JP5360091B2 - Nitrogen-containing wastewater treatment method and treatment equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wastewater treatment method and apparatus which can perform wastewater treatment excellent in quality of treated water and treatment capacity using facilities in a relatively small facility area. <P>SOLUTION: Raw water and returned sludge are introduced into a nitrification tank 1, and aeration-treated liquid is introduced into a sedimentation basin 4 and subjected to sedimentation separation treatment. The concentration of ammonia nitrogen in the aeration-treated liquid flowing into the sedimentation basin 4 from the nitrification tank 1 is adjusted to &le;1 mg/L, preferably to &le;0.5 mg/L. Hence, the concentration of BOD components in the sedimentation basin 4 is decreased to a sufficiently low level to prevent or suppress the denitrification reaction in the sedimentation basin 4, which prevents sludge rising due to the denitrification reaction. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  TECHNICAL FIELD The present invention relates to a method and apparatus for treating nitrogen-containing wastewater containing BOD and a nitrogen component, and more specifically, a method for treating wastewater containing an organic state and / or ammonia nitrogen in excess of the proportion required for BOD removal. And the apparatus.

  In general, in the activated sludge method, the nitrogen component necessary for BOD removal is set to 5 with respect to BOD 100, and it is preferable to add a nitrogen component as appropriate to waste water having a nitrogen concentration lower than this. When the nitrogen component exceeding this is contained in raw | natural water, a part of nitrogen component may be nitrified. When nitrate nitrogen generated by this nitrification flows into the sedimentation basin, a denitrification reaction occurs using the organic substances in the sludge, and the sludge in the sedimentation basin rises due to the generated nitrogen gas and the treated water quality deteriorates. In some cases, the MLSS concentration is lowered and the processing performance of the apparatus is lowered.

  In particular, when the concentration of remaining nitrate nitrogen was 10 mg / L or more, significant levitation often occurred (for example, paragraph 0003 of JP-A-2001-255319).

  Thus, in the waste water containing 5% or more of nitrogen components with respect to the BOD of raw water, the problem of sludge floating in the sedimentation basin is likely to occur. Therefore, conventionally, as shown in FIG. 4, the raw water is aerated in the nitrification tank 1 for nitrification, then denitrified in the denitrification tank 2, then re-aerated in the re-aeration tank 3, and then solid-liquid separated in the sedimentation tank 4. In this way, the nitrate nitrogen was removed by the denitrification tank 2 so as not to flow into the sedimentation tank 4 as much as possible.

JP 2001-255319 A

  In the conventional method of FIG. 4, the nitrification tank 1 and the re-aeration tank 3 are installed in two stages as the aeration equipment for removing the BOD component and the nitrogen component, and the equipment area is large.

  An object of this invention is to provide the processing method and processing apparatus of nitrogen containing waste_water | drain which can perform waste water treatment with favorable treatment water quality and processing performance with the installation of a comparatively small installation area.

The method for treating nitrogen-containing wastewater according to claim 1 is a method comprising treating nitrogen-containing wastewater containing BOD and organic and / or ammonia nitrogen in a weight ratio of N / BOD of more than 0.05 as raw water in the presence of activated sludge Aeration treatment is performed in the aeration tank, the aeration treatment liquid is solid-liquid separated by solid-liquid separation means, and the separated water is discharged as treated water without returning to the aeration tank, and the waste water is treated by a process that omits the denitrification tank In the method, the aeration treatment is performed so that the nitrification reaction proceeds until the ammoniacal nitrogen concentration in the aeration treatment liquid flowing into the solid-liquid separation means becomes 1 mg / L or less, and the solid-liquid separation means At least a part of the sludge is returned to the aeration tank, and treated water having S-BOD of less than 5 mg / L is obtained .

  The nitrogen-containing wastewater treatment method according to claim 2 is the method according to claim 1, wherein the ammonia nitrogen concentration in the aeration treatment liquid is measured with an ammonia nitrogen concentration meter, and based on the signal of the ammonia nitrogen concentration meter, By controlling the raw water supply amount, the ammoniacal nitrogen concentration in the aeration treatment liquid is set to 1 mg / L or less.

