JP3767736B2 - Organic waste treatment method and equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to the treatment of organic waste, and in particular, reduces the amount of organic sludge such as surplus activated sludge generated from the process of biological treatment of organic sewage such as sewage, and organic waste such as soot and waste oil. The present invention relates to a method and an apparatus for processing.
[0002]
[Prior art]
Conventionally, JP-A-8-299995 is known as a method for reducing the amount of excess sludge generated with biological treatment such as the activated sludge method. As shown in FIG. 2, this technology includes a “process for biologically treating organic sewage, a sludge digestion process for digesting surplus sludge discharged from the biological treatment process, and at least a portion of the digested sludge by ozone treatment. It is a method for treating organic drainage including an ozone treatment step that circulates in the digestion step.
The definition of the aerobic digestion method stipulates that “aerobic digestion is a method in which surplus sludge is introduced into a digestion tank and aerated, and a part of the aerated sludge is taken out and solid-liquid separated”.
[0003]
As can be seen from FIG. 2, this prior art supplies excess sludge to the aerobic digester as it is in a lean sludge concentration (about 1%) without concentrating it by mechanical means. Part of the digested sludge that has been separated into solid and liquid is ozone-oxidized and then returned to the aerobic digester.
However, this conventional technique has the following problems.
(1) There is little sludge decomposition effect in an aerobic digester.
(2) The hydraulic residence time of sludge in the aerobic digester is very long, about 7 days.
(3) Since the solubilizing means is limited to ozone, an expensive ozone generator is indispensable and the equipment cost is high.
(4) A large amount of SS tends to flow out into the solid-liquid separation liquid of aerobic digested sludge, and post-treatment is required.
[0004]
[Problems to be solved by the invention]
The present invention provides a treatment method and apparatus capable of effectively reducing the amount of organic waste such as excess sludge, soot and waste oil with a very simple system and low running cost, which solves the above-mentioned problems of the prior art. The task is to do.
[0005]
[Means for Solving the Problems]
In order to solve the above problems, in the present invention, an organic waste is a mixture of organic sludge and soot and / or waste oil, and the organic sludge is concentrated by a mechanical concentration means. In the treatment method for reducing the amount by aerobic digestion, the organic waste is obtained by aerobic digestion in a state where the treatment temperature is increased by 30 ° C. or more from the supply temperature by biooxidation heat in the aerobic digestion step. After the solubilized heated aerobic digested sludge is ultrasonically solubilized, the solubilized sludge is returned to the aerobic digestion step.
In the treatment method, the aerobic digested sludge can be solubilized by ultrasonication of the sludge separated by membrane separation.
Further, in the present invention, the organic sludge is a mixture of soot and / or waste oil, and the organic sludge is concentrated by mechanical concentration means, and the organic waste is aerobically digested to reduce the weight. An aerobic digester for aerobic digestion of organic waste in a state where the temperature of the organic waste is increased by biological oxidation heat, and an ultrasonic means for solubilizing digested sludge in the aerobic digester, And means for returning the solubilized sludge to the aerobic digester.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Next, the present invention will be described in detail.
FIG. 1 shows a flow configuration diagram for carrying out the processing method of the present invention. In FIG. 1, 1 is a mechanical sludge concentrator, 2 is an aerobic digester, 3 is a membrane separation module, 4 is a physicochemical solubilizing means, 5 is organic sludge, and 6 is organic waste.
Organic sludge 5 such as surplus sludge discharged from the biological treatment process of sewage is supplied to a mechanical sludge concentrating device 1 such as centrifugal concentration, flotation separation, screen separation, and membrane separation. In the sludge concentration apparatus 1, the biological sludge is concentrated to a solid concentration of 2% or more, preferably 3% or more. Since it is difficult to concentrate surplus activated sludge to this value in the gravimetric precipitation concentration method, it is preferable to apply a mechanical concentration means.
[0007]
Next, the concentrated sludge 7 having a high concentration and high viscosity is supplied to the aerobic digester 2 and aerated with the oxygen-containing gas 13 for about 3 to 4 days while mechanically stirring. As a result, the sludge temperature rises to about 50-70 ° C., which is 30 ° C. higher than the feed temperature, due to the biooxidation heat, without heating from the outside using a fuel such as petroleum. As a result, the sludge is highly oxidatively decomposed in an aerobic high temperature state, and the amount of SS is greatly reduced. The aerobic digestion tank 2 may naturally be a multistage series tank of 3 to 4 tanks instead of one tank. As the aeration gas, oxygen-enriched air and pure oxygen, which have a smaller amount of exhaust gas than air and can reduce exhaust heat, are suitable. In order to minimize heat radiation from the aerobic digestion tank 2, it is preferable to perform a heat insulation work. It is more preferable if it is buried underground.
