Strategies for the valorisation of a protein-rich saline waste stream into polyhydroxyalkanoates (PHA)

Polyhydroxyalkanoates Production by Mixed Microbial Culture under High Salinity

“…to 49 ± 3% wt., indicating a good culture adaptation to higher organic load and even leading to better culture performance. The obtained PHA contents at the end of the feast period were already quite high and comparable with other reported accumulation assays [23], which suggested the possibility of skipping the third stage of the traditional MMC PHA-accumulating process in order to lower operating costs. This culture showed a cycle profile very similar to that obtained in an OLR of 60 Cmmol/(L.d) (Figure 2B), whereas the VSS/TSS ratio shifted to 52 ± 0% wt.…”

“…The obtained values in the present study were also higher, as compared to a study by Alba Pedrouso et al, where the culture that had acclimatized at 5 g NaCl /L reached a qPHA of 0.24 Cmmol PHA /(Cmmol X .h) [21]. It was also considerably higher, as compared to the slowly adapted culture to 20 g NaCl /L in the work of Roibás-Rozas et al, where the qPHA was only 0.05 Cmmol PHA /(Cmmol X .h) [23]. The use of an inoculum obtained from a saline environment, a strategy that other studies have not followed, may have played a major role in the swiftness and favourable outcome of the enrichment reactor as the microorganisms were already adapted to their natural saline environments and were, therefore, able to outperform cultures that had not been naturally adapted.…”

“…The obtained values, namely in ACC-120, were considerably higher than the presented results of Roibas-Rozas et al, where an adapted MMC to a lower NaCl concentration (close to 20 g NaCl /L) was able to reach a PHA concentration of 41.5% wt. with a specific productivity of 68.1 mg PHA /(g X .h) [23]. These results were, however, obtained by using a real feed, rich in nitrogen, and the salt concentration was increased throughout the assay, starting from 5 g NaCl /L, and the VFA mixture used was 43:7:42:8 (Cmol basis) acetic/propionic/butyric/valeric acids [23].…”

“…with a specific productivity of 68.1 mg PHA /(g X .h) [23]. These results were, however, obtained by using a real feed, rich in nitrogen, and the salt concentration was increased throughout the assay, starting from 5 g NaCl /L, and the VFA mixture used was 43:7:42:8 (Cmol basis) acetic/propionic/butyric/valeric acids [23]. The obtained values in the present study were also significantly higher, as compared to those obtained by Oliveira et al of 33% wt.…”

“…using a synthetic mixture as feedstock. In another work with the same feedstock but with high salinity levels, Roibás-Rozas et al [23] were able to slowly adjust (throughout 100 days) the NaCl concentration in the selection reactor up to 20 g NaCl /L, starting from a previously PHA-accumulating MMC selected at 5 g NaCl /L. This culture was then also used for accumulation assays where the NaCl concentration was gradually increased throughout the assays until it reached 28 g NaCl /L, reaching a PHA content of 41% wt.…”