Agriculture in Tunisia faces acute problems of water quality and quantity caused by limited conventional water resources. One possibility to cope with low water resources is to purify wastewater for reuse. Among different methods for the disinfection of wastewater, the inactivation of fecal coliforms using a combination of a photosensitiser (Rose Bengal, Methylene Blue, cationic porphyrin) with sunlight was determined on a small scale. In parallel the sensitizer photobleaching was also followed under the same conditions. The results described in this paper show that the meso-substituted cationic porphyrin is more efficient and more photostable than Methylene Blue and Rose Bengal in wastewater. A lower cationic porphyrin concentration, 1 microM, resulted in very little cell death. Higher concentrations, 5 microM or 10 microM, produced more cell death. Nevertheless there was a small difference between concentrations 5 and 10 microM. By increasing the duration of irradiation we can improve the log reduction in bacteria and compensate for a low concentration of sensitizer or for a less efficient type of sensitizer. The same log reduction in fecal bacteria was obtained with 5 and 10 microM of cationic porphyrin during the fourth hour of treatment.
Helminth eggs and protozoan cysts were enumerated in raw and treated wastewater in Tunisia in order to determine their removal by wastewater treatment and to provide quantitative data for developing regulations for wastewater quality that are currently lacking. Raw and treated wastewater samples were collected from 17 plants in Tunisia during 2006-2007 and analyzed for parasites using the modified Bailenger method. Two groups of parasites, namely, Ascaris sp., Entamoeba coli, Enterobius vermicularis, and Taenia sp. (group 1) and Entamoeba histolytica/dispar, Giardia sp., and Taenia sp. (group 2) could statistically be distinguished according to their removal by wastewater treatment. Group 1 parasites were removed by 1.1 log(10) (92.4%) and group 2 parasites by 0.61 log(10) (76%). The ubiquitous presence of parasitic protozoa in Tunisian wastewater and ineffective wastewater treatment lead to their proliferation in surface waters with a high probability of exposure of human and animals to these parasites and consequent adverse health effects, as is apparent from epidemiologic data as well. This study provides a quantitative basis for risk assessment studies and development of mitigation strategies, such as improving wastewater treatment efficiency.
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