Une porphyrine comme photosensibilisant des eaux d'irrigation, photostabilité et efficacité

Le processus de photosensibilisation (phototraitement) de l'eau suscite beaucoup d'intérêt, car il implique trois composants qui sont individuellement inoffensifs pour le milieu biologique, à savoir le photosensibilisant, la lumière et l'oxygène moléculaire. La photostabilité de la porphyrine tétra-méso-cationique (T4MPyP) dans l'eau usée et l’efficacité du phototraitement dépend de la concentration du photosensibilisant, de la qualité de l'eau (contaminants organiques, turbidité, pH, taux d'oxygène dissous et épaisseur de la lame d'eau) ainsi que de l'intensité et de la nature du rayonnement lumineux. L’étude expérimentale consistait à apporter à un sol sableux i) de l’eau usée secondaire traitée par boues activées, ii) la même eau usée, mais phototraitée avec 5 μM∙L-1 de T4MPyP pendant 6 h d’ensoleillement, et iii) une eau de puits. L’eau usée phototraitée était conforme aux normes tunisiennes (NT 106.03) pour l’irrigation sans restriction au niveau du taux de bactéries indicatrices de pollution fécale (l’abattement des coliformes fécaux avoisinait 99,99 %), mais renfermait encore une concentration résiduelle de porphyrine (environ 35 % de la concentration initiale). À la fin de l’expérimentation, la configuration saline du sol dépendait de la qualité des eaux d’irrigation. Dans le cas des eaux usées secondaires, la couche de surface (0-5 cm) se caractérisait par une concentration élevée de sels solubles et par une prolifération d’algues contribuant ainsi au colmatage superficiel et à un manque de continuité des macropores. En revanche, le colmatage chimique et biologique était réduit suite à l’utilisation des eaux usées phototraitées. La salinité était plus importante au niveau de la couche profonde (5-15 cm) due à une importante mobilité des ions chlorures et sodium suivie des sulfates et du calcium de la couche 0-5 cm vers la couche 5-15 cm, ce qui peut être attribué à une oxydation plus élevée de la matière organique induite par la présence de porphyrine. Il ressort de cette étude que la valorisation des eaux usées avec des concentrations micromolaires de T4MPyP dans le domaine agricole inhiberait le développement d'algues à la surface du sol et conduirait à une meilleure infiltration des sels vers les profondeurs évitant ainsi l’installation du colmatage à la surface. En outre, une meilleure rétention des ions ammonium et orthophosphates a été observée dans le sol sableux lors de la percolation des eaux usées phototraiteées.The process of photosensitization (phototreatment) of water is gaining much interest as it involves three components that are individually harmless to the biological environment, namely, the photosensitizer, light, and molecular oxygen. Laboratory experiments on study factors affecting photostability of T4MPyP (meso-tetra [4-N-methylpyridyl] porphyrin) in water show that wavelength and intensity of incident light, concentration of photosensitizer and water quality (presence of organics contaminants, turbidity, pH, dissolved oxygen, and thickness of the water sheet) all affects the rate of photostability and phototreatment. The experimental study consisted in bringing i) secondary treated (by activated sludge) wastewater, ii) the same type of wastewater but photosensitized with 5 μM∙L-1 of T4MPyP during 6h of sunshine, and iii) well water to a sandy soil. Phototreated wastewater met Tunisian standards (NT 106.03) indicating that the porphyrin was efficient in removing indicator bacteria (fecal coliforms removal averaged 99.99%) but still contained a residual concentration of porphyrin (about 35% of the initial concentration). At the end of the experiment, the saline configuration of the soil depended on the irrigation water quality. In the case of the secondary wastewater, the surface layer (0-5 cm) was characterized by high concentration of soluble salts and by proliferation of some algae which resulted in surface clogging and lack of macropore continuity. In contrast, biological, chemical and physical clogging processes were reduced by using phototreated wastewater with a residual photosensitizer. The absence of algae in the surface layer of soil and the decrease of nutrients (nitrogen and phosphorus) and bacteria could reduce clogging of irrigated water. The higher salinity was observed in the deep layer (5-15 cm) due to a high mobility of the sodium and chloride ions followed by sulfates and calcium from the layer 0-5 cm to the layer 5-15 cm which can be attributed to the higher oxidation of organic matter induced by the presence of porphyrin. The results revealed that using wastewater with micromolar concentrations of T4MPyP in agriculture would inhibit the development of algae at the soil surface and lead to a better infiltration of salts in depths, which would prevent surface clogging. In addition, better retention of ammonium and orthophosphate ions was observed in the sandy soil during percolation of phototreated wastewater

