JP2007275740A - Treatment method of sludge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a treatment method of sludge which enables the stable sterilization of excess sludge by effectively adding hypochlorous acid. <P>SOLUTION: The treatment method of excess sludge comprises killing microbes in the excess sludge by loading the excess sludge produced in a water treatment system with a hypochlorous acid solution when organic wastewater is biologically treated, then repeatedly recirculating it to the water treatment system, and biologically decomposing/treating it, wherein an oxidation-reduction potential in a sludge treatment tank is measured to control the loading of the hypochlorous acid solution in the sludge treatment tank from the measured oxidation-reduction potential. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention sterilizes sludge microorganisms with hypochlorous acid against surplus sludge generated in the water treatment system by biologically treating organic wastewater, and then again with activated sludge microorganisms in the water treatment system. The present invention relates to a method for treating sludge that is biologically decomposed and treated.

  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 again A sludge reduction technology has been developed in which activated sludge microorganisms in the water treatment system are decomposed and treated by returning them to the water treatment system.

By the way, the present applicant pays attention to a method using the oxidizing power and sterilizing power of hypochlorous acid as a method for sterilizing microorganisms in such excess sludge, and adds a hypochlorous acid solution to the excess sludge. Proposed method.
Hypochlorous acid exists in solution in the form of hypochlorous acid or hypochlorite ions, and is 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 to excess sludge, it is necessary to control the amount of addition, but the components of hypochlorous acid solution are decomposed during storage and discharged out of the system as chlorine gas. For example, the bactericidal effect may be weakened.
Therefore, when the addition is controlled quantitatively, only the sterilizing components required for sterilization are not added, and accordingly, there is a concern that sufficient sterilization treatment of sludge microorganisms cannot be achieved.

  Alternatively, when the hypochlorous acid solution is intermittently added at intervals of time, if the non-addition time is lengthened, the free chlorine concentration in the treatment tank is lowered, so that a sufficient sterilizing effect cannot be obtained. In contrast, if the time of addition is long, there is a problem that it is excessively added.

  In view of the problems of the conventional sludge treatment method, the present invention provides a sludge treatment method capable of stably sterilizing excess sludge by effectively adding a hypochlorous acid solution. The purpose is to provide.

  In order to achieve the above-mentioned object, the sludge treatment method of the present invention adds surplus sludge by adding a hypochlorous acid solution to surplus sludge generated in a water treatment system when biologically treating organic wastewater. In the method of surplus sludge that is returned to the water treatment system again and biologically decomposed / treated, the oxidation-reduction potential in the sludge treatment tank (hereinafter referred to as “ It is characterized by controlling the addition of the hypochlorous acid solution in the sludge treatment tank based on the measured ORP.

  In this case, the temporal change of the ORP in the sludge treatment tank is measured, and the addition of the hypochlorous acid solution can be started when the temporal change becomes substantially zero.

  Moreover, ORP in the adjustment tank provided in the front | former stage of the sludge treatment tank can be measured together with the ORP in the sludge treatment tank, and the addition of the hypochlorous acid solution can be controlled based on the difference therebetween.

  Moreover, an acid can be added in the adjustment tank provided in the front | former stage of a sludge treatment tank or a sludge treatment tank so that pH in a sludge treatment tank may be set to about 3-6.

  According to the sludge treatment method of the present invention, the ORP in the sludge treatment tank is measured, and the addition of the hypochlorous acid solution in the sludge treatment tank is controlled based on the measured ORP. Therefore, the sludge microorganisms can be sterilized efficiently by always appropriately controlling the amount of the added.

  In this case, the temporal change of the ORP in the sludge treatment tank is measured, and when the temporal change becomes almost zero, the addition of the hypochlorous acid solution is started, so that the free chlorine in the sludge treatment tank is almost reduced. It is possible to take control to start adding a new hypochlorous acid solution from the point when it disappears.

  Moreover, together with the ORP in the sludge treatment tank, the ORP in the adjustment tank provided in the previous stage of the sludge treatment tank is also measured, and the addition of the hypochlorous acid solution is controlled based on the difference between them. Regardless of the state of excess sludge, the amount of hypochlorous acid solution actually added can be grasped.

