JP2005305254A - Treatment method for sludge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sludge treatment method which can prevent a deterioration of water treatment by incorporating a phosphorus removal process into a sludge solubilization process, and can remove phosphorus only by pulling out minimum sludge as surplus sludge. <P>SOLUTION: In the sludge treatment method for performing the biological treatment of organic sewage by activated sludge inside an aeration tank 2 and solubilizing the surplus sludge D generated by the biological treatment, and then returning the solubilized sludge E to the aeration tank 2 to decompose the sludge, strong acid water L obtained by the diaphragm electrolysis of salt water K is added to sludge sterilized and solubilized in a sludge solubilization tank 7 to release phosphorus, and then solubilized liquid G is obtained by solid-liquid separation, and strong alkaline water M obtained by the diaphragm electrolysis of the salt water K is added to the solubilized liquid G, which insolubilizes phosphorus again and settles and separates it. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for treating sludge, and in particular, organic wastewater such as sewage is biologically treated with activated sludge, and organic matter and phosphorus are removed to minimize the amount of sludge generated. The present invention relates to a method for treating sludge.

  Conventionally, in order to treat sewage flowing into a sewage treatment plant or the like, an activated sludge method has been used in which sewage is introduced into an activated sludge aeration tank, and this is aerated and stirred to perform biological treatment. Excess sludge generated in the water treatment process is usually landfilled after dehydration, but because the disposal site is gradually disappearing, ozone is added to the excess sludge to solubilize the sludge. Attempts have been made to eliminate sludge generation by biodegradation in the system.

  However, in the conventional sludge treatment method, since the solubilized sludge is returned to the aeration tank as it is, the load on the aeration tank increases, resulting in a lack of capacity in the aeration apparatus or deterioration in water quality. There's a problem. Another disadvantage of the technology that makes the discharged sludge zero is that phosphorus that has been discharged in the form of sludge cannot be removed at all.

  In view of the problems of the above-described conventional sludge treatment methods, the present invention incorporates a process for removing phosphorus into the sludge solubilization process, thereby preventing deterioration of water treatment and merely extracting the minimum sludge as excess sludge. Then, it aims at providing the processing method of the sludge which can also remove phosphorus.

  In order to achieve the above object, the sludge treatment method of the present invention comprises biologically treating organic sludge with activated sludge in an aeration tank, and solubilizing surplus sludge generated by biological treatment, and then solubilizing treatment. In the sludge treatment method in which sludge is returned to the aeration tank and decomposed, strongly acidic water obtained by diaphragm electrolysis of salt water is added to the sludge sterilized and solubilized in the sludge solubilization tank. After the release, the solubilized solution obtained by solid-liquid separation is neutralized by adding strong alkaline water obtained by subjecting brine to diaphragm electrolysis, so that phosphorus is insolubilized again and separated by precipitation. Features.

  In this case, chlorine gas generated at the anode of the diaphragm electrolytic cell can be introduced and blown into the sludge solubilization tank, and the dissolved hypochlorous acid can be used for sterilization of sludge microorganisms.

  Moreover, a part of the separated water obtained by precipitation separation of phosphorus can be returned to the diaphragm electrolytic cell, and the remaining salt content can be reused.

According to the sludge treatment method of the present invention, the organic sludge is biologically treated with the activated sludge in the aeration tank, and the excess sludge generated by the biological treatment is solubilized, and then the solubilized sludge is returned to the aeration tank. In the sludge treatment method, which is decomposed by the addition of strongly acidic water obtained by diaphragm electrolysis of salt water to the sludge sterilized and solubilized in the sludge solubilization tank, phosphorus is released, The solubilized solution obtained by liquid separation is neutralized by adding strong alkaline water obtained by subjecting salt water to diaphragm electrolysis, so that phosphorus is insolubilized again and precipitated and separated. While salt water is diaphragm-electrolyzed and manufactured in the system, phosphorus can be collected as sludge and discharged out of the field, and the phosphorus removal performance in the water treatment process can be enhanced.
In addition, since sterilized sludge and solubilized organic matter can be returned to the aeration tank and biodegraded by activated sludge, the amount of sludge to be transported outside the site is greatly reduced, and only inorganic sludge containing phosphorus is discharged. can do.

