JP4610977B2 - Method and apparatus for treating sludge return water - Google Patents

Description

  The present invention is produced by concentrating or dewatering first sedimentation basin sludge, final sedimentation basin sludge generated in a sewage treatment plant or digested sludge obtained by aerobically or anaerobically digesting them. The present invention relates to a method and apparatus for treating sludge return water.

At the sewage treatment plant, treatment and operation are performed mainly for the purpose of removing solids and organic matter in the sewage that has flowed in.
That is, primary sedimentation is provided for removing 夾 matters in the influent sewage, adsorption and decomposition by activated sludge microorganisms made in biological reactor to remove organics, in the settling tank and on the activated sludge microorganisms supernatant water By separating the water, good treated water can be obtained.
In some treatment plants, the sludge removed from the first sedimentation basin and the final sedimentation basin may be aerobically or anaerobically digested to stabilize the sludge. Digested sludge is obtained as sludge.

These initial sedimentation basin sludge, final sedimentation basin sludge and digested sludge need to be appropriately treated and disposed of in the subsequent sludge treatment system, and one of the treatment processes includes concentration treatment and dehydration treatment.
These processes are positioned as pretreatment for efficiently performing the subsequent treatment, and the main purpose is to separate the moisture and solid content in the sludge, thereby reducing the volume of the sludge.
The water obtained at this time is generally called return water, returned to the water treatment system and subjected to biological treatment again.
In the present specification, the return water generated in the sludge treatment system is simply referred to as sludge return water.

By the way, sludge return water contains high concentrations of organic substances, ammonia, phosphorus and the like, which may adversely affect the water treatment system.
That is, in the water treatment system, organic matter in the inflowing sewage is usually biologically treated using aerobic microorganisms, and it is necessary to forcibly introduce air, but the organic matter and ammonia in the sludge return water are simultaneously introduced. In order to process, it is necessary to introduce more air. However, if the capacity of the facility is insufficient, there is a problem that the water area that receives the treated water may be contaminated by flowing out of the system without sufficient treatment.

  Therefore, in order to deal with this problem, the sludge return water from the sludge treatment system may be treated before being returned to the water treatment system. For example, a flocculant is added to the sludge return water or the sludge return water is used. A method of adding a flocculant after mixing it with sludge (see Patent Document 1), a method of adding ozone and a flocculant to sludge return water (see Patent Document 2), an activated sludge method with addition of a carrier and agglomeration There is a processing method (see Patent Document 3) in which addition of an agent is used in combination.

  On the other hand, in recent years, as part of the utilization of biomass, there has been a movement to promote the effective use of organic waste, and the effective use of sewage sludge has also been achieved at sewage treatment plants. Sludge return water also contains a small amount of organic matter compared to the sewage sludge itself, and since a considerable amount is continuously discharged, it can be regarded as a stable biomass source.

The sludge return water treatment method described above can remove problematic organic substances, ammonia, phosphorus, etc., but when a flocculant is added to the sludge return water itself, the organic matter in the sludge return water is also removed. Since it coagulates and settles, a large amount of sludge is generated, resulting in a contradiction that a large amount of sludge is generated in the sludge treatment system for treating the sludge.
In addition, the treatment with ozone can decompose organic substances and oxidize ammonia with its strong oxidizing power, but the equipment is complicated and operating costs are increased, such as the need for ozone generator and waste ozone treatment equipment. Can be said to be a problem.
Moreover, in these methods, sludge return water is handled as waste to the last, and effective use such as recovery of useful materials and use of energy is not achieved.
Japanese Patent Application Laid-Open No. 07-256295 Japanese Patent Laid-Open No. 05-269478 JP 2004-025055 A

  In view of the problems of the above conventional sludge return water treatment method, the present invention can reduce the amount of sludge generated in the process of treating sludge return water as much as possible, and can effectively use the sludge return water itself. It aims at proposing the processing method and processing device of sludge return water.

