JP2005118642A - Water treatment method and apparatus, and ejector for water treatment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To further improve the generation efficiency of a hydroxy radical in accelerated oxidation treatment combining hydrogen peroxide with ozone treatment in comparison with conventional ones. <P>SOLUTION: Hydrogen peroxide is injected together with ozone by an ejector 4 for injecting the ozone to water to be treated. When hydrogen peroxide is injected into the upstream side of the ejector 4, the injected hydrogen peroxide reacts with organic substances to be consumed before it reaches the ejector 4, thereby a mixing ratio of hydrogen peroxide to ozone becomes inaccurate. When hydrogen peroxide is injected into the downstream side of the ejector 4, ozone injected before the hydrogen peroxide reacts with the organic substances to be consumed before it reacts with the hydrogen peroxide, thereby the above mixing ratio becomes inaccurate. As hydrogen peroxide is injected together with ozone by the ejector 4, their independent consumption can be avoided. As a result, the above mixing ratio becomes accurate and the proper mixing ratio can be obtained. Both hydrogen peroxide and ozone are vigorously agitated in the ejector 4. Thereby hydroxyl radicals are generated efficiently. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a water treatment method and apparatus using ozone and an ejector used for the water treatment, and more specifically, a water treatment method and apparatus by accelerated oxidation treatment using hydrogen peroxide together with the water treatment and the water treatment thereof. Related to the ejector.

  In recent years, there are many wastewaters (final disposal site leachate, incinerator exhaust gas cleaning wastewater, etc.) containing substances that are difficult to treat with ozone alone (hardly decomposable components such as COD and dioxins). As a method for treating organic wastewater containing such difficult-to-treat substances, accelerated oxidation treatment combining hydrogen peroxide with ozone treatment has been put into practical use.

  In the accelerated oxidation treatment in which hydrogen peroxide is combined with ozone treatment, hydroxy radicals having an oxidizing power greater than that of ozone are generated, thereby efficiently decomposing substances that are difficult to treat. As a water treatment system, one that injects ozone into water to be treated using an ejector is considered to be highly efficient, and hydrogen peroxide is usually injected upstream or downstream of the ejector (Patent Document). 1 and 2)

JP 2002-11485 A

JP 2002-79247 A

  Such accelerated oxidation treatment requires the generation of as many hydroxy radicals as possible. However, it has been found that the accelerated oxidation treatment so far generates fewer hydroxy radicals than the amount estimated from the ozone injection amount and the hydrogen peroxide injection amount.

  The applicant has already delivered a high-performance accelerated oxidation treatment system aimed at reducing dioxins and a small accelerated oxidation treatment system aimed at treating pool water. Hydrogen is injected in a gas-liquid separation reaction tank disposed upstream of the ejector.

  An object of the present invention is to provide a water treatment method and apparatus, and a water treatment ejector that can increase the production efficiency of hydroxy radicals in the accelerated oxidation treatment in which hydrogen peroxide is combined with ozone treatment.

  As described above, in the accelerated oxidation processing system that uses an ejector for ozone injection, hydrogen peroxide is injected upstream or downstream of the ejector. Specifically, the injection is performed in a tank upstream or downstream of the ejector. This is because the injection through the pipe is difficult due to the water pressure, and the forced injection by the pump is also difficult due to the invasion of bubbles, so the injection must be performed in the tank. As a result of detailed examination of such an injection point of hydrogen peroxide, the present inventor relates to an injection point at which hydroxy radicals are most efficiently generated, and an injection device that can be easily injected with an actual device as follows. I got a good knowledge.

  Ozone and hydrogen peroxide alone have oxidizing power and are consumed by reacting with organic substances in the water to be treated. For this reason, when hydrogen peroxide is injected in the tank on the upstream side of the ejector, the injected hydrogen peroxide reacts with the organic substance in the water to be treated before reaching the ejector and is consumed. On the other hand, when hydrogen peroxide is injected in the tank on the downstream side of the ejector, the ozone injected by the ejector is consumed by reacting with organic substances in the treated water before reaching the hydrogen peroxide injection point. End up. As a result, in any case, the mixing ratio of hydrogen peroxide to ozone becomes inaccurate.

  In the generation of hydroxy radicals in the accelerated oxidation treatment, the mixing ratio of hydrogen peroxide to ozone is important, and the amount of hydroxy radicals is reduced when hydrogen peroxide is too little or too much. That is, hydrogen peroxide is a radical scavenger consumed by hydroxy radicals as well as a source of hydroxy radicals. For this reason, when the amount of hydrogen peroxide is too small, the amount of hydroxy radicals is reduced. In addition, when the amount is too much, the amount of hydroxy radicals decreases due to the reaction of the hydroxyl radicals with excess hydrogen peroxide. There is an optimum value for the mixing ratio of hydrogen peroxide to ozone.