  The method for treating nitrogen-containing wastewater according to claim 3 is the method according to claim 1 or 2, wherein the solid-liquid separation means is of a sedimentation type, and when a part of sludge floats by the solid-liquid separation means, The collected sludge is collected and returned to the aeration tank.

A nitrogen-containing wastewater treatment method according to a fourth aspect is characterized in that, in any one of the first to third aspects, a carrier is not added to the aeration tank.
The nitrogen-containing wastewater treatment apparatus according to claim 5 comprises an aeration tank, raw water supply means for supplying raw water to the aeration tank, and a floating sludge scraper for solid-liquid separation of the mixed liquid in the aeration tank. And a means for returning the sludge settled in the settling tank and the floating sludge to the aeration tank, the denitrification tank is omitted, and the separated water of the settling tank is supplied to the aeration tank. In a treatment apparatus for nitrogen-containing wastewater discharged as treated water without returning it, an ammonia nitrogen concentration meter for measuring the ammonia nitrogen concentration in the mixed solution flowing into the precipitation tank, and a signal of the ammonia nitrogen concentration meter And a control means for controlling the raw water supply amount and / or the aeration amount by the raw water supply means to obtain treated water having an S-BOD of less than 5 mg / L.

The apparatus for treating nitrogen-containing wastewater according to claim 6 includes an aeration tank, raw water supply means for supplying raw water to the aeration tank, a floating separation tank for solid-liquid separation of the mixed liquid in the aeration tank, and the floating separation Means for returning at least part of the floating sludge of the tank to the aeration tank, omitting the denitrification tank, and discharging the separated water of the floating separation tank as treated water without returning to the aeration tank In the wastewater treatment apparatus, based on the ammonia nitrogen concentration meter for measuring the ammonia nitrogen concentration in the mixed liquid flowing into the floating separation tank, and the raw water supply means based on the signal of the ammonia nitrogen concentration meter And a control means for controlling the raw water supply amount and / or the aeration amount to obtain treated water having an S-BOD of less than 5 mg / L.

The apparatus for treating nitrogen-containing wastewater according to claim 7 is the treatment apparatus for nitrogen-containing wastewater according to claim 6 , further comprising a second flotation separation tank for further solid-liquid separation of the separated water in the flotation separation tank. The treated water is discharged without being returned to the aeration tank .
A nitrogen-containing wastewater treatment apparatus according to an eighth aspect is characterized in that, in any one of the fourth to seventh aspects, the aeration tank is not added with a carrier.

  In the present invention, the nitrification reaction is advanced by sufficiently aeration so that the ammoniacal nitrogen concentration in the aeration treatment liquid flowing into the solid-liquid separation means is 1 mg / L or less. In general, the nitrification reaction of the nitrogen component is slower than the aerobic decomposition reaction of the BOD component. Therefore, when the aeration treatment is sufficiently performed so that the ammonia nitrogen concentration in the aeration treatment liquid is 1 mg / L or less as described above, aeration is performed. The residual BOD concentration in the treatment liquid is also extremely low.

  Thus, even if the aeration process liquid with which residual BOD density | concentration became low, even if it introduce | transduces in a solid-liquid separation tank, denitrification reaction will not arise, and the rise of sludge resulting from this denitrification reaction is prevented.

  This will be described in further detail as follows.

In the case where the wastewater treatment method is performed by the process in which the denitrification tank 2 and the re-aeration tank 3 shown in FIG. 4 are omitted, means necessary for preventing sludge floating in the sedimentation tank 4 and performing a stable treatment are as follows.
(1) Nitrification sufficiently at the last stage of the biological treatment reactor so that ammonia nitrogen is 1 mg / L or less;
(2) Solid-liquid separation of a small amount of floating sludge in a sedimentation basin with equipment capable of recovering floating sludge.

  In order for the denitrification reaction to occur in the sedimentation basin, a substance that becomes an electron donor is required in water or sludge, and conversely, a biological treatment reaction that does not leave undegraded organic substances in the water and sludge. By performing sufficient decomposition in the tank, the electron donor necessary for the denitrification reaction is depleted, and the denitrification reaction can be suppressed.

