JP2011200844A - Apparatus and method for treating waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus for treating waste water capable of efficiently processing waste water containing dioxane at hundreds of mg/L high concentrations for decreasing the concentrations to several mg/L.SOLUTION: The apparatus for treating waste water 10 includes: a first reaction tank 12 in which waste water containing dioxane is injected; an ozone generator 16 for supplying ozone gas to the first reaction tank 12; an alkali agent tank 18 for supplying an alkali agent to the first reaction tank 12; a second reaction tank 14 in which the waste water treated by the first reaction tank 12 is injected; an ultraviolet irradiation apparatus which is placed in the second reaction tank 14; and a waste ozone tube 20 for supplying ozone gas to the second reaction tank 14.

Description

  The present invention relates to a wastewater treatment apparatus and a treatment method, and more particularly, to a wastewater treatment apparatus and a treatment method for removing dioxane contained in a high concentration of wastewater by oxidative decomposition.

  The organic oxidative decomposition method using ozone gas has long been used for deodorizing dyeing wastewater and decomposing odor components. Further, an accelerated oxidation method using ozone and ultraviolet rays in combination is applied to the hardly decomposable organic substances contained in the waste water. The accelerated oxidation method decomposes organic matter that cannot be removed by ordinary water treatment equipment (coagulation sedimentation or biological treatment).

  Dioxane, one of the hard-to-decompose organic substances, was regulated by the tap water standard in 2004 as a carcinogenic substance, and newly regulated as an environmental standard in 2009. Since the regulated value of environmental standards is a strict value of 0.05 mg / L or less, the accelerated oxidation method using ozone and UV is considered to be most effective as the dioxane treatment technology.

  The accelerated oxidation method generates OH radicals with excellent oxidizing power. The following three types are known as the accelerated oxidation method. (1) Combination of ozone and ultraviolet rays, (2) Combination of ozone and hydrogen peroxide, (3) Combination of ozone and alkaline agent (NaOH, CaO, etc.) generates OH radicals in water. To decompose dioxane.

  For example, Patent Document 1 treats endocrine disrupting substances and carcinogenic substances in two tanks: an ozone reaction tank using hydrogen peroxide and ozone, and an ultraviolet irradiation reaction tank using ultraviolet irradiation and ozone / hydrogen peroxide solution. Disclose the method. According to the method of Patent Document 1, it is effective when there is a suspension or chromaticity component in the target wastewater, and a carcinogenic substance such as dioxin or dioxane can be treated.

JP 2001-29966 A

  Patent Document 1 discloses that a dioxane concentration of 6.5 mg / L in wastewater can be treated to 0.45 mg / L. However, when the accelerated oxidation method of Patent Document 1 is applied to dioxane having a high concentration of several hundred mg / L, a large amount of hydrogen peroxide is consumed in addition to ozone, so that the utility of the chemical is low. In addition, there is a problem that the generation of OH radicals in ozone and hydrogen peroxide is slow and it takes a long time to decompose high-concentration dioxane, and it cannot be applied to the decomposition of high-concentration dioxane.

  Moreover, since the amount of hydrogen peroxide required is difficult to monitor, it will always be supplied quantitatively. Therefore, many times the required reaction amount is supplied. In addition, even if hydrogen peroxide is supplied to a reaction tank that uses ozone and ultraviolet rays, there is little merit just by promoting self-decomposition.

  In the method of Patent Document 1, excessive ozone gas or hydrogen peroxide is required to decompose dioxane contained in water at several hundred mg / L to 0.05 mg / L or less. Ozone generators, UV irradiation devices, etc. that become large-scale will become a system lacking practicality.

  The present invention has been made in view of such circumstances, and a wastewater treatment apparatus capable of efficiently treating wastewater containing dioxane having a high concentration of several hundred mg / L to a concentration of several mg / L at low cost and A processing method is provided.

  According to the aspect of the present invention, the waste water treatment apparatus is a first reaction tank into which waste water containing dioxane is injected, first ozone supply means for supplying ozone gas to the first reaction tank, and the first reaction. In order to adjust the pH of waste water in the tank, an alkali supply means for supplying an alkaline agent to the first reaction tank, a second reaction tank into which waste water treated in the first reaction tank is injected, and the second An ultraviolet irradiation device installed in the reaction tank; and second ozone supply means for supplying ozone gas to the second reaction tank.

