JP2010029842A - Method and apparatus for reducing sludge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for reducing sludge which safely and efficiently makes a part of the sludge generated in an aeration tank into a substrate by hypochlorous acid, repeatedly returns it to the aeration tank, and causes it to be digested. <P>SOLUTION: Dilute hydrochloric acid or dilute sulfuric acid is injected into and mixed with a part of the sludge removed out of a sedimentation tank (4), thereby turning it slightly acidic. Next, sodium hypochlorite aqueous solution is injected into and mixed with the sludge having a sludge concentration of 2,000 to 26,000 mg/L so as to set an effective chlorine concentration to 300 to 1,600 mg/l, thereby converting the sludge to a substrate. Sodium sulfite aqueous solution or sodium thiosulfate aqueous solution, as required, is injected into and mixed with the sludge as the substrate, and the sludge is returned to the aeration tank (3) and aeration treated, thereby cutting down the sludge. Thus, the sludge is reduced. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a sludge reduction method and a sludge reduction device, and more specifically, a part of sludge generated when wastewater containing organic matter is treated with activated sludge in an aeration tank is subjected to a weakly acidic second order. A method for reducing sludge that reacts with chlorous acid to form a substrate that can be decomposed by microorganisms, returns to the aeration tank again, and activates sludge, digests sludge and suppresses the generation of excess sludge, and The present invention relates to a sludge reduction device.

  The activated sludge method is known as one of the treatment methods for wastewater containing organic matter. As is well known in the art, this activated sludge method holds so-called floating organic sludge, that is, activated sludge inhabited by aerobic bacteria, protozoa, etc. This is a method in which drained wastewater is introduced and organic matter contained in the wastewater is preyed on by microorganisms such as aerobic bacteria and protozoa that live in activated sludge. The mixture of water and activated sludge treated in the aeration tank flows down to the settling tank, where it is separated into activated sludge and supernatant water, that is, treated water. Treated water is discharged into public water areas. The sedimented activated sludge is returned to the aeration tank as return sludge. According to this method, the organic matter in the wastewater is decomposed into water and carbon dioxide gas, so that there is an advantage that treated water containing almost no organic matter can be obtained.

  However, since microorganisms such as aerobic bacteria grow in large quantities in the aeration tank, if left as it is, the activated sludge increases too much, and the activated sludge and the treated water cannot be separated in the sedimentation tank. Therefore, surplus activated sludge generated by the aeration process is periodically extracted as surplus sludge from the settling tank. The extracted excess sludge is made into a dehydrated cake having a water content of about 85% by a dehydrating device, and is discarded after being incinerated. Alternatively, the dehydrated cake is directly landfilled in the landfill. By the way, incineration of a dehydrated cake requires a large amount of heavy oil, which is expensive. When landfilled, methane gas, a so-called global warming gas, is generated. Furthermore, there is a problem that the landfill itself is running short. Accordingly, there is a strong demand for sludge reduction in the treatment of wastewater containing organic matter.

JP-A-2005-305222 JP 2007-7546 A Japanese Patent No. 4183737

  Patent Document 1 describes a sludge reduction method in which ozone is added to the sludge extracted from the sedimentation tank and then returned to the aeration tank. When ozone is added to the sludge, the cell walls of microorganisms constituting the sludge are destroyed by oxidation and the cytoplasm inside the cells is eluted, or so-called sludge solubilization occurs in which aggregates of microorganisms, that is, flocs are subdivided. Since the solubilized sludge is easily engulfed by microorganisms such as bacteria, it can be digested and sludge can be reduced by returning it to the aeration tank and carrying out the activated sludge treatment. Patent Document 1 also describes a method of promoting solubilization of sludge by injecting sodium hypochlorite as an oxidizing agent, that is, sodium hypochlorite, in addition to ozone.

  Also by the sludge reduction method described in Patent Document 1, it is possible to solubilize the sludge and perform the activated sludge treatment again in the aeration tank, so that the effect of reducing the sludge is recognized. However, there are problems. For example, since a large amount of ozone is required to solubilize sludge, it is necessary to provide a particularly large ozone generator. Further, in order to generate a large amount of ozone, a large amount of electric power is required, and there is a problem that both initial cost and running cost are increased.

A technique for making sludge into a substrate by injecting weakly acidic hypochlorous acid into sludge is not well known as an auxiliary use of ozone, and is proposed in, for example, Patent Document 2. In addition, processing sludge and making it digestible in an aeration tank is generally expressed in terms of solubilization. However, according to the study by the present inventors, it was found that when sludge is reacted with hypochlorous acid, the sludge is changed to a component that can be digested in an aeration tank even if it is not in a solubilized state. did. Therefore, instead of the term “solubilization”, the term “substrateization”, which is a more realistic expression, is used in this specification. The volume reduction of sludge is expressed as sludge reduction, which is a stricter expression.
When the method described in Patent Document 2 is carried out, the equipment for injecting weakly acidic hypochlorous acid is advantageous because it is small and simple, so the initial cost is low, the drug is inexpensive, and the running cost is low. However, in the method described in Patent Document 2, the effective chlorine concentration of injected hypochlorous acid is not as high as 150 to 250 mg / L with respect to the sludge, and the sludge substrate is insufficient. There is also a drawback that sludge cannot be reduced sufficiently. If you simply inject a high concentration of hypochlorous acid to make sludge into a substrate enough, there is a risk that hypochlorous acid will be returned to the aeration tank in an unreacted state. This is because it is considered that a high concentration of hypochlorous acid cannot be injected because it has a serious effect. In Patent Document 3, a plurality of reaction tanks connected in series are provided, and a substrate that can sufficiently prevent hypochlorous acid from being consumed in such a reaction tank and reliably prevent the influence of the aeration tank on microorganisms. An apparatus is described. Since safety is ensured by such a substrate forming apparatus, it is possible to inject sludge into a substrate by injecting high concentration hypochlorous acid. That is, in the substrate conversion method described in Patent Document 3, in the uppermost tank of the reaction tank, the weakly acidic hypochlorous acid has a high effective chlorine concentration of 100 to 3000 mg / L with respect to sludge. Inject and stir. Next, the mixture is sent to the downstream tank and stirred, and further sent to the downstream tank and stirred for 5 minutes or more. If it does in this way, sludge can fully be made into a substrate and hypochlorous acid is also fully consumed. Therefore, sludge can be reduced safely. In addition, it has been conventionally considered that it is dangerous that hypochlorous acid remains and is returned to the aeration tank. However, when this method is performed, it is assumed that a small amount of hypochlorous acid is returned to the aeration tank. Has also been confirmed by experiments. For this reason, free chlorine with high bactericidal power is surely consumed when reacted for 5 minutes or more, and the returned hypochlorous acid is in a state of bound chlorine or in a state that has not been conventionally known in combination with sludge. It is presumed that the sterilizing power is sufficiently low.

  According to the sludge reduction method described in Patent Document 3, since weakly acidic hypochlorous acid is injected into the sludge so as to have a high concentration, the sludge can be sufficiently made into a substrate and can be sufficiently reduced. it can. In addition, hypochlorous acid reacts sufficiently with sludge so that it does not adversely affect microorganisms in the aeration tank. Therefore, it can be said that this is an excellent method for reducing sludge. However, there are also points to be improved, and specifically, there are points to be improved in a method for preparing weakly acidic hypochlorous acid or an injection method.

