JP4584173B2 - Method for electrolytic treatment of excess sludge - Google Patents

Description

  The present invention relates to a system for reducing surplus sludge generated by microbial treatment of organic wastewater. More specifically, surplus sludge that has been disposed so far is electrolyzed in an acidic region in an atmosphere containing chloride (“electricity” The present invention relates to a system in which microorganisms are killed by simplifying “decomposition” (represented by “electrolysis”), then returned to the aeration tank again, and excess sludge to be discarded can be efficiently reduced by these treatments.

  In microbial treatment of organic sewage, the microorganisms digest the soluble organic matter present in the sewage while causing microbial growth. The sludge containing the grown microorganisms needs to be discharged as so-called surplus sludge. This surplus sludge is either landfilled or decommissioned after being dehydrated, but the surplus sludge is hardly dehydrated and therefore usually has a water content of 70 to 80% by mass even after dehydration. It is. Therefore, even if this is landfilled as it is, it will be transported and landfilled with a solid content of about 20 to 30% by mass, and the mass and volume of the majority will be spent as moisture transportation and landfill costs. This is the current situation. In addition, even if it is incinerated, most of the energy is spent on drying and latent heat of evaporation due to the large amount of moisture in the excess sludge, and the cost is high. It has become.

  The amount of excess sludge has been increasing year by year, and the disposal cost is high for both landfill disposal and incineration. The problem has become obvious in both environmental and environmental aspects.

Under such a background, effective utilization of microbial treatment for the treatment of surplus sludge has been studied. It is well known that surplus sludge is digested with activated sludge in the same manner as organic matter digestion once the microorganisms contained therein are killed. After the surplus sludge grown by digestion of soluble organic matter is killed, the microorganism is digested by returning it to the aeration tank (activated sludge tank), and the surplus sludge is reduced (or reduced in volume). In other words, the surplus sludge that has been killed is decomposed into CO ₂ and H ₂ O and reduced in quantity by digesting the surplus sludge with microorganisms.

  Various methods have been proposed for reducing excess sludge, such as ozone oxidation, hydrogen peroxide oxidation, hypochlorous acid oxidation, acid / alkali treatment, and heat treatment. .

  However, none of the above-described treatment methods are always satisfactory because they use a large amount of chemicals and energy or require a large apparatus.

  Among the above methods, it is said that a method of reducing excess sludge by generating hypochlorite ions or hypochlorous acid by electrolysis is relatively low in running cost (see, for example, Patent Documents 1 and 2). .

  However, in these methods, the amount of excess sludge is reduced by using an alkali. In particular, in Patent Document 2, a partition wall is provided between the electrodes to generate hypochlorous acid and an alkali, and the hypochlorite thereof. Since the amount of excess sludge is reduced using chloric acid and alkali, it is effective in terms of weight reduction, but the effect of killing microorganisms (bactericidal effect) is not sufficient.

  That is, when alkali is used, it is suitable for weight reduction, but the effect of killing microorganisms is lower than when it is treated on the acidic side. Therefore, surplus sludge treated with alkali is returned to the aeration tank and digested. As a result, the digestion efficiency deteriorates, and there is a problem that the load on the aeration tank must be increased and the aeration tank must be enlarged.

  Therefore, if a strong acid is used to kill the microorganism, it is necessary to add an alkaline chemical again to return the sludge after the killing treatment of the microorganism to the aeration tank. This is because the conditions of the aeration tank change to conditions that are not suitable for digestion due to the returned sludge, and there are similar problems with heat treatment and ozone oxidation treatment, and it is possible to return to the aeration tank as it is after sterilization. Decide to keep costs down.

JP 2002-126782 A JP-A-10-76299

  The present invention solves the problems in the conventional treatment of organic sewage as described above, efficiently kills microorganisms in excess sludge, and has a low running cost, by microbial treatment of organic sewage. It aims at providing the electrolytic treatment method of the excess sludge which can reduce the excess sludge which arises efficiently.

