KR100382890B1 - Contact oxidation-type waste water disposal method for integrated septic tank - Google Patents

Abstract

The present invention relates to a catalytic oxidation wastewater treatment method, the flow rate adjustment tank (10); A reaction tank composed of an anaerobic tank 21, an anaerobic tank 22, and aeration tank 30; A degassing tank 40 and a settling tank 50; The anaerobic tank and the anaerobic tank is composed of an upflow (upflow) type tank by the porous diaphragm at the top of the anaerobic tank, the bottom is composed of anaerobic tank; The flow adjusting tank is connected to the anaerobic tank through the supply line, the anaerobic tank is connected to the aeration tank through the supply line, the aeration tank is connected to the settling tank through the supply line and connected to the degassing tank through the return line, the degassing tank is returned Provided is a contact oxidation type wastewater treatment apparatus for a combined purification tank and a wastewater treatment method using the same, connected to an anaerobic tank through a line and connected to an anaerobic tank through a sludge conveying line, and the wastewater treatment apparatus and method of the present invention are impacted. Excellent load buffering capacity, excellent organic matter, nitrification and denitrification efficiency, and the amount of sludge generated is very small, so there is no problem of sludge disposal and easy maintenance.

Description

Contact oxidation-type waste water disposal method for integrated septic tank

The present invention relates to a wastewater treatment method, and more particularly, to an apparatus and method for contact oxidation wastewater treatment for a combined purification tank.

In our country, water demand (about 30 billion ㎥ per year) continues to increase, but the use of river water is greatly reduced due to pollution of major rivers.

Therefore, the government is making a lot of efforts to increase the actual sewage treatment rate by expanding water quality environment facilities and greatly improving sewage pipes to improve the water quality of rivers and lakes nationwide. As part of this effort, the Sewerage Law has been amended to promote the installation of small-scale village sewerage systems, and mandatory installation of a merger and septic tank for treatment of domestic sewage generated outside the sewage terminal treatment area. Since 1997, the merger septic tank system has merged wastewater and general wastewater for food service businesses, lodgings, simple rest areas and bathhouses in rivers, lakes and coastal areas to treat BOD 20mg / L or less. . This is also being strengthened (BOD 20mg / L → BOD 10mg / L), and nutrients such as nitrogen and phosphorus are expected to be included in the future.

Generally, small and medium-sized sewage treatment technologies include organic material removal technology, nitrogen removal technology, and phosphorus removal technology.

Here, the organic material removal technology is achieved by adding contact aeration, sand filtration, flocculation, adsorption of activated carbon after the first physical treatment and the second biological treatment. In the secondary treated water, microbial flocs contain fine suspended solids (SS). These SS components not only cause direct oxygen oxygen demand (BOD) but also promote nitrification during BOD measurement due to nitrifying microorganisms contained in a large amount in SS, thereby increasing the BOD of the treated water. Sand filtration is to achieve the advanced treatment of organic matter by removing SS in the secondary treatment water, and methods such as contact aeration, flocculation (sedimentation or flotation), and adsorption of activated carbon are to remove colloidal and soluble organic substances at the same time. . Sand filtration uses upflow or downflow, and the filtration rate is 4-6m 3 / m 2 · h as standard, and activated carbon adsorption is the space velocity (SV) as 4-6m 3 / m 2 · h. Coagulation sedimentation is often used in combination with phosphorus removal and is rarely used in small and medium-sized sewage treatment facilities for the purpose of advanced treatment of organic materials (BOD, COD).

In addition, as the nitrogen removal technology, there are methods such as biological nitrification, denitrification, and ammonia stripping. In the case of small and medium-sized sewage treatment facilities, biological nitrification and denitrification are mainly used, and coagulation separation (sedimentation and flotation) is used. ), Crystallization, ion exchange, postrip, and biological removal. Coagulation sedimentation is used in most small sewage treatment facilities.

In accordance with the above-described trend, the present invention has a high removal efficiency of nitrogen, phosphorus, etc., as well as a small amount of sludge generation, strong against impact loads and load fluctuations (water quality and quantity fluctuations), and easy maintenance. It is a technical problem to provide a wastewater treatment apparatus and method.

In the study of the present inventors to solve the above problems, the contact oxidation process is adopted for the merger purification tank process that is resistant to impact load and load fluctuation, and the existing contact based on the result of the comparison of the characteristics of the sewage characteristics and the adhesion media by the source The oxidation process was improved, and the reaction tank process itself was improved to improve shock load buffering capacity and to improve organic matter, nitrification and denitrification efficiency.

