The present study has consisted to the disinfection of water by photosensitization with Bergamot essential oil. The results obtained show negligible inhibition of fecal coliforms in untreated water exposed to light. In contrast, for treated water exposed to light, complete inhibition of fecal coliforms was observed after one hour of exposure. In treated water kept in the dark, no inhibition of fecal coliforms was observed from the beginning to the end of the experiments. The activity observed in this oil is due to 5-methoxypsoralen (MOP-5). In the presence of light, this molecule is excited (1MOP-5*). The singlet excited form undergoes an intersystem crossing (transition from the singlet to the triplet state); from the triplet state, the 5-methoxypsoralen (3MOP-5*) transfers its energy to triplet oxygen (3O2). The triplet oxygen undergoes a transition from a triplet to a singlet state (1O2*). The singlet oxygen generated initiates a series of reactions with biomolecules, particularly the nitrogenous bases of DNA. These photo-oxidation reactions lead to the destruction of microorganisms.

This study aimed to improve solar water disinfection through the use of photosensitizing substances (coumarin extracts of Citrus reticulata, Citrus aurantium and Citrus maxima). Solar disinfection shows negligible inhibition of fecal coliforms after 60 minutes of exposition to the sunlight. On the other hand, for photodynamic disinfection, complete inhibition is noted after 60 minutes of exposition. Regarding fecal enterococci, negligible inhibition is noted after 30 minutes for solar disinfection. On the other hand, for all coumarin extracts (Citrus reticulata, Citrus aurantium and Citrus maxima), complete inhibition is noted after 30 minutes of exposition to the sunlight. These results show that the use of coumarin extracts of Citrus reticulata, Citrus aurantium and Citrus maxima significantly improves solar disinfection. Additionally, these results show that fecal enterococci are more sensitive to photodynamic disinfection than fecal coliforms. This difference in sensitivity is due to the constitution of their cell walls. The wall of fecal coliforms (Gram-) is rich in lipopolysaccharides. These constitute a barrier to the passage of singlet oxygen. Whereas, the wall of fecal enterococci (Gram+) is easily penetrated by singlet oxygen (1O2) because it lacks lipopolysaccharides. After its passage, singlet oxygen destroys cellular constituents. This leads to the death of the bacterial cell.