  In this case, chlorine gas generated at the anode of the diaphragm electrolytic cell is introduced into the sludge solubilization tank and blown, and the dissolved hypochlorous acid is used for sterilization of sludge microorganisms, so that chlorine gas as a by-product is also effectively produced. It can be used and the running cost can be reduced.

  In addition, the running cost can be reduced by returning a part of the separated water obtained by precipitation separation of phosphorus to the diaphragm electrolyzer and reusing the remaining salt.

  Embodiments of the sludge treatment method of the present invention will be described below with reference to the drawings.

In FIG. 1, one Example of the processing method of the sludge of this invention is shown.
The sewage A that has flowed into the sewage treatment facility such as a sewage treatment plant is removed from the sand and scum by the pretreatment facility 1, and then sent to the aeration tank 2 to be biologically treated with activated sludge.
The sewage treated in the aeration tank 2 is sent to the final sedimentation tank 3 as a sludge mixed solution, separated into solid and liquid and overflowed as treated water B.
The precipitated sludge is withdrawn intermittently or continuously by the sludge return pump 5 and returned to the aeration tank 2 as return sludge C.
Note that a flocculant addition device 4 for adding a metal salt type flocculant to the aeration tank 2 is provided for the purpose of performing a high degree of dephosphorization, but may be excluded if high degree treatment is not required. it can.

Part of the precipitated sludge withdrawn from the final sedimentation tank 3 is transferred as excess sludge D to the sludge solubilization tank 7 by the sludge transfer pump 6 to promote sterilization and solubilization of sludge microorganisms.
In addition, although the excess sludge is thrown directly into the sludge solubilization tank 7 in the figure, it can also be thrown into the sludge solubilization tank after being concentrated by gravity concentration or a mechanical concentrator to reduce the amount. .
Moreover, in the sludge solubilization tank 7, it is easy to use heat treatment or electrolytic treatment, but there is no particular limitation, and any means can be used as long as it can efficiently sterilize sludge microorganisms at low cost. be able to.

Phosphorus is released by adding a liquid containing hydrochloric acid to the sludge flowing from the sludge solubilization tank 7 into the phosphorus release tank 8 by the acid addition device 9 to make the sludge acidic.
In the solubilized sludge E, the sludge solid matter sterilized in the solid-liquid separation tank 10 in the subsequent stage is precipitated, and the released solubilized liquid G mainly composed of phosphoric acid overflows and is guided to the pH adjustment tank 11.
The sludge F precipitated in the solid-liquid separation tank 10 is returned to the aeration tank 2 via the sludge return pump 5 or a sludge pump provided separately.

In the pH adjustment tank 11, the alkaline addition device 12 adjusts the pH by injecting strong alkaline water containing a high concentration of hydroxide ions.
The pH adjustment may be performed in the pipe or in the precipitation separation tank 13, but it is more reliable to detect the pH and control the injection of the alkaline agent while stirring. It is appropriate to perform in the pH adjustment tank 11.

Since the liquid led to the precipitation separation tank 13 contains solid matter mainly composed of inorganic substances such as phosphate compounds precipitated by neutralization, the sludge is settled by allowing it to stand, and the sludge extraction pump 14 Thus, the sludge storage tank 15 is periodically withdrawn and temporarily stored.
The stored sludge J can be taken out of the treatment plant by a vacuum vehicle or the like, or can be provided with equipment such as a dehydrator and periodically dehydrated.
Moreover, the separated water I that has been separated by precipitation is returned to the aeration tank, and is also sent to the diaphragm electrolyzer 16 provided separately.

