JPH04277081A - Method for sterilizing water - Google Patents

Abstract

PURPOSE:To sterilize water containing ammoniacal nitrogen to be recirculated and reused without generating a chlorine smell, an irritant smell, the damage of the hair of a water user and the pain of an eye and a throat while preventing the generation of scale and improving the handling properties of a sterilizing agent. CONSTITUTION:A saline solution is electrolized in a diaphragm free electrolytic cell 15 to form sodium hypochlorite 40 which is, in turn, injected in circulating pool water 21 by a pump 31 and piping 30. The concn. of free residual chlorine in the pool water 21 is measured by a sensor 34 and the injection of sodium hypochlorite due to the pump 31 is controlled so that the measured concn. is received in a predetermined range.

Description

[Detailed description of the invention]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for sterilizing water, and more particularly, to a method for sterilizing water that contains ammonia nitrogen and is recycled.

0002

[Prior Art] Pool water, hot spring water, bath water, etc.
It is destined to contain ammonia nitrogen and E. coli, which are excreted from the human body in various forms. Therefore, when using such water for circulation, it is necessary to disinfect and sterilize it for hygiene reasons. For example, in the case of pool water, free residual chlorine can be reduced to 0.
．． It is required by law to contain 4 ppm or more.

Conventionally, in order to sterilize these water supplies,
Chlorine-based sterilizers are preferably used. When this chlorine-based sterilizer is added to water, as shown in Figure 2 taken from the "Air Conditioning and Sanitary Engineering Handbook," when the amount of chlorine added is relatively small, the combined residual chlorine increases as the amount is increased. The amount increases, once it decreases, and then starts to increase again (this is called a break point) before free residual chlorine appears. Since this free residual chlorine has a stronger sterilizing power than the combined residual chlorine, the chlorine-based sterilizing agent must be added above the above break point. When such a large amount of chlorine-based sterilizing agent is introduced, the proportion of trichloramine increases, as shown in FIG. 2. Trichloramine is the most volatile and has the strongest pungent odor, and is said to cause unpleasant chlorine odor, damage to hair, and sore eyes and throats.

[0004] Figure 2 above shows the measurement results for commercial water with a pH of 7, a temperature of 10°C, and containing 0.5 ppm of ammonia nitrogen, and a contact time of 2 hours between chlorine and the commercial water. be.

[0005]

[Problems to be Solved by the Invention] Specifically, solid chlorine-based sterilizers that are easy to handle are widely used for pool water, such as white powder and chlorinated sodium cyanurate. Since they are sprayed directly into the pool water, there is an excess of chlorine in the vicinity, making it easy for the trichloramines mentioned above to form.

[0006] In order to solve this problem, commercially available sodium hypochlorite is sometimes used as a chlorine-based sterilizing agent. In that case, since sodium hypochlorite is stored, caustic soda is added to the sodium hypochlorite to prevent its decomposition, and the pH is generally set to 12.6 or higher. However, when caustic soda is added in this way, the pH
When sodium hypochlorite with a pH of 12.6 or higher is injected into pool water, etc., the calcium ions in the water turn into calcium hydroxide at a pH of 12.6 or higher, which forms scale and adheres to the sterilant injection nozzle. . Therefore, in this case,
For example, it is necessary to disassemble and clean the injection system once a month, resulting in a large amount of maintenance costs.

[0007] Commercially available sodium hypochlorite generally has a relatively high concentration of about 12%, so if it is directly injected into water,
As with the use of solid chlorine-based sterilizers, trichloramine is likely to be generated locally. In order to prevent this, it is possible to dilute commercially available sodium hypochlorite with tap water to make it easier to diffuse, but if you do that, the calcium ions contained in the tap water will turn into calcium hydroxide.
It adheres to the sterilant injection pump and injection piping, making maintenance even more troublesome. It is also possible to neutralize sodium hypochlorite with hydrochloric acid in order to suppress the formation of scale, but this would generate toxic chlorine, causing the problem of poor handling of the sterilizing agent.

The present invention was made in view of the above circumstances, and it is possible to obtain drinking water that does not have chlorine odor or irritating odor, and does not cause damage to hair, eyes, or throat pain to users. The object of the present invention is to provide a method for sterilizing water that can minimize scale generation and also allows for easy handling of sterilizing agents.

