The application of an innovative continuous multiple tube reactor as a strategy to control the specific organic loading rate for biohydrogen production by dark fermentation Simone D. Gomes a,b , Lucas T. Fuess b,⇑ , Eduardo D. Penteado b , Shaiane D.M. Lucas a , Jackeline T. Gotardo a , Marcelo Zaiat b a Center of Exact and Technological Sciences, State University of West Paraná (UNIOESTE), 2069 Universitária Street, 85819-210 Cascavel, PR, Brazil b Biological Processes Laboratory, São Carlos School of Engineering (EESC), University of São Paulo (USP), 1100 João Dagnone Avenue, 13563-120 São Carlos, SP, Brazil highlights  An innovative reactor configuration was assessed for biohydrogen production.  The multiple tubes reactor prevents the accumulation of solids in the long-term.  Better performances were observed by placing support material at the outlet chamber.  Solid retention within the reactor reached up to 23% of the total biomass generated. article info Article history: Received 26 June 2015 Received in revised form 18 August 2015 Accepted 21 August 2015 Keywords: Continuous multiple tube reactor Innovative configuration Biohydrogen production Biomass washout Specific organic loading rate abstract Biohydrogen production in fixed-bed reactors often leads to unstable and decreasing patterns because the excessive accumulation of biomass in the bed negatively affects the specific organic loading rate (SOLR) applied to the reactor. In this context, an innovative reactor configuration, i.e., the continuous multiple tube reactor (CMTR), was assessed in an attempt to better control the SOLR for biohydrogen pro- duction. The CMTR provides a continuous discharge of biomass, preventing the accumulation of solids in the long-term. Sucrose was used as the carbon source and mesophilic temperature conditions (25 °C) were applied in three continuous assays. The reactor showed better performance when support material was placed in the outlet chamber to enhance biomass retention within the reactor. Although the SOLR could not be effectively controlled, reaching values usually higher than 10 g sucrose g 1 VSS d 1 , the vol- umetric hydrogen production and molar hydrogen production rates peaked, respectively, at 1470 mL H 2 L 1 d 1 and 45 mmol H 2 d 1 , indicating that the CMTR was a suitable configuration for bio- hydrogen production. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction Hydrogen production can be achieved by employing different technologies, such as water electrolysis, thermochemical and bio- logical processes. Considering biological processes in particular, anaerobic fermentation comprises the most attractive pathway because wastewater streams and organic wastes may be used as substrates (Hafez et al., 2010; Sreethawong et al., 2010). Most studies on fermentative biohydrogen (BioH 2 ) production have been conducted in batch mode, based on the simple operational and controlling features of such reactors. Although such studies are important to understand the behavior of the systems by simulating different operational conditions, large-scale plants would require continuous production processes for practical engineering reasons (Arimi et al., 2015). Several factors may influence continuous hydrogen production in biological reactors including the pH (Hwang et al., 2009; Antonopoulou et al., 2011), hydraulic retention time (HRT) (Kumar et al., 2014; Rosa et al., 2014), organic loading rate (OLR) (Hafez et al., 2010; Perna et al., 2013; Ferraz et al., 2014), temper- ature conditions (Gadow et al., 2013; Sivagurunathan et al., 2014), and type and concentration of the carbon source (Fontes Lima et al., 2013; Kumar et al., 2014; Lucas et al., 2015). The reactor con- figuration may also play a key-role in obtaining high BioH 2 produc- tion rates in continuous systems because the concentration of http://dx.doi.org/10.1016/j.biortech.2015.08.077 0960-8524/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +55 (16)3373 8360. E-mail address: ltfuess@sc.usp.br (L.T. Fuess). Bioresource Technology 197 (2015) 201–207 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech