JP6708864B2 - VOC contaminated water purification method - Google Patents

Description

The present invention relates to the purification treatment process of VOC contaminated water with microbubbles (less than 1mm from 1 [mu] m).

In general, VOC (volatile organic compound) countermeasures against groundwater pollution include methods for cleaning contaminated soil and groundwater in-situ, methods for extracting contaminated soil gas, methods for pumping contaminated groundwater, methods for excavating and removing contaminated soil, etc. Is mentioned.

Among them, in the method of pumping contaminated groundwater, the contaminated water is introduced into a water tank, and bubbling (contaminated water is 1 mm or more) of the contaminated water is carried out by an air diffuser or an ejector pump provided in the water to purify gas and liquid (aeration treatment). ) Has been done.

FIG. 5 shows an example thereof. In the figure, 1 is a raw water tank for storing contaminated water, 2 is an aeration tank, and a raw water pump 3 is placed in the raw water tank 1, whereby the aeration tank 2 is contaminated with water. Is sent.

The aeration tank 2 is provided with an underwater ejector 4 equipped with an intake pipe 5, by which contaminated water is bubbled to volatilize and desorb VOCs from the contaminated water, and the air containing the volatilized and desorbed VOCs is gas-liquid separated. The air is sent to the tank 6, the activated carbon is adsorbed on the activated carbon by the activated carbon adsorption tower 7, and the removed air is sent to the VOC management facility by the blower 8.

In addition, a drainage pit 9 having a drainage pump 10 installed therein is formed in the aeration tank 2, and the water obtained by volatilizing and desorbing VOCs from the contaminated water is sent to the muddy water treatment facility 11 by the drainage pump 10.

The method shown in FIG. 5 is a method of contacting contaminated water containing a volatile organic compound (VOC) with bubbles generated in an air diffuser or the like and contaminated water to remove VOC by gas-liquid separation. However, if this method is used to deal with a large amount of contaminated water, the tank will become large.

The purification efficiency of contaminated water largely depends on the uniformity of the aeration treatment of contaminated water in the treated water tank, but it is difficult to evenly agitate the entire aeration tank, so it is not possible to ensure uniformity with a single bubbling system. Difficult, especially in larger tanks.

On the other hand, fine air bubbles obtained by adding a device and a device in which a shirasu porous glass film (SPG film) is sealed and fixed are extremely uniform and fine, and the time during which the air bubbles stay in water Since it has a property that is not found in bubbles of millimeter size or larger, such as for an extremely long period of time, it is called "micro/nano bubble" and applied to various fields.

For example, micronization of bubbles increases the surface area in contact with water, and the bubbles remain for a long time and some of them disappear as they are. it can. Utilizing this property, plants as shown in the following patent documents, an oxygen water production device for the purpose of producing high-concentration dissolved oxygen water that promotes the growth of marine products, and water quality by improving the anoxic state of closed system water areas such as lakes and marshes. It is used for aeration treatment for the purpose of increasing oxygen concentration in water, such as for purification.
JP, 2009-18296, A

However, when applying to a method of separating VOCs by gas-liquid separation by contacting contaminated water containing volatile organic compounds (VOC) with bubbles generated in an air diffuser and contaminated water, the treatment target Micro/nano-sized micro bubbles, which can take a large contact surface area with water, are effective for gas-liquid separation, but they are another characteristic of micro pores. Therefore, since the VOCs that have been gas-liquid separated are dissolved again in the treated water, there is almost no actual application to the aeration treatment mainly using the gas-liquid separation using the fine bubbles.

The object of the present invention is to eliminate the disadvantages of the conventional example and to establish a new aeration treatment method utilizing the characteristics of micro/nano bubbles. An object of the present invention is to provide a method for purifying VOC-contaminated water, which can be made smaller than the capacity of an aeration tank used in conventional aeration processing by circulating treatment.

In order to achieve the above-mentioned object, firstly , the present invention provides a ceramic porous membrane tube having micro/nanopores and a nozzle capable of sealing and fixing the porous membrane tube and supplying high-pressure air to the sides, and at both ends thereof. When a ceramic module having a double-tube structure with an outer cylinder column having an opening through which liquid can be passed is used, and high-pressure air supplied from the outer cylinder column side is aerated from the outside of the porous membrane tube to the inside. Contacting the generated micro/nano-sized fine bubbles with the contaminated water containing VOC (volatile organic compound) passing through the porous membrane tube without adding a surfactant, second, ceramic The gist is that the pore diameter of the porous membrane tube is 1 mm>φ>0.05 μm.

The aeration process with micro/nano bubbles is more efficient than the aeration process with bubbles exceeding the usual millimeter size because of the size of the contact area with the water to be treated by the fine bubbles, and the gas-liquid between VOC and the water to be treated is more efficient. Separation can be expected, but at the same time, it was not an effective method as an aeration process for gas-liquid separation due to the VOC re-dissolution process (reverse process) due to fine bubbles.

Specifically, the VOC transfer process to the fine bubbles maintains the micro/nano-sized pore size, and after the transfer (after gas-liquid separation), it becomes bubbles of millimeter size or more and is quickly removed from the water to be treated. It is necessary.

According to the present invention, by not intentionally adding a surfactant, the aggregation of fine bubbles is promoted, and the millibubbles containing a high concentration of VOCs are rapidly removed from the water to be treated, thereby utilizing the characteristics of micro/nano bubbles. Highly efficient aeration process can be realized.