  Moreover, when measuring ORP in a sludge treatment tank by adding an acid in a sludge treatment tank or the adjustment tank provided in the front | former stage of a sludge treatment tank so that pH in a sludge treatment tank may be set to about 3-6. In addition, the addition of the hypochlorous acid solution can be controlled by adjusting the pH range so that the abundance ratio of hypochlorous acid is at least 90% or more and ORP at that time.

  Hereinafter, embodiments of the sludge treatment method of the present invention will be described with reference to the drawings.

In the control method in the sterilization treatment of sludge microorganisms, in a wastewater treatment facility that biologically treats organic wastewater using sludge microorganisms, by adding a hypochlorous acid solution to excess sludge generated in the water treatment system, The microorganisms in the sludge are sterilized and then returned to the water treatment system, so that the sterilized sludge is biologically decomposed and treated by the sludge microorganisms present in the water treatment system.
The sludge treatment method of the present invention measures the ORP in the sludge treatment tank and controls the amount of hypochlorous acid solution added in the sludge treatment tank in such a surplus sludge treatment system. .

The hypochlorous acid solution added to the sludge contains free chlorine (hypochlorous acid and hypochlorite ions), both of which are strong oxidizers. When the chloric acid solution is added, the amount of the oxidizing agent in the treatment tank increases, so that the ORP in the treatment tank rises.
In this case, an increase in ORP also means increasing the sterilizing ability against sludge microorganisms.
Therefore, by grasping in advance the concentration of free chlorine necessary for sterilization of sludge microorganisms and the increment of ORP in the sludge at that time, the required amount of hypochlorous acid solution added can be determined in the ORP in the sludge treatment tank. Can be controlled by.

On the other hand, the free chlorine in the hypochlorous acid solution added to the sludge is used for reaction with microorganisms in the sludge, that is, for sterilization of the microorganisms. Will decline.
Therefore, by observing the ORP in the treatment tank over time, it can be determined whether the free chlorine has completely disappeared or still remains.
Therefore, the temporal change of the ORP in the sludge treatment tank was measured, and when the change became almost zero, it was judged that the free chlorine in the treatment tank was almost gone, and a new hypochlorous acid solution was added. The first control can be taken.

Alternatively, not only the ORP in the sludge treatment tank but also the ORP in the sludge before being put into the treatment tank can be measured, and the addition of the hypochlorous acid solution can be controlled by the difference between them.
That is, the ORP in the excess sludge is measured in advance, and the increase (V1) of the ORP when the hypochlorous acid solution required for sterilization of the sludge microorganisms is measured in advance, before and after the sludge treatment tank. From the increase in ORP, it can be detected that a predetermined amount of hypochlorous acid solution has been added, and the solution injection pump can be stopped.
Similarly, the end of the sterilization treatment is detected by measuring the ORP when the sterilization treatment is finished and obtaining the difference (V2) from the ORP in the excess sludge before adding the hypochlorous acid solution. At the same time, the timing for newly adding the hypochlorous acid solution can be measured.
Thus, by controlling the addition of the solution according to the ORP difference before and after adding the hypochlorous acid solution, it is possible to grasp the amount of the solution actually added regardless of the state of the sludge before the addition. it can.

On the other hand, hypochlorous acid and hypochlorite ions in a hypochlorous acid solution not only have a great difference in oxidizing power, but also change their abundance ratio depending on the pH in the solution. In other words, hypochlorous acid has an oxidizing power several tens of times higher than that of hypochlorite ion, so that hypochlorous acid has higher sterilizing ability, and hypochlorite also has an ORP. Becomes higher.
Further, the existence ratio is 50% each when the pH is about 7.5, and the ratio of hypochlorous acid increases as the acidic region is reached, and becomes 100% near pH 5.
Therefore, when measuring the ORP in the sludge treatment tank, it is adjusted by adding acid so that the abundance ratio of hypochlorous acid is at least 90% or more, that is, 3 or more and 6 or less. The addition of hypochlorous acid solution can be controlled by ORP.
As described in claim 3 of the present invention, when the addition is controlled by ORP before and after adding the hypochlorous acid solution, the pH is increased by about 1 by adding the solution. The addition of acid can be controlled so that the pH of the solution is 3 or more and 5 or less.