In the sludge reduction method described in Patent Document 3, weakly acidic hypochlorous acid is mixed with 12% or less sodium hypochlorite aqueous solution and dilute hydrochloric acid so that the effective chlorine concentration is 500 to 15000 mg / L. Prepared by diluting with water. Then, a weakly acidic hypochlorous acid aqueous solution having a pH of 4.0 or more and less than 7.0 is obtained. Actually, as the effective chlorine concentration increases, the chlorine odor becomes stronger even if the pH is about 6.5, and deodorizing and exhausting measures are required. Furthermore, there is a problem that the reactivity becomes high and the corrosion of members such as piping of the adjusting device for adjusting the aqueous solution becomes severe. An effective chlorine concentration that is practically easy to handle is an aqueous solution of 10,000 mg / L or less, preferably 5000 mg / L or less. When such a weakly acidic hypochlorous acid aqueous solution is poured into sludge in large quantities, hypochlorous acid is diluted by sludge and the concentration is lowered, and the oxidizing power is weakened. In addition, since a large amount of water is required for preparing the aqueous solution, the cost increases. Furthermore, since the total amount of sludge returned to the aeration tank increases, a load is applied to the aeration tank. Such a problem becomes conspicuous when treating a sludge having a relatively high concentration such that the sludge concentration exceeds 20000 mg / L. In anticipation of being diluted with sludge, there is also a method of preparing a hypochlorous acid aqueous solution having a low pH value and a high concentration in advance. However, when the effective chlorine concentration of hypochlorous acid is increased, the above-described problems occur, and when the effective chlorine concentration is 5000 mg / L or more, as described above, the oxidizing power is increased and an aqueous solution is prepared. Preparation equipment, equipment to be injected, pipelines, etc. will deteriorate at an early stage. Moreover, when pH becomes 4.0 or less, the serious safety problem that toxic chlorine gas is generated arises. Therefore, it is not practical to adopt such a method.
Another important issue is the danger and economics of the equipment. The equipment for preparing weakly acidic hypochlorous acid aqueous solution with an effective chlorine concentration exceeding 1000 mg / L has a complicated structure, and it is also necessary to provide additional facilities such as subtanks to adjust the conditions around the equipment. is there. Such a preparation device requires a high level of technology for maintenance, and it is dangerous to operate easily without neglecting maintenance. In particular, when the effective chlorine concentration exceeds 5000 mg / L, it is necessary to frequently inspect and replace parts in order to maintain safety. Not only is the initial cost high, but it also costs a lot of maintenance.

  The present invention has been made in view of the above-described problems. Specifically, it takes a large amount of water and does not increase the load on the aeration tank. It is possible to react hypochlorous acid with a high effective chlorine concentration with sludge at an optimum pH, and to reduce sludge sufficiently by using sludge as a substrate. In addition, there is no need to install a special hypochlorous acid aqueous solution preparation device that may cause equipment troubles. Therefore, the initial cost required for the device can be reduced, and maintenance and management become easier. An object of the present invention is to provide a sludge reduction method and a reduction device capable of drastically reducing costs.

  In order to achieve the above object, in the present invention, when sludge is used as a substrate, dilute hydrochloric acid or dilute sulfuric acid is injected into the sludge and stirred or mixed. Next, an aqueous sodium hypochlorite solution is injected into the sludge having a sludge concentration of 2000 to 26000 mg / L so that the effective chlorine concentration is 300 to 1600 mg / L. Alternatively, an aqueous sodium hypochlorite solution is injected into the sludge so that the effective chlorine concentration is 3 to 20% of the sludge concentration. And it is comprised so that sludge may be made into a substrate by stirring for 5 minutes or more. In addition, it is configured to inject sodium sulfite aqueous solution or sodium thiosulfate aqueous solution into sludge that has been converted into a substrate as necessary, and return it to the aeration tank. The activated sludge treatment is performed on the sludge that has been returned to the aeration tank. And digest. That is, sludge is reduced. In addition, such a sludge reduction device is provided with an acid mixing tube of a predetermined length into which dilute hydrochloric acid or dilute sulfuric acid is injected, or an acid mixing tank of a predetermined capacity, and downstream thereof. A stirring reaction tank into which a sodium acid aqueous solution is poured is provided, and the stirring reaction tank is provided with a stirring device. Then, if necessary, a residual chlorine decomposition tank is provided downstream of the stirring reaction tank, and a sodium sulfite aqueous solution or a sodium thiosulfate aqueous solution is injected into the sludge. Further, a pH meter is provided in the stirring reaction tank, and it is monitored whether the acid mixing tube or the acid mixing tank and the stirring reaction tank are normal.

That is, in order to achieve the above-mentioned object, the invention according to claim 1 extracts a part of sludge from sludge generated when wastewater containing organic matter is treated with activated sludge in an aeration tank. In the method of reducing the sludge by converting the substrate into a substrate by acid and returning the substrate to the aeration tank and digesting the sludge by activated sludge treatment, when converting the portion of sludge into a substrate, dilute hydrochloric acid or dilute It is configured to inject sulfuric acid and stir or mix, and then inject sodium hypochlorite aqueous solution and stir for 5 minutes or more to turn sludge into a substrate.
According to a second aspect of the present invention, in the method of the first aspect, the dilute hydrochloric acid or dilute sulfuric acid has a pH value of 3.5 to 6.5 when the part of sludge is used as a substrate. Configured to inject.
The invention according to claim 3 is the method according to claim 1 or 2, wherein the sodium hypochlorite aqueous solution has an effective chlorine concentration of 300 to 1600 mg / L relative to sludge having a sludge concentration of 2000 to 26000 mg / L. It is configured to inject to L.
According to a fourth aspect of the present invention, in the method according to the first or second aspect, the sodium hypochlorite aqueous solution is injected so as to have an effective chlorine concentration of 3 to 20% of a sludge concentration. Composed.
A fifth aspect of the present invention is the method according to any one of the first to fourth aspects, wherein a sodium sulfite aqueous solution or a sodium thiosulfate aqueous solution is injected into the sludge formed as a substrate and stirred, and aeration is performed. Configured to return to tank.

The invention according to claim 6 includes an aeration tank for treating activated water sludge containing organic matter, and a precipitation tank for separating water containing sludge treated in the aeration tank into supernatant water and sludge. A sludge reduction device provided in a treatment facility for wastewater containing organic matter, wherein the sludge reduction device extracts a part of the sludge separated in the settling tank, and dilute hydrochloric acid or dilute An acid mixing tube of a predetermined length in which sulfuric acid is injected and mixed, or an acid mixing tank of a predetermined capacity, and provided downstream of the acid mixing tube or the acid mixing tank, and sodium hypochlorite aqueous solution in the sludge The stirring reaction tank is provided with a predetermined stirring device, and the sludge into which the sodium hypochlorite aqueous solution has been injected is stirred for 5 minutes or more and returned to the aeration tank. Configured to be
A seventh aspect of the present invention is the apparatus of the sixth aspect, wherein a residual chlorine decomposition tank is provided downstream of the stirring reaction tank, and a sodium sulfite aqueous solution or sodium thiosulfate is added to sludge in the residual chlorine decomposition tank. An aqueous solution is injected and configured to be returned to the aeration tank.
The invention according to claim 8 is the apparatus according to claim 6 or 7, wherein the stirring reaction vessel is provided with a pH meter, and dilute hydrochloric acid or dilute sulfuric acid injected into the acid mixing tube or the acid mixing vessel. The injection amount is configured to be monitored so that the sludge in the stirring reaction tank has a pH value of 3.5 to 6.5.
According to a ninth aspect of the present invention, in the apparatus according to any one of the sixth to eighth aspects, the stirring reaction tank is composed of a plurality of two or more tanks connected in series. Composed.