  In the first reaction tank, wastewater containing dioxane is oxidized by the alkaline ozone method. Thereby, the density | concentration of a dioxane can be reduced to several tens mg / L of the waste water containing the dioxane of the density | concentration of several hundred mg / L at low cost and for a short time.

  In the second reaction tank, waste water containing dioxane having a concentration of several tens mg / L is oxidized by the ultraviolet ozone method. Thereby, the density | concentration of a dioxane can be reduced to several mg / L for the waste water containing the dioxane of the density | concentration of several tens mg / L with a small scale installation.

  According to a preferred aspect of the wastewater treatment apparatus of the present invention, the alkali supply means adjusts the pH of the wastewater to 9 or more. By adjusting the pH of the wastewater to 9 or more, ozone self-decomposition can be enhanced. OH radicals are generated during this self-decomposition process, and wastewater can be oxidized by the OH radicals.

  According to a preferred aspect of the wastewater treatment apparatus of the present invention, the first reaction tank treats wastewater having a dioxane concentration greater than 40 mg / L, and the second reaction tank treats wastewater having a dioxane concentration of 40 mg / L or less.

  The waste water is oxidized by the alkaline ozone method in the first reaction tank until the dioxane concentration is higher than 40 mg / L until the dioxane concentration becomes 40 mg / L. According to the alkaline ozone method, wastewater can be treated at a desired decomposition rate until the dioxane concentration reaches 40 mg / L. On the other hand, in the alkaline ozone method, the decomposition rate decreases when the dioxane concentration is 40 mg / L or less.

  Therefore, the waste water having a dioxane concentration of 40 mg / L or less is oxidized in the second reaction tank by the ultraviolet irradiation ozone method. According to the ultraviolet irradiation ozone method, even if the dioxane concentration is 40 mg / L or less, wastewater can be treated at a desired decomposition rate.

  According to a preferred aspect of the wastewater treatment apparatus of the present invention, the first ozone supply means is an ozone generator, and the second ozone supply means supplies the ozone gas discharged from the first reaction tank to the second reaction tank. It is an ozone injection tube to be introduced.

  Since the ozone gas discharged from the first reaction tank is used in the second reaction tank, the utilization efficiency of the ozone gas can be increased.

  According to a preferred aspect of the wastewater treatment apparatus of the present invention, an ozone monitor is installed in the ozone injection pipe, and the flow rate and / or concentration of the first ozone supply means is controlled based on the value obtained by the ozone monitor. Then, the numerical value of the ozone monitor is adjusted to 20 mg / NL or more and 30 mg / NL or less.

  If the ozone gas is in the range of 20 mg / NL or more and 30 mg / NL, the concentration of dioxane at a concentration of several tens mg / L can be reduced to 0.05 mg / L of dioxane.

  According to another aspect of the present invention, there is provided a wastewater treatment method, wherein a wastewater containing dioxane is alkalinized and oxidized with ozone gas, and the wastewater treated in the first step is irradiated with ultraviolet rays. And a second step of oxidizing with ozone gas.

  According to a preferred aspect of the wastewater treatment method of the present invention, the pH of the wastewater is set to 9 or more in the first step.

  According to a preferred aspect of the wastewater treatment method of the present invention, wastewater having a dioxane concentration greater than 40 mg / L is treated in the first step, and wastewater having a dioxane concentration of 40 mg / L or less is treated in the second reaction step.

  According to a preferred aspect of the wastewater treatment method of the present invention, the ozone gas in the second step is the ozone gas discharged in the first step.

  According to the preferable aspect of the wastewater treatment method of the present invention, the ozone gas discharged in the first step is monitored, and the amount of ozone gas is adjusted to 20 mg / NL or more and 30 mg / NL or less based on the obtained value.

  According to the present invention, wastewater containing a high concentration of dioxane of several hundred mg / L can be efficiently processed at a low cost to a concentration of several mg / L.

The general | schematic flow sheet of this Embodiment. The graph which shows the decomposition | disassembly rate of a dioxane. The graph which shows exhaust ozone gas concentration. The graph which shows inflow ozone gas concentration, treated-water dioxane concentration, and exhaust ozone concentration.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. The present invention will be described with reference to the following preferred embodiments, but can be modified in many ways without departing from the scope of the present invention, and other embodiments than the present embodiment can be used. be able to. Accordingly, all modifications within the scope of the present invention are included in the claims. In the present specification, a numerical range represented by using “to” means a range including numerical values described before and after “to”.