As described above, the method for purifying VOC-contaminated water according to the present invention establishes a novel aeration treatment method that makes use of the characteristics of micro/nano bubbles, and the gas-liquid separation is performed in a compact module. By circulating the target water, the capacity of the aeration tank used in the conventional aeration treatment can be reduced.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is an explanatory view showing the principle of a method for purifying VOC-contaminated water according to the present invention, FIGS. 2 and 3 are front views of a ceramic module, and FIG. 3 is a sectional view taken along the line AA of FIG.

The ceramic module has a double tube structure including a ceramic porous membrane (SPG) tube 24 having a micro/nanoporous layer and an outer cylinder column 23 capable of sealing and fixing the ceramic porous membrane tube 24.

In the drawing, 18 is an O-ring fixing metal fitting, and 19 is a fixing nut, which seals and fixes the upper end of the ceramic porous membrane tube 24, and the lower end is sealed and fixed by the O-ring fixing metal fitting 20 and the fixing/adapting adapter 21. Reference numeral 22 in the figure denotes an SUS nipple.

The pore diameter of the ceramic porous membrane tube 24 is 1 mm>φ>0.05 μm, preferably <0.8 μm.

The outer cylinder column 23 is provided with nozzles 27 capable of supplying high-pressure air on its side portions, and has openings 25 and 26 at both ends through which liquid can pass. The opening 25 is a discharge port, and the opening 26 is a water supply port communicating with the ceramic porous membrane tube 24.

VOC-contaminated water is passed through the ceramic porous membrane tube 24 through the opening 26, and compressed air is introduced into the outer cylinder column 23 through the nozzle 27.

The high-pressure air supplied from the side part of the outer cylinder column 23 passes through the micro/nano size fine bubbles generated when the outer wall of the ceramic porous membrane tube 24 is aerated to the inside and the lower end or the upper end of the outer cylinder column 23. By making gas-liquid contact with the water to be treated containing the hydrated VOC, the VOC is highly efficiently transferred into the fine bubbles.

In order to prevent the reverse process in which VOCs are redissolved in the water to be treated from the fine bubbles, by intentionally aggregating the fine bubbles to form millimeter-sized bubbles by not intentionally adding a surfactant, it is possible to quickly remove them from the treated water. It is possible to remove bubbles.

It is further explained that this surfactant is not intentionally added. The aeration process with micro/nano bubbles has a higher efficiency than the aeration process with bubbles exceeding the usual millimeter size because of the size of the contact area with the water to be treated by the fine bubbles, and the gas-liquid between VOC and the water to be treated is more efficient. Separation can be expected, but at the same time, it was not an effective method as an aeration process for gas-liquid separation due to the VOC re-dissolution process (reverse process) due to fine bubbles.

Specifically, the VOC transfer process to the fine bubbles maintains the micro/nano size pore size, and after the transfer (after gas-liquid separation), it becomes bubbles of millimeter size or more and is quickly removed from the water to be treated. It is necessary.

By the way, in the method of generating fine bubbles using a ceramic porous membrane, it is necessary to add a surfactant separately in order to maintain the size of the fine bubbles, but by not adding the surfactant, the aggregation of fine bubbles can be prevented. It is possible to promptly and quickly remove the millibubbles containing a high concentration of VOC from the water to be treated.

Further, until now, in the aeration process for separating VOCs from contaminated water by gas-liquid separation, there has been little discussion about the relationship between the size of the bubbles themselves and the aeration efficiency.

Therefore, this time, the effect of gas-liquid separation when the micro/nano-sized pore diameter of the ceramic module was changed and the contaminated water was contacted and mixed in the module was confirmed by an indoor experiment.

Specifically, the pore size of the ceramic porous membrane (SPG) is <0.8 μm with respect to the membrane with a pore size of >5 μm, and the smaller the pore size, the greater the gas-liquid separation (aeration) effect. It was confirmed to be large (Fig. 4).

It is explanatory drawing which shows the principle of the purification processing method of VOC contaminated water of this invention. 1 is a front view of a ceramic module according to the present invention. It is the sectional view on the AA line of FIG. It is a graph which shows the influence of the membrane pore size which affects aeration efficiency. It is explanatory drawing which shows a prior art example.

1... Raw water tank 2... Aeration tank 3... Raw water pump 4... Underwater ejector 5... Intake pipe 6... Gas-liquid separation tank 7... Activated carbon adsorption tower 8... Blower 9... Drainage pit 10... Drainage pump 11... Turbid water treatment facility 18... O-ring fixing fitting 19... Fixing nut 20... O-ring fixing fitting 21... Fixing/adapting adapter 22... SUS nipple 23... Outer cylinder column 24... Ceramic porous membrane tube 25, 26... Opening 27... Nozzle

Claims (2)

A ceramic porous membrane tube having a micro/nanoporous structure, and an outer cylinder column having a nozzle capable of sealing and fixing the porous membrane tube and supplying high-pressure air on the side and having openings at both ends for liquid passage. Using a ceramic module having a double tube structure, micro/nano-sized fine bubbles generated when high-pressure air supplied from the outer cylinder column side is aerated from the outside of the porous membrane tube to the inside of the porous membrane. A method for purifying VOC contaminated water, which comprises contacting the contaminated water containing VOC (volatile organic compound) passed through a pipe with gas and liquid without adding a surfactant. The method for purifying VOC-contaminated water according to claim 1, wherein the pore diameter of the ceramic porous membrane tube is 1 mm>φ>0.05 μm.

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