FIG. 1 shows a first embodiment of the sludge treatment method of the present invention.
Excess sludge A generated in the water treatment system is charged into the sludge treatment tank 1 continuously or intermittently. A pH sensor 2 is installed in the treatment tank 1, and the pH in the treatment tank 1 is measured and sent to the pH controller 3 as a pH value signal B.
When operating the pH region in the sludge treatment tank 1 at 4.5 to 5.5, when the pH in the sludge treatment tank 1 is 5.5 or more of the upper limit value, the acid injection pump control command C is a pH controller. 3, the acid injection pump 4 is operated, and the acid D is added from the acid storage tank 5 to the sludge treatment tank 1.
The pH in the sludge treatment tank 1 is continuously measured. When the pH reaches the lower limit of 4.5 due to the addition of the acid D, an acid injection pump control command C is newly issued, and the acid injection pump 4 stops.

Similarly, an ORP sensor 6 is installed in the sludge treatment tank 1, the ORP in the treatment tank 1 is continuously measured, and the hypochlorous acid solution G is added. FIG. 2 shows the state of the ORP in the sludge treatment tank 1 and the control method of the hypochlorous acid solution addition at this time.
That is, the ORP in the sludge treatment tank 1 is continuously sent to the ORP control device 7 as the ORP value signal E, but the time when the control device 7 detects that the ORP has not changed is the set time τ. When the control device 7 reaches, a hypochlorous acid solution injection pump control command F is issued to operate the hypochlorous acid solution injection pump 8, and the hypochlorous acid solution G is transferred from the hypochlorous acid solution storage tank 9. Is injected into the sludge treatment tank 1.

  By adding the hypochlorous acid solution G, the concentration of free chlorine, that is, the oxidizing agent in the sludge treatment tank 1 increases, so that the ORP in the treatment tank 1 rises, but a predetermined set ORP value α Is reached, a hypochlorous acid solution injection pump control command F is newly issued from the ORP control device 7, and the hypochlorous acid solution injection pump 8 is stopped. Regarding the set ORP value α, the concentration of the hypochlorous acid solution necessary for sterilizing the microorganisms in the excess sludge A is obtained and set to the ORP value at this time.

The free chlorine in the hypochlorous acid solution G added to the sludge treatment tank 1 loses its oxidizing power by being used for sterilization of microorganisms in the excess sludge A, but with this, the ORP in the treatment tank 1 also It gradually decreases. Finally, when there is no free chlorine in the sludge treatment tank 1, there is no change in the ORP in the treatment tank 1, and when the period reaches the set time τ, the operation of the hypochlorous acid solution injection pump 8 starts again. To do.
In addition, the sludge which stayed in the sludge treatment tank 1 for a certain period of time and has been sterilized is discharged out of the tank as the treated sludge H and returned to the water treatment system again, but the activated sludge microorganisms retained in the treatment system Disassembled and processed.
In addition, since it is desirable that the inside of the sludge treatment tank 1 is sufficiently agitated and mixed, although not shown in FIG. 1 or FIG. 3 described later, gentle agitation is performed using a stirring blade or a diffuser tube. There is a need.

FIG. 3 shows a second embodiment of the sludge treatment method of the present invention.
Excess sludge A generated in the water treatment system flows into the adjustment tank 10 continuously or intermittently. In the adjustment tank 10, the operation of the acid injection pump 4 is controlled by the installed pH sensor 2 and pH controller 3. By doing so, the acid D is added so that the pH in the said adjustment tank 10 may be set to 3.5-4.5.
In addition, when the hypochlorous acid solution is added in the subsequent sludge treatment tank 1, the pH in the treatment tank 1 is 4.5 to 5. It was set to be about 5.

In the adjustment tank 10, the pH is adjusted, the ORP in the adjustment tank 10 is measured by the preceding ORP sensor 11 installed in the adjustment tank 10, and the preceding ORP value is sent to the ORP controller 7 as the initial ORP value β. Signal I is sent continuously.
The sludge whose pH has been adjusted flows out as adjusted sludge J and flows into the sludge treatment tank 1. An ORP sensor 6 is installed in the processing tank 1, and the ORP in the processing tank 1 is continuously measured and sent to the ORP controller 7 as an ORP value signal E.

