Metabolic shift and electron discharge pattern of anaerobic consortia as a function of pretreatment method applied during fermentative hydrogen production

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 (H₂) production. Experiments were performed with dairy wastewater as substrate using anaerobic mixed consortia as biocatalyst (pretreated individually and in combination). Cyclic voltammetry (CV) elucidated significant variation in the ED pattern of mixed consortia along with H₂ 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⁺) shuttling due to the suppression of methanogenic activity. Oxygen-shock method and untreated consortia showed lower H₂ production and higher SD among the variations studied, while, combined pretreated consortia resulted higher H₂ production and lower SD. Lower ED observed with untreated consortia suggests the H⁺ reduction during methanogenesis rather than the inter-conversion of metabolites, which is presumed to be necessary for H₂ production. ED observed with combined pretreated consortia corroborated well with the observed H₂ production. Redox pairs were visualized on the voltammograms with almost all the experimental variations studied except untreated consortia. The potentials (E₀) of redox pairs observed were corresponding to intracellular electron carriers viz., NAD⁺/NADH (E₀ −0.32 V) and FAD⁺/FADH₂ (E₀ −0.24 V).