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平成17年度 船舶バラスト水等処理技術実用化のための調査研究 報告書

 事業名 船舶バラスト水等処理技術実用化のための調査研究
 団体名 日本海難防止協会 注目度注目度5


3 REACTION OF OZONE AND BROMATE ION IN WATER
 Ozone is finally decomposed to oxygen and water by self-decomposition in water. Its half-life period in the seawater, for instance, is 5.8 seconds. Organics, inorganics, and other substances are contained in the water and Ozone reacts to them. Decomposition of Ozone is mainly caused by its reaction to such substances contained in nature. Other decomposition factors include temperature and pH.
 
 Ozone decomposition rate increases in accordance with the increase of temperature and pH. In the acidity range, however, the increase of decomposition rate is not high. The rate increases fast in the neutral to alkaline range at any temperature. This tendency accelerates with the increase of temperature. The pH value of ballast water is generally 5 to 8, in which range the self-decomposition of Ozone progresses fast. Therefore, it is hard to consider that the Ozone remains and gives any influence on the ecosystem where the ballast water is discharged.12
 
 Ozone is injected to the ballast water to maintain 4mg/L at the maximum in this system. Ozone self-decomposition is composed of two categories, which are firstly self-decomposition as described above and secondly reaction with organic and inorganic substances.
 
 In the seawater the latter reaction specifically occurs This is because bromate ion (BrO3) is generated by reacting with bromide ion which contains 60mg/L in the seawater. 3.3mg/L of bromate ion is generated when Ozone with 4mg/L at the maximum is injected to the ballast water. Half-life of bromate ion is about 12 hours. Discharge ballast water may cause a concern to the environment, depending on storage time in the tank after Ozone treatment.
 
 The materials generated by reacting with organic matters where low level of organic concentration in COD such as 0.5-2.0mg/L, average concentration in the normal seawater is very low compared with the quantity produced by reacting with bromate ion described above. This is the negligible amount.
 
 Ozone shows in the fresh water a behaviour different from one in the seawater. Since there exists little bromate ion in the fresh water bromate ion is not produced by reacting with Ozone. Furthermore, since the ratio of Ozone to be consumed by reacting with organic and inorganic matters is low. majority of Ozone decomposed in the fresh water will be consumed by self-decomposition. As half-life period of Ozone is 30 minutes in the fresh water, it is considered that it does not remain at time of ballast water discharge.
 
4 ANALYTICAL METHOD OF ACTIVE SUBSTANCES AND RELEVANT CHEMICAL
4.1 Analysis of Ozone
 
 Ozone concentration is measured as a gas or dissolved Ozone. Two analytical methods are used. The ultraviolet rays absorption method makes use of the fact that the Ozone has the absorption layer in the ultraviolet region. Another method is the iodine titration method. Actual analytical methods are referred in “IOA Standard Committee, Brussels, 1987”. No method has been specified about the analysis of Ozone in the seawater. This is because about 60 mg/L of bromide ion (Br 7 -), contained in the seawater and Ozone supplied into the seawater react fast to each other to generate bromate ion (BrO3 -), etc., and analysis of Ozone dissolved in the seawater is very difficult. Generally, dissolved Ozone in the seawater is measured as oxidant by the iodine titration method. Ozone concentration referred to in this application form was obtained by the iodine titration method. Analysis accuracy of this method is 0.1 mg/L. This accuracy is the most suitable for the practical use and provides a sufficient level from the viewpoint of the Ozone toxicity level.
 
4.2 Analysis of bromate ion
 
 Any specific method has not been established for the analysis of bromate ion concentration in the seawater. Usually, it is measured by the ion chromatogram or by the iodine titration method as oxidant. Values of bromate ion concentration in this application form were obtained by the iodine titration method. Measurement accuracy of iodine titration method is 0.15mg/L similar to Ozone.
 
 Analytical methods for Active Substance and relevant chemical are listed in Table 7.
 
Table 7. Analytical method for Ozone and Bromate ion
Substance Analytical Method Analytical accuracy Reference/Comment
Ozone (gas) and dissolved Ozone Ultraviolet rays absorption method few ppm±few%FS IOA Standardization Committee, 12)
Iodine titration method (as oxidant) 0.01mg/l±1%FS
Bromate ion Ion chromatogram 2μg/l AWWA13)
Iodine titration method (as oxidant) 0.01mg/l±1%FS IOA Standardization Committee, 12)
Ballast Water (seawater) Ion chromatogram
2μg/l
AWWA13)
Iodine titration method (as oxidant) 0.15mg/l±1%FS I
 
5 EXPOSURE SCENARIO
5.1 Exposure scenario to aquatic organisms
 
 As for the exposure to aquatic organisms, only exposure to bromate ion contained in the ballast water discharged after the treatment of seawater takes place.
 
5.2 Exposure scenario to human beings
 
 Ozone and bromate ion may be taken by men through aquatic organisms.
 
5.3 Exposure scenario to crew
 
 Exposure of Ozone to crew may take place by leaking from the Ozone generator, piping, etc.
 
5.4 Scenario of influence on hull
 
 Corrosion of the hull may take place due to the Ozone gas, dissolved Ozone, and bromate ion.


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更新日: 2019年9月21日

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