Development of Microbial Community, Polyhydroxyalkanoate (PHA) Yield and Composition Using Residual Streams of the Fruit Juice Industry

Biodegradable polymers in form of polyhydroxyalkanoates (PHA) have been produced using residual streams of the fruit juice industry and excess sludge from a municipal sewage treatment plant. In the first step of the process, PHA synthesizing bacteria were enriched, applying a feast-famine regime to supply the feedstock. The PHA accumulation potential was investigated closely during a 14-day long experiment, taking hourly samples during several eight-hour-long batch accumulations. For this, the substrate was provided to the enriched biomass using a feed-on-demand strategy considering the increase of the dissolved oxygen concentration. Hereby, the PHA yield of the mixed microbial culture (MMC) increased from 8% up to 65% of the dry matter. Furthermore, the monomeric composition of the produced PHA was analysed using gas chromatography. This allowed the observation of the changing composition of hydroxybutyrate (HB), hydroxyvalerate (HV) and hydroxyhexanoate (HH). Moreover, biostatistical analysis of the microbial community composition were performed, which showed a shift in the relative abundance of the PHA producing bacteria. Despite this observation, the PHA productivity of the biocenosis remained nearly stable, showing the resilience and thereby functional redundancy of the system.