JP2002059190A - Method of treating sewage and sludge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of treating sewage and sludge which is capable of performing the removal of organic matter and the advanced treatment of phosphorus simply by adding a dephosphorization function to a process of solubilizing the sludge and withdrawing the least possible sludge as the excess sludge and is capable of recovering the energy included in the sludge in the form of digester gas, such as gaseous methane. SOLUTION: The method of treating the sewage and sludge which performs the water treatment by an activated sludge method in a water treating process step consisting of a Complete anaerobic tank 2 and a reaction chamber 3 by adding the return sludge C to the inflow sewage A consists in introducing part of the activated sludge which incorporates the phosphorus into the bodies of microorganisms to an anaerobic digester 6 to generate the digester gas I, such as the gaseous methane, releasing the phosphorus from the sludge microorganisms, then subjecting the sludge to the separation of solid from the liquid, adding a flocculating agent to the separated water containing a high concentration of phosphorus, introducing the sludge to a coagulating sedimentation tank 13 where the flocculated sludge is settled and separated, introducing the thickened digested sludge D to a sludge solubilizing tank 11 and subjecting the sludge to solubilization treatment, then returning the sludge to the water treating process step.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating sewage and sludge, and more particularly, to treating an organic sewage containing phosphorus by an activated sludge method to remove organic substances and phosphorus and to reduce energy contained in the sludge. The present invention relates to a method for treating sewage and sludge that is collected in the form of digestive gas such as methane gas and minimizes the amount of generated sludge.

[0002]

2. Description of the Related Art Conventionally, as a method of treating sewage flowing into a sewage treatment plant or the like, sewage is introduced into a reactor for activated sludge,
The activated sludge method which performs a biological treatment by aerating and stirring this is adopted. And, in recent years, from the viewpoint of preventing eutrophication, it has been desired to remove not only organic matter in the inflowing sewage but also nitrogen and phosphorus in the sewage, and as a method therefor, a plurality of water tanks are used. Therefore, a method of biologically denitrifying and dephosphorizing is used, and excess sludge generated in this water treatment step is usually dewatered and then landfilled.

[0003]

In the above-mentioned conventional method for treating sewage and sludge, the excess sludge generated in the water treatment step needs to be dewatered and landfilled. It is difficult to find a disposal site for landfilling of excess sludge in the vicinity of the area, and there is a problem that a pollution problem occurs. As the disposal site is gradually disappearing, a method has been attempted in which excess sludge is added to ozone to solubilize the sludge and biodegrade in the system to reduce the amount of sludge generated to zero. However, such a technology for eliminating sludge has a new problem that phosphorus that has been conventionally recovered as excess sludge cannot be removed at all.

The present invention has been made in view of the above-mentioned problems of the conventional methods for treating wastewater and sludge, and has a dephosphorization function added to the process of solubilizing the sludge. It is an object of the present invention to provide a method for treating sewage and sludge that can remove ash and perform advanced treatment of phosphorus and can collect energy contained in sludge in the form of digestive gas such as methane gas.

[0005]

Means for Solving the Problems To achieve the above object, a method for treating wastewater and sludge in which return sludge is added to inflowed wastewater and water is treated by an activated sludge method in a water treatment step comprising a completely anaerobic tank and a reaction tank. At the same time, a part of the activated sludge incorporating phosphorus into the body of microorganisms is introduced into an anaerobic digestion tank to generate digestive gas such as methane gas, and phosphorus is released from the sludge microorganisms. To the separated water containing phosphorus at a concentration, a coagulant is added, and the coagulation sludge is precipitated and separated by introducing the coagulation sedimentation tank, and the concentrated digested sludge is guided to the sludge solubilization tank and subjected to solubilization treatment. It is characterized by returning to the water treatment process.

