Abstract

Tunisian untreated wastewater exhibits an average of 30 human helminth eggs per litre. After treatment, the concentration decreases to one egg per litre, or more in some cases. The percentage removal cited for wastewater processes provides no real indication of the destruction of the organisms, but merely of their transfer to another medium. In this study, we report the use of an environmentally friendly photoactive compound for wastewater disinfection. Photosensitization involves the generation of very toxic short-lived species on absorption of light by porphyrin. Microorganism photosensitization is potentially useful for sterilization and for the treatment of certain bacterial diseases. Gram-positive bacteria can be photoinactivated by a range of photosensitizers, but Gram-negative bacteria are not usually susceptible to photosensitized destruction. Our findings clearly demonstrate that the cationic meso-substituted porphyrin, tetra-(4-N-methyl-pyridyl) porphin tetra-tosylate (T₄MP_YP), is an efficient photosensitizer of helminth eggs on visible light illumination. The microscopic observation of helminth eggs shows that many types of ultrastructural alterations are potentially associated with exposure to T₄MP_YP and an adequate intensity of light: morphological changes without breakage; small alterations of eggshells; complete destruction. The degree of egg alteration increases with both increasing T₄MP_YP concentration and irradiation time. Moreover, the dissolved oxygen concentration, water quality and the type of eggs can influence the sensitivity of helminth eggs to photosensitization. Indeed, suspended solids (turbidity) were the most influential solution parameter on the efficiency of the photochemical process.