The surplus sludge electrolytic treatment method of the present invention is a surplus in which the solid content concentration generated by gravity sedimentation of activated sludge-containing water obtained by microbial treatment of organic sludge in an aeration tank is 0.3 to 2% by mass. Adding 0.1 to 3% by mass of chloride to the sludge, adjusting the pH to 2 to 6 by adding acid, and using the electrode in the electrolytic cell for sterilizing microorganisms in the excess sludge Reduce the content of insoluble organic matter in the excess sludge before and after the electrolytic treatment by setting the temperature of the excess sludge to 10 to 40 ° C. and subjecting the excess sludge to electrolytic treatment at a current density of 1 to 40 mA / cm ^2. It has a step of sterilizing microorganisms in surplus sludge at a rate of 25% by mass or less and a step of returning the above-treated surplus sludge to the aeration tank again.

  In the present invention, the chloride added to the excess sludge is preferably selected from sodium chloride, potassium chloride, magnesium chloride, and calcium chloride, and the acid is preferably selected from sulfuric acid and hydrochloric acid. The electrode used for the electrolytic treatment Is made of a carbon-based material such as amorphous carbon or graphite, or a metal plate such as a titanium plate or stainless steel plate coated with the carbon-based material, or directly or coated on the metal plate. The carbon-based material is preferably further coated with diamond or diamond-like carbon. Moreover, it is preferable to hold | maintain the excess sludge which carries out an electrolytic treatment in the range of 10-40 degreeC.

  In the present invention, the power source used for the electrolytic treatment is a direct current power source, and it is preferable to use the direct current as it is or to apply a reverse voltage to the direct current at regular intervals. Before and after, it is preferable that the decreasing rate of the content of the insoluble organic matter in the excess sludge is 25% by mass or less. Furthermore, it is preferable not to provide a diaphragm between the electrodes in the electrolytic cell for performing the electrolytic treatment.

  The inventors have found that the rate of decrease in the content of insoluble organic matter in the excess sludge before and after the electrolytic treatment is preferably 25% by mass or less. This is because of the reason. That is, in order to smoothly perform the digestion process in the aeration tank, the organic matter in the activated sludge needs to be a soluble organic matter. For this reason, it is necessary to kill microorganisms in activated sludge and change insoluble organic substances to soluble organic substances as much as possible. In this case, the present inventors have damaged the cell membrane or cell wall of microorganisms. It has been found that when microorganisms are killed in a state where they are dead, organic substances such as insoluble cell walls that cannot be digested remain in the aeration tank indefinitely, increasing the load in the aeration tank. Therefore, it is preferable to dissolve the cell wall from the inside by protease without damaging the cell wall by partially destroying the cell wall of the microorganism, without damaging the cell wall, which makes insoluble organic matter into soluble organic matter. They found it to be an effective means of changing efficiently. And as a judgment standard in that case, it is preferable to make the reduction | decrease in the electrolysis process of an insoluble organic substance into 25 mass% or less, and it is more preferable to set it as 20 mass% or less. The present invention improves the activated sludge treatment technology as described above, thereby making it possible to more efficiently reduce the excess sludge produced by the microbial treatment of organic wastewater than before.

  According to the present invention, it is possible to efficiently reduce excess sludge generated by microbial treatment of organic wastewater.

  That is, by setting the solid content concentration of the excess sludge to 0.3 to 2% by mass, the treatment efficiency of the excess sludge can be increased, and by adjusting the pH of the excess sludge to 2 to 6, the viscosity of the excess sludge is increased. By adding chloride, it is possible to efficiently generate hypochlorous acid with high bactericidal action, improve the electrolytic treatment efficiency, efficiently convert excess sludge into soluble organic matter, and in the aeration tank It is easy to decompose, and excess sludge generated by microbial treatment of organic wastewater can be efficiently reduced.

  Hereinafter, a preferred embodiment of the present invention will be described with reference to FIG.

  FIG. 1 is a diagram showing an outline of a processing process of the method of the present invention.

  In the treatment process, first, the organic sewage 1 is introduced into the aeration tank 2 and digested by microorganisms in the aeration tank 2. And the activated sludge containing liquid 3 discharged | emitted from the aeration tank 2 is introduce | transduced into the settling tank 4, and activated sludge precipitates by the gravity sedimentation method in the settling tank 4, and is isolate | separated into a concentrated sludge and a supernatant liquid. . The supernatant liquid in the settling tank 4 is discharged from the settling tank 4 as treated water 5, and the treated water 5 is sterilized and discharged out of the system.

  Then, the activated sludge that has settled at the bottom of the sedimentation tank 4 and has a high concentration is taken out from the sedimentation tank 4 as concentrated sludge 6, and a part of the sludge is returned to the aeration tank 2 as return sludge 7. The process so far is the same as in the case of the conventional microbial treatment of organic wastewater, but in the present invention, a part of the concentrated sludge in this conventional process is extracted as surplus sludge, and the surplus sludge is electrolyzed in a specific manner. The microorganisms in the excess sludge are killed, converted into soluble organic matter, the surplus sludge so treated is returned to the aeration tank again, digested with microorganisms, and this process is repeated to remove excess sludge. It is characterized by efficient reduction or almost zero.

  Hereinafter, the remaining processes which are the main part in the present invention will be described in sequence. The remaining concentrated sludge 6 is sent to the chemical mixing tank 9 as surplus sludge 8, and chloride is added to the surplus sludge 8 in the chemical mixing tank 9. Is added in an amount of 0.1 to 3% by mass, and an acid is added to adjust the pH to 2 to 6.

  As described above, when the concentrated sludge 6 generated by precipitation is introduced into the chemical mixing tank 9 as excess sludge 8, the solid content concentration of the excess sludge 8 is the solid content concentration of the precipitated sludge in the precipitation tank 4 (that is, concentrated sludge). The solid content concentration is preferably 0.3 to 2% by mass, and particularly preferably 0.8 to 1.5% by mass. If the solid content concentration of the excess sludge 8 is lower than 0.3% by mass, the amount of sludge around the electrode may be reduced when the sterilization (microbe killing) process is performed in the electrolytic cell, and the sterilization efficiency may deteriorate. On the other hand, when the solid content concentration of the excess sludge 8 is higher than 2% by mass, the viscosity is so high that it is difficult to stir, so that the electrolysis does not proceed sufficiently, and the dead sludge remains around the electrode and remains alive. The sludge becomes difficult to collect around the electrode, and the sterilization efficiency is lowered. In addition, if dead sludge stays around the electrode for a long time, the cell walls of microorganisms are damaged, and the cell walls cannot be dissolved from the inside by proteases, and may not be efficiently converted into soluble organic matter. .

  And in the chemical | medical agent mixing tank 9, a chloride is added to the excess sludge 8 as a salt, and an acid is added and it adjusts to pH 2-6.

  As the chloride, sodium chloride, potassium chloride, magnesium chloride, calcium chloride and the like are preferable. This is because these chlorides easily generate hypochlorous acid having a high bactericidal action in the subsequent electrolytic treatment process.

  In the present invention, the amount of chloride added to the excess sludge 8 is 0.1 to 3% by mass, for the following reason. That is, when the amount of chloride added to the excess sludge 8 is 0.1% by mass, the electrical resistance during the electrolytic treatment increases, and electric power is used for thermal energy, resulting in a reduction in processing efficiency. Therefore, it is necessary to lengthen the treatment time. However, if the treatment time is lengthened, the dead microorganisms are further treated, and the probability that the cell wall is destroyed is not preferable. In addition, since the concentration of hypochlorous acid produced is low, the sterilizing effect is reduced and the treatment time is extended, so that it is necessary to enlarge the electrolytic cell, leading to an increase in the price of the system. Further, when the amount of chloride added to the excess sludge 8 is more than 3% by mass, much more hypochlorous acid is generated than the amount necessary for sterilization (microbe kill), and the chloride is wasted. As well as increase running costs. In addition, there is a high possibility that the electrolytic treatment will proceed excessively, which may lead to the destruction of the cell wall. Accordingly, the amount of chloride added to the excess sludge needs to be 0.1 to 3% by mass, and preferably 0.2 to 0.8% by mass, as described above.

  In the chemical mixing tank 9, the acid added to the excess sludge 8 is added to enhance the bactericidal action (microbe killing action). As this acid, for example, a strong acid such as hydrochloric acid or sulfuric acid is preferable. In addition, it is possible to use nitric acid, phosphoric acid, etc., but when these are returned to the aeration tank and further separated into concentrated sludge and supernatant in the sedimentation tank, the supernatant contains nitrogen compounds and phosphorus compounds. Cause. Also, organic acids such as acetic acid are not preferred because they increase organic matter. Therefore, hydrochloric acid and sulfuric acid that do not affect the environment and are relatively inexpensive are preferable, and hydrochloric acid is particularly preferable because it also serves as a source of hypochlorous acid.

  In the present invention, hypochlorous acid generated by adding acid to surplus sludge as described above and adjusting to pH 2 to 6 is efficiently present to improve the bactericidal action. ~ 6 is preferred. When the pH is lower than 2, harmful chlorine gas is generated, and the cell wall is damaged. When the pH is higher than 6, the bactericidal action is lowered. In addition, when it is made alkaline, not only the bactericidal action is lowered, but the decrease of insoluble organic matter becomes severe, and the reduction rate of insoluble organic matter before and after electrolytic treatment exceeds 25% by mass. If it returns to the aeration tank 2 as it is, it will lead to the increase in the load at the time of the digestion process in the aeration tank 2. If alkaline, the cell wall of the microorganism is easily damaged, the cell wall cannot be dissolved from the inside of the microorganism by protease, and the insoluble organic substance cannot be efficiently converted into the soluble organic substance.

  Further, when returning the sludge after the electrolytic treatment to the aeration tank, it is preferable not to change the environment of the aeration tank, and it is preferable to maintain the pH of the aeration tank between 6 and 7, particularly 6.5 to 7 It is preferable to keep it in between. In the sedimentation tank 4, since activated sludge is concentrated about 100 times by precipitation using gravity sedimentation, if the pH is about 4.5, it is not necessary to adjust the pH at the time of return, but if lower than that, It is necessary to adjust the pH of the sludge to 4.5 or more with alkali.

In the present invention, surplus sludge mixed with chemicals (that is, chloride and acid) in the chemical mixing tank 9 is introduced into the electrolytic tank 11 as the chemical mixed sludge 10 and electrolyzed in the electrolytic tank 11, whereby the electrode surface Is sterilized by hypochlorous acid. Then, surplus sludge sterilized by this electrolytic treatment is returned to the aeration tank 2 as electrolytically treated sludge 12. The larger the current density at the time of electrolysis, the shorter the electrolysis time is. However, the voltage between the electrodes rises and water is decomposed to reduce the sterilization efficiency. Therefore, the current density should be 1 to 40 mA / cm ^2. needs, 3~20mA / cm ² is preferred.

  The surface of the electrode used for electrolysis is preferably composed of a carbon-based material such as amorphous carbon or graphite. By using a carbon-based material for the electrode, the sterilization efficiency can be improved and the consumption of the electrode can be reduced.

  However, if an electrode is made of only a carbon-based material, it is easy to break. Therefore, an electrode obtained by coating the above-mentioned carbon-based material on a titanium plate or stainless steel plate may be used. An electrode coated with like carbon may be used. The diamond or diamond-like carbon is preferably doped with boron or the like in order to impart conductivity.