1 illustrates a preferred embodiment of the present invention.

Apparatus schematically showing a contact oxidation type wastewater treatment apparatus for a combined septic tank.

2 is a wastewater treatment system diagram of the apparatus of FIG. 1;

3 shows the experiments of the examples

Plots of changes in BOD concentration and removal rates during operation.

4 is a BOD during the driving period in the experiment of the embodiment

Graph of concentration change and runoff BOD concentration.

5 shows the BOD volume load in the experiments of the Examples.

A plot of the effluent BOD concentrations along.

6 shows the experiments of the examples

A plot of the change in COD concentration and removal rate during the run.

7 is a diagram illustrating the operation period during the experiment of the embodiment.

Graph of COD concentration change and effluent COD concentration.

8 shows the COD volume load in the experiments of the Examples.

A plot of effluent COD concentrations along the way.

9 is a diagram illustrating the operation period during the experiment of the embodiment.

Graph of SS concentration change and removal rate.

Figure 10 shows the period of operation during the experiment of the embodiment

Plot of T-N concentration change and removal rate.

Figure 11 shows the periods of operation during the experiments of the examples.

Graph of BOD concentration change and effluent T-N concentration.

12 shows the BOD volume load in the experiments of the Examples.

A plot of the effluent T-N concentration along.

Figure 13 shows the periods of operation during the experiments of the examples.

Plot of T-P concentration change and removal rate.

According to the present invention to solve the above problems, the contact oxidation type wastewater treatment apparatus comprising: a flow rate adjusting tank; A reaction tank consisting of an anaerobic tank, an anaerobic tank and aeration tank; A degassing tank and a settling tank; The anaerobic tank and the anaerobic tank is composed of an upflow (upflow) type tank by the porous diaphragm at the top of the anaerobic tank, the bottom is composed of anaerobic tank; The flow adjusting tank is connected to the anaerobic tank through the supply line, the anaerobic tank is connected to the aeration tank through the supply line, the aeration tank is connected to the settling tank through the supply line and connected to the degassing tank through the return line, the degassing tank is returned It is connected to the anaerobic tank through the line, the lower end of the settling tank is provided with a contact oxidation type wastewater treatment apparatus for a combined purification tank, characterized in that connected to the anaerobic tank.

According to the present invention, the aeration tank is composed of a first aeration tank and a second aeration tank, and the volume ratio of the first aeration tank to the second aeration tank is 5: 5 to 7: 3, the contact oxidation type wastewater treatment for the combined purification tank. An apparatus is provided.

In addition, according to the present invention, there is provided a contact oxidation type wastewater treatment apparatus for a combined septic tank, characterized in that the filling rate of the filter medium filled in the aeration tank is 30 to 45%.

Further, according to the present invention, there is provided a contact oxidation type wastewater treatment apparatus for a combined purification tank, characterized in that a wastewater treatment means for phosphorus removal is additionally provided.

According to the present invention, there is provided a contact oxidation type wastewater treatment method for a combined purification tank, characterized in that the wastewater is treated in the wastewater treatment apparatus.

In addition, according to the present invention, in order to obtain effluent water having a BOD concentration of 10 mg / L or less, a COD concentration of 40 mg / L or less, and a TN concentration of 20 mg / L or less, the BOD volume load is maintained at 0.2 kg BOD / m 3 / day or less, and the COD Provided is a contact oxidation type wastewater treatment method for a combined septic tank, characterized by maintaining a volume load of 0.4 kg COD / m 3 / day or less.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

1 shows a contact oxidation type wastewater treatment apparatus for a combined purification tank according to a preferred embodiment of the present invention. The illustrated device includes a flow rate adjusting tank 10, an anaerobic tank 21, an oxygen-free tank 22, an aeration tank 30, a degassing tank 40, and a settling tank 50.

Here, the anaerobic tank 21 and the anaerobic tank 22 is divided into a single tank 20 in the form of upflow (upflow) by the porous diaphragm 23, the upper end is composed of an anaerobic tank 22, the lower end anaerobic tank ( 21). Anaerobic and anaerobic tanks should be designed to shut off the air supply. Anaerobic and anaerobic tanks are also equipped with warming means (not shown).

