JP2005254079A - Ozone oxidation system for sewage - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-cost ozone oxidation system for sewage which has high ozone utilization efficiency, can efficiently oxidize organic pollutants, such as bacteria and organic chemical substances, in the sewage, does not exert a bad influence upon environment and health, and does not require a high equipment cost and running cost. <P>SOLUTION: In the ozone oxidation system for the sewage which oxidizes the sewage containing the organic pollutants by using ozone, fine bubbles of a ozone-containing gas are diffused into the sewage, a plurality of diaphragms is vibrated at a vibration frequency of 20-70 Hz, and the sewage is oxidized with ozone while being agitated. It is preferable that the size of the fine bubble of the ozone-containing gas is 5-300 μm. The ozone oxidation system can treat surplus sludge-containing sewage as a target. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a wastewater ozone oxidation treatment system, and more specifically, wastewater ozone that can efficiently oxidize wastewater containing organic pollutants with a small amount of ozone and that does not adversely affect the environment and health. The present invention relates to an oxidation treatment system.

Conventionally, various methods have been proposed for purifying sewage containing organic pollutants such as bacteria and organic chemicals by oxidative decomposition using ozone having strong oxidizing power.
JP-A-6-15282 Japanese Utility Model Publication No. 5-80291

  The basic structure of these conventional methods is that air or oxygen gas containing ozone generated by silent discharge or the like is diffused as bubbles into the sewage through an air diffuser or ejector disposed in the sewage to be treated. At the same time, it aims to dissolve these bubbles in water as much as possible by the water flow of the ejector. In other words, ozone dissolved in water is allowed to act on organic pollutants such as bacteria and organic chemicals in the sewage, and it is sterilized or oxidatively decomposed by the extremely excellent oxidizing power of ozone.

  The biggest problem of such a conventional method is that bubbles containing ozone float on the surface of the sewage liquid in a very short time and are diffused into the atmosphere, and only a small amount of ozone enters the water. It cannot be dissolved. Generally, the amount of ozone dissolved in water is about several percent of the amount blown by an ejector, etc., and most of the generated ozone is wasted in the atmosphere without being used for its original purpose. Will be. On the other hand, ozone is also a gas that adversely affects health, and there are many cases where facilities for detoxifying ozone released into the atmosphere are required. Therefore, conventional methods that dissolve ozone in water and oxidize organic pollutants such as bacteria and organic chemicals in sewage must produce ozone in excess of the amount required for oxidation. In addition, due to health considerations, exhaust facilities and the like are indispensable, and there are problems that the cost of facilities including maintenance and running costs are inevitably increased.

Also, in order to increase the reactivity between ozone and organic pollutants, make ozone fine bubbles and stir it with a rotor such as a propeller to efficiently oxidize the fine bubbles of ozone into organic pollutants. The proposal has become.
JP-A-8-1332099 JP 2000-189981 A

  In the methods described in Patent Documents 3 to 4, it is possible to create a flow superior to the buoyancy of fine bubbles by stirring up to a certain level, but because of the unidirectional flow that is not turbulent, There was also a problem that the frequency of contact with organic pollutants was much lower. In addition, the high-speed stirring has problems that air is involved and the tank structure is limited to a circular shape. Furthermore, the power required for rotation increases with the size of the rotating body, and the methods described in Patent Documents 3 to 4 cannot be said to be suitable for high-speed stirring in a large-scale tank. .

  The present invention solves the problems of the prior art as described above, has high ozone use efficiency, can efficiently oxidize organic pollutants such as bacteria and organic chemicals in wastewater, and An object of the present invention is to provide an inexpensive ozone oxidation treatment system for sewage that does not adversely affect the environment and health, and does not require expensive equipment costs or large running costs.

  The present invention relates to a system that oxidizes sewage containing organic pollutants such as bacteria and organic chemicals using ozone, and disperses fine bubbles of gas containing ozone into the sewage, thereby providing a plurality of diaphragms. By vibrating at a frequency of 20 to 70 Hz and oxidizing the wastewater with ozone while stirring the wastewater, the use efficiency of ozone is high, and organic pollutants such as bacteria and organic chemicals in the wastewater are efficiently oxidized. The present invention solves the above-mentioned problems by providing an inexpensive ozone oxidation treatment system that can be performed, has no adverse effects on the environment and health, and does not require expensive equipment costs and large running costs.

  In the present invention, two techniques are incorporated in order to solve the above-mentioned problems. One of them is the microbubble generation of ozone. In order to efficiently dissolve the same amount of ozone in water, it is advantageous to increase the total surface area of the bubbles, and this can be realized by making the bubbles of ozone finer.

  In addition, the effect of micronization of ozone bubbles is not limited to that. Ozone bubbles directly act on organic pollutants such as bacteria and organic chemicals that aggregate at the gas-liquid interface of the bubbles due to surface tension. The frequency has increased dramatically, and it has been found that not only the oxidative action of dissolved ozone, but also gaseous ozone contributes to the oxidative decomposition of organic pollutants.

  Since the ratio that contributes to the oxidation treatment of the organic pollutant of ozone in the gas state is relatively low, as a second countermeasure to further increase this, in the present invention, the stirring technique using the vibrations of a plurality of diaphragms Has been introduced. The purpose is to create a high-speed turbulent flow, and it is necessary to dramatically increase the residence time in the sewage without causing the fine bubbles to rise to the surface of the sewage in a short time. Since the flow generated by this high-speed turbulent flow is larger than the buoyancy of the microbubbles themselves, the bubbles move in the sewage up and down, left and right for a long time as if they were suspended particles. The contact frequency is greatly improved.

  Therefore, in the present invention, by introducing the above two improvement measures, the ratio of contributing directly to the oxidation action on the surface of the fine bubbles is greatly increased without dissipating the generated ozone into the atmosphere, and the generated ozone is almost 100%. % Effective use. As a result, it is possible to solve the low efficiency of ozone use, the equipment cost, environmental and health problems caused by the conventional method, and to provide an inexpensive and safe ozone oxidation treatment system that users demand. It becomes possible.

  According to the present invention, ozone is highly used, organic pollutants in wastewater can be efficiently oxidized, and there is no adverse effect on the environment and health, and expensive equipment costs and large running costs An inexpensive ozone oxidation treatment system for wastewater that does not require costs can be provided.

  That is, in the present invention, since the use efficiency of ozone is high, the amount of ozone used is small, and the organic pollutants in the sewage can be efficiently oxidized, so the purification efficiency of the sewage is increased. . In the present invention, the generated ozone is rarely dissipated in the atmosphere, so there is no adverse effect on the environment and health, and in addition to the effective use of ozone, exhaust facilities are unnecessary, Sewage can be oxidized without expensive equipment and large running costs.

  In the present invention, it is necessary to vibrate the vibration frequency of the diaphragm in the range of 20 to 70 Hz. If the vibration frequency of the diaphragm is set within this range, the reaction efficiency between ozone and organic pollutants in the sewage can be improved without disturbing the surface of the ozone oxidation treatment tank and releasing ozone into the atmosphere. it can. The material and size of the diaphragm can be appropriately selected according to the size of the ozone oxidation treatment tank to be stirred, but any material that does not cause problems in mechanical strength and corrosion resistance can be used. In general, 1/3 to 1/4 of the length of the ozone oxidation treatment tank (this is a case where a diaphragm is installed only on one side wall surface, and about half of that when a diaphragm is installed on both wall surfaces) is preferable. The thickness is not particularly limited as long as there is no problem with durability during vibration. Further, the number and amplitude of the diaphragm may be appropriately selected depending on the properties of the sewage and the tank structure, but the amplitude of the diaphragm is preferably about 1 to 20 mm.

  In the present invention, the size of fine bubbles of ozone-containing gas is preferably 5 μm to 300 μm. By adjusting the size of the bubbles within this range, buoyancy can be reduced, the amount released to the atmosphere can be reduced, and sewage can be purified with less energy. A more preferable range of the size of the bubbles is 20 μm to 100 μm. The size of the gas bubbles containing ozone can be controlled by the following method, for example. As shown in the examples described later, in the method of stirring the gas introduced into the water at high speed with the rotating blades of the motor together with the water, the shape can be controlled by the shape of the rotating blades, the number of rotations, the amount of introduced gas, etc. . The size of the bubbles can be measured by, for example, a photographed image of bubbles passing near the focal point with a microscope scale plate and a fiberscope type actual microscope.

  Moreover, in the ozone oxidation treatment system of the present invention, when sewage containing excess sludge is targeted, the solubilization rate of excess sludge can be increased with less energy, which is effective.

  Next, a preferred embodiment of the present invention when oxidizing sewage containing organic pollutants using ozone is described with reference to FIG.

