JP4956016B2 - Apparatus and method for treating organic wastewater containing hardly biodegradable substances - Google Patents

Description

  The present invention relates to a treatment apparatus and treatment method for organic waste water containing a hardly biodegradable substance.

  Wastewater or waste liquid is discharged from private industrial facilities, public facilities, third sector facilities, etc. in various forms such as aqueous solutions, slurries, emulsions, micelles, suspensions, concentrated liquids, sludge mixed liquids and the like. These wastewaters or waste liquids need to be rendered harmless by water treatment before being discharged into public waters. The most commonly used water treatment method for waste water or waste liquid is biological treatment, and since the treatment cost is relatively low, it has been widely used for a long time. Biological treatment is broadly divided into aerobic treatment and anaerobic treatment. The former is mainly used when the chemical oxygen demand (CODCr) of wastewater is several tens to several thousand mg / L or less, and the latter is mainly used when CODCr of wastewater is 1000 mg / L or more. In addition, since denitrification treatment cannot be completed by aerobic treatment or anaerobic treatment alone in human waste treatment or sewage treatment, a combination of aerobic biological treatment and anaerobic biological treatment may be used, taking advantage of both features. is there.

  However, such as when wastewater containing chemical substances or chemically synthesized substances derived from petrochemicals or cells with hard cell walls such as organic sludge or methane fermentation sludge from sewage treatment plants are included. In addition, it may be difficult to apply biological treatment to wastewater containing a large amount of substances having low biodegradability. Moreover, even if it is a naturally occurring substance such as lignin and humin, the biodegradability may be very low when it is a polymer having a benzene ring functional group in the molecule.

  Furthermore, biological treatment may be extremely difficult if a pigment component is contained in the wastewater, such as dyed wastewater. Since pigment components are generally difficult to biodegrade to microorganisms, when wastewater containing pigment components is subjected to biological treatment, even if CODCr and BOD can be removed sufficiently, there may be little chromaticity. .

  Generally and as used herein, “refractory biodegradable substance” refers to a substance that is difficult to biodegrade.

  An electrochemical treatment method has been proposed as a treatment method for such a hardly biodegradable substance. The electrochemical treatment method is relatively easy to control, and can be treated with equipment on a small scale as compared with biological treatment. In recent years, a treatment method using a conductive diamond electrode has attracted attention as an example of a method for electrochemically treating an organic substance dissolved in water. A conductive diamond electrode has characteristics that are not found in conventional noble metal electrodes. When a DC voltage is applied in water, the water is oxidized at the anode to generate hydroxy radicals (OH radicals). Since this OH radical has a very high oxidizing ability, almost all organic substances can be decomposed into carbon dioxide and water. Conventional noble metal electrodes have very low generation efficiency of OH radicals, but it has been shown in the literature that conductive diamond electrodes can generate OH radicals very efficiently. (Ghrardini et al .: Electrochemical Oxidation of 4-chlorophenol for wastewater treatment, J. Electrochemical Society, 148, D78-D82, 2001).

  In water treatment using a conductive diamond electrode, the required amount of electricity required for theoretical electrolytic treatment to decompose CODCr1g is about 3.4 Ah / g-CODCr. The cell voltage of the conductive diamond electrode when actually carrying out the electrolytic reaction needs to be at least 4 to 5 V or more. Although it depends on the operating current density, the electrolyte temperature, the electrical conductivity of the drainage, etc., an example of a general operating value of the cell voltage (voltage between electrodes of a single electrolytic cell) is about 7V. Therefore, the power required for decomposing CODCr1g is 3.4 Ahx7V = 23.8 VAh, which is approximately equal to 24 Wh / g-CODCr or 24 kWh / kg-CODCr, and there is a problem that the treatment cost is higher than biological treatment.

In general, organic waste water contains a hardly biodegradable substance and an easily biodegradable substance. When direct electrolysis is performed on such wastewater, for example, OH radicals generated by electrolysis using a conductive diamond electrode can be selected non-selectively without distinguishing between readily biodegradable substances and hardly biodegradable substances. Since the oxidation treatment of the organic substance is performed, an electrolytic treatment with a high treatment cost is applied even to the treatment of the readily biodegradable substance, and as a result, the treatment cost may increase.
Ghrardini et Al .: Electrochemical Oxidation of 4-chlorophenol for wastewater treatment, J. Electrochemical Society, 148, D78-D82, 2001

  An object of the present invention is to provide a low-cost treatment method and apparatus that matches the properties of organic matter contained in wastewater by utilizing the characteristics of the electrochemical treatment method.

  As a result of diligent research, the present inventors have first carried out biotreatment of a readily biodegradable substance, and then electrolytically treated the hardly biodegradable substance using a conductive diamond electrode. Wastewater containing substances and hardly biodegradable substances can be treated with lower power than the case of electrolytic treatment alone. A large amount of readily biodegradable substances such as organic acids (volatile fatty acids (VFA), hereinafter referred to as VFA) are produced, and the biodegradability of treated water is improved, and the present invention has been completed. That is, in the electrolytic treatment process, the electrolytic treatment is performed with an electric power that does not completely decompose the carbon dioxide and water to obtain electrolytic treated water containing an easily biodegradable substance. By returning the part to the biological treatment process and performing the biological treatment, the cost in the electrolytic treatment is further reduced, and the cost of the entire treatment process can be reduced. In addition, when the biological treatment process is anaerobic treatment, there is an advantage that the amount of biogas generated is increased by increasing the load of easily biodegradable substances introduced into the biological treatment process.

  According to a first aspect of the present invention, there is provided a biological treatment apparatus, an electrolytic treatment tank located downstream of the biological treatment apparatus and provided with a conductive diamond electrode, and at least a part of effluent water from the electrolytic treatment tank. An organic wastewater treatment apparatus containing a hardly biodegradable substance, characterized by comprising return means for returning to the biological treatment apparatus.

  According to a second aspect of the present invention, there is provided a biological treatment apparatus, an electrolytic treatment tank located downstream of the biological treatment apparatus and provided with a conductive diamond electrode, a concentration apparatus located downstream of the electrolytic treatment tank, Returning means for returning at least a part of the concentrated water from the concentrating device to the biological treatment device. An organic wastewater treatment device containing a hardly biodegradable substance.

  According to a third aspect of the present invention, there is provided a biological treatment apparatus, a concentration apparatus located downstream of the biological treatment apparatus, and an electrolytic treatment tank provided with a conductive diamond electrode, located downstream of the concentrated water side of the concentration apparatus. And a return means for returning the effluent from the electrolytic treatment tank to the biological treatment apparatus.

  According to a fourth aspect of the present invention, there is provided a biological treatment step of biologically treating an organic wastewater containing a hardly biodegradable substance to obtain biologically treated water; and at least a part of the biologically treated water with a conductive diamond electrode. A non-biodegradable substance-containing organic, comprising: an electrolytic treatment step that uses electrolytic treatment to obtain electrolytic treatment water; and a return step that returns at least a portion of the electrolytic treatment water to the biological treatment step. This is an effluent treatment method.

  According to a fifth aspect of the present invention, there is provided a biological treatment step of biologically treating an organic wastewater containing a hardly biodegradable substance to obtain biologically treated water, and electrolytic treatment of the biologically treated water using a conductive diamond electrode. An electrolytic treatment step for obtaining electrolytic treatment water, a concentration step for concentrating the electrolytic treatment water to obtain concentrated water, and a return step for returning at least a part of the concentrated water to the biological treatment step. This is an organic wastewater treatment method containing a hardly biodegradable substance.

  The sixth aspect of the present invention is a biological treatment step of biologically treating an organic wastewater containing a hardly biodegradable substance to obtain biologically treated water, and a concentration for concentrating the biologically treated water to obtain concentrated water. And an electrolytic treatment step of electrolytically treating at least a part of the concentrated water using a conductive diamond electrode to obtain electrolytically treated water, and a returning step of returning the electrolytically treated water to the biological treatment step. This is an organic wastewater treatment method containing a hardly biodegradable substance.

  According to a seventh aspect of the present invention, in the electrolytic treatment step, the electric quantity of 10 to 90% of the electric quantity required for the theoretical electrolytic treatment is imparted. This is an organic wastewater treatment method.

  Hereinafter, the present invention will be described in detail.

  According to the present invention, an organic wastewater containing a hardly biodegradable substance is biologically treated to obtain biologically treated water, and at least a part of the biologically treated water is electrolyzed to provide electrolytically treated water. There is provided an organic wastewater treatment method containing a hardly biodegradable substance, characterized by comprising an electrolytic treatment step for obtaining the above and a return step for returning at least a part of the electrolytically treated water to the biological treatment step.

  Examples of wastewater that can be treated by the organic wastewater treatment method of the present invention include sludge mixed liquids in sewage treatment plants and water treatment plants; various sludges such as methane fermentation processes; wastewater and wastewater from oil refineries and petroleum product plants; Wastewater and wastewater from pharmaceutical factories; wastewater and wastewater from pharmaceutical manufacturing plants and hospitals; wastewater and wastewater from various processes in semiconductor processes (photoresist process, cleaning process, and plating process); photodevelopment wastewater; and various used cutting fluids from machining plants (Oil-based, water-soluble) wastewater; washing water / drainage for paint manufacturing process; painting process washing water / drainage for can manufacturing factory, body factory, sheet metal factory; drainage / waste liquid for agrochemical manufacturing process; dyeing wastewater; dye factory wastewater; Examples include, but are not limited to, ion exchange reclaimed wastewater (condensate wastewater); plating wastewater and plating washing water of plating plants containing organic matter and ammonia. Effective wastewater treatment in the biological treatment alone outside can be applied to difficult drainage.

  The biological treatment process of the present invention may be a biological treatment usually performed in the wastewater treatment field, and specifically includes an aerobic biological treatment process or an anaerobic biological treatment process. An appropriate biological treatment process can be used according to the properties of the organic waste water to be treated.

  The aerobic biological treatment method that can be used in the present invention is not particularly limited. For example, it is a floating type activated sludge treatment method that is a standard aerobic biological treatment (sludge floats in an aeration tank). Alternatively, a biofilm filtration method in which microorganisms are immobilized on a membrane may be used. Furthermore, the aerobic biological treatment may be performed by aerobic microorganisms immobilized on a carrier such as activated carbon, anthracite (coal-based carbon), or sand. Further, as a variation of the floating method, a method may be used in which microorganisms are immobilized using a granular or sponge-like hydrophilic polymer or activated carbon as a carrier. Further, it may be a catalytic oxidation type aerobic biological treatment in which microorganisms are immobilized on a string-like, net-like or honeycomb-like carrier. Alternatively, it may be a rotating disk type aerobic biological treatment that directly takes in oxygen from the air without performing air aeration. Rotating disc type aerobic biological treatment is a disk on which a sponge or the like is attached, with its upper half exposed from the drainage to the air. By rotating this disc, the disc is drained directly from the air. This is an aerobic biological treatment method characterized by incorporating oxygen into the water.

