Abstract
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.
Highlights
Production of sewage sludge is intrinsic to treatment of domestic wastewater, and its potential reuse as a fertilizer in agriculture provides a better alternative than incineration and landfilling
Taeniid eggs were present in 74.1% (86/116), Hymenolepis nana with 67.2% (78/116), and H. diminuta only in 1.7% (2/116) of samples (Table 3)
The saturated sucrose flotation technique was successfully used to evaluate the majority of helminth eggs and protozoan cysts in sun-dried sludge samples
Summary
Production of sewage sludge is intrinsic to treatment of domestic wastewater, and its potential reuse as a fertilizer in agriculture provides a better alternative than incineration and landfilling. It has been estimated that 16 and 22% of all sludge/biosolids are either incinerated or landfilled, respectively, based on US EPA reporting data [1]. Agricultural use of sewage sludge has been recognized worldwide as a promising way to manage this resource, as it can minimize environmental pollution and contribute to circular economy from “waste to resources” [2]. The organic matter content in sludge can improve soil physical, chemical, and biological properties and produce favorable plant yield responses, when used as an organic fertilizer [3,4]. There may be a risk in sludge reuse due to potentially concentrated harmful contents such as heavy metals, emergent pollutants, and pathogens
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