JP2007044612A - Apparatus for treating sludge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for treating sludge capable of sterilizing a microbe in excess sludge efficiently and stably by controlling the amount of hypochlorous acid and hypochlorite to be generated. <P>SOLUTION: The method for treating the excess sludge comprises biologically decomposing organic waste water by activated sludge held in a bioreactor, sterilizing the microbe in the sludge by loading the generated activated sludge with the solution of hypochlorous acid, circulating the sterilized sludge to the bioreactor, and decomposing it, wherein the concentration of free chlorine remaining in a sludge sterilization tank 1 is measured and in response to the measured concentration of free chlorine, the amount of the solution of hypochlorous acid to be loaded is controlled. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for treating surplus sludge generated by biologically treating organic wastewater, and in particular, after sterilizing by using a hypochlorous acid solution, it is biologically treated by activated sludge microorganisms in a water treatment system. The present invention relates to a method for treating sludge that is decomposed automatically.

  In recent years, surplus sludge generated in the water treatment system of a sewage treatment plant is treated using at least one of physical, chemical or biological means, that is, microorganisms in the surplus sludge are sterilized and water treatment is performed again. A sludge volume reduction technology has been developed in which activated sludge microorganisms in the water treatment system are decomposed and treated by returning them to the system.

The present applicant pays attention to the method of utilizing the oxidizing power and sterilizing power of hypochlorous acid solution as a method of sterilizing microorganisms in excess sludge, and hypochlorite such as sodium hypochlorite directly on the excess sludge. A method of adding a solution or a method of generating hypochlorous acid by adding a chloride salt to excess sludge and performing electrolytic treatment is proposed.
The main components of the hypochlorous acid solution added or generated are hypochlorous acid and hypochlorite ions, which are collectively called free chlorine. Free chlorine has a strong oxidizing power, and the oxidizing power can sterilize sludge microorganisms in excess sludge.

When adding hypochlorous acid solution or chloride salt to surplus sludge, a certain amount per surplus sludge volume or solid weight is added, but depending on the properties of the surplus sludge and the condition of the treatment equipment, The free chlorine concentration required for sterilization may not be reached. In this case, the required sludge sterilizing effect cannot be obtained, and therefore, a sufficient amount of excess sludge cannot be reduced.
In order to avoid these problems, it may be possible to add an excessive amount of hypochlorous acid solution or chloride salt. In this case, however, the operating cost increases and the concentration of chloride returned to the water treatment system. May increase and adversely affect subsequent processes and processing apparatuses.

  In view of the problems of the above-described conventional sludge treatment methods, the present invention controls the amount of hypochlorous acid and hypochlorite ions that are generated to efficiently and stably sterilize microorganisms in excess sludge. It aims at providing the processing method of sludge which can be done.

  In order to achieve the above object, the sludge treatment method according to the first aspect of the present invention biologically decomposes organic wastewater with activated sludge retained in a biological reaction tank, and a hypochlorous acid solution is added to the generated surplus sludge. In the method for treating surplus sludge in which microorganisms in the sludge are sterilized by adding, and the sterilized sludge is returned to the biological reaction tank and decomposed, the concentration of free chlorine remaining in the sludge sterilization tank is measured, and the measurement The amount of the hypochlorous acid solution to be added is controlled according to the concentration of free chlorine.

  In this case, as a hypochlorous acid solution, a sodium hypochlorite solution, calcium hypochlorite or liquid chlorine and other chlorine-based disinfectants dissolved in water can be used.

  On the other hand, in order to achieve the same purpose, the sludge treatment method according to the second aspect of the present invention biologically decomposes organic wastewater with activated sludge retained in a biological reaction tank, and also converts chloride salt into the generated surplus sludge. Addition and electrolytic treatment to generate hypochlorous acid to sterilize microorganisms in the sludge, and return the sterilized sludge to the biological reaction tank for decomposition treatment. It is characterized in that the concentration of free chlorine remaining in the tank is measured, and the amount of chloride salt to be added or the electrolytic current value is controlled according to the measured free chlorine concentration.

  In this case, the sludge in the sludge sterilization tank is solid-liquid separated by physical means, and the free chlorine concentration in the obtained supernatant water can be measured.

  In addition, solid-liquid separation can be performed using a microfiltration membrane.

