Data analysis
The SRT was determined by the amount of solids
(gTSS·d-1) discharged from the system compared to the
total amount of solids (gTSS) present in the reactor. The chemical
oxygen demand (COD) balance could only be made over the soluble
compounds measured in the effluent and averaged VSS production.
Furthermore, it was assumed that all VSS consisted for 100% out of
biomass.
A mathematical model was made for obtaining the conversions and
qSmax of the enrichment. An elaborated description of
the model is shown in the supplementary material. The model was based
upon two/three reactions.
(i) Direct glucose fermentation towards extracellular products, biomass
and storage polymer:
\(Glucose\rightarrow a\ Acetate+\ b\ Lactate+c\ Propionate+d\ Butyrate+\ e\ Biomass+f\ Storage\ polymer\ \left[gCODgCOD\right]^{-1}\ \)
(ii) The conversion of storage polymer to extracellular products and
biomass
\begin{equation}
Storage\ polymer\rightarrow g\ Acetate+\ h\ Lactate+i\ Propionate+j\ Butyrate+\ k\ Biomass\ \left[gCODgCOD\right]^{-1}\nonumber \\
\end{equation}(iii) A fixed stoichiometry for lactate conversion as described in (J.
Tamis et al., 2015)
\begin{equation}
Lactate\rightarrow 0.21\ acetate+0.73\ propionate+0.06\ VSS\ \left[gCODgCOD\right]^{-1}\ \nonumber \\
\end{equation}Furthermore, to make the model fitting the following assumptions were
made:
- The biomass conversion factor used was 1.42
gCOD·gVSS-1 (Rittmann, Crawford, & Tuck, 1986)
- The storage polymer amount was set to 1 gCOD at the start of a cycle
and should be 1 ± 0.05 gCOD at the end of the cycle
- There was no restriction for the COD-balances to be closed, allowing
identification of missing fermentation products
- The production/consumption of H2 was not incorporated
in the model