In addition, the aeration tank 30 may be installed in one or a plurality of tanks, and preferably, divided into a first aeration tank 31 and a second aeration tank 32 by a partition 33 capable of fluid communication, as shown. will be. At this time, it is preferable that the first aeration tank 31 and the second aeration tank 32 are divided into a ratio of 5: 5 to 7: 3, preferably 6: 4, so that organic matter removal and nitrification are performed in each tank. Moreover, although the filling factor of the aeration tank 30 changes with the form of a filtering medium, about 30 to 45%, More preferably, 35 to 45% is suitable. If the filter medium filling rate is too low, the wastewater treatment efficiency is poor, if the filter medium filling rate is too high, the wastewater treatment efficiency does not increase any more, the installation cost is increased, and even the wastewater treatment efficiency may be reduced. The air blower 34 is installed in the aeration tank.

The flow rate adjustment tank 10 is connected to the anaerobic tank 21 through the supply line (L1), the anaerobic tank 22 is connected to the aeration tank 30 through the supply line (L2), the aeration tank 30 is the supply line It is connected to the settling tank 40 through (L3) and connected to the degassing tank 50 through the conveying line (L4), the degassing tank 50 is connected to the anaerobic tank through the conveying line (L5), the settling tank (40) The bottom of the is connected to the anaerobic tank 21 through the sludge conveying line (L6).

The flow rate adjusting tank 10, the anaerobic tank 21, the anoxic tank 22, and the degassing tank 40 are each equipped with a stirrer driven by the motor M.

The apparatus may additionally be equipped with wastewater treatment means for phosphorus removal.

Examples of such means include agglomeration separation (sedimentation, flotation) means, crystallization dephosphorization means, ion exchange means, postrip (Phostrip) means, biological phosphorus removal means and the like.

2 shows a process flow diagram in the FIG. 1 apparatus. Referring to the wastewater treatment method of the present invention with reference to the treatment system diagram of Figure 2, first, the influent water is supplied to the flow rate adjustment tank after removing the floating garbage through the screen. The influent supplied to the flow control tank is fed to the anaerobic tank in a fixed quantity and treated in an anaerobic tank. The water treated in the anoxic tank is treated while passing through the first and second aeration tanks, and then some are supplied to the settling tank and some are supplied to the degassing tank. The water supplied to the degassing tank is degassed after being air stripped and retreated with anoxic acid, and the water supplied to the sedimentation tank is discharged after sedimenting the sludge, and the sludge deposited in the sedimentation tank is supplied again to the anaerobic tank for treatment. .

By using this method, the BOD volume load is kept below 0.2 kgBOD / m 3 / day in order to achieve a BOD concentration of 10 mg / L or less, a COD concentration of 40 mg / L or less, and a TN concentration of 20 mg / L or less. It is desirable to maintain the COD volume load at 0.4 kg COD / m 3 / day or less.

Hereinafter, the treatment efficiency according to the change of organic load (volume load) of the catalytic oxidation tank process using the biofilm according to the present invention and the treatment efficiency according to the change in the hydraulic residence time (HRT) in the reaction vessel are verified, and the applicability to the merger purification tank is as follows. The present invention will be described in more detail on the basis of the experiments performed for the purpose.

EXAMPLE

1. Experiment apparatus and operation

(1) Experiment apparatus

One set of laboratory scale reactors were made of transparent acrylic to determine the organic and nutrient removal characteristics. Figure 1 illustrates the combined purification tank reactor used in the experiment. The reactor consisted of anaerobic tank, anaerobic tank and aeration tank. The effective capacity of each reactor was 4.17L, 2.08L, 16.67L and the total capacity was 22.92L. The media used in the experiments were the media of Daehosan-si, and the median filling rate was 35%.

In addition, the anaerobic tank and the anaerobic tank is an upflow type single reactor and the upper end is anoxic tank, and the lower end is composed of an anaerobic tank. In addition, the aeration tank was divided into 6: 4 ratios so that organic matter removal and nitrification were performed in each tank. Sewage injection and internal conveyance were continuously injected using a small amount of fixed amount (Masterflex Tubing Pump). The anaerobic and anaerobic tanks cut off the air supply and gently mixed by using a reduction motor, and the aeration tank was an air blower. Was installed to maintain complete mixing and proper DO concentration.

