JP2004008843A - Method for treating organic waste water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for treating organic waste water by which the cost for operation and facilities can be reduced, excess sludge is efficiently decomposed to recover gas essentially comprising methane gas and the gas can be effectively used as a fuel or the like in a method for treating waste water by which the amount of excess sludge can be eliminated or at least the volume can be reduced. <P>SOLUTION: The method for treating organic waste water includes steps of: (1) aerobic biological treatment of organic waste water; (2) solid-liquid separation of the sludge in the mixture liquid after the biological treatment; (3) sludge returning process to return at least a part of the separated sludge to the aerobic biological treatment step; (4) solubilization to solubilize at least a part of the residual sludge; (5) ammonia stripping process to eliminate ammonia in the solubilized liquid after the solubilization; (6) anaerobic digestion to anaerobically digest the solubilized liquid from which ammonia is eliminated; and (7) digested sludge returning process to return the digested sludge after the anaerobic digestion treatment to the aerobic biological treatment step. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a wastewater treatment method for biologically treating organic wastewater, and more specifically, reduces the amount of excess sludge generated in the step of aerobically treating organic wastewater, decomposes sludge, and efficiently processes methane gas. The present invention relates to a method for treating organic wastewater which can be collected and used effectively.
[0002]
[Prior art]
BACKGROUND ART Conventionally, as an apparatus for treating organic wastewater (hereinafter sometimes referred to as raw water) such as sewage, food wastewater, kitchen wastewater or septic tank sludge, an activated sludge treatment apparatus, a fixed-bed biological treatment apparatus or a fluidized-bed treatment apparatus is used. An aerobic treatment device such as the above is used.
[0003]
In the activated sludge treatment apparatus, wastewater is supplied to a treatment tank in which sludge, which is an aerobic microorganism, is floated, and aerated with air, thereby oxidatively decomposing organic substances in raw water by the biological action of sludge. In the case of a fixed-bed type biological treatment device, a fixed bed of a biological holding carrier made of synthetic resin or the like is provided in the treatment tank, and microorganisms adhere to and grow on the surface of the carrier by aeration with air. It is a device that oxidatively decomposes organic matter in raw water by the biological action of attached microorganisms.Furthermore, a fluidized bed type treatment device is made of synthetic resin particles that can flow into a liquid in an aerobic biological treatment tank. This is a device that oxidizes and decomposes organic matter in raw water by the biological action of microorganisms that have adhered and proliferated on the surface of the fluidized biological holding carrier by supplying raw water and aerating with air by filling the raw water with the biological support. is there.
[0004]
In any of the above biological treatment apparatuses, a large amount of microorganisms that have proliferated are generated as sludge as biological substances are biologically decomposed. The generated sludge is separated and concentrated in a sedimentation tank, etc., and a part of it is circulated to the biological treatment process, but the remainder is discharged out of the system as excess sludge.The excess sludge is concentrated, dewatered, and then incinerated or landfilled. Has been disposed of. It is said that the surplus sludge amount is 20 to 50% of the organic matter amount (BOD) in the raw water introduced into the biological treatment step.
[0005]
In the conventional method of disposing of excess sludge, in the method of concentrating and dewatering sludge and then incineration or landfill disposal, even after concentration and dewatering of sludge, the water content is as high as 70 to 80 wt%, and the bulk is large. In the case of requesting a waste disposal company to dispose of the waste, the collection cost is high, and currently the wastewater treatment accounts for much of the cost.
[0006]
Further, in the landfill disposal, the remaining years of the industrial waste landfill are decreasing, and the collection cost is increasing year by year. In addition, in the case of incineration, fuel consumption is high due to high water content, fuel costs are high, and furthermore, it is necessary to treat exhaust gas and incineration ash. It is a situation that is becoming more common.
