JP2003053394A - Method and equipment for treatment of organic waste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new technique capable of rapidly decreasing the amounts of organic wastes, such as sludge, with saving of energy without using artificial heating means at all. SOLUTION: The method of treating the organic wastes comprises supplying the organic wastes, such as organic sludge, to a multistage aeration mixing vessel, raising the temperature in the vessel by the heat of the biooxidation of the supplied organic matter through oxygen-containing gas higher by >=40 deg.C than the temperature of the supplied matter and circulating the sludge from the rear stage vessel to the front stage vessel of the multistage aeration mixing vessel. The treatment equipment for the organic wastes has the multistage aeration mixing vessel which is introduced with the organic wastes, has oxygen- containing gas supplying means and raises the temperature in the vessel higher by >=40 deg.C than the temperature of the supplied matter and the equipment is provided with piping for circulating the sludge from the rear stage vessel to the front stage vessel of the multistage aeration mixing vessel.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a biodegradable organic waste such as surplus sludge, sewage aquatic sludge, and garbage in a process of biologically treating organic sewage such as sewage and industrial wastewater, which is extremely simple. Technology that can significantly reduce energy consumption with various devices.

[0002]

[Prior art and problems] Large amounts of organic sludge (excess sludge, raw sludge, etc.) are generated daily from activated sludge treatment facilities such as sewage, industrial wastewater, human waste, and landfill wastewater, and annually throughout Japan. Over 10 million tons. The treatment and disposal of this excess sludge is the biggest problem. Since organic sludge is difficult to dehydrate, a large amount of dehydration aid (polymer etc.) is added and dehydrated to a water content of about 85% with a sludge dehydrator, and the dehydrated cake is either landfilled or incinerated. However, there are many problems such as dewatering aid cost, shortage of dewatering cake landfill, shortage of incineration ash disposal place, incineration equipment cost, and high cost of heavy oil for incineration.

In order to solve such a problem, artificial heating and solubilizing means by thermophilic bacteria as shown in FIG. 3 are applied.
Various sludge solubilization technologies have been proposed. Note that FIG.
In the above, the sewage 20 is treated in the activated sludge aeration tank 21 while supplying an oxygen-containing gas (not shown), the activated sludge mixed liquid 22 is precipitated and separated in the sedimentation tank 23, and the supernatant water is treated water 2
Most of the settled sludge 25 is returned as sludge 2 and returned sludge 2
6 is returned to the activated sludge aeration tank 21, and the remaining extracted sludge 27 is solubilized in a solubilization tank 29 to which culture thermophile 28 has been added.
Then, a thermophilic treatment is performed by heating with the heating source 30.
The solubilized sludge 31, which is the treated sludge, is returned to the activated sludge aeration tank 21. The sludge solubilization technology using thermophiles has been reported in detail in the following documents. a) Katsura, Hasegawa, Miura: Activated sludge process that does not generate excess sludge using thermophilic microorganisms: Journal of Japan Society on Water Environment, Vol. 21, No. 6, 360
-366 (1998) b) Hasegawa: Technology for reducing sludge by thermophilic bacteria: Workshop material "Most advanced technology of sludge non-generation, volume reduction and reduction" (May 1, 200)
Held on the 6th).

In this sludge solubilization technique, an amount of activated sludge larger than the amount of surplus sludge generated is withdrawn from the activated sludge treatment process of organic wastewater, and separately cultivated thermophilic bacteria are added to the activated sludge by a heating means such as steam. In this method, the temperature is heated to about 65 ° C., the sludge is solubilized by the action of thermophilic bacteria, and the sludge is returned to the activated sludge treatment step. According to these documents, in order to solubilize activated sludge with thermophiles, separately cultivated thermophiles are added to the sludge, and the sludge temperature is adjusted to a temperature suitable for the activity of thermophiles (about 65 ° C). ), It is specified that an external heat source such as steam is essential for heating. However, the sludge reduction technology using thermophiles has a high sludge heating cost due to steam, etc., and therefore requires a boiler,
It is necessary to provide a heat exchanger for recovering heat from the heated sludge, and there are drawbacks such as increase in equipment cost and scale trouble of the heat exchanger caused by heating the sludge.

Conventionally known “aerobic digestion method” for organic sludge
Supplies sludge to a single tank aeration tank, and
This is a method of reducing the amount of sludge by aeration for a very long time of about 5 to 20 days so that biooxidative decomposition of sludge and endogenous respiration of microorganisms occur. In the aerobic digestion method, sludge is supplied as it is without being mechanically concentrated, so that the sludge is operated in a state in which the effect of raising the temperature due to biological oxidation is extremely small.
The oxygen-containing gas is supplied in a large amount so that dissolved oxygen is in an aerobic state of about 1 to 2 mg / liter.