(2) reactor operation

The reaction was carried out under the specifications and operating conditions of each reactor as shown in Table 1. The reactor volumes were fixed at 4.17 L, 2.08 L and 16.67 L, respectively, and the influent flow rates were 50 L / day, 40 L / day, 33.3 L /. The optimal HRT was calculated by changing the hydraulic residence time (HRT) at 1 hour, 13.75 hours, 16.5 hours, and 22 hours during the day and 25 L / day. The return for denitrification was 100%, and the degassing tank could be separately installed to reduce the effect of the oxygen free tank due to the high DO concentration in the reaction water. Sludge conveyance was not carried out because the sludge actually generated was insignificant. The temperature during the operation ranged from 13.6 to 16.5 ° C.

division Anaerobic tank Anaerobic Abandonment Reactor Volume (L) 4.17 2.08 16.67 HRT (hr) 11 2 One 8 13.75 2.5 1.25 10 16.5 3 1.5 12 22 4 2 16 Recycle (%) 100 Temperature (℃) 13.6 ~ 16.5 ℃

(3) Influent sewage

Table 2 shows the characteristics of the C Logistic Center wastewater used in the experiment. The inflow sample was collected directly from the simple storage tank of the C General Logistics Center and transported to the storage tank and then transferred to the storage tank.In the storage tank, the agitator was installed to eliminate the effects of sedimentation. A metering pump was used. In the case of SS, 102.5 ~ 305.2 mg / L and COD were 170.1 ~ 409.2mg / L. The BOD / T-N ratio was in the range of 2.3 to 5.7, and the BOD / T-P ratio was 16.4 to 31.0.

Item Concentration (mg / L) range Average pH 6.7-7.6 7.11 SS 102.5-305.2 200.1 VSS 95.2-256.0 177.7 TCODcr 170.1-409.2 282.0 SCODcr 69.5-137.5 107.6 TBOD 99.5-127.3 159.7 SBOD 47.5-116.5 80.1 T-N 17.5-87.0 53.0 T-P 4.2-11.5 6.4 Alkalinity 109.5-342.5 226.5 BOD / T-N 2.3-5.7 3.0 BOD / T-P 16.4-31.0 24.5

(4) Analysis method

The water analysis method used in this experiment was based on the standard method and the test method for environmental pollution process in Korea, and the analysis method for each item is shown in Table 3. The sample was analyzed by inflow, treated water and final effluent at daily intervals.In the case of BOD experiment, Formula 2533 was used as Nitrification Inhibitor to exclude oxygen consumption by nitrification. (HACH Co., Ltd.) was added to carry out.

Item Analytical Methods and Instruments pH ORION 230A, pH meter DO YSI Model 57 Oxygen Meter TBOD Winkler Method Azide Modification SBOD Filtration and Winkler Method Azide Modification TCODcr K ₂ Cr ₂ O ₇ Closed Reflux Method SCODcr Filtration and K ₂ Cr ₂ O ₇ Lung Reflux SS Gravimetric Method, Electric Dry Oven (105 ° C) VSS Gravimetry, Electric Muffle Furnace (550 ° C) Alkaline Titration Method T-P Persulfate Digestion and Ascorbic Acid Methods S-P Filtration, Persulfate Dipping and Ascorbic Acid Methods TKN Micro Kjeldahl Method NO ₂ -N Diazo Method NO ₃ -N Brucine Method NH ₃ -N Phenate Method

2. Results and Discussion

In the early stage of operation, it took about 10 days for the microorganisms to fully adhere to the media and adapt to the environment, and about 14 days for nitrification. Up to this period, the total hydraulic residence time (HRT) was fixed at 13.8 hr, and from 26 days when nitrification was sufficient, it was operated at 11 hr HRT. However, due to the high organic load, the nitrification rapidly decreased and the HRT was increased to 16.5hr. As a result, nitrification occurred to some extent, but the concentration was only about 4.66 mg / L. HRT was increased to 22 hr again for high nitrogen removal rate, and the return was carried out at the return rate of 100% from day 43.

And, the sample for analysis was taken out of the natural runoff, anaerobic tank and anaerobic tank consists of a single reactor of the upflow type, the anaerobic tank located at the bottom omitted the analysis due to the loss of microorganisms in the reaction tank due to sampling. In addition, the aeration tank is designed to move the reactor to the lower part in the ratio of 6: 4 to separate organic matter and nitrification. However, due to the mixing caused by abandonment, there was almost no difference between the front and rear end of the sample analysis. Therefore, the aeration tank effluent was collected and analyzed.

