Chemical Engineering Science 57 (2002) 3819–3830 www.elsevier.com/locate/ces Mathematicalmodellingandoptimizationofhydrogencontinuous productioninaxedbedbioreactor E.Palazzi,P.Perego,B.Fabiano * DICheP Chemical and Process Engineering Department “G.B. Bonino”, University of Genoa, via Opera Pia 15, 16145 Genova, Italy Received 29 January 2002; received in revised form 16 April 2002; accepted 19 July 2002 Abstract Thepurposeofthispaperistoinvestigate,boththeoreticallyandexperimentally,hydrogenproductionfromagro-industrialby-products usingacontinuousbioreactorpackedwithamixtureofspongyandglassbeadsandinoculatedwith Enterobacter aerogenes. Replicated series of experimental runs were performed to study the eects of residence time on hydrogen evolution rate and to characterize the criticalconditionsforthewashout,asafunctionoftheinletglucoseconcentrationandoftheuidsupercialvelocity.Afurtherseriesof experimentalrunswasfocusedontheeectsofbothresidencetimeandinletglucoseconcentrationoverhydrogenproductivity.Akinetic model of the process was developed and showed good agreement with experimental data, thus representing a potential tool to design a large-scalefermenter.Infact,themodelwasappliedtotheoptimaldesignofabioreactorsuitableoffeedingaphosphoricacidfuelcell ofatargetpower. ? 2002 Elsevier Science Ltd. All rights reserved. Keywords: Bioreactors; Fermentation; Hydrogen production; Immobilization; Optimization; Packed bed 1. Introduction Alternative renewable energy forms are gaining increas- ing importance to complement and, possibly, substitute conventional energies, of fossil origin. Energy production usingbiomassistoberegardedasapotential,unpolluting energysource.Inparticular,molecularhydrogenisconsid- ered a suitable fuel for a future climate-constrained world (Tsygankov,Borodin,Rao,&Hall,1999).Hydrogencanbe producedchemically,electrochemically,asaby-productof oil/coalprocessing,orbytheuseofmicroorganisms.While othermethodsofproductionhavebeenusedindustriallyand oertheadvantageofscaleeconomy,microbialproduction isarelativelynewtechnologystilluntestedonalargescale. There are two systems to obtain microbial hydrogen production, namely photochemical and fermentative. The former consists in producing by means of photosynthetic microorganismssuchasalgae(Kumazawa&Mitsui,1981) and photosynthetic bacteria (Miyake & Kawamura, 1987; Sasikaia, Ramana, & Raghuveer Rao, 1992; Segers & Verstraete, 1983; Stevens, Vertonghen, de Vos, & Ley, ∗ Corresponding author. Tel.: +39-010-353-2585; fax: +39-010-353-2586. E-mail address: brown@unige.it (B. Fabiano). 1984). The latter is carried out by fermentative hydrogen producing microorganisms, such as facultative anaerobes (Brosseau & Zajic, 1982; Tanisho, Wakao, & Kosako, 1983; Tanisho, Suzuki, & Wakao, 1987) and obligate anaerobes (Karube, Urano, Matsunaga, & Suzuki, 1982; Taguchi, Chang, Takiguchi, & Morimoto, 1992; Taguchi, Chang,Mizukami,Salto-Taki,&Hasegawa,1993). Hydrogenproductionbyfermentationseemstobeavery expectable method in comparison with the photochemi- cal one, because of the higher rate of hydrogen evolution (Tanisho et al., 1987). Other advantages of the fermenta- tive hydrogen production lie on the possibility of utilizing assubstrateindustrialand/oragriculturalwastesandofob- taining other metabolites suitable for valorization, such as organicacidsandalcohols. Clostridia and Escherichia coli areprobablythemostex- tensivelystudiedinordertobeusedasfermentativehydro- genproducingorganisms. Clostridium butyricum hasbeen reportedtoevolvehydrogenatarateof7:3mmolg -1 cells h -1 under anaerobic cultivation of wastewater from an alcohol factory(Tanisho,Kamiya,&Wakao,1989). The metabolism of glucose by Enterofacter aerogenes isamplyknowntofollowtheEmbden–Meyerhopathway (Gottschalk, 1986). The rst step, corresponding to gly- colyses,producespyruvate;inthesubsequentfermentative 0009-2509/02/$-see front matter ? 2002 Elsevier Science Ltd. All rights reserved. PII:S0009-2509(02)00322-6