Metal-free lignin-derived activated carbon for reducing fluoroquinolone residues in raw milk with minimal quality loss

This study evaluates metal-free lignin-derived activated carbons (L-ACs) as a processing aid to reduce fluoroquinolone residues in milk without compromising product quality. Two carbons prepared via K 2 CO 3 (L-AC-K 2 CO 3 -1.0) or KOH (L-AC-KOH-2.0) activation were characterised; the KOH sample showed higher surface area and microporosity ( S BET 1,480 m 2 g −1 ; V mic 0.62 cm 3 g −1 ) than the K 2 CO 3 analogue (1,120 m 2 g −1 ; 0.48 cm 3 g −1 ). In buffer, Langmuir fits yielded q max (mg g −1 ) of 182/156 for ciprofloxacin/ofloxacin on L-AC-KOH-2.0 and 135/118 on L-AC-K 2 CO 3 -1.0; pseudo-second-order kinetics indicated rapid uptake. In milk (0.5 g L −1 , 30 min), removals reached 76/71% in raw and 84/79% in skim matrices (CIP/OFL). In a minicolumn (EBCT ≈30 s), breakthrough occurred at ∼4 × 10 2 bed volumes at C / C 0 = 0.1. Post-treatment quality shifts were small (Δfat/protein/lactose ≤0.05%, ΔpH ∼0.01, ΔE* ∼0.3–0.7). Ethanol (70%) regeneration preserved >90% capacity over five cycles. These results highlight L-ACs as practical, food-compatible sorbents for antibiotic mitigation in dairy processing.