1. Biogas production: current state and perspectives;Weiland;Appl. Microbiol. Biotechnol.,2010
2. World Energy Outlook-2050,2006
3. Exploring the Future: Energy Needs, Choices and Possibilities – Scenarios to 2050;Global Business Environment Shell International,2001
4. World Energy Outlook,2009
5. The Biorefinery Concept–An Integrated Approach;Clark,2008