Fungi (Aspergillus sp. + Penicillium sp.) immobilized on biochar removed 83.65% of manganese from highly acidic water (pH 3.0) starting at 50 mg/L within 7 days, outperforming free-floating fungi and starting cleanup 2 days earlier. The system worked by shifting fungal metabolism to raise pH and trap metals through adsorption, precipitation, and accumulation in cell walls, enabling reliable cleanup of toxic wastewater in extreme conditions where standard treatments fail.