As described above, according to the present invention, when sludge generated by processing activated sludge from wastewater containing organic substances in an aeration tank is extracted and used as a substrate, diluted hydrochloric acid or dilute sulfuric acid is injected into the sludge. And stirring or mixing, and then pouring an aqueous solution of sodium hypochlorite. That is, since it is configured to directly inject dilute hydrochloric acid or dilute sulfuric acid, and an aqueous sodium hypochlorite solution, there is no need to use a large amount of water without deteriorating the injecting equipment and pipes. And even if sludge is returned to an aeration tank, the load with respect to an aeration tank can be suppressed to the minimum. In addition, because it is configured to inject dilute hydrochloric acid or dilute sulfuric acid and sodium hypochlorite aqueous solution individually, it is possible to easily lower the pH value or increase the effective chlorine concentration of hypochlorous acid. become. The sodium hypochlorite aqueous solution is injected with dilute hydrochloric acid or dilute sulfuric acid and injected into the stirred and mixed sludge, so that an effect unique to the present invention is obtained that there is no possibility of generating chlorine gas. In other words, if the aqueous solution of sodium hypochlorite is first poured into the sludge and stirred, and then dilute hydrochloric acid or dilute sulfuric acid is injected, the pH value of the injected portion will drop instantaneously, so there is a risk of chlorine gas being generated. According to the method of the present invention, when the sodium hypochlorite aqueous solution is injected, the sludge has a uniform pH value, that is, since it does not have an extremely low pH value, no chlorine gas is generated. Therefore, it is safe. In this way, it is possible to lower the sludge pH value or increase the effective chlorine concentration of hypochlorous acid. Furthermore, since it is configured to stir for more than 5 minutes, Can be used as a substrate. Therefore, if it returns to an aeration tank and digests, it becomes possible to fully reduce sludge.
According to another invention, dilute hydrochloric acid or dilute sulfuric acid is injected so that the pH of the reacted sludge is 3.5 to 6.5. Can be reliably prevented from occurring. And according to the invention injecting the sodium hypochlorite aqueous solution into the sludge having a sludge concentration of 2000 to 26000 mg / L such that the effective chlorine concentration is 300 to 1600 mg / L, or the sodium hypochlorite aqueous solution Is injected at a dilution rate that results in an effective chlorine concentration of 3 to 20% of the sludge concentration, a sufficient amount of hypochlorous acid can be reacted with the sludge, and the sludge is a sufficient substrate It is guaranteed that In addition, according to the invention in which sodium sulfite aqueous solution or sodium thiosulfate aqueous solution is injected into the sludge that is made into a substrate and stirred and returned to the aeration tank, the residual chlorine in the sludge returned to the aeration tank is guaranteed to be sufficiently low. Therefore, the microorganisms in the aeration tank are not affected.
Then, a part of the sludge separated in the settling tank is extracted, and a dilute hydrochloric acid or dilute sulfuric acid is injected and mixed, and a predetermined length of the acid mixing pipe or a predetermined capacity of the acid mixing pipe and an acid mixing pipe or According to the invention in which the sludge reduction device is configured from the stirring reaction tank that is provided downstream of the acid mixing tank and into which the sodium hypochlorite aqueous solution is injected into the sludge, the apparatus is configured simply, It is possible to provide an apparatus that can reduce the cost significantly with few failures.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows typically the processing apparatus of the organic waste_water | drain which concerns on embodiment of this invention, The (a) is typically the processing equipment of the organic waste water provided with the sludge reduction apparatus which concerns on this embodiment. The side view shown to (1) is the side view which shows typically the sludge reduction apparatus which concerns on this Embodiment. It is a side view which shows typically the sludge reduction apparatus which concerns on this 2nd form.

  Embodiments of the present invention will be described below. As shown in FIG. 1A, the wastewater treatment facility 1 containing organic matter according to the present embodiment has a flow rate adjusting tank 2 in which the wastewater containing organic matter flows and the flow rate is adjusted. An aeration tank 3 in which wastewater containing organic matter is treated with activated sludge, a sedimentation tank 4 in which sludge containing treated water treated with activated sludge flows and separates into treated water and sludge of the supernatant water are provided in the sedimentation tank 4 The sludge reducing device 6 according to the present embodiment is configured such that a part of the sludge extracted from the settling tank 4 is used as a substrate.

  The flow rate adjusting tank 2 is a kind of buffer tank, and the wastewater containing organic matter supplied from the drainage supply pipe 8 stays in the flow rate adjusting tank 2 for a predetermined time and is uniformed and controlled to an appropriate flow rate. , And sent to the aeration tank 3. Such a flow control tank 2 may be comprised from a conventionally well-known raw | natural water pit. As is well known in the art, the aeration tank 3 has a large number of air ejection holes at the bottom. Pressurized air is supplied from a blower provided outside these air holes. Further, a stirring blade may be provided in the aeration tank 3 as necessary. A sedimentation tank 4 is connected to the discharge end of the aeration tank 3 configured in this way. In the aeration tank 3, microorganisms such as aerobic bacteria grow.

  The sedimentation tank 4 is configured as a sedimentation tank in which sludge is sedimented by gravity in the present embodiment, and has a funnel shape as a whole, and a sludge extraction pipe 5 for extracting the sedimentation sludge is connected to the lower end portion thereof. The sludge extraction pipe 5 returns sludge to the aeration tank via the return sludge pump 10.

  The sludge reduction apparatus 6 according to the embodiment of the present invention is composed of a plurality of tanks connected in series as shown in FIG. First, the sludge pump 9 enters the sludge measuring tank 11 in the middle of the return sludge pipe 12 connected to the settling tank 4 or from the sludge extraction pipe 5. Although the specific structure of the sludge measuring tank 11 is not shown in (a) of FIG. 1, it is comprised from the container which exhibits a box shape. The inside of the container is partitioned into a plurality of chambers by a plurality of partition plates provided with predetermined notches, and a triangular weir is formed in the partition plate on the most downstream side. Moreover, the sedimentation sludge extracted from the sedimentation tank 4 is supplied to the upstream chamber. The upstream chamber is provided with a gate that slides in the vertical direction, and the height position of the gate is adjusted to a set height. The sedimented sludge overflowing from this gate joins the sludge return pipe 12 and is returned to the aeration tank 3. In addition, the sludge from the triangular weir is sent to the sludge reducing device 6 through the sludge supply pipe 13. The sludge reduction device 6 includes an uppermost acid mixing tank 15 connected to the sludge supply pipe 13, a rapid stirring reaction tank 16 connected in order toward the downstream, a slow stirring reaction tank 17, and residual chlorine. It comprises a decomposition tank 18. The acid mixing tank 15 is provided with a dilute hydrochloric acid injection device including a dilute hydrochloric acid storage tank 20 and a dilute hydrochloric acid injection pump 21, and dilute hydrochloric acid is injected into the sludge in the acid mixing tank 15. The acid mixing tank 15 is provided with a stirring device 22 provided with a predetermined stirring blade. The dilute hydrochloric acid injection pump 21 and the stirring device 22 are connected to the control panel 24 by a predetermined signal line so that abnormalities of various pumps such as the sludge pump 9 and the stirring device are detected.

