JP4363568B2 - Surplus sludge reduction system - Google Patents

Description

  The present invention relates to a system for reducing surplus sludge, and more specifically, surplus sludge generated by microbial treatment of organic sludge can be operated with simple equipment and low running cost, and surplus sludge can be efficiently reduced. The present invention relates to a system for reducing excess sludge.

  In the activated sludge treatment of organic sewage, soluble organic substances present in the sewage are digested while causing the growth of microorganisms. The sludge in which the grown microorganisms are dispersed in water needs to be discharged and disposed as so-called surplus sludge. In the large-scale treatment facility, the disposal method is decomposed into carbon dioxide gas and water through the steps of concentration → dehydration → drying → incineration. However, in a small-scale treatment plant that does not have such an incineration facility, the activated sludge-containing liquid after gravity concentration has to be transported to a facility having a concentration facility or an incineration facility for processing. It is a big economic burden.

  Against this background, development of technology for reducing the volume using microorganisms (changing surplus sludge into carbon dioxide and water) suitable for small-scale treatment plants is underway. In this volume reduction process with microorganisms, first, a sterilization process for treating microorganisms with surplus sludge is important. This sterilization step has the meaning of supplying the surplus sludge as an easily digestible organic substance to microorganisms that purify water by digesting organic substances in the wastewater.

Conventionally, as this sterilization method, ozone (Patent Document 1) or chlorine compound (Patent Document 2) having strong oxidizing power is used to oxidize microorganisms that are the main component of sludge, and sterilization methods using alkali or acid ( Patent Document 3) has been proposed.
JP-A-9-150186 JP 2002-126782 A JP-A-4-131184

  In these conventional treatment methods, the above-mentioned sterilizing agent is mixed in the excess sludge storage tank, ozone is bubbled into the excess sludge when ozone is used, or acid or alkali is used or generated by electrolysis. In the case of using a chlorine compound to be used, stirring by a mechanical device is generally employed as a means for exerting a bactericidal action on microorganisms in excess sludge.

  However, all of the above conventional treatment methods use a large amount of chemicals and energy, and the apparatus becomes large, so in a small-scale treatment plant that must achieve a high volume reduction effect at low cost, It was not always a satisfactory method.

  For example, a method using an alkali or an acid requires a large amount of chemicals, so it is not only economical, but also has a heavy burden on safety and the environment, and is particularly suitable for small-scale treatment plants. It was hard to say.

  In addition, the method of using ozone has the advantage of so-called solubilization, which destroys the cell wall of excess sludge and elutes the internal cytoplasm by its extremely strong oxidizing power, but it is shown below. Has the following problems. First, when using dissolved ozone, even if ozone generated by silent discharge or the like is blown into water, the amount of ozone dissolved in water is generally less than several percent of the blown amount. That is, most of the ozone floats to the surface of the water before it dissolves and is released into the atmosphere as a harmful gas to the human body, so it is necessary to supply much more ozone than is necessary for sterilization treatment. In addition to an increase in cost and an increase in size of the apparatus, there are also problems of adverse effects on the environment and health.

  Furthermore, because the solubilized cytoplasm can produce highly viscous sludge water, sticky bubbles that are extremely difficult to defoam will grow when the gas is blown in. Therefore, it is inevitable that more space than necessary is inevitable. It was a big operational problem.

  In addition, the method of producing chlorine compounds such as hypochlorous acid by electrolytic treatment of sludge and applying it to the surrounding sludge to sterilize can produce the necessary amount of sterilizing components on the spot at a low cost. (This is because the sterilizing component regenerates sterilizing components such as hypochlorous acid on the electrode surface again after the sterilizing component oxidizes and sterilizes microorganisms and loses sterilizing power). Since the production of chloric acid and the like is limited to the vicinity of the electrode, the sterilization action is also limited to the vicinity of the electrode, and as it is, it is difficult to uniformly act on the entire electrolytic cell. That is, hypochlorous acid and the like have a very strong bactericidal power, and are quickly consumed by the oxidation of nearby organic matter from the generated buckwheat. As a result, while there are regions that are oxidized many times, there are regions that cannot be sufficiently oxidized, and there is a problem from the viewpoint of efficient sterilization over the entire region.