In this method for treating wastewater and sludge, in a completely anaerobic tank in the water treatment step, the returned sludge is made completely anaerobic so that the sludge microorganisms take in phosphorus in the body in the form of polyphosphorus in a water-soluble manner. Phosphoric acid is released out of the sludge as phosphoric acid, so the phosphoric acid concentration temporarily increases, but the released phosphoric acid etc.
By making the sludge aerobic, it absorbs more phosphorus than the microorganisms released, and at this time, phosphorus contained in the influent water is also taken up by the sludge microorganisms,
Dephosphorization can be performed. Phosphorus taken into the sludge withdraws a part of the sludge from the return line from the sedimentation tank to the anaerobic digestion tank, and performs acid fermentation and methane fermentation with stirring for about 1 to 4 weeks to produce sludge. Partial solubilization decomposes organic matter and generates digestive gas such as methane gas.During this time, excess phosphorus that has been taken in by the sludge microorganisms as polyphosphoric acid is released again as water-soluble phosphoric acid and the like. The phosphorus contained in the solubilized sludge is also eluted. The digested sludge is sequentially transferred to the subsequent sedimentation and concentration tank, and subjected to sedimentation and separation, so that the concentrated separation water containing a high concentration of phosphorus is sequentially overflowed, and when flowing into the subsequent coagulation and sedimentation tank, a metal salt system is used. By adding and mixing a flocculant, water-soluble phosphoric acid and the like are reacted with the metal salt to insolubilize and coagulate and precipitate. The sludge concentrated in the sedimentation concentration tank is led to the sludge solubilization tank, and the cell wall and cell membrane of sludge microorganisms can be further improved by adding an oxidizing agent that generates ozone or radicals, or by performing high-temperature / high-pressure treatment or ultrasonic treatment. Can be solubilized. The organic matter of the solubilized sludge can be easily biodegraded, so it is returned to the water treatment step and decomposed by activated sludge. Thus, the sludge generated in the water treatment step is solubilized and decomposed, The sludge discharged to the tank is only coagulated sludge, which is about 1/10 of the conventional sludge. Sludge can be easily treated, digestion gas such as methane gas can be recovered from sludge, and phosphorus can be simultaneously removed.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the method for treating sewage and sludge of the present invention will be described below with reference to the drawings.

FIG. 1 is a process flow showing the method for treating sewage and sludge of the present invention. Sewage A flowing into a sewage treatment facility, for example, a sewage treatment plant, is first introduced into a pretreatment facility 1 where necessary pretreatment such as dust removal and sand removal or sludge removal is performed, and then a complete anaerobic tank 2 , And sequentially overflowed into the reaction tank 3. During this step, the organic matter in the sewage was biodegraded and phosphorus was taken up in the sludge, and then introduced into the final sedimentation tank 4 and flowed into the final sedimentation tank 4. The sludge mixture is separated into treated water and sludge by gravity separation, etc., and treated water B is discharged outside the system after disinfection, while most of the sludge settled in the final settling tank 4 is returned sludge. The water is continuously treated by the pump 5 in a water treatment step in which the sludge is returned to the complete anaerobic tank 2 as returned sludge C. In this case, the reaction tank 3 is provided with an aeration device (not shown) capable of intermittent aeration so as to perform denitrification in the reaction tank 3, or the reaction tank 3 is divided into a front chamber and a rear chamber (not shown). )
The anterior chamber was an anaerobic tank for denitrification, and the anterior chamber was an aerobic tank for nitrification. The anterior chamber and the posterior chamber were connected by a circulation line (not shown) composed of a pump and piping, and nitrification was performed. The liquid may be circulated from the rear chamber to the anaerobic tank in the front chamber.

In the water treatment step, a part of the settled sludge (returned sludge C) drawn out of the final settling tank 4 by the returned sludge pump 5 is guided to the anaerobic digestion tank 6. A gas tank 8 and a precipitation / concentration tank 7 are connected to the anaerobic digestion tank 6. The sludge led to the anaerobic digestion tank 6 is decomposed anaerobically by staying in the anaerobic digestion tank 6 for about one to several weeks, and phosphorus in the sludge is gradually released outside the sludge microorganisms. A digestive gas I containing methane gas as a main component is generated. The generated digestive gas I is guided to a gas tank 8 and stored therein. On the other hand, the sludge digested in the sedimentation concentration tank 7 is referred to as digested sludge D. It is introduced by successively overflowing into the subsequent concentration / concentration tank 7.

A sludge solubilization tank 11 and a coagulation sedimentation tank 13 are connected to the precipitation concentration tank 7. In this precipitation concentration tank 7,
When the sedimentation and separation of the digested sludge D is performed, the phosphorus having a high concentration overflows together with the concentrated separation water to flow into the coagulation sedimentation tank 13 sequentially. In this case, a coagulant adding device 12 for adding a coagulant is provided during the flow of the concentrated separation water into the coagulation / sedimentation tank 13. By injecting a metal salt-based coagulant from the coagulant adding device 12 into the concentrated separation water and mixing it, high-concentration phosphorus (such as phosphoric acid) contained in the concentrated separation water is insolubilized and converted into coagulated sludge.

