic and aerobic circulation method, the mixed liquid is extracted from the last reaction tank. The withdrawn sludge mixture is sent to a concentrated sedimentation basin outside the system as excess sludge for treatment. In the present invention, the amount of sludge withdrawn / the amount of sludge mixed solution withdrawn is adjusted by a pump so that the SRT is inversely proportional to the inflow load into the reaction tank.
That is, the sludge withdrawal amount is increased or decreased according to the increase or decrease of the inflow load amount. In the present invention, the ratio of the aerobic treatment time to the anaerobic treatment time is adjusted according to the inflow load into the reaction tank. In general, this adjustment can be performed by adjusting one or both of the aeration time and the aeration pause time performed by feeding air into the reaction tank. The present invention intends to control the ASRT to a constant level by combining the adjustment of the sludge withdrawal amount and the adjustment of the aerobic time ratio. The ASRT is the residence time (days) of solids in the reaction tank under aerobic conditions. SRT = Activated sludge amount in the reaction tank (same as the solid matter amount in the reaction tank) (kg) / Excess sludge amount (kg / day), and if excess sludge is drawn directly from the reaction tank, SRT = MLSS × V / (MLSS × Qe) Here, MLSS: Activated sludge concentration in the reaction tank (same as solid matter concentration in the reaction tank) (mg / L) V: Reaction tank volume (m ³ ) Qe: Excess sludge withdrawal amount (M ³ / day) HRT = 24 × V / Q When this equation is solved by V, V = (Q / 24) × HRT Therefore, SRT is represented by the following equation. SRT = MLSS × (Q / 24) × HRT / (MLSS × Qe) = Q × HRT / (Qe × 24) where Q: inflowing wastewater (m ³ / day) HRT: hydraulic retention time (hour) ASRT = SRT × X where X: aerobic processing time ratio (−) (Aerobic processing time ratio in one day, aerobic processing time / 24 hours). That is, the ASRT refers to the time (days) during which aerobic treatment is performed in the residence time of activated sludge (same as the residence time of solids), and the ASRT in the anaerobic aerobic treatment method is the extraction surplus. It is determined by the adjustment of the amount of sludge and the setting of the aerobic treatment time (however, in a method using only aerobic treatment, SRT = ASRT). According to the present invention having the above-described structure, the sludge amount drawn directly from the reaction tank and the aerobic treatment time ratio can be adjusted according to the increase / decrease of the inflow load into the reaction tank. ASRT
Is controlled to be constant, a good treatment function is always exhibited even in a treatment plant where the load variation is large, and efficient wastewater treatment can be achieved. Embodiments of the present invention will be described below with reference to the accompanying drawings and tables. Example 1 (1) This example is directed to a single-tank method, and the apparatus used is as shown in FIG. Underwater aerator 2 for supplying oxygen and oxygen
To supply and stop the air (oxygen) from the compressor C by switching a switch, etc., so that only the mixing and stirring can be performed when the supply of the air is stopped. The state and the anaerobic state can be alternately formed. 3 sedimentation tank, 4 is a concentrate sedimentation tank, sludge sedimentation 3 is returned to the reaction tank 1 by a pump p ₁ as return sludge, supernatant is discharged out of the system. Further, the reaction vessel 1 is a pump P ₂ for withdrawing the sludge mixture is provided from the bottom, withdrawn mixture is sent to the concentration sedimentation tank 4, separated sludge as a concentrated excess sludge The discharged water is returned to the reaction tank 1. (2) Experimental Conditions As shown in Table 1, the treatment amount was 2.0 m ^{3 for} two days, with one cycle being seven days.
/ Day, and for the other 5 days, the load was changed by reducing the load to 1.0 m ³ / day. Water quality varies with time,
When viewed on a daily basis, BOD is around 170 mg / L, T-N
Was about 25 mg / L, and the load on the reaction tank 1 became almost proportional to the fluctuation in the amount of water. The amount of inflow water during 24 hours a day was constant. The anaerobic-aerobic time ratio X is adjusted by turning on / off the air supply from the compressor. In the experiment of the present invention, the 0.5 day is set to 0.5 on the 6th and 7th days when the load is large, and the 60 minute ON, OFF is repeated for 60 minutes, and the ratio X is set to 0.25 on the first to fifth days when the load is small.
ON for 30 minutes and OFF for 90 minutes were repeated. In the control experiment, the ratio was uniformly set to 0.5, and ON for 60 minutes and O for 60 minutes.
FF was performed through a 7 day cycle. The amount of excess sludge directly withdrawn from the reaction tank 1 is as follows:
Since the amount of excess sludge generated is almost proportional to the amount of inflow water,
The withdrawal amount was determined in proportion to the inflow water amount. That is, 0.05 m ³ / day on the 1st to 5th days, and 0.1 m ³ / day on the 6th to 7th days.
1 m ³ / day. The Itoyoshika and SRT were 40 and 20 days, respectively. In addition, by setting the anaerobic-aerobic time ratio X, in the present invention, the ASRT was constant at 10 days, and in the control experiment, 1 to 5 days was 20 days, and 6 to 7 days was 10 days. The returned sludge was made proportional to the amount of inflow water so that the MLSS in the reaction tank was almost constant, and the return ratio was 100%. [Table 1] (3) Experimental Results The results of the above experiments are shown in FIG. In the present invention, when the amount of inflow water is small and the load is small, the aerobic time is reduced. Conversely, when the amount of inflow water is large and the load is large, the aerobic time is increased so that the ASRT is controlled to be constant. _NH 4 -N in the treated water, N
O _x -N concentration is low and stable, approximately 80% throughout the week
