Weathering of plastic SODIS containers and the impact of ageing on their lifetime and disinfection efficacy

This work aims to study the ageing of plastic materials suitable for manufacturing solar water disinfection (SODIS) containers, such as PET, polymethylmethacrylate (PMMA), and polypropylene (PP) with and without UV-stabiliser. The evolution of mechanical and optical properties, and disinfection rates were studied over different weathering periods. PMMA and PP with a 1% content by weight of UV-stabiliser were shown to be excellent candidate materials for manufacturing SODIS devices, since they presented stable optical and mechanical properties, and both transmit UVB radiation. Since PMMA is a UV resistant but fragile, easily scratched material with a lifetime above one year, it should be selected for static SODIS devices, while PP with 1% of UV-stabiliser should be chosen for portable devices because of its great resistance and elasticity for up to nine months of solar exposure. Both materials were considered profitable on the basis of their lifetime/costs ratio. PET showed great mechanical properties for one year but, in contrast, suffered of a deterioration of its optical properties and disinfection rates. PP without UV-stabilisers suffered a dramatic degradation after a very short exposure of 2 months. Finally, a kinetic model that considers the radiation spectral distribution (thus, the transmittance spectra of the plastics as a function of the ageing time) is proposed to estimate the required solar exposure time to achieve water disinfection for the proposed plastic SODIS containers. A good agreement between predicted and experimental data was achieved, especially for containers manufactured with PET and both PPs (errors below 25%).