On the other hand, the diaphragm electrolytic cell 16 is divided into two zones on the right and left by a central diaphragm 17, each provided with an anode (+) and a cathode (−) electrode, and salt water K containing sodium chloride or potassium chloride is supplied. While being supplied, it is configured to perform electrolysis with a DC power source.
As the diaphragm 17, an asbestos membrane is generally used, but other membranes such as an ion exchange membrane can also be used.
In addition, it is appropriate that the anode is a titanium base material coated with a noble metal catalyst, and the cathode is a nickel electrode. However, the anode is not limited to these, and carbon and various metal electrodes can be used in combination.
Although not shown in the drawing, a space is provided in the upper part of the diaphragm electrolytic cell 16, and the anode side has a sealed structure, and a pipe for guiding the generated chlorine gas N to the sludge solubilization tank 7 through an air pump. An air diffusing tube is incorporated in the solubilization tank so that air can be diffused.
On the cathode side, hydrogen gas is generated, but normally there is no application that can be used. Therefore, a facility for releasing the atmosphere as it is or forcibly exhausting it through a pipe is provided.
Further, the strongly acidic water L generated at the anode due to the effect of electrolysis and the diaphragm is sent to the acid storage part of the acid addition device 9, and the strong alkaline water M generated at the cathode is the alkali storage part of the alkali addition device 12. Piping is provided to feed water to

Next, the operation of this embodiment will be described.
The surplus sludge D introduced into the sludge solubilization tank 7 by the sludge transfer pump 6 contains a phosphoric acid compound insolubilized by the addition of a flocculant, phosphoric acid incorporated into the microorganism, and solid solid phosphorus. Yes.
When the treatment such as heating is performed in the sludge solubilization tank 7, the sludge microorganisms are sterilized and a part of the solid matter is solubilized.
At this time, chlorine gas N generated by diaphragm electrolysis is blown into the solubilization tank 7 and is dissolved in water, and is converted into a component having strong oxidizing power such as hypochlorous acid. it can.
Subsequently, in the phosphorus release tank 8, when the strongly acidic water L is injected so that the pH is 3 or less, preferably 2 or less, phosphorus is dissolved from the phosphate compound into the water by the action of the acid, or the phosphorus is in the microorganism body. Most of the phosphorus is released from sludge and solids into the water.
That is, in the sludge solubilization tank 7, sludge microorganisms are killed, cell walls and cell membranes constituting the microorganisms are broken and the cytoplasm in the cells is eluted, and in the phosphorus release tank 8, acid addition is performed. Due to the action, phosphorus in the solid is mainly converted into a phosphoric acid state and released into the water of the solubilized sludge.

Of the solubilized sludge E from which phosphorus has been released, solid matter is precipitated in the solid-liquid separation tank 10, and the solubilized liquid G overflows and is led to the pH adjustment tank 11. In addition, solid-liquid separation can also be performed using membrane separation instead of precipitation separation.
In the pH adjusting tank 11, when strong alkaline water M is added to the separated solubilized liquid G to neutralize it, most of the dissolved phosphorus becomes solid again, and phosphoric acid is also a metal salt of a flocculant. It reacts to become a phosphoric acid compound and is insolubilized.
At this time, since the inorganic substance dissolved by the acid also returns to a solid substance as the pH rises, the sludge H obtained by precipitation in the subsequent precipitation separation tank 13 becomes a sludge mainly composed of an inorganic substance such as a phosphate compound.
The separated water I overflowed as the supernatant water in the sedimentation separation tank 13 contains organic substances dissolved in the process of solubilization, but has been converted to easily decomposable components by lowering the molecular weight. It can be biodegraded by returning it to
Further, since the salt water remains in the separated water I, a part of the separated water I can be reused in addition to the salt water K used for diaphragm electrolysis.

  On the other hand, in the sludge F precipitated in the solid-liquid separation tank 10, microorganism cell walls, cell membrane fragments, and microorganisms that maintain the cell morphology remain, but they have been killed by the solubilization treatment, so the aeration tank 2 If it is returned to, it is gradually reduced in molecular weight by enzymes produced by sludge microorganisms, and finally decomposed into water and carbon dioxide.