[0007]
In view of the above circumstances, various methods for reducing the volume of generated sludge as much as possible have been disclosed. However, similarly to the present invention, the sludge is solubilized, and the treated solubilized solution is subjected to an anaerobic treatment step. Devices for reducing the volume of sludge are disclosed in JP-A-2-21299, JP-A-9-001179, JP-A-2001-157900, and the like. A method of performing anaerobic treatment of the solubilized solution by treating the solubilized solution is disclosed in Japanese Patent No. 2659895 and Japanese Patent Application Laid-Open No. 6-099199.
[0008]
The method disclosed in JP-A-2-21299 is a method in which organic sludge is solubilized in an appropriate solubilization treatment step, and then subjected to anaerobic digestion treatment in a predetermined pH range and treatment days. The method disclosed in Japanese Patent Application Laid-Open No. 9-001179 is a method of subjecting sedimented and separated sludge to solubilization under high-temperature conditions and anaerobic treatment of separated water and a solubilized solution. In the method disclosed in the above, an organic sludge is digested anaerobically, the anaerobic digested sludge after the treatment is solid-liquid separated, the sludge is concentrated, and the concentrated sludge is appropriately modified (solubilizing step). And returns to the anaerobic treatment step.
[0009]
Further, the method disclosed in Japanese Patent No. 2659895 makes the sludge alkaline, solubilizes it by hot alkali treatment in a predetermined temperature range, and makes the solubilized solution anaerobic in a predetermined pH range and a predetermined temperature range. In the digestion treatment, the method disclosed in Japanese Patent Application Laid-Open No. 6-099199 makes the excess sludge alkaline, solubilizes it by hot alkali treatment within a predetermined temperature range, and uses an anaerobic treatment solution. This is a digestion method.
[0010]
[Problems to be solved by the invention]
In the method of volume reduction by anaerobic digestion, the organic matter in sludge is decomposed into methane gas or carbon dioxide gas by the biological action of anaerobic microorganisms, and methane gas is effective for fuel etc. Although it is a preferable method because it has an advantage that it can be used, in the above-mentioned various devices and methods, since the operation of removing ammonia in the sludge subjected to the aerobic biological treatment is not performed, the solubilized treatment may be performed. There is a problem that the activity of anaerobic microorganisms in the anaerobic digestion step is inhibited by the influence of ammonia ions in the solubilized solution, and the digestion cannot be performed efficiently.
[0011]
In addition, it is said that the higher the ammonia concentration, the greater the inhibition of activity against anaerobic microorganisms, methane bacteria, and it is said that methane fermentation becomes substantially impossible at 2000 mg / L or more. Further, even if the sludge is simply made alkaline and mechanically stirred, ammonia cannot be efficiently volatilized and removed, so that the above problem cannot be solved.
[0012]
The present invention has been made in view of the problems in the conventional sludge disposal and volume reduction treatment, and has been implemented in a wastewater treatment method capable of reducing the amount of excess sludge generated or at least reducing the volume. Purpose of providing an organic wastewater treatment method that can reduce expenses and equipment costs, and efficiently decompose excess sludge to recover gas mainly composed of methane gas and make it possible to use it effectively as fuel. It was made in.
[0013]
[Means for Solving the Problems]
The gist of the present invention to achieve the above object is a method for treating organic wastewater, which comprises the following steps in the invention described in claim 1.
A) an aerobic biological treatment step of aerobic biological treatment of organic wastewater; b) a solid-liquid separation step of solid-liquid separation of sludge in the mixture biologically treated in the aerobic biological treatment step; c) A sludge return step of returning at least a part of the sludge separated in the solid-liquid separation step to the aerobic biological treatment step as return sludge; and d) a solubilization treatment of solubilizing at least a part of the remaining separated sludge. E) an ammonia stripping step of stripping the ammonia in the solubilization solution subjected to the solubilization treatment in the solubilization treatment step with a carrier gas; and f) an ammonia stripping step in which the ammonia is removed in the ammonia stripping step. An anaerobic digestion treatment step of anaerobically digesting the solubilized liquid; and g) returning the digested sludge subjected to the anaerobic digestion treatment in the anaerobic digestion treatment step to the aerobic biological treatment step. Of sludge returning step.
