Use of Novel Additives in Combination with Sodium Dichloroisocyanurate for Enhanced Disinfection of Cryptosporidium parvum in Drinking Water

In settings where adequately treated, continuously pressurized piped drinking water is not available, household water treatment and safe storage (HWTS) interventions including chemical disinfection, primarily chlorination, are widely used methods for improving the microbial quality of drinking water. Sodium dichloroisocyanurate (NaDCC) tablets are used for HWTS applications in many point-of-use and emergency settings as they are safe, inexpensive, easy to use, and have a long shelf life. However, while NaDCC disinfectants rapidly inactivate many bacteria and viruses, protozoan parasites such as Cryptosporidium parvum are more resistant to chlorine. The aim of this research was to assess the potential of novel chemical disinfectants combining NaDCC (as a source of free chlorine) with one or more sources of novel additive disinfectants (together, called “candidate disinfectant”) for inactivating Clostridium sporogenes spores (as an indicator for disinfection of chlorine-resistant spores) and C. parvum oocysts in drinking water. NaDCC was dosed either separately or in combination with selected additives at concentrations below levels of health concern to batch reactors seeded with microorganisms in natural surface water (20-25°C). In addition, the surface water was acidified in many trials (e.g. pH 4.0 – pH 6.0) to facilitate disinfection. In natural surface water, similar disinfection rates were observed for C. sporogenes spores in the long term, with significant difference between NaDCC and candidate disinfectant at t= 10 minutes. Slightly faster disinfection was observed for C. parvum oocysts in the presence of the candidate disinfectant. Free chlorine residuals were measured during inactivation trials and found to decrease significantly over experiment contact times. Furthermore, free chlorine decreased much more rapidly in disinfection reactors with 50% headspace than in reactors which were completely filled, and inactivation proceeded more slowly in reactors with 50% headspace. As expected, a significant negative association between pH and inactivation rate was also observed (p<0.05): log reduction value of C. parvum in natural surface water to which the candidate disinfectant had been added was greater at lower pH values (r = 0.88) over the pH range 4-7. Future work may include disinfection experiments with: additional combinations of novel additives (as well as continued evaluation of those currently studied) and/or the addition of safe and nontoxic natural coagulant materials. In addition, disinfection kinetics will be further characterized.Master of Science in Public Healt