  The rapid stirring reaction tank 16 and the slow stirring reaction tank 17 are tanks into which a sodium hypochlorite aqueous solution is injected to make sludge into a substrate, and in the present embodiment, they are constituted by two independent tanks. The rapid stirring reaction tank 16 and the slow stirring reaction tank 17 may be composed of a single tank, or the slow stirring reaction tank is composed of two or more tanks, and is composed of a total of three or more tanks. Even if it is done, it can be implemented similarly. In the present embodiment, the rapid stirring reaction tank 16 is composed of a relatively small tank, and the slow stirring reaction tank 17 is composed of a large capacity tank. Such a rapid stirring reaction tank 16 is provided with a sodium hypochlorite injection device comprising a sodium hypochlorite storage tank 25 and a sodium hypochlorite injection pump 26, and hypochlorite is added to sludge in the tank. An aqueous sodium acid solution is injected. Since the rapid stirring reaction tank 16 is provided with the stirring device 28, the sludge into which the sodium hypochlorite aqueous solution has been injected is rapidly stirred and mixed and sent to the slow stirring reaction tank 17. ing. The slow stirring reaction tank 17 is similarly provided with a stirrer 29, and the sludge sent from the rapid stirring reaction tank 16 stays in the slow stirring reaction tank 17 for 5 minutes or more while being sufficiently stirred. It becomes a substrate. A pH meter 31 is provided in the vicinity of the discharge port of the slow stirring reaction tank 17, and a pH value measured by the pH meter 31 is transmitted to the control panel 24 by a predetermined signal line. Therefore, automatic monitoring is performed so that the pH value measured in the control panel 24 falls within a predetermined range, and when an abnormality is detected, the apparatus is completely stopped or the pumps are completely stopped. . In addition, it is possible to control the injection amount of dilute hydrochloric acid in the acid mixing tank 15 with the pH value, but in this case, it should be noted that the pH meter cannot be used to detect an abnormal situation. The sodium hypochlorite injection pump 26 and the agitators 28 and 29 are also connected to the control panel 24 by a predetermined signal line, and the control panel 24 stops the apparatus when the pump or the agitator is detected to be stopped. It is like that. Further, it is preferable to provide a device for notifying an administrator from the control panel when an abnormality is detected.

  The residual chlorine decomposition tank 18 is a tank that decomposes hypochlorous acid remaining in the sludge and adjusts it to a concentration that does not affect microorganisms in the aeration tank 3. The residual chlorine decomposition tank 18 is provided with a sodium sulfite injection device comprising a sodium sulfite storage tank 32 and a sodium sulfite injection pump 33, and an aqueous sodium sulfite solution is supplied to the sludge sent from the slow stirring reaction tank 17. Injected. It should be noted that the sodium sulfite aqueous solution is aerated even if an amount of about 2 to 5 times the amount necessary for the reaction with the remaining hypochlorous acid is injected, as is apparent from the experiment in Example 9. The microorganisms in the tank 3 are not affected. Further, as is clear from Example 10 and Example 11, there is no problem even if the amount of sodium sulfite aqueous solution injected is small. Accordingly, a predetermined amount of the sodium sulfite aqueous solution is injected. The residual chlorine decomposition tank 18 is provided with a stirring device 34 so that sludge is stirred. Such a sodium sulfite injection pump 33 and the stirring device 34 are connected to the control panel 24 by a predetermined signal line so that an abnormal signal is detected. The pipeline discharged from the residual chlorine decomposition tank 18 is connected to the sludge return pipe 12 so that the sludge treated in the residual chlorine decomposition tank 18 is returned to the aeration tank 3 and again processed by aerobic microorganisms. It has become.

According to the treatment equipment 1 for wastewater containing organic matter according to the present embodiment, the sludge reduction device 6 includes the control panel 24, and the amount of mud fed by the sludge pump 9, the amount of various chemicals injected, the operation of the stirrer, etc. Monitoring. Therefore, if any abnormality is detected, the sludge reduction device 6 is stopped in principle. The most important factor for sludge reduction equipment using hypochlorous acid is the abnormal operation, that is, generation of chlorine gas and large amount of residual chlorine. In the wastewater treatment facility 1 containing organic matter according to the present embodiment, there is substantially no possibility that chlorine gas is generated due to an abnormality such as a stop of the chemical injection pump or a stop of the stirrer. For example, safety and conditions thereof can be confirmed by experiments of Examples 3 to 5 and an agitation stop experiment of Example 6 described later. However, in order to further improve safety, it is important to provide a mechanism capable of detecting an abnormality in various apparatuses and to take safety measures such as stopping operation when an abnormality is detected.
If there is a large amount of residual chlorine, the activated sludge in the aeration tank 3 may die, and it will be impossible to treat the wastewater for a long time until the activity is restored. In the present embodiment, a metering pump is applied to each chemical injection pump indicated by reference numerals 22, 28, and 29. Such a metering pump is inexpensive and hardly breaks down, and only stops when an abnormality occurs, and an accident in which an excessive amount of medicine is injected is unlikely to occur. Further, as already described, abnormalities of the pump and the stirrer are monitored by the control panel 24, and there is no possibility that the operation is stopped at the time of abnormality and no problem is caused.
In addition to such a method of injecting a certain amount of medicine, automatic control for optimally controlling the amount of medicine to be injected by feedback control can be performed. For example, it is possible to detect the pH value and control the optimal injection amount of dilute hydrochloric acid, or to control the required injection amount of dilute hydrochloric acid / sodium hypochlorite from the sludge flow rate value measured by the sludge flowmeter. It is. However, when automatic control is performed, there is a risk that an abnormal amount of chemicals may be injected when an abnormality occurs in a measuring instrument such as a pH meter or a flow meter. It will be high. It is necessary to pay attention to safety.

Hereinafter, the operation of the wastewater treatment facility 1 including organic matter provided with the sludge reduction device 6 according to the present embodiment will be described. A description will be given from the state of steady operation. When the waste water containing organic matter flows into the flow rate adjustment tank 2, the waste water stays in the flow rate adjustment tank 2 for a predetermined time, and then is controlled to an appropriate flow rate and sent to the aeration tank 3. In the aeration tank 3, it is treated with activated sludge as is conventionally known. That is, the air supplied from the blower is ejected in the form of bubbles to supply oxygen to the microorganisms in the activated sludge, so that the organic matter contained in the wastewater is preyed on by the microorganisms and decomposed into water and carbon dioxide. Since microorganisms divide and multiply, the propagated microorganisms form flocs together with undegraded organic matter, etc., and become new sludge. The sludge generated in this way is sent to the next settling tank 4 together with the treated water.

  At the inlet of the settling tank 4, a flocculant is injected as necessary. Flock and the like aggregate and are separated into sludge and treated water due to the difference in specific gravity and gravity. By such separation, supernatant water, that is, treated water is obtained at a position above the settling tank 4. Since the treated water contains almost no organic matter, it is appropriately drained into rivers. On the other hand, the precipitated sludge is drawn out from a sludge extraction pipe 5 provided at the bottom of the settling tank 4 and returned to the aeration tank 3 by a return sludge pump 10. Further, a part thereof is sent to the sludge measuring tank 11 by the sludge pump 9. In addition, the sludge extracted from the sludge extraction pipe 5 is periodically sent to a predetermined tank as excess sludge, dehydrated, and then appropriately transported to a disposal site or the like. However, if the sludge is sufficiently reduced by the sludge reduction device 6, the excess sludge may not be discharged.