  The anaerobic biological treatment system that can be used in the present invention may be standard 20-day methane fermentation or high-temperature methane fermentation operated at a temperature of about 55 ° C. In the case of high temperature methane fermentation, since the speed of biological treatment is high, there is an advantage that the treatment time can be shortened to 10 to 15 days. In the present invention, as biological treatment, UASB method (Upflow Anaerobic Sludge Blanket) in which granules (granulated methane-fermenting bacteria) are added, or EGSB method (Expanded Granular) that can be operated at higher speed and higher load is used. Sludge Bed) can also be adopted. When these anaerobic treatments are performed as biological treatments in the present invention, there is an advantage that energy recovery can be performed in the form of methane gas.

  In the present invention, in the biological treatment process, the readily biodegradable substance in the organic waste water is biologically treated and removed. Therefore, in the biologically treated water obtained in the biological treatment process, the hardly biodegradable substances that existed in the organic wastewater remain mainly. This biologically treated water is then sent to the electrolytic treatment step for electrolytic treatment. The electrolytic treatment process of the present invention is characterized by using a conductive diamond electrode. The conductive diamond electrode that can be used in the present invention may be a conductive diamond electrode having any configuration known in the art. For example, a conductive diamond thin film is deposited on the surface of a conductive metal material such as nickel (Ni), tantalum (Ta), titanium (Ti), molybdenum (Mo), tungsten (W), zirconium (Zr) as an electrode substrate Conductive diamond electrode, conductive diamond electrode formed by depositing a thin film of conductive diamond on the surface of a semiconductor material such as a silicon wafer as an electrode substrate, and deposited conductive polycrystalline diamond in a plate shape Examples thereof include conductive diamond electrodes. The conductive diamond thin film is obtained by doping a predetermined amount of a dopant such as boron or nitrogen when the diamond thin film is formed on the substrate to provide conductivity, and boron is generally used as the dopant. Is. In the present invention, a conductive diamond electrode may be used for both the anode and the cathode, or a conductive diamond electrode may be used only for the anode.

  In the electrolytic treatment process of the present invention, the density of OH radicals generated at the conductive diamond electrode can be controlled by the current density applied to the conductive diamond electrode. In the electrolytic treatment process, a plurality of different current densities may be applied depending on the CODCr concentration of the wastewater to be treated. In this case, it is possible to prevent excessive generation of OH radicals by giving a high current density to wastewater with a high CODCr concentration and giving a low current density to wastewater with a low CODCr concentration. It reduces the consumption of the conductive diamond electrode due to OH radicals, extends the life of the electrode, and also saves electrolysis power.

  In the electrolytic treatment step, the temperature of the waste water that contacts the conductive diamond electrode is 40 ° C to 95 ° C, preferably 60 ° C to 85 ° C. The electrical conductivity is temperature dependent. The higher the temperature, the higher the electrical conductivity. When the electrical conductivity is increased, the required voltage can be kept low. In order to maintain the electrolytic treatment temperature within the above range, heat can be applied from an external heat source, but it is possible to efficiently utilize the heat generated with the temperature rise of the wastewater due to the electrolytic reaction using the conductive diamond electrode. More preferred. In particular, it is desirable to install heat exchangers at the inlet and outlet of the electrolytic cell so that the heat generated in the electrolytic cell can be efficiently reused so that heat can be exchanged between them.

  In the electrolytic treatment process, organic substances in the wastewater to be treated are mineralized to carbon dioxide and water, and a large amount of easily biodegradable low-molecular intermediate products such as VFA are produced as intermediate products. Increases biodegradability of wastewater. To obtain electrolyzed water containing a lot of readily biodegradable substances in electrolysis using a conductive diamond electrode, the amount of electricity is 10 to 90% of the amount of electricity required for theoretical electrolysis (3.4Ah / g-CODCr). Preferably, the amount of electricity is preferably 30 to 80%.

  In order to easily estimate the biodegradability of the electrolyzed water, BOD / CODCr or pH in the electrolyzed water can be measured. The higher the BOD / CODCr, the higher the rate of biodegradability in the total organic matter, so depending on the nature of the raw wastewater, the BOD / CODCr value in the electrolyzed water is 0.3 or more, more preferably It is desirable to perform the electrolytic treatment in the electrolytic treatment step so that it becomes 0.4 or more. In addition, since the pH decreases when the proportion of VFA is high, depending on the composition of the raw wastewater, the VFA concentration is high when the pH value is low, that is, the electrolyzed water contains a lot of readily biodegradable substances. You can think of it as being.

  In the present invention, at least a part of the electrolytically treated water is returned to the biological treatment process. The entire amount of electrolytically treated water may be returned to the biological treatment process. The amount of electrolytically treated water returned to the biological treatment process varies depending on various factors such as the initial organic matter concentration of the raw wastewater, the concentration tolerance of the electrolytic treatment water, and the treatment capacity of the biological treatment process. For example, when the initial organic matter concentration of raw wastewater is high, the amount of electrolytically treated water returned to the biological treatment process is increased to dilute the raw wastewater in the biological treatment process and relatively reduce the concentration of hardly biodegradable substances. Can be made.