[0009]

[Means for Solving the Problems] The method for sterilizing commercial water according to the present invention is, as described above, in the method of sterilizing commercial water that contains ammonia nitrogen and is used for circulation. Inject the treated sodium hypochlorite into the above-mentioned water, measure the free residual chlorine concentration in this water, and control the injection of sodium hypochlorite so that the measured concentration falls within a predetermined range. It is characterized by this.

0010

[Operation and Effects of the Invention] When sodium hypochlorite is obtained by electrolyzing salt water in a non-diaphragm electrolytic cell, what is stored is the salt, and the sodium hypochlorite is stored. There will be no need. Therefore, as mentioned above, there is no need to add caustic soda to sodium hypochlorite for the purpose of preventing decomposition, and scale is not likely to be generated due to the pH increase due to the addition of caustic soda.

[0011] As mentioned above, even if caustic soda is not added, if sodium hypochlorite has a high effective chlorine concentration and a high pH itself, scale is likely to occur to some extent. Therefore, when we investigated the correlation between the effective chlorine concentration of sodium hypochlorite and scale generation in pool water, we found that no calcium or magnesium scale formation was observed when the pH was below 9.1, and when the pH exceeded 9.2, magnesium Scale formation was observed, and calcium scale formation was observed at 12.6 or higher. On the other hand, if this pH is less than 4, chlorine is generated, so it is preferable to maintain the sodium hypochlorite injected into the water in the present invention at a pH of 4 to 9.1.

[0012] If scale generation can be prevented as described above, disassembly and cleaning of the sterilizing agent injection system becomes unnecessary, or the frequency thereof is greatly reduced, and maintenance costs are significantly reduced.

[0013] Also, the free residual chlorine concentration of the water was measured,
If you control the injection of sodium hypochlorite based on that,
By keeping this concentration close to the breakpoint shown in FIG. 2, it is possible to suppress the generation of trichloramine as much as possible. If that happens, the chlorine smell and pungent smell mentioned above,
In addition, it can eliminate all problems of hair damage, eyes, and sore throats for water users.

Further, in the present invention, since it is not necessary to neutralize sodium hypochlorite with chlorine, the sterilizing agent can be easily handled.

[0015] The use of sodium hypochlorite obtained by electrolyzing common salt in a non-diaphragm electrolytic cell for disinfection and sterilization has been practiced for example for tap water and sewage. However, tap water does not inherently contain much ammonia nitrogen, and even if chloramine is generated in sewage, it does not normally come into contact with the human body, so the problem that the present invention seeks to solve will not occur. do not have.

On the other hand, when water containing ammonia nitrogen is used for circulation, the above-mentioned problems of trichloramine generation and scale generation occur. Conventionally, this problem has been dealt with by decomposing the generated trichloramine with ozone or activated carbon, or by cleaning the generated scale. In other words, in the past, active suppression of scale formation was not considered for this type of water, and sodium hypochlorite obtained by electrolyzing table salt in a non-diaphragm electrolytic tank was used as a sterilizing agent. That had not been thought of at all.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained in detail below with reference to the drawings.

FIG. 1 is a flow diagram of a system for disinfecting and sterilizing pool water, by way of example, according to the method of the present invention. As shown in the figure, the salt 10 is stored in a salt dissolving tank 11.
and is dissolved in water supplied there through piping 9. The obtained saturated saline solution is sent to the electrolyzer 13 through the pipe 12. In the electrolyzer 13, the pump 1
4, a saturated salt solution is supplied in a constant quantity to the non-diaphragm electrolytic cell 15, and dilution water is supplied in a fixed quantity to the electrolytic cell 15 by a pump 14' to prepare an approximately 3% salt solution, and this salt water is electrolyzed. Sodium hypochlorite is produced. The obtained sodium hypochlorite is sent to the sodium hypochlorite storage tank 17 through piping 16 and stored there.

On the other hand, pool water 21 stored in the pool 20
The water is extracted from the bottom through piping 22 or overflows and collected in a balancing tank 23, from which it is sucked up through piping 24 by a circulation pump 25, filtered by a filter 26, and then returned to the pool 20 through piping 27.