  The power source for electrolysis is preferably a direct current power source, and the direct current may be used as it is. However, it is preferable to apply a reverse voltage to the direct current at regular intervals.

  This is because, as electrolysis progresses, metal deposits on the electrode surface to form a coating, alters the surface of the electrode and lowers the production efficiency of hypochlorous acid, and oxidizes and drops the metal coating by reverse voltage. is there. The time for applying the reverse voltage is preferably 1 to 5 seconds in 60 seconds. When the time for applying the reverse voltage is shorter than 1 second, oxidation of the metal film hardly occurs, and even if it is longer than 5 seconds, there is no increase in the effect, and there is a possibility that the generation efficiency of hypochlorous acid is rather lowered. There is. The reverse voltage is preferably 1.5 to 10 V, particularly preferably 2 to 5 V. When the reverse voltage is lower than 1.5V, the current is reduced, so that the reaction rate for oxidizing the metal is slow. On the other hand, when the reverse voltage is higher than 10 V, the electrolysis rate is increased, the generation of gas is increased, the generation efficiency of hypochlorous acid is lowered, and the sterilization efficiency is lowered.

  Further, the relationship between the amount of the electrolytic solution and the electric power is preferably 0.2 to 1 Ah / l, and particularly preferably 0.3 to 0.7 Ah / l. When the power with respect to the amount of electrolyte is less than 0.2 Ah / l, the generation of hypochlorous acid is reduced and the electrolysis time is prolonged, and when the power with respect to the amount of electrolyte is more than 2 Ah / l, insoluble organic matter There is a possibility that the decrease of the increase becomes larger and the load becomes larger.

  Moreover, the temperature of the sludge at the time of electrolysis has preferable 10-40 degreeC. When the temperature is higher than 40 ° C., the amount of insoluble organic matter increases to 40% by mass or more of the whole, resulting in an increase in load, and when returned to the aeration tank, a part of the activated sludge in the aeration tank is killed. Therefore, the load increases, which is not preferable. Moreover, when temperature is lower than 10 degreeC, since electrolysis efficiency falls by the increase in a viscosity, it is not preferable similarly.

  Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.

Example 1
Organic sewage having a pH of 6.7, BOD of 200 mg / liter and SS of 75 mg / liter was introduced into an aeration tank, and the organic sewage was subjected to microbial treatment at 30 ° C. for 8 hours to decompose organic matter with microorganisms. The aeration tank is an oxidation ditch tank.

  The activated sludge-containing liquid obtained by microbial treatment in the aeration tank as described above is introduced into the precipitation tank, left for 2 hours to precipitate the activated sludge, and the supernatant liquid is discharged from the precipitation tank as treated water. (This treated water is sterilized and released to the outside of the treatment system), and the sludge which has settled and has a high concentration was taken out from the sedimentation tank as concentrated sludge. The solid content concentration in the concentrated sludge at this time, that is, MLSS was 11850 mg / liter.

  25% by mass of the concentrated sludge is returned to the aeration tank (the sludge to be returned to the aeration tank is called “return sludge”), and the remaining 75% by mass is introduced into the chemical mixing tank as surplus sludge. Sodium chloride was added to the excess sludge so as to have a concentration of 0.5 mass%, and hydrochloric acid was added to adjust the pH of the excess sludge to 4.5.

  And the chemical | medical agent mixing sludge taken out from the chemical | medical agent mixing tank was sent to the electrolysis tank, and it electrolyzed and killed the microorganisms in a sludge (sterilization process).

