Impact of different physicochemical parameters in the antimicrobial Photodynamic Therapy success

Wastewater (WW) containing identified and emergent pathogenic microorganisms (MO), is subject of great concern, due to the impact of these effluents on the quality of natural receiving waters [1,2]. A secondary biological treatment in a well-operated treatment plant can be very efficient for the removal of carbon (85-95%), nutrients (nitrates and phosphates) and suspended solids content in raw WW. However, this process is inefficient on the inactivation of MO, including pathogens that can survive through the treatment and an additional oxidation process is often required for effluent disinfection [1]. The traditional tertiary treatments, based on disinfection methods to reduce pathogens concentration in WW (e.g., chlorination, ozonation, UV) are expensive, sometimes ineffective, and unsafe, highlighting the need for new technologies [3]. The promising in vitro results of antimicrobial Photodynamic Therapy (aPDT) to eradicate MO suggest its effective application as a disinfection process to improve WW quality before its release into the environment [4]. One of the aims of our work was to assess if the principles of aPDT can be successfully extended to real contexts, namely for the microbial inactivation on WW. We have been performed experiments with different water matrices compositions to inquire about the influence of some of their physicochemical parameters in the effectiveness of microbial photodynamic inactivation of the bacterium Escherichia coli (used as bacterial model of faecal contamination) [2]. The results of bacterial photoinactivation in water samples from aquaculture and wastewater treatment plants (receiving domestic or industrial WW, or a mixture of domestic and industrial WW) facilities, seawater (from different locations) will be presented and discussed.