JP7268448B2 - BIOLOGICAL TREATMENT SYSTEM AND METHOD OF ORGANIC WASTEWATER - Google Patents

Description

TECHNICAL FIELD The present invention relates to a biological treatment system and a biological treatment method for organic wastewater.

A fixed-bed anaerobic biological treatment apparatus can retain bacteria in the tank without solid-liquid separation and sludge return in the latter stage, and can perform stable treatment. However, in a biological treatment tank such as a microbial power generator that does not aerate in the biological treatment tank and does not generate gas accompanying treatment such as methane fermentation, the inside of the tank is close to plug flow. become. In that case, the pH locally changes in the tank due to CO ₂ and NH ₃ generated along with the biological treatment, deviating from the pH condition suitable for biological treatment, and the treatment performance deteriorates. Therefore, by circulating part of the treated water of the biological treatment apparatus, the inside of the tank is nearly completely mixed and the pH is made uniform.

On the other hand, when organic wastewater containing easily degradable organic matter and slowly degradable organic matter with different decomposition rates is treated in a biological treatment tank using a biofilm, microorganisms that decompose easily degradable organic matter dominate the carrier surface. Microorganisms that adhere to and proliferate on the surface and decompose the slow-degrading organic matter are not retained, so treatment of the slow-degrading organic matter may not progress at all. Therefore, in some cases, a plurality of biological treatment tanks are provided in series, and the slowly degradable organic matter is removed in the subsequent biological treatment tank into which the water to be treated from which the readily degradable organic matter has been removed flows (see, for example, Patent Document 1).

However, in a biological treatment tank that does not aerate in the biological treatment tank, such as a microbial power generator, and does not generate gas as a result of treatment like methane fermentation, part of the effluent at the final stage is used for the above reasons. is circulated to the front stage to bring the entire apparatus close to complete mixing, there is a problem that the microorganisms that decompose easily degradable organic matter proliferate in each tank, and the decomposition of slowly degradable organic matter does not progress. rice field.

JP 2012-239929 A

The present invention provides a biological treatment system for organic wastewater that can stably perform biological treatment even when the organic matter contains organic matter with different decomposition rates by organisms, such as easily degradable organic matter and slowly degradable organic matter. An object of the present invention is to provide a biological treatment method.

The organic wastewater biological treatment system of the present invention comprises first to n-th (n is 2 or more) biological treatment apparatuses having biofilms, which are installed so that the water to be treated is sequentially passed through. A biological treatment system for organic wastewater, wherein each biological treatment device has a plurality of chambers through which water to be treated is passed in series or in parallel, and part of the effluent from the first biological treatment device is A return means is provided for returning to the inflow side of the first biological treatment apparatus.

The organic wastewater biological treatment method of the present invention is a method of biologically treating organic wastewater using the organic wastewater biological treatment system of the present invention, wherein at least part of the effluent from the first biological treatment apparatus A portion is returned to the inflow side of the first biological treatment device.

In one aspect of the present invention, in the second and subsequent biological treatment apparatuses, part of the effluent from each biological treatment apparatus is returned to the inflow side of the biological treatment apparatus. Preferably, when the ratio of slowly degradable organic matter contained in the inflow to the second and subsequent biological treatment apparatuses to the total organic matter is 30 wt% or more, part of the effluent of each biological treatment apparatus is added to the biological treatment apparatus. Return to the inflow side.

In one aspect of the present invention, the biological treatment apparatus is a plug flow permeable anaerobic biological treatment apparatus.

In one aspect of the invention, the biological treatment device is a microbial power generation device comprising a plurality of anode chambers.

In one aspect of the present invention, the water flow LV in each biological treatment apparatus is set to 10 to 50 m/hr.

According to the organic wastewater biological treatment system and method of the present invention, at least part of the effluent from the first biological treatment apparatus is returned to the inflow side of the first biological treatment apparatus, so that the raw water contains a large amount of easily decomposable organic matter. Even when it is contained, the easily decomposable organic matter is fully biologically treated in the first biological treatment device. As a result, the concentration of easily decomposable organic matter in the inflow water from the second biological treatment apparatus onwards becomes low, the microorganisms that decompose slowly decomposable organic matter proliferate sufficiently, and the slowly degradable organic matter is also sufficiently decomposed.