  Since the gate of the sludge measuring tank 11 is adjusted to a predetermined height, precipitated sludge addressed to a predetermined amount is discharged from the triangular weir and sent to the sludge reduction device 6 through the sludge supply pipe 13. On the other hand, the precipitated sludge overflowing the gate joins the sludge return pipe 12 and is returned to the aeration tank 3 as return sludge. Thereby, the organic substance density | concentration in the aeration tank 3 is maintained appropriately, and the activity of activated sludge does not fall.

  Sludge sent from the sludge supply pipe 13 is supplied to the acid mixing tank 15. In the acid mixing tank 15, a predetermined concentration, for example, 8.5% diluted hydrochloric acid is injected into the sludge from the diluted hydrochloric acid injection pump 21. The sludge is stirred and mixed by the stirring device 22, and the sludge is adjusted to an acidity of pH 2.5 to 7.0, preferably pH 3.5 to 6.5. In addition, although the pH value of sludge is measured with the pH meter 31 provided in the slow stirring reaction tank 17, when a sodium hypochlorite aqueous solution is inject | poured in the rapid stirring reaction tank 16, it is. Since it changes toward neutrality, the measured pH value is higher than the pH value of the sludge in the acid mixing tank 15. Therefore, in the control panel 24, such a change in pH value is taken into consideration, a dangerous value is set, and an abnormal value is detected.

The sludge into which dilute hydrochloric acid is injected in the acid mixing tank 15 is sent to the rapid stirring reaction tank 16. In the rapid stirring reaction tank 16, a predetermined concentration, for example, 12% sodium hypochlorite aqueous solution is injected into the sludge from the sodium hypochlorite injection pump 26. Examples of the implantation concentration are shown in Example 7 and Example 8. The sludge concentration of the sludge in the tank is, for example, 2000-26000 mg / L, and the injected sodium hypochlorite aqueous solution has an effective chlorine concentration of 300-1600 mg / L, preferably 400-1200 mg / L. Inject at dilution rate. Or it inject | pours at the dilution rate which becomes 3-20% of the value of sludge density | concentration, Preferably it is 3-16%, More preferably, it becomes 3-12% effective chlorine concentration. In the rapid stirring reaction tank 16, the sludge is stirred and mixed by the stirring device 22, and is allowed to stay for about 1 to 5 minutes. Thus, when sodium hypochlorite aqueous solution is inject | poured into the sludge adjusted to weak acidity, and it stirs and mixes, hypochlorous acid will be produced | generated like the following formula | equation.
HCl + NaOCl → HOCl + NaCl Formula (1)
Or it can also be considered that hypochlorite ion changes to hypochlorous acid under weak acidity as in the following formula.
H ⁺ + OCl ⁻ → HOCl Formula (2)
Since hypochlorous acid has a strong oxidizing power, the cell membranes of microorganisms constituting sludge and a part of the hardly decomposable organic matter are oxidized. That is, sludge is turned into a substrate. It is known that when hypochlorous acid becomes acidic at pH 4.0 or lower, it reacts as shown in the following formula to generate chlorine gas.
HCl + HOCl → Cl ₂ + H ₂ O Formula (3)
However, as revealed by experiments in Example 3, Example 4, etc., chlorine gas is not generated even under acidic conditions of pH 4.0 or lower. The reason for this is not clear, but in sludge containing organic matter, the reaction shown in the following formula preferentially progresses over the reaction shown in the above formula, so chlorine gas is less likely to be generated. I guess that.
HOCl + organic matter → oxidized organic matter + HCl Formula (4)
The sludge treated in the rapid stirring reaction tank 16 is sent to the slow stirring reaction tank 17.
Comparison of the effect of substrate formation by the method of the present invention and the conventional method of directly injecting a hypochlorous acid aqueous solution was performed in Example 1 and Example 2. According to Example 1, there was no difference when viewed from the reaction amount of chlorine. In the sludge reduction experiment of Example 2, the sludge reduction rate of the present invention was higher. The reason for the high reduction rate is not clear, but it can be said that it is at least not inferior.

  In the slow stirring reaction tank 17, sludge stays while being stirred by the stirring device 28 for 5 minutes or more, preferably 30 minutes or more. If it does so, sludge will be fully made into a substrate by hypochlorous acid. The pH value is detected by the pH meter 31. When an abnormal pH value is measured, the sludge pump 9, the dilute hydrochloric acid injection pump 21, the sodium hypochlorite injection pump 26, the sodium sulfite injection pump 33, etc. are stopped. The stirring devices 28, 29, and 34 may be stirred. Then, even when an abnormality occurs in the sludge reduction device 6, the aeration tank is not affected.

Sludge sufficiently converted into a substrate in the slow stirring reaction tank 17 is sent to the residual chlorine decomposition tank 18. In the residual chlorine decomposition tank 18, an aqueous solution of sodium sulfite (Na ₂ SO ₃ ) is injected into the sludge. Then, residual chlorine remaining unreacted in the sludge is decomposed. After being sufficiently stirred by the stirring device 34, the sludge that has been made into a substrate is returned to the aeration tank 3. When activated sludge treatment is performed in the aeration tank 3, the sludge that has become a substrate is digested by aerobic microorganisms. That is, sludge can be reduced.

  The sludge reduction device 6 according to the present embodiment can be variously modified. For example, the acid mixing tank 15 can also be comprised from the pipe | tube of predetermined length. FIG. 2 shows a sludge reduction apparatus 6 ′ according to the second embodiment in which an acid mixing pipe 36 is provided instead of the acid mixing tank 15. The same number is attached | subjected to the apparatus or member similar to the structural apparatus and structural member which concerns on previous embodiment, and it does not explain in detail. In the sludge reducing apparatus 6 ′ according to the second embodiment, the acid mixing pipe 36 is provided with a predetermined length. Therefore, when diluted hydrochloric acid is injected into the sludge upstream of the acid mixing pipe 36, Will be mixed easily. Such an acid mixing pipe 36 is easily mixed when it is composed of a plurality of bent pipes, and when the pipe diameter is large and the flow rate of sludge is high, the Reynolds number increases and becomes turbulent. Promoted.

In the sludge reduction apparatus 6 according to the present embodiment, there may be a case where it can be carried out without the residual chlorine decomposition tank 18. That is, depending on the amount of the sodium hypochlorite aqueous solution injected, most of the hypochlorous acid remaining in the sludge is consumed. In such a case, the residual chlorine decomposition tank 18 is unnecessary. become. In the present embodiment, the medicine to be injected can be modified. For example, although it has been described that dilute hydrochloric acid is injected into the acid mixing tank 15 or the acid mixing pipe 36, the pH value of sludge can be adjusted similarly even with dilute sulfuric acid. 35% hydrochloric acid can be used instead of dilute hydrochloric acid. Further, although it has been described that a sodium sulfite aqueous solution is injected in the residual chlorine decomposition tank 18, even if it is a sodium thiosulfate (Na ₂ S ₂ O ₃ ) aqueous solution, hypochlorite remaining in the sludge. The acid can be decomposed.

