Synergistic remediation of phenanthrene–cadmium co-contaminants by an immobilized acclimated bacterial–fungal consortium and its community response

Bioremediation has tremendous potential to mitigate the serious threats posed by polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HMs). In the present study, nine bacterial–fungal consortia were progressively acclimated under different culture conditions. Among them, a microbial consortium 1, originating from activated sludge and copper mine sludge microorganisms, was developed through the acclimation of a multi-substrate intermediate (catechol)-target contaminant (Cd2+, phenanthrene (PHE)). Consortium 1 exhibited the best PHE degradation, with an efficiency of 95.6% after 7 d of inoculation, and its tolerance concentration for Cd2+ was up to 1800 mg/L within 48 h. Bacteria Pandoraea and Burkholderia–Caballeronia–Paraburkholderia, as well as fungi Ascomycota and Basidiomycota predominated in the consortium 1. Furthermore, a biochar-loaded consortium was constructed to better cope with the co-contamination behavior, which exhibited excellent adaptation to Cd2+ ranging of 50–200 mg/L. Immobilized consortium efficiently degraded 92.02–97.77% of 50 mg/L PHE within 7 d while removing 93.67–99.04% of Cd2+. In remediation of co-pollution, immobilization technology improved the bioavailability of PHE and dehydrogenase activity of the consortium to enhance PHE degradation, and the phthalic acid pathway was the main metabolic pathway. As for Cd2+ removal, oxygen-containing functional groups (-OH, C=O, and C–O) of biochar or microbial cell walls and EPS components, fulvic acid and aromatic proteins, participated through chemical complexation and precipitation. Furthermore, immobilization led to more active consortium metabolic activity during the reaction, and the community structure developed in a more favorable direction. The dominant species were Proteobacteria, Bacteroidota, and Fusarium, and the predictive expression of functional genes corresponding to key enzymes was elevated. This study provides a basis for combining biochar and acclimated bacterial–fungal consortia for co-contaminated site remediation.