JPS6048239B2 - wastewater treatment equipment - Google Patents

Description

[Detailed description of the invention] The present invention relates to a wastewater treatment device using activated sludge.

Wastewater treatment technology using activated sludge is gradually becoming popular, but the removal rate of nitrogen and phosphorus from wastewater is extremely low with any treatment technology, generally 30% for the former and 10% for the latter.
It is about %.

Therefore, once treated water treated by the conventional activated sludge method is discharged into a river etc., algae, for example, use the residual nitrogen and phosphorus as nutrients, while absorbing sunlight and carbon dioxide in the air. They were used to breed in large numbers and became a pollutant in rivers and other areas.

The present invention utilizes the nitrification and denitrification effects of bacteria in activated sludge to continuously remove nitrogen from wastewater with high efficiency and at low cost, without requiring the addition of organic compounds as hydrogen donors. Some companies are trying to provide a wastewater treatment system that can obtain the desired results.

Treatment conditions: The present invention converts organic nitrogen and ammonia nitrogen (N-N) into nitrate nitrogen (NO).

-N) and the nitrification process to convert it into nitrate nitrogen (NO.
-N) to nitrogen (N), a denitrification process that involves two biological reactions that require completely different biological culture conditions. Therefore, the wastewater treatment conditions of the present invention will be described below, divided into three parts: (1) nitrification process, (2) denitrification process, and (3) circulation speed of the wastewater-sludge mixture. In addition, NO in the following experiment. -N is based on the nitrate pursin method (edited by Japan Sewage Works Association: Sewage Test Methods), and NH3-N is based on the indophenol method J. ROdier；Anal
ysisOfwater, Paho 116, (1975)
, JOhnwily & SOn, Newy Ork -
It was then measured. (1) Nitrification step: This step preferably has a high activated sludge concentration and is under aerobic conditions.

The reason is explained below. Synthetic wastewater with the composition shown in Table 1 was mixed with activated sludge concentration. (Hereinafter referred to as MLSS.

MLS is expressed as the weight of the sediment obtained by ultracentrifuging a certain amount of a mixture of wastewater and sludge at 10' x G for 5 minutes. However, G indicates gravitational acceleration. ) is 43
Using activated sludge of 347 TL da/l, the cycle was carried out at pH 7.4 and temperature of 22.0'C. Biological nitrification treatment was carried out using a fractionation method. The results are shown in FIG. In addition, C in Table 1
ODcr indicates chemical oxygen demand measured based on the potassium chromate method, and TKN indicates total nitrogen. (However, TKN = (NH3-N) + (organic nitrogen)) As shown in the figure, organic nitrogen in wastewater changes to ammonia nitrogen (NH.-N) and nitrate nitrogen (NO3) through biological nitrification reaction. −
It can be seen that it is being converted into N). NH3-N
The decrease in NO3-N and the increase in NO3-N can be approximated by a nearly zero-order reaction. Because NH. - The rate of decrease in N concentration is NH. - It becomes slow below NLOm9/l, so to be exact, Michaelis-Menten (Michaelis-Menten)
Therefore, the following equation (4) can be derived. Now, NH. -N concentration is Sm9/l, sludge concentration is Xm9/l, and NH. If the specific decreasing speed of -N is ν, then the following equation holds true. 1dsvmS ν= −ーー − ・・・・・・・・・・・・・・・・・・
...(1)XdtKm+S where Km is sludge NH3-
It is an affinity constant for N, and is a small value of 1 ppm or less.

Therefore, the relationship between Km and S is as shown in equation (2). K
m<<S ・・・・・・・・・・・・・・・・・・・・・
- (2) From equations (1) and (2), equation (3) holds true.

1DSν = Matarako νm ゜ ゜ ゜ ゜ ゜ ゜ ゜ ゜ ゜ ゜ ゜ ゜ ゜ ゜ ゜ ゜ ゜ ゜ ゜ ゜ ゜ (3) Equation (4) is obtained.

Ds −■=νMX・・・・・・・・・・・・・・・・・・(
4) Formula (4) is NH.