In addition, by supplying easily biodegradable organic waste 6 such as straw and waste oil to the aerobic digestion tank 2, the biooxidation heat generation wall is greatly improved and the temperature rise effect is improved. Speed and digestibility are improved.
[0008]
Next, the aerobic digested sludge 8 whose temperature has been increased is subjected to solid-liquid separation by membrane separation, precipitation separation, etc., and a physicochemical solubilization process (oxidation with hypochlorous acid, oxidation with hydrogen peroxide, ultrasonic treatment, ozone treatment) Supplied to physicochemical solubilization means 4) such as oxidation, alkali treatment, mechanical grinding such as mill, etc., solubilizes aerobic digested sludge.
In the following description, the physicochemical solubilization means 4 using ultrasonic waves will be described as an example.
That is, when the sludge is extracted from the aerobic digestion tank 2 in which the membrane separation module 3 of FIG. 1 is immersed and irradiated with ultrasonic waves, the ultrasonic vibration is applied to the sludge cells at a certain moment and a decompression force at the next moment. This action is repeated while acting as a compressive force and applying ultrasonic vibrations.
[0009]
In this repetition, when a decompression force acts on water, a vacuum cavity is generated in the water, and gas (oxygen, carbon dioxide, etc.) dissolved in water is adsorbed to generate cavitation bubbles. At the next moment, a compressive force acts on the water, and the bubbles are compressed with a large force. At this time, the bubbles are in an adiabatic compression state, the inside of the bubbles becomes a high temperature and a high pressure, and finally they are crushed and broken into original molecules. At this time, hydroxy radicals having a strong oxidizing power are generated from oxidant molecules such as hydrogen peroxide and water molecules.
Furthermore, when the bubbles disappear, the oxidant molecules and water molecules that have been surrounding the bubbles rush to the traces of the disappearance of the bubbles and collide with each other. appear. In addition, since the ultrasonic energy is finally replaced by heat in the water, the water temperature rises. The powerful shock wave, the strong oxidizing action of radicals, and the temperature raising effect are combined to effectively destroy the activated sludge cell wall and solubilize the activated sludge.
[0010]
Since the sludge solubilization effect by the ultrasonic wave is proportional to the ultrasonic generation energy per SS amount of sludge, the required energy of the ultrasonic generator can be reduced as the SS amount of the target sludge is small. Therefore, in the present invention, since the sludge SS is greatly reduced in the aerobic digester that supplies high-concentration sludge, the required energy of the ultrasonic generator can be greatly reduced, and the energy saving effect is great.
As the ultrasonic irradiation energy per 1 kg · SS of activated sludge, the range of 1 to 3 kWh / kg · SS has a large sludge solubilizing effect. The ultrasonic irradiation time may be as short as several tens of seconds. As for the suitable ultrasonic frequency, it is recognized that if the frequency is too high, the sludge solubilization effect is deteriorated, and 10 to 100 kHz, more preferably 15 to 50 kHz is suitable.
[0011]
In addition, since the sludge solubilization process using ultrasonic waves improves the solubilization efficiency as the concentration of the target sludge SS increases, the concentrated sludge may be supplied to the solubilization process and supplied to the aerobic digester after the solubilization process. This is a preferred means.
In the present invention, in the aerobic digestion tank 2, the temperature rises as the sludge temperature rises to 50 ° C. or more by the self-acid heating of the organic waste, and the ultrasonic irradiation energy finally changes to heat. Therefore, the solubilization effect is further improved (the higher the sludge temperature, the better the solubilization effect by ultrasonic waves).
[0012]
【Example】
Hereinafter, the present invention will be described specifically by way of examples.
Example 1
Based on the process of FIG. 1, the verification test of the present invention was conducted under the following treatment conditions for surplus activated sludge of sewage and household garbage.