[0014]
By providing the above step, since the solubilized solution supplied to the anaerobic digestion treatment step contains almost no ammonia, the activity of the anaerobic microorganisms in the anaerobic digestion step is affected by the ammonia ions. The digestion treatment can be performed efficiently without being hindered, and the amount of excess sludge generated can be reduced to zero or at least reduced. Further, the generated methane gas can be effectively used as fuel or the like, and operation costs and equipment costs can be reduced.
[0015]
In the above, in the aerobic biological treatment step, in addition to a normal activated sludge treatment tank, a fixed-bed treatment tank or a biological holding carrier in which a biological holding carrier such as a synthetic resin or a fibrous material is fixed and filled is flowably filled. A fluidized bed biological treatment tank may be used. In the anaerobic digestion treatment step, there is a single tank treatment using an anaerobic digestion tank, a two-tank treatment apparatus combining an acid fermentation tank and an anaerobic digestion tank, or an upward anaerobic treatment apparatus. .
[0016]
In the solid-liquid separation step, a sedimentation tank, a filtration device, a filtration membrane separation device, a centrifuge, or the like can be used. Furthermore, in the solubilization step, biological solubilization by thermophilic bacteria, chemical solubilization such as alkali method and ozone method, physical solubilization such as ultrasonic method and mechanical crushing method, or a method of combining them It can be used as appropriate.
[0017]
In the ammonia stripping step, steam, air, etc. can be used as a carrier gas, and an aeration tank, a tray tower or a packed tower can be used as appropriate, but the tray tower is taken into account in consideration of the stripping effect and the influence of sludge. Preferably, it is used. Note that, depending on the solubilization method in the solubilization treatment step, it is necessary to adjust the pH by adding an alkali before supplying the solubilization treatment solution to the stripping step or during the stripping step, and after the stripping step. It is necessary to adjust the pH before supplying the solubilized solution to the anaerobic digestion process.
[0018]
In the anaerobic digestion tank in the anaerobic digestion treatment step, the treatment is performed at a temperature of 25 to 75 ° C, preferably 38 to 60 ° C, and a residence time of 24 hours to 2 weeks. When the temperature is lower than 25 ° C., there is a problem that the biological anaerobic digestion treatment does not easily proceed, and when the temperature is higher than 75 ° C., there is a problem that the anaerobic microorganisms hardly survive.
[0019]
Further, in the above, a sludge concentration step of concentrating excess sludge may be provided, and the solubilization treatment step may be configured as a solubilization treatment step of solubilizing at least a part of the concentrated sludge. By supplying to the anaerobic digestion treatment step through the treatment step, the solubilization treatment is performed quickly, and also in the anaerobic biological treatment, more suitable water content and organic matter concentration can be obtained, and the treatment capacity can be reduced. Therefore, the methane gas can be obtained efficiently and the solubilization of the sludge can be performed efficiently.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a system diagram of a wastewater treatment apparatus to which an organic wastewater treatment method according to one embodiment of the present invention is applied.
[0021]
In the figure, 1 is an adjusting tank for adjusting the amount of supply and pH value of organic wastewater (raw water) such as sewage, food wastewater, kitchen wastewater or septic tank sludge, and 2 is provided with an air diffusion means 7 at the bottom. The activated sludge treatment tank, which is an aerobic biological treatment step for aerobically and biologically treating organic matter in the raw water by aerating the supplied raw water with an oxygen-containing gas such as air, is subjected to biological treatment. A sedimentation tank, which is a solid-liquid separation step for sedimenting and separating the sludge in the mixed liquid, and an alkali solubilization apparatus, which is a solubilization treatment step for solubilizing at least a part of the sludge settled and separated, 5 Is a tray-type stripping tower in an ammonia stripping step of stripping ammonia in a solubilized solution with a carrier gas, and 6 is a stripped solubilized solution. Anaerobic digester is anaerobic digestion treatment step of digestion with temper.