-The rate of decrease of N is NH. - It can be approximated as a zero-order reaction that is unrelated to the N concentration, and it is shown that it is proportional only to the sludge concentration. In other words, increasing the sludge concentration is an essential condition for increasing the biological nitrification rate. Therefore, next, a biological nitrification experiment was conducted while maintaining the MLSS concentration at a high concentration of 10,000 mg/l or more, and it was confirmed that the above inference was valid.

Figure 2 shows the nitrification results. The wastewater used in this experiment was similar to the above, synthetic wastewater mainly containing peptone and meat scratches (CODcl=500TrL, /', TKN=85m9
/'). In this nitrification experiment, the solid-liquid separation tank S was equipped with a filter F as shown in Fig.
This was carried out continuously using a device installed in a nitrification tank (capacity 6.8e). In addition, the mixed liquid in the nitrification tank contains 51/Mjn.
Aeration was performed to maintain the dissolved oxygen concentration DO at 0.5 to 7 ppm.

The experimental results are shown in Figure 2. The quantitative ratio between the chemical oxygen demand CODO and the activated sludge amount SS in the steady state (August 3 to August 9, 197 years), so-called CODc. -SS load was 0.14 kg C0D0r/K9 MLSS Day, and MLSS concentration was 14000 mg/e. When the activated sludge with the inflow total nitrogen concentration of TKN was subjected to a nitrification reaction, the treated water contained a high concentration of NO3-N, and at the same time, a low concentration of NH3-N of 0.5 ppm or less was detected. The proportion of the inflowing total nitrogen TKN that was oxidized to nitrate nitrogen NO3-N, that is, the nitrification rate, was 90 to 100%, as shown by the dotted line in FIG. C
The removal rate of ODc was about 90%.

In addition, since the nitrogen form of the synthetic wastewater mainly composed of meat industry scratches and peptone used in the above experiment was more than 99% organic nitrogen, the inflow total nitrogen TKN can be regarded as the inflow total nitrogen TOtal - N. can. Therefore, the nitrification rate was expressed as the ratio of NO3-N in the treated water to TKN in the influent wastewater. Here (TOtal-N) = (TKN) + (NO3-
N)+(NO2-N). From the above experimental results, it can be said that it is preferable to increase the activated sludge concentration in the wastewater nitrification process and maintain the aerobic method, for example, the dissolved oxygen concentration DO at 0.5 to 7 ppm.

In addition, when the activated sludge concentration is as high as 60,000 mg/e, the oxygen supply during the nitrification process cannot keep up with the oxygen consumption rate of the sludge microorganisms, and there is a risk that the specified aerobic conditions cannot be maintained. be.

Therefore, the concentration of activated sludge in the nitrification process is 5000 m
g/e~30000mg/f1 preferably 8000mg
/f~1500mg/e is recommended. (2
) Denitrification process: In this process, if the process is anaerobic and the activated sludge concentration is made high, the denitrification reaction can occur sufficiently without supplementing a C source from outside the system. The reason for this will be explained below. Denitrification tests were conducted by varying the CODO and -SS loads.

The results are shown in FIG. MLSS of activated sludge used
The concentration is 5000mg/e1, the concentration is 20'C, and the pH is 8.
It was 0 to 8.5. Also, the dissolved oxygen concentration DO in the denitrification tank
was maintained at 0 ppm. The numbers in parentheses in the figure indicate the C/N ratio. By adding, for example, methanol as a C source, the COD c. - As the SS load (hereinafter referred to as L) is increased, the denitrification rate Ud increases, as is clear from FIG.

From FIG. 3, L. The relationship with l5Ud is expressed by equation (5). When L is larger than 0.26 (VCODO, /YM?S·Y), Ud is constant, and is expressed by equation (6). On the other hand, when L is O, that is, when no C source is added at all, Ud is shown as the following value.

This value is the denitrification rate due to sludge self-decomposition. Equation (7) above indicates that activated sludge has the property of denitrifying NO3-N through self-decomposition of the sludge under anaerobic conditions such as in the denitrification process, even when no C source is added. It shows.

Therefore, the amount of added carbon is now C (weight of carbon atoms q/Da
y), and the total sludge amount is X(QM?S), L is C. l
5X ratio (L = daily inflow CODe, / total sludge volume =
C/X), the above formula (5) is expressed as formula (8).

Here, if only the sludge amount is multiplied by n, equation (9) is obtained.

