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: