Good optical transparency is not an essential requirement for effective solar water disinfection (SODIS) containers

The efficacy of 10 L polypropylene (PP) transparent jerry cans (TJCs) to inactivate E. coli, MS2-phage and Cryptosporidium parvum via solar water disinfection (SODIS) was tested in well water or general test water under natural sunlight. Food-safe PP was used to manufacture the TJCs and a clarifying agent was added to improve optical transparency in the UV–visible range. 10 L PP TJCs and 2 L polyethylene terephthalate (PET) bottles were filled with well water, spiked separately with (~106 CFU/mL of E. coli, ~106 PFU/mL of MS2 phage and 5 ×105C. parvum oocysts per litre) and exposed to natural sunlight for 6 h. While the 10 L PP TJC prototype had poorer transparency (UV-B 0.001%, UV-A 4.29%, and visible 92% for TJCs without clarifier and UV-B 1.36%,
UV-A 8.01%, and visible 90.01% for TJCs with clarifier) than standard 2 L PET (UV-B 0.72%, UV-A 10–85%, and visible 80–90%); log reduction values (LRVs) > 5, 2 and 0.8 for E. coli, MS2-phage, and C. parvum, respectively, were observed for the TJCs within six hours respectively, which is a minimum standard for drinking water established by the World Health Organisation (WHO). We observed similar inactivation kinetics for all three organisms in PP TJCs and PET bottles despite the poorer optical transparency properties of the SODIS jerry cans. Therefore, for effective SODIS, container optical transparency is not as important as previously believed. We conclude that good visible transparency is not a necessary requirement for containers intended for SODIS use.