JP2002172396A - Method for reducing ph of raw water in water cleaning facilities and apparatus used therein - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the pH of raw water in water cleaning facilities using carbon dioxide. SOLUTION: A carbon dioxide dissolving apparatus is constituted by attaching a dispersing header, which has a plurality of gas dispersing pipes for discharging carbon dioxide in an amount of not less than 20 kg/h per the surface area of 1 m2 of the dispersing pipes under an internal pressure condition of (water pressure +3) kPa or more, to the water channel of water cleaning facilities in an up and down movable manner. By using this carbon dioxide dissolving apparatus, carbon dioxide is dispersed and dissolved in water with a water depth of 1 m or more so that a bubble size of carbon dioxide becomes 5 mm or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for dissolving carbon dioxide in raw water to be purified in a water purification facility.
The present invention relates to a method for reducing the pH of raw water, and a carbon dioxide dissolving device for water purification for the method. More specifically, the present invention relates to a water purification system in which a gas dispersion pipe is attached to a water channel having a depth of 1 m or more in a water channel of a water purification facility, and carbon dioxide is released in a size of 5 mm or less to reduce the pH of raw water. The present invention relates to a processing method and a carbon dioxide dissolving device therefor.

[0002]

2. Description of the Related Art In recent years, surface waters of lakes, marshes, dams, rivers, and the like have become eutrophic due to the incorporation of domestic wastewater and the like, and water quality has tended to deteriorate significantly. As a result of eutrophication, algae proliferate, and due to the photosynthesis, the pH of water is increasing sharply, and the pH of these waters exceeds 9 in many places. In a water purification facility using surface water as raw water, it is urgently necessary to appropriately correct the pH of the raw water. In other words, in addition to ensuring the proper pH as tap water, a water purification facility requires a process of coagulating and separating an underwater suspension as part of its treatment. It is outside the optimum pH range for coagulation, which makes coagulation operation extremely difficult. As a method for reducing the pH of raw water, there is a method of injecting sulfuric acid, hydrochloric acid, or carbon dioxide.However, in the sulfuric acid injection method, sulfate ions enter clean water, and in the hydrochloric acid injection method, chlorine ions enter. Increase in ions,
It is not preferable from the viewpoint of preventing corrosion of facilities such as water pipes.
On the other hand, although carbon dioxide does not have such inconveniences, there has been a demand for a method and an apparatus capable of effectively dissolving the carbon dioxide in a large amount and performing good maintenance. Such equipment is required when the pH of the raw water rises, due to seasonal factors, which may require continuous use for several months or use for several months. In some cases, a device that can be easily attached and detached is desired.

[0003] At present, there are few places where an acid injection equipment for pH adjustment is installed in water purification facilities, and the acid generated from aluminum sulfate (sulfuric acid band) or polyaluminum chloride (PAC), which is a coagulant, is used for coagulation. Inject too much agent and p
At present, H is lowered to secure an appropriate pH range for the coagulation / precipitation treatment. However, excessive injection of coagulant increases the concentration of sulfate and chloride ions in the filtered water,
There are problems such as an increase in generated soil or an increase in the cost of a flocculant chemical.

[0004]

In view of the above-mentioned situation, the present inventors have intensively studied a method of correcting the pH of raw water to an appropriate range by directly using carbon dioxide in a so-called raw gas state. As a result, carbon dioxide was bubbled 5 mm in diameter.
When injecting into water at a depth of 1 m or more from a gas dispersion pipe of a carbon dioxide dissolving device that can be released in the following size, it is possible to dissolve almost all of the injected carbon dioxide,
The present inventors have found that the pH of raw water can be brought to a desired appropriate range, and have reached the present invention. Therefore, an object of the present invention is to correct the pH of raw water to a desired appropriate range by using carbon dioxide directly in a so-called raw gas state,
It is an object of the present invention to provide a method for correcting the pH of raw water before a coagulation / sedimentation separation step in a water purification facility to an appropriate range for coagulation / sedimentation separation, and a carbon dioxide dissolving apparatus used for the method. Further, the present invention provides a method and a device capable of correcting the pH of purified water to an appropriate range as tap water.