Assessment of the parasitological quality of water stored in private cisterns in rural areas of Tunisia

Limited access to safe water enhances poverty, hunger and diseases. This study evaluated the drinking water quality stored in home-based systems, located in rural areas of Tunisia. Water management was also documented as an improvement of good practice as most of the water contamination could be related to behavioral patterns. Thirty-nine water samples from five different sources (rainwater, truck cistern, mix, etc.) were screened for enteric parasitic contamination with the modified Bailenger technique. This technique allowed the detection of three protozoa: Giardia spp.; Entamoeba histolytica/dispar/moshkovskii; Entamoeba coli and one helminth specie: Ascaris spp. The overall prevalence of these intestinal parasites was approximately 97% with a relatively high frequency of protozoa over helminths and more specifically E. histolytica/dispar/moshkovskii. This incidence could be correlated to the lack of hygiene practices, sanitation and education. This situation requires the need for frequent monitoring of the water quality and management in these areas

Parasitological Assessment of Sewage Sludge Samples for Potential Agricultural Reuse in Tunisia

Wastewater sludge represents an important resource for reuse in agriculture. However, potentially harmful pathogens are a main threat in this context. Thus, the aim of this study was to examine the presence of helminth ova and protozoan cysts in dried sewage sludge samples collected from ten wastewater treatment plants (WWTPs) located in eight governorates in Tunisia. Based on morphological criteria, protozoan cysts of Giardia spp., Entamoeba histolytica/dispar/moshkovskii, and Entamoeba coli, were detected in all dried sludge composite samples (N = 116) from the investigated WWTPs. The mean concentration ranged from 1.4 to 10.7 cysts per 100 g dry matter (DM). The identified helminth eggs were Ascaris spp., Strongyles, Taeniid eggs, Hymenolepis nana, Enterobius vermicularis, and hookworm species. Ascaris spp. and Taeniid eggs were detected in 56.9 and 74.1% of analyzed samples, respectively. The presence of Trichuris spp., Hymenolepis diminuta, and Toxo-cara spp. eggs in dried sewage sludge samples was low (0.9, 1.7, and 2.6%, respectively). The mean concentration of helminth eggs during the three-year study was less than 1 egg/100 g DM. All ex-amined dried sewage sludge sample contents were below the WHO (2006) and US EPA (2003) rec-ommendations, and thus, the sludge can potentially be reused in agriculture

How Can Sewage Sludge Use in Sustainable Tunisian Agriculture Be Increased?

In recent years, farmers in Beja, an agricultural governorate in northwestern Tunisia, have expressed their willingness to use urban sewage sludge as agricultural fertilizer, especially with the unavailability of chemical fertilizers and the soil type of the region that is poor in organic matter. However, there is an imbalance between the important farmers’ demand versus the limited quantity of sludge produced by the Beja wastewater treatment plants (WWTPs). In the face of this, this study aims to identify the problems related to the agricultural reuse of sludge in Beja and propose solutions to solve them. The quality of the sludge produced by the five Beja WWTPs was assessed based on physicochemical and microbiological parameters. The data were collected using the Delphi method, with 15 experts representing different positions on the issue treated. The SWOT-AHP methodology was used to define the strategies promoting the sustainable use and management of urban sewage sludge for sustainable agricultural development in Beja. Results showed that there were no problems with compliance with the Tunisian standards NT 106.20 for the sludge produced. A set of twelve practical conclusions was identified, constituting the strategies of Strengths–Opportunities, Strengths–Threats, Weaknesses–Opportunities, and Weaknesses–Threats deduced from the SWOT-AHP