(1) organic matter removal characteristics

The organic concentration changes and average removal rates during the run are shown in Table 4. For BOD, the runoff concentration for each HRT was 17.4 mg / L. 26.6 mg / L, 16.5 mg / L, 7.6 mg / L and the removal rates at that time were 84.8%, 88.5%, 91.9%, 94.7%. For COD, the runoff concentrations were 34.3 mg / L, 57.1 mg / L, 42.7 mg / L, and 40.0 mg / L. The removal rates were 84.8%, 85.0%, 87.1%, and 85.2%. In the case of SS, the effluent concentrations were 6.7mg / L, 11.2mg / L, 11.7mg / L, and 10.9mg / L. The removal rate was 95.9%, 95.6%, 95.0%, and 94.1%. The BOD Volumetric Loading Rate was calculated as 0.21, 0.51, 0.31, 0.20 kgBOD / m3 / day during the operation period.

division BOD COD SS VLR ^* (kgBOD / ㎥ / day) Onset HRT: 13.8hr Inflow (mg / L) 121.9 231.0 168.6 0.21 Runoff (mg / L) 17.4 34.3 6.7 % Removal 84.8 84.8 95.9 HRT: 11 hr Inflow (mg / L) 234.7 380.9 262.9 0.51 Runoff (mg / L) 26.6 57.1 11.2 % Removal 88.5 85.0 95.6 HRT: 16.5hr Inflow (mg / L) 211.4 337.6 236.3 0.31 Runoff (mg / L) 16.5 42.7 11.7 % Removal 91.9 87.1 95.0 HRT: 22 hr Inflow (mg / L) 145.4 271.4 191.4 0.2 Runoff (mg / L) 7.6 40.0 10.9 % Removal 94.7 85.2 94.1

* The load for the total reactor volume was calculated.

end. BOD removal characteristic

The graph of FIG. 3 plots the organic matter removal characteristics of the BOD concentration change during the operation period. BOD removal rate was over 90% from 16.5hr residence time during the operation. In addition, looking at the graph of Figure 4 and the graph of Figure 5 in order to maintain the BOD concentration of the effluent to 10mg / L or less appeared to maintain the BOD volume load of 0.20 kgBOD / ㎥ / day or less.

I. COD removal characteristics

The graph of FIG. 6 plots the COD concentration change and removal rate during the reactor operation period. In the case of COD, there was no difference in removal rate according to residence time, unlike BOD, and the average removal rate was 85.5%. 7 and 8 show that the COD volume load should be maintained at about 0.4kgCOD / m 3 / day or less to maintain the effluent COD concentration below 40 mg / L.

All. SS removal characteristic

The graph of Figure 9 plots the SS concentration change and removal rate during the operation period. SS removal rate was 95.2% on average regardless of the retention time, and the effluent concentration ranged from 4.3 mg / L to 15.3 mg / L and 9.4 mg / L on average.

(2) nitrogen removal characteristics

Table 5 shows the change in TN concentration and removal rate during the reactor operation. Mean COD / TN ratios by residence time during operation were 6.5, 5.8, 5.0, 5.4, and 4.9. Nitrogen removal rates were low at 25.0%, 26.1%, and 35.3% at 11hr and 16.5hr. After that, the residence time was increased to 55.4% at 22hr and further increased to 69.5% after the start of conveyance. The reason for the increase to 55.4% even without the return is due to the denitrification in the thickened biofilm in the aeration tank due to the amount of NH ₃ degassed in the aeration tank and the characteristics of the biofilm method.

division T-N Inflow (mg / L) Runoff (mg / L) % Removal COD / T-N On start (HRT: 13.8hr) 41.6 31.21 25.0 6.5 HRT: 11hr 67.2 49.7 26.1 5.8 HRT: 16.5hr 68.9 44.8 35.3 5.0 HRT: 22hr No return 49.8 22.3 55.4 5.4 Return (100%) 55.7 17.0 69.5 4.9

Figure 10 is a plot of the T-N concentration change and removal rate during the reactor operation period. During the operation period, the removal efficiency was insignificant due to the high organic load, and the removal efficiency was insignificant due to the high organic load, and the retention time was increased to 22hr, resulting in more than 50% of the TN removal rate in the non-conveying operation. Was investigated. As can be seen in the graphs of Figures 11 and 12 it can be seen that in order to maintain the T-N concentration of the effluent to 20mg / L or less, the BOD volume load should be maintained below 0.2kgBOD / ㎥ / day.

(3) Phosphorus Removal Characteristics

T-P and S-P concentration changes and removal rates during the reactor operation are shown in Table 6 and the graphs of FIG. 12. In case of TP, effluent concentration by residence time was 5.6mg / L, 7.1mg / L, 8.3mg / L, 5.6mg / L, 5.1mg / L, and removal rate was 6.6%, 8.5%, -6.6%, 6.4 The removal rate was very low at 14.8%. In the case of S-P, the effluent concentrations were 5.1 mg / L, 6.7 mg / L, 7.6 mg / L, 5.2 mg / L, and 4.6 mg / L.

In the case of no transport, the phosphorus removal rate is very low or the increase of the phosphorus concentration in the effluent is caused by the elution of phosphorus in the anaerobic tank and the presence of a substrate available for phosphorus accumulation bacteria (PAO) in the anaerobic tank. Phosphorus elution occurred again, due to the nature of the biofilm process in the aerobic tank, phosphorus intake takes place in the aerobic layer on the surface of the biofilm, but phosphorus elution occurs in the anaerobic layer inside the biofilm, and microbial accumulation occurs in aerobic conditions.

In addition, Gerber (1986) and others studied the relationship between organic substrates, nitrates, and phosphorus in biological nutrient removal processes. If present, phosphorus elution may be known and phosphorus elution may occur depending on environmental conditions even in aerobic conditions. Phosphorus content of microorganisms in the general biological treatment system is about 1.5-2% by dry weight, and it was difficult to see enough uptake of phosphorus to 1.4% when a part of the microorganisms in the aeration tank was collected and tested.

On the other hand, in the conveyed state, the removal rate of TP increased to 14.8% and the SP concentration of the effluent decreased compared to the influent, which was caused by the increase of DO concentration and nitrate nitrogen concentration in the anaerobic tank due to the return of the aeration tank effluent. Judging. Kern-Jeepersen Henze (1993) also studied phosphorus intake under anaerobic and aerobic conditions and found that oxygen or nitrate could be used as an electron donor in the presence of oxygen or nitrate in anoxic conditions. It has been announced. Biological removal means accumulation as an energy source in microbial cells rather than removal by substantial conversion of phosphorus, and in the exact sense phosphorus removal can be achieved by discarding excess sludge. In this process, the amount of sludge generated is very small to remove excess sludge and phosphorus by biofilm method. Therefore an impulsive removal process is required.

division T-P S-P Inflow (mg / L) Runoff (mg / L) % Removal Inflow (mg / L) Runoff (mg / L) % Removal On start (HRT: 13.8hr) 6.0 5.6 6.6 4.9 5.1 -6.8 HRT: 11hr 8.1 7.1 8.5 6.9 6.7 -5.3 HRT: 16.5hr 7.8 8.3 8.3 7.2 7.6 -5.5 HRT: 22hr No return 5.9 5.6 5.6 4.7 5.2 -11.0 Return (100%) 6.1 5.1 5.1 5.2 4.6 10.2

Waste water treatment apparatus and method of the present invention as described above is excellent in shock load buffering capacity, excellent in organic matter, nitrification, denitrification efficiency, and the amount of sludge generated is very small, there is no problem of sludge disposal and easy maintenance. Has the advantage.

Claims (6)

A flow rate adjusting tank 10; A reaction tank composed of an anaerobic tank 21, an anaerobic tank 22, and aeration tank 30; A degassing tank 40 and a settling tank 40; The anaerobic tank and the anaerobic tank is composed of an upflow (upflow) single tank 20 by the porous diaphragm 23, the upper end is composed of an anaerobic tank, the lower end is composed of anaerobic tank; The flow adjusting tank is connected to the anaerobic tank through the supply line, the anaerobic tank is connected to the aeration tank through the supply line, the aeration tank is connected to the settling tank through the supply line and connected to the degassing tank through the return line, the degassing tank is returned In the contact oxidation type wastewater treatment system for the combined purification tank connected to the anaerobic tank through the line and the bottom of the settling tank connected to the anaerobic tank through the sludge return line. In order to obtain effluents having a BOD concentration of 10 mg / L or less, a COD concentration of 40 mg / L or less, and a TN concentration of 20 mg / L or less, the BOD volume load is kept at 0.2 kg BOD / m 3 / day or less, and the COD volume load is 0.4 kg COD / Contact oxidation type wastewater treatment method for a combined septic tank, characterized in that it is maintained at ㎥ / day or less. delete delete delete delete delete