In order to achieve the above object, the sludge return water treatment method of the present invention is a sludge such as a first sedimentation basin sludge, a final sedimentation basin sludge, or a digestion sludge obtained by aerobic / anaerobic digestion generated in the process of sewage treatment. In the treatment method of sludge return water generated by concentrating and dewatering sludge in the sludge treatment system for treating sewage, the organic matter in the sludge return water is used as the fuel source of the microbial fuel cell. On the side, oxygen gas or oxygen contained in the air and nitrifying bacteria are introduced and removed.

In this case, denitrifying bacteria can be introduced to the negative electrode side of the microbial fuel cell kept in an anaerobic state, and a solution containing nitrate ions can be circulated to the negative electrode side.

  Further, nitrifying bacteria involved in nitrification can be held on the positive electrode of the microbial fuel cell, and denitrifying bacteria involved in denitrification can be held on the negative electrode of the microbial fuel cell.

On the other hand, in order to achieve the same purpose, the sludge return water treatment apparatus of the present invention is the first sedimentation basin sludge, final sedimentation basin sludge generated in the process of sewage treatment, digested sludge obtained by aerobic / anaerobic digestion, etc. In the sludge treatment system that treats sludge in the sludge treatment system, sludge return water is generated by concentrating and dewatering sludge. A battery is provided , and oxygen and nitrifying bacteria contained in oxygen gas or air are introduced into the positive electrode side of the microbial fuel cell .

In this case, denitrifying bacteria can be introduced to the negative electrode side of the microbial fuel cell kept in an anaerobic state, and a solution containing nitrate ions can be circulated to the negative electrode side.
The denitrifying bacteria are held on the negative electrode side of the microbial fuel cell kept in an anaerobic state, and a solution in which ammonia ions are oxidized to nitrate ions is circulated to the negative electrode side, and reduced to nitrogen gas by the denitrifying bacteria to be removed. it can.

  Further, nitrifying bacteria involved in nitrification can be held at the positive electrode of the microbial fuel cell, and denitrifying bacteria involved in denitrification can be held at the negative electrode of the microbial fuel cell.

According to the method and apparatus for treating sludge return water of the present invention, sludge such as first sedimentation basin sludge, final sedimentation basin sludge, or digestion sludge obtained by aerobic / anaerobic digestion generated in the process of sewage treatment is treated. In the sludge treatment system, sludge return water produced by concentrating and dewatering sludge is removed by using organic matter in the sludge return water as a fuel source of the microbial fuel cell. The sludge return water can be treated without the generation of a large amount of sludge in the sludge treatment system, which tends to be a problem in the treatment method.
In particular, it is possible to treat organic substances and ammonia in sludge return water with good treatment, and electrical energy can be recovered from sludge return water, so-called organic waste can be utilized. .

Then , by introducing oxygen gas or oxygen contained in the air and nitrifying bacteria into the positive electrode side of the microbial fuel cell, ammonia ions contained in the sludge return water can be oxidized to nitrate ions.

  Further, by introducing denitrifying bacteria to the negative electrode side of the microbial fuel cell kept in an anaerobic state and circulating a solution containing nitrate ions to the negative electrode side, a solution in which ammonia ions are oxidized to nitrate ions is removed by denitrifying bacteria. It can be reduced to gas and removed.

  Further, by holding nitrifying bacteria involved in nitrification at the positive electrode of the microbial fuel cell and denitrifying bacteria involved in denitrification at the negative electrode of the microbial fuel cell, nitrifying bacteria and denitrifying bacteria can be efficiently converted into a microbial fuel cell. Can be thrown in.

  Hereinafter, embodiments of the method and apparatus for treating sludge return water of the present invention will be described with reference to the drawings.

1 to 4 show an embodiment of the method and apparatus for treating sludge return water of the present invention.
This sludge return water treatment method is used in sludge treatment systems that treat sludge such as first sedimentation basin sludge, final sedimentation basin sludge, or digestion sludge obtained by aerobic / anaerobic digestion during the sewage treatment process. The sludge return water produced by concentrating and dewatering the sewage is treated, and organic matter in the sludge return water is removed by using it as a fuel source of the microbial fuel cell.

