JP3212904B2 - Organic wastewater treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to wastewater containing organic sludge, for example, raw sludge or biological sludge discharged from sewage treatment processes such as sewage treatment plants and human waste treatment plants, food plants, chemical plants and the like. The present invention relates to a method for treating organic wastewater containing organic sludge discharged from a wastewater treatment process by biological digestion.

[0002]

2. Description of the Related Art Conventionally, organic wastewater of this type has been treated by aerobic or anaerobic microbial decomposition such as aerobic digestion and anaerobic methane fermentation. Bio-digestion of organic components of anaerobic sludge to convert organic matter into gas components such as carbon dioxide gas and methane gas, as well as surplus sludge consisting of microbial biomass (mainly microbial cells) generated by bio-digestion and untreated residual sludge The treated water is appropriately drained by separating the treated sludge into individual liquids in a sedimentation tank or the like, while the excess sludge is usually treated by ocean dumping or land reclamation.
However, dumping into the ocean will lead to environmental destruction, and in recent years when global environmental protection is being called for, it is almost banned. Also,
In land reclamation, it is becoming more difficult every year to secure landfill sites.

[0003] Therefore, the applicant of the present invention, when trying to treat excess sewage sludge, has both effects of oxidative decomposition reaction by microorganisms (thermophilic bacteria) contained in excess sewage sludge and physicochemical thermal denaturation by heat. At the same time, as a method of digesting sludge that efficiently and sufficiently generates sludge and biologically oxidatively decomposes sludge to greatly reduce the volume of sludge, `` excessive sludge containing organic matter or raw sludge is subjected to digestion treatment under high temperature conditions and medium temperature When performing biological digestion by alternately performing digestion under conditions, digestion under sludge is characterized by operating digestion under high temperature conditions in a temperature range of 60 to 70 ° C. Patent Application for “Method” (Japanese Unexamined Patent Publication No.
No. 95).

However, in the method described in the above-mentioned patent publication, the temperature of the high-temperature reaction vessel is 60 to 70 ° C., and the temperature is still quite high. The supply amount of oxygen flowing into the reaction tank becomes large. As a result, the exhaust gas discharged outside the reaction system removes the heat retained in the reaction tank, so that a large amount of heat source is required to maintain the reaction.

[0005] On the other hand, the amount of oxygen required in the process of sludge being biologically oxidatively decomposed is not constant as described below. That is, generally, the biological oxidative decomposition reaction of an organic substance in batch processing changes as schematically shown in FIG. The vertical axis of the figure shows the concentration of each substance,
The horizontal axis indicates elapsed time. As shown in FIG. 6, the amount of the soluble organic matter (symbol "") decreases along with the oxidative decomposition reaction by the microorganism, and the amount of the microorganisms (symbol "") increases correspondingly. At the same time, the amount of dissolved oxygen (DO, symbol "") in the water to be treated also decreases. Then, the amount of the "protease" (symbol ""), which is an enzyme produced by the microorganism, increases with a slight delay from the increase in the microorganism. With the production of the protease (), the amount of dissolved oxygen () decreases rapidly, and changes to almost “zero”. Eventually, when the organic matter () is depleted, the microorganism () and the protease () gradually decrease. In this case, if the amount of air flowing into the reaction tank is constant,
Dissolved oxygen () shows a tendency to increase contrary to the decrease of protease (). However, when the organic matter has disappeared, a large amount of oxygen is not required in the reaction tank, but only a small amount of oxygen necessary for the survival of the microorganisms. However, when a certain amount of air (oxygen) is introduced into the reaction tank, there is a disadvantage that a large amount of exhaust gas not contributing to the oxidative decomposition reaction brings out the heat retained in the reaction tank outside the system.

The present invention has been made in view of the above-mentioned problems of the prior art, and an object thereof is to control the amount of air supplied into a reaction system according to the progress of the reaction. Another object of the present invention is to provide a method for treating organic wastewater, which can promote the reaction economically.

[0007]

In order to achieve the above-mentioned object, the present invention provides a method for controlling the temperature of water to be treated in a reaction tank to a temperature at which both biological digestion and thermal denaturation can be promoted. By controlling the amount of air supplied to the reaction tank in accordance with the biological activity in the water, an appropriate amount of air (oxygen) can be supplied according to the progress of the reaction. The amount of heat left is reduced, and the reaction can proceed economically.