[0022]
Further, in the above-described embodiment, a normal activated sludge treatment apparatus is used for the aerobic biological treatment step, but a fixed-bed treatment tank in which a biological holding carrier such as synthetic resin or fibrous material is fixed and filled. Alternatively, a fluidized bed biological treatment tank filled with a biological holding carrier so as to be able to flow may be used. In the solubilization process, an alkali solubilizer is installed. However, biological solubilization by thermophilic bacteria, chemical solubilization such as acid and ozone methods, ultrasonic method and mechanical crushing method, etc. Respective devices by physical solubilization or a combination thereof are used.
[0023]
In the anaerobic digestion treatment step, a single tank with an anaerobic digestion tank is used. However, a two-tank treatment apparatus combining an acid fermentation tank and an anaerobic digestion tank or an upward anaerobic digestion apparatus In the solid-liquid separation step, a sedimentation tank is used, but a centrifugal separator, a filtration membrane separator, a filtration device, or the like may be used. Further, in the ammonia stripping step, a plate tower is used, but an aeration tank or a packed tower can be appropriately used. Furthermore, a heat exchanger for exchanging heat between the concentrated sludge solid-liquid separated in a sedimentation tank and the sludge solubilized in the solubilization treatment tank, or steam of the solubilization treatment tank by blowing steam into the solubilization treatment tank. A heating means may be additionally provided.
[0024]
Next, a treatment method for treating organic wastewater with the wastewater treatment apparatus having the configuration shown in FIG. 1 will be described in detail below.
Raw water is supplied from the raw water supply flow path 20 to the regulating tank 1 and temporarily stored therein. After pH and the like are adjusted as necessary, the amount of wastewater supplied is adjusted and supplied to the activated sludge treatment tank 2 from the regulated raw water supply flow path 21. Then, by aeration with an oxygen-containing gas such as air supplied from the air diffuser 7, organic matter in raw water is efficiently oxidatively decomposed by the biological action of sludge, which is a floating aerobic microorganism. . The treatment temperature in the activated sludge treatment tank 2 is preferably from 10 to 45 ° C.
[0025]
The mixed liquid containing the sludge treated in the aerobic biological treatment step in the activated sludge treatment tank 2 is introduced into the sedimentation tank 3 from the mixed liquid discharge flow path 22, where the sludge is spontaneously settled and separated by standing. The purified treated water is discharged from the treated water discharge channel 23 to the outside of the system. The sludge settled and separated in the solid-liquid separation step in the sedimentation tank 3 is withdrawn from the sludge discharge channel 24 of the sedimentation tank 3, and partly returned to the activated sludge treatment tank 2 from the sludge return channel 25. You. Further, at least a part of the remaining separated sludge is supplied to the solubilization treatment device 4 from the sludge supply passage 27, and a part of the remaining separated sludge is discharged outside the system from the sludge discharge passage 26 as surplus sludge. Then, it is treated by a sludge treatment device not shown. In some cases, it may not be necessary to discharge excess sludge.
[0026]
To the sludge supplied to the solubilization treatment device 4, a sodium hydroxide solution is added from an alkali solution storage tank (not shown) via an alkali supply flow path 29, and the pH is 8.0 to 12.0, preferably the pH is 10.0 to 10.0. The mixture is adjusted to 11.0 and stirred at a temperature of 30 to 75 ° C., preferably 40 to 65 ° C., and a residence time of 10 to 100 hours, so that the microorganisms constituting the sludge are efficiently killed and decomposed to reduce the molecular weight. And solubilized. As the alkali to be made alkaline in the solubilization treatment step, an aqueous solution such as sodium carbonate or potassium hydroxide can be used in addition to the sodium hydroxide solution.
