Bioremediation of α-terpineol-contaminated flotation wastewater using biochar-immobilized biosurfactant-producing bacteria

α-Terpineol, a persistent and toxic frother in mineral flotation wastewater, poses significant environmental risks due to its resistance to natural degradation and potential to elevate chemical oxygen demand (COD). This study developed a novel bioremediation strategy using Pseudomonas asiatica S4, a newly isolated strain able to degrade α-terpineol efficiently by producing rhamnolipid biosurfactants. The strain S4 achieved over 90% removal of 1000 mg/L α-terpineol with rhamnolipid-enhanced solubilization and enzymatic catabolism within 48 h under optimized conditions. For the first time, the α-terpineol biodegradation pathway and its key genes were elucidated through intermediate identification, genomic analysis, and qPCR validation. The biochar immobilized strain S4 demonstrated exceptional performance in actual alkaline flotation wastewater (pH 9.5) containing multiple heavy metals, with simultaneous removal of α-terpineol and COD over 85% within 11 days, significantly outperforming those by free cells or biochar alone. The immobilized system also exhibited sustained efficiency over multiple treatment cycles in virtue of biochar's protective microenvironment and upregulation of catabolic genes (2∼8.7-fold). This work combines biosurfactant-mediated bioavailability enhancement with robust biochar-microbe synergy, presenting a sustainable and integrated approach for the remediation of refractory flotation reagents in mining wastewater.