Studies on biodiversity of hydrogen producers and enhancement of dark fermentative hydrogen production process

Abstract

In view of the realization that fossil fuels reserves are limited due to their excessive utilization, various options for generating energy are being explored. Biological method appears to be the most promising as it is non polluting and can exploit biological wastes as substrate. Microbial diversity from different environments such as contaminated food, nitrogen rich soil, activated sludges from pesticide and oil refineries effluent treatment plants has been studied. Bacterial isolates from these habitats were found to belong to belonging to CFB Group of bacteria; firmicutes- Aneuribacillus, Anoxybacillus, Planomicrobium and Bacillus; α-proteobacteria - Rhodobacter; β-proteobacteria - Bordetella and γ-proteobacteria - Alcanivorax, Enterobacter, Marinobacter, Microbacterium, Proteus, Pseudomonas and a marine bacterium on the basis of 16S rRNA gene sequence analysis. Under dark fermentative conditions, maximum hydrogen (H2) yields (mol/mol of glucose added) were recorded to be 0.68 with Enterobacter aerogenes EGU16 followed by 0.63 with Bacillus cereus EGU43 and Bacillus thuringiensis EGU45. H2 constituted 63-69% of the total biogas evolved. Some strains had high hydrolytic activities (zone of hydrolysis): lipase (34-38 mm) - Bacillus sphaericus EGU385, EGU399 and EGU542; protease (56-62 mm) - Bacillus sp. strains EGU444, EGU447 and EGU445; amylase (23 mm) - B. thuringiensis EGU378, marine bacterium strain EGU409 and Pseudomonas sp. strain EGU448. These strains with high hydrolytic activities had relatively low H2 producing abilities in the range of 0.26-0.42 mol/mol of glucose fed. Mixed microbial cultures (MMCs) based on 11 isolates belonging to Bacillus spp., Bordetella avium, E. aerogenes and Proteus mirabilis were employed to produce hydrogen (H2) under dark fermentative conditions. Under batch culture conditions, optimization of process parameters lead to enhanced yield of 1.4 mol/mol glucose with MMC4 and MMC6.