  As described above, in the reduction of excess sludge, the prior art has not been able to sufficiently satisfy the needs of consumers, such as cost reduction and device simplification.

  The present invention solves the problems of the prior art as described above, and can reduce excess sludge with simple equipment and low running cost, which is required especially in small-scale sewage treatment facilities, and efficiently. The purpose is to provide a system for reducing excess sludge.

  The present invention allows surplus sludge to flow into the flow path, and from a large number of jet outlets provided above the flow path, water containing hypochlorous acid or ozone is sprayed downward in a shower shape to form surplus sludge. The problem is solved based on the action.

  That is, according to the present invention, the activated sludge-containing liquid obtained by microbial treatment of organic sewage in an aeration tank is subjected to gravity concentration in a sedimentation tank so that the solid matter concentration in the activated sludge is 0.8 to 2% by mass. The first step of returning a part of the concentrated sludge to the aeration tank, the remaining concentrated sludge as surplus sludge, and flowing the surplus sludge into the flow path, A second step in which hypochlorous acid or ozone-containing water is jetted downward in a shower-like manner from a large number of outlets provided above the flow path to act on excess sludge, and the hypochlorous acid or ozone is A surplus sludge reduction system including a third step of returning surplus sludge treated with water contained therein to the aeration tank again, and in the second step, solids in the surplus sludge flowing in the flow path per unit time The amount is w (g), the concentration of hypochlorous acid or ozone is p ppm), when the amount of water containing hypochlorous acid or ozone that is sprayed downward in a shower-like manner per unit time and acts on excess sludge is defined as v (kg), the above w, p, and v are set to 0. The present invention relates to a surplus sludge reduction system characterized by being in a range of 05 ≦ w / vp ≦ 3.0.

  According to the present invention, it is possible to provide a surplus sludge reduction system that can be operated at a low running cost with a simple facility that is required particularly in a small-scale sewage treatment facility, and that can be reduced efficiently. it can.

  In the present invention, as described above, surplus sludge is passed through the flow path in the second step. The surplus sludge (hereinafter sometimes referred to as “sludge” in some cases) flowing through the flow path has a thickness of 5 to 5. 30 mm is preferable, and 10 to 20 mm is particularly preferable. If the thickness of the excess sludge flowing through this flow path is set within this range, a sufficient flow rate is ensured, and the stirring action by the shower is spread over the entire sludge so that the sterilization action is sufficient.

  When reducing the volume of excess sludge, that is, reducing the excess sludge, the amount of sludge to be sterilized is enormous, and therefore efficient treatment is essential from the viewpoint of cost and equipment. In this case, in order to achieve an efficient treatment, it is necessary to let hypochlorous acid or ozone having strong oxidizing power uniformly act on microorganisms in the sludge. The reason is due to the extremely strong oxidizing power of hypochlorous acid or ozone. That is, the bactericidal power generated by the action of strong oxidizing power is very immediate. Therefore, when a large amount of oxidizable substances (sludge) is dispersed, hypochlorous acid or ozone is not This is because it does not spread between the dispersed sludges by stirring or the like, but acts simultaneously with contact with the sludge organic matter and loses sterilizing power on the spot. In other words, the huge amount of sludge's organic matter will kill the sterilizing power one after another, so the area to be sterilized will not spread easily. In order to avoid this, it is the present situation that hypochlorous acid or ozone is dispersed and distributed to the treatment tank, but it is not found conventionally except by relying on a stirring device. However, even with this agitation technique, in the case of hypochlorous acid or ozone that immediately acts on nearby organic substances, a very large amount of disinfectant is required to expand the disinfection effect throughout the treatment tank, and only the cost is required. It is also a problem in terms of safety and environmental considerations.