A sludge storage tank 15 is connected to the coagulation / sedimentation tank 13 via a sludge extraction pump 14. This allows
The coagulated sludge F precipitated in the coagulation sedimentation tank 13 is periodically withdrawn from the bottom by the sludge withdrawal pump 14 and transferred to the sludge storage tank 15. The coagulated sludge F extracted by the sludge extraction pump 14 is supplied to a sludge storage tank 15.
After being stored for about one to several weeks, it is carried out as extracted sludge H.

The supernatant water separated in the coagulation / sedimentation tank 13 is caused to overflow or to be drawn out by a pump, and is returned to the water treatment step, for example, the complete anaerobic tank 2 as separated water G. The supernatant water generated in the sludge storage tank 15 can be returned to the water treatment step together with the supernatant water from the coagulation settling tank 13.

On the other hand, the sludge concentrated in the precipitation concentration tank 7 is
The sludge solubilization tank 11 is connected to the sludge solubilization tank 11 so as to be guided to the sludge solubilization tank 11 by the sludge transfer pump 9 and subjected to solubilization. Thereby, the oxidizing agent that generates ozone and radicals is supplied from the sludge solubilization device 10 into the sludge solubilization tank 11, or in the sludge solubilization device 10, by ultrasonic waves, high temperature and / or high pressure, or Sludge is physically broken and solubilized.
The solubilized sludge E solubilized in the sludge solubilization tank 11 is guided to the completely anaerobic tank 2 by a pump (not shown) or by natural flow.

Next, the operation of the method for treating sewage and sludge of the present invention will be described. In the completely anaerobic tank 2 in the water treatment step, the sludge C returned from the final sedimentation tank 4 is made completely anaerobic, so that the phosphorus that the sludge microorganisms take up in the body in the form of polyphosphoric acid is converted into a water-soluble phosphate state. Released into the sludge. This is added to the phosphorus contained in the inflowing sewage A, and the phosphoric acid concentration temporarily increases. The released phosphoric acid and the like are contained in the influent water at this time because when the sludge is brought into the aerobic state in the reaction tank 3 at the subsequent stage, the phosphorus absorbed by the microorganisms is excessively absorbed in the microorganisms. Phosphorus is also taken up and dephosphorization occurs.

The sludge that has taken in phosphorus precipitates in the final sedimentation tank 4 and is mostly returned sludge as a completely anaerobic tank 2.
Therefore, the above processing is repeated, and the phosphorus concentration in the sludge gradually increases. A part of the returned sludge is sent to the anaerobic digestion tank 6 and is stirred under anoxic condition for about one to several weeks. At this time, the sludge is decomposed by the action of acid fermentation bacteria and methane bacteria growing in the tank. The sludge organic matter is converted into organic acids and digestive gas such as methane gas. The digestion gas I mainly composed of methane gas volatilized in the upper space from the sludge is led to the gas tank 8 and can be used as a useful energy source for gas power generation and the like.

During the period of one to several weeks in the anaerobic digestion tank 6, most of the phosphorus (polyphosphorus) excessively contained in the sludge microorganisms is released outside the body as phosphoric acid or the like again.
Further, phosphorus contained in the solubilized sludge is also eluted.

By guiding such digested sludge D to the sedimentation / concentration tank 7 and letting it stand still, the high-concentration phosphorus contained in the supernatant water overflows sequentially as concentrated separation water, and flows into the coagulation / sedimentation tank 13. During the addition, a flocculant is added to convert to a phosphoric acid compound. The coagulant to be added here is suitably an iron or aluminum-based metal salt. When added, water-soluble phosphoric acid reacts with the metal salt to insolubilize it, so that it is precipitated in the coagulation sedimentation tank 7.

Next, the sludge concentrated in the sedimentation concentration tank 7 is led to a sludge solubilization tank 11 where the sludge is solubilized. The means for solubilization is not particularly limited. Also, a method of adding an oxidizing agent that generates a radical, particularly an oxidizing agent that generates an OH radical, is effective. In addition, irradiate ultrasonic waves, temperature higher than normal temperature,
By using a method in which the treatment is performed at a pressure higher than the atmospheric pressure or both, the cell membrane is crushed, and the cytoplasm in the cells is eluted into the mixture.

