The opportunity to apply an immobilized-cell biotechnological process in the remediation of polyethoxylated nonylphenol (NPnEO) contaminated water was studied in this work. To this purpose, three identically configured aerobic column reactors packed with different materials (silica beads, granular activated carbon, or glass spheres) were developed, inoculated with the NPnEO-degrading Pseudomonas sp. strain BCb 12/3, and compared for their ability to biodegrade the two NPnEO industrial mixtures Igepal CO-520 and CO-21 0 fed in synthetic wastewater at concentrations in the range 30-90 mg/L. The three biofilm reactors, tested under batch conditions, showed comparable degradation capabilities and specificities, being able to remove from 77 to 99% of the total Igepal mixtures supplied after 9 days of batch treatment. NPnEOs were mostly removed through biodegradation, as suggested by the accumulation of two metabolites typical of NPnEO aerobic biodegradation, such as phenol and 4-nonylphenol, and by the low NPnEO amounts recovered from the reactors at the end of the study. Fluorescent in situ hybridization and DAPI staining performed at the end of the study showed that the bacteria] biofilm was well and homogenously developed on the packed beds of the three reactors and that it was mostly composed by bacteria belonging to Garnmaproteobacteria, i.e., the Proteobacteria class which includes the genus Pseudomonas.