  Therefore, in the present invention, surplus sludge is allowed to flow through a wide flow path, and water containing hypochlorous acid or ozone is jetted downward in a shower-like manner from a large number of outlets provided on the flow path. Act on sludge. Thereby, the ratio of the amount of sterilizing water (water containing hypochlorous acid or ozone) to the amount of excess sludge to be treated can be significantly reduced as compared with the conventional method. It should be noted that the sterilization can be more efficiently realized by setting the ratio of the amount of sludge to be treated (excess sludge) and the amount of sterilized water within a certain range. That is, in the present invention, the amount of sludge (solid content) to be treated per unit time is w (g), the amount of sterilizing water per unit time is p × v [p is the concentration (ppm), and v is the amount of shower water ( kg)], by setting the above w and p × v to 0.05 ≦ w / p × v ≦ 3.0, it is possible to efficiently sterilize and efficiently reduce excess sludge. This w / pv value represents the amount of sludge treated per unit amount of the disinfectant. The larger the value, the less disinfectant and energy to be used. By setting this w / p × v value within the above range, The excess sludge can be effectively reduced without using too much disinfectant.

  Furthermore, in the present invention, prior to the sterilization treatment, by sending fine air bubbles to the excess sludge tank, the solid content can be concentrated and the sterilization treatment can proceed more efficiently. In this way, the solid content concentration in the sludge when the excess sludge is concentrated is preferably 5% by mass or more and 20% by mass or less considering the efficiency of the sterilization treatment and the efficiency at the time of concentration.

  Next, a preferred embodiment for reducing surplus sludge generated by microbial treatment of organic wastewater according to the present invention will be described with reference to FIG.

  FIG. 1 is a diagram schematically showing an outline of a treatment process when the surplus sludge reduction system of the present invention is implemented.

  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 sedimentation tank 4, an activated sludge is settled by the gravity concentration method in the sedimentation tank 4, and it isolate | separates into a concentrated sludge and a supernatant liquid. . The supernatant liquid in the sedimentation tank 4 is discharged from the sedimentation tank 4 as the treated liquid 5 and then sterilized and released outside the system.

  On the other hand, the activated sludge precipitated at the bottom of the settling tank 4 is taken out from the settling tank 4 as concentrated sludge 6, and part of it is returned to the aeration tank 2 as return sludge 7. The process so far is the same as that in the case of the conventional microbial treatment of organic sewage, but in the present invention, the concentrated sludge other than the returned sludge in this conventional process is extracted as the excess sludge 8 and a specific aspect of the excess sludge 8 In this process, water containing hypochlorous acid or ozone is allowed to act to kill microorganisms in the excess sludge, convert it into soluble organic matter, return the treated excess sludge to the aeration tank again, and digest it with microorganisms. It is characterized by reducing excess sludge efficiently by repeating this process.

  Hereinafter, the remaining processes which are the main part in the present invention will be described in order. The remaining concentrated sludge 6 is sent to the wide and shallow flow path 9 as surplus sludge 8, and preferably 5 to 5 on the flow path 9. Flowed with a thickness of 30 mm. Separately, water containing hypochlorous acid or ozone, which is generated and adjusted in concentration by a sterilizing water supply device (water supply device containing hypochlorous acid or ozone) 10, is supplied to the flow path 9 via the valve 11. From the nozzle 12 which has many jet nozzles provided above, it ejects more like a shower and supplies it to the excess sludge 8. The water containing hypochlorous acid or ozone ejected downward from the nozzle 12 having a large number of ejection ports exerts an oxidizing action on the excess sludge 8 flowing in the lower flow path 9, and is efficient within a short time. The microorganisms in the excessively large amount of excess sludge 8 are killed. The surplus sludge 8 that has undergone the oxidation treatment is temporarily stored in the storage tank 13 or returned to the aeration tank 2 as it is.

  In order to further concentrate the first excess sludge, fine air bubbles are supplied to the excess sludge 8 from the bubble generating device 15 below the tank in the concentration tank 14 to float and concentrate the suspended solids. The further concentrated highly concentrated sludge 15 can be sent from the concentration tank 14 to the flow path 9 by overflow or a scraper. In this method, when adding a so-called advanced treatment process to separate phosphorus and heavy metals from the sterilized surplus sludge, the treatment time and cost can be greatly reduced by greatly reducing the amount of water to be treated. This is a particularly preferable application mode. Of course, even when advanced treatment is not applied, the efficiency of sterilization treatment can be increased by highly concentrating microorganisms, so that cost reduction can be realized, and making highly concentrated sludge reduces excess sludge. In this case, this is a preferred embodiment.

  Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples. In the following examples and the like,% indicating the solid content concentration in the sludge is mass% unless otherwise specified.

