Biohydrogen processes

The low energy density of solar energy places severe economic restrictions on potential light-dependant biohydrogen processes. For example, at very favorable locations the yearly average solar irradiation could be as high as 5 kWh/m2/day which would give 6.6GJ/year. 

Incorporation of dietary unsaturated fat into milk fat by ruminants is low because of the efficient ruminal biohydrogenation process (Jenkins, 1993). Nevertheless, dietary fatty acids have profound effects on milk fat composition that have led to a prodigious amount of literature in the past 20 years (for reviews see Sutton, 1989 Grummer, 1991 Palmquist et al., 1993 Kennedy, 1996 Mansbridge and Blake, 1997 Chilliard et al., 2000, 2001). 

In food, CLA is found in milk fat, the tissue fat of ruminant animals, and products derived from them, although there are exceptions. About 90% of the CLA is represented by the cis-9, trani-11-isomer or rumenic acid (RA) (4). This isomer is produced in the rumen by the action of a linoleic acid isomerase on dietary linoleic acid as a first step in the biohydrogenation process. Further hydrogenation produces trans- - %. or vaccenic acid (VA), the predominant trans monounsaturat-ed fatty acid of milk and animal tissue fat. The major polyunsaturated fatty acids of pasture, a-and y-linolenic acid, cannot be converted to RA, but they do produce VA. A proportion of RA and VA escape further hydrogenation in the rumen and after absorption pass via the circulatory system to adipose tissue and the mammary gland where A -desaturases convert VA to RA. About 70% of RA in milk fat is produced by this pathway (5). 

Vaccenic acid is an intermediate of the bacterial biohydrogenation process of dietary PUFA that is absorbed and found in tissues of dairy cows and beef cattle. 

Figure 10.1 The biohydrogenation process in the rumen as it affects linoleic (18 2n-6) acid. The semifinal product is a /ra/w-ll-octadecenoic add (vaccenic, M8 l/i-7), and the final product would be octadecanoic add (stearic, 18 0).

Tannins were primarily considered as anti-nutritional biochemicals due to then-adverse effects on feed intake and nutrient utilization (Kumar and Vaithiyanathan 1990). Nevertheless in recent years, they have been recognized as nsefnl phytochemicals for beneficially modulating the rumen microbial fermentation. The effects of tannins on ruminant production have been published in the past, which primarily focused on the adverse effects of tannins on animal systan, with some discussion on their positive effects on protein metabolism and prevention of bloat (Mangan 1988 Kumar and Vaithiyanathan 1990 Aerts et al. 1999 Barry and McNabb 1999 McSweeney et al. 2001a Min et al. 2003 Mueller-Harvey 2006 Waghom 2008). This chapter focuses on the effects of tannins on ruminal microbial populations that affect N metabolism, methanogenesis and ruminal biohydrogenation process in the mmen. 

Single-strand conformation polymorphism (SSCP) Wastewater bioreactors (including denitrifying and phosphate-removal system, Chinese traditional medicine wastewater treatment system, beer wastewater treatment system, fermentative biohydrogen producing system, and sulfate-reduction system) Microbial community structures, diversity and distribution in different wastewater treatment processes, and relationship between the structures and the status of processes [157]... 

The use of such natural hydrogen production machines in combination with the natural process of photosynthesis is the topic of an international NEDO project for the development of a semiartificial device for hydrogen production. On the occasion of the second meeting of all groups involved in this project, an international symposium on Biohydrogen was organized in Kyoto 2002. The state of the art of biohydrogen production from participants of this symposium is summarized in the chapters of this book. 

Hydrogen produced by microalga and bacteria is biohydrogen (Benemann, 1998). There are currently no practical biohydrogen production processes. However, several concepts have promise for near to long-term process development (Benemann, 1998). 

Dark fermentation is the fermentative conversion of organic substrate to biohydrogen, it is a complex process manifested by a diverse group of bacteria by a series of biochemical reactions involving three steps similar to anaerobic conversion. Dark fermentation differs from photofermentation because it proceeds without the presence of light. 

Hydrogen from biomass. There are a number of biological projects for manufacturing Biohydrogen, and there are various thermal and hydro-thermal processes being developed. 

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