JPH04197497A - Treatment of sewage - Google Patents

Abstract

PURPOSE:To properly hold reaction times in an oxygen free state and an aerobic state and to effectively perform nitrification, denitrification and dephos phorization by repeatedly changing over both states by setting the anaerobic level time and aerobic level time in one cycle of intermittent aeration. CONSTITUTION:Sewage is intermittently aerated under continuous stirring in a single reaction tank 1 and the tank 1 is alternately changed over to an anaerobic state and an aerobic state to treat sewage. At this time, operation is executed so that the ratio A/B of an anaerobic level time A bringing DO in the liquid mixture in the tank to 0.2mg/l or less and an aerobic level time B bringing said DO to 0.5mg/l or more in one cycle of intermittent aeration becomes 0.5-1.0. As a result, nitrification, denitrification and dephosphorization can be effectively performed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention is suitable for small-scale nitrification-denitrification treatment of wastewater such as sewage and industrial wastewater. The present invention relates to a method for treating wastewater using a single tank system, and in particular to an effective control method for intermittent aeration.

1. Prior Art) Methods for nitrification-denitrification treatment of wastewater include a batch method in which wastewater is alternately introduced into reaction tanks maintained in an aerobic or anaerobic state to perform nitrification-denitrification treatment; The reaction tank is partitioned by partition walls.

A modified circulation method that performs nitrification-denitrification treatment by circulating the water in the tank in an aerobic state on one side and an anaerobic state on the other, or adjusting the amount of oxygen supplied by the aeration device by lengthening one reaction tank. The OD method is widely known in which nitrification-denitrification treatment is performed by creating aerobic and anaerobic regions along the circumference of the reaction tank and circulating the flow inside the reaction tank.

However, the batch method requires multiple reaction tanks, which not only increases the installation area, but also makes the treatment unstable if the amount of wastewater flowing in fluctuates, so an adjustment tank must be installed to adjust the flow rate. It has the disadvantage that it cannot be used. In addition, in the 4-cycle circulation method, while separately managing the inside of the partitioned reaction tank,
It is necessary to circulate the water in the tank, which has the disadvantage that control is complicated and expensive. In addition, the OD method creates an intermediate boundary between neither aerobic nor anaerobic conditions in the reaction tank, and this boundary does not contribute to nitrification or denitrification, resulting in wasted space and is uneconomical. There are drawbacks.

Therefore, it is possible to efficiently nitrify and denitrify wastewater in a single reaction tank without requiring a large installation area, and it is easy to operate, making it particularly suitable for small-scale nitrification and denitrification treatment of wastewater. As an effective sewage treatment method, the method described in Japanese Patent Application Laid-Open No. 1-310798 has been proposed, and its superiority over other methods has been confirmed through experiments. In this method, a stirring device and an aeration device are installed inside the reaction tank, and while the stirring device continuously stirs the wastewater inside the reaction tank, the aeration device intermittently aerates the water, and the same reaction is carried out at each required time. By alternately switching the inside of the tank between an anaerobic state and an aerobic state, wastewater is nitrified and denitrified.

In experiments using this method, anaerobic and aerobic conditions have been carried out cyclically by repeatedly stopping and starting the blower according to a time set in advance using a timer.

(Problem to be Solved by the Invention) However, in actual wastewater treatment, due to load fluctuations, the actual aerobic time and anaerobic time may differ from the timer setting time.

For example, at night, when there is little inflow water and the load is small, D
O becomes too high, and even if the blower is stopped, it takes a long time for the inside of the aeration tank to become anoxic, resulting in a short anaerobic time, which reduces the effectiveness of nitrogen removal. A phenomenon was observed. Under these circumstances, it has been found that there is a problem in how to perform control in response to load fluctuations in inflowing sewage in sewage treatment at actual facilities.

The present invention aims to solve the problems of the prior art and provide a novel wastewater treatment method that can effectively treat wastewater.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the inventor of the present invention has conducted extensive research and determined that the ratio of the anaerobic level time to the aerobic level time in one cycle of intermittent aeration is within a predetermined range. It has been discovered that good processing results can be obtained by doing so, and the present invention has been developed.