This electrolytic treatment will be described in detail. The internal volume of the electrolytic cell is 120 liters, the positive electrode is made of amorphous carbon, the negative electrode is also made of amorphous carbon, and the effective area is 10,000 cm ^{2 for} both the positive electrode and the negative electrode. The current density was 8 mA / cm ² . The flow rate of the chemical mixed sludge, that is, the surplus sludge used for electrolysis to the electrolytic cell is 80 liters, the temperature of the surplus sludge during electrolysis is kept at 30 ° C., and the electrolysis time is 20 minutes. there were. That is, the electric power used for the electrolytic treatment was 0.33 Ah / l with respect to the amount of the electrolytic solution. Then, in order to increase the contact efficiency between hypochlorous acid and microorganisms at the electrode and prevent sludge from floating due to gas generation, the mixture was stirred using a vibration type stirrer.

  The killing rate of microorganisms by this electrolytic treatment, that is, the sterilization rate was 98% or more, and the MLSS of the sludge after electrolytic treatment was 10430 mg / liter. The reduction rate of MLSS due to the electrolytic treatment was about 12% on a mass basis, and the soluble organic matter STOC increased from 15 mg / liter to 490 mg / liter. As described above, MLSS decreased from 11850 mg / liter to 10430 mg / liter by electrolytic treatment. Some of the microorganisms in the sludge were damaged by electrolytic treatment, and soluble organic substances inside the cell elute out of the cell wall. It is because of having done. That is, the microorganisms in the sludge by the electrolytic treatment are killed without damaging the cell wall and remain as solids (this changes to soluble organic matter in the aeration tank over time) and the cell wall is damaged and the cell wall The internal soluble organic matter flows out of the cell wall and is divided into those mainly composed of the cell wall (this remains as an insoluble organic matter thereafter), and immediately after electrolytic treatment, both constitute a solid matter, MLSS is reduced by the soluble organic matter eluted from the cell wall to the outside.

  The sterilization rate of 98% by the electrolytic treatment was determined as follows. That is, air was bubbled through the sludge after electrolytic treatment for 10 minutes, and the reduction rate of the dissolved oxygen was measured. Prior to measurement of the rate of decrease in dissolved oxygen, organic sewage (raw water) containing BOD 200 mg / liter and SS 75 mg / liter was digested and the rate of sterilization determined from the rate of decrease in dissolved oxygen immediately before being brought into the settling tank The sterilization rate determined from the decrease rate of dissolved oxygen (no decrease) in distilled water is 100%, and the sterilization rate of activated sludge obtained by diluting 20% of the raw water with distilled water is 20%. The calibration curve was drawn with the sterilization rate of the activated sludge diluted with distilled water as 50% and the sterilization rate of the activated sludge solution diluted as 70% as distilled water as 70%. As a result, the sterilization rate was 98% as described above. Moreover, MLSS of the sludge before and behind the electrolytic treatment was reduced by about 12% on a mass basis.

  And the sludge after this electrolytic treatment was again supplied to the aeration tank, and this was repeated, and the excess sludge was reduced. The MLSS in the aeration tank after performing this series of treatments for 30 consecutive days (after 30 days of treatment) was stabilized at 3200 mg / liter, and was treated as a supernatant liquid (hereinafter referred to as “supernatant” in the precipitation tank). The water quality of the wastewater) is pH 6.5, BOD 5 mg / liter, SS 11 mg / liter, and the wastewater in the process of discarding excess sludge before adopting the system for reducing excess sludge by this electrolytic treatment. The water quality was almost the same.

  In addition, the water quality of the supernatant drainage is required to have a pH of 6 to 8, a BOD of 60 mg / liter or less, and an SS of 120 mg / liter or less. Can be satisfied sufficiently.