Example 1
Example 1 will be described with reference to FIG. 1. Sludge 6 having a solid concentration of 1.3% by mass adjusted by a gravity concentration method (active sludge-containing liquid 3 obtained by microbial treatment of organic waste water 1 in an aeration tank 2 is precipitated. A part of the concentrated sludge 6) having a solid content concentration of 1.3% adjusted to the gravity concentration method in the tank 4 is used as surplus sludge 8, and a stainless steel flow path 9 (width 1 m, length 3 m) as the second step. ) At a thickness of 20 mm and a flow rate of 1.67 cm / sec. At a height of 1 m above the flow path 9, a total of 27 nozzles 12 having a large number of jet outlets toward the flow path are arranged at 3 m in the lateral direction and 9 rows in the longitudinal direction. From this nozzle, water containing hypochlorous acid or ozone as sterilizing water is ejected in the form of a shower on its lower surface.

In Example 1, the amount of excess sludge 8 flowing through the flow path 9 is 20 liters / minute, and water containing hypochlorous acid is electrolytically treated with an aqueous hydrochloric acid solution using an electrolytic device (MP240 manufactured by Morinaga Engineering Co., Ltd.). And was supplied from the sterilizing water supply apparatus 10 to the excess sludge through the valve 11 and the nozzle 12 in a shower form. The concentration of hypochlorous acid in the water containing hypochlorous acid at this time is 10 ppm, and the supply amount is 13 liter / min · m ² per unit area with respect to surplus sludge having a solid content concentration of 1.3%. The supply water pressure was 1 kg / cm ² , and the water containing hypochlorous acid was ejected from the nozzle 12 having a large number of ejection ports into the excess sludge below in the form of a shower. The above-mentioned hypochlorous acid-containing water (water containing hypochlorous acid) is ejected from an ejection port composed of a large number of pores provided at the tip of the nozzle 12, and surplus is caused by the water pressure increased by the pores While stirring and mixing the sludge, it is sent downstream. In the meantime, the excess sludge 8 flowing through the flow path 9 is subjected to an oxidizing action necessary and sufficient for the resident microorganisms to die, and then returned to the aeration tank 2.

In the present invention, since an oxidizing (sterilizing) action on microorganisms can be exerted uniformly, a large amount of sludge can be treated efficiently in a short time. And also in this Example 1, since the excess sewage can be concentrated in the concentration tank 14 so that the sterilization effect can be more efficiently achieved, the processing capacity can be improved. No. 1 can treat 1.2 m ³ / h of excess sludge without such concentration treatment.

  In Example 1, the solid content w in the excess sludge is 260 g per unit time (1 minute), the concentration p of hypochlorous acid is 10 ppm, and the amount of hypochlorous acid-containing water v is the unit time (1 minute). Since the weight is 39 kg, w / vp is 0.67, which is within the range of 0.05 ≦ w / vp ≦ 3.0 defined in the present invention.

In the first embodiment, as described above, the nozzles 12 for ejecting water containing hypochlorous acid from a large number of outlets are arranged at a height of 1 m on the flow path at intervals of 30 cm, three in the transverse direction and nine in the longitudinal direction. 27, a total of 27 nozzles were installed, but the mounting height and mounting pitch of the nozzles 12 having a large number of jet nozzles are not fixed to the above values, and hypochlorous acid is contained evenly over the entire flow path. It does not matter as long as it can supply water. In addition, it is effective means to increase the sterilization efficiency in the flow path by providing a baffle plate to meander the surplus sludge in the flow path or the more highly concentrated sludge flow, and it is effective to adopt as appropriate. It is. Furthermore, in this Example 1, surplus sludge was processed at 1.2 m ³ / hr. However, as an excellent point of the present invention, depending on the amount to be processed, for example, the width or length of the flow path and the sludge flow For example, it is possible to cope with changes in the processing amount by simply changing the path length. Moreover, in this Example 1, what was provided in the nozzle was used as many fountain ports, However, Other things may be used.

Example 2
Instead of the water containing hypochlorous acid used in Example 1, water containing 15 ppm of ozone was used, the amount of excess sludge flowing through the flow path was 30 liters / minute, the thickness was 10 mm, and the flow rate was 5 cm. Excess sludge was reduced in the same manner as in Example 1, except that the amount of ozone-containing water was 8.67 liters / minute · m ² per unit area of the flow path.

