Abstract
The agricultural spreading of sewage sludge requires a precise assessment of trace metal elements (TME) to ensure soil protection. This preliminary study presents the first physicochemical characterization of sludge from the Aïn El Beïda wastewater treatment plant, based on two samples collected one year apart (S1, S2). Analyses combining XRF, XRD, and FTIR, together with measurements of pH, carbonates, nitrates, and COD, reveal a complex organo-mineral matrix dominated by calcite, quartz, and phyllosilicates (illite, smectite), with a slightly alkaline pH (7.87) and high carbonate content (30.96%). XRF reveals both essential nutrients and TME. Chromium exceeds the French regulatory limit in S1 (1720 mg/kg DM vs. 1000 mg/kg DM), restricting the cumulative application to 8.7 t DM/ha over 10 years, while S2 remains compliant (160 mg/kg Cr), allowing a cumulative application of 21.3 t DM/ha. The mineralogical assemblage (carbonates, clays, oxides) suggests potential TME immobilization mechanisms, although validation by sequential extraction is required. These results emphasize the need for systematic analytical monitoring of each sludge batch prior to land application and provide essential baseline data for ensuring safe sludge reuse in the local context.