The effect of sludge substrate formation for the case of injecting an aqueous solution prepared by mixing dilute hydrochloric acid and sodium hypochlorite aqueous solution in advance, so-called biomaster solution, and for injecting dilute hydrochloric acid and sodium hypochlorite aqueous solution separately An experiment was conducted to confirm whether there was a difference between the two.
The biomaster solution is mixed with a predetermined amount of 8.5% dilute hydrochloric acid and a predetermined amount of 12% aqueous sodium hypochlorite solution and then diluted with water so that the pH is 6 and the effective chlorine concentration is 4000 mg / L. And prepared.
A predetermined amount of activated sludge having a sludge concentration of 15300 mg / L was placed in four containers A1, A2, A3, and A4. Next, bio-master liquids having an effective chlorine concentration of 600 mg / L and 1200 mg / L, respectively, were added to the sludge in containers A1 and A2 and stirred for 40 minutes. On the other hand, 8.5% dilute hydrochloric acid in an amount equivalent to the dilute hydrochloric acid injected into each of the containers A1 and A2 was injected into each of the sludges in the containers A3 and A4. Then, 12% sodium hypochlorite aqueous solution equivalent to sodium hypochlorite injected into each of container A1 and container A2 is injected into each of the sludge of container A3 and container A4 and stirred for 40 minutes. did.
The concentration of hypochlorous acid remaining in each of the containers A1, A2, A3, and A4 is quantified with an aqueous sodium sulfite solution using an indicator composed of potassium iodide, and the ratio of hypochlorous acid that has reacted with sludge. That is, when the reaction rate was examined, the reaction rate was 91 ± 2% in both the container A1 and the container A3, and the reaction rate was 79 ± 1% in both the container A2 and the container A4.
It was found that there was no difference in the reaction rate between the case where the biomaster liquid was injected into the sludge and the case where the diluted hydrochloric acid and the sodium hypochlorite aqueous solution were separately injected. That is, it turned out that there is no difference in the effect of making sludge into a substrate.

An experiment was conducted from the sewer to examine whether there is a difference in the sludge reduction rate when biomaster liquid is injected into sludge and when dilute hydrochloric acid and sodium hypochlorite aqueous solution are injected separately. It was carried out by a batch test that treated the raw water.
Three aeration tanks X1, X2, and X3 were prepared, the same amount of activated sludge was put therein, and the raw water collected from the sewer was put into 180 L each. After aeration for 21 hours in each of the aeration tanks X1, X2, and X3, the aeration was stopped and sludge was precipitated. After the precipitation, the supernatant water, that is, the treated water was discarded from the aeration tanks X1, X2, and X3, and all left only 50 L of sludge. 10 L of sludge is extracted from the aeration tank X2, taken into the container Y2, and the biomaster liquid having an effective chlorine concentration of 4000 mg / L prepared in Example 1 is added so that the effective chlorine concentration is 360 mg / L. After stirring for 30 minutes, the residual chlorine was decomposed with sodium sulfite and returned to the aeration tank X2. 10L of sludge is extracted from the aeration tank X3, taken into the container Y3, poured in the same amount of dilute hydrochloric acid as the biomaster liquid added to the container Y2, stirred, and then equivalent to the biomaster liquid added to the container Y2. An amount of aqueous sodium hypochlorite solution was injected. After stirring container Y3 for 30 minutes, residual chlorine was decomposed with sodium sulfite and returned to aeration tank X3. No particular treatment was performed on the aeration tank X1.
In such aeration tanks X1, X2, and X3, raw water collected from the sewer was put into 180 L, aerated for 30 minutes, precipitated again, and the supernatant water was drained so that only 50 L of sludge remained. Next, raw water collected from the sewer was put into the aeration tanks X1, X2, and X3, and aeration was performed for 21 hours.
Such an operation was repeated for 3 weeks, and after a habituation operation, the operation was further repeated for 3 weeks. Excess sludge generated in each of the aeration tanks X1, X2, and X3 was weighed and the sludge reduction rates of the aeration tanks X2 and X3 with respect to the aeration tank X1 were found to be 71% and 89%, respectively. In the case of the aeration tank X3 into which dilute hydrochloric acid and sodium hypochlorite aqueous solution were separately injected, the sludge reduction rate was higher than the aeration tank X2 in which dilute hydrochloric acid and sodium hypochlorite aqueous solution were mixed and injected as a biomaster solution. . The reason for the high reduction rate is unknown. However, when a sodium hypochlorite aqueous solution is injected after injecting and mixing dilute hydrochloric acid, the sodium hypochlorite aqueous solution is injected in a state in which the sludge has a relatively low pH value. Hypochlorous acid will act at a pH value closer to .5 to 3.0, and it is possible that the sludge becomes neutral in terms of charge, making hypochlorous acid more reactive. . Thus, although the cause of the high reduction rate is not certain, it is certain that the method of injecting dilute hydrochloric acid and sodium hypochlorite aqueous solution separately is at least as good as the method of injecting biomaster. In addition, the sludge can be easily adjusted to a pH value in the vicinity of the isoelectric point, and it is possible to inject a sodium hypochlorite aqueous solution after such adjustment.

An experiment was conducted to examine whether or not chlorine gas was generated when an aqueous sodium hypochlorite solution was injected into the sludge adjusted to acidity.
Sludge having a sludge concentration of 17100 mg / L was taken in a 500 mL beaker, and 0.9 mL of 8.5% dilute hydrochloric acid was injected to adjust the pH to 3.5 while stirring with a stirrer. Next, a 12% sodium hypochlorite aqueous solution was titrated to 1 mL to confirm whether or not chlorine gas was generated, and the pH value at that time was also measured. The experimental results are shown in the table.

  As shown in Table 1, it was found that chlorine gas was not generated even when sodium hypochlorite aqueous solution was injected into sludge having a pH of 3.5. In addition, when a dilute hydrochloric acid and sodium hypochlorite aqueous solution are made to react, hypochlorous acid will be produced | generated like Formula (1). Considering this reaction, the equivalent of 12% sodium hypochlorite aqueous solution with respect to 0.9 mL of 8.5% dilute hydrochloric acid is 1.2 mL. According to Table 1, even if this 3 mL of sodium hypochlorite aqueous solution exceeding 1.2 mL was titrated, the pH of the sludge was slightly acidic at 6.2. As described above, the pH value does not change to the alkali side even when the sodium hypochlorite aqueous solution is injected in excess of the equivalent amount, as shown in the formula (4), hydrochloric acid is generated. Because. Since the produced hydrochloric acid reacts with sodium hypochlorite again, hypochlorous acid is produced. In this way, even if hydrochloric acid is consumed in the reaction with sodium hypochlorite, if there is a reacting organic sludge, it is regenerated from hypochlorous acid, so the hydrochloric acid concentration in the sludge is stable and the sludge Will remain weakly acidic.

An experiment was conducted to examine whether chlorine gas is generated when a sodium hypochlorite aqueous solution is injected into a relatively high acid sludge.
Sludge having a sludge concentration of 17100 mg / L was taken in a 500 mL beaker, and 3.4 mL of 8.5% dilute hydrochloric acid was added to pH 2.5 while stirring with a stirrer. Next, a 12% sodium hypochlorite aqueous solution was titrated to 1 mL to confirm whether or not chlorine gas was generated, and the pH value at that time was also measured. The experimental results are shown in the table.

  Hypochlorous acid is known to change into harmful chlorine gas when the pH is 4.0 or less, particularly pH 3.0 or less, and such a relatively strong acidity is considered dangerous. Has been. However, this experiment confirmed that chlorine gas was not generated even under relatively strong acidity with a pH of 2.5 to 4.0. This is probably because hypochlorous acid is preferentially consumed for reaction with organic matter in the sludge rather than changing to chlorine gas.