[0005]

According to the present invention, a carbon dioxide dissolving device capable of moving up and down is provided in a raw water channel of a water purification facility, and the carbon dioxide dissolving device has a bubble diameter of carbon dioxide gas released of 5 mm or less. The present invention relates to a method for reducing the pH of raw water by injecting and dissolving carbon dioxide into water at a depth of 1 m or more from this dispersion tube, wherein a plurality of gas dispersion tubes capable of being discharged with a size of at least 1 cm are provided at intervals wider than at least 10 cm. In addition, the present invention is provided in the water channel of the water purification facility,
A carbon dioxide dissolving device for reducing H, wherein a plurality of upright guide rails disposed in a substantially rectangular water channel have a carbon dioxide supply pipe, a gas dispersion pipe having fine holes or slits for gas dispersion. The present invention relates to a carbon dioxide dissolving apparatus for water purification treatment, which is provided with a gas disperser header provided with a plurality of gas dispersers so as to be vertically movable.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS It is widely known that carbon dioxide dissolves when injected into alkaline water, but it dissolves almost all of the carbon dioxide injected into water and corrects raw water to a desired pH. There was no known means of doing so. In the present invention, when surface water is used as raw water, at least a landing well, a mixing well, a coagulation sedimentation basin, a water passage of a water purification treatment facility including a filtration basin and a distribution basin, a relatively narrow width connecting each pond or well. Refers to a channel whose cross section is substantially rectangular,
Inject carbon dioxide into any of the channels before the coagulation sedimentation tank and dissolve it to lower the pH to the desired value.

In such a channel, water is usually 0.15 m /
It flows at a flow rate of less than a second and exhibits a different behavior in dissolving carbon dioxide from static water. This flow rate 0.15m
In flowing water at a depth of 1 m or more, and preferably at a depth of 1 m or more, preferably near the bottom of the water, the carbon dioxide is dispersed into the water at a depth of 1 m or more from a gas dispersion pipe of a carbon dioxide dissolving apparatus capable of releasing carbon dioxide with a bubble diameter of 5 mm or less. When injecting carbon, bubbles that have come out of the gas dispersion tube dissolve and disappear before reaching the water surface. When the gas release position is shallower than 1 m in water depth or when the bubbles coming out of the gas dispersion pipe are larger than 5 mm, the carbon dioxide gas is not completely dissolved until reaching the water surface and is discharged to the atmosphere, which is not preferable. The amount of carbon dioxide required to be injected into the raw water is determined by measuring the pH and alkalinity of the water to be treated and calculating the ion balance. Then, in order to inject the amount, a required amount of carbon dioxide is injected by giving an output signal to a flow control valve of the carbon dioxide dissolving device.

As the carbon dioxide dissolving apparatus, for example, an apparatus as shown in FIG. 1 can be used. In FIG. 1, reference numeral 1 denotes a gas disperser header, on which a plurality of gas dispersing tubes 2 having fine bubbles or slits for generating bubbles (hereinafter, referred to as “nozzles”) are attached. Reference numeral 3 denotes a pipe connected to a liquefied carbon dioxide storage tank (not shown). The pipe 3 is preferably detachably attached to the carbon dioxide storage tank at a position close to the dissolving device. Further, it is preferable that all or a part of the pipe is a flexible pipe, and it is particularly preferable that a part near the gas distributor header is a flexible pipe. Reference numeral 4 denotes a guide rail for moving the gas distributor header 1 up and down, and the guide rail is preferably fixedly installed on a road wall of a waterway. Along the guide rail, the gas distributor header 1 is mounted so as to be vertically movable by an electric elevator 5. Preferably, as shown in FIG. 2, wheels 6 are mounted on the gas distributor header 1 which is in contact with the guide rails to facilitate the ascending and descending movement. Reference numeral 7 denotes a stopper. Each gas dispersion tube has a bubble generation nozzle capable of generating a carbon dioxide bubble diameter of 5 mm or less,
Carbon dioxide can be emitted in the following cell diameter 5 mm, and a surface area 1 m ² per 20 gas pressure (water pressure +3) kPa in dispersion pipe
Preferably, it can release more than kg / h. Further, the gas dispersion pipe 2 is preferably provided at an interval where the generated bubbles spread to the full width of the water channel and the bubbles generated from the respective dispersion pipes do not overlap and coalesce. Depending on the distance, more than 10 cm, preferably 1 cm
It is 5 cm to 50 cm, more preferably 15 cm to 30 cm. In addition, the gas dispersion tube 2 is a metal tube, a sintered ceramic tube, a resin porous tube, or the like having a large number of nozzles in which the size of bubbles generated therefrom and the gas pressure of (water pressure + 3) kPa or more are adjusted to generate bubbles. Can be used experimentally.