A microbial fuel cell is a fuel cell that uses an organic substance as a fuel source and a microorganism as a biocatalyst, and a conceptual diagram thereof is shown in FIG.
The microbial fuel cell comprises a negative electrode chamber 2 provided with a negative electrode 1 and a positive electrode chamber 4 provided with a positive electrode 3, which are separated by a proton permeable membrane 5, and the negative electrode 1 and the positive electrode 3 are connected to an external circuit 6. Connected by. The negative electrode chamber 2 is maintained under anaerobic conditions in which molecular oxygen does not exist, and anaerobic microorganisms 7 are retained.

The organic matter 8 put into the negative electrode chamber 2 is metabolized by the anaerobic microorganism 7, and in the process, generates electrons 10 and releases hydrogen ions 9 as metabolites.
On the other hand, in the metabolic mechanism by the anaerobic microorganism 7, electrons 10 are exchanged intracellularly or with the final electron acceptor, but the negative electrode 1 is made to hold iron (III) ions, manganese (IV) ions, or the like. Then, these act as a final electron acceptor, and can transfer electrons to the negative electrode 1.

The electrons 10 taken into the negative electrode 1 move to the positive electrode 3 through the external circuit 6. Further, molecular oxygen 11 is introduced into the positive electrode chamber 4, and is combined with electrons 10 and hydrogen ions 9 that have passed through the proton permeable membrane 5 on the positive electrode 3 holding platinum or the like to form water molecules 12. Change.
As for the proton permeable membrane 5, by utilizing this, a favorable reaction proceeds by selectively allowing hydrogen ions 9 to permeate from the negative electrode chamber 2 to the positive electrode chamber 4, but a cation exchange membrane can be used instead. It is possible to proceed the reaction without installing the permeable membrane itself.
By a series of these reactions, the electrons 10 are moved between the negative electrode 1 and the positive electrode 3, and electric energy is generated.

As described above, the microbial fuel cell is an apparatus that generates electric energy using an organic substance as a fuel source, but can also be regarded as an apparatus that can simultaneously treat wastewater containing the organic substance.
That is, the organic matter in the wastewater is decomposed and removed by the metabolism of anaerobic microorganisms, that is, the growth of microorganisms.
However, because it is under anaerobic conditions, the conversion efficiency from organic matter to new cells of microorganisms is much lower than under aerobic conditions such as water treatment systems, and the growth of microorganisms, that is, the generation of sludge is kept low. There is an advantage that can be.
Furthermore, in microbial fuel cells, electrons are acquired from microorganisms. In addition to acquiring electrons as the final electron acceptor, there is a method of acquiring electrons from the middle of the metabolic process. Since it also has an inhibitory function, the amount of sludge generated can be further reduced.

Further, in the positive electrode chamber 4 in FIG. 1, molecular oxygen 11 is introduced to receive the electrons 10, and ammonia contained in the sludge return water is oxidized to nitrate ions using this oxygen and nitrifying bacteria. It is also possible.
Furthermore, by providing a tank holding denitrifying bacteria in the subsequent stage, nitrate ions can be reduced to nitrogen gas and nitrogen removal from the sludge return water can be performed.

Phosphorus is somewhat reduced by passing through a treatment apparatus using a microbial fuel cell, but most of it cannot be treated, so it must be removed by adding a flocculant or the like as in the prior art.
However, unlike conventional ones, organic matter is removed, so there is no need to generate more coagulated sludge, compared to the amount of sludge generated when flocculant is added to the sludge return water itself as before. A small amount.

