JP4685385B2 - Power generation method using surplus sludge - Google Patents

Description

  The present invention relates to a power generation method using surplus sludge, and particularly to obtain electric energy in the process of treating surplus sludge generated in a water treatment system that decomposes wastewater containing organic components using activated sludge microorganisms. The present invention relates to a power generation method using surplus sludge.

  Conventionally, many biological treatment methods using activated sludge microorganisms have been introduced as treatment methods for wastewater and wastewater containing organic substances. That is, wastewater containing organic substances is introduced into a container holding activated sludge microorganisms, and these are agitated or aerated as necessary to bring activated sludge microorganisms into contact with organic substances. Is used to decompose and treat organic substances in wastewater.

  On the other hand, the activated sludge microorganism group synthesizes and proliferates new cells by assimilating organic substances in the wastewater. In order to maintain a healthy treatment status in water treatment systems, it is necessary to appropriately pull out the activated activated sludge microorganisms as excess sludge outside the system for treatment and disposal, but it is difficult to secure the disposal site. In view of the current situation and the situation that most of the excess sludge is an organic substance, the idea of effective use is increasing.

Effective utilization methods include composting and use as a fertilizer or soil conditioner in green farmland, and bricks and pipes made by melting, etc., and use as building materials. There are methods of generating methane gas by sexual digestion and pelletizing excess sludge and using it as a solid fuel.
Among these, anaerobic digestion is to decompose and stabilize activated sludge microorganisms by utilizing the ability of anaerobic microorganisms in the absence of molecular oxygen, and it is combustible as one of its by-products. In recent years, methane gas, which is a natural gas, can be obtained and used for power generation and the like.

On the other hand, in the 1980s, research was conducted to extract electrical energy from organic substances using the metabolic function of microorganisms. In order to distinguish from fuel cells that acquire electrical energy from pure substances such as hydrogen, microbial fuel cells is called.
The concept of the microbial fuel cell is as shown in FIG. 2, and comprises a negative electrode 2 and a positive electrode 3, an external circuit 4 connecting them, and a diaphragm 5 separating the negative electrode side and the positive electrode side. Microorganisms 6 are held on the negative electrode side and metabolize using organic substances 7 to generate metabolites 8 and electrons 9. In addition, the electron transfer agent 10 is also held on the negative electrode side at the same time, and this takes away the electrons 9 generated in the microorganism and becomes a reduced electron transfer agent 11.

  The reduced electron transfer agent 11 delivers electrons 9 in the negative electrode 2, changes again to the electron transfer agent 10, and is used for acquiring electrons from the microorganism 6. The reaction on the negative electrode side is performed under so-called anaerobic conditions in which no molecular oxygen is present. Under anaerobic conditions, there are hydrogen ions as the metabolite 8, which moves to the positive electrode side through the diaphragm 5 due to a concentration gradient. Therefore, a hydrogen permeable membrane or a cation exchange membrane is used as the diaphragm 5.

  The electrons 9 transferred to the negative electrode 2 move to the positive electrode 3 through the external circuit 4. An oxidant 12 is introduced on the positive electrode side, receives electrons 9 on the positive electrode 3, and changes to a reduced oxidant 13. Note that oxygen is often used as the oxidant 12, which is reduced and combined with the hydrogen ions that have moved from the negative electrode side to change to water.

  In recent years, coupled with the progress of fuel cell technology, progress has been made in the materials constituting the microbial fuel cell, and its power generation capacity is being improved. In connection with this, some studies have also been conducted to apply this microbial fuel cell to wastewater treatment. In the paper shown in Non-Patent Document 1, the results of experiments to acquire electrical energy from the inflow water of a sewage treatment plant are shown. It has been reported. This paper reports that the higher the concentration of organic matter in the inflowing water, the greater the amount of power generated, and the use of a microbial fuel cell increases the ability to remove organic matter compared to when it is not.

