JPH10109091A - Treatment of water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To minimize the clogging of a filter membrane by executing a separating treatment with the filter membrane after removing a suspended matter in the water to be treated by subjecting the water to floatation with rising bubbles by dissolving under pressure a gas containing air or ozone to the water to be treated or supplying as a pressurized gas. SOLUTION: The water 1 to be treated containing the suspended matter is mixed with a chemical 3 such as flocculating agent at a mixer 2 and mixed with a pressurized gas saturated water 5 at a contractor 4 to form a gas-solid associated body of suspended matter particles with fine bubbles. Frothes 7 floated and separated on the water surface of a floatation tank 6 by this way are scrapped and collected with a skimmer 8 and discharged to out of system. On the other hand, the water from which the suspended matter is separated is flowed into an overflow tank 10 and a membrane immersing tank 11 and becomes a treated water 13 by filtering with a membrane filtering device 12. The pressurized gas saturated water is prepared by introducing the water in which a part of the water to be treated is taken out from the overflow tank 10 as a circulating water 14 and pressurized with a pressure pump and the gas 17 pressurized with a gas compressor 16 to a pressurized gas saturating tank 18 and bringing them into contact with each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating water by membrane separation in tap water, sewage or central water.

[0002]

2. Description of the Related Art In the advanced treatment of tap water and sewage, a flocculant such as bansulfate or polyaluminum chloride (PAC) is generally used, and the treatment is performed through a combination of flocculation, precipitation, and sand filtration. This method has a problem that a large amount of chemicals such as a flocculant is consumed and a large equipment area and equipment cost are required.

[0003] Recently, as an alternative to this, interest in a water treatment method using a filtration membrane has been increasing, and development has been promoted mainly for small-scale water supply, but there are many unsolved problems. In many cases, the filtration membrane used for water supply is loaded with all the suspensions contained in the raw water without prior removal of the suspended matter by a sedimentation tank or the like, and the filtration membrane is easily clogged. In addition, frequent treatments such as back washing of the filtration membrane using air or the like are required, and the power cost is increased. Further, if clogging is not recovered by backwashing or the like, so-called chemical washing with acid, alkali, hypochlorite, or the like, or mechanical washing is required. Also, when treating river water, pollutant components increase immediately after rainfall, a high pollution load is applied to the membrane, and they are directly suspended during the season when various algae and microorganisms are easy to propagate. In many cases, the load became turbid and the amount of permeated water decreased significantly. However, at present, no appropriate countermeasures have been taken against these problems.

[0004]

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, the present invention relates to a water treatment method using a filtration membrane, in which the raw water is suspended before the raw water is supplied to the filtration membrane. It is an object of the present invention to provide a processing method for removing suspended substances reliably in response to a change in a substance load and minimizing clogging of a filtration membrane.

[0005]

In a water treatment method using a filtration membrane, air or an ozone-containing gas is dissolved in water to be treated under pressure or supplied as a pressurized gas to remove suspended substances in the water to be treated. This is a method for treating water in which a separation treatment is performed by a filtration membrane after removing by floating separation with rising bubbles.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to the drawings. FIG. 1 is a diagram for explaining one embodiment of the present invention. The water to be treated 1 containing the suspended substance to be treated is mixed with a chemical 3 such as a flocculant as required by a mixer 2,
The gas is mixed with the pressurized gas-saturated water 5 in the contactor 4, and fine bubbles form a gas-solid association with the suspended particles, the apparent specific gravity decreases, and the particles float in the flotation tank 6 at a high flotation speed. ,
Accumulate as floss 7 on the water surface. The floss is a concentrate having a concentration of usually 2 to 3% as a solid, and is intermittently or continuously scraped by the skimmer 8 and discharged out of the system to be treated as a waste. On the other hand, the water from which the suspended matter has been separated flows into the overflow tank 10 from the lower part of the baffle wall 9 and then flows into the membrane immersion tank 11 from the overflow tank, and the membrane filtration device 12
, And supplied as treated water 13 for tap water. The membrane filtration device may be of the immersion type that is immersed in a membrane immersion tank as shown in the figure and suctioned by a suction pump to obtain permeate, or may be the casing storage type that supplies pressurized water to obtain permeate. You may.