This equation (9) shows that when the amount of sludge is increased by n times (n is a natural number), the amount of NO3-N removed per unit sludge decreases.

By the way, the amount of denitrification per day Ru MNO-NremOVed(t) The amount of sludge is X and D
ay), from equations (8) and (9) respectively, the following equation (
10) and (11).

Ru=UdxX=205C+9.5X・・・・・・・・・
・・・・・・・・・(10tRu=UdxnX=205C+
9.5nX...(11).

Therefore, the increase amount ΔRu in the daily denitrification amount Ru is (
11) According to (10), it is expressed by equation (12). ΔR
u=9.6(n-1)X ・・・・・・・・・(12)
In the end, by increasing the amount of sludge, the amount of denitrification increased by the amount caused by sludge self-decomposition. Therefore, the inventors believe that if the denitrification process is maintained anaerobically and high-concentration activated sludge is used, the inflow wastewater supplied from outside the system to this deoxidation process will be deoxidized due to self-decomposition of the sludge. Because of the nitrogen properties, it was thought that sufficient denitrification could be achieved without adding a C-source.

Below, we will show that this inference holds true in an actual denitrification reaction when the activated sludge concentration was 950, which is approximately twice that in the above experiment.
Proof using 0 mg/l sludge.

．． The conditions for the denitrification test are as follows. Capacity of denitrification tank ・・・・・・・・・・・・4.951 Dissolved acid concentration (
DO)・・・・・・・・・・・・0ppm Inflow NO.

-N ・・・・・・・・・・・・Approx. 80ppm Inflow wastewater amount ・・・・・・・・・・・・0.751/HrC/N
Ratio・・・・・・・・・0.4～1.3Temperature・
・・・・・・・・・・・・25゜CMLSS・・・・・・
・・・・・・The results of the 9500y/l experiment are shown in Figures 4 and 2.
Shown in the table.

For complete denitrification, the MLSS concentration must be 5000 m
In the case of 9/l, as is clear from Fig. 3, the C/N
The ratio must be 1.7 or more, but when the MLSS concentration is 9500 m9/l, the C/N ratio may be 1.3, as is clear from FIG.

This indicates that supplementary carbon sources can be saved by increasing the sludge concentration. Table 2 shows the above experimental results in comparison with the Ud value calculated from the above equation (5).

According to Table 2, the C/N ratio is 1.0 and 1.3, respectively.
In this case, the calculated value and the measured value of Ud are extremely similar.

Therefore, it has become clear that the above formula (5) holds true in an actual denitrification reaction. (3) Circulation speed: The circulation speed Qr at which the wastewater-sludge mixture in the denitrification process is circulated to the nitrification process is 1 to 8 times, preferably 3 times, the flow rate Q at which the treated water flows out of the system from the solid-liquid separation process. It is set to ~5 times.

The reason is explained below. In the denitrification process, the following biological reactions occur due to activated sludge microorganisms. If the wastewater sludge mixture is not circulated from the denitrification process to the nitrification process, not only will the nitrification-denitrification system not be established, but the circulation rate will be
Unless r is chosen to be quite large, the product NH from the above biological reaction.

-N flows out of the system as it is, and as a result, the efficiency of removing nitrogen from wastewater decreases. In addition, if the wastewater-sludge mixture is not circulated and the sludge is left in an anaerobic state for a long period of time, the settling properties of the sludge will deteriorate, making it impossible to reuse the sludge, so a stable wastewater treatment system must be established. I won't be able to do that. Therefore, it is preferable to select the return speed Qr of the wastewater-sludge mixture as large as possible.
, 2 and 3, when the return rate Qr is increased from 3 times to 5 times the amount of treated water Q, the nitrogen removal rate is 84
．． There is no significant increase, only an increase of about 5.6%, from 2% to 89.8%.

