Adelaide Almeida
University of Aveiro, Portugal
Title: Photodynamic inactivation of microorganisms in waste water: An effective approach with low environmental impact
Biography
Biography: Adelaide Almeida
Abstract
Waste water (WW) with a high content of pathogens, containing even multidrug resistant microorganisms, particularly when hospital effl uents are included, is a current area of concern aff ecting the quality of natural water. Hospital WW effl uents are discharged as conventional urban effl uents to the municipal sewage system without prior treatment. Secondary treatment of WW is usually considered suffi cient; however, the secondary effl uent still contains infective concentrations of microorganisms (MO). In order to reduce the concentration of pathogens in WW to levels comparable to those found in natural water, the tertiary effl uent is usually subjected to disinfection with chlorine, ozone or ultraviolet light (UV). Chlorination and UV may lead to the formation of toxic products and also might result to the selection of resistant genes. Th e antimicrobial photodynamic inactivation (PDI) may represent an alternative to the traditional expensive, unsafe and not always eff ective disinfection methods. PDI with photosensitizers (PS) and visible light has demonstrated to be eff ective in the destruction of MO via photogeneration of reactive oxygen species (ROS) able to induce microbial inactivation. As PDI is a multi-target approach, the selection of photo-resistant strains aft er treatment is unlikely. Th e main goal of this work was to assess the effi ciency of PDI on non-clinical and on clinical multidrug-resistant (MDR) bacteria in domestic and hospital waste water in order to evaluate its potential use to treat WW effl uents. Th e effi ciency of PDI was assessed using a cationic porphyrin as photosensitizer (PS), non-clinical bacteria and clinical MDR-bacteria either in phosphate buff ered saline or in fi ltrated domestic and hospital waste water. Th e synergistic eff ect of PDI and antibiotics (ampicillin and chloramphenicol) was also evaluated. Th e results show an effi cient inactivation of non-clinical and MDR bacteria in PBS (reduction of 6-8 log aft er 270 min). In waste water, the inactivation of bacteria was also effi cient and the decrease in bacterial survival starts even sooner. A faster decrease in bacterial survival occurred when PDI was combined with the addition of antibiotics. It can be concluded that PDI has potential to be an eff ective alternative for the inactivation of bacteria, even MDR; in waste waters and that the presence of antibiotics in hospital WW may enhance its eff ectiveness.