Polyhydroxyalkanoates production from a waste-derived feedstock driven by the reactor operating conditions: the role of biomass microbiome and its reactivation capacity

In the last years, the production of plastics at large-scale has been an issue of great concern due to their environmental and health impacts. Biobased and biodegradable plastics, such as polyhydroxyalkanoates (PHA), have emerged as a possible more ecological and sustainable alternative to those conventional plastics. PHA can be produced by mixed microbial cultures (MMC) from waste-based feedstocks. This work aimed to maximize the PHA production from fermented brewer's spent grain by selecting an efficient PHA-accumulating MMC, applying different organic loading rates (OLR, 45 or 60 Cmmol_FP/(L.d)) and sludge retention times (SRT, 4 or 2 days). Additionally, the biomass reactivation capacity after storage was evaluated. The global PHA productivity depends on the operating conditions, achieving its maximum (3.55 ± 0.8 g_PHA/(L.d)) at the highest OLR and SRT tested. After storage, the global PHA productivity was similar to the one achieved before the starvation period. Depending on the operating conditions, the microbiome has its own bacterial composition signature containing various PHA-producers genera (e.g., Acidovorax, Amaricoccus, Brevundimonas, Leucobacter, Leadbetterella and Thauera) that persisted over time, albeit at different relative abundancies. A comprehensive overview of PHA production with data on system performance and microbiome is presented, which thereby can further contribute to the upscale of such valorisation processes.