In the diaphragm electrolytic cell 16, when a direct current is supplied while adding the salt water K, hydrochloric acid and hypochlorous acid are generated on the anode side, and the pH of the solution is lowered. It becomes a molecule and volatilizes on water.
The strongly acidic water L containing the generated hydrochloric acid is injected into the phosphorus release tank 8 through the acid addition device 9 and used for phosphorus release, and the generated chlorine gas N is supplied to the sludge solubilization tank 7 by an air pump. When blown into sludge, it dissolves in neutral sludge and is converted to hypochlorous acid having a high sterilizing power, so that it can be used to sterilize sludge microorganisms.
Further, on the cathode side of the diaphragm electrolytic cell 16, strong alkaline water such as sodium hydroxide or potassium hydroxide is generated according to the kind of added salt, and part of hydrogen ions is converted into hydrogen gas. Strong alkaline water M containing a high concentration of hydroxide ions is sent to the pH adjustment tank 11 via the alkali addition device 12, and hydrogen gas is diffused into the atmosphere.

As described above, the sludge treatment method of the present embodiment sterilizes and solubilizes surplus sludge generated in the activated sludge method, returns it to the aeration tank, biodegrades it with activated sludge in the aeration tank, and small amounts of phosphorus. Therefore, the amount of sludge discharged can be reduced to about 1/10 of the conventional activated sludge method, and the phosphorus removal performance is not deteriorated in water treatment.
Furthermore, the acid and alkali to be added can be produced in the system by subjecting salt water to membrane electrolysis, and the by-product chlorine gas can be used for sterilization of sludge microorganisms.
Further, since the separation water obtained by precipitation separation of phosphorus-based sludge contains salt water, the running cost can be reduced by returning it to the membrane electrolytic cell and reusing it.

  As mentioned above, although the processing method of the sludge of the present invention was explained based on the example, the present invention is not limited to the composition described in the above-mentioned example, the composition described in the example is appropriately combined, etc. The configuration can be changed as appropriate without departing from the spirit of the invention.

  The sludge treatment method of the present invention has the property of preventing phosphorus from being deteriorated by simply removing a minimum amount of sludge as excess sludge, and is therefore limited to domestic wastewater such as sewage. First, it can be applied to an industrial wastewater treatment facility that uses the activated sludge process to discharge excess sludge.

It is a system flowchart which shows one Example of the processing method of the sludge of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pretreatment equipment 2 Aeration tank 3 Final sedimentation tank 4 Coagulant addition apparatus 5 Sludge return pump 6 Sludge transfer pump 7 Sludge solubilization tank 8 Phosphorus release tank 9 Acid addition apparatus 10 Solid-liquid separation tank 11 pH adjustment tank 12 Alkali addition apparatus 13 Precipitation separation tank 14 Sludge extraction pump 15 Sludge storage tank 16 Diaphragm electrolysis tank 17 Diaphragm A Wastewater B Treated water C Return sludge D Surplus sludge E Solubilized sludge F Sludge G Solubilized liquid H Extracted sludge I Separated water J Discharged sludge K Salt water L Strong acid water M Strong alkaline water N Chlorine gas

Claims (3)

  A method for treating sludge, in which organic sludge is biologically treated with activated sludge in an aeration tank, and excess sludge generated by biological treatment is solubilized, and then returned to the aeration tank for decomposition. In the sludge sterilized and solubilized in the sludge solubilization tank, strong acid water obtained by diaphragm electrolysis of salt water is added to release phosphorus, and then the solubilized solution obtained by solid-liquid separation And a strong alkaline water obtained by subjecting salt water to membrane electrolysis to neutralize, and insolubilize phosphorus again to precipitate and separate.   The method for treating sludge according to claim 1, wherein chlorine gas generated at the anode of the diaphragm electrolyzer is introduced and blown into a sludge solubilization tank, and the dissolved hypochlorous acid is used for sterilization of sludge microorganisms.   The method for treating sludge according to claim 1 or 2, wherein a part of the separated water obtained by precipitation separation of phosphorus is returned to the diaphragm electrolyzer, and the remaining salinity is reused.

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