What is chlorine disinfection of well water? Sterilizers and injection amounts [Basic knowledge]

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■What determines the injection amount? The injection rate of the disinfectant is set considering water quality, retention time, season, and other factors to ensure that the residual chlorine concentration at the water supply faucet always maintains the specified level. As a guideline, the Large-Scale Cooking Facility Hygiene Management Manual states that when using well water for disinfection, it is necessary to check daily that the free residual chlorine is at least 0.1 mg/L. ■Caution regarding hydrogen sulfide and ammonia! The components dissolved in well water consume some of the injected chlorine. The chlorine consumption per 1 mg/L of component is as follows, compared to 0.6 mg/L of divalent iron and 1.3 mg/L of divalent manganese: 1. Hydrogen sulfide: 8.5 mg/L 2. Ammonia: 7.6 to 15 mg/L 3. Nitrite: 1.5 mg/L It is evident that the consumption is significantly higher compared to iron and manganese. ■Estimating the injection amount A 5% effective chlorine solution contains approximately 50 mg of effective chlorine per 1 mL, not considering specific gravity. If you want to add 0.5 mg/L of chlorine to a water flow rate of 20 L/min, that would be 10 mg per minute, which means approximately 0.2 mL of the solution per minute. In practice, the consumption due to components will be added, so adjustments are made while measuring the residual chlorine at the faucet.

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■ Chlorine is present, but E. coli?! There have been cases where pathogenic E. coli was detected in the water used at a ryokan (traditional inn) that uses spring water, where chlorine was directly added to the piping connected to the kitchen. It is presumed that the water was supplied before the chlorine had an effect. On the other hand, facilities that added chlorine to the piping flowing into the water storage tank did not detect E. coli. ■ Place the injection point as upstream as possible To ensure sufficient contact time, the injection should be done just before the receiving tank if there is one, or as close to the water source as possible if there isn't. This is because time is needed for the water to come into contact with the disinfectant to achieve its effect. ■ What causes the injection to stop? In injection systems, injection failures can occur due to the formation of air bubbles or scale. Therefore, it is also important to check the actual injection amount. There have been cases in deep well facilities where residual chlorine levels dropped due to hose blockages. ■ Be cautious of chemical degradation in summer! Sodium hypochlorite decomposes and loses effectiveness when stored for long periods, especially at high temperatures. At Torii, we offer consultations regarding sodium hypochlorite and injection equipment. Please feel free to reach out to us for advice.