Furthermore, the setting of the circulation speed Qr depends on the economic efficiency of the circulation pump, the concentration of wastewater components, and the C/N ratio in the wastewater. Therefore, it is effective to set the circulation rate Qr to IQ-8Q), preferably Ω to 1000m. Therefore, in the wastewater treatment of the present invention, (a) feeding inflow wastewater to the denitrification process, (b) using highly concentrated activated sludge in both the nitrification and denitrification processes, and (c) ) the nitrification step is maintained under aerobic conditions with a dissolved oxygen concentration of 0.5 to 7 ppm), preferably 3 to 5 ppm; (d) the denitrification step is maintained at a dissolved oxygen concentration of 0.5 to 7 ppm;
(e) Maintaining anaerobic conditions at 0.5 ppm or less; (e)
The wastewater-sludge mixture in the denitrification process is 1 to 8 times the amount of treated water Q that flows out of the system from the solid-liquid separation process, preferably 3 to 8 times.
By meeting the conditions of recycling to the nitrification process five times faster, nitrogen, biological oxygen demand (BOD) and Chemical oxygen demand (CODcr and CODMn) can be removed.

However, CODMn indicates the chemical oxygen demand measured based on the potassium permanganate method. Examples of the wastewater treatment method and apparatus of the present invention are shown below.

Example 1 Plugflow type nitrification tank
A nitrification tank (capacity 6.81) was used, and a complete mixing type denitrification tank (capacity 7.01) was used as the denitrification tank.

Synthetic wastewater having the composition shown in Table 1 above was mixed with an MLSS concentration of about 1.
Using activated sludge of about 170 Da at 2000 m9/l, the temperature is 2.
Processing was carried out at 0°C. The treatment method is to process the above synthetic wastewater into
．． 017/. Denitrification process (DO: 0ppm
). The sludge-wastewater mixture in the denitrification process is 3.0
Nitrification process at a ratio of 1/Mjn (aeration rate 5.01/Min
, DO4-7ppm). This return rate, that is, the sludge-wastewater mixture circulation rate Qr, is the same as that in the denitrification process.
This corresponds to three times the amount Q of treated water discharged outside the system from the subsequent solid-liquid separation step (at the same rate as the amount of inflow wastewater). The processing results are shown in Table 3. As shown in Table 3 above, TO in the treated water
tal-N is 13.7 m9/l, and the TO of influent wastewater
84.2% of 86.9 mg/l of tal-N was removed.

CODcr and CODMn are 93.2 and 92 respectively
．． 2% has been removed. In addition, total nitrogen TOtal-N
is (TOtal-N) (TKN) + (NO2-N)
+ (NO3-N) is displayed. Example 2 Synthetic wastewater having the composition shown in Table 1 above was mixed with an MLSS concentration of about 1
Using activated sludge of 2000m9/l of approximately 168 da
It was treated at 0°C.

The treatment method was the same as in Example 1 above, but in Example 2, a treatment experiment was conducted with Qr=4Q. The treatment results are shown in Table 4. As shown in Table 4 above, TOtal-N in the treated water is 12.6 mg/l, and TOtal-N in the influent wastewater is 89. 86.0 of Omg/l
% has been removed.

CODc and CODMn are 93.7% and 9, respectively.
2.0% has been removed. Example 3 Synthetic wastewater having the composition shown in Table 1 above was treated with an MLSS concentration of about 120
The treatment was carried out using approximately 165 da of activated sludge of 00 m9/l at a temperature of 20°C.

In this case, Qr was adjusted to Qr=ω and a processing experiment was conducted. The treatment results are shown in Table 5. As shown in Table 5 above, 89.8% of TOtal-N in the influent wastewater was removed. Furthermore, 93.5% and 93.0% of CODc and CODMn were removed, respectively. Example 4 Synthetic wastewater having the composition shown in Table 1 above was treated with an MLSS concentration of 8000.
The treatment was carried out using 110 mg/l activated sludge at a temperature of 20'C.

In this case, the treatment experiment was conducted by adjusting Qr to Qr=pounds. The treatment results are shown in Table 6. As shown in Table 6 above, 82.5% of TOtal-N in the influent wastewater was removed.

Also, CODcr and CODMn are each 91.0.
% and 90.0% were removed. Example 5 Synthetic wastewater having the composition shown in Table 1 was treated with an MLSS concentration of 1500.
The treatment was carried out using 210 da of activated sludge of 0 m9/l at a temperature of 20°C.

In this case, the treatment experiment was conducted by adjusting Qr to Qr=pounds. The treatment results are shown in Table 7. As shown in Table 7 above, 91.0% of TOtal-N in the influent wastewater was removed.

