JP2007245001A - Water cleaning method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water cleaning method with clean water as a water source by which a stable operation with the increased membrane filtration flux of a separation membrane can be attained without using flocculants at all. <P>SOLUTION: Fine bubbles with a diameter of ≤100 μm are poured into the raw water extracted from a water source such as ground water, subsoil water, well water, river water and lake water utilizing a fine bubble pouring apparatus 3. In this way, fine organic matters included in the raw water of a trace amount are oxidatively decomposed, and are further filtered with a separation membrane 4 as an MF (Micro-filtration) membrane or an UF (Ultra-filtration) membrane to obtain clean water. Since the fine organic matters included in the raw water having a possibility of clogging the face of the membrane are oxidatively decomposed, there is no concern about the clogging of the membrane face even if the membrane filtration is performed at a high flux, and high flux filtration can be performed in such a manner that the amount of the flocculants to be used is reduced or without using flocculants. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a water purification method for groundwater, underground water, well water, river water, lake water, and the like.

  Clear water such as groundwater, underground water, and well water is suitable as a source of purified water, and it contains less COD and SS than general water sources. In many cases, it can be used as tap water. However, in recent years, even in water treatment plants that can use clear water as a water source, purified water that uses raw membranes to filter raw water using separation membranes such as MF membranes and UF membranes that can reliably remove microorganisms and protozoa in raw water. Processing systems are spreading (Patent Document 1).

  In such a water purification method using a separation membrane, an operation of adding a flocculant to raw water and aggregating fine organic substances contained in the raw water as flocs and then performing membrane filtration is common. In particular, when clarified water is used as the water source, a very small amount of flocculant is added to the raw water, and membrane filtration operation is performed. In this way, the flocculant is added to the raw water because if the flocculant is not added, even if clear water is used as the water source, the separation membrane will be clogged in a short period of time and stable operation will not be possible. is there. If the membrane filtration flux is kept low for stable operation, the membrane area required to secure the amount of membrane filtration water that satisfies the water demand increases, and many separation membranes must be installed. It will be up. For this reason, conventionally, membrane filtration to which a flocculant has been added has been performed.

However, the method of adding flocculant and separating flocs in this way inevitably increases the amount of sludge generated mainly from flocs separated by the membrane. For this reason, the sludge generated at the water treatment plant must be treated by industrial waste treatment or transported to the sewage treatment plant, and the cost for this sludge treatment cannot be ignored. In particular, operators of water treatment plants that use clear water such as groundwater, underground water, well water, etc., are psychologically aware that sludge is generated by adding flocculant even though clear water is used as the water source. Often has resistance.
JP 2005-246156 A

  The present invention solves the above-described conventional problems, reduces the amount of flocculant used to increase the amount of sludge generation, or does not use any flocculant, and stable operation with increased membrane filtration flux of the separation membrane. It aims at providing the possible water purification method.

  The present invention made to solve the above problems is characterized in that fine bubbles are introduced into raw water collected from a water source to oxidize and decompose fine organic substances contained in a trace amount in the raw water, and then filter through a separation membrane. It is what. The fine bubbles are preferably air-containing gas such as air or bubbles such as ozone having a diameter of 100 μm or less, and the separation membrane is preferably an MF membrane or a UF membrane.

  In the water purification method of the present invention, the amount of flocculant used can be reduced by introducing fine bubbles and oxidizing and decomposing fine organic substances contained in the raw water. In the case of a clear water source, instead of adding a flocculant to the collected raw water as in the past, fine bubbles are introduced to oxidatively decompose fine organic substances contained in a minute amount in the raw water. The fine bubbles used in the present invention are preferably bubbles having a diameter of 100 μm or less, and are referred to as nanobubbles or microbubbles. Such fine bubbles can not only make the total contact surface area with the surrounding water extremely large, but also the inside of the bubbles due to surface tension, compared to normal size bubbles (macro bubbles) with a diameter of 1 mm or more. When the pressure of the material becomes extremely hard, the active oxygen is generated by the impact when it collapses and exhibits strong oxidizing power.