Here, FIG. 4 shows an example of a control method for changing the ORP in the sludge treatment tank 1 and adding the hypochlorous acid solution.
In the sludge treatment tank 1, when the hypochlorous acid solution G is added to the adjusted sludge J, the ORP in the treatment tank 1 gradually increases compared to the initial ORP value β, and the increment is set in advance. When the upper limit value γ is reached, a hypochlorous acid solution injection pump control command F is generated, and the hypochlorous acid solution injection pump 8 stops.
At this time, the hypochlorous acid solution G required for the sterilization of the sludge microorganisms is injected into the sludge treatment tank 1, and the sterilization process of the sludge microorganisms proceeds.

As the sterilization process proceeds, the concentration of the added free chlorine decreases, so the ORP in the sludge treatment tank 1 decreases.
Thereafter, when the difference between the ORP in the treatment tank 1 and the initial ORP value β reaches the set lower limit value δ, a new hypochlorous acid solution injection pump control command F is generated from the ORP control device 7, and The chloric acid solution injection pump 8 is operated, and the hypochlorous acid solution G is injected from the hypochlorous acid solution storage tank 9. When the set lower limit value δ is detected, the sludge treatment tank 1 is in a state where the amount of free chlorine required for the sterilization treatment of sludge microorganisms is insufficient.

  By such control, the sludge microorganisms are sterilized in the sludge treatment tank 1, but the sludge that remains for a certain period of time and is sterilized is discharged out of the tank as treated sludge H and returned to the water treatment system again. Then, it is decomposed and treated by the activated sludge microorganisms held in the treatment system.

  As mentioned above, although the processing method of the sludge of the present invention was explained based on the example, the present invention is not limited to the composition described in the above-mentioned example, suitably combining the composition described in the example, The configuration can be changed as appropriate without departing from the spirit of the invention.

  Since the sludge treatment method of the present invention can stably carry out sterilization of excess sludge by effectively adding a hypochlorous acid solution, for example, use of efficient solubilization of excess sludge Can be suitably used.

It is explanatory drawing which shows 1st Example of the processing method of the sludge of this invention. It is a graph which shows an example of 1 point type | mold ORP control using the control method by the Example. It is explanatory drawing which shows 2nd Example of the processing method of the sludge of this invention. It is a graph which shows an example of 2 point | piece type ORP control using the control method by the Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sludge processing tank 2 pH sensor 3 pH control device 4 Acid injection pump 5 Acid storage tank 6 ORP sensor 7 ORP control device 8 Hypochlorous acid solution injection pump 9 Hypochlorous acid solution storage tank 10 Adjustment tank 11 Pre-stage ORP sensor A Excess sludge B pH value signal C Acid injection pump control command D Acid E ORP value signal F Hypochlorous acid solution injection pump control command G Hypochlorous acid solution H Treated sludge I Pre-stage ORP value signal J Adjusted sludge α Setting ORP value β Initial ORP value γ Setting upper limit value δ Setting lower limit value τ Setting time

Claims (4)

  When biologically treating organic wastewater, a hypochlorous acid solution is added to the excess sludge generated in the water treatment system to kill microorganisms in the excess sludge and then return to the water treatment system again. In the treatment method of surplus sludge that is biologically decomposed and treated, the oxidation-reduction potential in the sludge treatment tank is measured, and the hypochlorous acid solution is added to the sludge treatment tank based on the measured oxidation-reduction potential. A method of treating sludge characterized by controlling.   2. The sludge treatment according to claim 1, wherein the temporal change of the oxidation-reduction potential in the sludge treatment tank is measured, and the addition of the hypochlorous acid solution is started when the temporal change becomes substantially zero. Method.   In addition to the oxidation-reduction potential in the sludge treatment tank, the oxidation-reduction potential in the adjustment tank provided in the previous stage of the sludge treatment tank is also measured, and the addition of the hypochlorous acid solution is controlled based on the difference between them. The method for treating sludge according to claim 1 or 2.   The sludge according to claim 1, 2, or 3, wherein an acid is added in a sludge treatment tank or an adjustment tank provided in front of the sludge treatment tank so that the pH in the sludge treatment tank is about 3 to 6. Processing method.

Images