Source- and Particle Size-Dependent Composition and Contaminant Mobility of Wastewater-Derived Mineral Residues: Implications for Resource Recovery

Mineral residues from wastewater may constitute potential secondary resources; however, their heterogeneous composition and potential to release contaminants through leaching require careful evaluation. This case study compared grit chamber (GC) waste and sewer cleaning (SC) waste collected from a municipal wastewater management system, focusing on their physicochemical properties, chemical composition, particle size distribution, and leaching behavior. The tested materials were separated into coarse (≥2 mm) and fine (<2 mm) fractions and subsequently subjected to solid-phase analyses and leaching tests. Both types of waste had similar median particle sizes (D50: 0.247 mm for GC and 0.230 mm for SC) but differed considerably in chemical composition and leaching behavior. The coarse GC fraction contained substantially more organic carbon (22.79%) than the fine fraction (1.78%), whereas the fine fractions were enriched in SiO2. Sulfate concentrations in aqueous extracts from GC reached 1511 mg/L, compared with 98.6–105 mg/L in extracts from SC. Under the applied leaching conditions, the release of selected trace elements was limited. The results indicate that particle size alone does not fully explain the observed differences in contaminant distribution and release. Although SC waste exhibited relatively favorable properties for raw material recovery, these findings are limited to the tested material batches and laboratory conditions. Therefore, before material recovery is considered, detailed characterization is necessary, taking into account waste origin, appropriate pretreatment, and an environmental assessment tailored to the intended application.