How long you leave the material in a batch digester depends on
temperature (2 weeks at 50°C up to 2 months at 15°C).
The average is
around 1 month – so gauge how much material you will add each day, and
multiply it by 30 to calculate the size of the digester.
While
anaerobic digestion occurs between 32° F (0°C) and 150° F (65°C), the
optimum temperature range for methane generating microbial activity is
85°F (29°C) to 95° F (35°C).
Little gas production occurs below
60°F (16°C).
In colder climates placing the digester in a greenhouse,
and perhaps using some of the methane to warm the system, are possible
strategies.