  Moreover, a hypochlorous acid solution can be utilized as a backwashing liquid for the microfiltration membrane.

In any of the sludge treatment methods of the first and second inventions, surplus sludge and a hypochlorous acid solution composed of hypochlorous acid or hypochlorite ions are brought into contact with each other. Chloric acid and hypochlorite ions are called free chlorine.
These free chlorines act as a strong oxidant, and by utilizing the oxidizing power, cell walls and cell membranes constituting sludge microorganisms can be damaged and the microorganisms can be inactivated.
On the other hand, active sludge microorganisms release degrading enzymes outside the body to reduce the molecular weight of organic substances outside the body, making them easier to incorporate into cells, and releasing substances that protect themselves from degrading enzymes.
However, sludge microorganisms that have been inactivated by free chlorine cannot release substances that protect themselves, and are therefore decomposed by decomposing enzymes released by activated sludge retained in the biological reaction tank. Therefore, it is possible to reduce the amount of surplus sludge that is finally discharged from the water treatment system.
Here, in order to sterilize or inactivate sludge microorganisms in excess sludge, it is necessary to contact with free chlorine at an appropriate concentration for a certain period of time. However, chlorine in free chlorine volatilizes as chlorine gas during storage, or when the concentration of soluble organic matter in excess sludge is high, it reacts immediately with the organic matter and is used for sterilization of sludge microorganisms. The amount that is played may be reduced.
In addition, when hypochlorous acid is generated by adding chloride salt to excess sludge and performing electrolytic treatment, chlorine gas is also generated by electrolytic treatment, but the amount of chlorine gas generated increases depending on the operating conditions. Sufficient hypochlorous acid is not generated, and the sludge microorganisms in the excess sludge may not be sufficiently sterilized.
Therefore, in the sludge treatment methods of the first and second inventions, in a sludge sterilization tank such as sludge to which a hypochlorous acid solution has been added or sludge to which chloride salt has been added and subjected to electrolytic treatment in the sludge sterilization tank. By measuring the amount of free chlorine and adjusting the amount of hypochlorous acid solution added, the amount of chloride salt added or the electrolysis current value so as to reach the free chlorine concentration necessary for sterilization of sludge microorganisms, Microorganisms in excess sludge can be sterilized efficiently and stably.

  In this case, free chlorine required for sterilization can be obtained by using a sodium hypochlorite solution, a calcium hypochlorite solution such as liquid hypochlorite dissolved in water as a hypochlorous acid solution. Can be easily obtained.

  In addition, when measuring the free chlorine concentration in the treated sludge, it cannot be accurately measured if the solid-liquid concentration is high, so measure the free chlorine concentration in the resulting supernatant water by solid-liquid separation. be able to.

In addition, by performing solid-liquid separation using a microfiltration membrane, it is possible to obtain a supernatant water that is microfiltered and almost free of solid matter, and thus, an accurate free chlorine concentration can be measured.
In addition, for the concentration measurement with a free chlorine concentration meter, it is only necessary to obtain a very small amount of supernatant water, the microfiltration membrane unit is small, and a short operation time is sufficient.

  In addition, when obtaining supernatant water by microfiltration, air bubbles are sent from the bottom of the microfiltration membrane unit to eliminate clogging of the membrane surface, and the membrane surface is washed. A chloric acid solution can be used as a backwash solution to decompose organic substances that cause clogging of the microfiltration membrane.

In the sludge treatment method according to the present invention, the microorganisms in the sludge are sterilized by adding a hypochlorous acid solution to the excess sludge or by adding a chloride salt to the excess sludge and subjecting it to electrolytic treatment. An experiment was conducted to grasp the effect.
For example, a sodium hypochlorite solution was added to surplus sludge having a solid concentration of 10 g / liter discharged from a sewage treatment facility, and the number of microorganisms after stirring for 30 minutes was measured.
FIG. 2 shows the relationship between the number of cells and the number of cells before addition to determine the bactericidal rate and the amount of free chlorine in the added sodium hypochlorite solution. As shown in FIG. 2, the sterilization rate increases rapidly as the amount of added free chlorine increases, but after the added amount per liter of sludge exceeds 80% at 150 milligrams, the sterilization rate increases. The rate was low, reaching about 90% at about 250 milligrams.