As described above, a technique for acquiring electrical energy from the inflow water of a sewage treatment plant using a microbial fuel cell is being established, but the organic substance that is the fuel source of the microbial fuel cell is retained in the cell. It must be in a form that is easy for microorganisms to use. In the case of inflow water from a sewage treatment plant, as the current treatment status by activated sludge microorganisms shows, the organic substances contained in the inflow water are in a form that can be easily used by microorganisms.
By the way, most of the excess sludge targeted by the present invention is a microorganism itself, and the organic matter concentration is high and an increase in the amount of power generation is desired, but it has a strong cell membrane and cell wall, and the microorganism is metabolized in a short time. It is difficult to use as it is, and it is very difficult to use it as a fuel source of a microbial fuel cell as it is.
Hong Liu et.al .: Production of Electricity during Wastewater Treatment Using a Single Chamber Microbial Fuel Cell, Environmental Science Technology Vol. 38, No. 7, 2004, p.2281-2285

  Therefore, an object of the present invention is to provide a technology that can obtain electric energy by treating surplus sludge into a form that can be easily used by microorganisms as a fuel source in a subsequent microbial fuel cell.

In order to achieve the above object, the power generation method using surplus sludge of the present invention is a physicochemical which destroys the cell membrane and cell wall of sludge microorganisms against surplus sludge generated by biologically treating organic wastewater. A power generation method using surplus sludge as a fuel source for a microbial fuel cell, which is treated so as to be solubilized or easily assimilated by microorganisms, and by applying the physicochemical treatment, organic matter in the surplus sludge After the components are eluted, solid-liquid separation is performed, and the separated water is used as a fuel source of the microbial fuel cell, and the solid content is treated by an anaerobic digestion method .

In this case, as the physicochemical treatment, at least one of heat treatment, chemical treatment, and ultrasonic treatment can be performed.

  In this case, as the heat treatment, excess sludge can be heated at 30 ° C. or higher and lower than 300 ° C., preferably 50 ° C. or higher and 100 ° C. or lower.

  In addition, as the chemical treatment, the pH of the excess sludge is set to 10 or more using an alkali agent such as sodium hydroxide, the pH of the excess sludge is set to 5 or less using an acid such as hydrochloric acid, or ozone or hydrogen peroxide. Etc. can be added to the excess sludge.

  In addition, as the ultrasonic treatment, ultrasonic waves can be generated in water to generate fine bubbles and burst bubbles due to adiabatic compression.

  According to the power generation method using surplus sludge of the present invention, surplus sludge generated by biologically treating organic wastewater is subjected to physicochemical treatment that destroys the cell membrane and cell wall of sludge microorganisms. Since it is used as a fuel source for microbial fuel cells by making it easily solubilized or assimilated by microorganisms, the excess sludge that is not suitable as a fuel source for microbial fuel cells is changed to a form in which microorganisms can easily metabolize. As a result, electric energy can be obtained as a fuel source of the microbial fuel cell.

And after eluting the organic component in the excess sludge by performing the physicochemical treatment, solid-liquid separation is performed, and the separated water is used as a fuel source of the microbial fuel cell, and the solid content is anaerobically digested. Can improve the solid-liquid separability of the surplus sludge after treatment, and can provide a superior state for the sludge treatment in the latter stage. Not only can it be increased, but the sludge after treatment is in a form that is relatively easy to break down due to damage to the cell membrane and cell wall. Can be planned.
Thereby, not only the power generation by the microbial fuel cell but also the improvement of the power generation amount by the anaerobic digestion is seen, so that a lot of electric energy can be obtained.

In this case, as the physicochemical treatment, by performing at least one of heat treatment, chemical treatment and ultrasonic treatment, the cell membrane and cell wall of the sludge microorganisms constituting the excess sludge are altered or damaged in the cell membrane. The existing cytoplasm can be eluted to the solution side, and the effect can be increased synergistically by combining these treatments.

  In this case, as the heat treatment, the excess sludge is heated at 30 ° C. or more and less than 300 ° C., preferably 50 ° C. or more and 100 ° C. or less, and the activated sludge microorganisms constituting the excess sludge are sterilized, and the cell membrane and cell wall are formed. Changes in sugars and proteins can be achieved.

  Further, as the chemical treatment, the pH of the excess sludge is increased to 10 or more using an alkali agent such as sodium hydroxide, or the pH of the excess sludge is decreased to 5 or less using an acid such as hydrochloric acid, The cell wall can be made brittle and the cytoplasm can flow out to the solution side. In addition, oxidants such as ozone and hydrogen peroxide can be added to the excess sludge to sterilize microorganisms using strong oxidizing power. Alternatively, the cell membrane and cell wall can be damaged.

  Further, as the ultrasonic treatment, by generating ultrasonic waves in water, generating fine bubbles and rupturing bubbles by adiabatic compression, the cell membranes and cell walls of sludge microorganisms in the water are affected by the impact force at this time. Can be destroyed.