That is, the wastewater treatment method of the present invention involves intermittently aerating wastewater while continuously stirring it in a single reaction tank, and alternately switching between an anaerobic state and an aerobic state in the tank. In a method for treating sewage, in one cycle of intermittent aeration, the anaerobic level time A at which the DO of the mixed liquid in the tank becomes 0.2 g/β or less, and the DO at the same time becomes 0.5 B/β or more. The A/B ratio, which is the ratio to the aerobic level time B, is 0.6.
It is characterized by operating within the range of 1.0 to 1.0.

In the present invention, an intermittent aeration tank is equipped with a device that performs mixing and agitation and oxygen supply, such as an underwater air radar, as well as a DO meter and a timer that operates in conjunction with it. It is assumed that an aerobic state can be formed, and when anaerobic, the air supply from the compressor is stopped and only stirring is performed, and when aerobic, oxygen supply can be performed at the same time as mixing and stirring.

A necessary condition to promote effective nitrogen removal by intermittent aeration is to maintain appropriate reaction times in anoxic and aerobic conditions through the aeration cycle, and to repeat this cycle. The ratio of anaerobic level time to time is important.

The above anaerobic level time A is set to 0゜2■g/
When the temperature is below I2, set the aerobic level time B to the Do of the mixed liquid.
is 0.5B/β or more, this AZB ratio and K j
Many experiments have been conducted on the relationship between the e-N removal rate, the NOx-N concentration in treated water, and the T-N removal rate.
The results shown in Figure 4 were obtained. According to it, A
/B ratio increases, that is, as the anaerobic level time increases, the nitrification reaction is suppressed, and as shown in Figure 3, Kj
The e-N removal rate will continue to decrease. On the other hand, A/B
When the ratio is small, that is, when the anaerobic time is short, the denitrification reaction is inhibited, and as shown in Figure 4, the N0x-N in the treated water is
21 degrees will be high. Also, looking at Figure 5, which shows the T-N removal rate, when the A/B ratio is small, denitrification is insufficient and T-N removal rate is small.
The N removal rate decreases, and conversely, if the A/B ratio is too high, nitrification becomes insufficient, and the TN removal rate similarly decreases.

Judging comprehensively from the above Kje-N removal rate, residual NOx-N concentration in treated water, and TN removal rate, the ratio of anaerobic level time to aerobic level time, that is, the A/B ratio, is 0. A range of 6 to 1.0 is appropriate, and better results will be obtained if the aerobic level time is equal to the anaerobic level time, or if the aerobic level time is slightly longer.

The above aeration cycle was tested with various lengths and short lengths for the case of raw sewage caught by boat, but it was judged that about 120 minutes was appropriate from the viewpoint of treatment stability and removal performance.For example, an aeration cycle of 120 minutes (60 minutes of aeration, 60 minutes of aeration stop), the maximum DO (just before II aeration stop) is 2 to 3 yag/1
If the air volume is adjusted to 2, it is possible to operate clearly in an anoxic state and an aerobic state based on the oxygen consumption rate at this time.

(Function) In the method of the present invention having the above configuration, the wastewater that has continuously flowed into the reaction tank is intermittently aerated while being continuously stirred by the aeration and stirring device, and is kept in a predetermined aerobic state and anaerobic state. By repeating this, nitrification, denitrification, and dephosphorization treatments are effectively performed.

(Example) Next, an example of the present invention will be described with reference to the attached drawings.

Fig. 1 shows the flow sheet of the device, in which 1 is a 7 intermittent aeration tank used as a reaction tank, and a submersible aerator 2 is installed in the center lower part of the tank. When air is supplied from compressor C, the inside of tank 1 becomes an aerobic state, and when it is stopped, only stirring is performed, and the inside of tank 1 becomes an anaerobic state. Air supply and stop are not shown in the diagram. 0N-O of the timer that operates according to the predetermined value of the DO meter
This is done by FF. A settling tank 3 is provided adjacent to the reaction tank 1, and receives the treated wastewater discharged from the reaction tank 1 and separates it into solid and liquid. A part of the sludge 4 settled at the bottom of the settling tank 3 is returned to the reaction tank 1 through a return pipe 4a by a sludge pump P, and the remaining sludge is discharged 4b as surplus sludge. Then, the treated water is sent to settling tank 3.
The water will be discharged from the top of the tank. Further, the inflowing sewage enters the raw water storage tank 6, and is continuously supplied from there to the reaction tank 1 by the raw water supply pump P.

