Dark fermentation on biohydrogen production: Pure culture

Microbial bioproducts from cheese whey through fermentation with wastewater sludge Clostridium isolates

We demonstrated the production of hydrogen, ethanol, and a variety of acids by several Clostridium species using cheese whey as substrate. These species were isolated from the anaerobic sediments of a municipal wastewater stabilization pond. Eight isolates were obtained and all were classified taxonomically as Clostridium spp. based on 16S rRNA sequencing. Sludge isolates showed maximum bioproduct production yields and productivities after approximately 24 h of batch cultivation with 6% (m/v) cheese whey. Fermentation byproducts measured included hydrogen, ethanol, acetic acid, butyric acid, and lactic acid. The maximum yields of bioproducts were 0.59 mol H(2)/mol lactose, 0.071 g ethanol/g, 0.204 g acetic acid/g, 0.218 g butyric acid/g, and 0.144 g lactic acid/g. The production of these high value biofuels and biofuel intermediates from cheese whey could have significant implications for conversion of waste to high value bioproducts to enhance domestic energy economies.

Trends in biohydrogen production: major challenges and state-of-the-art developments

Hydrogen has shown enormous potential to be an alternative fuel of the future. Hydrogen production technology has gained much attention in the last few decades due to advantages such as its high conversion efficiency, recyclability and non-polluting nature. Over the last few decades, biological hydrogen production has shown great promise for generating large scale sustainable energy to meet ever increasing global energy demands. Various microorganisms, namely bacteria, cyanobacteria, and algae which are capable of producing hydrogen from water, solar energy, and a variety of organic substrates, are explored and studied in detail. Current biohydrogen production technologies, however, face two major challenges such as low-yield and high production cost. Advances have been made in recent years in biohydrogen research to improve the hydrogen yield through process modifications, physiological manipulations, through metabolic and genetic engineering. Recently, cell immobilization such as microbes trapping with nanoparticles within the bioreactor has shown an increase in hydrogen production. This review critically evaluated various biological hydrogen production technologies, key challenges, and recent advancements in biohydrogen research and development.

A comprehensive and quantitative review of dark fermentative biohydrogen production

Biohydrogen production (BHP) can be achieved by direct or indirect biophotolysis, photo-fermentation and dark fermentation, whereof only the latter does not require the input of light energy. Our motivation to compile this review was to quantify and comprehensively report strains and process performance of dark fermentative BHP. This review summarizes the work done on pure and defined co-culture dark fermentative BHP since the year 1901. Qualitative growth characteristics and quantitative normalized results of H2 production for more than 2000 conditions are presented in a normalized and therefore comparable format to the scientific community.Statistically based evidence shows that thermophilic strains comprise high substrate conversion efficiency, but mesophilic strains achieve high volumetric productivity. Moreover, microbes of Thermoanaerobacterales (Family III) have to be preferred when aiming to achieve high substrate conversion efficiency in comparison to the families Clostridiaceae and Enterobacteriaceae. The limited number of results available on dark fermentative BHP from fed-batch cultivations indicates the yet underestimated potential of this bioprocessing application. A Design of Experiments strategy should be preferred for efficient bioprocess development and optimization of BHP aiming at improving medium, cultivation conditions and revealing inhibitory effects. This will enable comparing and optimizing strains and processes independent of initial conditions and scale.