[0006] The aerobic digestion method has a drawback that a large amount of undecomposed sludge remains even after aeration for a long time of 20 days, and the sludge reduction rate is only about 50% at the maximum, and a large aeration tank volume. Since there is a fatal drawback that a large amount of aeration power is required, there are almost no examples of implementation at sewage treatment plants in Japan, and the method is abandoned. For this reason, sewage treatment plants in Japan usually adopt an anaerobic digestion method that can recover methane gas without the need for aeration.

Further, there is known a method of decomposing and mineralizing food waste and organic sludge by the "high temperature aerobic fermentation method" utilizing the principle of sludge composting. In this method, wood chips, rice husks, etc. are filled in the tank, air is supplied while gently stirring this, and garbage with a small amount of water and organic sludge are supplied little by little to bio-oxidize and become inorganic. It is a technique for converting water into organic solids to be evaporated by heat of biological oxidation. (For example, the 32nd Annual Meeting of the Japan Society on Water Environment, p461- (1998): Li, Chiba, Treatment characteristics of pig house waste by high temperature aerobic fermentation method during long-term operation)

However, in this technique, it is essential to evaporate the moisture of the input organic waste to dry it. Therefore, unless almost all the input organic waste is bio-oxidized to generate heat of oxidation, the moisture evaporation will occur. I can't cover the latent heat. Therefore, it is necessary to reduce the water content of the organic waste to be input as much as possible, and when the water content of the sludge is high, the cake dehydrated by a mechanical dehydrator is supplied or the water content is 95%.
% Of sludge as it is, there was a drawback that the amount of sludge would be very small and the waste oil (vegetable oil, etc.) would have to be replenished for insufficient heat of oxidation to evaporate water. . In addition, the ammonia odor of the exhaust gas from the high temperature aerobic fermentation tank was intense, and there was a problem that a deodorizing device was indispensable.

[0009]

DISCLOSURE OF THE INVENTION The present invention solves the problems of the above-mentioned prior art, and saves organic waste such as sludge in a short time in an energy-saving manner without using any artificial heating means. The challenge is to provide new technologies that can be reduced.

[0010]

The present inventors have found that the above problems can be achieved by applying aeration treatment of highly concentrated sludge with an oxygen-containing gas in a novel manner. That is, the present invention has the following configurations.

(1) Organic waste such as organic sludge,
It is supplied to the multi-stage aeration stirring tank, and the temperature inside the tank is raised by 40 ° C. or more from the temperature of the feed by the biological oxidation heat of the supplied organic material through the oxygen-containing gas, and the sludge is transferred from the rear stage tank to the front stage tank of the multi-stage aeration stirring tank A method for treating organic waste, which is characterized by recycling.

(2) An organic waste is introduced, an oxygen-containing gas supply means is provided, and a multistage aeration stirring tank for performing biological oxidation is provided. Sludge is transferred from the latter stage tank to the front stage tank of the multistage aeration stirring tank. An apparatus for treating organic waste, which is provided with a circulating pipe. (3) It has a solid-liquid separation tank provided at the latter stage of the multi-stage aeration and stirring tank, a physicochemical solubilizing means for the separated sludge, and a return pipe for the solubilized sludge to the multi-stage aeration and stirring tank. The apparatus for treating organic waste according to (2) above, which is characterized.

That is, the point of the present invention is to supply organic waste such as organic sludge concentrated to a solid concentration of 2% or more to a multistage aeration and stirring tank so that the inside of the tank does not become anaerobic condition. By supplying a minimum amount of oxygen-containing gas for biooxidation, the temperature inside the tank is raised by 40 to 50 ° C from the temperature of the feed without artificial heating from the outside, and as a result, thermophilic bacteria naturally grow. Bio-oxidation is carried out,
Without the need to add thermophiles cultivated separately from the outside, oxidative decomposition of organic waste such as organic sludge is carried out
By reducing S, the concentration of organic solids in the final stage multi-stage aeration and agitation tank effluent is significantly reduced to about 0.5%.

[0014]

DETAILED DESCRIPTION OF THE INVENTION An embodiment of the present invention will be described in detail with reference to FIG. For simplification of description, an organic waste, for example, excess activated sludge as the organic sludge 1 will be described as an example. A mechanical concentrator 2 using mechanical concentrating means such as centrifugal separation, flotation concentration, screen separation, etc., in which a concentrated sludge 3 that is excess activated sludge concentrated to a solid concentration of 2% or more (preferably 3% or more) is multistage Aeration stirring tank (hereinafter also referred to as "stirring tank") 5 is supplied, and a small amount of oxygen-containing gas (air, oxygen-enriched air, pure oxygen) 7 is supplied while mechanically stirring the inside of tank 5 with a motor 6. Aerate for 2 to 4 days.