Of sludge return water, particularly those obtained from anaerobic digested sludge may contain a large amount of solids, but when solids are included that impede the operation of the treatment apparatus according to the present invention. Does solid-liquid separation by gravity sedimentation or mechanical concentration, but does not add a flocculant so as not to remove organic matter more than necessary.
As another method for reducing solids, solids can be dissolved by physicochemical techniques such as solubilization, but this method not only reduces the amount of solid-liquids but also solids. It is expected that the concentration of organic substances in the solution due to liquefaction will be increased, that is, the amount of fuel input to the microbial fuel cell will increase.

In FIG. 2, an example of the processing apparatus of the sludge return water by this invention is shown.
In addition, the sludge return water which was made into the object in a present Example contains the return water from anaerobic digestion, and shall contain many solid substances, and in order to remove this, the solid-liquid separation tank is provided in the front | former stage.
Sludge return water A is subjected to solid-liquid separation in the gravity sedimentation basin 13 to obtain supernatant water B and precipitated sludge C.
The recovered sludge C collected here is returned to the water treatment system, but was originally contained in the sludge return water A and does not become sludge newly generated in the sludge treatment system.

The supernatant water B flows into the microbial fuel cell separated by the partition wall 14 from the negative electrode chamber 2 and the positive electrode chamber 4, but first flows into the negative electrode chamber 2 kept under anaerobic conditions.
Here, the organic matter in the supernatant water B is decomposed and removed by the microorganisms held in the negative electrode 1, and electrons obtained from the metabolic process are guided to the positive electrode 3 through the external circuit 6.
In the present embodiment, microorganisms involved in the decomposition of organic substances are held in the negative electrode 1, but can be suspended in the negative electrode chamber 2.

The supernatant water B from which organic substances have been removed flows through the partition wall 14 and is guided to the positive electrode chamber 4, but here air D is introduced by the air diffuser 15.
Oxygen contained in the introduced air D reacts with electrons passing through the external circuit 6 on the positive electrode 3 holding platinum or the like and hydrogen ions in the supernatant water B to become water.
Further, nitrifying bacteria are held in the positive electrode chamber 4, and ammonia ions in the supernatant water B are oxidized to nitrate ions.

  The solution that has undergone these series of treatments flows into the denitrification tank 16 as primary treated water E. Here, nitrate ions are removed from the system as nitrogen gas by the action of the denitrifying bacteria retained in the denitrification tank 16. Released / removed. In this denitrification process, organic substances in the solution are used for denitrifying bacteria, and therefore can be further removed.

The solution from which nitrogen has been removed flows out as the secondary treated water F, but since the solution still contains phosphorus, a flocculant G is added to remove this, and in the coagulation sedimentation tank 17 Solid-liquid separation is achieved with phosphorus removal.
The supernatant water obtained by this is returned to the water treatment system as the final treated water H, but since organic substances and the like have been sufficiently removed, no great load is given to the water treatment system.
On the other hand, in the coagulation sedimentation tank 17, coagulation sludge I is generated as a solid content, but most of organic substances other than phosphorus are removed by the treatment in the negative electrode chamber 2, the positive electrode chamber 4 and the denitrification tank 16 in the previous stage. There is no risk of generating more sludge than necessary.

In FIG. 3, an example of the processing apparatus of sludge return water using the principle of a microbial fuel cell is shown.
The sludge return water A is introduced as an upward flow from the lower end of the negative electrode chamber 2 kept under anaerobic conditions. In the upper part of the negative electrode chamber 2, a negative electrode 1 holding microorganisms is installed, which decomposes and removes organic substances in the sludge return water A, transfers electrons from the microorganisms to the negative electrode 1, and passes through an external circuit 6. Electron transmission to the positive electrode 3 is performed.

