Integrated adsorption–microbial process using natural and modified clays with Streptomyces for ciprofloxacin removal

The occurrence of ciprofloxacin in aquatic environments and its poor removal in wastewater treatment plants highlight the need for integrated and sustainable remediation approaches. This study evaluates a coupled adsorption–microbial removal strategy based on clays combined with Streptomyces sp. M7 under ionic conditions. A natural sodium bentonite (NC), an iron-pillared clay (Fe-PILC), and a chitosan-coated Fe-PILC (Fe-PILC-Cs) were characterized and assessed through adsorption kinetics, isotherms, and clay-bacteria removal assays. Adsorption capacity decreased with clay modification and increasing ionic strength, accompanied by changes in retention mechanisms. Under glucose-supplemented conditions, Streptomyces sp. M7 alone did not remove the contaminant; however, higher removal was observed in the presence of clays, suggesting a synergistic interaction. The tolerance of Streptomyces sp. M7 to ciprofloxacin, supported by the identification of putative resistance determinants, was consistent with sustained microbial viability under antibiotic exposure. At 72 h, maximum total ciprofloxacin removal in the clay-bacteria systems reached 50.0% for NC, 46.8% for Fe-PILC-Cs, and 39.7% for Fe-PILC. Notably, in the Fe-PILC-Cs system, the estimated microbial contribution exceeded adsorption from 48 h onward, indicating a greater relative role of biological removal. The observed link between adsorption-site heterogeneity and microbial contribution suggests that low-affinity domains favored antibiotic bioavailability at the clay–biofilm interface, supporting co-metabolic microbial transformation. Overall, combining adsorption and microbial activity through clay-based materials represents a promising approach for ciprofloxacin removal from water.