As a result, as disclosed in the prior art, the means for externally adding separately cultivated thermophiles and the means for artificially heating by steam from the outside are not applied at all, and It was found that the internal temperature of 5 easily rises by 40 ° C. or more due to the heat of sludge self-oxidation. At the stage when the temperature rises to this temperature, the thermophilic bacterium is naturally proliferating, so that a complicated operation of adding separately cultivated thermophilic bacterium is not necessary.

The oxygen-containing gas 7 for aerating the concentrated sludge
Although air is sufficient, the use of oxygen-enriched gas or pure oxygen is more preferable because the amount of heat carried out by the exhaust gas is reduced and the temperature of the stirring tank 5 is easily increased. The temperature of the stirring tank 5 is very important, and if the temperature is less than 50 ° C., the digestibility (treated sludge SS / supplied organic matter SS) will be greatly deteriorated. When the concentration is 2-4%, this stirring tank 5 (retention days 3 days)
In the process of staying in the room, the temperature in the tank 5 rises by 40 ° C or more only by the heat of biological oxidation without artificial heating, and the temperature rises to 60 to 75 ° C or more depending on the ambient temperature (normal temperature). Raises and oxidatively decomposes the organic sludge 1 to reduce SS, and the sludge (effluent) of the final stage stirring tank (aerobic digestion tank) 5
It was experimentally confirmed that the solid concentration of 9 markedly decreased to about 0.5%.

In the present invention, it is important to bio-oxidize while feeding a small amount of air 7 under the condition that the sludge concentration is high, the viscosity is high, and the fluidity is poor. Therefore, the sludge is mechanically strongly stirred. However, it is important to aerate with a small amount of air 7. Since sludge does not flow with only a small amount of air aeration, it is necessary to use a stirring means. The stirring may be performed by a pump circulation method instead of stirring by a stirring blade. In particular, an underwater stirrer in which the motor unit 6 is immersed in water is optimal because the heat generated by the motor 6 can be used to raise the liquid temperature.

According to the present invention, surprisingly, even when the temperature of the feed is about 20 ° C. and the concentration of the supplied sludge is 2%, the organic matter is not heated by a heater or steam from the outside at all. It was found that the temperature in the tank rises significantly to 50 ° C or higher (when the concentration of supplied sludge is 3%, the temperature in the tank rises to 70 ° C or higher) due to the effect of only the heat of biological oxidation. The reason for this is that, unlike the “high-temperature aerobic fermentation method” of the present invention, there is no need to evaporate water, so latent heat of water evaporation is not required, and only sensible heat for raising the liquid temperature is required. This is because the internal temperature can be easily increased.

Here, the above sludge temperature rises by 40 ° C. or more due to the heat of self-oxidation generated in the process until the organic matter in the sludge is biooxidized and mineralized, and 60 to 70 ° C.
The phenomenon that rises to some extent can be quantitatively explained as follows. Decomposition rate of sludge by agitation tank is 35%, calorific value is 4,500 cal / kg-DS, and supply sludge temperature is 20 ° C.
Then, when 1000 kg of sludge having a water content of 95%, that is, water contents of 950 kg and 50 kg DS is biooxidized in the stirring tank 5 which is an aerobic reaction tank for aerating air, the heat of self-oxidation generated, that is, the calorific value Q is Q = 50 × 0.
35 × 4500 = 78,750 kcal. on the other hand,
The amount of heat required to raise 1 kg of 20 ° C sludge to 55 ° C is 52,250 kcal, so even if the stirring tank is raised to 75 ° C and natural heat dissipation from the stirring tank to the outside air is considered,
It can be seen that it produces sufficient heat of autoxidation to maintain

By supplying easily biodegradable organic waste such as kitchen waste to the stirring tank 5, the amount of heat generated by biooxidation is greatly improved and the temperature raising effect is further improved. It is more preferable because the temperature can be raised. The kitchen waste may be crushed and then thrown in as the kitchen waste pulverized product 8 as it is. As a result, the solid matter such as the sludge 1 and the garbage waste 8 is effectively biologically oxidized and decomposed in a high temperature state, and most of SS is liquefied and the solid matter is almost disappeared.

