Pham C H, Cu T T T, Jin M T and  Sommer S G 2011 Test batch fermentation techniques, biogas measurement methods and methane concentration determination methods.  Workshop on Reducing Greenhouse Gas Emissions from Livestock and Soils (Editors: Reg Preston and Sisomphone Southavong). National Institute of Animal Science, Hanoi, 14-15 November 2011. httm://www.mekarn.org/workshops/GHG-CC/cuong.htm