Also, CODc and CODMn were each 94.0%.
and 93.2% were removed. Example 6 FIG. 5 shows a schematic diagram of the wastewater treatment apparatus of the present invention.

This device is a denitrification tank D (capacity 7.
01), a nitrification tank N (capacity 6.81) for performing biological nitrification having an inflow end N1 with a valve V2 for returning the wastewater-sludge mixture from the denitrification tank D, and a nitrification tank N (capacity 6.81) provided in the denitrification tank D. , a solid-liquid separation tank S that separates solid and liquid from the wastewater-sludge mixture using a filter F) using a liquid level difference, for example, a so-called nylon scrubbing brush called Scotchibrite, a product of 3M Co., Ltd. Outflow end N2 of nitrification tank N
and the inflow end D2 of the denitrification tank D are connected by a flow path ND.
In addition, a circulation pump P2 is provided in the return pipe R connecting the denitrification tank D and the nitrification tank N, and circulates the mixed liquid in the denitrification tank D into the nitrification tank N through the return pipe R at a predetermined circulation speed Qr. It is configured like this. The denitrification tank D is further equipped with an agitator A (rotation speed: 120 rpm) having a turbine-type propeller to completely mix the mixed liquid in the tank. The bottom of the nitrification tank N is provided with, for example, perforated plates N3, N3, . . . , so that air for aeration and stirring is blown into the tank. In addition,
N4 and N4 are partition walls that partition the inside of the nitrification tank N. The bottom of the solid-liquid separation tank S equipped with the filter F is placed in the wastewater-sludge mixture in the denitrification tank D at a predetermined depth from the liquid level.

Therefore, the mixed liquid in the denitrification tank D that is in contact with the filter F is subjected to deep water pressure depending on the immersion depth of the solid-liquid separation tank S. As a result, the mixed liquid in contact with the filter F passes through the filter F and enters the solid-liquid separation tank S. This infiltration continues until the infiltrated water, that is, the treated water, reaches the same level in the solid-liquid separation tank S as the water level of the mixed liquid in the denitrification tank D. On the other hand, activated sludge is blocked from flowing out by filter F. Therefore, when wastewater is supplied into the denitrification tank D at a constant flow rate Q, the treated water continuously flows out from the outlet S1 at the same speed Q as the wastewater supply rate and is discharged into a river or the like. 1 for this device
The so-called nylon scrubbing brush used as an example has characteristics such as good drainage, easy drying, durability, and elasticity.

Therefore, it is more suitable for filtering and separating a mixed liquid of wastewater and activated sludge than the various mesh wire meshes, punched metals, etc. that have conventionally been generally used as filters. Embodiment 7 The apparatus shown in FIG. 6a is different from the apparatus of Example 4 in the structure of the solid-liquid separation tank.

As shown in FIG. 6b, in this device, a solid-liquid separation tank 1 composed of a hollow rotating drum 3 is arranged in a denitrification tank D, and the solid-liquid is connected from the mixed liquid in the denitrification tank D. It is constructed so that wastewater treatment can be performed continuously by separating the wastewater. That is, the solid-liquid separation tank 1 communicates with the denitrification tank D through multiple holes in the wall surface. and a pair of opposing walls 12 of the solid-liquid separation tank 1,
Hollow through cylinders 2, 2 are fixed to 12. A rotary drum 3 is attached to outer cylinders 20, 20 which are rotatably fitted into the through cylinders 2, 2. For example, a filter 3 made of a so-called nylon scrubbing brush called Scotchiplite, a trade name of Sumitomo 3M Ltd., which is the same as the filter F of the above-mentioned embodiment 4, is provided on the perforated surface 31 of the rotating drum 3.
0 is attached. This rotating drum 3 is connected to a motor 33 by a J belt 32 such as a stainless steel roller chain, and rotates at a rotation speed of, for example, 60 rpm or less. On the other hand, each of the hollow tubes 2, 2 has a tank wall 12 at each end,
It is electrically connected to the outside of the tanks 1 and D through holes 120, 120 provided in the portion that abuts on the tank 12. The hollow cavity of one cylinder 2 has a suction port 40 into the rotating drum 3 through an open end 21 and a wall hole 120, and a drainage vibrator 4 having a water spout outside the tank.
However, the hollow cavity of the other cylinder 2 has a wall hole 120 and an open end 22.
A cleaning water supply vibrator 5 is disposed through each. Then, by driving a suction pump (not shown) connected to the drainage vibrator 4, the pressure inside the rotary drum 3 is reduced, e.g.
Filter the mixed liquid 10 in the tank 1 to 0 mmHg through the filter 30.
It is configured to filter through. Further, the tip of the cleaning water supplying vibrator 5 is disposed in the upper part of the rotating drum 3, and cleaning water injection holes 50, 50, . . . are provided on the surface thereof facing upward toward the filter 30. The liquid level is adjusted by adjusting the rotation speed of the drum 3 so that these injection holes 50, 50, . . . are always exposed above the liquid level of the mixed liquid 10 in the tank 1. Therefore, the top of the rotating drum 3 is always exposed to the air from the liquid level, and the cleaning water injection holes 50, 50...
A part of the filter 30 is always cleaned by a jet of cleaning water from the filter 30. Providing a cover above the filter 30 prevents sludge and the like from scattering due to the injection of washing water. The other end of the cleaning water supply vibrator 5 is connected to a cleaning water supply source (not shown), such as the above-mentioned drainage vibrator 4, by a known means via a pump or the like, so that a part of the treated water can be used as cleaning water. It's becoming like that. 300 indicates a filter support member attached to the rotating drum 3.

