The Role of C/N Ratio on the Modulation of Sewage Sludge Microbiota for Producing Polyhydroxyalkanoates

Polyhydroxyalkanoates (PHA) can be generated by the products of an excess sewage sludge fermentation process. An efficient method reported is to enrich a PHA-producing community in an aerobic feast/anoxic famine enrichment strategy. This work evaluated the effect of different C/N feed ratios of 3.5, 2 and 1 g COD/g N. The study was executed on a pilot plant scale with municipal excess sludge as an organic carbon source. System performance in PHA production was monitored over the three experimental periods characterised by the different C/N ratios. Preliminary results show that a lower C/N ratio decreased the PHA production (20, 24 and 26% w/w of PHA produced, for COD/N ratios of 1, 2 and 3.5 g COD/g N respectively). Metataxonomic analysis revealed an increase of PHA producers’ microorganisms at the ratio of 3.5 g COD/g N. The insights gained from the study demonstrate the negative effect of low C/N ratios on PHA production. Moreover, the metataxonomic proved to be useful in highlighting relationships between operating conditions, microbiota, and the achievement of specific outputs.