A part of the solution overflowed from the negative electrode chamber 2 is led to the positive electrode chamber 4 as the negative electrode chamber effluent J. Other than that, the solution is circulated for further processing and securing an upward flow velocity in the negative electrode chamber 2. .
The negative electrode chamber effluent J excluding the circulation is introduced as an upward flow from the lower end of the positive electrode chamber 4. An air diffuser 15 is provided at the bottom of the positive electrode chamber 4 to provide air into the tank, but oxygen in the air, electrons that have passed through the external circuit 6, and hydrogen in the negative electrode effluent J Ions react on the positive electrode 3 to generate water molecules.
In addition, a nitrifying bacteria holding carrier 18 is provided on the upper stage of the positive electrode 4, and ammonia ions in the negative electrode chamber effluent J are oxidized to nitrate ions by the action of the held nitrifying bacteria.

  A part of the cathode chamber effluent K overflowing from the cathode chamber 4 is discharged out of the system as the treatment liquid L, but the others are circulated to the cathode chamber 4 or returned to the anode chamber 2. The portion circulated to the positive electrode chamber 4 is used for further promoting nitrification and ensuring an appropriate upward flow velocity in the positive electrode chamber 4.

On the other hand, with respect to the portion of the positive electrode chamber effluent K that is returned to the negative electrode chamber 2, nitrate ions in the solution are caused by the action of the denitrifying bacteria held in the denitrifying bacteria holding carrier 19 installed in the lower stage of the chamber. Reduced to nitrogen gas.
The negative electrode chamber effluent J is used for securing the flow rate as described above, but is also necessary for securing the time required for denitrification.

The two-tank sludge return water treatment device shown in Example 2 can be a single-tank device, and a cross-sectional view of an example thereof is shown in FIG.
The sludge return water A is introduced into the treatment tank 21 as an upward flow through the introduction pipe 20. Inside the tank, a cylindrical inner wall 22 is provided, and the introduced sludge return water A flows upward in the inner wall 22 as shown by the broken line arrow in FIG. It flows between the outside and the treatment tank 21 as a circulating fluid M in a downward flow.

The inner wall 22 plays a role of supporting the electrode, the microorganism holding carrier and the air diffuser in addition to generating the upward / downward flow as described above.
That is, the denitrifying bacteria holding carrier 19, the negative electrode 1, the air diffuser 15, the positive electrode 3, and the nitrifying bacteria holding carrier 18 are supported in order from the lower end.
In this embodiment, the denitrifying bacteria holding carrier 19 and the nitrifying bacteria holding carrier 18 represent a type of carrier that is fixed to the inner wall 22, but a floating type carrier provided with a mechanism that does not flow out. Can also be used.

The organic matter in the sludge return water A is decomposed and removed by the microorganisms held on the negative electrode 1, and electrons transferred to the electrode in this metabolic process go to the positive electrode 3 provided in the upper stage through the external circuit 6. Moving.
An air diffuser 15 is provided on the upper stage of the negative electrode 1, and air D is introduced through the air pipe 23, and oxygen contained in the air D passes through hydrogen ions generated in the negative electrode 1 and the external circuit 6. It reacts on the positive electrode 3 together with the electrons sent to the positive electrode 3 to generate water.
Further, oxygen contained in the air D is used by the nitrifying bacteria held in the nitrifying bacteria holding carrier 18 to oxidize ammonia ions in the sludge return water A to nitrate ions, and the remaining organic substances are removed. It is also used to decompose aerobically.

A part of the solution that has passed through the inner wall 22 passes through the overflow wall 24 and is discharged out of the system as treated water L, and the other is a circulating fluid M that flows between the inner wall 22 and the treatment tank 21 as a downward flow. It flows.
During this time, the oxygen contained in the solution has a low specific gravity, so it moves upward and is released to the atmosphere, or consumed for the reaction with the remaining organic matter, etc., and the oxygen concentration in the solution gradually decreases, and at the bottom Almost zero, that is, anaerobic state.

  The circulating fluid M that has reached the bottom of the treatment tank 21 flows again as an upward flow inside the inner wall 22 together with the sludge return water A flowing from the introduction pipe 20, but at the lower end of the inner wall 22, the denitrifying bacteria holding carrier 19. The denitrifying bacteria held in the carrier 19 are denitrified using nitrate ions in the circulating fluid M and organic matter in the sludge return water A, that is, nitrate ions are reduced to nitrogen gas, This makes it possible to remove nitrogen from the solution.

