Hydrogen production in reactors: The influence of organic loading rate, inoculum and support material Rog  erio Vilela a , Fl  avia Talarico Saia b , Gustavo Bueno Gregoracci b , Rubens Duarte c , Pedro Andrade d , Bas van der Zaan e , Alette Langenhoff f , M  arcia H.R. Z. Damianovic a,* a Biological Process Laboratory, S~ ao Carlos School of Engineering, University of S~ ao Paulo, Environmental Engineering, Bloco 4-F, Av. Jo~ ao Dagnone, 1100, Santa Angelina, 13563-120, S~ ao Carlos, SP, Brazil b Marine Institute, Federal University of S~ ao Paulo, Rua Dr. Carvalho de Mendonc ¸a 144, 11070-102, Santos, SP, Brazil c Center of Biological Sciences, Federal University of Santa Catarina, Campus Reitor Jo~ ao David Ferreira Lima, Bairro Trindade, 88040-900, Florian opolis, SC, Brazil d Department of Soil Science, “Luiz de Queiroz” College of Agriculture, University of S~ ao Paulo, 13418-900, Piracicaba, SP, Brazil e Deltares, Daltonlaan 600, 3584 BK Utrecht, the Netherlands f Department of Environmental Technology, Wageningen University and Research, P.O. Box 17, 6700 AA, Wageningen, the Netherlands highlights  Sugarcane molasses was suitable for thermophilic hydrogen production.  Inocula, support material and OLR influenced hydrogen production.  Thermoanaerobacterium, Clostridium sensu stricto and Thermotuga were selected. article info Article history: Received 30 June 2019 Received in revised form 20 August 2019 Accepted 22 August 2019 Available online 13 September 2019 Keywords: Thermophilic Hydrogen production Acidogenic structured bed reactor Sugarcane molasses Microbiota abstract Hydrogen production was evaluated in two thermophilic structured bed (USBR) reactors. USBR1was inoculated with auto-fermented sugarcane vinasse and low-density poly- ethylene cubes were used as support material. USBR2 was inoculated with anaerobic sludge from an up-flow anaerobic sludge blanket (UASB) reactor treating sugarcane vinasse, and polyurethane foam matrices was used as support material. The reactors were operated in parallel with sugar cane molasses at organic loading rate (OLR) from 30 to 120 g COD L 1 d 1 during 45 days. Hydrogen production was detected during the whole opera- tional period, with maximum values of 1123 mL H 2 d 1 L 1 and 2041 mL H 2 d 1 L 1 for USBR1 and USBR2, respectively. The number of gene copies encoding for Fe-hydrogenase was higher in USBR2 for all OLR applied. DNA sequences related to Thermoanaerobacterium and Clostridium sensu stricto were predominant in USBR1. In USBR2, in addition to these mi- croorganisms, Lactobacillus, Pseudomonas and Thermotuga, and sequences with low fre- quency of abundance (<5%) involved directly and indirectly in hydrogen production were also present. The taxonomical and functional more diverse inoculum of USBR2 was * Corresponding author. E-mail address: ftsaia@yahoo.com.br (M.H.R.Z. Damianovic). Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 44 (2019) 27259 e27271 https://doi.org/10.1016/j.ijhydene.2019.08.180 0360-3199/© 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.