TN removal rate was secured. On the other hand, in the control experiment, when the load is low, nitrification proceeds and NH ₄ -N decreases, but a large amount of NO _x -N remains. On the contrary, when the load is high, a large amount of NH ₄ -N remains. I do.
This is because even if the facility is designed for a high load and the operating conditions are determined, the predetermined performance is not exhibited if the load fluctuation is large. In this experimental example, even under the same load conditions in the present invention and the control experiment, NH ₄ -N
There is a difference in the nitrification rate of This is due to the difference in whether the activity of nitrifying bacteria is maintained at a high level under a large load fluctuation condition. In order to adjust the ASRT as in the present invention, it is necessary to reduce the aerobic time at a low load. This is because, if a proper measure is taken, a load of a certain amount or more will always be applied to the nitrifying bacteria, and the activity will not decrease even when the load becomes high next time. Example 2 (1) This example is an example of a modified anaerobic / aerobic circulation method, and the apparatus used is a reaction tank 1 as shown in FIG.
Is divided into multiple stages, in this case, five stages, and is cascaded with 1a to 1e.
An underwater aeration device 6 connected to the air pipe 7 from the blower B via a valve 8 is installed. Supply and stop of air are performed by opening and closing the valve 8, and when stopped, anaerobic stirring is performed. which is to be the aerobic state and for supplying air by a pump P ₃ from the end of the vessel 1e, the liquid is circulated to the starting end of the vessel 1a. The sewage is supplied to the starting tank 1a. For example, the denitrification reaction proceeds in the first two tanks 1a and 1b, and the nitrification reaction proceeds in the second three tanks 1c, 1d and 1e, and a part of the nitrified mixture is circulated and desorbed. Nitrogen will form. The sludge mixture is withdrawn by pump P ₂ from the bottom of the last tank 1e.
The other configuration is the same as that of the first embodiment. (2) Experimental conditions The reaction tanks were each of the tanks 1a to 1e.
Are 0.1 m ³ (100 L), respectively, and
Is the capacity of 5m ^3. The experimental conditions are as shown in Table 2. In the present invention, the amount of excess sludge is increased or decreased in accordance with the inflow load (≒ treated water amount), and the operation method of each of the tanks 1a to 1e is selected between anaerobic and aerobic. Was changed to substantially adjust the time ratio of anaerobic and aerobic conditions in the entire reaction tank 1 to keep the ASRT almost constant (8.4 to 9 days). On the other hand, in the control experiment, the amount of excess sludge was adjusted in the same manner, but the operation method of each of the tanks 1a to 1e was constant regardless of the load variation. As a result, the ASRT was 16.8 days on weekdays (days 1 to 5) and 9 on weekends (days 6 and 7).
The day has changed. After acclimatization for about one month under the above conditions, data was collected. The amount of circulating fluid was constant at 0.8 m ³ / day during the entire experiment. In addition, the MLSS calculated that the return ratio was 100% of the
The range was from 0 to 3300 mg / L. [Table 2] (3) Experimental Results Table 3 shows the results of the above experiments. In the present invention, BO is not affected by load fluctuation.
It can be seen that D, SS and nitrogen were successfully removed. On the other hand, in the control experiment, on weekdays with a small load, the removal of BOD and SS was good, but the load on the nitrification tank (aerobic tank) was too small, so that NH ₄ -N was well treated. However, the dissolved oxygen in the nitrification circulating fluid was high, and this brought in that the denitrification in the anaerobic tank became insufficient. On the weekend, the results were obtained under the same processing conditions as the present invention, but the nitrogen removal rate was poor. This is due to the fact that when the nitrifying bacteria were lightly loaded on weekdays, the load became too light and their activity was reduced, and a high load was applied on the weekend, and it was not possible to cope with the load. Table 3
As shown in Table 2, in the present invention, BOD, SS and nitrogen were successfully removed without being affected by load fluctuation. [Table 3] As described above, according to the present invention, the excess sludge is extracted according to the inflow load, and the ASRT is controlled to be constant by adjusting the substantial aerobic time ratio. As a result, the amount of nitrifying bacteria can be appropriately maintained without death of the nitrifying bacteria at a low load, and good treatment can be performed without reducing the activity even under a large load fluctuation.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of an apparatus applied to an embodiment of the method of the present invention. FIG. 2 is a schematic diagram of another device. FIG. 3 is a diagram showing experimental results of Example 1. [Reference Numerals] 1 1 a to 1 e reaction vessel 2 water aerator 3 sedimentation tank 4 and concentrated sedimentation basin 5 stirrer 6 underwater aeration device 7 air pipe 8 valve B Blower C compressor _P 1 to P ₃ pump

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Shoroku Kawauchi 2-26-7 Shinkanjima, Konohana-ku, Osaka Hanshin Power Machinery Co., Ltd. (56) References JP-A-4-166295 (JP, A) (58) ) Surveyed field (Int.Cl. ⁶ , DB name) C02F 3/30 C02F 3/34 C02F 3/12

Claims (1)

(57) All Claims anaerobic, the reaction vessel to the activated sludge process is repeated aerobic, withdrawal means for discharging a portion of the sludge mixture directly out of the system provided, increase of the inflow water amount, almost reduced Proportion of sludge mixture
Adjust the increase / decrease of the withdrawal amount, and thereby change the SR
Substantially the aerobic processing time for the anaerobic processing time for T
Ratio of aerobic processing time in a day
Adjust the load small when the load is small and large when the load is large.
By Rukoto, characterized by being adapted to control the ASRT constant, activated sludge treatment of sewage.