One end of a sodium hypochlorite injection pipe 30 is connected to the filter outlet pipe 27, and the other end of this pipe 30 is connected to a discharge port of a sodium hypochlorite injection pump 31. The sodium hypochlorite injection pump 31 injects the sodium hypochlorite 40 stored in the aforementioned storage tank 17 into the circulation pool water through the piping 30. On the other hand, a pipe 32 is connected to the filter inlet pipe 24, and the pool water 21 before filtration is sent through the pipe 32 to a residual chlorine sensor 34 of a residual chlorine monitor 33.

The residual chlorine monitor 33 monitors the pool water 2.
1 and sends a signal S indicating the measured concentration to the pump control panel 35. The sodium hypochlorite injection pump 31 is operated by being supplied with electric power by the pump power cable 36, but the pump control panel 35 controls the operation of the pump 31 according to the free residual chlorine concentration indicated by the signal S.
N, turn off.

In this example, the sodium hypochlorite injection pump 31 is operated when the free residual chlorine concentration is 0.45 ppm or less, and when it reaches 0.5 ppm, the pump 31 is stopped and the next operation is performed. Discontinue sodium chlorite injection. Also, the capacity of the sodium hypochlorite injection pump 31 is 100
0cc/min, pool water circulation amount is 90m3/hour. The main specifications of the electrolyzer 13 are as follows.

[0023] Total electrolysis current
160A
Anode material
Pt (50%) Pd on Ti plate

(50%) coated alloy
Sodium hypochlorite production capacity 150 g/hour

Generated sodium hypochlorite concentration 1050
0 ppm
pH of generated sodium hypochlorite
9.1
By controlling the sodium hypochlorite injection as described above, the free residual chlorine concentration in the pool water 21 is kept in the range of 0.4 ppm to 0.7 ppm, and the trichloramine concentration is 0.1 It was suppressed to less than ppm. At this time, no chlorine odor was felt around pool 20. Further, even after operating this system for one year, no scale trouble occurred in each piping for injecting sodium hypochlorite 40.

In place of the diaphragmless electrolytic cell 15 of the above embodiment and the anode of this diaphragmless electrolytic cell 15 (this is referred to as anode A), an anode B in which a Ti plate is coated with an alloy of Pt and Ir is used. The relationship between the effective chlorine concentration and pH of the produced sodium hypochlorite was investigated using an electrolytic cell using an anode C having a Ti plate coated with Pt and an electrolytic cell using an anode C in which a Ti plate was coated with Pt. The results are shown in FIG. As shown in the figure, in order to generate at pH 9.1, the effective chlorine concentration of the generated sodium hypochlorite is 10.5 g/l when using anode A, and 3.5 g/l when using anode B. g/l, 1.0 g/l for anode C
becomes. Although the requirements for trichloramine production and scale prevention are satisfied with Anode A, Anode B, and Anode C, it is more economical to use a smaller unit of salt, so Anode A
It is preferable to use

[Brief explanation of the drawing]

FIG. 1 is a flow diagram showing a pool water sterilization system implementing the method of the present invention.

[Figure 2] Graph showing the relationship between the amount of chlorine input to water, the amount of residual chlorine, and ammonia nitrogen related to the present invention

[Figure 3
] The relationship between the effective chlorine concentration and pH of sodium hypochlorite,
Graphs shown for each anode material of the electrolytic cell

[Explanation of symbols]

10 Salt 11 Salt dissolving tank 9, 12, 16, 22, 24, 27, 30, 32
Piping 13 Electrolyzer 15 Diaphragmless electrolytic cell 21 Pool water 25 Pool water circulation pump 31 Sodium hypochlorite injection pump 33
Residual chlorine monitor 34 Pump control panel 40 Sodium hypochlorite

Claims (2)

[Claims] Claim 1: A method for sterilizing circulating water containing ammonia nitrogen, which comprises injecting sodium hypochlorite obtained by electrolyzing saline water in a non-diaphragm electrolytic cell into the water. A method for sterilizing drinking water, comprising: measuring the concentration of free residual chlorine in the drinking water; and controlling the injection of the sodium hypochlorite so that the measured concentration falls within a predetermined range. 2. The method for sterilizing water according to claim 1, wherein a metal electrode containing palladium is used as the anode of the membraneless electrolytic cell.