  FIG. 1 shows a flow sheet of the present embodiment. As shown in FIG. 1, the wastewater treatment apparatus 10 includes a first reaction tank 12 and a second reaction tank 14 arranged in series.

  An ozone generator 16 that is a first ozone supply means is connected to the first reaction tank 12. The ozone generator 16 supplies ozone gas to waste water in the first reaction tank 12. An alkaline agent tank 18 that is a means for supplying the alkaline agent is connected to the first reaction tank 12. An alkaline agent such as caustic soda is supplied from the alkaline agent tank 18. The waste water in the 1st reaction tank 12 is made into an alkaline state, for example, pH9 or more with an alkaline agent.

  An exhaust ozone pipe 20 is disposed between the first reaction tank 12 and the second reaction tank 14 and communicates the first reaction tank 12 and the second reaction tank 14. The ozone gas discharged from the first reaction tank 12 is supplied to the second reaction tank 14 via the exhaust ozone pipe 20. The exhaust ozone pipe 20 functions as an ozone injection pipe of the second reaction tank 14. An ozone monitor 22 is installed in the exhaust ozone pipe 20. The ozone monitor 22 measures the concentration of ozone gas discharged from the first reaction tank 12. A flow control device 28 is electrically connected to the ozone monitor 22 and the ozone generator 16. The fluid control device 28 controls the flow rate and / or concentration of the ozone gas of the ozone generator 16 based on the monitoring value of the ozone monitor 22.

  An ultraviolet lamp (not shown) is disposed in the second reaction tank 14. The ultraviolet lamp is connected to a UV power source 24. The ultraviolet lamp irradiates the waste water in the second reaction tank 14 with predetermined light energy. An ozone exhaust pipe 26 is connected to the second reaction tank 14. Ozone gas is discharged out of the system from the ozone exhaust pipe 26.

  A wastewater treatment method using the wastewater treatment apparatus 10 will be described. Waste water containing a hardly decomposable organic substance such as dioxane is supplied to the first reaction tank 12. Alkaline agent (for example, caustic soda) is supplied from the alkali agent tank 18 to the waste water in the first reaction tank 12. Thereby, waste water is adjusted to pH 9 or more. Further, ozone gas is introduced from the ozone generator 16 into the waste water. Since the pH of the wastewater is adjusted to 9 or more, the self-decomposition of ozone can be enhanced. OH radicals are generated during this self-decomposition process. The wastewater containing several hundred mg / L of dioxane is oxidized by this OH radical until the dioxane becomes several tens mg / L (for example, 40 mg / L). An efficient decomposition effect can be obtained by using ozone gas and an inexpensive alkaline agent in combination with wastewater containing several hundred mg / L of dioxane.

  Next, the waste water flowing out from the first reaction tank 12 flows into the second reaction tank 14. The wastewater is irradiated with predetermined light energy by an ultraviolet lamp installed in the second reaction tank 14. Further, ozone gas discharged from the first reaction tank 12 is blown into the second reaction tank 14 via the exhaust ozone pipe 20. OH radicals are generated by ultraviolet irradiation, and wastewater containing several tens mg / L (for example, 40 mg / L) of dioxane is oxidized until dioxane reaches 0.05 mg / L. According to the accelerated oxidation method using ultraviolet rays and ozone gas in combination, the dioxane decomposition effect is high and the dioxane can be decomposed to a low concentration.

  As a method of setting the dioxane concentration of the waste water flowing out from the first reaction tank 12 to 40 mg / L, for example, the TOC (total organic carbon concentration meter) of the outflow water from the first reaction tank 12 may be automatically measured. This has a correlation between the dioxane and the TOC concentration, and dioxane is usually 1.8 times the TOC, so that a control value can be set. In addition, when the drainage dioxane concentration is relatively stable, the facility operating conditions can be adjusted by sampling and analyzing the effluent from the first reaction tank 12.

  The ozone gas concentration of the ozone gas vented from the first reaction tank 12 to the second reaction tank 14 is measured by the ozone monitor 22 in the middle of the exhaust ozone pipe 20. The exhaust ozone concentration is adjusted to 20 mg / NL or more and 30 mg / NL or less. The exhaust ozone concentration is adjusted by the ozone gas concentration and / or the amount of ozone gas blown into the first reaction tank 12. Specifically, the fluid control device 28 controls the flow rate and / or concentration of the ozone gas in the ozone generator 16 based on the monitoring value of the ozone monitor 22.