The main purpose of the experiment was to remove nitrogen, and the experimental conditions in the reaction tank (intermittent aeration tank) used in the experiment are as shown in Table 1.

Table 1 In addition, Table 2 shows the water quality of the sample raw water and treated water in this experiment.

Table 2 An example of the temporal changes in DO and ORP in the reaction tank 1 in this experiment is shown in Fig. 2, which is during an aeration cycle of 120 minutes (60 minutes of aeration, 60 minutes of stopping). After the aeration of the aeration cycle begins, the DO in the tank begins to rise rapidly, and when the aeration stops, it decreases due to oxygen consumption as the sludge breathes.

This volume increase and the time for DO to become zero vary depending on the maximum value of Do and the oxygen consumption rate of the mixed liquid. As seen in this figure, in the intermittent aeration process, anaerobic and aerobic conditions alternate over time. Furthermore, ORP closely reflects changes in the redox state in conjunction with the stoppage of oxygen (air) supply.

In this experiment, the BOD of the treated water was 811g.
/J2 or less, and 90% showed 6 intestinal gi or less, and good treated water quality was obtained. In terms of BOD-VSS$ load, BOD removal rate is 90% or more within the range of 0.05 to 0.30Kg/VSS-Kg・day, treated water BOD6+wg
/12 or less was obtained. In addition, the treated water T-N was all below 711 g/β, and the cumulative frequency of T-N below 5 mg/β was as high as 80%, and stable nitrogen removal performance was obtained. In addition, the Kje-N removal rate is high, especially for BOD-VSS.
When the load is less than 0.15Kg/VSS-Kg-day, approximately h
A Kje-N removal rate of 85 to 95% was stably obtained.

According to the above experimental results, it is clear that aeration conditions are an important operating factor regarding nitrogen removal in the flash aeration process.

(Effects of the Invention) As explained above, the method of the present invention provides the following excellent effects.

(1) By setting the anaerobic level time and aerobic level time in one cycle of intermittent aeration, the reaction time in anoxic state and aerobic state is maintained appropriately, and by repeating this,
It is capable of efficient anaerobic and aerobic operation, and in particular, nitrogen removal can be performed stably with high efficiency. (2) The removal rate of organic matter and SS is also good.

(3) Anaerobic and aerobic treatment is repeated in the same reaction tank, so it does not require a large installation area, and the facility cost is low, making it particularly suitable for small-scale wastewater treatment.

[Brief explanation of the drawing]

Figure 1 is a flow sheet diagram of an apparatus according to an embodiment of the present invention ≦ Figure 2 is a diagram showing changes over time in Do and ORP in the reaction tank, Figure 3 is an anaerobic level versus aerobic level time in 1 cycle Figure 4 shows the relationship between the time ratio and Kje-N removal rate, Figure 4 shows the relationship with the treated water N0x-N concentration, and Figure 5 shows the relationship with the TN removal rate. FIG. 1...Reaction tank, 2...Underwater aerator. 3...Final sedimentation tank $1 Figure 2

Claims (1)

[Claims] In a method of treating wastewater by aerating the wastewater intermittently while continuously stirring it in a single reaction tank, and switching the tank alternately between an anaerobic state and an aerobic state, one method of intermittent aeration is During the cycle, the DO of the mixed liquid in the tank is 0.
Anaerobic level time A below 2 mg/l and DO
A sewage treatment method, characterized in that the operation is carried out so that the A/B ratio, which is the ratio of the aerobic level time B at which the aerobic level is 0.5 mg/l or more, is within the range of 0.6 to 1.0.