Solar Water Disinfection Made Quantitative: A UV-A Dose Model for a PET Bottle and a Fixed-Geometry Reflector Backing

A quantitative UV-A dose model for solar water disinfection (SODIS) in a 1.5 L PET bottle: solar irradiance is converted to in-water UV-A fluence using a UV-A fraction of 0.046, PET transmittance 0.85, and depth-averaged turbidity attenuation, and compared with a 3-log E. coli fluence requirement of 200 kJ/m2. A fixed-geometry foil V-trough reflector backing (aperture ratio 2.2, modelled clear-sky gain 1.72, materials cost $0.96) cuts the clear mid-latitude summer time to 3-log E. coli from 1.97 h to 1.23 h, but does not make a single overcast day dependable for viruses (600 kJ/m2) or Giardia cysts (1000 kJ/m2). SIMULATED, NOT MEASURED.