A Comparative Evaluation of Dye Removal in Batch and Air-Lift Systems by Commercial and Crude Laccase Immobilized on Biochar

Biochar has emerged as a highly attractive, sustainable support for enzyme immobilization, with dual benefits: valorization of available lignocellulosic waste and use as a stable, porous matrix for enzyme binding. This study investigated acid-modified sour cherry stone biochar (SCBM) as support for two laccases of different origins: crude laccase (Bjerkandera adusta TMF1 (CL)) and purified commercial laccase (Trametes versicolor (TvL)). The aim was to compare immobilization efficiency, activity retention and Brilliant Green (BG) decolorization in batch and air-lift reactors (ALRs). Immobilization of crude (SCBM-CL) and commercial (SCBM-TvL) laccase was successfully achieved and confirmed by SEM-EDX and FTIR-ATR analyses. Under optimized batch conditions, SCBM-TvL achieved approximately 92% of BG removal within 4 h and maintained high catalytic activity over nine consecutive cycles, whereas SCBM-CL reached almost 66% removal, with a progressive loss of activity upon reuse. In the ALR, using a 25-fold lower biochar-to-solution ratio, SCBM-TvL achieved almost complete BG decolorization within 4 h, while SCBM-CL achieved 57% within the same time. After treatment, BG solution exhibited a phytostimulatory effect, no antimicrobial activity, and 87% COD reduction, indicating reduced toxicity and organic load after enzyme treatment. Furthermore, the BG decolorization achieved by SCBM-TvL in ALRs highlights the economic advantage of this system and supports its potential for further scale-up.