Waste-Derived Biochars and Iron-Based Materials for Sorption and Immobilization of Diclofenac, Carbamazepine and Fexofenadine Across Water–Soil–Sludge Systems

Abstract Pharmaceutical (PAC) residues in soils and sewage sludges may occur in water-extractable forms, representing potential diffuse sources of contamination for groundwater and surface waters via leaching and runoff. Waste-derived sorbents may decrease this potentially mobile PAC fraction, while valorizing residual materials within circular-economy-based remediation. Five waste-derived sorbents (two biochars and three iron-based materials) were tested for removal and operationally defined immobilization of carbamazepine (CBZ), diclofenac (DCF) and fexofenadine (FEX) at environmentally relevant aqueous concentrations and controlled solid-matrix levels. Sorption was assessed in single- and multi-compound aqueous systems. The best-performing sorbents were then applied to spiked sewage sludge and soil followed by water extraction. In aqueous tests, sewage sludge biochar (BSS) showed consistently high removal (single: 97% CBZ, 92% DCF, 99.5% FEX; multi: 93% CBZ, 95% DCF, 97% FEX). Zero-valent iron grit (CH) showed compound-dependent sorption (83% CBZ, 56% DCF, 99% FEX), with improved DCF removal in the mixture (94%). Hardwood biochar (BHW) was less effective and iron sludges (R, S) showed low or partly non-evaluable performance. In sewage sludge, BSS and CH did not significantly change aqueous PAC concentrations and spike release remained high (31–63%). In soil, BSS and CH showed mean water-extractable fractions that were 53%, 27% and 66% lower for CBZ, DCF and FEX, respectively, compared with unamended spiked control, and nutrient release was altered. Overall, BSS and CH showed practical potential to decrease readily extractable PAC amounts in the tested soil under laboratory conditions, whereas sewage sludge showed stronger matrix control and may require adapted immobilization strategies.