Pyrolysis refers to material chemical change caused by the application of thermal energy in the presence of air or nitrogen (Fukuda et al, 2001). The pyrolysis of different triglycerides was used for fuel supply in different countries during the First and Second World Wars. For instance, a tung oil pyrolysis batch system was used in China as a hydrocarbon supply during the Second World War (Lima et al, 2004).

Different types of vegetable oils produce large differences in the composition of the thermally decomposed oil (Lima et al., 2004). Many kinds of vegetable oil species have been subjected to pyrolysis conditions. Some of these vegetable oils are soybean (da Rocha Filho et al., 1993; Lima et al., 2004), rapeseed (Billaud et al., 1995), palm tree (Alencar et al., 2002; Lima et al., 2004,), castor (Lima et al., 2004), safflower (Billaud et al., 1995), olive husk (Demirbas et al., 2000) and tung (Chand and Wan, 1947). Soybean oil pyrolysed distillate, which consists mainly of alkanes, alkenes and carboxylic acids, has a cetane number of 43, exceeding that of soybean oil (37.9) and the ASTM (American Society for Testing and Materials) minimum value of 40. The viscosity of the distillate was higher than the ASTM specification for diesel fuel but considerably below that of soybean oil (Lima et al., 2004). Short-term engine tests have been successfully carried out on this fuel (Hu et al., 2000). Used frying cottonseed oil pyrolysate has also been investigated (Knothe et al., 1997).

Biological production of hydrogen (bio-hydrogen) has received special attention during the last decade because it can be operated at an ambient temperature and pressure and is more environmentally friendly compared to other processes (Mohan et al., 2007). Due to the low cost and regeneration properties, biotechnology of hydrogen production might be the most important way for energy production in the near future (Balat and Balat, 2009). Furthermore, it offers sustainable supply of hydrogen with low pollution and high efficiency from a variety of renewable resources (Cheong and Hansen, 2006; Wu and Chang, 2007). Biological hydrogen production can be classified into the following groups:

1 Direct biophotolysis: The process uses the photosynthetic capability of green algae and cyanobacteria to split water by the directly absorbed light energy and concomitant transfer of electrons to a hydrogenase or a nitrogenase for H2 production (Kovacs et al., 2006).

2 Indirect biophotolysis: This process involves a photosynthetic biomass production step and an anaerobic dark fermentation of the biomass to produce H2. Several models to achieve indirect biophotolysis have been developed. These systems use algae in most cases and intend to exploit their capability to produce high biomass yield per surface. Main research includes production of algal biomass, which is rich in easily fermentable storage carbohydrates (Benemann, 1998).

3 Biological water-gas shift reaction.

4 Photo-fermentation.

5 Dark fermentation: This process is able to use biomass provided by a photosynthetic solar energy conversion system to H2 production (Keasling et al., 1998). Dark microbial H2 production is driven by the anaerobic metabolism of the key intermediate, pyruvate. The complete oxidation of glucose would yield a stoichiometry of 12 mol. H2 per mole of glucose, but in this case, no energy would be gained to support growth and metabolism of the producing organism (van Niel et al., 2002).

In a proposed integrated system, dark fermentation and photo-fermentation are combined in order to achieve maximal conversion of the substrate to biohydrogen (deVrije and Claassen, 2002).

Starch, cellulose or hemicellulose content of wastes, carbohydrate-rich food industry effluents or waste biological sludge can be further processed to convert the carbohydrates to organic acids and then to hydrogen gas by using proper bioprocessing technologies.

4.5 Acknowledgements

Authors want to give their sincere thanks to the following people and organisations for their generosity in letting us use their photos: Shu Suehiro, Hannes Grobe, Fabio Visentin, Huw Williams, Professor Krishna K. Shrestha (Central Department of Botany, Tribhuvan University), Hans Hillerwaer, Botanische tuin (TU Delft),

J. M. Garg, Paul Fenwick, Rich Weber (Native Trees of Indiana website), Iwata Kenichi (Okayama University), Mehmet Karatay, Moreno Clementi, Mehmet Karatay, Marco Schmidt (Senckenberg Research Institute), Teck Long Chen (Suriachem), Daniel Georg Dohne, Biofuels Center of North Carolina, Jose Maria Fernandez (University of Cordoba) and Brad Lashua. Authors gratefully acknowledge support for this research from the Spanish Ministry of Education and Science (ENE2007-65490/ALT and HI2008-0229) and from the Spanish International Development Cooperation Agency (AECID, PCI-C/019212/08).