# Urban Biorefinery Demonstration: Production of Polyhydroxyalkanoates from a Municipal Solid Waste
## 3 Results
### Accumulation of scl-PHA in Microorganisms  
Once the fermenter reached steady conditions, MMC in the enrichment fermenter was ready to start with the accumulation stage. Therefore, a total amount of 39 accumulation batches were performed. This accumulation stage was performed in the 3 m\({}^{3}\) fermenter to increase the amount of PHA stored in the MCC. Every batch performed in the scl-PHA accumulation stage consisted of a fed-batch mode at a constant flow rate of the free phosphorus VFA-rich solution into a fixed volume of the daily discharge of the enrichment fermenter. Initially, the applied COD feeding rate was similar than the COD consumption rate obtained in the least phase of the enrichment fermenter. In this study, different COD feeding rates in the accumulation fermenter were analyzed. First, ten accumulation batches were performed using the biomass obtained in selected enrichment cycles between 111 and 131. The COD consumption rate was 13.91 mg COD/L.min (Table 3). Thus, the COD feeding rate was varied from 9.86 to 24.44 mg COD/L.min to study the scl-PHA storage capacity influenced by the COD feeding rate. Moreover, the aeration and agitation were automatically controlled in a cascade control by varying the aeration and agitation from 0 to 700 m\({}^{3}\)/h, and 20 to 190 rpm, respectively, assuring a DO concentration higher than 20%. Table 4 summarizes the data of the first ten accumulation batches. The influence of the COD feeding rate as function of the percentage of scl-PHA in the biomass from accumulation batches 1 to 10 can be seen in Figure 5.  
To deeply study the influence of DO, a second set of 29 accumulation batches was run. In this case, the discharge of the enrichment fermenter from cycle 136 up to cycle 204 was employed. The COD consumption rate during those cycles was 19.56 mg COD/L.min (Table 3). Aeration and agitation were set to the maximum values allowed by the 3 m\({}^{3}\) fermenter system (700 m\({}^{3}\)/h and 190 rpm, respectively). The high aeration and agitation rates ensured a dissolved oxygen concentration exceeding 70%, thereby deactivating the cascade control. Table 5 summarizes the data of this second set of accumulation batches. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**N\({}^{*}\)**} & \multirow{2}{*}{**Cycle**} & \multirow{2}{*}{\begin{tabular}{c} **COD Feeding Rate** \\ **(mg COD/L.min)** \\ \end{tabular} } & **Initial** & \multirow{2}{*}{\
\begin{tabular}{c} **Scl-PHA** \\ **TSS** \\ **(g/L)** \\ \end{tabular} } & **Final TSS** & **El-PHA** & \multirow{2}{*}{
\begin{tabular}{c} **Scl-PHA** \\ **(g/L)** \\ \end{tabular} } & **Scl-PHA** & & & & **Scl-PHA** & & **Generated** \\  & & & **(g/L)** & & **(wt.\%)** & & **(kg/100 kg COD (mg/L)** \\ \hline
1 & 111 & 9.86 & 2.75 \(\pm\) 0.26 & 4.61 \(\pm\) 0.09 & 2.08 & 0.10 & 0.82 & \\
2 & 121 & 11.54 & 2.91 \(\pm\) 0.08 & 5.19 \(\pm\) 0.12 & 2.30 & 0.12 & 1.89 & \\
3 & 119 & 12.07 & 3.05 \(\pm\) 0.10 & 2.61 \(\pm\) 0.50 & 2.00 & 0.05 & 0.68 & \\
4 & 117 & 13.59 & 3.67 \(\pm\) 0.59 & 5.01 \(\pm\) 0.17 & 1.72 & 0.09 & 0.97 & \\
5 & 117 & 13.80 & 3.51 \(\pm\) 0.47 & 3.69 \(\pm\) 0.57 & 2.48 & 0.09 & 0.88 & \\
6 & 127 & 17.05 & 3.16 \(\pm\) 0.10 & 6.92 \(\pm\) 0.87 & 2.61 & 0.18 & 2.72 & \\
7 & 132 & 20.28 & 4.12 \(\pm\) 0.90 & 14.72 \(\pm\) 0.15 & 6.71 & 0.99 & 12.16 & \\
8 & 128 & 20.61 & 3.32 \(\pm\) 0.18 & 6.43 \(\pm\) 0.21 & 7.65 & 0.49 & 6.35 & \\
9 & 129 & 24.44 & 3.16 \(\pm\) 0.05 & 6.11 \(\pm\) 0.11 & 12.44 & 0.76 & 6.11 & 237 \\
10 & 131 & 24.44 & 2.84 \(\pm\) 0.28 & 7.44 \(\pm\) 0.27 & 16.06 & 1.19 & 10.48 & 299 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Data from accumulation batches 1 to 10 performed with an average COD consumption rate in enrichment fermenter of 13.91 mg COD/L.min. Figure 5: Influence of the scl-PHA percentage in the biomass varying the COD feeding rate to the accumulation reaction having the enrichment fermenter a COD consumption rate of 13.91 mg COD/L.min.