Applications of synthetic non-porphyrinoid photosensitizers for antimicrobial photodynamic disinfection of natural water systems

Inefficiently treated wastewater (WW) poses public health risks by harboring pathogenic microorganisms, highlighting the need for effective disinfection technologies without promoting antimicrobial resistance, in accordance with Sustainable Development Goal 6 and the One Health approach. Conventional WW treatment methods, such as chlorination, ozonation, and UV irradiation, can reduce microbial loads but often generate harmful byproducts, promote microbial resistance, and possess other limitations of being expensive, unsafe, or partially ineffective. Therefore, as an alternative disinfection approach, Antimicrobial Photodynamic Disinfection (APDD) has emerged as a promising strategy, employing light-activated photosensitizers (PS) to inactivate microorganisms upon irradiation with light of a specific wavelength in the presence of molecular oxygen. Although antimicrobial photodynamic therapy has demonstrated broad-spectrum activity against a wide range of microorganisms, including resistant ones and biofilms, it has not yet been approved and commonly used for practical, real-world applications of APDD of WW. This review summarizes the progress made with synthetic non-porphyrinoid PSs, as they were the first dye-based PSs used for photochemical water disinfection, thus highlighting their antimicrobial activities and modes of action, for potential application in WW disinfection. The review further discusses the current shortcomings of the practical application of APDD in WW treatment, and future developments, such as integration into solid support materials and solar-powered light sources, to improve the techno-economic viability to maximize its potential to provide microbes-free water in resource-limited settings and challenging environmental conditions.