1 is a configuration diagram of a biological treatment system according to an embodiment; FIG. 1 is a schematic longitudinal sectional view of a microbial power generation device according to an embodiment; FIG. 1 is a schematic longitudinal sectional view of a microbial power generation device according to an embodiment; FIG. It is a graph which shows an experimental result.

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a biological treatment system and a biological treatment method for organic waste water according to the present invention will be described below in detail with reference to the drawings.

Raw water to be treated by the biological treatment system and biological treatment method of the present invention is preferably organic wastewater containing at least one readily degradable organic substance and at least one slowly degradable organic substance.

Examples of easily decomposable organic substances include lower fatty acids having 4 or less carbon atoms such as formic acid, acetic acid, propionic acid and butyric acid, and lower alcohols having 4 or less carbon atoms such as methanol, ethanol, propanol and isopropanol.

Examples of slow-degrading organic substances include TMAH, DMSO, phenol, terephthalic acid, benzene, and starch.

Examples of organic wastewater containing easily degradable organic matter and slowly degradable organic matter include, but are not limited to, electronic industry wastewater, chemical factory wastewater, and pharmaceutical wastewater.

FIG. 1 is a flow diagram showing a schematic configuration of the biological treatment system for organic waste water of the present invention.

In this embodiment, first, second and third microbial power generation devices 11, 12 and 13 are installed as biological treatment devices. However, the number of steps of the microbial power generator is not limited to this, and may be 2 or 4 or more (preferably 5 or less). Moreover, you may use the anaerobic-biological-treatment apparatus of a plug-flow water flow system other than a microbial power generation apparatus.

In FIG. 1, raw water is supplied to neutralization tank 30 . The water to be treated in the neutralization tank 30 is supplied to the anode chamber of the first microbial power generation device 11 via a pipe 31, a pump 32 and a pipe 33, and subjected to a microbial power generation reaction. After the microbial power generation reaction, the liquid in the anode chamber flows out to the pipe 34 and part of it is returned to the inflow pipe 31 via the pipe 35 .

The rest of the liquid flowing out to the pipe 34 is supplied to the anode chamber of the second microbial power generation device 12 via the pipe 41, the pump 42, and the pipe 43, and is subjected to the microbial power generation reaction. After the microbial power generation reaction, the liquid in the anode chamber flows out to the pipe 44 and part of it is returned to the inflow pipe 41 via the pipe 45 .

The rest of the liquid flowing out to the pipe 44 is supplied to the anode chamber of the third microbial power generator 13 via the pipe 51, the pump 52, and the pipe 53, and is subjected to the microbial power generation reaction. After the microbial power generation reaction, the liquid in the anode chamber flows out to the pipe 54 and part of it is returned to the inflow pipe 51 via the pipe 55 .

The rest of the liquid that has flowed out to pipe 54 is taken out as treated water via pipe 61 . A part of the treated water that has flowed out to the pipe 61 may be returned to the neutralization tank 30 through the pipe 56 . However, it is preferably 1/10 or less of the flow rate in each anode chamber.

In this embodiment, as shown in FIGS. 2 and 3 described later, each of the microbial power generators 11 to 13 has a cathode chamber, and an oxygen-containing gas such as air, pure oxygen, or oxygen-enriched air is supplied to each cathode chamber. be done. The oxygen-containing gas may be supplied in series or parallel by connecting the cathodes of each microbial power generator.

In FIG. 1, part of the anode chamber effluent is returned to the inflow pipes 41 and 51 in the second and third microbial power generators 12 and 13 as well. The anode chamber effluent may be returned to the inflow pipe 41 or 51 of the microbial power generation device only in the microbial power generation device 12 and/or 13 having a ratio of 30 wt % or more.

Next, the configuration of each of the microbial power generators 11, 12, 13 will be described with reference to FIG.

In each of the microbial power generators 11 to 13, a plurality of ion-permeable non-conductive membranes 2 are arranged in parallel within the tank body 1, thereby alternately partitioning the cathode chambers 3 and the anode chambers 4. As shown in FIG. A positive electrode 5 is arranged in each cathode chamber 3 so as to be in contact with the ion-permeable non-conductive membrane 2 .