  Further, according to the present invention, as another aspect, a biological treatment step of biologically treating organic wastewater containing a hardly biodegradable substance to obtain biologically treated water, and electrolytic treatment of the biologically treated water to perform electrolysis An electrolytic treatment step for obtaining treated water, a concentration step for concentrating the electrolytic treatment water to obtain concentrated water, and a return step for returning at least a part of the concentrated water to the biological treatment step. An organic wastewater treatment method containing a non-biodegradable substance is provided.

  This aspect is suitable when it is desirable to perform advanced cleaning treatment that is required to achieve not the sewer discharge standard but the drainage standard for direct discharge into the natural environment such as rivers and sea areas.

  This embodiment is characterized in that the electrolytically treated water is concentrated to obtain concentrated water, and this concentrated water is returned to the biological treatment process. As an aspect of concentration, an appropriate method known in the field of solute concentration can be used. For example, membrane separation concentration such as reverse osmosis (RO) membrane, loose RO membrane (NF membrane), evaporation concentration that evaporates water by heating or decompression, concentration by electrodialysis, etc. can be preferably used, such as calcium carbonate Loose RO membrane (NF membrane) separation with a high inorganic ion permeability is most preferred because it suppresses the generation of scale by inorganic compounds.

Concentration process separated water has a different name depending on the mode of concentration. For example, it means permeated water in the case of membrane separation and concentration, distilled water in the case of evaporation and concentration, and demineralized water in the case of electrodialysis.
Concentrated water contains easily biodegradable substances generated in the electrolytic treatment process, and they are easily decomposed in the biological treatment process. The concentrated water contains various inorganic ions contained in normal organic waste water, such as calcium, magnesium, phosphorus, and the like. Since these inorganic ions are taken into the sludge in the biological treatment process, and the inorganic ions taken into the sludge can be discharged to the outside as surplus sludge, generation of scale can be prevented.

When concentrated water contains a large amount of solutes such as calcium, magnesium, and phosphorus that cause scale formation, part of the concentrated water is discharged to the outside regularly or biologically treated water, electrolytic treatment HAP (hydroxyapatite, Ca ₅ (OH) (PO ₄ ) ₃ ) or MAP (magnesium ammonium phosphate, Mg (NH ₄ ) PO ₄ ) treatment for one or more of water or concentrated water The components that cause scale formation such as calcium, magnesium, and phosphorus may be crystallized and removed.

  Alternatively, scale formation may be prevented by adding an acid such as hydrochloric acid or sulfuric acid before the concentration step.

  Furthermore, according to the present invention, as another aspect, a biological treatment step of biologically treating an organic wastewater containing a hardly biodegradable substance to obtain biologically treated water, and concentrating the biologically treated water for concentration A concentration step for obtaining water, an electrolytic treatment step for obtaining electrolytic treatment water by electrolytically treating at least a part of the concentrated water, and a return step for returning the electrolytic treatment water to the biological treatment step. An organic wastewater treatment method containing a non-biodegradable substance is provided.

  This aspect is characterized in that after the biologically treated water is concentrated, electrolytic treatment is performed, and this electrolytically treated water is returned to the biological treatment step. By returning the electrolytically treated water to the biological treatment step, the easily biodegradable low molecular weight intermediate product produced by the electrolytic treatment is treated in the biological treatment step and not introduced into the concentration step. In other words, the separation water separated from the concentration process does not contain an easily biodegradable low-molecular intermediate product, so that the water quality can be greatly improved and can be directly released into the environment.

  The concentration factor in the concentration step of this aspect affects the processing efficiency and processing cost of the electrolytic processing step. The higher the salt concentration of the concentrated water, the lower the power consumption in the electrolytic treatment process, and the lower the concentration of organic matter in the concentrated water, the lower the electrolytic treatment efficiency.

  According to the present invention, an organic wastewater containing a hardly biodegradable substance is biologically treated to obtain biologically treated water, and the biologically treated water is electrolytically treated to obtain electrolytically treated water. By returning to the biological treatment process again, the load in the biological treatment process can be increased and the load in the electrolytic treatment process can be reduced, resulting in a reduction in the amount of power required for the electrolytic treatment. Cost savings can be achieved. In addition, when the biological treatment process is an anaerobic biological treatment process, the amount of biogas generated increases as the biological treatment load increases, and the amount of energy recovered increases, so part of the electrical energy required for the electrolytic treatment process It can also be used as Furthermore, by returning the electrolytically treated water whose water temperature has risen due to Joule heat in the electrolytic treatment process to the biological treatment process, it can be used as part of the thermal energy required in the biological treatment process. As described above, the organic wastewater treatment method of the present invention can use the energy generated along with the material flow in each process as the required energy of the system, and achieves a significant energy saving as the entire system. be able to.

DESCRIPTION OF PREFERRED EMBODIMENTS

  Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings, but the present invention is not limited thereto.