By starting the motor 33, the rotating drum 3 is
The mixture 10 is rotated at a slow rotational speed of rpm or less.

The liquid in the rotating drum 3 is sucked out by the action of a suction pump (not shown) connected to the drainage vibrator 4. As a result, the mixed liquid 10 around the drum 3 is filtered by the filter 30 and flows into the drum. The liquid, that is, the treated water, is sucked through the suction port 40 of the drainage vibrator 4 and discharged to the outside of the tank. On the other hand, activated sludge accumulates on the surface of the filter 30 in the liquid. When the drum 3 rotates and the filter 30 comes to a position where it is exposed above the liquid surface, the filter 30 is exposed to the injection hole 50.
, 50 . . . are sprayed from the back side for cleaning. Therefore, the activated sludge deposited on the surface of the filter 30 is washed away and returns to the liquid mixture 10 by trickling down the filter surface. This apparatus can effectively and continuously treat wastewater even when the activated sludge concentration is as high as 5,000 to 30,000 ppm.

Note that the outflow amount Q of treated water is maintained in a predetermined numerical relationship with the wastewater-sludge mixed liquid circulation rate Qr by adjusting the drainage pump. Example 8 The apparatus shown in FIG. 7 differs from those of Examples 6 and 7 in the structure of the solid-liquid separation tank.

In this device, a clarification separation tank T that utilizes the sedimentation properties of sludge is used as a solid-liquid separation tank. This clarification separation tank T is arranged outside the denitrification tank D in connection with the denitrification tank D. The settled sludge at the bottom of the tank is returned to the nitrification tank N through the sludge return pipe R1. The use of the clarification separation tank T is particularly effective when the concentration of sludge from the denitrification tank D is relatively low, such as 3000 to 4000 m9/l, which is approximately the concentration used in wastewater treatment with normal activated sludge.

However, even if the sludge concentration is 10,000 m9/l, if the sludge index SVI (SludgeVOlumeIndex) is as low as about 50, solid and liquid can be effectively separated. Furthermore, instead of the clarification tank T, it is also recommended to use a so-called flotation tank T1, as shown in FIG.

When compressed air is blown into the solid-liquid mixture in the tank, the bubbles that have dissolved into molecules are reduced to atmospheric pressure and become fine particles, with the floating blades floating and concentrating the sludge flocs. Such flotation concentration treatment has the advantage that solid-liquid separation can be carried out in a short period of time, and that the sludge changes into a state that is easily concentrated, since many fine particles of air bubbles are mixed into the sludge. In this way, the present invention adopts a method of directly supplying inflow wastewater to the denitrification process where activated sludge has strong adsorption properties, and furthermore, by adjusting the internal circulation rate Qr of the wastewater-sludge mixture, the denitrification process can be improved. The anaerobic mixture in the nitrification process and the aerobic mixture in the nitrification process were completely diluted and mixed.

