Controlled Continuous Bio-Hydrogen Production Using Different Biogas Release Strategies S. Esquivel-Elizondo & I. Chairez & E. Salgado & J. S. Aranda & G. Baquerizo & E. I. Garcia-Peña Received: 18 February 2014 /Accepted: 14 May 2014 # Springer Science+Business Media New York 2014 Abstract Dark fermentation for bio-hydrogen (bio-H 2 ) production is an easily operated and environmentally friendly technology. However, low bio-H 2 production yield has been reported as its main drawback. Two strategies have been followed in the past to improve this fact: genetic modifications and adjusting the reaction conditions. In this paper, the second one is followed to regulate the bio-H 2 release from the reactor. This operating condition alters the metabolic pathways and increased the bio-H 2 production twice. Gas release was forced in the continuous culture to study the equilibrium in the mass transfer between the gaseous and liquid phases. This equilibrium depends on the H 2 , CO 2 , and volatile fatty acids production. The effect of reducing the bio-H 2 partial pressure (bio-H 2 pp) to enhance bio-H 2 production was evaluated in a 30 L continuous stirred tank reactor. Three bio-H 2 release strategies were followed: uncon- trolled, intermittent, and constant. In the so called uncontrolled fermentation, without bio-H 2 pp control, a bio-H 2 molar yield of 1.2 mol/mol glucose was obtained. A sustained low bio-H 2 pp of 0.06 atm increased the bio-H 2 production rate from 16.1 to 108 mL/L/h with a stable bio-H 2 percentage of 55 % (v/v) and a molar yield of 1.9 mol/mol glucose. Biogas release enhanced bio-H 2 production because lower bio-H 2 pp, CO 2 concentration, and reduced volatile fatty acids accumulation prevented the associated inhibitions and bio-H 2 consumption. Keywords Controlled continuous culture . Continuous intermittent gas release . Hydrogen partial pressure . Dark fermentation Appl Biochem Biotechnol DOI 10.1007/s12010-014-0961-8 S. Esquivel-Elizondo : I. Chairez : E. I. Garcia-Peña (*) Bioprocesses Department, Unidad Profesional Interdisciplinaria de Biotecnología, Instituto Politécnico Nacional, P.O. Box 07340, Mexico City, Mexico e-mail: egarciap@ipn.mx E. Salgado : J. S. Aranda : G. Baquerizo Bioengineering Department, Unidad Profesional Interdisciplinaria de Biotecnología, Instituto Politécnico Nacional, P.O. Box 07340, Mexico City, Mexico Present Address: S. Esquivel-Elizondo Swette Center for Environmental Biotechnology, The Biodesign Institute at Arizona State University, P.O. Box 875701, Tempe, AZ 85287-5701, USA