Metabolic shift and electron discharge pattern of anaerobic consortia as a function of pretreatment method applied during fermentative hydrogen production S. Srikanth, S. Venkata Mohan*, V. Lalit Babu, P.N. Sarma Bioengineering and Environmental Centre, Indian Institute of Chemical Technology, Hyderabad 500 607, AP, India article info Article history: Received 25 September 2009 Received in revised form 18 January 2010 Accepted 12 February 2010 Available online 20 March 2010 Keywords: Dairy wastewater Acidogenic fermentation Volatile fatty acids (VFA) Wastewater treatment Redox mediators Cyclic voltammetry abstract We have made an attempt to evaluate the variation in the electron discharge (ED) pattern of anaerobic consortia as a function of pretreatment viz., chemical, heat-shock, acid and oxygen-shock in comparison with untreated mixed consortia during fermentative hydrogen (H 2 ) production. Experiments were performed with dairy wastewater as substrate using anaerobic mixed consortia as biocatalyst (pretreated individually and in combina- tion). Cyclic voltammetry (CV) elucidated significant variation in the ED pattern of mixed consortia along with H 2 production and substrate degradation (SD) as a function of pretreatment method applied. Higher ED was observed with all pretreated consortia which can be attributed to the stable proton (H þ ) shuttling due to the suppression of methano- genic activity. Oxygen-shock method and untreated consortia showed lower H 2 production and higher SD among the variations studied, while, combined pretreated consortia resulted higher H 2 production and lower SD. Lower ED observed with untreated consortia suggests the H þ reduction during methanogenesis rather than the inter-conversion of metabolites, which is presumed to be necessary for H 2 production. ED observed with combined pre- treated consortia corroborated well with the observed H 2 production. Redox pairs were visualized on the voltammograms with almost all the experimental variations studied except untreated consortia. The potentials (E 0 ) of redox pairs observed were corresponding to intracellular electron carriers viz., NAD þ /NADH (E 0 0.32 V) and FAD þ /FADH 2 (E 0 0.24 V). ª 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved. 1. Introduction Harnessing energy in the form of biohydrogen (H 2 ) by dark fermentation process using renewable source like wastewater as substrate is gaining prominence due to its sustainable nature [1,2]. Controlling the metabolic pathway towards acidogenesis and inhibiting methanogenesis reported to facilitate higher H 2 yields [2,3]. Pretreatment of biocatalyst plays a vital role in selective enrichment of mixed consortia for the metabolic shift towards acidogenesis [3–8]. Typical anaerobic mixed cultures cannot produce higher H 2 as it gets rapidly consumed by H 2 -consuming or CH 4 -producing meth- anogenic bacteria (MB) [9]. The most effective way to enhance H 2 production from anaerobic culture is to restrict or termi- nate methanogenesis by allowing H 2 to become a metabolic end product. Physiological differences between H 2 -producing acidogenic bacteria (AB) and H 2 -consuming bacteria (MB) forms main basis for the preparation of biocatalyst to start-up * Corresponding author. Tel.: þ91 40 27191664. E-mail address: vmohan_s@yahoo.com (S. Venkata Mohan). Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 35 (2010) 10693–10700 0360-3199/$ – see front matter ª 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2010.02.055