Ridha Slaimi

The use of treated wastewater (TWW) for crop irrigation has increased worldwide as an alternative to preserving freshwater resources. However, choosing this alternative still requires more data about its impact on the environment, crop quality, and human health. In this regard, the present study aimed to assess the irrigation impact with TWW for a long time (35 years) on soil properties and on cereal and bean yield. To evaluate this effect, two sites were studied: the first one irrigated with TWW (S1) and the second irrigated with tap water (S2). Soil analysis from S1 revealed higher salinity and high levels of inorganic and organic pollutants compared to FAO standards (3.39 ± 0.45 µg/g MS for Cd and 68 ± 1.9 µg/g MS for Cu, respectively). In TWW, the concentrations were 1.15 ± 0.05 µg/L for Cd, 0.32 ± 0.18 µg/L for Ni, and 1.11 ± 0.01 µg/L for Pb, respectively. Additionally, high concentrations of organochlorine compounds were detected with chromatography coupled with mass spectrometry (GC–MS) in TWW, such as Aldrin (0.01 µg/mL) and γ-HCH (0.016 µg/mL), as well as in soil (0.883 µg/g). These compounds exceeded the Tunisian standards (NT: 106.03) and the FAO guidelines for irrigation. Also, irrigation with TWW over 35 years increased the aerial biomass of Triticum turgidum and Hordeum vulgare but negatively affected the plant growth of Medicago sativa L. Organic contaminants, such as pesticides, reduced soil fertility and biodiversity. Furthermore, mineral pollutants accumulated in soil, such as heavy metals, affect plant growth, which poses a risk directly for the food chain and indirectly for human health. Continuous irrigation with wastewater alters the physicochemical properties of the soil and leads to the accumulation of inorganic pollutants in food crops. This alteration depends not only on the soil’s physical and chemical properties but also on the duration of irrigation. Based on this study, long-term irrigation with TWW poses significant risks to both human health and ecosystems. Therefore, continuous monitoring and proper management of TWW irrigation are crucial to mitigate these potential risks and ensure the long-term sustainability of agricultural practices.

The use of fast-growing tree species, such as Casuarina glauca for wastewater treatment could improve the quality of wastewater and offer an ecological and sustainable system. A hydroponically experiment was conducted to evaluate C. glauca ability to remove heavy metals from secondary treated urban wastewater (SWW). The effect of the SWW on plant biomass, some physiological parameters, heavy metals (Cd, Pb, Ni and Zn) bioaccumulation and removal from wastewater was evaluated. After 28 days, wastewater treatment C. glauca showed high efficiency for the removal of pathogenic bacteria such as faecal coliforms and faecal streptococci from SWW. A significant reduction was found for electrical conductivity, biochemical oxygen demand, chemical oxygen demand and suspended solids with 31%, 92%, 83% and 31% respectively. Casuarina glauca plants were able to remove heavy metal ions Cd, Pb, Ni and Zn from SWW and the removal efficiency was 92%, 77%, 83% and 73%, respectively. Casuarina glauca plants accumulated concentrations of heavy metals (Cd, Pb, Ni and Zn) in their roots higher than the shoots. SWW had a remarkable effect on plant growth and photosynthetic capacity in C. glauca compared with plants grown in tap water (control). The results indicated that C. glauca can act as scavengers of heavy metal ions from polluted water and confirms their ability for wastewater treatment.