  For these reasons, ozone and hydrogen peroxide are effectively injected by simultaneous injection with no ineffective consumption of both and easy to ensure the optimum ratio, and the negative injection is the simultaneous injection point. The ejector found to be efficient. By the way, in the case of the conventional accelerated oxidation process in which hydrogen peroxide is injected in the upstream or downstream tank of the ejector, the injected ozone and hydrogen peroxide are ineffectively consumed until they are mixed. It cannot be obtained, and a decrease in the amount of hydroxy radicals produced is inevitable.

  The water treatment method and apparatus and the water treatment ejector of the present invention have been completed based on such knowledge, and the water treatment method is a water treatment method for injecting ozone into water to be treated using an ejector. Hydrogen peroxide is injected into the water to be treated by an ejector for injecting ozone.

  Further, the water treatment apparatus of the present invention includes a treated water distribution system that pressurizes treated water and distributes the treated water to an ejector, an ozone supply system that supplies ozone to the ejector, and a hydrogen supply system that supplies hydrogen peroxide to the ejector. And a hydrogen oxide supply system.

  Moreover, the ejector for water treatment of this invention is an ejector used in order to inject | pour ozone into to-be-processed water, and has two or more injection agent suction ports in a negative pressure mixing part.

  Here, at least one of the two or more injection agent suction ports is an ozone suction port, and at least one other is a hydrogen peroxide suction port.

  In the present invention, hydrogen peroxide is simultaneously injected by an ejector for injecting ozone. In the ejector, since the suction injection is performed, simultaneous injection of hydrogen peroxide is technically easy, and the simultaneous injection with the ejector has an advantage that both of them are sufficiently stirred. Such simultaneous injection and sufficient agitation in the ejector suppresses ineffective consumption of ozone and hydrogen peroxide. As a result of effective use of both and accurate management of the mixing ratio, the production efficiency of hydroxy radicals increases.

  Further, since the injection by the ejector is not the push-in by the pump but the suction, it is not necessary to inject into the pipe having a high water pressure, and a high-power pump is not necessary. Also, if hydrogen peroxide is left unattended, bubbles are generated, and in the case of pushing in, air bubbles are generated by these bubbles, so it is difficult to push and inject into the pipe with the actual device, but there is a problem with injection with the ejector. Absent.

  The amount of ozone injected is preferably 0.1 to 3000 mg / L, and 50 to 300 mg / L is preferable for the purpose of decomposing dioxins in the final disposal site leachate. If the amount is too small, the treatment effect is insufficient, and if it is too large, the economic efficiency is deteriorated.

  The mixing ratio of hydrogen peroxide to ozone is preferably selected within the range of 0.05 to 10, and when dioxins are targeted, it is preferably selected within the range of 0.05 to 1. As described above, if the mixing ratio is too small or too large with respect to the optimum ratio existing in this range, the production efficiency of hydroxy radicals is lowered. As for the optimum ratio, there is an optimum ratio specific to the quality of the water to be treated and the target substance, so the optimum ratio suitable for the water to be treated is found and designed by lab tests. Is done.

As the ozone gas to be used, a higher concentration ozone gas having an ozone concentration of 120 g / Nm ³ or more is preferable because the higher the ozone injection rate, the lower the gas amount and the better the ozone dissolution efficiency in water. When the amount of gas is small, the suction of hydrogen peroxide by the ejector is also stable.

  According to the water treatment method of the present invention, in the accelerated oxidation treatment in which hydrogen peroxide is combined with ozone treatment, the hydrogen radical is simultaneously injected by an ejector for injecting ozone, thereby improving the generation efficiency of hydroxy radicals. Processing efficiency can be increased.

  The water treatment apparatus of the present invention includes a treated water circulation system that pressurizes treated water and circulates it to an ejector, an ozone supply system that supplies ozone to the ejector, and a hydrogen peroxide that supplies hydrogen peroxide to the ejector. By supplying ozone and hydrogen peroxide at the same time with an ejector, the generation efficiency of hydroxy radicals can be increased as compared with the conventional method, and the processing efficiency can be increased.