  When the dioxane to be treated in the second reaction tank 14 is considered to be 10 mg / L, the necessary amount of ozone concentration supplied to the second reaction tank 14 is predicted. In this case, the minimum ozone gas concentration is 20 mg / NL.

  When the concentration of ozone gas supplied to the second reaction tank 14 exceeds 30 mg / NL, the concentration of ozone gas discharged from the second reaction tank 14 increases. For this reason, the load on the catalyst decomposition facility at the time of release into the atmosphere is increased. In the present embodiment, ozone gas exhausted from the first reaction tank 12 is efficiently utilized in the second reaction tank 14. Therefore, the amount of ozone gas discharged from the ozone exhaust pipe 26 is small.

  By feeding the waste water of the first reaction tank 12 having a pH of 9 or more to the second reaction tank 14, the second reaction tank 14 becomes weakly alkaline with a pH of 8-9. This pH increase has the effect of further promoting the reaction. In the first reaction tank 12, the pH in water is adjusted to 9 or more. It enhances the self-decomposition of ozone and generates OH radicals during this self-decomposition process. Therefore, if the treatment liquid from the first reaction tank 12 is in an alkaline state, there is an advantage that the reaction in the second reaction tank 14 is accelerated.

  FIG. 2 shows a comparative graph of decomposition characteristics of three types ((1) a combination of ozone and ultraviolet light, (2) a combination of ozone and hydrogen peroxide, and (3) a combination of ozone and an alkali agent). The vertical axis represents dioxane concentration (mg / L), and the horizontal axis represents time (min). As for the combination of ozone and ultraviolet light, and the combination of ozone and an alkaline agent, the dioxane decomposition proceeded at a dioxane decomposition rate of 200 mg / L · H or more, up to several tens of mg / L (approximately 40 mg / L). Since the reaction of the combination of ozone and hydrogen peroxide was slow, the dioxane decomposition proceeded slowly compared to the above two methods.

  About the combination of ozone and the alkali agent, when the dioxane concentration was 40 mg / L or less, the decomposition rate was lowered. On the other hand, the combination rate of ozone and ultraviolet rays hardly changed the decomposition rate of dioxane even at a trace concentration of several mg / L or less.

  FIG. 3 is a graph showing the concentration of exhaust ozone gas during the comparative experiment. The vertical axis represents the exhaust ozone concentration (mg / NL), and the horizontal axis represents time (min). In the combination of ozone and an alkaline agent, the exhaust ozone gas concentration increases when the dioxane concentration in water is about several tens mg / L. 30-40% of the inflowing ozone gas (ozone gas concentration at the time of experiment: 85 mg / NL) is exhausted. Compared with the combination of ozone and an alkali agent, the exhaust ozone gas concentration was 5 to 10% in the case of a combination of ozone and ultraviolet rays. In the combination of ozone and hydrogen peroxide, since the reaction was slow, 28 to 36% of the inflowing ozone gas was exhausted. As a result, the combination of ozone and hydrogen peroxide has a poor reaction efficiency of the supplied ozone, and it is necessary to supply a larger amount of ozone gas than the above two methods in order to obtain the same treated water quality.

  From the above comparative experiment, the following can be derived.

  (1) As for the combination of ozone and an alkaline agent, an efficient decomposition effect can be obtained by using ozone gas and an inexpensive alkaline agent in combination with wastewater containing several hundred mg / L of dioxane. On the other hand, when dioxane is at a low concentration, the degradation rate is low, so the efficiency is lowered.

  (2) The combination of ozone and ultraviolet rays has a high dioxane decomposition effect and can be decomposed to a low concentration. However, when the service life of the ultraviolet lamp is exceeded, the equipment needs to be renewed. Therefore, complicated maintenance is required, and the cost is higher than the combination of ozone and an alkali agent. On the other hand, the combination of ozone and ultraviolet light is effective for a relatively low concentration of dioxane. Moreover, even if the ozone gas concentration is low, a sufficient ozone utilization rate can be obtained.

  That is, when the dioxane concentration in water is greater than a certain concentration, the combination of ozone and an alkaline agent is highly efficient and economical. Moreover, when the dioxane concentration in water is below a certain concentration, the combination of ozone and ultraviolet light is highly efficient.

