Semi-continuous adsorption-biocatalysis systems using waste-derived biochar functionalized with laccase for...

Diclofenac (DCF) is a widely consumed anti-inflammatory drug, frequently detected in aquatic environments worldwide due to the limited removal efficiency of conventional wastewater treatment processes. This work investigates the valorisation of brewery waste into functionalized carbon-based materials to mitigate the entry of DCF into aquatic systems. Biochar (BC) was produced from spent brewery grains via microwave-assisted pyrolysis, contributing to Sustainable Development Goal 12 by repurposing agro-industrial by-products. A biocatalytic composite (BC-LAC) was synthesized through laccase (Trametes versicolor, ≥0.5 U/mg) immobilization onto BC. The materials produced (BC and BC-LAC) were characterized by N₂ physisorption and scanning electron microscopy, revealing a well-developed microporous structure, with specific surface areas of 301 m² g^-1 and 191 m² g^-1 for BC and BC-LAC, respectively. DCF removal from aqueous matrices (buffered ultrapure water and urban wastewater) was evaluated using BC and BC-LAC, under batch conditions and in semi-continuous operation mode, employing stirred tank and fixed-bed column configurations. For the semi-continuous operation modes, the effect of materials dose (0.5-2.0 g L^-1) and flow rate (6.94 ⋅ ${10}^{-4}$ - 2.78 ⋅ ${10}^{-3}$ L min^-1) in the breakthrough curves were evaluated. In wastewater, fixed-bed column experiments with BC showed higher removal efficiency than BC-LAC, with the former treating a volume of effluent five times higher than the latter. Nevertheless, in the stirred tank, BC-LAC breakthrough curves revealed an initial improvement in DCF removal compared with BC, suggesting enhanced hydrodynamics and oxygen availability. Despite this fact, the treated volume (0.25 and 0.26 L, for BC and BC-LAC, respectively), as well as the operating times, are similar for both materials, under the tested conditions (0.5 g L^-1 of materials and 6.94 ⋅ ${10}^{-4}$ L min^-1). Overall, the results confirm the potential of the produced waste-derived BC as an effective adsorbent, in line with circular strategies and sustainable water treatment. The results highlight that the application of BC-LAC did not present enhanced cost-effectiveness, requiring further optimization to enable a successful integration of combined adsorption and enzymatic degradation approach.