Treatment conditions Excess sludge treatment amount: 25 l / d,
Sludge concentration: 8 g / l,
Sludge concentration method: Centrifugation,
Concentrated sludge solids concentration and temperature: 4%, 26 ° C,
Disposer ground garbage supply amount: 1000 g / d,
Aerobic digestion tank volume: 20 liters (cover the tank with heat insulation material),
Aerobic digester temperature: 70-82 ° C (effect by bio-oxidation heat),
Heating with an external heat source:
Solids concentration in aerobic digester: 4600-5500 mg / l,
[0013]
Membrane separation module products: Rotating disc flat membrane MF membrane,
Membrane separation flux: 1 m / d,
Supply sludge flow rate from aerobic digestion tank to sonication tank: 2 liters / d,
Ultrasonic irradiation energy per 1kg of sludge / SS: 2kWh / kg · SS,
Ultrasonic frequency: 20 kHz
Ultrasonic irradiation time: 20 sec.
Under the above conditions, a continuous test was conducted for one year without disposing the sludge in the aerobic digester outside the system. As a result, even after one year, the sludge concentration in the aerobic digester was 4000 to 5000 mg / l, and it was confirmed that the excess sludge and garbage were reduced by 100%.
The water quality of the membrane separation water was very good with SS zero and BOD 10 mg / l, and no post-treatment was required.
[0014]
Comparative Example 1
In Example 1, the surplus activated sludge was supplied to the aerobic digester of Example 1 as it was without mechanically concentrating it. We did not supply garbage.
As a result, the temperature of the aerobic digester was only raised to 30 degrees, and the sludge concentration in the aerobic digester after 1 month increased to 25000 mg / l, and that after 2 months increased to 36800 mg / l. The surplus sludge that was produced did not decompose and tended to accumulate. At this point, the membrane separation flux was also greatly reduced to 0.12 m / d, and sludge could not be supplied.
[0015]
【The invention's effect】
According to the present invention, the following effects can be achieved.
(1) Rather than aerobic digestion of sludge in a dilute state, it is performed after mechanically concentrating, so the temperature can be raised sufficiently by only the oxidation heat of sludge, and the sludge reduction effect by aerobic digestion large. In addition, the temperature of the aerobic digester can be further increased by supplying organic waste such as soot and waste oil that generates a large amount of biooxidation heat.
(2) Therefore, there is no need for an external heat source such as a boiler or heater for heating the aerobic digester, and the energy saving effect is great.
(3) Since most of the sludge SS is biologically decomposed and mineralized and reduced before physicochemical solubilization, the cost of physicochemical solubilization treatment such as ultrasonic and ozone oxidation Can be greatly reduced.
(4) Since the sludge whose temperature has been raised by the self-oxidation heat of organic waste is subjected to physicochemical solubilization such as ozone and ultrasonic waves (the higher the temperature, the greater the solubilization effect), so improves.
(5) Since sludge does not flow into the effluent from the aerobic digestion process, the water quality is good and no post-treatment is required.
[Brief description of the drawings]
FIG. 1 is a flow configuration diagram for carrying out a processing method of the present invention.
FIG. 2 is a flowchart showing a conventional technique.
[Explanation of symbols]
1: mechanical sludge concentrator, 2: aerobic digester, 3: membrane separation module, 4: physicochemical solubilization means, 5: organic sludge, 6: organic waste, 7, 9: concentrated sludge, 8: Aerobic digested sludge, 10: Solubilized sludge, 11, 12: Separated water, 13: Oxygen-containing gas

Claims (3)

In the processing method of reducing the organic aerobic digestion and reducing the organic waste, which is a mixture of organic sludge and soot and / or waste oil, and the organic sludge is concentrated by mechanical concentration means , The organic waste is subjected to aerobic digestion in a state where the treatment temperature is increased by 30 ° C. or more from the supply temperature by biooxidation heat in the aerobic digestion step, and the resulting heated aerobic digestion sludge is ultrasonicated. A method for treating organic waste, wherein the solubilized sludge is returned to the aerobic digestion step after being solubilized. The aerobic digestion sludge processing method according to claim 1 Symbol placement organic waste, characterized in that the sludge that is separated by membrane separation, solubilized treated with ultrasound. In a processing apparatus for reducing the amount of organic sludge by aerobic digestion of organic waste, which is a mixture of organic sludge and soot and / or waste oil, and the organic sludge is concentrated by mechanical concentration means , An aerobic digester that aerobically digests organic waste in a state where the temperature is increased by bio-oxidation heat, ultrasonic means for solubilizing digested sludge in the aerobic digester, and the solubilized sludge An organic waste processing apparatus comprising a means for returning to an aerobic digester.

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