The modified Gompertz equation was utilized to the observed
cumulative CH4 production curves to determine the maximum
CH4 production potential (P), CH4 production rate (Rmax), and lag
phase (k) as shown in equation (Gurung et al., 2012):
YðtÞ ¼ P exp exp
Rmax e
p ðk tÞ þ 1
where, Y(t) is the cumulative CH4 production (mL CH4/g VS) at time
t; P is the maximum CH4 potential (mL CH4/g VS) at the end of incubation
time; t is time (h); Rmax is the CH4 production rate
(mL CH4/g VS d); k is the lag phase (h) and e is exp (1), i.e.
2.71828. Parameters of P, Rmax, and k were estimated by
curve-fitting using Origin software version 8.0.