  Since organic matter decomposition normally proceeds prior to the nitrification reaction, the load and operating conditions should be adjusted so that ammonia nitrogen is substantially completely nitrified to 1 mg / L or less in the last stage of the biological treatment reaction tank. Thus, the organic material can be kept in a sufficiently decomposed state. Thereby, it is possible to ensure a substantially stable separation property of the sedimentation basin.

  However, if a sudden load change occurs, a small amount of sludge may temporarily rise. Therefore, by installing a facility that can collect a small amount of floating sludge in the sedimentation basin, it is possible to cope with such temporary load fluctuations and to obtain a stable treated water quality.

It is a flowchart of the waste water treatment equipment concerning an embodiment. It is a flowchart of the waste water treatment equipment concerning an embodiment. It is a flowchart of the waste water treatment equipment concerning an embodiment. It is a flowchart of a prior art example.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  1 to 3 are all flow charts of a wastewater treatment apparatus suitable for carrying out the wastewater treatment method of the present invention.

  In FIG. 1, raw water and return sludge are introduced into a nitrification tank 1 as a biological treatment reaction tank, and an aeration treatment liquid is introduced into a sedimentation basin 4 for sedimentation treatment. In the vicinity of the water level of the sedimentation basin 4, a floating sludge outflow prevention plate 4a is provided at a distance from the inner peripheral side of the tank wall. The aeration treatment liquid is introduced near the center of the settling basin 4, and the settled sludge is returned to the nitrification tank 1 through a sludge return line 5. Part of the sludge that has floated is collected in a mud collection box (not shown) by the scraper 4 b and returned to the nitrification tank 1 by the floating sludge return line 6. Excess sludge is discharged through a sludge discharge line 5 a branched from the sludge return line 5.

  The supernatant water from which the sludge has been separated is taken out from the outer peripheral side of the outflow prevention plate 4a by the treated water outlet pipe 7.

  When raw water is treated by this wastewater treatment apparatus, the ammoniacal nitrogen concentration of the aeration treatment liquid flowing from the nitrification tank 1 to the settling basin 4 is 1 mg / L or less, preferably 0.5 mg / L or less.

  Thereby, the BOD component density | concentration in the sedimentation basin 4 also becomes a sufficiently low thing, the denitrification reaction in the sedimentation basin 4 is prevented thru | or suppressed, and sludge floating resulting from this denitrification reaction is prevented.

  In addition, sludge sometimes floats in the sedimentation basin 4 due to a sudden load fluctuation or the like. In such a case, the floating sludge is scraped off by the scraper 4b and returned to the nitrification tank 1.

  As described above, in order to set the ammonia nitrogen concentration in the aeration treatment liquid to 1 mg / L or less, the ammonia nitrogen concentration in the aeration treatment liquid is measured with an ammonia nitrogen concentration meter, and the ammonia nitrogen concentration is determined. It is preferable to suppress the amount of raw water flowing into the nitrification tank 1 and the amount of aeration so that the measured value of the meter is 1 mg / L or less.

  In order to sufficiently decompose organic substances with this wastewater treatment device, the water temperature is 15 ° C. or higher, preferably 20 ° C. or higher, the sludge load is 0.3 kg-BOD / kg-VSS / d or lower, and the SRT is 7 days or longer. It is preferable to adjust the conditions. In this case, the MLSS concentration is desirably 4000 to 6000 mg / L, and the sludge return rate is 0.5 Q or more, preferably 1.0 Q or more, relative to the raw water flow rate Q.

  Moreover, when the support | carrier 10 is added to the nitrification tank 1, while the load per reaction tank is raised, since it can be drive | operated by a low MLSS density | concentration, the more efficient and less process of sludge floating will be attained. Since carriers such as sponges can hold the cells at high density, adding them to the biological treatment reaction tank increases the concentration of the cells and enables treatment in a smaller reaction vessel. On the other hand, by adding a carrier, the same treatment is possible even if the MLSS concentration is reduced. Therefore, when the carrier is added to keep the MLSS concentration low, it is possible to perform a process that is less likely to cause floating in the sedimentation basin. The filling rate of the carrier is an apparent volume of 10 to 70%, preferably 20 to 50% with respect to the tank volume, and the MLSS concentration is desirably 3000 to 5000 mg / L.