The positive electrode (cathode) 5 is a three-dimensional body made of a conductive material (graphite, titanium, stainless steel, etc.). The material constituting the positive electrode may be appropriately selected according to the type of electron acceptor. When oxygen is used as an electron acceptor, it is preferable to use an oxygen reduction catalyst such as platinum. For example, graphite felt may be used as a base material to support platinum.

A liquid containing potassium hexacyanoferrate(III) (potassium ferricyanide), for example, may be supplied into the cathode chamber 3 instead of the oxygen-containing gas. In this case, as the positive electrode 5, an inexpensive graphite electrode may be used as it is (without supporting platinum).

A three-dimensional negative electrode 6 made of a conductive material (graphite, titanium, stainless steel, etc.) is arranged in each anode chamber 4 . Power-generating microorganisms are held in the anode chamber 4 .

In this embodiment, the inside of the cathode chamber 3 is empty, an oxygen-containing gas such as air is introduced through the gas inlet pipe 7, and the exhaust gas is discharged through the gas outlet pipe 8.

As the ion-permeable non-conductive film 2 for partitioning the cathode chamber 3 and the anode chamber 4, almost any material can be used as long as it is non-conductive and ion-permeable. Ion-exchange membranes, paper, woven fabrics, non-woven fabrics, so-called organic membranes (microfiltration membranes), honeycomb molded bodies, grid-like molded bodies, and the like can be used. In order to allow ions to easily pass through, the thickness is preferably as thin as 10 μm to 1 mm, particularly 30 to 100 μm.

The organic substance-containing liquid is introduced into the anode chamber 4 through the pump 32, 42 or 52 and the pipe 33, 43 or 53, and the reaction waste liquid is discharged from the outflow pipe 34, 44 or 54. The inside of the anode chamber 4 is sealed and made anaerobic.

A portion of the treated water that flows out from the final-stage microbial power generator 13 to the outflow pipe 54 and is further taken out through the pipe 61 is circulated to the neutralization tank 30 through the pipe 56, as described above, to dilute the raw water. be done. A pH adjuster such as an aqueous sodium hydroxide solution is added to the neutralization tank 30 to adjust the pH to 7-9. The temperature condition of the anode chamber 4 of each microbial power generation device is preferably from room temperature to middle to high temperature, specifically about 10 to 70°C.

The circulation ratio of the outflow water from the anode chamber is set to 1:10 or more, particularly 1:50 or more, in terms of organic matter-containing liquid inflow to circulating water (flow ratio), so that the inside of the anode chamber 4 is nearly completely mixed, and the BOD concentration of the raw water is 1:200 or higher is preferred for high concentrations exceeding 10,000 mg/L.

In the present invention, by setting the water flow LV in the anode chamber 4 to 10 m/hr or more, for example, 10 to 50 m/hr, the inside of the anode chamber is brought close to complete mixing, and the biofilm on the surface of the negative electrode and the substrate in the raw water are mixed. Contact efficiency can be improved.

An oxygen-free gas such as nitrogen gas may be continuously or intermittently supplied to the anode chamber 4 . A shearing force is applied to the negative electrode surface by the gas, and in addition to increasing the effect of preventing clogging due to excessive adhesion of biofilm, especially when oxygen is used as an electron acceptor in the cathode chamber 3, aerobic slime grows. It also has the effect of removing oxygen permeating from the cathode chamber 3 to the anode chamber 4, which leads to deterioration in performance.

Due to the electromotive force generated between the positive electrode 5 and the negative electrode 6, a current flows through the terminals 20 and 21 to an external resistor (not shown).

By passing the oxygen-containing gas through the cathode chamber 3 and circulating the negative electrode solution through the anode chamber 4,
(Organic matter) + H ₂ O→CO ₂ + H ⁺ +e ⁻
reaction proceeds. This electron e ⁻ flows to the positive electrode 5 through the negative electrode 6 , terminal 2 1 , external resistor, and terminal 20 .

When the ion-permeable non-conductive membrane 2 is a cation exchange membrane, the protons H 2 ⁺ generated in the above reaction move to the positive electrode 5 through the cation exchange membrane. At the positive electrode 5,
O ₂ +4H ⁺ +4e ⁻ →2H ₂ O
reaction proceeds. H ₂ O generated by this positive electrode reaction is discharged together with the cathode exhaust gas.

