This study reports on the application of an innovative structured-bed reactor (FVR) as an alternative to conventional packed-bed reactors (PBRs) to treat high-strength solid-rich wastewaters. Using the FVR prevents solids from accumulating within the fixed-bed, while maintaining the advantages of the biomass immobilization. The long-term operation (330 days) of a FVR and a PBR applied to sugarcane vinasse under increasing organic loads (2.4-18.0 kg COD m(3) day (1)) was assessed, focusing on the impacts of the different media arrangements over the production and retention of biomass. Much higher organic matter degradation rates, as well as long-term operational stability and high conversion efficiencies (>80%) confirmed that the FVR performed better than the PBR. Despite the equivalent operating conditions, the biomass growth yield was different in both reactors, i.e., 0.095 gVSS g(-1)COD (FVR) and 0.066 gVSS g(-1)COD (PBR), indicating a clear control of the media arrangement over the biomass production in fixed-bed reactors. (C) 2017 Elsevier Ltd. All rights reserved.