Efficient solar disinfection (SODIS) using polypropylene based transparent jerrycans: An investigation into its effectiveness, viability, and water sample toxicity

Abstract

By 2025 it is believed that over 50% of the world’s population will have insufficient access to safe drinking water. This issue is of considerable importance in rural areas that lack access to water disinfection technology and require a relatively low cost disinfection method. Solar Disinfection (SODIS) has been identified as a suitable method for water disinfection using 2-L polyethylene terephthalate (PET) bottles. In this study, we have examined the use of 10-L polypropylene (PP) transparent jerrycans (TJC) as an alternative plastic container for SODIS. These low cost TJC could be used in rural areas for the collection and treatment of drinking water. The PP TJC were analysed for their ability to inactivate a range of microorganisms, their structural properties after advanced weathering and their cytotoxicity after extended use. Escherichia coli, MS2 and Cryptosporidium parvum were used as microbial indicators in well water to ascertain the efficacy of the SODIS process. SODIS was capable of a 6 log reduction value (LRV) in E. coli after 105 min, a 3 LRV in MS2 after 5 h and 3 LRV in C. parvum after 2 days of treatment. This inactivation corresponds to a 2 star performance according to the Household Water Treatment and Safe Storage (HWTS) from the WHO guidelines. Toxicity analysis using the MTT assay of water samples stored in the TJC over 9 months found that all samples had a cell viability of above 80%. According to ISO 10993–5, this indicates the samples are non-toxic to the cell line and are biocompatible. Advanced weathering of the PP found that, after 5 weeks, the plastic underwent photodegradation resulting in a decrease in UVA and UVB transmission that stabilised at 20% and 5%, respectively. The photodegradation also impaired the mechanical properties of the plastic causing it to become brittle and more susceptible to breaks after two weeks. The PP was found to be effective at inactivation of microorganisms, non-toxic to human cells but it was found to degrade after two weeks of accelerated ageing. Within the first two weeks of accelerated ageing the plastic retained its plasticity and had elongation of breaks of 570% and 550% for week 1 and 2, respectively, but after this period of time the plastic became brittle and the elongation of break dropped to 10%. Future studies are directed toward developing appropriate UV stabiliser for PP to increase the structural lifetime.