[Embodiment 1]
FIG. 5 is a schematic explanatory diagram illustrating one embodiment of the present invention. According to FIG. 5, organic wastewater raw water (hereinafter simply referred to as “drainage raw water”) 1 containing a hardly biodegradable substance is first introduced into a biological treatment process (biological treatment apparatus) 2, and biological treatment process 2 , The biodegradable substance is separated and removed, and the biologically treated water 3 containing a large amount of hardly biodegradable substance is obtained. Subsequently, the biologically treated water 3 is introduced into an electrolytic treatment process (electrolytic treatment tank) 4, and the hardly biodegradable substance in the electrolytic treatment process (electrolytic treatment tank) 4 is an easily biodegradable substance such as VFA, carbon dioxide and water. And is discharged as electrolyzed water 5. A part of the electrolytically treated water 5 is returned to the biological treatment process (biological treatment device) 2 as electrolytically treated return water 6, and the readily biodegradable substance contained in the electrolytically treated return water 6 is biologically treated.

  The biological treatment step 2 may be an aerobic biological treatment step and / or an anaerobic biological treatment step usually used in the art. The biological treatment apparatus that can be used in the biological treatment step 2 includes an aerobic biological treatment tank such as an aeration tank, an anaerobic biological treatment tank, and a precipitation tank that are usually used in the field.

  The electrolytic treatment tank 4 only needs to include a conductive diamond electrode (not shown) as at least an anode, and the form is not particularly limited. As a method for installing the conductive diamond electrode in the electrolytic treatment tank 4, it is preferable to have a structure in which gas can be removed as well as possible. If degassing cannot be performed satisfactorily, bubbles accumulate between the electrodes, causing the interelectrode voltage to increase. Therefore, it is preferable to install the electrodes vertically rather than horizontally in the electrolytic treatment tank 4. Further, when the electrodes are installed horizontally in the electrolytic treatment tank 4, at least a conductive diamond electrode serving as an anode and / or a cathode, such as a mesh shape, a punching plate shape, or an expanded metal shape, can be well vented. It is desirable to make it. As a method for energizing the electrolytic treatment tank 4, a monopolar (single electrode) electrode method may be used, or a bipolar electrode method (bipolar) may be used. When a large electrode area is required, the bipolar has the advantage of making the device more compact.

  The operation of the electrolytic treatment tank 4 may be a batch type, a circulating batch type, or a continuous type.

  In the case of a batch type, the electrolytic treatment tank 4 may be in the form of a tank having an anode and a cathode formed of conductive diamond electrodes. The biologically treated water 3 from the biological treatment process 2 is sent to the electrolytic treatment tank 4 and subjected to electrolytic treatment in the electrolytic treatment tank 4 for a certain period of time. When BOD / CODCr becomes 0.3 or more, it contains an easily biodegradable substance. The electrolyzed water 5 to be obtained can be obtained.

  In the case of the circulating batch type, as shown in FIG. 6, an electrolytic cell 4a having an anode and a cathode composed of conductive diamond electrodes is provided outside the tank 4b, and drainage is performed from the tank 4b by a pump or the like. The liquid can be sent to 4a and the treated water of the electrolytic cell 4a can be returned to the drainage tank 4b. In this case, since the drainage of the pumped liquid can be forced between the anode and the cathode in the electrolysis cell 4a, the electrolysis efficiency can be maintained better than when the electrodes are simply immersed in the drainage tank. Also in this circulation batch type, the electrolyzed water 5 containing an easily biodegradable substance can be obtained when the BOD / CODCr of the waste water in the tank becomes 0.3 or more.

  In the case of the continuous type, a plurality of tanks having batch-type electrodes and / or a combination of a circulation batch-type electrolytic cell and a tank are arranged in series, and each electrolytic treatment tank 4 has a predetermined residence time. To be secured. When performing treatment by arranging a plurality of electrolytic treatment tanks in series, the wastewater treated in the first-stage electrolytic treatment tank is sent to the next electrolytic treatment tank, and in this electrolytic treatment tank, the conductive diamond electrode is similarly formed. It becomes the structure of performing the used electrolytic treatment. In the electrolytic treatment tank having such a configuration, the treated water obtained from the final electrolytic treatment tank is the electrolytic treated water 5. In the electrolytic treatment tank 4 having such a configuration, there is an advantage that the operating conditions of the electrolytic cell in each stage can be set depending on the CODCr concentration of the waste water. For example, wastewater from the high-concentration CODCr region from the biological treatment process flows into the first stage, so it becomes a high-current density electrolytic treatment tank. By setting it as a tank, the electrolytic treatment operation using a more efficient conductive diamond electrode can be performed.

[Embodiment 2]
FIG. 7 is a schematic explanatory view showing another embodiment of the present invention. The quality of the electrolytically treated water 5 in the first embodiment may not be sufficiently clear, and although the exclusion standard when discharging into the sewer is satisfied, it satisfies the drainage standard for direct discharge into the environment such as rivers or sea areas. It may not be possible. When the treated water is directly discharged into the environment, the quality of the treated water can be improved by providing a concentration step (concentration device) 8 after the electrolytically treated water 5 of the first embodiment.

