The aim of this study was to evaluate the influence of hydraulic retention time (HRT) on linear alkylbenzene sulfonate (LAS) removal in fluidized bed reactors (FBRs). FBR1 (HRT of 8 h) and FBR2 (HRT of 12 h) were fed laundry wastewater with 18.6 +/- 4.1 to 27.1 +/- 5.6 mg/L of LAS in the following conditions: ethanol and nitrate addition (Phases I, II and III), nitrate (Phase IV), ethanol (Phase V) and laundry wastewater (Phase VI). LAS removal was 93 +/- 12% (FBR1) and 99 +/- 2% (FBR2). In FBR1, nitrate influenced significantly on LAS removal (99 +/- 3% - Phase IV) compared to the phase without nitrate (90 +/- 15% - Phase V). In FBR1 the absence of ethanol was more favourable for LAS removal (99 +/- 3% - Phase IV) compared to ethanol addition (87 +/- 16% - Phase II). In FBR2, 99 +/- 2% LAS removal was found up to 436 days. By microbial characterization were identified bacteria as Acinetobacter, Dechloromonas, Pseudomonas and Zoogloea. (C) 2016 Elsevier Ltd. All rights reserved.