Beyond the Pipeline: Assessing the Efficiency Limits of Advanced Technologies for Solar Water Disinfection

This critical review analyzes and compares the efficiency of select technologies that harness solar energy for point-of-use water disinfection, including photocatalysts, photosensitizing chromophores, UVC light-emitting diodes, and visible-to-UVC upconversion phosphors. The volume rate of water that each material can treat to achieve 99% inactivation of model microorganisms, given the same sunlight exposure, was estimated on the basis of literature data and theoretical predictions, in the context of both currently reported efficiencies and theoretical thermodynamic maximum efficiencies. Each material is further critiqued in terms of the spectral match with sunlight, quantum efficiency, and the relative strength of the resulting disinfecting agent such as hydroxyl radicals, singlet oxygen, and UVC radiation. This review emphasizes critical needs for disinfection strategies that can efficiently inactivate more than one type of microorganism. In addition, the approach described herein can guide future research in efforts to identify more efficient materials and technologies for capturing sunlight for water disinfection