  As mentioned above, although the processing method and processing apparatus of sludge return water of the present invention were explained based on a plurality of examples, the present invention is not limited to the composition described in the above-mentioned example, and is described in each example. The configurations can be appropriately changed without departing from the gist of the configurations, for example, by appropriately combining the configurations.

  The method and apparatus for treating sludge return water according to the present invention has the characteristics that the amount of sludge generated in the process of treating sludge return water is minimized and the sludge return water itself is effectively utilized. For example, it can be suitably used in a sewage treatment plant.

It is a conceptual diagram which shows a microbial fuel cell. It is a flowchart which shows 1st Example of the processing apparatus of sludge return water of this invention. It is a flowchart which shows the 2 tank type processing apparatus of the sludge return water of this invention. It is sectional drawing which shows the 1 tank type processing apparatus of the sludge return water of this invention.

DESCRIPTION OF SYMBOLS 1 Negative electrode 2 Negative electrode chamber 3 Positive electrode 4 Positive electrode chamber 5 Proton permeable membrane 6 External circuit 7 Anaerobic microorganism 8 Organic substance 9 Hydrogen ion 10 Electron 11 Molecular oxygen 12 Water molecule 13 Gravity sedimentation basin 14 Partition 15 Aeration apparatus 16 Denitrification tank 17 Aggregation Precipitation tank 18 Nitrifying bacteria holding carrier 19 Denitrifying bacteria holding carrier 20 Introduction pipe 21 Treatment tank 22 Inner wall 23 Air piping 24 Overflow wall A Sludge return water B Supernatant water C Precipitation sludge D Air E Primary treated water F Secondary treated water G Aggregation Agent H Final treated water I Aggregated sludge J Anode chamber effluent K Cathode chamber effluent L Treated water M Circulating fluid

Claims (6)

Concentrate and dewater sludge in a sludge treatment system that treats sludge such as first sedimentation basin sludge, final sedimentation basin sludge, or digested sludge obtained by aerobic / anaerobic digestion during the sewage treatment process. When the organic matter in the sludge return water is removed as a fuel source for the microbial fuel cell, oxygen and nitrogen contained in the oxygen gas or air are nitrified on the positive electrode side of the microbial fuel cell. A method for treating sludge return water, characterized by introducing bacteria . Introducing denitrifying bacteria to the negative of the microbial fuel cell which is kept in anaerobic conditions, the sludge return running water processing method according to claim 1, wherein the solution is characterized by circulating the negative electrode side containing nitrate ions. The method for treating sludge return water according to claim 2, wherein nitrifying bacteria involved in nitrification are held in the positive electrode of the microbial fuel cell, and denitrifying bacteria involved in denitrification are held in the negative electrode of the microbial fuel cell. Concentrate and dewater sludge in a sludge treatment system that treats sludge such as first sedimentation basin sludge, final sedimentation basin sludge, or digested sludge obtained by aerobic / anaerobic digestion during the sewage treatment process. In the treatment apparatus for sludge return water produced by the above, sludge return water flows in, a microbial fuel cell using the organic matter of the sludge return water as a fuel source is provided , and contained in oxygen gas or air on the positive electrode side of the microbial fuel cell The sludge return water treatment apparatus is characterized in that oxygen and nitrifying bacteria are introduced . The apparatus for treating sludge return water according to claim 4 , wherein denitrifying bacteria are introduced to the negative electrode side of the microbial fuel cell kept in an anaerobic state, and a solution containing nitrate ions is circulated to the negative electrode side. . 6. The apparatus for treating sludge return water according to claim 5, wherein nitrifying bacteria involved in nitrification are held in the positive electrode of the microbial fuel cell, and denitrifying bacteria involved in denitrification are held in the negative electrode of the microbial fuel cell.

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