When an anion exchange membrane is used as the ion permeable non-conductive membrane 2, the positive electrode 5 is
O ₂ +2H ₂ O+4e ⁻ →4OH ⁻
reaction proceeds. OH ⁻ generated by this positive electrode reaction permeates the anion exchange membrane as the ion-permeable non-conductive membrane 2 .

In the anode chamber 4, the pH tends to decrease due to the generation of CO ₂ by the decomposition reaction of water by microorganisms. Therefore, alkali is added to the neutralization bath 30 so that the pH is preferably 7-9.

FIG. 3 shows a microbial power generator according to another embodiment of the invention. In the microbial power generator shown in FIG. 2, the negative electrode solution is passed through each anode chamber 4 in parallel. On the other hand, in FIG. 3, each anode chamber 4 is connected in series, and the negative electrode solution is passed through in series. Other configurations in FIG. 3 are the same as in FIG. 1, and the same reference numerals denote the same parts.

In the present invention, the microorganism that is held in the anode chamber and produces electrical energy is not particularly limited as long as it functions as an electron donor. For example, Saccharomyces, Hansenula, Candida, Micrococcus, Staphylococcus, Streptococcus, Leuconostoa, Lactobacillus, Corynebacterium, Arthrobacter, Bacillus, Clostridium, Neisseria, Escherichia, Enterobacter, Serratia, Achromobacter, Alcaligenes, Flavobacterium, Acetobacter, Moraxella, Nitrosomonas, Nitorobacter , Thiobacillus, Bacteria belonging to the genera Gluconobacter, Pseudomonas, Xanthomonas, Vibrio, Comamonas, Proteus (Proteus vulgaris), Shewannell and Geobacter, filamentous fungi, yeast and the like can be mentioned. As sludge containing such microorganisms, activated sludge obtained from biological treatment tanks for treating organic matter-containing water such as sewage, microorganisms contained in effluent from primary sedimentation tanks of sewage, anaerobic digestion sludge, etc. are used as inoculum for the anode. A chamber can be supplied to retain the microorganisms on the negative electrode. In order to increase power generation efficiency, it is preferable that the amount of microorganisms retained in the anode chamber is high, for example, the concentration of microorganisms is preferably 1 to 50 g/L.

[Comparative Example 1]
In an anode chamber (volume: 87.5 mL) of 7 cm × 25 cm × 0.5 cm (thickness), a stainless steel wire was adhered to a 0.5 cm thick graphite felt with a conductive paste to form an electrical lead wire. Filled as material to form a negative electrode. A cathode chamber was formed through a polyolefin nonwoven fabric having a thickness of 30 μm in the thickness direction of the anode chamber. The cathode chamber also has a size of 7 cm×25 cm×0.5 cm (thickness), and is filled with a conductive material such as a stainless steel wire adhered to a 0.5 cm thick graphite felt with a conductive paste to form an electrical lead wire. A positive electrode was formed. A microbial power generator (cell) was produced by connecting with a resistance of 3Ω.

Three of these microbial power generation cells were connected in series as shown in FIG. 1 to prepare a biological treatment system for organic waste water. The anode chamber effluent (treated water) from the third cell was received in the treated water tank, and the anode chamber effluent was adjusted to pH 7.5 with 2N HCl or 2N NaOH in the treated water tank at a flow rate of 152 mL/min (9.1 L/hr). circulated to the neutralization tank, mixed with the raw water, and passed through the anode chamber of the first microbial power generation cell in an upward flow.

From the neutralization tank to the first microbial power generation cell, 160 mL of raw water containing 1,000 mgC/L isopropyl alcohol (IPA), 1,000 mgC/L tetramethylammonium hydroxide (TMAH), 50 mM phosphate buffer, and yeast extract. /hr.

This biological treatment system was installed in a room controlled at 35°C. In addition, prior to the passage of the raw water, the outflow water from the microbial power generator in operation was passed as inoculum. A positive electrode solution containing 50 mM potassium ferricyanide and a phosphate buffer was supplied to the cathode chamber of each microbial power generation cell at a flow rate of 70 mL/min.

All of the effluent water from the anode chambers of the first and second microbial power generation cells was sent to the second and third microbial power generation cells, respectively. As described above, 152 mL/min of the effluent from the anode chamber of the third microbial power generation cell was returned to the first microbial power generation cell, and the remainder was taken out as treated water.