  In FIG. 1, sewage 1 containing an organic pollutant is stored in an ozone oxidation treatment tank 2. Ozone is introduced into the microbubble generator 4 as air or oxygen gas containing ozone generated by the ozone generator 3, where it is made into microbubbles, and the sewage 1 in the ozone oxidation treatment tank 2 from the microbubble generator 4. Dissipated as fine bubbles. At that time, the size of the bubbles is preferably adjusted to 5 μm to 300 μm. A stirring device 7 including a plurality of diaphragms 5 and a motor 6 for driving the diaphragms 5 is attached to one or the wall surface of the ozone oxidation treatment tank 2, and the vibrations of the diaphragms 5 cause vibrations. The high-speed turbulent flow is efficiently generated in the sewage 1 in the ozone oxidation treatment tank 2. As shown in the drawing, the plurality of diaphragms 5 are composed of a plurality of plates attached substantially perpendicular to the sewage 1 from the wall surface of the ozone oxidation treatment tank 2. In the present invention, the frequency of the diaphragm 5 is 20. It is controlled to ˜70 Hz.

  The microbubbles diffused in the sewage 1 in the ozone oxidation treatment tank 2 from the microbubble generator 4 are extremely small in size, and therefore, the ozone oxidation treatment is performed by the turbulent flow generated by the stirring much stronger than the buoyancy of the microbubbles. Continue to move up and down, left and right in the tank 2.

  From the fine bubbles of ozone that stay in the ozone oxidation treatment tank 2 for a long time due to this stirring, dissolved ozone is efficiently supplied, and the frequency of direct contact between the ozone-containing bubbles and the organic pollutant is increased. Due to the adhesion of organic pollutants, the oxidizing power of the bubbles themselves directly acts on the organic pollutants. As a result, almost 100% of the generated ozone is consumed for the oxidation of organic pollutants in the sewage and hardly leaks outside. FIG. 1 schematically shows the treatment process of the ozone oxidation treatment system for sewage according to the present invention, and the fine bubbles are shown in a large size so that the fine bubbles can be easily seen. The size of about 5 μm to 300 μm is preferable, and actually it is much smaller than other members.

  In the above-described prior art, the method generally uses the oxidizing power of ozone dissolved in water, but in the present invention, as well as contributing to the oxidation treatment of ozone dissolved in water, in addition to the above, Since ozone in the fine bubbles directly contributes to the oxidation treatment, the speed of the oxidation treatment with ozone is further accelerated. That is, according to the present invention, in addition to the effective utilization of ozone almost 100%, the oxidation treatment is accelerated by the improvement of the contact frequency with the oxide (organic pollutant) due to the high-speed turbulent flow. This is considered to be due to the fact that ozone present as a gas has a longer life than dissolved ozone, and the effect becomes obvious.

  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
In Example 1, water containing parachlorophenol is selected as the wastewater to be subjected to the ozone oxidation treatment, which is based on the following reason.
Among chlorinated compounds, chlorophenols such as parachlorophenol are materials that are frequently used in organic synthesis, etc., but they are hardly degradable and toxic. It cannot be purified. However, even this refractory chemical-containing sewage is oxidized by ozone, and its molecular weight is reduced by ozone oxidation. Therefore, it can be purified by biological treatment following ozone oxidation. In other words, biological treatment and purification of chlorophenols cannot normally be expected, but when combined with ozone oxidation treatment, biodegradability can be obtained by reducing the molecular weight by ozone oxidation treatment. Is possible. In Example 1, this will be clarified.

  In this Example 1, water containing 80 mg / liter of parachlorophenol was selected as waste water to be subjected to ozone oxidation treatment, 15 liters of water was injected into the ozone oxidation treatment tank, and ozone-containing oxygen gas having a concentration of 8000 ppm generated by the ozone generator was used. Through a fine bubble generator (manufactured by Nomura Electronics Co., Ltd.), fine bubbles having a size of 50 μm to 100 μm were generated, and 0.5 liters per minute was introduced into the sewage in the ozone oxidation treatment tank. At the same time, the diaphragm was operated, and after stirring for 10 minutes, the supply of fine bubbles and stirring were stopped. As the vibration plate, a stainless steel (SUS) plate having a size of 60 mm in width, 120 mm in length, and 5 mm in thickness was used. Four diaphragms were installed in a rectangular ozone oxidation treatment tank having a water depth of 200 mm, the frequency was 50 Hz, and the amplitude was 6 mm.

  Next, the sewage subjected to the ozone oxidation treatment as described above was aerated by a biological treatment method. That is, the above-mentioned ozone-oxidized sewage was placed in an Erlenmeyer flask, and while adding nutrients thereto, activated sludge was added and aerated while stirring. The MLSS of the used activated sludge was 3500 mg / liter, and after aeration treatment for 3 days, the COD of filtered water was measured. The results are shown in Table 1 below.

Example 2
Ozone oxidation treatment followed by ozone oxidation treatment in the same manner as in Example 1 except that the ozone-containing oxygen gas having a concentration of 8000 ppm produced by the ozone generator was diffused through the air diffusing tube to 0.5 liters per minute into the sewage in the ozone oxidation treatment tank. Biological treatment was performed. The size of the bubbles diffused through the air diffuser as described above was 1 mm to 2 mm. And COD of the water which performed the ozone oxidation process and the biological treatment following it as mentioned above was measured. The results are shown in Table 1 below.

Comparative Example 1
Ozone oxidation treatment was performed in the same manner as in Example 1 except that generation and introduction of ozone-containing bubbles were performed with an air diffuser and stirring was performed simultaneously with rotating blades. Subsequent biological treatment was performed in the same manner as in Example 1. The size of bubbles generated by the air diffuser was 2 mm to 3 mm. Then, the COD of water subjected to ozone oxidation treatment and subsequent biological treatment was measured as described above. The results are shown in Table 1 below.

Comparative Example 2
Except for the frequency of the diaphragm being 100 Hz, ozone oxidation treatment and subsequent biological treatment were performed in the same manner as in Example 1. Then, the COD of water subjected to ozone oxidation treatment and subsequent biological treatment was measured as described above. The results are shown in Table 1 below.

  As described above, Table 1 shows COD (chemical oxygen demand) in water after the ozone oxidation treatment and the subsequent biological treatment in Examples 1-2 and Comparative Examples 1-2. Shows the COD of the raw water (that is, the water to be treated).

  As is clear from the results shown in Table 1, Examples 1 and 2 had less COD after biological treatment than Comparative Examples 1 and 2, and were able to efficiently purify sewage. From this result, sewage containing parachlorophenol cannot be purified in such a short time even if biological treatment is subsequently performed by conventional ozone oxidation treatment, but the ozone oxidation treatment and biological treatment in the configuration of the present invention It turns out that it can purify efficiently by combining. This is considered to be because the ozone oxidation treatment of the present invention was able to efficiently reduce the molecular weight of hardly decomposable parachlorophenol and convert it into a biodegradable substance. On the other hand, in the conventional ozone oxidation treatment, the efficiency of the oxidative decomposition reaction is low, and sufficient biodegradability cannot be obtained in a short time treatment, so that the final COD remains high. Further, as is clear from the comparison between Example 1 and Example 2, COD can be further reduced by setting the bubble size of the gas containing ozone to 5 to 300 μm.

Example 3
In Example 3, an example will be described in which the present invention is applied to surplus sludge discharged from a sewage treatment plant as sewage inhabited by bacteria and the like. Excess sludge is the water excluding the supernatant water after wastewater treatment in a sewage treatment plant that purifies organic wastewater by microbial treatment, and contains about 0.6 to 1.5% of bacterium that has grown. As for this excess sludge, efforts are being made to reduce the volume microbiologically for the purpose of reducing the discharge amount, and oxidation treatment with ozone is one effective method. In sludge volume reduction, biodegradability by microorganisms is promoted by so-called solubilization in which cell membranes are oxidized to elute cell contents. Therefore, it is required to solubilize as efficiently as possible and with a small ozone blowing amount.

  15 liters of surplus sludge having a solid content concentration of 0.6% (hereinafter sometimes referred to as “sludge” for simplification) is introduced into an ozone oxidation treatment tank, and the ozone oxidation is performed through the same fine bubble generator as in Example 2. Ozone-containing oxygen gas having a bubble size of 50 μm to 100 μm was diffused into the sludge in the treatment tank at 0.5 liters per minute. At the same time, the diaphragm installed on the inner wall of the ozone oxidation treatment tank was vibrated and stirred for 5 minutes, and then the supply of fine bubbles was stopped, and stirring was further performed for 5 minutes. The diaphragm is a stainless steel plate having a width of 60 mm, a length of 120 mm, and a thickness of 5 mm. Four diaphragms are installed in a rectangular ozone oxidation tank having a water depth of 200 mm, the frequency is 50 Hz, and the amplitude is Was 6 mm. Then, DOC (dissolvable organic carbon concentration) and TOC (total organic carbon concentration) of raw water sludge and the treated water were measured, and the ratio (DOC / TOC) was obtained.