[0008]

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for biologically treating organic wastewater containing excess sludge containing organic matter or raw sludge, comprising the steps of: to a temperature capable of promoting both the heat denatured, the processing
Pro, an enzyme produced by microorganisms in water
The dissolved oxygen concentration is adjusted to correspond to the amount of the
When it is 0.5mg / L or less
Ventilate an air volume of 0.3 vvm or more, and the dissolved oxygen concentration
When the amount is 0.5 mg / L or more,
It is characterized in that less air is vented into the reaction tank .

According to the present invention configured as described above,
When biologically treating excess sludge containing organic matter or organic wastewater containing raw sludge, the temperature in the reaction tank is controlled by oxidative decomposition reaction by microorganisms ((thermophilic bacteria)) and physicochemical thermal transformation by heat. The sludge can be biologically oxidatively decomposed and reduced in volume by carrying out the reaction under a temperature at which both of the above-mentioned actions efficiently and sufficiently occur, that is, at a temperature in the range of 60 to 70 ° C.

In the process of oxidative decomposition of sludge by such microorganisms, while measuring the biological activity in the water to be treated, an appropriate amount of air (oxygen) is introduced into the reaction tank so as to correspond to the known biological activity. By doing so, the reaction can proceed economically. That is, it is preferable to increase the amount of air supplied to the reaction tank at a time when the production of the protease, which is an enzyme produced by the microorganism, is active compared to other times.

The structure of the reaction tank is not particularly limited, and any structure can be used as long as a diffuser is provided in the reaction tank. The reaction tank can be used in either a batch system or a continuous system. However, in the case of the continuous system, it is possible to use a plug flow, but the structure and the measurement of the biological activity of the plug flow reactor are more complicated than those of the batch reactor. In the plug flow method, if the complete plug flow is used, the same effect as that of the batch method can be obtained, but it is difficult to use a complete plug flow reaction tank. Therefore, the batch type is preferred.

[0012]

EXAMPLE As shown in FIG. 1, an organic wastewater 2 was treated in a reaction vessel 1 made of a cylindrical glass having an effective volume of 5 liters. The organic wastewater is a YP medium, that is, a yeast extract,
Peptone was 1 g / liter and 2 g / liter, respectively. Then, the organic wastewater in the reaction tank 1 is heated by the heater 3, and a thermophilic bacterium having protease activity in this embodiment as sludge decomposing activity is added.
To maintain the temperature of the organic wastewater 2 at 65 ° C. The amount of aeration into the reaction tank 1 was set such that the amount of air passing through the float flow meter 5 was 0.1 vvm, the amount of air passing through the float flow meter 6 was 0.2 vvm, and the amount of dissolved oxygen in the organic wastewater. The float type flow meter 6 was turned on and off by opening and closing the solenoid valve 8 so as to correspond to the dissolved oxygen amount measured by a DO (dissolved oxygen) meter 7 for measuring the flow rate. In addition, 1vvm
"5 liter air volume / 5 liter reaction tank volume / mi"
n. In the present example, the amount of dissolved oxygen in the reaction tank was set to 0.5 mg / liter for on / off control.

The amount of cells was measured by the absorbance at a wavelength of 600 nm (A600), and the protease activity was determined by measuring azocol (trade name, manufactured by Sigma), a substrate for non-specific protease assay, at pH 7.0. An equivalent amount of a sample is added to 0.7 ml of a solution (5 mg / ml) suspended in a phosphate buffer solution, and incubated at 70 ° C. for 30 minutes. After the reaction is completed, the absorbance at a wavelength of 520 nm is measured. ” A520).

FIG. 2 is a diagram showing another embodiment.
(A) is a method in which one of the two blowers 9 is turned on / off in accordance with the dissolved oxygen amount measured by the DO meter 7,
FIG. 2 (b) shows a method of controlling the rotation speed of the blower 9 according to the dissolved oxygen amount measured by the DO meter 7, and FIG. 2 (c) shows a method of controlling the rotational speed of the blower 9 according to the dissolved oxygen amount measured by the DO meter 7. 9 is a method for controlling the opening of the flow control valve 10 on the outlet side.