  FIG. 2 shows an embodiment in which a floating separation device 8 is used instead of the sedimentation basin 4. In this case, since it is relatively difficult to keep the suspended sludge concentration high, it is desirable to add the carrier 10 to the nitrification tank 1. The carrier filling rate is 10 to 70%, preferably 20 to 50% of the volume of the nitrification tank 1 in terms of apparent volume, and the MLSS concentration is desirably 2000 to 5000 mg / L. There is no need to return the sludge.

  The floating separation equipment is more preferable because the quality of the treated water is improved by adding a flocculant. As shown in FIG. 3, a floating separator 9 that adds a flocculant and performs a floating separation process may be added after the floating separator 8 that returns sludge.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.

Example 1
With the apparatus shown in FIG. 1, the following water quality nitrogen-containing wastewater was used as raw water for treatment at a treatment rate of 180 L / day, and nitrification water quality and treated water quality are shown in Table 1.

[Raw water quality]
Kjeldahl nitrogen 166.3 mg / L
NH ₄ -N 22.9 mg / L
BOD 872mg / L
[Nitrification tank]
Tank capacity 300L
MLSS 4000mg / L
[Sedimentation pond]
Separation area 0.5m ²
Return sludge volume 180L / day Floating sludge return volume 20L / day

Comparative Example 1
The same raw water as in Example 1 was treated at the same treatment amount (180 L / day) with the apparatus shown in FIG. The specifications of the nitrification tank and the sedimentation basin were the same as in Example 1. The denitrification tank capacity was 200L, and the re-aeration tank capacity was 100L. Table 1 shows the nitrification water quality and treated water quality at this time.

Example 2
The raw water similar to that in Example 1 is treated at the same flow rate in the same apparatus as in Example 1 except that a carrier is added to the nitrification tank 1 and the following conditions are set. Table 1 shows the nitrification water quality and treated water quality. It was shown to.
[Nitrification tank]
Tank capacity 300L (same as Example 1)
Carrier Add 50% of tank capacity in apparent volume of 3mm square sponge.
MLSS 3000mg / L

Example 3
Assuming the apparatus shown in FIG. 2, the nitrification tank treated water of Example 2 was subjected to batch-type pressurized flotation separation under the following conditions. Nitrogen tank treated water (300 ml) was placed in a column, pressurized water (pressurized and dissolved by air saturation) was injected from the bottom, and treated water was collected from the bottom 5 minutes after the injection. The treated water SS at this time (corrected with the amount of pressurized water) is shown in Table 1.
[Floating separator]
Pressurized water pressure 0.4 MPa
Pressurized water volume ratio (nitrification tank treated water: pressurized water = 4: 1)
Separation column φ46mm 500ml

Example 4
Assuming the apparatus shown in FIG. 3, polyaluminum chloride (PAC) was added as a flocculant to the treated water of Example 3, and batch pressure flotation separation was performed under the following conditions. The flocculant was added to 300 ml of the treated water of Example 3 and taken into a column, pressurized water (pressurized and dissolved in air with saturation) was injected from the lower part, and treated water was collected from the lower part 5 minutes after the injection. The treated water SS (corrected with the amount of pressurized water) is shown in Table 1.
[Floating separator]
Pressurized water pressure 0.4 MPa
Pressurized water volume ratio (nitrification tank treated water: pressurized water = 4: 1)
Separation column φ46mm 500ml
Flocculant PAC 300mg / L

  From Table 1, the following is clear.

  In Examples 1 and 2, good treated water quality equivalent to that of Comparative Example 1 was obtained.

  In the result of Example 3, if the treated water SS concentration is slightly high, but the wastewater has a high concentration of about BOD 500 mg / L or more, the generated bacterial cell concentration (usually about 30% of BOD) exceeds the outflow SS concentration, so the nitrification tank The necessary sludge can be secured.

  In Example 4, good treated water quality is obtained by adding the flocculant.