In the sludge treatment method according to the present invention, the sterilized sludge is returned to the bioreactor of the water treatment system, but the sludge that has not been sterilized continues to survive in the bioreactor. It will increase the concentration.
On the other hand, in the water treatment system, it is necessary to keep the microbial concentration in the biological reaction tank constant, but in the system that does not discharge any sludge from the sewage treatment plant as in the present invention, the amount of sludge to be sterilized is increased. It is possible to achieve that purpose.
Accordingly, when there is a large amount of sludge that has not been sterilized, the amount to be treated increases, which increases the system size, increases the operation time, increases the amount of added chemicals, and so on, resulting in an increase in cost.
Accordingly, in the sludge treatment method according to the present invention, the amount of free chlorine per liter of sludge is added at least about 150 to 250 milligrams in consideration of the efficient amount of sodium hypochlorite solution added. Can be reached.

Based on the above experimental results, in the sludge treatment method according to the present invention, the amount of sodium hypochlorite solution added so that the free chlorine concentration in the tank for sterilizing sludge is 150 mg / liter to 250 mg / liter. To control.
In addition, since the relationship between the free chlorine concentration and the sterilization rate may change depending on the resistance of the target excess sludge to free chlorine, the sterilization rate in the tank is 80% or more, preferably 90%. It is also possible to control the concentration range so as to be about%.

In the present invention, the pump for injecting the sodium hypochlorite solution is controlled so that the free chlorine concentration is 150 mg / liter to 250 mg / liter. FIG. 3 shows an example of the control method. is there.
Since the free chlorine concentration is low at the start of the treatment, the sodium hypochlorite solution is continuously injected, but when the value indicated by the free chlorine concentration meter exceeds 200 milligrams / liter, the injection pump is stopped. Thereafter, the free chlorine concentration slowly rises due to the response of the free chlorine concentration meter, etc., but after reaching about 250 milligrams / liter, it gradually falls because it is used for sterilization of sludge.
Thereafter, when the free chlorine concentration decreases to 200 milligram / liter again, the operation of the hypochlorous acid solution injection pump is restarted. After that, it starts to rise again.
In this way, by controlling the free chlorine concentration in the sludge sterilization tank that sterilizes sludge and the operation of the hypochlorous acid solution injection pump, the free chlorine concentration in the tank is kept within a predetermined range, and efficient Can be processed.

Next, application of the wastewater treatment method and treatment apparatus according to the present invention to wastewater treatment will be described with reference to the drawings.
In FIG. 1, one Example of the processing method of the sludge of this invention is shown.
Excess sludge A generated in the water treatment system is introduced into the sludge sterilization tank 1 and provided in the sludge sterilization tank 1 and the hypochlorous acid solution B added by the chemical pump 3 from the hypochlorous acid solution storage tank 2. Stirring is performed by the agitator 4.
As the hypochlorous acid solution, a sodium hypochlorite solution is appropriate. However, it is also possible to use solid chlorine such as calcium hypochlorite and liquid chlorine dissolved in water. is there.
The sludge microorganisms in the excess sludge A stay in the sludge sterilization tank 1 for a certain period of time, and are stirred by the oxidizing power of free chlorine such as hypochlorous acid and hypochlorite ions in the hypochlorous acid solution. It is sterilized, flows out of the tank as treated sludge C, and is returned to the water treatment system.

On the other hand, the sludge sterilization tank 1 is provided with a microfiltration membrane unit 5 and a cleaning air pipe 6.
A suction pump 7 provided outside the tank is connected to the microfiltration membrane unit 5 and operates at regular intervals to obtain a filtrate D. Air E is guided to the cleaning air pipe 6 for a short time before and after the suction pump 7 is operated to clean the surface of the membrane of the microfiltration membrane unit 5.
In this embodiment, the stirrer 4 is installed in the sludge sterilization tank 1 and used for stirring in the tank. However, the cleaning air pipe 6 is installed on the entire surface to be used for stirring in the tank. Is also possible.