The pressurized gas-saturated water is obtained by extracting a part of the water to be treated from the overflow tank 10 as circulating water 14, and is pressurized by a pressurizing pump 15 and pressurized by a gas compressor 16. The gas 17 is introduced into the pressurized gas saturation tank 18 and brought into contact therewith to be prepared.

The gas to be saturated and dissolved in water may be air, but by using an ozone-containing gas, coloring components such as humic acid and fulvic acid in raw water, off-flavor components such as 2-methylisoborneol, iron and manganese, etc. Of the inorganic compound can be removed by oxidation. When an ozone-containing gas is used, it is necessary to decompose ozone remaining in exhaust gas from a flotation tank, overflow tank, or the like in an ozone decomposer equipped with a decomposition catalyst or the like, detoxify the ozone, and discharge the ozone.

The pressurized levitation separation in the present invention is to generate fine gas bubbles by injecting pressurized water in which a gas is dissolved to form a gas-solid association with the fine bubbles attached. Not only water but also pressurized gas may be injected into the lower part of the flotation tank to generate fine bubbles.

The treatment method of the present invention is effective for maintaining stable operation of water treatment using a filtration membrane. Particularly, the treatment method is used when raw water having a high turbidity (for example, 50 degrees or more) immediately after rainfall, or in lakes, dams and the like. It is effective against water in which algae breeding, which is inevitable when flooding is used as raw water,
A normal load can be applied to the membrane filtration device, and stable operation can be performed. In particular, the occurrence of algae may occur suddenly due to environmental factors such as a change in temperature, but the method of the present invention can sufficiently cope with such a problem.

Further, in the method of the present invention, since the floating is mainly based on the difference in specific gravity between water and the gas-solid aggregate in which microbubbles are associated with the suspended substance particles, the flocculant has a crosslinking effect on the aggregate. It is enough to assist. On the other hand, if it is attempted to separate by only a flocculant, water containing algae generally has a pH of 8
When the algae are separated by a flocculant, a large amount of the flocculant is required to adjust the pH to a neutral range. Therefore, the amount of the flocculant to be added can be reduced in the method of the present invention. Depending on the water quality and properties of the raw water, it is possible to float and separate chemicals such as flocculants without addition, and the flotation method is capable of high-load operation and has a much shorter residence time than the flocculation and sedimentation method. The treatment in the separation tank may be sufficient.

[0012]

As described above, in the water treatment method using a filtration membrane, membrane filtration is carried out as a pretreatment after suspended particles in the water to be treated are floated using air or an ozone-containing gas, so that high turbidity immediately after rainfall is obtained. It also reduces fluctuations in the quality of the water to be treated during breeding and algae breeding, constantly applies an appropriate load to the membrane filtration device, greatly reduces the frequency of washing the filtration membrane, and enables stable operation for a long period of time.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Water to be treated, 2 ... Mixer, 3 ... Drug, 4 ... Contactor, 5
... pressurized gas saturated water, 6 ... flotation tank, 7 ... floss, 8 ...
Skimmer, 9: baffle wall, 10: overflow tank, 11: membrane immersion tank, 12: membrane filtration device, 13: treated water, 14: circulating water,
15 ... Pressure pump, 16 ... Gas compressor, 17 ... Pressurized gas, 18 ... Pressurized gas saturation tank

Claims (1)

[Claims] In a water treatment method using a filtration membrane, air or an ozone-containing gas is dissolved under pressure or supplied as a pressurized gas to water to be treated, and suspended substances in the water to be treated are lifted by rising bubbles. A method for treating water, comprising performing a separation treatment by a filtration membrane after removing by separation.