However, to support efficient use of the technology, there must be strong local competence to assess the biogas production potential and to develop appropriate management schemes.ДЄt present, end-users in Vietnam, China and India often fail to control the technology efficiently, due to poor management competence ( Jiang et al., 2011). Due to the many benefits of biogas digestion, it is anticipated that this technology will also be promoted in other developing countries, such as the Philippines, Thailand, Nepal and Brazil. For similar reasons, the Chinese government has supported the construction of 30 million small biogas plants, and in India about 4 million biogas plants are planned or already in operation ( Bhattacharya and Jana, 2009 Jiang et al., 2011). Consequently, the Vietnamese government supports the construction of biogas digesters, with plans for 180,000 farm biogas digesters to be in operation by 2011 ( Cu et al., 2012). In regions without energy infrastructure, clean biogas energy is very important in reducing the costly use of fossil fuels, limiting deforestation and improving the livelihood of women cooking food ( Cu et al., 2012). One of the most cost-effective technologies for reducing environmental pollution related to manure management is biogas production, which is known to improve hygiene, reduce odours and GHG emissions, and also reduce the need for mineral fertilizers and pesticides ( Sommer et al., 2004 Jiang et al., 2011 Triolo et al., 2012). Manure management has to be adapted to the new production systems in order to prevent the expansion in livestock production from causing excessive pollution in the form of greenhouse gases (GHG), eutrophication, the spread of diseases and odour ( Xiong et al., 2008 Davidson, 2009 Sutton et al., 2011).

In Vietnam, the amount of manure collected is also increasing, not only because of the increase in livestock production, but also because livestock is increasingly being raised in animal houses. Increases in world population, changes in human diets ( Godfray et al., 2010) and new intensive livestock production methods are causing a massive increase in collected excreta (Bouwman et al., 2011). This indicates that the LRM method could be used to determine biomethane concentration in biogas in laboratories with limited access to GC. In determination of biomethane concentration, the values obtained using the liquid replacement method (LRM) were comparable to those obtained using gas chromatography (GC). In precision tests, the repeatability of the relative standard deviation (RSDr) for all batch methods was very low (4.8 to 8.1%), while the reproducibility of the relative standard deviation (RSD R) varied widely, from 7.3 to 19.8%. The first-order kinetics constant k for the cumulative methane production curve was highest when two animal manures were fermented using the VDI 4630 method, indicating that this method was able to reach steady conditions in a shorter time, reducing fermentation duration.

Degradation rate assessed by methane formation rate showed wide variation within the batch method tested. The biodegradability using a ratio of BMP and theoretical BMP (TBMP) was slightly higher using the Hansen method, but differences were not significant. The biochemical methane potential (BMP) (CH 4 NL kg в€’1 VS) of pig manure, cow manure and cellulose determined with the Moller and VDI methods was not significantly different in this test (p>0.05). This study tested and validated methods for measuring total biogas and methane (CH 4) production using batch fermentation and for characterizing the biomass. They may also be unable to produce valid estimates of an international standard that can be used for articles published in international peer-reviewed science journals. Laboratories in these countries have little access to advanced gas measuring equipment, which may limit research aimed at improving local adapted biogas production. In developing countries, biogas energy production is seen as a technology that can provide clean energy in poor regions and reduce pollution caused by animal manure.

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