Comparative Example 3
Excess sludge having a solid content concentration of 0.6% was treated in the same manner as in Example 3 except that the ozone supply method and the stirring method were changed to the conventional technology. That is, while stirring the sludge with the rotary blade, the ozone-containing oxygen gas having a concentration of 8000 ppm is supplied to the surplus sludge in the ozone oxidation treatment tank at 0.5 liter / min with the air diffuser, the gas supply is 2.5 liters, and the stirring is 10 minutes. The sludge was subjected to ozone oxidation treatment under the conditions described above. The size of bubbles generated by the air diffuser was 2 mm to 3 mm. Thereafter, the DOC and TOC of the treated water were measured in the same manner as in Example 3, and the ratio (DOC / TOC) was determined. The results are shown in Table 2.

  Table 2 shows TOC, DOC, and DOC / TOC of the water treated in Example 3 and Comparative Example 3 as described above. In Table 2, raw sludge (solid content concentration) TOC, DOC, and DOC / TOC of 0.6% surplus sludge) are also shown.

  As shown in Table 2, when treated in Example 3, DOC / TOC is as high as 0.92, 92% of TOC in sludge is changed to DOC, treatment efficiency is high, and TOC in sludge. Was efficiently changed to DOC.

  From this result, it can be seen that when treated with the ozone oxidation treatment system of the present invention, the cell membrane of the microorganism is destroyed by the oxidizing power of ozone, and solubilization in which the cytoplasm is eluted in water is proceeding very efficiently. . This is because fine ozone-containing bubbles stay in the sludge for a long time, and they efficiently generate dissolved ozone, and also move by high-speed stirring, which could not be expected with conventional ozone oxidation treatment, This is thought to be due to the result of a dramatic increase in the contact frequency between the ozone and the oxide. In the treatment process in Comparative Example 3, bubbles from the air diffuser floated on the water surface of the oxidation treatment tank within a short time, and the odor was remarkable. However, in Example 3, the odor of ozone was not recognized.

Example 4
In Example 4, the livestock urine sewage after biological treatment was used as the organic pollution-containing sewage, and the ozone oxidation treatment was performed. Livestock urine sewage after biological treatment, like methane nitrification liquid, has a brownish hue that cannot be removed by biological treatment, so it is required to decolorize it when it is discharged into the river. This pigment component is an organic polymer that is hardly degradable to microorganisms.

  15 liters of livestock urine sewage (COD value: 240 mg / l) after biological treatment was introduced as raw water into an ozone oxidation treatment tank. The ozone-containing oxygen gas having a concentration of 8000 ppm produced by the ozone generator as in Example 2 is supplied to the sewage in the ozone oxidation treatment tank through the fine bubble generator used in Example 2 at 0.5 liters per minute. Then, the vibration plate was vibrated, and after stirring for 5 minutes, the supply of fine bubbles was stopped, and only stirring by vibration of the vibration plate was further performed for 5 minutes. In this process, the color of the liquid was gradually decolored and became almost transparent after 10 minutes of treatment. The COD value of the sewage after the treatment decreased to 150 mg / liter, and was below the river discharge standard value (160 mg / liter).

Comparative Example 4
The fine bubble generating apparatus of Example 3 was replaced with an ejector, and ozone gas having the same concentration as Example 3 was blown into the ozone oxidation treatment tank for 10 minutes. In this case, stirring was performed with a water flow generated by an ejector. When this ozone oxidation treatment was carried out for 10 minutes, the COD value was 200 mg / l, and the color still remained considerably.

It is a figure which shows typically the outline | summary of the process of the ozone oxidation processing system of the sewage of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sewage 2 Ozone oxidation treatment tank 3 Ozone generator 4 Microbubble device 5 Vibrating plate 6 Motor 7 Stirrer

Claims (3)

An ozone oxidation treatment system for sewage that oxidizes sewage containing organic pollutants using ozone, wherein fine bubbles of a gas containing ozone are diffused into the sewage, and a plurality of diaphragms have a frequency of 20 to 70 Hz. The wastewater ozone oxidation system is characterized in that the wastewater is oxidized and oxidized with ozone while stirring the wastewater. 2. The ozone oxidation treatment system for wastewater according to claim 1, wherein the size of fine bubbles of gas containing ozone is 5 to 300 [mu] m. 2. The wastewater ozone oxidation treatment system according to claim 1, wherein surplus sludge is contained in the wastewater.

Images