  Hereinafter, an embodiment of a power generation method using surplus sludge of the present invention will be described based on the drawings.

  FIG. 1 shows a flow diagram in which a power generation method using surplus sludge according to the present invention is incorporated in a sludge treatment system.

Excess sludge is generated by, for example, biological treatment of organic wastewater such as domestic wastewater with activated sludge microorganisms in a biological reaction tank (not shown) in a sewage treatment plant.
The surplus sludge A discharged from the water treatment system is guided to the pretreatment tank 14, where it is heated to 80 ° C. by the heater 15 and pH by the sulfuric acid B added from the sulfuric acid tank 16. Is maintained at about 1.5.
Thereby, the cell membrane and cell wall of the sludge microorganisms contained in the excess sludge A are damaged, and a part of the cell membrane and the cytoplasm in the cell membrane flow out to the solution side.
Specifically, the ratio of the soluble COD to the COD of the entire excess sludge was several percent before this treatment, but increases to about 20 percent when the treatment is performed, making it easy for microorganisms to use. be able to. In addition, when this process is performed, the solid-liquid separation is facilitated by improving the sedimentation property of the solid-liquid component, and thus high-concentration sludge can be provided for the subsequent process.

  The sludge that stays in the pretreatment tank 14 for a certain period of time flows out as the treated sludge C and is guided to the settling tank 17, but the treated sludge C has improved sedimentation properties and is solidified while it remains in the settling tank 17. Liquid separation. In addition to the precipitation separation by gravity, mechanical separation means such as centrifugation, flotation separation or membrane separation can be used as the solid-liquid separation means.

  The obtained supernatant water D containing a high concentration of soluble organic components is led to the microbial fuel cell 18 and converted into electric energy by utilizing the microorganisms retained in the microbial fuel cell. Thus, the residual liquid E from which most of the organic substances have been removed is returned to the water treatment system for processing.

  On the other hand, the solid content generated by the solid-liquid separation in the precipitation tank 17 is extracted as the concentrated sludge F. However, since the pH is low as it is, an adverse effect on the subsequent anaerobic digestion can be considered. G is added and adjusted to an appropriate pH. The sludge whose pH has been adjusted is put into the anaerobic digester 20 and further decomposed by anaerobic microorganisms, and by-products such as methane gas are recovered and converted into electrical energy.

Digested sludge H extracted from the anaerobic digestion tank 20 is decomposed by anaerobic microorganisms as described above, and the soluble organic content is increased. Soluble organic components can be recovered and used as a fuel source for microbial fuel cells.
Alternatively, all or part of the circulating sludge I containing anaerobic microorganisms is guided to the pretreatment tank 14 as reprocessed sludge J, and the anaerobic microorganisms contained in the sludge are also heated and treated with acid to dissolve. It is also possible to increase the concentration of the organic component and use it as a fuel source for the microbial fuel cell.

  Thus, in the power generation method using surplus sludge of this example, the surplus sludge generated by biologically treating organic wastewater is subjected to physicochemical treatment to destroy the cell membrane and cell wall of sludge microorganisms, Since it is used as a fuel source of a microbial fuel cell by making it easily solubilized or microorganisms, specifically, microorganisms held in the microbial fuel cell, it is not suitable as a fuel source of the microbial fuel cell 18 as it is. The surplus sludge can be changed to a form in which microorganisms can be easily metabolized, whereby electric energy can be obtained as a fuel source of the microbial fuel cell 18.

Moreover, the solid-liquid separation property of the surplus sludge after the treatment is improved, and not only can the sludge concentration to be introduced into the anaerobic digestion tank 20 be increased, but the sludge after the treatment is relatively decomposed due to the damage of the cell membrane and the cell wall. Since it is easy to form, the digestion performance can be improved, that is, the amount of power generation can be increased by increasing the amount of methane gas generated. In other words, after the organic components in the excess sludge are eluted by applying physicochemical treatment, solid-liquid separation is performed, and the separated water is used as a fuel source of the microbial fuel cell 18 and a high-concentration solid content is removed. It can be processed by anaerobic digestion.
Thereby, not only the power generation by the microbial fuel cell 18 but also the improvement of the power generation amount by anaerobic digestion is seen, so that a lot of electric energy can be acquired.