When such a carbon dioxide dissolving apparatus is used, the gas dispersion pipe is preferably placed near the water bottom at a depth of 1 m or more in the waterway so that the gas dispersion pipe is perpendicular to the water flow as shown in FIG. Deploy. The amount of carbon dioxide calculated by the ion balance calculation from the gas dispersion pipe is continuously generated as bubbles of 5 mm or less at a depth of 1 m or more by adjusting the gas flow rate control valve or the gas pressure. The carbon dioxide discharged from the gas dispersion pipe dissolves before reaching the water surface, and the entire amount thereof dissolves in water, effectively contributing to the reduction of the pH of raw water. This does not deteriorate the environment because the carbon dioxide injected into the water is not released into the atmosphere.

[0010] The surface water used as the purified water does not have a constant property and is constantly changing, but the amount of carbon dioxide to be changed may be injected while calculating and correcting the ion balance. It is also known that surface water greatly changes seasonally, and its pH is high and alkaline in summer when algae breed.
H is relatively low and does not require injection of carbon dioxide for pH adjustment. In summer, when heavy rains and algae occur frequently, a large amount of contaminants may flow into the landing well and adhere to the carbon dioxide dispersion pipe, resulting in uneven gas dispersion or interruption of gas injection. In such a case, if necessary, the gas distributor header 1 is pulled out of the water to clean the gas distribution tube. Further, during a period in which the injection of carbon dioxide is not required, the gas distributor header 1 is pulled out from the water, and the gas distribution tube is cleaned and stored. For this purpose, it is essential that the disperser header 1 provided with the gas dispersion tube be configured to be drawn out of the water.

In such a configuration, the gas distribution tube is detachably attached to the gas distributor header, and the gas distributor header 1 can be moved up and down. As a preferred configuration of the lifting mechanism, a plurality of guide rails and one or more wheels are respectively provided on the side surfaces of the disperser header attached thereto, and it is desirable that the lifting mechanism be operated by an electric lifting device.

[0012]

According to the present invention, it is possible to directly dissolve carbon dioxide to increase the pH of tap water, especially surface water, in the water purification step, and to adjust the pH to each desired value. In addition, by specifying the depth of water into which carbon dioxide is injected and the size of generated bubbles, almost the entire amount of injected carbon dioxide can be dissolved and used. Therefore, it is possible to avoid excessive use of a flocculant at the time of flocculation and sedimentation treatment of surface water and use of hydrochloric acid or sulfuric acid which is strongly corrosive with a strong acid.

[0013]

[Experimental example] In the experiment, width 50mm, length 5000mm, height 2000mm
A water outlet was provided at a height of 500 mm, 750 mm, 1000 mm, 1250 mm, 1500 mm from the gas dispersion tube to change the water depth of the resin carbon dioxide gas dispersion tube at the bottom of the tank and the gas dispersion tube at the side of the tank. Using an absorption tank, as a carbon dioxide gas dissolving device, gas pressure from any of the above positions is water pressure + 3 kPa
A dispersion tube (φ63 × 50 mm) “Caliox” (trade name, manufactured by Showa Rubber Co., Ltd.) having a slit in which the size of bubbles generated at the time of (1) was 5 mm or less was used. The experiment on carbon dioxide absorption efficiency was as follows: River water with pH 9.10, alkalinity 35 mg / l, calcium hardness 40 mg / l was flowed at 42 tons / h, and simultaneously carbon dioxide was 0.19 Nm ³ / h (gas pressure was +3 kPa Adjustment). The injection rate of carbon dioxide was 9 mg / l.
At the outlet of the absorption tank, running water was sampled and analyzed to determine the carbon dioxide absorption efficiency. The carbon dioxide gas injection speed of the gas dispersion tube was 38 kg / m ² · h.

[Table 1] 水 Gas dispersion pipe water depth 500mm 750mm 1000mm 1250mm 1500mm ──処理 Treated water pH 7.04 7.00 7.00 6.98 6.98 CO ₂ absorption efficiency 90.5 93.4 99.1 99.7 99.9か ら From this experiment, it was found that the position of the gas dispersion pipe was It was found that when the size of the released bubbles is 5 mm or less, carbon dioxide is absorbed with an absorption efficiency of 99% or more and can be used effectively without being released into the atmosphere.