[Example 1]
With the same device configuration as in Comparative Example 1, the effluent water from the anode chamber of each microbial power generation cell was circulated through the inflow pipe of each cell at a flow rate of 152 mL/min (9.1 L/hr). That is, the effluents of the anode chambers of the first and second microbial power generation cells are each branched and mixed with the anode chamber inflow of each cell at a flow rate of 152 mL/min (9.1 L/hr) to produce the third microbial power generation. The cell anode compartment effluent was branched upstream of the treated water tank and mixed with the anode compartment influent of the third microbial power generation cell at a flow rate of 152 mL/min (9.1 L/hr). As a result, the flow rate of the anode chamber inflow water and the anode chamber outflow water of each cell was 312 mL/min. Other conditions were the same as in Comparative Example 1.

<Results>
FIG. 4 shows changes in the TOC concentration in the treated water of Comparative Example 1 and Example 1. As shown in FIG. In Comparative Example 1, the TOC concentration in the treated water leveled off at 1,000 to 1,100 mgC/L after 3 weeks from the start-up, and TMAH remained in the treated water when the water quality was analyzed. On the other hand, in Example 1, the TOC concentration in the treated water was higher than in Comparative Example 1 at the beginning of the start-up, but continued to decrease even after 3 weeks had passed, and after about 2 months it became stable at around 200 mg / L, and the water quality TMAH was also removed by analysis.

These examples and comparative examples demonstrate that the effect of removing organic matter is improved by circulating part of the outflow water from the anode chamber to the inflow water of the cell.

REFERENCE SIGNS LIST 1 tank body 2 ion-permeable non-conductive membrane 3 cathode chamber 4 anode chamber 5 positive electrode 6 negative electrode 11, 12, 13 microbial power generator 10 raw water tank

Claims (8)

First to n-th (n is 2 or more) having a biofilm, installed so that organic wastewater containing at least one easily degradable organic substance and at least one slow-degradable organic substance is sequentially passed through ) biological treatment system for organic wastewater, comprising
Each biological treatment device is a microbial power generation device having a plurality of anode chambers through which the organic wastewater is passed, and the biofilm is attached to the negative electrode surface of the microbial power generation device,
Each biological treatment device has a plurality of chambers through which water to be treated is passed in series or in parallel,
A biological treatment system for organic waste water provided with return means for returning part of the effluent from the first biological treatment apparatus to the inflow side of the first biological treatment apparatus. 2. A biological treatment system for organic wastewater according to claim 1, wherein the second and subsequent biological treatment apparatuses are provided with return means for returning part of the effluent from each biological treatment apparatus to the inflow side of the biological treatment apparatus. . The microbial power generation device is
a tank body (1);
a cathode chamber (3) and an anode chamber (4), which are alternately partitioned by a plurality of ion-permeable non-conductive membranes (2) arranged in parallel in the tank body (1);
a positive electrode 5 disposed in contact with the ion-permeable non-conductive membrane (2) in the cathode chamber (3);
said negative electrode (6) made of a conductive material located in said anode chamber (4);
The organic wastewater biological treatment system according to claim 1 or 2, having 4. A biological treatment system for organic waste water according to any one of claims 1 to 3, wherein the cathode chamber (3) is empty and is vented with an oxygen-containing gas . A biological treatment method for organic wastewater containing at least one readily degradable organic substance and at least one slowly degradable organic substance, using the organic wastewater biological treatment system according to any one of claims 1 to 4, ,
A biological treatment method for organic wastewater, wherein at least part of the effluent from the first biological treatment apparatus is returned to the inflow side of the first biological treatment apparatus. When the ratio of slowly degradable organic matter contained in the inflow to the second and subsequent biological treatment apparatuses to the total organic matter is 30 wt% or more, part of the outflow water from each biological treatment apparatus is The organic wastewater biological treatment method according to claim 5, wherein the organic wastewater is returned to the side. 7. The method for biologically treating organic wastewater according to claim 5 or 6, wherein the easily decomposable organic substance is a lower fatty acid having 4 or less carbon atoms and/or a lower alcohol having 4 or less carbon atoms. The biological treatment method for organic waste water according to any one of claims 5 to 7, wherein the water flow LV in each biological treatment device is 10 to 50 m/hr.

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