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 Toxocara 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 examined dried sewage sludge sample contents were below the WHO (2006) and US EPA (2003) recommendations, and thus, the sludge can potentially be reused in agriculture.