FIG. 3 is a diagram showing the effect of aeration on protease production, and the vertical axis represents absorbance. As shown in the figure, it can be seen that the production of protease is small at 0.1 vvm, and that a ventilation volume of about 0.3 vvm is required to promote the production of protease.

Therefore, as shown in FIG. 4, the reaction vessel 1 is filled with 0.1 μm only during a time period when the amount of produced protease (symbol “◇”) is large and the amount of dissolved oxygen (symbol “*”) is extremely small. The air was ventilated at 3 vvm, and at other times, the air was ventilated at 0.1 vvm. The symbol “■” in FIG.

FIG. 5 shows a conventional method, in which 0.3 vvm was aerated in the reaction tank 1 in all time zones. for that reason,
The amount of dissolved oxygen (symbol “*”) is extremely large even after the amount of protease (symbol “Δ”) production decreases. The symbol “■” in FIG. According to the method of the present invention shown in FIG. 4, the air flow rate is reduced by about 2 / compared to the conventional method shown in FIG.
3 could be reduced. The experimental results of actually treating sludge by this method are as described below. That is, in the sewage treatment system having the flow as shown in FIG. 7, the excess sludge 11 in the sewage treatment plant is adjusted to a concentration of 2%, and the float type flow meter 6 is controlled by the reaction tank 1 having the configuration as shown in FIG. When normally closed (comparative example, ventilation rate 0.1
vvm), when it is normally open (conventional method, air flow rate 0.
3vvm) and the solubilization rate of sludge when on / off control was performed according to the amount of dissolved oxygen (the method of the present invention). The results are shown in Table 1 below. According to the method of the present invention, the same solubilization rate could be obtained with about 2/3 of the gas flow rate of the conventional method.

[0018]

[Table 1]

As a method for measuring the biological activity, a method for detecting the amount of dissolved oxygen is preferably used because it is easy and accurate. In addition, the oxidation-reduction potential and CO ₂ in the exhaust gas discharged from the reaction tank are also used. It is also possible to use a method for measuring the concentration or the O ₂ concentration.

[0020]

As described above, according to the present invention, an amount of air suitable for the progress of the reaction in the reaction tank can be introduced into the reaction tank. Since the amount of supplied air can be greatly reduced as compared with the conventional method which has been introduced into the inside, the amount of heat dissipated from the reaction tank decreases, and the heat source capacity for maintaining the reaction temperature can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment of an apparatus for performing a method of the present invention.

FIGS. 2 (a) to 2 (c) are schematic structural views showing another embodiment of an apparatus for carrying out the method of the present invention.

FIG. 3 is a graph showing the effect of aeration on protease production.

FIG. 4 is a diagram showing the time course of the amount of protease, the amount of bacterial cells, and the amount of dissolved oxygen when the method of the present invention is performed.

FIG. 5 is a diagram showing the time course of the amount of protease, the amount of bacterial cells, and the amount of dissolved oxygen when a conventional method is performed.

FIG. 6 is a view schematically showing a state in which sludge is biologically oxidatively decomposed.

FIG. 7 is a flowchart illustrating an example of a sewage treatment system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Reaction tank 2 ... Organic waste water 3 ... Heater 5, 6 ... Float type flow meter 7 ... DO meter 9 ... Blower

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-9-85297 (JP, A) JP-A-5-237488 (JP, A) JP-A-63-294994 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) C02F 3/12

Claims (1)

(57) [Claims] 1. A method for biologically treating organic wastewater containing excess sludge or raw sludge containing organic matter,
The temperature of the water to be treated within the reaction vessel to a temperature capable of promoting both the biological digestion and heat denatured, the microorganisms in the water to be treated
Corresponds to the amount of protease that is produced
As described above, when the dissolved oxygen concentration is 0.5 mg / L or less
In the above, air volume of 0.3vvm or more is ventilated into the reaction tank
When the dissolved oxygen concentration is 0.5 mg / L or more,
In addition, air that is smaller than the air amount is ventilated into the reaction tank.
A method for treating organic wastewater.