  FIG. 4 shows the relationship between the treated water DOX concentration and the exhaust ozone gas concentration discharged outside the tower with respect to the inflow ozone gas concentration. FIG. 4 shows an example of treatment performance when the supply ozone gas concentration is changed with respect to the wastewater containing 25 mg / L of dioxane flowing out from the first reaction tank. When the inflow ozone gas concentration is 20 mg / NL or more, the treated dioxane concentration is 0.5 mg / L or less. Even if the concentration of the inflowing ozone gas is increased further, the exhausted ozone becomes high, which is not efficient. In this figure, the wastewater containing dioxane 25 mg / L was taken as an example, but it has been confirmed that the wastewater containing dioxane concentration 40 mg / L is 0.5 mg / L or less when the ozone gas concentration is 30 mg / NL or more.

  From the above, it can be understood that dioxane decomposition can be efficiently performed in the second reaction tank by adjusting the outlet ozone gas concentration from the first reaction tank to 20 to 30 mg / NL. In order to maintain the ozone gas concentration flowing into the second reaction tank at 20 to 30 mg / NL, it is effective to monitor the exhaust ozone gas from the first reaction tank and adjust the ozone concentration supplied to the first reaction tank by the monitoring value It is.

  Table 1 summarizes the dioxane decomposition effect, the required amount of electricity, and cost comparison according to Example 1 and Comparative Examples 1 and 2. In Example 1, a combination of ozone and an alkaline agent is used as a front stage, and a combination of ozone and ultraviolet light is used as a rear stage. Comparative Example 1 is a combination of ozone and ultraviolet light, and Comparative Example 2 is a combination of ozone and hydrogen peroxide. According to Table 1, it can be understood that a combination of ozone and an alkaline agent in the preceding stage and a combination of ozone and ultraviolet light in the latter stage is economical and highly efficient.

  DESCRIPTION OF SYMBOLS 10 ... Waste water treatment apparatus, 12 ... 1st reaction tank, 14 ... 2nd reaction tank, 16 ... Ozone generator, 18 ... Alkaline agent tank, 20 ... Waste ozone pipe, 22 ... Ozone monitor, 24 ... UV power supply, 26 ... Ozone exhaust pipe, 28 ... Flow control device

Claims (10)

A wastewater treatment device,
A first reaction vessel into which waste water containing dioxane is injected;
First ozone supply means for supplying ozone gas to the first reaction tank;
Alkaline agent supply means for supplying an alkaline agent to the first reaction tank in order to adjust the pH of the wastewater in the first reaction tank;
A second reaction tank into which wastewater treated in the first reaction tank is injected;
An ultraviolet irradiation device installed in the second reaction tank;
Second ozone supply means for supplying ozone gas to the second reaction tank;
A wastewater treatment apparatus comprising:   The wastewater treatment apparatus according to claim 1, wherein the alkali supply means adjusts the pH of the wastewater to 9 or more.   The wastewater treatment apparatus according to claim 1 or 2, wherein the first reaction tank treats wastewater having a dioxane concentration greater than 40 mg / L, and the second reaction tank treats wastewater having a dioxane concentration of 40 mg / L or less. Processing equipment.   4. The wastewater treatment apparatus according to claim 1, wherein the first ozone supply unit is an ozone generator, and the second ozone supply unit is configured to remove ozone gas discharged from the first reaction tank. 2 Waste water treatment equipment that is an ozone injection pipe to be introduced into the reaction tank.   5. The wastewater treatment apparatus according to claim 4, wherein an ozone monitor is installed in the ozone injection pipe, and the flow rate and / or concentration of the first ozone supply means is controlled based on a value obtained by the ozone monitor. The waste water treatment apparatus which adjusts the numerical value of the ozone monitor to 20 mg / NL or more and 30 mg / NL or less. A wastewater treatment method,
A first step of converting wastewater containing dioxane into an alkaline state and oxidizing with ozone gas;
A wastewater treatment method comprising: a second step of oxidizing the wastewater treated in the first step with ultraviolet irradiation and ozone gas.   The wastewater treatment method according to claim 6, wherein in the first step, the pH of the wastewater is 9 or more.   The wastewater treatment method according to claim 6 or 7, wherein in the first step, wastewater having a dioxane concentration greater than 40 mg / L is treated, and in the second reaction step, wastewater having a dioxane concentration of 40 mg / L or less is treated. Method.   The wastewater treatment method according to any one of claims 6 to 8, wherein the ozone gas in the second step is the ozone gas discharged in the first step.   The wastewater treatment method according to claim 9, further comprising the step of monitoring the ozone gas discharged in the first step and adjusting the amount of ozone gas to 20 mg / NL or more and 30 mg / NL or less based on the obtained value. Wastewater treatment method.

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