  In preparation of the water containing ozone used in Example 2, an ozone generator manufactured by Nomura Electronics Co., Ltd. and a microbubbler were used in combination, and the ozone dissolution efficiency was increased by mixing fine ozone gas bubbles. .

  And w / vp of this Example 2 was 3.0 by the above condition setting.

Example 3
Excess sludge was reduced in the same manner as in Example 1 except that the thickness of the surplus sludge flowing through the flow path was about 33 mm and the flow rate was 1.5 cm / sec.

  And w / vp of this Example 3 was also set to 0.67 like Example 1 by the above condition setting.

Comparative Example 1
Example except that the amount of hypochlorous acid-containing water used in Example 1 to the surplus sludge on the flow path was set to 2.7 liters / minute · m ² and w / vp = 3.2. In the same manner as in No. 1, excess sludge was reduced.

Comparative Example 2
Instead of the method of sterilizing with hypochlorous acid or ozone in the flow path of the present invention, surplus sludge was directly subjected to electrolytic treatment.

That is, according to the method described in Japanese Patent Application Laid-Open No. 2002-126782, a platinum-coated titanium plate was used as an anode and a stainless steel plate was used as a cathode as an electrode. 0.2 liter of surplus sludge having a solid content concentration of 1.3% was placed in a 300 cc beaker, 1% NaCl was added thereto, and DC electrolysis was performed for 1 minute with stirring. At this time, the electrode area was 5 cm × 5 cm, and the current density was 1 A / cm ² .

  In Examples 1 to 3 described above, 20 to 30 liters of excess sludge is processed per minute, so in this example too, it should be 20 liters per minute, but experimentally 0.2 liters per minute (100% This was designated as Comparative Example 2 because it can be scaled up as it is.

  The sterilization rate of microorganisms in the activated sludge when treated in Examples 1 to 3 and Comparative Examples 1 and 2 was examined. The sterilization rate was determined from the change in the amount of dissolved oxygen that live activated sludge actively consumed was measured for 10 minutes after treatment. The amount of dissolved oxygen was measured with a dissolved oxygen meter (OM15 manufactured by Horiba, Ltd.).

  When microorganisms in the activated sludge die, the consumption of dissolved oxygen decreases, and the time change of the dissolved oxygen consumed becomes gradual. When the microorganisms in the activated sludge are killed, the dissolved oxygen is not consumed, so the time change of the dissolved oxygen is not seen. The result of obtaining the sterilization rate is referred to as its treatment method (however, the method of spraying water containing hypochlorous acid or ozone into the excess sludge flowing in the flow path in the form of a shower is called “this method”. / Vp value does not matter), the w / vp value and the thickness of excess sludge flowing through the flow path. In addition, the processing amount of excess sludge is 100 liters in 5 minutes.

  As shown in Table 1, in Examples 1 to 3 where w / vp is 0.67 or 3.00 and 0.05 ≦ w / vp ≦ 3.0, the sterilization rate is 95%. That's it. The sterilization rate is preferably 95% or more, and it is not preferable when the sterilization rate is lower than 95%.

  In contrast, Comparative Example 1 having w / vp of 3.2 and larger than the range of 0.05 w / vp <3.0 defined in the present invention had a sterilization rate of 85% and lacked appropriateness. That is, as in Comparative Example 1, the range of w / vp> 3.0 has a bactericidal action on 95% or more of microorganisms because the amount of bactericidal agent is small even when this efficient method is adopted. It will be impossible. On the other hand, the range of 0.05> w / pv is suitable in terms of the sterilization rate, but the amount of the sterilizing agent (hypochlorous acid or ozone) used for treating excess sludge increases. Therefore, in terms of running cost and capital investment, the advantage over the conventional method is reduced, which is not preferable.