  In the embodiment shown in FIG. 7, the raw wastewater 1 is introduced into a biological treatment process (biological treatment device) 2 to separate and remove easily biodegradable substances, and biologically treated water 3 containing a large amount of hardly biodegradable substances. can get. The biologically treated water 3 flows into the electrolytic treatment process (electrolytic treatment tank) 4, the hardly biodegradable substance is decomposed in the electrolytic treatment process (electrolytic treatment tank) 4, and is discharged as the electrolytic treatment water 5. The electrolytically treated water 5 is introduced into a concentration process (concentration device) 8 to obtain concentrated water 9 and concentrated process separation water 10. Part or all of the concentrated water 9 is returned to the biological treatment process (biological treatment apparatus) 2. The concentration device 8 may be a solute concentration device, for example, a membrane separation concentration device such as an RO membrane or a loose RO membrane (NF membrane), an evaporation concentration device that evaporates water by heating or decompression, or a concentration device such as electrodialysis. . The concentration process separation water 10 means permeated water when the concentration process is a membrane separation method, distilled water when the concentration process is an evaporative concentration method, and desalted water when the concentration process is electrodialysis.

  The readily biodegradable substance contained in the concentrated water 9 can be easily treated in the biological treatment process (biological treatment apparatus) 2. In addition, components that cause scale generation such as calcium, magnesium, and phosphorus contained in the concentrated water 9 can be taken into sludge in the biological treatment step (biological treatment device) 2 and discharged to the outside as excess sludge. . When the biological treatment process (biological treatment apparatus) 2 includes an anaerobic / aerobic treatment tank, more phosphorus can be fixed to the excess sludge.

Further, as shown by a dotted line in FIG. 11, in order to prevent scale formation, any one or more of the biologically treated water 3, the electrolytically treated water 5, and the concentrated water 9 is targeted for HAP (hydroxyapatite, Ca ₅ (OH). ) (PO ₄ ) ₃ ) or MAP (magnesium ammonium phosphate, Mg (NH ₄ ) PO ₄ ) treatment is carried out in the crystallization tank 11, and components that cause scale formation such as calcium, magnesium, phosphorus, etc. It can also be set as the structure removed from water in the form.

  Alternatively, it is possible to add an acid such as hydrochloric acid or sulfuric acid before the concentrating device 8 to prevent scale formation.

[Embodiment 3]
FIG. 8 is a schematic explanatory view showing another embodiment of the present invention. In the second embodiment, since the concentration device 8 is downstream of the electrolytic treatment tank 4, an easily biodegradable substance contained in the electrolytic treatment water 5 is introduced into the concentration device 8. Among the intermediate products generated in the electrolytic treatment tank 4, formic acid (molecular weight 46, boiling point 101 ° C.), acetic acid (molecular weight 60, boiling point 118 ° C.), etc. have low molecular weight and relatively low boiling point. In particular, it is conceivable that a part of the concentrated RO separation membrane is moved to the permeate side, and the evaporative concentration process is partly moved to the distilled water side. This embodiment is suitable for improving the water quality of the concentration process separation water 10.

  In the embodiment shown in FIG. 8, the raw waste water 1 is introduced into a biological treatment process (biological treatment device) 2 to separate and remove easily biodegradable substances, and biological treated water 3 containing a large amount of hardly biodegradable substances. can get. The biologically treated water 3 is introduced into a concentration step (concentration device) 8 to obtain concentrated water 9 and concentrated step separation water 10. Part or all of the concentrated water 9 is introduced into the electrolytic treatment step (electrolytic treatment tank) 4, and the hardly biodegradable substance is decomposed in the electrolytic treatment step (electrolytic treatment tank) 4, and electrolysis containing the readily biodegradable substance is performed. Treated water 5 is obtained. Subsequently, the electrolytically treated water 5 is returned to the biological treatment process (biological treatment device) 2, and the readily biodegradable substance contained in the electrolytically treated water 5 is separated and removed. In this embodiment, since the low molecular intermediate product contained in the electrolytically treated water 5 is not introduced into the concentration step (concentration device) 8, the water quality of the concentration step separation water 10 can be greatly improved.

  Hereinafter, the present invention will be described in more detail with reference to examples.

  Electrolytic treatment using a diamond electrode was conducted for industrial wastewater A, and changes in the biodegradability of the treated water accompanying the electrolytic treatment were investigated. Industrial wastewater A was a wastewater containing a lot of non-biodegradable substances with CODCr of 7500 (mg / L), BOD of 1450 (mg / L) and BOD / CODCr of about 0.2.

As the electrolytic treatment tank, an electrolytic treatment tank using a conductive diamond electrode as an anode and a titanium electrode as a cathode was used. The diamond electrode is formed by depositing conductive diamond on a silicon wafer substrate by a hot filament CVD method. The electrode area was about 140 cm ² and the current value was 14 A. The experiment was carried out in a circulating batch system, with an initial water volume of 3 L and a pump flow rate from the tank to the electrolysis cell of 1 L / min.

  Fig. 1 shows the relationship between the input electricity (Ah / g-CODCr), CODCr (mg / L), and BOD (mg / L), and Fig. 2 shows the input electricity (Ah / g-CODCr) and BOD / The relationship of CODCr is shown.

  When the electrolytic treatment is started, CODCr decreases almost linearly, but BOD increases up to about 1.5 Ah / g-CODCr input power, then decreases with increasing input power, about 5 Ah / g-CODCr. Both CODCr and BOD became almost zero. BOD / CODCr was about 0.2 at the beginning of the experiment, but when the amount of electricity of 2Ah / g-CODCr was added, it increased to about 0.5, and the biodegradability of the treated water was improved. When the amount of electricity input exceeded 2Ah / g-CODCr, BOD / CODCr decreased.