  When the sludge to be used as a substrate is sufficiently supplied, that is, when organic substances are sufficiently contained, chlorine gas may be added depending on the injection amount when injecting sodium hypochlorite aqueous solution into sludge having a pH of 2.5. Consider whether it can occur. From the results in Table 2, it is clear that no problem occurs when the amount of sodium hypochlorite aqueous solution injected is small. Consider the case of large injection volume. The equivalent amount of sodium hypochlorite aqueous solution that reacts with the injected dilute hydrochloric acid is 5 mL, but even when such an amount is injected into the sludge, the pH is maintained at 4.2, and the chlorine gas is Does not occur. In addition, since the sodium hypochlorite aqueous solution is made alkaline and transported and stored, even if an equivalent amount or more of sodium hypochlorite aqueous solution is injected into the sludge, the pH value rises and chlorine gas is generated. Absent. That is, when the sludge to be used as a substrate is sufficiently supplied, if the sludge has a pH of 2.5 or more, there is no possibility of generating chlorine gas regardless of the amount of sodium hypochlorite injected.

  Next, a case where the sludge flowing into the rapid stirring reaction tank is reduced due to a sludge pump failure or the like, that is, a case where sufficient organic matter is not included will be examined. Even in this case, a small amount of hypochlorous acid produced when a small amount of aqueous sodium hypochlorite solution is injected is consumed by reacting with organic substances. At this time, as shown in Table 2, the pH value gradually increases as the sodium hypochlorite aqueous solution is injected. Further inject sodium hypochlorite aqueous solution. Then, since the organic substance which reacts with the hypochlorous acid produced | generated is lost, hypochlorous acid remains without being consumed. However, since hypochlorous acid does not react with organic substances, hydrochloric acid is not generated, and the pH value increases rapidly. That is, it changes to alkaline. Then, chlorine gas is not generated. When the diluted hydrochloric acid and the sodium hypochlorite aqueous solution are injected by the sludge reducing apparatus according to the present embodiment, chlorine gas will not be generated if the sludge has a pH of 2.5 or more.

The following experiment was conducted to confirm the safety when sodium hypochlorite aqueous solution was injected under stronger acidity.
Sludge having a sludge concentration of 17100 mg / L was taken in a 500 mL beaker, and 9.6 mL of 8.5% dilute hydrochloric acid was poured into the pH 2.0 while stirring with a stirrer. Next, a 12% sodium hypochlorite aqueous solution was titrated to 1 mL to confirm whether or not chlorine gas was generated, and the pH value at that time was also measured. The experimental results are shown in the table.

  Chlorine gas was not generated until the titration amount of the sodium hypochlorite aqueous solution was 4 mL, but chlorine gas was generated when titration was further performed. At the beginning of titration, hypochlorous acid was sufficiently consumed by reacting with organic matter in sludge, but when titrating more than 4 mL, there was almost no organic matter in sludge reacting, so chlorine gas was generated. It is considered a thing. When the pH of the sludge was 2.0, it was found that depending on the injection amount of the sodium hypochlorite aqueous solution, chlorine gas is generated, which is dangerous.

In the sludge reduction apparatus according to the present embodiment, it is necessary to evaluate the risk of whether or not chlorine gas is generated when the stirring apparatus fails. An experiment was conducted to inspect the presence or absence of chlorine gas by injecting sodium hypochlorite aqueous solution into the sludge without stirring.
The experiment was performed by changing some of the conditions performed in Example 3 and using the same conditions for the other conditions. The changed condition is to stop the stirrer during and after the injection of the aqueous sodium hypochlorite solution. As a result of the experiment, chlorine gas was not generated. In the sludge reduction apparatus according to the present embodiment, it was confirmed that there was no danger even if the stirring apparatus of the rapid stirring reaction tank failed.

The following experiment was conducted to investigate the amount of sodium hypochlorite aqueous solution suitable for making sludge into a substrate.
A predetermined amount of sludge having a sludge concentration of 25600 mg / L was taken in a beaker, and 8.5% dilute hydrochloric acid was added in an amount necessary for hypochlorous acid generation while stirring with a stirrer. This sludge was divided into containers B1, B2, B3 and B4. In such containers B1, B2, B3, and B4, 12% sodium hypochlorite aqueous solution was injected so that the effective chlorine concentrations after dilution were 400, 800, 1200, and 1600 mg / L, respectively. After the containers B1, B2, B3, and B4 were stirred with a stirrer for 30 minutes, the residual chlorine concentration was measured to check for the presence of free chlorine. The experimental results are shown in the table.

  According to the experiment, it was found that free chlorine was detected in the container B4, and when the effective chlorine concentration was 1600 mg / L, the amount of sludge was slightly excessive with respect to the sludge having a sludge concentration of 25600 mg / L. The hypochlorous acid that has not been consumed in this manner needs to be decomposed by a reducing agent such as sodium sulfite and returned to the aeration tank. For the sludge used in the experiment, it was found that sodium sulfite is unnecessary when the sodium hypochlorite aqueous solution is injected so that the effective chlorine concentration is 1200 mg / L or less.

Further experiments were conducted to examine the amount of sodium hypochlorite aqueous solution suitable for making sludge as a substrate.
A predetermined amount of sludge having a sludge concentration of 2000 mg / L was taken in a beaker, and 8.5% dilute hydrochloric acid was injected in an equimolar amount necessary for producing hypochlorous acid while stirring with a stirrer. This sludge was divided into containers C1, C2, C3, C4, and C5, and 12% sodium hypochlorite aqueous solution was injected into each. The effective chlorine concentration after dilution in each container C1 to C5 was injected so as to be 5%, 6%, 10%, 12%, and 20%, respectively, with respect to the sludge concentration. That is, the effective chlorine concentration after dilution was injected to be 100, 120, 200, 240, and 400 mg / L, respectively. The containers C1 to C5 were stirred with a stirrer for 30 minutes to examine the state of sludge as a substrate.
Comparing container C1, container C2, and container C3, it was found that sludge became a substrate as the amount of sodium hypochlorite injected increased. However, when the container C3 and the container C4 are compared, the state of sludge as a substrate has not changed much, and residual chlorine has increased in the container C4. In the container C5, free chlorine was detected and the sludge was completely bleached. In the case of this sludge, it has been found that the amount of sodium hypochlorite injected is appropriately converted into a substrate when injected at a dilution rate that results in an effective chlorine concentration of 12% or less of the sludge concentration. When sodium hypochlorite is injected further, hypochlorous acid remains, so it must be decomposed by a reducing agent such as sodium sulfite and returned to the aeration tank.

