Photodynamic inactivation of microorganisms in wastewater using porphyrin-based dendrimers solutions

Antimicrobial photodynamic inactivation (aPDI) is an emerging alternative for reducing microbial loads in complex matrices such as wastewater. In this work, a porphyrin-dendrimer conjugate (Pf-Ds-G2.0) was synthesized, structurally characterized and evaluated as a photosensitizer under visible light. Pf-Ds-G2.0 generated singlet oxygen with a quantum yield of 0.35 and exhibited light-dependent antimicrobial activity in real wastewater samples. Under visible-light irradiation, Pf-Ds-G2.0 produced moderate reductions in microbial biomass (~ 20% microbial reduction after 6 min irradiation), supported by both OD and CFU measurements, while dark controls showed no inhibition. Partial regrowth was observed at longer irradiation times, likely due to oxygen depletion and the heterogeneous nature of the microbial community. These findings demonstrate the potential of dendritic porphyrins for wastewater aPDI and highlight the need for further optimization of irradiation conditions, oxygen availability and sensitizer formulation to achieve more sustained inactivation in complex systems.