  Fig. 3 shows the relationship between the input electricity (Ah / g-CODCr) and VFA (mg / L), and Fig. 4 shows the relationship between the input electricity (Ah / g-CODCr) and pH. The most produced VFA was formic acid, followed by almost the same amount of acetic acid and lactic acid. The sum of these concentrations is shown in FIG. 3 as the VFA concentration. Up to about 2Ah / g-CODCr, the amount of VFA generated increased with the increase in the amount of electricity, and the pH decreased.However, when the amount of input electricity exceeded about 2Ah / g-CODCr, the VFA increased with an increase in the amount of electricity. The amount produced decreased and the pH increased. When the amount of electricity input exceeded about 3Ah / g-CODCr, VFA decreased rapidly. The reason why the biodegradability of treated water was improved was that VFA was generated.

A test was conducted on industrial wastewater B. The test was performed according to the processing flow shown in FIG. In the biological treatment process (biological treatment device) 2, medium temperature methane fermentation was performed. As the electrolytic treatment step (electrolytic treatment bath) 4, an electrolytic treatment bath using a conductive diamond electrode as an anode and a titanium electrode as a cathode was used. The diamond electrode is formed by depositing conductive diamond on a silicon wafer substrate by a hot filament CVD method. The electrode area was about 280 cm ² . As a control, the test was performed in a treatment flow in which the return from the electrolytic treatment step (electrolytic treatment tank) 4 shown in FIG. 9 to the biological treatment step (biological treatment apparatus) 2 was not performed.

  A comparison of the test results is shown in Table 1. Experiment 1 and Experiment 2 in Table 1 are the results of testing with the processing flow shown in FIG. 5, and Experiment 3 is the result of testing with the processing flow shown in FIG. In Experiment 1, the flow rate of the electrolyzed return water 6 was set to 3 times the raw water flow rate, and in Experiment 2, the flow rate of the raw water was 6 times. In the table, “inflow water” represents the wastewater raw water 1, and “outflow water” represents the electrolyzed water 5.

  Experiment 1 required about 30% lower electrolysis power in the electrolytic treatment process (electrolytic treatment tank) 4 than Experiment 3, and the generated methane gas from methane fermentation was about 1.3 times higher. Moreover, by increasing the return flow rate, the generated methane gas further increased and the electrolysis power decreased.

  A test was conducted on industrial wastewater C. The test was performed according to the processing flow shown in FIG. In the biological treatment process (biological treatment device) 2, medium temperature methane fermentation was performed. The electrolytic treatment tank (electrolytic treatment tank) 4 is an electrolytic treatment tank using a conductive diamond electrode as an anode and the titanium electrode as a cathode. The concentration process (concentration device) 8 is a loose RO membrane (product name: NTR-7250 manufactured by Nitto Denko). ) Was used. The diamond electrode is formed by depositing conductive diamond on a silicon wafer substrate by a hot filament CVD method.

The electrode area was about 280 cm ² and the current value was 6 A. As an object, the test was performed according to the processing flow shown in FIG.

  A comparison of the test results is shown in Table 2. Experiment 4 in Table 2 is a result of testing with the processing flow shown in FIG. 7, and Experiment 5 is a result of testing with the processing flow shown in FIG. In Experiment 4, the concentration rate in the concentration step (concentration device) 8 was tripled, and the concentrated water 9 was returned to the biological treatment step (biological treatment device) 2 at three times the raw water flow rate. In Experiment 5, the flow rate of the electrolytic treatment return water 6 was made three times the raw water flow rate and returned to the biological treatment process (biological treatment device) 2. In the table, “inflow water” represents the raw waste water 1, “outflow water” represents the concentration process separation water 10 in the flow shown in FIG. 7, and electrolytic treatment water 5 in the flow shown in FIG. 5.

  In Experiment 4, the effluent was further purified compared to Experiment 5. Furthermore, the amount of methane gas generated was 1.5 times higher. Further, in Experiment 4, since the inorganic ions are concentrated in the concentration process (concentration device) 8 and the electrical conductivity is increased, the voltage required to pass a predetermined current in the electrolytic treatment process (electrolysis process tank) 4 is determined in Experiment 5. It was low compared with.

Tests were conducted on industrial wastewater D with a relatively low CODCr concentration. The test was performed according to the processing flow shown in FIG. In the biological treatment process 2, standard activated sludge treatment was performed. As the concentrating device 8, a membrane separation concentrating device having a loose RO membrane (product name: NTR-7250 manufactured by Nitto Denko) is used, and as the electrolytic treatment tank 4, electrolytic treatment using a conductive diamond electrode as an anode and a titanium electrode as a cathode A tank was used. The diamond electrode is formed by depositing conductive diamond on a silicon wafer substrate by a hot filament CVD method. The electrode area was about 280 cm ² . As a control, the treatment flow shown in FIG. 7 and the treatment flow (FIG. 10) in which the electrolytically treated water 5 is introduced again into the concentration step (concentration device) 8 instead of the biological treatment step (biological treatment device) 2 were also tested. . In the processing flow shown in FIG. 10, it was necessary to lower the pH to about 5 by adding sulfuric acid before the concentrating device 8 in order to prevent scale formation by calcium carbonate. In the treatment flow shown in FIGS. 8 and 7, since calcium was removed together with the excess sludge from the biological treatment step 2, addition of sulfuric acid was unnecessary. In each processing flow, the concentration factor in the concentrator 8 was tripled.