Example 4
The treatment was carried out by further concentrating 20 liters / min of excess sludge having a solid content concentration of 1.3% similar to that used in Example 1. That is, surplus sludge having a solid content concentration of 1.3% was introduced into the concentration tank 14 to increase the solid content concentration to about 7%. In the concentration, air is blown as fine bubbles from a fine bubble generating device provided at the bottom of the concentration tank 14, and the fine bubbles adhere to solid organic matter dispersed and suspended in excess sludge water, thereby causing them to float. Was used. Note that a micro bubbler (MB400) manufactured by Nomura Electronics Co., Ltd. was used as the bubble generating device 15 for generating fine bubbles. A large amount of fine bubbles of less than 100 μm are supplied from the bubble generating device 15 into the water, and the solid content is floated and separated in a short time. The floating part was scraped off and flowed to the flow path as highly concentrated sludge. The thickness of the highly concentrated sludge in the flow path was 10 mm. The w / vp value at this time was 1.7. As described above, the solid content concentration of the scraped floating portion is about 7%, and the processing amount is reduced to about 1/5 compared with the first embodiment.

And in this Example 4, in order to obtain the processing capacity corresponding to the processing amount of 20 liters / minute of the excess sludge having a solid content concentration of 1.3% in Example 1, hypochlorine is added to the highly concentrated sludge in the flow path. Water containing 10 ppm of acid was ejected at a rate of 5 liters / minute · m ² to reduce excess sludge. In Example 4 as well, when the sterilization rate was determined in the same manner as in Example 1, the sterilization rate exceeded 96%.

Example 5
In Example 4 above, a highly concentrated sludge with a solid content concentration of 7% corresponding to 20 liter / min of excess sludge with a solid content concentration of 1.3% was treated, but in this Example 5, This was further developed and treated with an excess sludge having a solid content concentration of 7% and an amount increased to 6.5 liters / minute (35 liters / minute in terms of solid content concentration of 1.3%).

Then, the concentration of hypochlorous acid ejected into the highly concentrated sludge flowing through the flow path is set to 5.1 ppm, and the water containing 5 ppm of hypochlorous acid is contained in the highly concentrated sludge flowing through the flow path at 10 liters / minute · m. Ejected at a rate of ² to reduce excess sludge. Also in this Example 5, when the sterilization rate was determined in the same manner as in Example 1, the sterilization rate was almost 95% and w / pv was 2.97.

  The sterilization rates in Examples 4 to 5 are shown in Table 2 together with the treatment method, w / vp value, and the thickness of excess sludge flowing through the flow path.

It is a figure which shows typically the outline | summary of the process of the reduction system of the excess sludge of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 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 Flow path 10 Disinfection water supply device (water supply device containing hypochlorous acid or ozone)
DESCRIPTION OF SYMBOLS 11 Valve | bulb 12 Nozzle 13 Storage tank 14 Concentration tank 15 Bubble generator 16 High concentration sludge

Claims (3)

Concentrated sludge by concentrating the activated sludge-containing liquid obtained by microbial treatment in the aeration tank of organic sludge so that the solids concentration in the activated sludge is 0.8-2 mass% by gravity concentration method in the sedimentation tank. And the first step of returning a part of the concentrated sludge to the aeration tank and the remaining concentrated sludge as surplus sludge, flowing the surplus sludge into the flow path and providing it above the flow path. A second step in which water containing hypochlorous acid or ozone is sprayed downward from a large number of outlets in the form of a shower and acts on excess sludge, and the surplus treated with water containing hypochlorous acid or ozone A surplus sludge reduction system including a third step of returning sludge to the aeration tank again, wherein in the second step, the solid content in the surplus sludge flowing in the flow path per unit time is expressed as w (g), The concentration of chlorous acid or ozone is p (ppm) per unit time When the amount of water containing hypochlorous acid or ozone that is jetted downward in the form of an hour and acts on excess sludge is v (kg), w, p, and v are 0.05 ≦ w / vp ≦ A surplus sludge reduction system characterized by being in the range of 3.0. The surplus sludge reduction system according to claim 1, wherein in the second step, the thickness of the surplus sludge flowing through the flow path is 5 to 30 mm. In the second step, by sending fine air bubbles to the excess sludge, the solid content concentration of the excess sludge before the action of water containing hypochlorous acid or ozone is concentrated to 5% by mass or more and 20% by mass or less. After that, the surplus sludge reduction system according to claim 1, wherein water containing hypochlorous acid or ozone is allowed to act.

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