The stirring tank 5 functions as an aerobic digestion tank, but the amount of the supply air 7 to the tank 5 is such that the inside of the tank 5 does not become an anaerobic condition. When a large amount of air 7 is supplied, the amount of air 7 supplied becomes excessive and the amount of exhaust gas increases, so the amount of heat taken out by the exhaust gas increases and the temperature raising effect decreases. In addition to the air 7, oxygen-enriched air or pure oxygen may be used as the aeration gas in order to reduce the amount of exhaust gas.
In order to reduce the heat radiation from the stirring tank 5 as much as possible, it is preferable to carry out heat insulation work.

The important point of the present invention is that the sludge concentration is 2%.
In the state of being raised above, a small amount of oxygen-containing gas 7 was added to the stirring tank 5.
Is aerated and the temperature in the tank is raised by 40 ° C. or more from the feed temperature by the heat of biooxidation. Even if excess sludge having a low sludge concentration is supplied to the stirring tank 5 of the present invention, the heat of biooxidation The generated amount is small, the effect of temperature rise is very small, and the effect of sludge decomposition and liquefaction decreases unless artificial heating is performed. In addition, it is important that the stirring tank 5 has multiple stages, and if the single stage is used, the sludge SS weight reduction effect decreases. The cause is
This is because in a single stage, there are many short paths of the supplied organic matter 1, and thermophilic bacteria that decompose sludge at a high temperature flow out of the system. It is sufficient that the number of stages is 3 to 5, and even if the number of stages is increased, the effect is not improved. In addition, it is important to circulate the sludge from the latter-stage stirring tank 5 to the former-stage stirring tank 5. That is, since the sludge SS decreases in the latter stage, the sludge SS concentration in the digester tank 5 in the former stage decreases, the viscosity decreases, the mechanical stirring power can be reduced, and a large amount of thermophilic bacteria proliferating in the latter stage. Since it is supplied to the first stage, the oxidation of the organic matter in the first-stage stirring tank 5 rapidly progresses, and the temperature rising rate increases.

Further, in the process of liquefying and mineralizing the sludge 1, phosphorus and nitrogen components contained in the sludge 1 are eluted to the liquid side as phosphate ions and ammonium ions, so that a stirring tank (aerobic digestion) is used. When Ca or Mg is added in the tank 5 or the effluent (sludge sludge) 5, calcium phosphate and magnesium ammonium phosphate precipitates, which can be solid-liquid separated to recover phosphorus as a valuable phosphorus resource as a fertilizer. . In FIG. 1, 4 is the separated water of the mechanical concentrator 2, and 10 is the circulating sludge.

Since the SS in the sludge flowing out from the stirring tank 5 is greatly reduced, a coagulant is added as it is to dehydrate it with a sludge dewatering machine (solid-liquid separation device) 11, a biological treatment facility for wastewater such as sewage. As shown in FIG. 2, sludge solubilization treatment is performed by a physicochemical solubilization device 14 such as ozone treatment, and the solubilization-treated sludge is returned as circulation sludge to the agitation tank 5 by a return pipe, and the solubilized sludge is returned. It may be biologically decomposed.

By applying the method of
Can disappear. That is, as shown in FIG. 2, sludge that has not been decomposed in the aeration and agitation tank 5 is drawn out, and the sludge solubilization treatment is performed by a physicochemical solubilization device 14 such as ultrasonic treatment, ozone oxidation, and hydrogen peroxide oxidation under high temperature conditions. By doing so, the cell wall of the sludge is destroyed and the biodegradability of the sludge is greatly improved. When the solubilized sludge 15 is circulated and returned to the aeration mechanical stirring tank 5 through the return pipe, the solubilized sludge undergoes biodegradation and SS is reduced. Therefore, the supplied organic sludge 1 and kitchen waste 7
Can be disassembled. In addition, in FIG. 2, 12 is a separation liquid of the solid-liquid separation means 11.

[0026]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

Example 1 A demonstration test of the present invention was conducted on excess activated sludge of sewage, based on the process shown in FIG. Table 1 shows the test conditions.

[0028]

[Table 1]

A one-month test was conducted under the above test conditions. As a result, the system became stable and became a steady state after 10 days. The tank temperature in the steady state is the first tank 71 ℃, the second tank 75
C., the third tank was 78.degree. C., and the tank temperature could be maintained at a high temperature only by the heat of biological oxidation. SS concentration in the first tank runoff sludge is 1800
0 mg / liter, SS concentration of 2nd tank runoff sludge is 9700
mg / liter, SS concentration in the final stage tank sludge is 480
0 mg / liter, SS concentration of supplied sludge 42000
88.6% of mg / liter was reduced.