  Table 3 shows the test results. Experiment 6 represents the processing result according to the processing flow shown in FIG. 8, Experiment 7 represents the testing result according to the processing flow shown in FIG. 7, and Experiment 8 represents the testing result according to the processing flow shown in FIG. In the table, “influent water” represents the raw drainage water 1 and “outflow water” represents the concentration process separation water (permeated water) 10.

    From Table 3, the runoff water in Experiment 6 was highly purified compared to Experiment 7 and Experiment 8. This is because, in Experiment 6, an easily biodegradable low-molecular intermediate product such as VFA contained in the electrolytically treated water 5 is introduced into the biological treatment process (biological treatment apparatus) 2, and is added to the concentration process (concentration apparatus) 8. This is because was not introduced. In Experiment 7 and Experiment 8, the electrolyzed water 5 was introduced into the concentration step (concentrator) 8, and a part of the VFA contained in the electrolyzed water 5 permeated the loose RO membrane.

FIG. 1 is a graph showing an example of the relationship between the amount of electricity input (Ah / g-CODCr), CODCr (mg / L), and BOD (mg / L) in electrolytic treatment using a conductive diamond electrode. FIG. 2 is a graph showing an example of the relationship between the amount of electricity charged (Ah / g-CODCr) and BOD / CODCr in electrolytic treatment using a conductive diamond electrode. FIG. 3 is a graph showing an example of the relationship between the amount of electricity input (Ah / g-CODCr) and VFA (mg / L) in electrolytic treatment using a conductive diamond electrode. FIG. 4 is a graph showing an example of the relationship between the input electric quantity (Ah / g-CODCr) and pH in the electrolytic treatment using a conductive diamond electrode. FIG. 5 is a schematic explanatory diagram of a processing flow according to the first embodiment of the present invention. FIG. 6 is a schematic explanatory view showing an example of a circulating batch type electrolytic treatment tank used in the present invention. FIG. 7 is a schematic explanatory diagram of a processing flow according to the second embodiment of the present invention. FIG. 8 is a schematic explanatory diagram of a processing flow according to the third embodiment of the present invention. FIG. 9 is a schematic explanatory diagram of a processing flow according to a conventional example used as a control in the first embodiment. FIG. 10 is a schematic explanatory diagram of a processing flow in which the electrolytically treated water used as a control in Example 3 is not sent to the biological treatment process. FIG. 11 is a schematic explanatory diagram of a partial deformation process flow according to the second embodiment of the present invention.

Explanation of symbols

1: Raw wastewater 2: Biological treatment process (biological treatment equipment)
3: Biologically treated water 4: Electrolytic treatment process (electrolytic treatment tank)
5: Electrolyzed water 6: Electrolyzed return water 8: Concentration step (concentrator)
9: Concentrated water 10: Concentrated process separation water (permeated water)
11: Crystallization tank

Claims (7)

A biological treatment device;
An electrolytic treatment tank provided with a conductive diamond electrode located downstream of the biological treatment device and electrolytically treating biologically treated water obtained by the biological treatment device ;
Return means for returning at least part of the effluent from the electrolytic treatment tank to the biological treatment apparatus;
An organic wastewater treatment apparatus containing a hardly biodegradable substance. A biological treatment device;
An electrolytic treatment tank comprising a conductive diamond electrode located downstream of the biological treatment apparatus;
A concentrator located downstream of the electrolytic treatment tank;
Return means for returning at least a portion of the concentrated water from the concentrator to the biological treatment device;
An organic wastewater treatment apparatus containing a hardly biodegradable substance. A biological treatment device;
A concentration device that is located downstream of the biological treatment device and concentrates biological treatment water obtained by the biological treatment device;
An electrolytic treatment tank provided with a conductive diamond electrode located on the downstream side of the concentrated water side of the concentrator and electrolytically treating the concentrated biological treated water ;
Returning means for returning effluent water from the electrolytic treatment tank to the biological treatment apparatus. A biological treatment process for obtaining biologically treated water by biologically treating organic wastewater containing a hardly biodegradable substance;
An electrolytic treatment process for obtaining electrolytically treated water by subjecting at least a part of the biologically treated water to electrolytic treatment using a conductive diamond electrode;
Returning at least a portion of the electrolytically treated water to the biological treatment step;
An organic wastewater treatment method containing a non-biodegradable substance, comprising: A biological treatment process for obtaining biologically treated water by biologically treating organic wastewater containing a hardly biodegradable substance;
Electrolytic treatment of the biologically treated water using a conductive diamond electrode to obtain electrolytically treated water;
A concentration step of concentrating the electrolytically treated water to obtain concentrated water;
Returning at least a portion of the concentrated water to the biological treatment process;
An organic wastewater treatment method containing a non-biodegradable substance, comprising: A biological treatment process for obtaining biologically treated water by biologically treating organic wastewater containing a hardly biodegradable substance;
A concentration step of concentrating the biologically treated water to obtain concentrated water;
An electrolytic treatment process for obtaining electrolytically treated water by electrolytically treating at least a part of the concentrated water using a conductive diamond electrode;
Returning the electrolytically treated water to the biological treatment step;
An organic wastewater treatment method containing a non-biodegradable substance, comprising:   The organic wastewater treatment method according to any one of claims 4 to 6, wherein in the electrolytic treatment step, an amount of electricity of 10 to 90% of the amount of electricity required for the theoretical electrolytic treatment is applied.

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