  The ejector for water treatment of the present invention has two or more injection agent suction ports in the negative pressure mixing section, thereby enabling simultaneous injection of ozone and hydrogen peroxide. Thereby, the production | generation efficiency of a hydroxyl radical can be improved conventionally, and processing efficiency can be improved.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a water treatment apparatus showing an embodiment of the present invention, and FIG. 2 is a cross-sectional view of an ejector used in the water treatment apparatus.

  In this embodiment, it is a ternary accelerated oxidation treatment system that treats water to be treated containing a hardly decomposable harmful substance such as dioxins with ozone, hydrogen peroxide, and ultraviolet irradiation. The treated water is first introduced into the gas-liquid separation reaction tank 1 as shown in FIG. The gas-liquid separation reaction tank 1 is separated into an upstream part and a downstream part by a weir 2, and water to be treated is introduced into the downstream part of the gas-liquid separation tank 1.

  The water to be treated introduced into the downstream portion of the gas-liquid separation tank 1 is pressurized by the circulation pump 3 and sent to the sleeve-like ejector 4. As shown in FIG. 2, the ejector 4 includes a front throttle part 41, a straight negative pressure mixing part 42 and a throat part 43, and a forward widening part 44, which are connected from the inlet side to the outlet side. The negative pressure mixing part 42 can suck external gas and liquid through the two suction parts 45, 46, and the sucked fluid is fed into the water to be treated that has passed through the throttle part 41. It has a structure that can be mixed sufficiently.

  The two suction portions 45 and 46 are provided through the ejector 4 in the radial direction so as to communicate with the negative pressure mixing portion 42 at two symmetrical positions sandwiching the negative pressure mixing portion 42. One suction part 45 is an ozone suction part and is connected to the ozone generator 8. The other suction portion 46 is a suction portion for hydrogen peroxide, and is connected to the hydrogen peroxide injection device 9. Each suction part also serves as a base mounting part into which a base for connecting to the pipe is screwed.

  The water to be treated sent to the ejector 4 is simultaneously injected with ozone and hydrogen peroxide when passing through the negative pressure mixing section 42. The treated water that has passed through the ejector 4 is then sent to the UV reaction tower 10. The UV reaction tower 10 has a built-in ultraviolet lamp 11, and irradiates the water to be treated that passes through the reaction tower from the bottom to the top in the longitudinal direction. The treated water that has passed through the UV reaction tower 10 is returned to the upstream portion of the gas-liquid separation tank 1. And this to-be-processed water is extracted from the upstream part of the gas-liquid separation tank 1 as treated water.

  In the present embodiment, when the water to be treated passes through the ejector 4, ozone gas generated by the ozone generator 8 is injected into the water to be treated. Further, hydrogen peroxide is simultaneously injected by the hydrogen peroxide injection device 9. By the coexistence of ozone and hydrogen peroxide, a highly reactive hydroxy radical (OH.) Is generated (Chemical Formula 1).

  When hydrogen peroxide is injected on the upstream side of the ejector 4, the injected hydrogen peroxide is consumed by reacting with an organic substance or its reduced positive substance alone before reaching the ejector 4. The mixing ratio of hydrogen becomes inaccurate. When hydrogen peroxide is injected on the downstream side of the ejector 4, the previously injected ozone is consumed by reacting with an organic substance or its reduced positive substance alone until it starts reacting with hydrogen peroxide. Therefore, the mixing ratio of hydrogen peroxide to ozone is still inaccurate. However, when hydrogen peroxide is injected simultaneously with ozone by the ejector 4, each individual consumption is avoided, so that the mixing ratio becomes accurate and an appropriate ratio is obtained. Further, both of them are vigorously stirred in the ejector 4. For these reasons, hydroxy radicals are efficiently generated.

  The produced hydroxy radical reacts with an organic substance (RH) in the water to be treated to produce an organic radical (R.). The generated organic radical (R.) becomes an oxidation product by reaction with ozone. Thus, the organic substance in the water to be treated is decomposed by hydroxy radicals (Chemical Formula 2). Generation of a large amount of hydroxy radicals increases the decomposition efficiency of organic substances.

  In the accelerated oxidation treatment, the pH of the water to be treated is said to affect the treatment efficiency. That is, as shown in Chemical Formula 3, carbonate ions in the water to be treated become bicarbonate ions by dissociation at pH 9 or higher. Both carbonate and bicarbonate ions are radical scavengers consumed by radicals, but the reaction rate is about 10 times faster for bicarbonate ions than for carbonate ions. For this reason, it is desired to make the pH lower than 9 to suppress the formation of bicarbonate ions and suppress the consumption of radicals. That is, from the viewpoint of suppressing radical consumption, the pH is preferably smaller than 9.