[0027]
Further, the solubilized treatment liquid is supplied from the solubilization treatment liquid supply passage 28 to the ammonia stripping tower 5, and mixed with carrier gas such as air or steam supplied from the lower carrier gas supply passage 30. Ammonia in the solubilization treatment liquid is volatilized and removed from the ammonia discharge flow path 31 into the atmosphere by the carrier gas together with the carrier gas due to the countercurrent contact. After being purified by treatment, adsorption removal treatment, etc., it is released into the atmosphere. The pH of the solution in the stripping step is preferably from pH 8.0 to 12.0, more preferably from pH 10.0 to 11.0. At a pH lower than pH 8.0, volatilization and removal of ammonia is sufficient. If the pH is higher than 12.0, the effect of stripping and removing ammonia is not improved even though the amount of chemicals used is large, and a neutralization step with an acid is required to supply the anaerobic treatment step in the subsequent step. Is required.
[0028]
The solubilized solution from which ammonia has been removed in the ammonia stripping tower 5 is supplied to the anaerobic digestion tank 6 from the deammonified solution supply channel 32, and has a temperature of 25 to 75 ° C, preferably 45 to 60 ° C, and a residence time. By treating for 24 hours to 2 weeks, organic matter is decomposed and a digestive gas mainly composed of methane is generated. The generated digestive gas mainly composed of methane is discharged out of the system from the generated gas discharge channel 33, and after being subjected to desulfurization treatment as required, is stored in a gas holder or the like, and is effectively used as fuel gas or the like.
[0029]
The digested sludge generated in the anaerobic digestion treatment step in the anaerobic digestion tank 6 is circulated and supplied from the sludge circulation channel 34 to the activated sludge treatment tank 2, and together with the organic matter in the raw water, the sludge, which is a floating aerobic microorganism, is removed. By being efficiently oxidatively decomposed by the biological action, the volume of the generated sludge can be reduced, and the amount of excess sludge generated can be reduced to zero or at least.
[0030]
【Example】
Organic wastewater discharged from a food factory was treated with activated sludge, and the generated sludge was solubilized by adding an alkaline solution while stirring with a stirrer. In the apparatus having the structure shown in FIG. 1, the generated sludge is solubilized by adding an alkali solution while stirring with a stirrer, and ammonia is stripped off from the solubilized solution using air as a carrier gas to remove ammonia. As a result of a test on Example 1 in which the solubilized solution was digested anaerobically, the digestibility was about 50% in Comparative Example 1, 70 to 90% in Example 1, and the amount of methane gas generated was In Comparative Example 1, the input sludge was 0.3 m3 / kg. In Example 1, it was 0.4 m3 / kg. Therefore, it was found that the sludge treatment efficiency in the example was increased.
[0031]
【The invention's effect】
The present invention provides a wastewater treatment method capable of reducing the amount of surplus sludge generation to zero or at least reducing the amount of operation and equipment costs, and efficiently decomposing surplus sludge to produce methane gas. This is a wastewater treatment method that recovers mainly gas and enables effective use as fuel.
[Brief description of the drawings]
FIG. 1 is a system diagram of a wastewater treatment apparatus to which an organic wastewater treatment method according to an embodiment of the present invention is applied.
1: Conditioning tank 2: Aerobic biological treatment process (activated sludge treatment tank)
3: Solid-liquid separation step (sedimentation tank)
4: solubilization process (solubilization device)
5: Ammonia stripping step (stripping tower)
6: Anaerobic digestion process (anaerobic digestion tank)

Claims (1)

A method for treating organic wastewater, comprising the following steps:
A) an aerobic biological treatment step for aerobic biological treatment of organic wastewater;
B) a solid-liquid separation step of solid-liquid separation of sludge in the mixed liquid biologically treated in the aerobic biological treatment step;
C) a sludge return step of returning at least a part of the sludge separated in the solid-liquid separation step to the aerobic biological treatment step as return sludge;
D) a solubilization step of solubilizing at least a part of the remaining separated sludge;
E) an ammonia stripping step of stripping the ammonia in the solubilized solution that has been solubilized in the solubilization process with a carrier gas;
F) an anaerobic digestion step of anaerobically digesting the solubilized solution from which ammonia has been removed in the ammonia stripping step;
G) a digested sludge return step of returning the digested sludge subjected to the anaerobic digestion treatment in the anaerobic digestion treatment step to the aerobic biological treatment step

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