Abstract:
Anaerobic digestion is a widely used conversion
process for recovering energy from bio degradable waste
materials. Dry anaerobic co-digestion of lignocellulosic biomass
such as rice straw (RS) with cow dung (CD) offers various
benefits other than mono digestion or liquid state anaerobic
digestion. However dry anaerobic co-digestion of lignocellulosic
biomass has restrictions due to low moisture content and
retarded mass transfer within the mixture of substrates which
contains in the reactor. Three consecutive batch experiments (E-
1, E-2, and E-3) were conducted by reusing solid digestate of E-
1 as an inoculum to E-2 and solid digestate of E-2 as an inoculum
for E-3 in lab scale reactors using RS and CD as substrates. In
E-1, CD was the only inoculum and it acted as a substrate as
well. Total solids (TS) content of the substrate mixtures of E-1,
E-2 and E-3 were 15%, 16%, and 20% respectively. Then
mathematical modeling was applied to estimate kinetic
parameters related to dry anaerobic co-digestion process using
the modified Gompertz model for the three experiments.
Modified Gompertz model very closely predicted the ultimate
methane yield (Mmax) with R2 almost 0.99 in each scenario.
Degradation kinetics improved drastically with the strategy of
reusing of digestate, as for the E-2 the lag phase period (λ)
reduced from 14 days to almost zero. Ultimate methane yield
increased by 104% through this approach. Degradation kinetics
were negatively affected with the increase of TS% within the
substrate mixture even though digestate was reused as an
inoculum. In E-3 ultimate methane yield was 138 ml/g volatile
solids (VS) which was a 38% reduction compared to E-2, even
though digestate was used as the main inoculum source for the
both experiments. But it was a 27% increase compared to E-1
which CD was used as the only inoculum.