Since the solubilized sludge organic matter can be easily biodegraded, it is guided to the completely anaerobic tank 2 (or the reaction tank 3) and decomposed by activated sludge. As described above, the sludge generated in the water treatment step is solubilized and decomposed, so that the sludge discharged out of the system is only coagulated sludge, which is about 1/10 of the conventional sludge, and can be simultaneously dephosphorized. Becomes
In the processing flow shown in FIG. 1, the final sedimentation tank 4, the sedimentation concentration tank 7, and the coagulation sedimentation tank 13 were all subjected to gravity sedimentation, but other solid-liquid separation means such as membrane separation and centrifugation were used. Can also be used.

The anaerobic digestion tank 6 performs acid fermentation and methane fermentation in a single tank, but may be divided into two stages. The temperature of the anaerobic digestion tank 6 can be set at a medium temperature of about 35 to 40 ° C., but it is preferable to heat the digestion gas I such as methane gas and perform digestion at a high temperature of 55 to 60 ° C. However, the reaction rate is high, the digestion days can be shortened, and the amount of the oxidizing agent for solubilization in the subsequent stage can be reduced.

Further, in the water treatment step, in order to enhance the effect of dephosphorization, a method of biologically dephosphorizing by an anaerobic and aerobic method was used in two stages of a completely anaerobic tank and a reaction tank. Even if it is omitted, a certain amount of phosphorus is absorbed into the body when the sludge microorganisms proliferate, so it can be discharged as coagulated sludge by eluting this phosphorus from the sludge in the anaerobic digestion tank. .

[0022]

According to the method for treating sewage and sludge of the present invention, in the water treatment step, the organic matter in the sewage is decomposed and phosphorus is taken into the sludge, and the sludge from the settling tank is returned from the line. Of the sludge to the anaerobic digestion tank to decompose the sludge and collect digestive gas such as methane gas,
After releasing the phosphorus from the sludge, solid-liquid separation is performed, and a coagulant is added to the supernatant water containing a high concentration of phosphorus, mixed and precipitated and separated in a coagulation sedimentation tank.
After leading to the sludge solubilization tank and solubilizing sludge microorganisms,
Since it is led to the water treatment process and decomposed by activated sludge, dephosphorization can be performed in the water treatment process, and digestive gas such as methane gas that can be effectively used as an energy source can be recovered in sludge treatment. And the amount of generated sludge is 1/1 of the conventional activated sludge method.
It can be reduced to about 10. Further, since it becomes inorganic sludge, the land required for landfill disposal after dehydration is reduced, and there is no problem such as generating odor due to anaerobic rot.

[Brief description of the drawings]

FIG. 1 is a process flow diagram of a sewage treatment facility that implements the method for treating sewage and sludge of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Pretreatment equipment 2 Complete anaerobic tank 3 Reaction tank 4 Final sedimentation tank 5 Return sludge pump 6 Anaerobic digestion tank 7 Sedimentation concentration tank 8 Gas tank 9 Sludge transfer pump 10 Sludge solubilizer 11 Sludge solubilizer 12 Coagulant addition apparatus 13 Coagulation sedimentation tank 14 Sludge extraction pump 15 Sludge storage tank A Sewage B Treatment water C Return sludge D Digestion sludge E Solubilized sludge F Coagulation sludge G Separation water H Export sludge I Digestion gas (methane gas)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D028 AC01 BC28 BD11 BE01 BE02 BE04 4D040 BB01 BB33 BB51 4D059 BA01 BA11 BA31 BE55 BK12 BK22 DA43 4D062 BA19 BA23 BB05 CA20 EA32 FA12 FA24 FA26

Claims (1)

[Claims] 1. A wastewater and sludge treatment method in which return sludge is added to inflow wastewater and water is treated by an activated sludge method in a water treatment step comprising a completely anaerobic tank and a reaction tank. A part of the sludge is introduced into the anaerobic digestion tank to generate digestive gas such as methane gas, and phosphorus is released from the sludge microorganisms.Then, solid-liquid separation is performed. Is added to the coagulation sedimentation tank to precipitate and separate the coagulated sludge, and the concentrated digested sludge is guided to the sludge solubilization tank, solubilized, and then returned to the water treatment step. Wastewater and sludge treatment method.