Examples 2-5 and Comparative Examples 1-2
The pH of the excess sludge used for the electrolytic treatment is 1.5 (Comparative Example 1), 2.0 (Example 2), 3.0 (Example 3), 5.5 (Example 4), 6.0 (implementation). Except for changing to Examples 5) and 6.5 (Comparative Example 2), the same treatment as in Example 1 was carried out to reduce excess sludge, and the sterilization rate by electrolytic treatment and the reduction rate of MLSS, after 30 days of treatment The amount of MLSS in the aeration tank and the quality of the supernatant drainage were examined in the same manner as in Example 1. In addition, when pH was 3 or less, after electrolytic treatment, sodium hydroxide was added, pH was returned to 4.5, and it returned to the aeration tank. Moreover, since the MLSS changes at the time of experiment, the excess sludge by electrolytic treatment was evaluated as the reduction rate. Table 1 shows the pH of the excess sludge to be subjected to electrolytic treatment, the sterilization rate by electrolytic treatment, and the reduction rate of MLSS, and Table 2 shows the MLSS amount in the aeration tank after 30 days treatment and the BOD amount and SS amount of the supernatant drainage. .

  As is clear from the results shown in Tables 1 and 2, in Examples 2 to 5 in which the pH of the excess sludge to be subjected to the electrolytic treatment is in the range of 2.0 to 6.0, the sterilization rate by the electrolytic treatment is high, The reduction rate of MLSS is not too large as 24% or less, and as a result, the amount of MLSS in the aeration tank after 30 days treatment is within the range of 4000 mg / l or less, and excess sludge can be made efficient. In addition, the water quality of the supernatant drainage was able to be maintained within an appropriate range with a BOD of 37 mg / l or less and an SS of 50 mg / l or less.

  In contrast, in Comparative Example 1 in which the pH was 1.5, the MLSS reduction rate due to the electrolytic treatment was too large, so the load on the aeration tank increased, and the amount of MLSS in the aeration tank after 30 days treatment Since it exceeds 4800 mg / liter and 4000 mg / liter, it is difficult to separate in a sedimentation tank as is generally known, and the quality of the supernatant drainage water deteriorated to BOD 60 mg / l and SS 170 mg / l. For this reason, it was necessary to appropriately discard excess sludge to prevent deterioration of water quality. Moreover, in the comparative example 2 which made pH 6.5, the disinfection rate by an electrolysis process becomes low, As a result, the amount of MLSS in an aeration tank increases, and the water quality of supernatant water drainage along with it, BOD is 120 mg / l, It decreased to SS 280 mg / l.

Examples 6-11 and Comparative Examples 3-4
Except for changing the current density and electrolysis time, the same treatment as in Example 1 was performed to reduce excess sludge. The current density and electrolysis time at that time are shown in Table 3. As a result of the above reduction treatment, that is, the sterilization rate and MLSS reduction rate by the electrolysis treatment, the amount of MLSS in the aeration tank after 30 days treatment, and the supernatant drainage Table 4 shows the BOD amount and SS amount.

As is apparent from the results shown in Tables 3 to 4, in Examples 6 to 11 in which the current density is in the range of 1 to 40 mA / cm ² , the sterilization rate by electrolytic treatment is high, and the reduction rate of MLSS is also high. As a result, the amount of MLSS in the aeration tank after the treatment for 30 days is also within the range of 4000 mg / l or less, and the excess sludge is efficiently reduced. The water quality was also maintained within an appropriate range with a BOD of 35 mg / l or less and an SS of 30 mg / l or less.

In contrast, the current density is in large Comparative Example 4 small Comparative Example 3 and the current density 0.5 mA / cm ² is a 50 mA / cm ^2, a number MLSS in the aeration tank after treatment 30 days, the excess sludge Reduction was not sufficient, and the quality of the supernatant drainage water was large in BOD, and could not be maintained within an appropriate range.

Examples 12-14 and Comparative Examples 5-6
Excess sludge was reduced in the same manner as in Example 1 except that the amount of sodium chloride added was changed. Table 5 shows the sterilization rate of the electrolytic treatment and the reduction rate of MLSS, the MLSS amount in the aeration tank after 30 days treatment, the BOD amount and SS amount in the supernatant drainage, together with the amount of sodium chloride added.

