The digester used in this study was a 2.5-L filter bottle with a
working volume of 2 L and consisted of a sampling outlet, a gas
sampling port, and a feed inlet. It was sealed using a rubber stopper
in which there was a pipe to extract biogas. The digester was connected
to a gas collection system consisting of a saturated brine
displacement bottle and a brine gathering bottle. Prior to operation,
the reactors were purged with nitrogen gas for 5 min to ensure
anaerobic conditions. Thereafter, the digesters were placed
in a water bath at 37 ± 1 C. Each digester was manually mixed
twice a day. The experiments were terminated when no significant
gas production was observed.
All of the reactors were started at an initial substrate concentration
of 54 g VS/L. The substrate, inoculum, and water were added
according to the desired experimental conditions (Table 2). All
batch digesters were run in duplicate.