An experiment was conducted to examine the effect on the aeration tank when an excessive amount of sodium sulfite aqueous solution that decomposes hypochlorous acid was injected.
The experiment was performed under the same conditions as in Example 2 except that sodium sulfite was excessively injected. That is, the experiment was conducted under the same conditions except that excess sodium sulfite was injected into the sludge collected from the aeration tanks X2 and X3 and made into a substrate in the containers Y2 and Y3. Sodium sulfite was injected in containers Y2 and Y3 so that the residual chlorine concentration was measured and doubled as necessary to decompose the residual chlorine concentration. Such treatment was continued for 3 weeks, but no abnormality was found in the aeration tanks X2 and X3. Sedimentation was also better than the aeration tank X1.
Furthermore, an experiment was conducted in which the sludge collected from the aeration tanks X2 and X3 into the containers Y2 and Y3 was set to 7 L, and the hypochlorous acid injected into these sludges was reacted at an effective chlorine concentration of 290 mg / L. did. Sodium sulfite was added so as to be 3 to 5 times the injection amount of sodium sulfite necessary for the residual chlorine concentration measured in each of the containers Y2 and Y3. Then, after operating the aeration tank for 2 weeks, a part of these activated sludge was taken and observed with a microscope. The protozoa was observed by moving the preparation on which the sample was placed by 72 mm using an optical microscope with a magnification of 100 times. As a result, the type and number of protozoa were the largest in the aeration tank X3 and the second in the aeration tank X2. The untreated aeration tank X1 had the fewest protozoa. It was confirmed that the injection of 3-5 times the amount of sodium sulfite aqueous solution necessary for the decomposition of residual chlorine had no effect on the aerobic microorganisms in the sludge in the aeration tank.
From the above, after treating sludge with dilute hydrochloric acid and sodium hypochlorite, it was confirmed that there was no danger even if residual chlorine was decomposed with excess sodium sulfite, and even if excess sodium sulfite was injected. In the hypochlorous acid treatment, it was confirmed that there was no change in the sedimentation property of the sludge in the aeration tank and the phenomenon that the microbial activity increased.

When the sodium sulfite aqueous solution is not injected or the injection amount is small, sludge containing residual chlorine is returned to the aeration tank. In this case, an experiment was conducted to evaluate the effect of residual chlorine on the aeration tank.
Aeration tanks E1, E2, E3, and E4 were prepared, and 5 L of sludge having a sludge concentration of 5000 mg / L was placed in each tank. The following operation was performed once a day. After removing 1L of sludge from each aeration tank E1 to E4, putting it in containers F1 to F4, injecting dilute hydrochloric acid into containers F1 to F4, aqueous sodium hypochlorite solution so that the effective chlorine concentration becomes 400 mg / L And stirred for 30 minutes. When the residual chlorine concentration of each container F1-F4 was investigated, all were 135 mg / L. The sludge in the container F1 was returned to the aeration tank E1 as it was. About sludge of containers F2-F4, respectively, 30%, 60%, and 100% of the amount of sodium sulfite aqueous solution necessary for decomposing residual chlorine are injected and stirred, and then returned to aeration tanks E2-E4, respectively. It was. Thereafter, the aeration tanks E1 to E4 were aerated. Such an operation was repeated for 10 days.
Ten days later, the protozoa of the sludge in the aeration tanks E1, E2, E3, and E4 were observed, and the types of the protozoa were compared. As a result, protozoa could not be found in the aeration tank E1, and protozoa could be confirmed in the aeration tanks E2 to E4. In the aeration tank E2, the number of protozoa was slightly smaller than that in the aeration tank E3, but the number of protozoa in the aeration tank E3 and the aeration tank E4 was almost the same. As for the injection of the sodium sulfite aqueous solution, about 30% of the amount necessary for the decomposition of residual chlorine is sufficient, but it has been found that when it exceeds 60%, the aeration tank is not substantially affected.

A demonstration experiment was conducted at an organic wastewater treatment facility that is actually in operation. In a treatment facility with a wastewater amount of 1200 m3 / day, a sludge substrate conversion device was installed and operated for one year. The sludge substrate forming apparatus is provided downstream of the apparatus for preparing the biomaster liquid described in Example 1 and its injection apparatus, the stirring reaction tank for stirring the sludge into which the biomaster is injected, and the stirring reaction tank. It comprised from the sodium sulfite aqueous solution injection device etc. In the sludge substrate conversion device, a predetermined amount of sludge is drawn out from the sedimentation tank so that the sludge is converted into a substrate, and the sludge converted into a substrate is returned to the aeration tank. The operation was performed such that the residual chlorine in the sludge after the sodium sulfite aqueous solution was injected was 15 mg / L.
As a result of operation for one year, the sludge was greatly reduced compared to the conventional one, the sludge activity was increased, and the sedimentation was improved.

DESCRIPTION OF SYMBOLS 1 Processing equipment 3 Aeration tank 4 Settling tank 6 Sludge reduction apparatus 15 Acid mixing tank 16 Rapid stirring reaction tank 17 Slow stirring reaction tank 18 Residual chlorine decomposition tank 20 Dilute hydrochloric acid storage tank 21 Dilute hydrochloric acid injection pumps 22, 28, 29 Stirrer 24 control Panel 25 Sodium hypochlorite storage tank 26 Sodium hypochlorite injection pump 31 pH meter 32 Sodium sulfite storage tank 33 Sodium sulfite injection pump

Claims (9)

Of the sludge generated when wastewater containing organic matter is treated in the activated sludge in the aeration tank, a portion of the sludge is extracted and made into a substrate with hypochlorous acid, and the sludge made into a substrate is returned to the aeration tank and activated sludge treatment. In a method to digest and reduce sludge,
When the partial sludge is used as a substrate, dilute hydrochloric acid or dilute sulfuric acid is injected into the partial sludge and stirred or mixed, and then an aqueous sodium hypochlorite solution is injected and stirred for 5 minutes or more to remove the sludge. A method for reducing sludge, characterized by using a substrate. The method according to claim 1, wherein the dilute hydrochloric acid or dilute sulfuric acid is injected so that the pH value when the partial sludge is converted into a substrate is 3.5 to 6.5. Reduction method. 3. The method according to claim 1, wherein the aqueous sodium hypochlorite solution is injected such that an effective chlorine concentration is 300 to 1600 mg / L with respect to sludge having a sludge concentration of 2000 to 26000 mg / L. Characteristic sludge reduction method. The method according to claim 1 or 2, wherein the sodium hypochlorite aqueous solution is injected so as to have an effective chlorine concentration of 3 to 20% of the sludge concentration. The method according to any one of claims 1 to 4, wherein the sludge formed as a substrate is injected with a sodium sulfite aqueous solution or a sodium thiosulfate aqueous solution and stirred to return to the aeration tank. Reduction method. Treatment of wastewater containing organic matter, comprising an aeration tank for treating sludge containing organic matter with activated sludge, and a sedimentation tank for separating water containing sludge treated in the aeration tank into supernatant water and sludge A sludge reduction device provided in the facility,
The sludge reduction device is configured to extract a part of the sludge separated in the settling tank and inject a dilute hydrochloric acid or dilute sulfuric acid into a predetermined length of an acid mixing tube or a predetermined volume of acid mixed A tank,
It is provided downstream of the acid mixing pipe or the acid mixing tank, and comprises a stirred reaction tank in which a sodium hypochlorite aqueous solution is injected into sludge,
The stirring reaction tank is provided with a predetermined stirring device, and the sludge infused with the aqueous sodium hypochlorite solution is stirred for 5 minutes or more and returned to the aeration tank. Sludge reduction equipment to be used. The apparatus according to claim 6, wherein a residual chlorine decomposition tank is provided downstream of the stirring reaction tank, and a sodium sulfite aqueous solution or a sodium thiosulfate aqueous solution is injected into sludge in the residual chlorine decomposition tank, and the aeration tank A sludge reduction device characterized by being returned to the factory. The apparatus according to claim 6 or 7, wherein a pH meter is provided in the stirring reaction tank, and an injection amount of dilute hydrochloric acid or dilute sulfuric acid injected in the acid mixing tube or the acid mixing tank is within the stirring reaction tank. The sludge reduction apparatus is characterized in that the sludge is monitored so as to have a pH value of 3.5 to 6.5. The apparatus according to any one of claims 6 to 8, wherein the stirring reaction tank comprises a plurality of tanks of two or more tanks connected in series.

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