  For this reason, it is possible to reduce the amount of fine organic substances that may be contained in trace amounts in the collected raw water by oxidative decomposition with fine bubbles, so membrane filtration is performed when separating this raw water with a separation membrane. Even in a state where the flux is increased, it becomes difficult to block, and stable operation is possible. In addition, even when a flocculant is used, the amount of the flocculant used can be reduced, so that a large amount of sludge is not generated as in the prior art, and the processing cost is not required, so that a significant cost reduction is possible. The fine bubbles also have an effect of oxidizing metals such as manganese and iron contained in the raw water, and the metal oxide can be aggregated and removed from the raw water.

Preferred embodiments of the present invention are shown below.
FIG. 1 is a view showing a flow of the present invention, wherein 1 is a raw water tank, 2 is a reaction tank equipped with a fine bubble injection device 3, and 4 is a separation membrane. Raw water collected from water sources such as groundwater, underground water, well water, river water, and lake water enters the raw water tank 1 first and is sent to the reaction tank 2. At the bottom of the reaction vessel 2, there is installed a fine bubble injection device 3 capable of generating fine bubbles having a diameter of 100 μm or less and introducing them into water.

  As the fine bubble injection device 3, a macro bubble having a diameter of about 1 mm generated by a normal bubbling device is physically sheared by a stirring blade or the like to generate a fine bubble having a diameter of 100 μm or less. An apparatus for reducing the size by applying an impact by sound waves has been developed and is already on the market.

  By contacting the fine bubbles inside the reaction tank 2, the fine organic matter contained in a minute amount in the clear raw water is oxidatively decomposed by the strong oxidizing power of the fine bubbles. Here, the fine organic matter is a general term for fine organic matter containing colloids, viruses, microorganisms and the like contained in clear raw water. As described above, when such a fine organic substance enters the separation membrane 4 as it is, the membrane surface is blocked in a short period of time. However, when it is oxidized and decomposed, the molecular weight becomes small and it is difficult to block the membrane surface.

  The raw water exiting the reaction tank 2 is driven into the separation membrane 4 by the filtration pump 5. As the separation membrane 4, an MF membrane or a UF membrane is used. The material may be a polymer film or a ceramic film. As the membrane shape, any shape such as a flat membrane, a hollow fiber membrane, a spiral membrane, a monolith membrane, and a tubular membrane can be selected. Furthermore, the pressurization method to the film surface may be an external pressure type or an internal pressure type. As described above, the type of the separation membrane 4 is not particularly limited. However, since the fine bubbles have a strong oxidizing power, a monolithic ceramic membrane having high membrane strength and excellent durability is required for stable operation. It is preferable to use it.

  The raw water is filtered through the separation membrane 4 and the filtered water is taken out as purified water. In order to increase the water recovery rate at a water treatment plant, it is common to adopt a dead-end filtration method. As described above, since the fine organic matter in the raw water that may clog the membrane surface is decomposed in the previous stage, there is no possibility of clogging even if membrane filtration is performed at a considerably high flux, and the flocculant is completely removed. Although it is not used, high flux filtration equivalent to or higher than the conventional case using a flocculant is possible. Moreover, in the conventional case where a flocculant is used, a large amount of floc is recovered as sludge, but according to the present invention, sludge is reduced or hardly generated, so that the post-treatment cost of sludge is greatly reduced. An effect is obtained.

  In the embodiment of FIG. 1, the fine bubbles and the raw water are brought into contact with each other inside the reaction tank 2, but the reaction tank 2 is omitted as in the other embodiments shown in FIG. Thus, the raw water may be directly driven into the separation membrane 4, and the fine bubble injection device 3 may be provided in the middle of the driving line. Since the flow rate is high in this implantation line, the fine bubbles are easy to be mixed uniformly in the raw water. The charging device 3 is preferably installed on the inlet side of the filtration pump 5. Moreover, when the water conduit for raw water to the water purification plant is long, the fine bubble injection device 3 may be provided in the middle of the water conduit.

It is explanatory drawing which shows the 1st Embodiment of this invention. It is explanatory drawing which shows the 1st Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Raw water tank 2 Processing tank 3 Fine bubble injection apparatus 4 Separation membrane 5 Filtration pump

Claims (3)

  A water purification treatment method comprising introducing fine bubbles into raw water collected from a water source to oxidize and decompose fine organic substances contained in a minute amount in the raw water, and then subjecting the raw water to membrane filtration using a separation membrane.   The water purification method according to claim 1, wherein the fine bubbles are bubbles having a diameter of 100 μm or less.   The water purification method according to claim 1, wherein the separation membrane is an MF membrane or a UF membrane.

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