2.3. Batch assays
Batch assays to determine the specific methanogenic activity
(SMA) of the reactor sludges were performed in duplicate
using 120mLserum bottles. Each bottle received 2–4 g
VSS (volitile SS) L−1 of sludge, and one of the substrates,
either domestic sewage or nutrient solution.[17] Distilled
water was then added to produce a liquid volume of 60 mL.
The headspaces were flushed with nitrogen gas and the bottles
were sealed with butyl rubber stoppers and aluminium
crimps, after which they were incubated in static cultures at
35◦C. Fermentation tubes were used for gas collection and
CO2 was absorbed by 5% of NaOH solution. SMAs were
calculated according to the following equation:
SMA =
K
VX
T0
T
, (1)
where K is the linear production rate of methane (L
CH4 h−1) is calculated from the steepest slope of cumulative
methane production curves; V is the sludge volume
(L); X is the VSs content of the sludge (g VS L−1); T0 is