[0014]

[Example] Surface water having a pH of 9.10, a total alkalinity of 35 mg / l, a calcium hardness of 40 mg / l, and a turbidity of 5 degrees is put into a landing well of a water purification facility at 120,000 tons / day, and carbon dioxide is injected. The pH was adjusted. Suitable for coagulation sedimentation of pH 9.10 surface water
The carbon dioxide injection rate required to make H7.0 is 120, when the ion balance is calculated from the alkalinity of the above surface water.
23 Nm ³ / h of carbon dioxide was required for 000 tonnes / day of surface water. Similar to the gas dispersion tube used in the experimental example, the carbon dioxide dissolution apparatus is a gas dispersion tube (φ63 × 500 m
m) Carryox (trade name: Showa Rubber Co., Ltd.)
It has a structure as shown in Fig. 1 in which 10 are installed at intervals of 12 cm, and a water channel (2 m wide, 6 m deep: water flow rate of 0.
At 12m / sec), the guide rail was fixed to the road wall. Carbon dioxide was injected by placing the gas dispersion tube at a depth of 5 m, injecting 23 Nm ³ / h of carbon dioxide at a gas pressure of 53 kPa, and sampling water at the sampling unit 7 m downstream to analyze water quality. PH 6.98, total alkalinity 35 mg
/ l, calcium hardness 40mg / l, free carbonic acid 7mg / l, and the absorption efficiency of carbon dioxide was 99.9%. When 20 mg / l of flocculant PAC was added to this water, flocculation and sedimentation of suspended matter was successfully performed.

[Brief description of the drawings]

FIG. 1 is a view showing a carbon dioxide dissolving apparatus according to the present invention.

[Explanation of symbols]

 1 is a gas distributor header 2 is a gas distribution pipe 3 is a carbon dioxide supply pipe 4 is a guide rail 5 is an electric lifting device

FIG. 2 is a cross-sectional view of a connection portion between a guide of the carbon dioxide dissolving apparatus and a gas disperser header.

[Explanation of symbols]

 6 is a wheel 7 is a stopper

FIG. 3 is a diagram showing an example in which the carbon dioxide dissolving device according to the present invention is attached to a water channel.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C02F 1/66 530 C02F 1/66 530Z 540 540Z

Claims (8)

[Claims] 1. A carbon dioxide dissolving device capable of moving up and down is provided in a raw water channel of a water purification facility, a plurality of gas dispersion tubes are provided in the carbon dioxide dissolution device, and carbon dioxide is provided in the gas dispersion tube. A method for reducing the pH of raw water in a water purification facility, comprising supplying carbon dioxide into water at a depth of 1 m or more from a fine hole or slit capable of being discharged with a bubble diameter of 5 mm or less. 2. A carbon dioxide dissolving device is provided in a water channel before the coagulation sedimentation tank in at least one of a water purification treatment facility consisting of a landing well, a mixing well, a coagulation sedimentation tank, a filtration pond, and a distribution reservoir. A plurality of gas dispersion tubes are provided in the apparatus, and carbon dioxide is supplied into water at a depth of 1 m or more from micropores or slits provided in the gas dispersion tube and capable of discharging bubbles with a bubble diameter of 5 mm or less. A method for reducing the pH of raw water in a water purification facility. 3. The gas pressure in the gas dispersion pipe is (water pressure + 3).
At least 10 cm of gas dispersion tube that emits carbon dioxide at 20 kg / h or more per 1 m ² of surface area of the gas dispersion tube at kPa or more
The pH reduction method according to claim 1, wherein a plurality of carbon dioxide dissolving devices are mounted at wider intervals. 4. The amount of carbon dioxide to reach the target pH is:
Measure the pH and alkalinity of the raw water, calculate the ion balance, give an output signal to the flow control valve of the carbon dioxide dissolving device to dissolve the amount,
2. The pH according to claim 1, wherein carbon dioxide is injected into water at a depth of 1 m or more from a gas dispersion pipe capable of being discharged with a size of 1 m or less.
Reduction method. 5. An apparatus for dissolving carbon dioxide in raw water in a water purification facility, comprising: a plurality of upright guide rails disposed in a water channel having a substantially rectangular cross section; A carbon dioxide dissolving apparatus for water purification treatment, comprising a gas disperser header provided with a gas dispersing tube having fine holes or slits as described above. 6. When the gas dispersion tube emits carbon dioxide at a gas pressure of (water pressure + 3) kPa or more and carbon dioxide at a pressure of 20 kg / h or more per 1 m ² of surface area of the gas dispersion tube, the gas discharged from the dispersion tube has a bubble diameter of 5 mm. The carbon dioxide dissolving apparatus for water purification according to claim 5, which is a gas dispersion pipe capable of being discharged in the following sizes. 7. The carbon dioxide dissolving apparatus for water purification treatment according to claim 5, wherein a plurality of gas dispersion tubes are attached to the gas distributor header at intervals larger than at least 10 cm. 8. The carbon dioxide dissolving apparatus for water purification according to claim 5, wherein the gas dispersion pipe is detachable on the water surface.