Valorizing agro-waste for the biodegradation of Remazol Turquoise Blue G-133 by white-rot fungi: toward sustainable wastewater treatment

Abstract

The extensive use of synthetic dyes in textiles generates highly coloured effluents, with reactive dyes posing major environmental challenges due to their stability and resistance to degradation. This study evaluates a sustainable bioremediation approach using white-rot fungi immobilized on agro-industrial residues for treating Remazol Turquoise Blue G-133 (RTB G-133). Two systems were tested: Pleurotus ostreatus on garlic peel-coffee husk (1:1 w/w) and Marasmiellus palmivorus on potato peel-cassava peel (7:3 w/w). Bioreactors operated under intermittent immersion for 12 days at dye concentrations of 100, 150, and 300 ppm with three treatments: fungal substrate (P1), substrate only (P2), and control (K). Maximum decolorization occurred at 100 ppm: 28.57% for P. ostreatus and 18.99% for M. palmivorus, while P2 achieved comparable removal (28.89% and 29.46%), suggesting that adsorption by the lignocellulosic substrate was the dominant mechanism; fungal hyphal colonization in P1 likely reduced substrate porosity and occupied adsorption sites, thereby limiting dye uptake relative to the uncolonized substrate. At 300 ppm, colour removal was negligible, highlighting concentration-dependent limitations. Enzyme assays confirmed ligninolytic activity in fungal treatments, with laccase ranging from 30-69 U/L and 31-61 U/L, and peroxidase up to 24.71 U/L and 16.88 U/L for P. ostreatus and M. palmivorus, respectively. Thin-layer chromatography and LC50 toxicity tests revealed structural modification and reduced toxicity in P1 samples compared to controls. These findings suggest that agro-waste-based fungal biocatalysts provide a cost-effective, eco-friendly strategy for dye wastewater treatment, though further optimization is required for higher dye loads.