  Further, as the physicochemical treatment, at least one of heat treatment, chemical treatment, and ultrasonic treatment is performed, so that the cell membrane and the cell wall of the sludge microorganisms constituting the excess sludge are altered or damaged to be present in the cell membrane. The cytoplasm can be eluted to the solution side, and the effect can be increased synergistically by using these treatments together.

  In this case, as the heat treatment, the excess sludge is heated at 30 ° C. or more and less than 300 ° C., preferably 50 ° C. or more and 100 ° C. or less, and the activated sludge microorganisms constituting the excess sludge are sterilized, and the cell membrane and cell wall are formed. Changes in sugars and proteins can be achieved.

  Further, as the chemical treatment, the pH of the excess sludge is increased to 10 or more using an alkali agent such as sodium hydroxide, or the pH of the excess sludge is decreased to 5 or less using an acid such as hydrochloric acid, The cell wall can be made brittle and the cytoplasm can flow out to the solution side. In addition, oxidants such as ozone and hydrogen peroxide can be added to the excess sludge to sterilize microorganisms using strong oxidizing power. Alternatively, the cell membrane and cell wall can be damaged.

  Further, as the ultrasonic treatment, by generating ultrasonic waves in water, generating fine bubbles and rupturing bubbles by adiabatic compression, the cell membranes and cell walls of sludge microorganisms in the water are affected by the impact force at this time. Can be destroyed.

  As mentioned above, although the electric power generation method using the excess sludge of this invention was demonstrated based on several Example, this invention is not limited to the structure described in the said Example, The structure described in each Example The configuration can be changed as appropriate without departing from the spirit of the invention, for example, by combining them appropriately.

  The power generation method using surplus sludge according to the present invention has a characteristic of acquiring electric energy as a fuel source in a subsequent microbial fuel cell by processing the surplus sludge into a form that can be easily used by microorganisms. For example, it can be suitably used as a useful treatment method for excess sludge generated in a biological reaction tank or the like of a sewage treatment plant.

It is a flowchart which shows one Example of the electric power generation method using the excess sludge of this invention. It is a conceptual diagram which shows a microbial fuel cell.

DESCRIPTION OF SYMBOLS 1 Container 2 Negative electrode 3 Positive electrode 4 External circuit 5 Diaphragm 6 Microorganism 7 Organic substance 8 Metabolite 9 Electron 10 Electron transfer agent 11 Reduction type electron transfer agent 12 Oxidant 13 Reduction type oxidant 14 Pretreatment tank 15 Heater 16 Sulfuric acid tank 17 Precipitation tank 18 Microbial fuel cell 19 Alkaline tank 20 Anaerobic digester A Excess sludge B Sulfuric acid C Treated sludge D Supernatant water E Residual liquid F Concentrated sludge G Sodium hydroxide H Digested sludge I Circulating sludge J Reprocessed sludge

Claims (7)

The surplus sludge generated by biological treatment of organic wastewater is subjected to physicochemical treatment to destroy cell membranes and cell walls of sludge microorganisms, solubilized or easily assimilated by microorganisms. A power generation method using surplus sludge as a fuel source for a battery , wherein the organic components in the surplus sludge are eluted by performing the physicochemical treatment, followed by solid-liquid separation, and the separated water is used as a microbial fuel. A power generation method using surplus sludge, characterized in that it is used as a fuel source for a battery and solids are processed by an anaerobic digestion method. The product as physicochemical treatment, heat treatment, chemical treatment and power generation method using excess sludge according to claim 1, characterized in that at least one processing sonication. The power generation method using surplus sludge according to claim 2 , wherein surplus sludge is heated at 30 ° C or more and less than 300 ° C, preferably 50 ° C or more and 100 ° C or less as the heat treatment. The power generation method using surplus sludge according to claim 2 , wherein as the chemical treatment, the pH of the surplus sludge is set to 10 or more using an alkali agent such as sodium hydroxide. The power generation method using surplus sludge according to claim 2 , wherein as the chemical treatment, an acid such as hydrochloric acid is used to adjust the pH of the surplus sludge to 5 or less. The power generation method using surplus sludge according to claim 2 , wherein an oxidizing agent such as ozone or hydrogen peroxide is added to the surplus sludge as the chemical treatment. The power generation method using surplus sludge according to claim 2 , wherein as the ultrasonic treatment, ultrasonic waves are generated in water to generate fine bubbles and burst bubbles by adiabatic compression.

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