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The quality of the dilution water has a significant meaning to the accuracy of the determination results. Therefore, it is required that the oxygen consumption of the dilution water blank for 5 days must be less than 0.2mg/L, and it is best to control it below 0.1mg/L. Should be between 0.3-1.0mg/L.
The key to ensuring the quality of dilution water is to control the lowest organic content and the lowest content of substances inhibiting the reproduction of microorganisms. Therefore, it is best to use distilled water as the dilution water. It is not advisable to use pure water made from ion exchange resins as the dilution water. Ionized water often contains organic matter separated from the resin. If the tap water used to prepare distilled water contains certain volatile organic compounds, in order to prevent them from remaining in the distilled water, a pretreatment to remove organic compounds should be performed before distillation. The distilled water produced by the metal distiller should pay attention to check the metal ion content in it to avoid suppressing the reproduction and metabolism of microorganisms and affecting the accuracy of the BOD5 determination results.
If the dilution water used does not meet the application requirements due to organic matter, add a suitable amount of aeration tank inoculum and store it at room temperature or 20oC for a certain period of time to eliminate the impact. The amount of inoculation is based on the principle that the oxygen consumption is about 0.1mg/L in 5 days. In order to avoid the propagation of algae, the storage must be carried out in a dark room. If there is sediment in the diluted water after storage, only the supernatant can be used, and the sediment can be removed by filtration.
In order to ensure that the dissolved oxygen of the dilution water is close to fullness, if necessary, a vacuum pump or a water jet can be used to inhale the purified air, or a micro air compressor can be used to inject the purified air, or an oxygen bottle can be used to inject pure oxygen, and then The oxygenated diluted water is placed in the 20oC incubator for a certain period of time to balance the dissolved oxygen. Dilution water placed at a lower room temperature in winter may contain too much-dissolved oxygen. In summer, the high-temperature season is just the opposite. Therefore, when the room temperature is significantly different from 20oC, it must be placed in the incubator for a period of time to ensure that it is stable. Cultivate the balance of oxygen partial pressure in the environment.
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