The Role of Organic Loading Rate on the Modulation of Sewage Sludge Microbiome for the Production of Polyhydroxyalkanoates in Wastewater Treatment Plants

Over the past decade, a crucial shift in wastewater treatment plants (WWTPs) has emerged to foster environmentally sustainable development. The sewage sludge produced in WWTPs became a resource rather than awaste,mainly because of the high value-added chemicals that can be recovered from it, such as polyhydroxyalkanoates (PHA). Unlike in the past, where pure cultures predominantly produced PHA, current research emphasises using mixedmicrobial consortia( MMC)ormicrobiota residing the sewage sludge.MMCbased PHAproduction leverages natural selection and competition principles among microorganisms, favouring those proficient in PHA storage. Municipal WWTPs, serving as platforms for PHA production, are gaining attention due to the favourable attributes of MMC, including reduced costs and simplified operation and maintenance compared to pure cultures. Integrating PHA production into existing wastewater treatment infrastructures presents challenges, balancing organic carbon and nutrient removal within legislative limits while optimising conditions for PHA production. Understanding the impact of the operational parameters in the PHA production by MMC is crucial to optimising the process and obtaining insights regarding the microbiota role. In this study, different volumetric organic loading rates (vOLR) were applied in the enrichment reactor of a pilot plant scheme aimed at producing PHA from sewage sludge MMC. The results revealed microbiota structure changes by metataxonomic analysis. A vOLR of 1.3 g COD L−1 d−1 determined an increase of PHA producer bacteria such as the Proteobacteria.