Influence of co-digestion on process kinetics
A first-order exponential model was used to correlate the evolution
of the methane production with digestion time (Figs. 1
and 2). This kinetic model is normally applied to assess the performance
and kinetics of batch anaerobic digestion processes of
easily biodegradable substrates (Li et al., 2012).
The first-order exponential model is given by the following
expression:
B ¼ Bmax$½1 exp ð k$tÞ (2)
where: B (mL CH4/g VS) is the cumulative specific methane production,
Bmax (mL CH4/g VS) is the ultimate methane production, k
is the specific rate constant or apparent kinetic constant (d1) and t
(d) is the digestion time.
The adjustment by non-linear regression of the pairs of experimental
data (B, t) using Sigmaplot software (version 11.0) allowed
the calculation of the parameters k and Bmax for methane production,
which are summarized in Table 4. The high values of the R2
and the low values of the standard error of estimate demonstrate
the goodness of the fit of experimental data to the proposed model.
Fig. 1. Biochemical methane potential (mL CH4/g SVadded) of 100%WAS (-), 100% LSBB
(▫) and different co-digestion mixtures tested: 75% WAS-25% LSBB (◊); 50% WAS-50%
LSBB (:) and 25% WAS-75% LSBB (A). Vertical bars represent standard deviation
between triplicates.
Table 2
Calculated methane yield values obtained from Eq. (1) and the experimental data
obtained through co-digestion of WAS and lipid-spent Botryococcus braunii. Values
between parentheses represent standard deviation between triplicates.