Residual Maintenance Using Sodium Hypochlorite, Sodium Dichloroisocyanurate, and Chlorine Dioxide in Laboratory Waters of Varying Turbidity

Sodium hypochlorite (NaOCl) and sodium dichloroisocyanurate (NaDCC) are commonly used for household water treatment (HWT); chlorine dioxide (ClO2) is a potential new HWT option. We compared the residual maintenance of NaOCl, NaDCC, and ClO2 over 24 hours using recommended dosages (2 and 4 mg/L) in waters of varying turbidity (0-300 NTU, from kaolin clay or creek-bottom sediments) and total organic carbon (TOC) concentrations (0-100 mg/L), for a total of 324 reactors. NaOCl and NaDCC had similar free chlorine decay rates, and ClO2 decayed more rapidly across all of the tested conditions. Little variability was observed across clay-based turbidity levels and TOC concentrations. With a dosage of 2 mg/L, a residual >= 0.2 mg/L was maintained at 30 NTU for NaOCl and 100 NTU for NaDCC; for ClO2, 4 mg/L were required to maintain >= 0.2 mg/L under all conditions except at zero turbidity. Comparisons with data from the literature suggest that the three compounds would inactivate E. coli, rotavirus, and Giardia cysts within 1 hour under all conditions, except 300 NTU for NaOCl and NaDCC. All three disinfectants are similarly efficacious for this usage; however, differences are seen in decay rates that may influence disinfectant selection depending on water storage time.