  On the other hand, the dissociation of hydrogen peroxide represented by the formula (1) in Chemical Formula 1 proceeds in the alkaline region and does not proceed in the acidic region. For this reason, from the viewpoint of radical generation, the alkali range, that is, pH 7 or higher is preferable. Under such circumstances, it is generally preferred that the pH of water to be treated in the accelerated oxidation treatment in which hydrogen peroxide is combined with ozone is preferably controlled to 6.5 to 8.

  However, when ozone and hydrogen peroxide are simultaneously injected by the ejector 4, it has been confirmed from experiments by the present inventors that the pH of the water to be treated hardly affects the treatment efficiency. The reason is not clear, but the following is presumed. The reaction rate of production and consumption of hydroxy radicals is very fast. If ozone, hydrogen peroxide, and water to be treated meet at the same point and subjected to forced mixing, it is presumed that the reaction ends before the influence of pH appears.

  Next, comparative test results will be shown to clarify the effects of the present invention. FIG. 3 is a block diagram of the test apparatus, and FIGS. 4 to 6 are graphs showing the test results.

  In the test apparatus, a closed loop is formed in which the water to be treated in the water storage tank 12 is circulated to the water storage tank 12 through the ejector 14 and the reaction tower 15 by the circulation pump 13. In this test, ozone is injected by the ejector 14 at a rate of 2 mg per liter of water to be treated every minute. Hydrogen peroxide is injected at point A upstream from the ejector 14, point B in the ejector 14, point C further downstream from the reaction tower 15, and point D in the water storage tank 12. The injection amount of hydrogen peroxide is 0.2 mg per liter of water to be treated per minute, and the injection ratio of hydrogen peroxide to ozone is 0.1.

  The test was conducted while circulating the water to be treated in a closed loop. And the to-be-processed water was extracted from the sampling port in processing time 0, 60, 120, and 240 minutes, and TOC in to-be-processed water was measured. Further, during the test, the amount of exhausted ozone was measured with an exhausted ozone gas concentration monitor, and the ozone absorption efficiency was measured.

  FIG. 4 shows the ozone absorption efficiency when hydrogen peroxide is injected at the points A to D. FIG. 5 shows the change in TOC over time in each injection mode. As can be seen from both figures, the simultaneous injection in the ejector 14 (point B) is a high value for both ozone absorption efficiency and treatment efficiency.

  In addition, FIGS. 5A and 5B show the influence of the pH of the water to be treated on injection (simultaneous injection) in the ejector 14 (point B) and injection in the water storage tank 12 (point D). It is. It can be seen that the simultaneous injection is hardly affected by the pH of the water to be treated as compared with the tank injection.

  In the above-described embodiment, the ozone suction port 45 and the hydrogen peroxide suction port 46 are provided at the same position in the axial direction. However, the ozone suction port 45 and the hydrogen peroxide suction port 46 may be displaced in the axial direction as long as they are within the same negative pressure portion. Also in the circumferential direction, it is not always necessary to provide a symmetrical position across the center line.

It is a block diagram of the water treatment apparatus which shows one Embodiment of this invention. It is sectional drawing of the ejector used for the water treatment apparatus. It is a block diagram of a test apparatus. It is a graph which shows the influence which the injection | pouring point of hydrogen peroxide has on ozone absorption efficiency. It is a graph which shows the influence which the injection | pouring point of hydrogen peroxide has on process efficiency. It is a graph which shows the influence which pH of to-be-processed water has on processing efficiency about the case of simultaneous injection and tank injection.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Gas-liquid separation reaction tank 2 Weir 3 Circulation pump 4 Ejector 42 Negative pressure mixing part 45 Ozone suction part 46 Hydrogen peroxide suction part 8 Ozone generator 9 Hydrogen peroxide injection apparatus 10 UV reaction tower 11 UV lamp

Claims (4)

  A water treatment method for injecting ozone into water to be treated using an ejector, wherein water is injected into the water to be treated by an ejector for injecting ozone.   A treated water distribution system for pressurizing the treated water to flow to the ejector, an ozone supply system for supplying ozone to the ejector, and a hydrogen peroxide supply system for supplying hydrogen peroxide to the ejector. A water treatment device characterized.   A water treatment ejector, which is an ejector used for injecting ozone into water to be treated, and has two or more injecting agent suction ports in a negative pressure mixing section.   4. The water treatment ejector according to claim 3, wherein at least one of the two or more injection agent suction ports is an ozone suction port, and at least one other is a hydrogen peroxide suction port.

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