  As is clear from the above examples and comparative examples, according to the present invention, the denitrification tank and the re-aeration tank can be omitted, and the nitrification tank can be made small. In addition, the methanol required for denitrification is unnecessary, and the running cost can be reduced.

DESCRIPTION OF SYMBOLS 1 Nitrification tank 2 Denitrification tank 3 Re-aeration tank 4 Sedimentation basin 4a Floating sludge outflow prevention plate 4b Scraper 8,9 Flotation separation device

Claims (8)

Nitrogen-containing wastewater containing BOD and organic and / or ammonia nitrogen in which N / BOD exceeds 0.05 by weight is used as raw water.
Aeration treatment is performed in an aeration tank in the presence of activated sludge, the aeration treatment liquid is solid-liquid separated by solid-liquid separation means, and the separated water is discharged as treated water without being returned to the aeration tank. In a method of treating wastewater by a process,
Performing the aeration treatment so that the nitrification reaction proceeds until the ammoniacal nitrogen concentration in the aeration treatment liquid flowing into the solid-liquid separation means is 1 mg / L or less;
A method for treating nitrogen-containing wastewater, wherein at least part of the sludge separated by the solid-liquid separation means is returned to an aeration tank to obtain treated water having an S-BOD of less than 5 mg / L. In Claim 1, the ammonia nitrogen concentration in the aeration treatment liquid is measured with an ammonia nitrogen concentration meter,
Nitrogen-containing wastewater characterized in that the ammonia nitrogen concentration in the aeration treatment liquid is controlled to 1 mg / L or less by controlling the raw water supply amount and / or the aeration amount based on the signal of the ammonia nitrogen concentration meter. Processing method. In Claim 1 or 2, the solid-liquid separation means is of a sedimentation type,
A method for treating nitrogen-containing wastewater, characterized in that, when part of sludge is floated by the solid-liquid separation means, the sludge that has floated is collected and returned to the aeration tank.   The method for treating nitrogen-containing wastewater according to any one of claims 1 to 3, wherein a carrier is not added to the aeration tank. An aeration tank;
Raw water supply means for supplying raw water to the aeration tank;
A settling tank equipped with a levitating sludge scraper for solid-liquid separation of the mixed liquid in the aeration tank;
Means for returning at least part of the sludge settled in the settling tank and the floating sludge to the aeration tank;
In a treatment apparatus for nitrogen-containing wastewater that omits the denitrification tank and discharges the separated water of the settling tank as treated water without returning it to the aeration tank,
An ammonia nitrogen concentration meter for measuring the ammonia nitrogen concentration in the mixed solution flowing into the precipitation tank;
And a control means for controlling the raw water supply amount and / or the aeration amount by the raw water supply means on the basis of the signal of the ammonia nitrogen concentration meter to obtain treated water having an S-BOD of less than 5 mg / L. Nitrogen-containing wastewater treatment equipment. An aeration tank;
Raw water supply means for supplying raw water to the aeration tank;
A flotation separation tank for solid-liquid separation of the liquid mixture in the aeration tank;
Means for returning at least part of the floating sludge of the floating separation tank to the aeration tank;
In a treatment apparatus for nitrogen-containing wastewater that omits the denitrification tank and discharges the separated water of the floating separation tank as treated water without returning it to the aeration tank,
An ammonia nitrogen concentration meter for measuring the ammonia nitrogen concentration in the liquid mixture flowing into the floating separation tank;
And a control means for controlling the raw water supply amount and / or the aeration amount by the raw water supply means on the basis of the signal of the ammonia nitrogen concentration meter to obtain treated water having an S-BOD of less than 5 mg / L. Nitrogen-containing wastewater treatment equipment.   7. The method according to claim 6, further comprising a second flotation separation tank for further solid-liquid separation of the separation water of the flotation separation tank, and discharging the separation water of the second flotation separation tank as treated water without returning to the aeration tank. A nitrogen-containing wastewater treatment apparatus.   The treatment apparatus for nitrogen-containing wastewater according to any one of claims 5 to 7, wherein a carrier is not added to the aeration tank.

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