Experimental Study on the Relationship Between the Change of Free available Chlorine and the Increase Rate of Disinfection by-products according to Operating Conditions of three Types of Sodium Hypochlorite

Objectives : This study was conducted to suggest field operating conditions that can minimize disinfection by-products for three types of sodium hypochlorite.Methods : In this study, changes in free available chlorine, chlorate and bromate were analyzed according to storage temperature, storage time and presence or absence of sunlight for three types of sodium hypochlorite(two types of bleach and one type of sodium hypochlorite made on-site hypochlorite generator).Results and Discussion : In the case of bleach with 12% free available chlorine, when operating with a target of 10% of more of free available chlorine, the storage time for each storage temperature was 3 days at 40℃, 13 days at 30℃, 27 days at 20℃, 85 days at 10℃, and 200 days at 5℃. In the case of bleach with 5% free available chlorine, when operating with a target of 4% of more of free available chlorine, the storage time for each storage temperature was 37 days at 35℃, 255 days at 20℃, 1,343 days at 10℃, and 4,821 days at 4℃. In the case of sodium hypochlorite with 0.8% free available chlorine made on-site hypochlorite generator, when operating with a target of 0.7% of more of free available chlorine, the storage time for each storage temperature was 10 days at 3 5℃, 42 days at 20℃, 470 days at 10℃, and 1,770 days at 4°C. As a result of evaluating the quality change according to the presence or absence of UV protection, the free available chlorine decreased rapidly when exposed to sunlight, whereas the free available chlorine decreased slowly in the case of indoor storage.Conclusion : Bleach with 12% free available chlorine can be stored for about 60 days at 15℃, and bleach with 5% free available chlorine can be used within about 6 months at 15℃. And sodium hypochlorite with 0.8% free available chlorine can be used within 10 days at room temperature. In addition, when storing sodium hypochlorite, it is suggested that it be stored indoors protected from sunlight.