As a result, more than 90% of nitrogen in wastewater can be removed without supplementing carbon sources and therefore at a significantly lower cost.
Both Mn can be removed by 90% or more. In addition, CODc,,
Since the relationship between CODMn and BOD (biological oxygen demand) is generally CODc,<BOD<CODMn, BOD was not particularly measured in this study. Furthermore, since the present invention is a so-called total oxidation treatment method in which sludge is not drawn out, no excess sludge is produced.

As a result, sludge treatment costs are unnecessary. Furthermore, since activated sludge is used at a wide range of concentration from 5000 to 30000 m9/l, particularly at a high concentration from 8000 to 15000 m9/l, the wastewater treatment rate can be increased. Therefore, the plant can be downsized and the installation area of the plant can be small. Furthermore, activated sludge can be used in high concentrations;
Can respond to fluctuations in wastewater quality.

[Brief explanation of the drawing]

Figures 1 to 4 show examples of the wastewater treatment method of the present invention.
Figure 2 shows the relationship between the production rate of nitrate nitrogen and the rate of decrease in ammonia nitrogen, Figure 2 shows the results of a nitrification test of wastewater using high-concentration activated sludge, and Figure 3 shows the relationship between CODc, -SS loading and depletion. Fig. 4 shows the denitrification test results when activated sludge with a certain concentration is used, Fig. 5 is a schematic diagram of one embodiment of the wastewater treatment equipment of the present invention, and Fig. 6 shows the relationship with the nitrification rate. In the second embodiment of the apparatus, a is a schematic diagram thereof, b is a partially cutaway side view of the solid-liquid separation tank 1, and FIGS. 7 and 8 are schematic diagrams of the third and fourth embodiments, respectively. N...Nitrification tank, D...Denitrification tank, S, I, T...Solid-liquid separation tank, R...Return pipe, Pl, P2, 33...Pump.

Claims (1)

[Scope of Claims] 1. A denitrification tank having a wastewater inflow end with a valve, and a wastewater-sludge mixture outflow end connected to the wastewater-sludge mixture inflow end of the denitrification tank, and a wastewater-sludge mixture outflow end of the denitrification tank. A nitrification tank having an inflow end with a circulation valve and a solid-liquid separation tank connected to the denitrification tank, and a pump connected to a wastewater-sludge mixture circulation pipe connecting the denitrification tank and the nitrification tank. The wastewater-sludge mixture in the denitrification tank is circulated at a predetermined circulation speed, and the sludge separated in the solid-liquid separation tank is transferred to the sludge return pipe leading to the nitrification tank or the wastewater-sludge mixture in the denitrification tank. A total oxidation treatment type wastewater treatment device that does not produce excess sludge, characterized in that the wastewater-sludge mixture is returned to the nitrification tank through a wastewater-sludge mixture circulation pipe that connects the denitrification tank and the nitrification tank. 2 As the solid-liquid separation tank, use a solid-liquid separation tank in which a filter is attached to the bottom at a predetermined depth from the liquid level in the denitrification tank and a treated water outlet is provided at the top, so that the liquid level in the denitrification tank and the above-mentioned filter are According to claim 1, the mixed liquid in the denitrification tank is allowed to enter the solid-liquid separation tank through a filter due to the pressure difference between the denitrification tank and the denitrification tank, and the treated water that has entered the tank is made to flow out from the treated water outlet. wastewater treatment equipment. 3 The solid-liquid separation tank includes a hollow cylinder fixed inside the solid-liquid separation tank and communicating with the denitrification tank through a wall hole and communicating with the outside of the tank, a rotating drum rotatably attached to the cylinder, and a rotating drum that is rotatably attached to the cylinder. a drum drive motor, a filter attached to the surface of the rotating drum, a drainage pipe arranged to pass through the hollow cavity of the cylinder and have a suction port inside the rotating drum and a water outlet outside the tank; A solid-liquid separation tank equipped with a washing water supply pipe arranged to have a washing water injection hole in the upper part of the drum through a hollow cavity is disposed in the denitrification tank, and The mixed liquid in the denitrification tank is sucked through the filter, and the cleaning water is sprayed from the cleaning water injection hole onto the back of the filter, which is exposed above the liquid surface, and the activated sludge is returned from the filter surface to the mixed liquid in the denitrification tank. A wastewater treatment apparatus according to claim 1.