Biogas production from steer manures in Vietnam: Effects of feed supplements and tannin contents.

In developing countries, the simple biogas digesters installed underground without heating or stirring are seen as a 'green' technology to convert animal waste into biogas, a source of bio-energy. However, quantitative estimates of biogas production of manures from steers fed local feed diets at actual incubation temperatures have yet to be carried out. The aim of this study was to determine the methane (CH) production potential of manures from steers in Vietnam offered traditional feed rations or supplemental diets. Biochemical CH production (BMP) was measured in batch tests at 30°C using manures collected from two different experiments of steers fed diets containing feed supplements. BMP was 110.1 (NLkgVS) for manure from steers receiving a control diet, significantly lower 79.0 (NL kgVS) for manure from steers fed a diet containing 0.3% tannin (%DM), but then showed an increasing trend to 90.9 and 91.2 (NL kgVS) for manures from steers receiving 0.4 and 0.5% tannin (%DM) supplements, respectively. Similarly, the CH production (NL kgVS) of manure from steers was 174 for control, 142 for control supplemented concentrate (C), 143 for control added rice straw treated with urea (R), and 127 for control supplemented C and R. Our results show there was a decrease in CH emissions from steer manures through using supplemented rations.