The filtrate D that has passed through the microfiltration membrane unit 5 is guided to the filtrate tank 8, and first flows into the measurement chamber 10 that is provided in the tank and in which the free chlorine concentration meter 9 is installed. In the measurement chamber 10, the free chlorine concentration in the sludge sterilization tank 1 is grasped by measuring the free chlorine concentration in the filtrate D.
The measured numerical value is sent to the control device 11 as an electric signal, and the operation of the chemical pump 3 is managed by a method as shown in FIG. 3 according to a preset concentration range. That is, when the concentration of the sludge sterilization tank 1 is lower than the set value, the chemical pump 3 is operated, and when the concentration is higher than the set value, the pump is stopped.

The filtrate D overflowed from the measurement chamber 10 is stored in the filtrate tank 8, but when a certain amount is retained, it is sent to the microfiltration membrane unit 5 as the backwash solution F, and the clogging of the filtration membrane is washed away. In addition, when sending back washing | cleaning liquid F, you may provide a pump separately, but the use can also be made by making suction pump 7 reversely rotate.
In addition, when the hypochlorous acid solution B is added, it is directly put into the sludge sterilization tank 1 by the chemical pump 3, but once put into the filtrate tank 8 and diluted with tap water G such as tap water, the backwash solution It is also possible to put it into the sludge sterilization tank 1 as F.
In this case, since the amount of water for back-cleaning the microfiltration membrane unit 5 increases, sufficient cleaning can be performed, and the performance of the unit can be maintained over a long period of time.

As described above, in the above examples, the hypochlorous acid solution is added to the excess sludge. In addition to this method, hypochlorite and hypochlorous acid are added by adding a chloride salt to the excess sludge and performing electrolytic treatment. It is also effective for a method in which chlorate ions are generated, microorganisms in the sludge are sterilized by the generated hypochlorous acid solution, and then returned to the water treatment system.
In this case, while measuring the concentration of free chlorine remaining in the sludge sterilization tank, by controlling the amount of chloride salt to be added or by controlling the electrolysis current value, the same effect as in the above embodiment can be exhibited. Is possible.

  Although the sludge treatment method of the present invention has been described based on a plurality of examples, the present invention is not limited to the configuration described in the above examples, and the configuration described in each example is appropriately combined, etc. The configuration can be changed as appropriate without departing from the spirit of the invention.

It is a flowchart which shows one Example of the processing method of the sludge of this invention. It is a graph which shows the relationship between free chlorine concentration and the disinfection rate of sludge. It is a graph which shows the relationship between free chlorine concentration and control of a chemical pump.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sludge sterilization tank 2 Hypochlorous acid solution storage tank 3 Chemical liquid pump 4 Stirrer 5 Microfiltration membrane unit 6 Air pipe for washing 7 Suction pump 8 Filtrate tank 9 Free chlorine concentration meter 10 Measurement room 11 Control device A Excess sludge B Chloric acid solution C Treated sludge D Filtrate E Air F Backwash G Water

Claims (6)

  The organic wastewater is biologically decomposed by activated sludge retained in the biological reaction tank, and the microorganisms in the sludge are sterilized by adding a hypochlorous acid solution to the generated surplus sludge. In the treatment method of surplus sludge that is returned to the biological reaction tank and decomposed, the concentration of free chlorine remaining in the sludge sterilization tank is measured, and the amount of hypochlorous acid solution to be added according to the measured free chlorine concentration A method for treating sludge, characterized by controlling the temperature.   The sludge treatment according to claim 1, wherein a sodium hypochlorite solution, calcium hypochlorite or liquid chlorine is dissolved in water. Method.   In addition to biologically decomposing organic wastewater using activated sludge retained in a biological reaction tank, adding chloride salts to the generated surplus sludge and applying electrolytic treatment to generate hypochlorous acid in the sludge In the surplus sludge treatment method in which the microorganisms are sterilized and the sterilized sludge is returned to the biological reaction tank and decomposed, the concentration of free chlorine remaining in the sludge sterilization tank is measured, and the measured free chlorine concentration is And the amount of chloride salt to be added or the electrolysis current value is controlled.   The sludge treatment method according to claim 1, 2, or 3, wherein the sludge in the sludge sterilization tank is solid-liquid separated by physical means and the free chlorine concentration in the obtained supernatant water is measured.   The sludge treatment method according to claim 4, wherein solid-liquid separation is performed using a microfiltration membrane.   6. The method for treating sludge according to claim 5, wherein a hypochlorous acid solution is used as a backwash liquid for the microfiltration membrane.

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