Comparative Example 1 In Example 1, the operation was carried out under the same conditions except that the sludge circulation was stopped. As a result, the effect of increasing the temperature in the tank was slightly deteriorated, and the first tank was 65 ° C, the second tank was 68 ° C, and the third tank was 70 ° C. The SS concentration of the sludge discharged from the final stage tank was 8800 mg / liter, and the sludge SS reduction rate was 79%.

Comparative Example 2 The operation was carried out under the same conditions as in Example 1, except that the stirring tank was a single stage, the residence time was set to 3 days, and the sludge circulation was stopped. As a result, the SS of the sludge discharged from the stirring tank was 15600 mg.
/ Liter, and the SS reduction rate was 62.8%.

Comparative Example 3 As a result of operating under the same conditions as in Example 1 except that the excess activated sludge having a solid content of 1% was supplied, the temperature of the stirring tanks was 40 ° C. or less (38 to 40) in all three tanks. ℃). SS concentration of the final stage digester sludge is 29400 mg
/ Liter, and the sludge reduction rate was only 30%.

[0033]

According to the present invention, the following excellent effects can be obtained. (1) Utilizing only the biological heat of oxidation of organic matter, without using any artificial heating means, the temperature in the tank 40 from the feed temperature
Since it is possible to raise the temperature by ℃ or more, biooxidation can proceed at a high temperature of 50 ℃ or more, so the effect of reducing organic SS is very excellent, and the equipment cost for reducing sludge, This is a very useful technology for users who want to carry out sludge reduction treatment because operating costs are extremely low. (2) By increasing the number of stirring tanks and circulating the sludge from the latter stage to the former stage, thermophilic bacteria are less likely to flow out of the system, and the short path of the organic material to be supplied is small, so that the weight reduction effect is further enhanced.

(3) Since the amount of ventilated air is very small, the aeration power is small and the heat taken out by the exhaust gas is small, so that the temperature raising effect is further large. (4) The solubilization cost (proportional to the amount of SS to be treated) needs to be solubilized by physicochemical solubilization, such as ozone and ultrasonic irradiation, only for sludge that has undergone biooxidation at high temperatures and has significantly reduced SS The solubilization cost will increase). (5) Since sludge heated to a high temperature by biooxidation heating can be supplied to the physicochemical solubilization treatment step, the solubilization effect is large. The higher the temperature, the better the solubilizing effect of ultrasonic waves, ozone, etc.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an organic waste treatment apparatus of the present invention.

FIG. 2 is a block diagram showing a mode in which a physicochemical solubilizing means of the apparatus for treating organic waste of the present invention is additionally provided.

FIG. 3 is a block diagram showing an example of a conventional apparatus for solubilizing excess activated sludge.

[Explanation of symbols]

1 organic sludge 2 Mechanical concentrator 3 concentrated sludge 4 separated water 5 Aeration stirring tank 6 motor 7 Oxygen-containing gas 8 Garbage crushed product 9 Outflow (sludge outflow) 10 Circulation sludge 11 Solid-liquid separator 12 Separation liquid 13 Separation sludge 14 Physicochemical solubilizer 15 Solubilized sludge 20 dirty water 21 Activated sludge aeration tank 22 Activated sludge mixture 23 Settling tank 24 Treated water 25 Settled sludge 26 Return sludge 27 Extracted sludge 28 Cultured thermophile 29 Solubilization tank 30 heating source 31 Solubilized sludge

Continued front page    F-term (reference) 4D004 AA03 AC04 CA19 CB05 CB27                 4D059 AA03 BA03 BJ03 BK12 BK22                       CC01 DA03 DA08 DA43

Claims (3)

[Claims] 1. An organic waste such as organic sludge is supplied to a multi-stage aeration and stirring tank, and the temperature inside the tank is 40 than the supply temperature due to the heat of biological oxidation of the supplied organic material through an oxygen-containing gas.
A method for treating organic waste, which comprises raising the temperature to ℃ or more and circulating sludge from the latter stage tank to the former stage tank of the multi-stage aeration stirring tank. 2. An organic waste is introduced, an oxygen-containing gas supply means is provided, and a multi-stage aeration stirring tank for performing biological oxidation is provided, and sludge is circulated from a rear tank to a front tank of the multi-stage aeration stirring tank. An apparatus for treating organic waste, characterized by being provided with a pipe. 3. A solid-liquid separation tank provided at a subsequent stage of the multistage aeration and agitation tank, a physicochemical solubilizing means for the separated sludge, and a return pipe for the solubilized sludge to the multistage aeration and agitation tank. The apparatus for treating organic waste according to claim 2, wherein: