JPS59115793A - Treatment of organic sewage - Google Patents

Abstract

PURPOSE:To remove efficiently BOD and nitrogen in org. sewage by repeating successively the stage of subjecting the org. sewage in an aeration tank to a repetition of aeration and stopping of aeration or decreased aeration then settling activated sludge and discharging supernatant liquid. CONSTITUTION:The treatment for removing BOD with an aerobic treatment by aeration, nitrating a nitrogen component then removing NO3-N by the anaerobic treatment of stopping aeration or performing decreased aeration is repeated and thereafter the aeration is stopped and the activated sludge is settled then supernatant liquid is discharged as treated water 4, in a batch type activated sludge treatment method of the constitution wherein org. sewage 1 is introduced into an aeration tank 2 and is aerated by an aerator 3 and treated wate 4 cleaned up by the aeration is discharged. The liquid in the tank 2 having the decreased inside volume is aerated to remove the residual BOD and to accelerate the nitration reaction of low reaction rate, whereafter the sewage 1 is again introduced into said tank and the above-mentioned stage is successively repeated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention &-J1 relates to an improvement in a batch-type activated sludge treatment method, which is one of the biological treatment methods for organic sewage.

FIG. 1 is a flow sheet diagram showing a conventional batch activated sludge method. In this batch activated sludge method, organic wastewater 1 is first introduced into an aeration tank 2.

In the aeration tank 2, an enzyme-containing gas (generally air) is sent from the aeration device 3, and the activated sludge in the aeration tank 2 and the 4JA sewage are stirred, mixed, and brought into contact with each other to activate the activated sludge. Sewage treatment is performed using sludge.

After performing aeration treatment for a certain period of time, aeration is stopped and the activated sludge mixture is allowed to stand, allowing the activated/reformed sludge to settle. Thereafter, the precipitated supernatant water is discharged out of the system as treated water 4, and an amount of organic wastewater 1 approximately equal to the discharged treated water acid is introduced into the aeration tank 2, and the aeration process is started again. If this is shown in a chart for the driving tie, it will look like Fig. 2 (1).

・In this way, in the batch activated sludge method, the aeration tank 2 is also used as a sedimentation tank, and the two functions of aeration and sedimentation are used depending on whether or not the aeration device 3 is in operation. This is one of the biological treatment methods in which the treated water 4 is introduced continuously and the treated water 4 is discharged intermittently. In this biological treatment, BOD, nitrogen, etc. can be mentioned as pollutants that can be treated. The reaction formula in these biological treatments is as follows.

[BOD removal reaction] →xco2+ T y H2O・・・・・・・・・・・・
・・・(1) [Nitrogen removal reaction] NH4+202 →No +H20+2H・・・・・・・・・・・・(2
)2NO3+ 10H →N2 ↑+4H20+ 20H・・・・・・・・・(
3) Nitrogen in wastewater is not only in the form of NH4, but also organic nitrogen, but organic nitrogen is often converted to the form of NH4+ by the deamination action of microorganisms. NH is a typical example of nitrogen in wastewater.
4, the above reaction BOD removal is an aerobic reaction as shown in equation (1). Therefore, the reaction proceeds by providing sufficient aeration reaction conditions. On the other hand, nitrogen removal consists of an aerobic reaction shown in equation (2) and an anaerobic reaction shown in equation (3). Therefore, nitrogen is not removed only by applying warm air reaction conditions, and even if a sufficient aeration reaction is carried out, nitrogen remains in the treated water in the form of nitrate nitrogen (No3-N).

In the conventional batch activated sludge method, in order to effectively use the entire aeration tank for the oxidation reaction, an aeration method was used in which the entire aeration tank became aerobic. Therefore, although it is possible to remove BOD using the conventional batch activated sludge method, it is almost impossible to remove nitrogen.

In recent years, research has been conducted to add and strengthen the denitrification function to the batch activated sludge process by improving the aeration method. An example of this is the 21st ffl (It).

(To) shown in the driving time chart, (It),
([0 is the aeration tank under aerobic conditions' (aeration equipment operating state)
and anaerobic conditions (aeration equipment stopped state) are repeated a desired number of times, and formulas (1) and (2) under aerobic conditions are obtained.
and the reaction of formula (3) under anaerobic conditions.

However, even with these recent improved methods, there were some problems.

One of them is that since BOD removal proceeds first, there is a shortage of OD, which is needed to escape from the 1st century. In other words, the formula (1
), the nitrification reaction shown in equation (2), and the denitrification reaction shown in equation (3).

Both the BOD removal reaction and the nitrification reaction are aerobic reactions, but their reaction rates are different, with the former reaction being faster. Therefore, when wastewater containing BOD and NH4+-N is subjected to warm air treatment, the BOD removal reaction progresses faster. However, in the CI diagram in Figure 2, ([[In the recent improved method shown in D, aeration is started immediately after the introduction of raw wastewater,
First, BOD removal proceeds and the nitrification reaction is delayed. Therefore, since the nitrification reaction is insufficient, the removal treatment of the primary element is also insufficient. Furthermore, in the denitrification reaction shown in equation (3), an organic carbon source (formula (
3) Hydrogen donor (denoted by H) is required in the raw sewage, but in order to cause the denitrification reaction without adding organic substances such as methanol from the outside, it is necessary to It is necessary to effectively utilize long-term components, that is, BOD. However, in the recent improved method shown in (It) and ([D] in Figure 2, aeration is started immediately after the raw wastewater is introduced, and the BOD is improved. The gaseous removal process takes precedence.For this reason, when the nitrification reaction ends and the denitrification process begins, the OD required for the denitrification reaction will be insufficient.

One of the other problems is that BOD busyness becomes a rate-limiting factor. That is, the No. produced as a result of the nitrification reaction of formula (2)
When 3-N is treated by the denitrification reaction of formula (3), it is desirable that a large amount of BOD be present as an organic carbon source so that it does not become a rate-determining factor, and in that case, anaerobic conditions are used. There is a need. However, (■) and (
In the recent improved method shown in g), aeration is performed immediately after introducing raw wastewater, so BOD is removed during this time.
Even if an attempt is made to make the denitrification reaction anaerobic in the next step, the amount of BOD is small and becomes a rate-limiting factor.

The present invention was made in view of the above circumstances, and its purpose is to provide a method for treating organic wastewater that can efficiently remove BOD and nitrogen in a batch activated sludge method. That is.

That is, the present invention includes a step of repeating aeration and aeration stop or reduction 1 (・A air) for organic wastewater placed in an aeration tank, a step of stopping aeration, precipitating activated sludge, and discharging supernatant water, A step of aerating the inside of the aeration tank after discharging the supernatant water;
The first feature is that the process of adding organic wastewater after aeration is repeated in sequence.

In addition, a step of reducing aeration of the organic wastewater placed in the aeration tank, and a step of repeating aeration and stopping or reducing aeration;
The first step is to sequentially repeat the steps of stopping the μ air to precipitate activated sludge and draining the supernatant water, aerating the tank after discharging the supernatant water, and adding organic sewage after the aeration. 2.

The method of the present invention will be explained in detail below based on an example of the operation time chart shown in FIG.

For the organic wastewater in the 1V aeration tank, aeration operation and reduced aeration or aeration stop are repeated a desired number of times to form aerobic conditions and anaerobic conditions. Aerobic condition! ,! When repeating the aeration state and the 91g aeration state, it is effective to divide the aeration time into short periods for denitrification treatment.

This means that the longer the aeration time, the more BOD will be generated during the aeration process.
This is because the organic carbon is processed and cannot be used as an organic carbon source for denitrification. Normally, the aeration time in one cycle is, for example, 3 to 2
It will take about 2 hours. Further, according to recent research, the operation of repeating aerobic and anaerobic conditions is said to be effective in removing phosphorus, and is also effective from this point of view. This repetition is performed, for example, about 3 to 10 times. To form an aerobic state and an anaerobic state in the same aeration tank, the operation of the aeration device,
FFI flights are most likely to be due to suspension of operation. In order to form an anaerobic state, it is not necessarily necessary to completely stop the l aeration system f[ffi, and a reduced aeration state in which the rl element supply rate is relatively small compared to the oxygen consumption rate may be used. Rather, No.3- in sludge and water 1111, which are the main subjects of denitrification reactions,
From the viewpoint of increasing the contact efficiency with N, it is preferable to stir the inside of the aeration tank by reducing aeration. In the case of reduced aeration, it is necessary to maintain the dissolved oxygen level in the tank as low as 0.5 mfl/ or less. On the other hand, under aerobic conditions, dissolved 1!2 in the tank
It is preferable to aerate so that the element 1f becomes 1.0119//- or more.

After repeating the process of aeration and reduced aeration (stopping aeration) a desired number of times, the aeration is stopped, the activated sludge is allowed to settle, and the sedimented and separated supernatant water is discharged outside the system as treated water.
The air suspension time is set to gf-, for example, about 60 to 120 minutes.

Therefore, in the present invention, aeration is performed after the treated water is discharged to reduce the liquid storage capacity in the aeration tank. During this 11゛ period,
For example, do this for about 60 to 240 minutes. According to this aeration treatment, since the sludge concentration is in a relatively high state, it is possible to promote the BOD removal reaction and the nitrification reaction, especially the nitrification reaction which has a slow reaction rate. In addition, this aeration treatment is performed once
Reducing aeration (stopping aeration) is repeated to reduce BOD on the water side. Therefore, self-extinguishment occurs during BOD removal, reducing the amount of sludge, which has the advantage of requiring less processing of excess sludge. Furthermore, as a result of BOD removal and removal due to self-digestion, the BOD removal and removal content in the sludge decreases, and the proportion of nitrifying bacteria increases relatively, so that the nitrification activity of the sludge improves. In addition, during the autolysis process, NH4+-N is generated by hydrolysis of sludge components such as sludge, but this is also converted to No3-N through the nitrification reaction, and later nitrogen is removed as a result of the denitrification reaction. This improves the nitrogen removal rate. Furthermore, since the sludge is in such a starved state that it undergoes self-digestion, its ability to adsorb and remove sludge components from the raw sewage that is subsequently introduced increases, making it possible to obtain clear treated water or treated water with a low BOD concentration. It is valid.

When performing mechanical aeration or diffused aeration after discharging precipitated supernatant water, the water level is lowered, so stirring resistance and water head pressure are lowered, and the power required for aeration is lowered, contributing to energy-saving operation.

After this aeration treatment, organic sewage (raw water) is then flowed in, and the aeration and 1;', ÷ sudden stop F or reduced aeration are regenerated.

In this process, for one aeration time, the BOD load relative to the total aeration time is o, aky + BOD/k17・M
Lss/day or less, the total nitrogen load is Q, 1 kg・T
It is desirable to set it to be less than -N/klil・MLSS/day.

Also, total reduction +1. A distraction period (or total aeration stop time) is
The total nitrogen load for the total time is 0.4 to 9 T-
It is desirable to set it to less than N/kg・MLSS/day. The sedimentation time is determined in relation to the sedimentation rate of the sludge, the shape of the aeration tank, and the amount of water to be treated, and should be sufficient time to obtain sedimentation supernatant water equal to the amount of water to be treated. The raw water inflow time and treated water drainage time are determined comprehensively based on the raw water generation situation, storage tank capacity, inflow and discharge pump capacity, and other conditions.

Next, another embodiment shown in FIG. 4 will be explained.

In this method, organic wastewater (raw water) is brought into a reduced aeration state or aeration stopped state immediately after introduction, and then the same operation as in the method shown in FIG. 3 is performed. According to this method, aeration - reduced aeration (
The demolding reaction of formula (3) can be promoted by bringing the generated and residual No3-N into contact with the high-temperature BOD and placing it in an anaerobic state. Furthermore, in this method, BOD is reduced by being used in a denitrification reaction under anaerobic conditions immediately after raw wastewater is introduced, and then subjected to -gas treatment. Therefore, the BOD load when removing BOD by storing air is substantially reduced, and it is also effective in removing BOD.

Therefore, the effect of aeration after discharging treated water and the effect of reducing aeration (or stopping aeration) after raw wastewater enters the beach combine to further improve the nitrogen removal effect.

Next, an example in which organic sewage treatment was carried out by the method of the present invention will be described based on the time charts shown in FIGS. 3 and 4.

In this example, school lunch center wastewater was used as raw wastewater. Its composition is as shown in Table 1. As a conventional method for comparison, a batch activated sludge treatment experiment based on the time chart shown in (II) of FIG. 2 was also conducted. The capacity of the tank is 100t, and the treated water]d is 20t/
It was a day. 1. When processing is stable. +11LSS in Toki 4J・11 was approximately 2600 my/l.

Water 1 of treated water obtained by the method of the present invention and the conventional method, respectively
Two guns are shown in Table 1.

From the results shown in Table 1, it was found that the method of the present invention yields better treated water with lower BOD, nitrogen, and phosphorus contents than the conventional method.

The mechanism of phosphorus removal in the method of the present invention is currently unknown, but as has been said in recent years, phosphorus is incorporated into sludge when sludge is repeatedly exposed to anaerobic and aerobic conditions. it is conceivable that.

As explained above, according to the present invention, aerobic conditions and anaerobic conditions are effectively formed to efficiently carry out denitrification treatment, so that the 47 element content of treated water can be reduced, and
It has the remarkable effect of slightly reducing BOD and phosphorus content.

[Brief explanation of the drawing]

Figure 1 is a flow sheet diagram showing a batch type activated sludge equipment;
FIG. 2 is an operation time chart for the conventional batch activated sludge method, and FIGS. 3 and 4 are different operation time charts for the batch activated sludge method in the method of the present invention. 1... Characteristic wastewater, 2... Aeration tank, 3... Aeration equipment Wi'0,... Treated water.

Claims (2)

[Claims] (1) A process of repeating aeration and stopping or reducing the aeration for organic sewage placed in an aeration tank, a process of stopping heating to precipitate activated sludge and discharging supernatant water, and a process of discharging supernatant water. 1. A method for treating specific wastewater, characterized in that the steps of aerating the inside of the aeration tank and adding organic wastewater after 11 aerations are carried out in sequence. (2) I put it in the aeration tank! A step of reducing aeration or stopping aeration, a step of repeating M air and stopping M air or reducing aeration, a step of stopping 1M air to precipitate activated sludge and discharge supernatant water, A method for treating organic sewage characterized by sequentially repeating a step of aerating the gas phase after discharge and a step of introducing organic sewage after the aeration.