  As is apparent from the results shown in Table 5, in Examples 12 to 14 in which the amount of sodium chloride added was in the range of 0.1 to 3% by mass, the sterilization rate by electrolytic treatment was high, and the reduction rate of MLSS was also high. As a result, the amount of MLSS in the aeration tank after the treatment for 30 days is also within the range of 4000 mg / l or less, and the excess sludge is efficiently reduced. The water quality was maintained within a proper range with a BOD amount of 18 mg / l or less and an SS amount of 30 mg / l or less.

Examples 15-17
Excess sludge was reduced by treating in the same manner as in Example 1 except that the chloride added to the excess sludge to be subjected to electrolytic treatment was changed from sodium chloride in Example 1 to other chlorides. Table 6 shows the sterilization rate and MLSS reduction rate by electrolytic treatment at that time, the MLSS amount in the aeration tank after 30 days treatment, and the BOD amount and SS amount in the supernatant drainage together with the type of chloride.

  As is clear from the results shown in Table 6, the sterilization rate by electrolytic treatment in all of Example 15 using potassium chloride, Example 16 using calcium chloride, and Example 17 using magnesium chloride as chlorides. And the reduction rate of MLSS is not too high, and as a result, the amount of MLSS in the aeration tank after 30 days treatment is within the range of 4000 mg / l or less, and excess sludge is efficiently reduced. In addition, the water quality of the supernatant drainage at that time was maintained within an appropriate range with a BOD of 14 mg / l or less and an SS of 16 mg / l or less.

Examples 18-19
Example 1 except that both the positive electrode and the negative electrode were made of amorphous carbon in Example 1 instead of those made of graphite and those in which a graphite layer coated on a titanium plate was further coated with diamond-like carbon. In the same way, excess sludge was reduced. Table 7 shows the sterilization rate and MLSS reduction rate by electrolytic treatment at that time, the MLSS amount in the aeration tank after 30 days treatment, the BOD amount and SS amount in the supernatant drainage, together with the material on the electrode surface.

  As is apparent from the results shown in Table 7, both the Example 18 in which the electrode was made of graphite and the Example 19 in which the electrode was further coated with diamond-like carbon on the graphite layer in which the electrode was coated on a titanium plate were subjected to electrolytic treatment. As a result, the amount of MLSS in the aeration tank after 30 days treatment is within the range of 4000 mg / l or less, and the excess sludge can be efficiently reduced. In addition, the quality of the supernatant drainage water at that time was maintained within an appropriate range with a BOD of 17 mg / l or less and an SS amount of 16 mg / l or less.

It is a figure which shows the outline | summary of the process by the electrolytic treatment method of the excess sludge which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Organic sewage 2 Aeration tank 3 Liquid containing activated sludge 4 Precipitation tank 5 Processed liquid 6 Concentrated sludge 7 Return sludge 8 Surplus sludge 9 Chemical mixing tank 10 Chemical mixing sludge 11 Electrolysis tank 12 Electrolyzed sludge

Claims (2)

To excess sludge having a solid content concentration of 0.3 to 2% by mass generated by gravity sedimentation of activated sludge-containing water obtained by microbial treatment of organic sludge in an aeration tank, chloride is added to 0.1 to 3%. The step of adding acid% and adjusting the pH to 2 to 6 by adding an acid, and using an electrode in an electrolytic cell for sterilizing microorganisms in the excess sludge, the temperature of the excess sludge is 10 to 40 ° C. The surplus sludge is subjected to electrolytic treatment at a current density of 1 to 40 mA / cm ² , and the reduction rate of the content of insoluble organic matter in the surplus sludge before and after the electrolytic treatment is reduced to 25% by mass or less in the surplus sludge. A surplus sludge electrolysis method characterized by comprising a step of sterilizing the microorganisms and a step of returning the electrolyzed surplus sludge to the aeration tank again.   The method for electrolytic treatment of excess sludge according to claim 1, wherein sodium chloride, potassium chloride, magnesium chloride or calcium chloride is added as a chloride, and sulfuric acid or hydrochloric acid is added as an acid.

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