Explain how methane can be generated from biomass.

processes:
a. generated from waste animal/plant material;
b. material placed in a digester/fermenter/bioreactor;
c. bacteria/microorganisms convert organic waste into organic acids and alcohol;
d. all processes are anaerobic / fermentation;
e. other bacteria act on waste to convert to acetate/carbon dioxide and hydrogen;
f. methanogenic bacteria produce methane anaerobically;
g. from acetate/carbon dioxide and hydrogen;

conditions:
h. digester needs to be damp/warm for reactions to occur;
i. pH conditions not too acidic / in absence of oxygen;
j. temperature rise needs to be controlled to prevent killing the useful bacteria;

This was probably the most successful third question of the whole paper, perhaps because it was based on factual information, but also because candidates were able to incorporate precise details and present the process in a logical order. Most candidates, obviously well prepared, gained many if not all the marks for this, but some irrelevant answers were also seen.