In this study we investigated the feasibility of producing polyhydroxyalkanoate (PHA) by
microbial enrichments on paper mill wastewater. The complete process includes (1) paper
mill wastewater acidogenic fermentation in a simple batch process, (2) enrichment of
a PHA-producing microbial community in a selector operated in sequencing batch mode
with feast-famine regime, (3) Cellular PHA content maximization of the enrichment in an
accumulator in fed-batch mode. The selective pressure required to establish a PHA-
producing microbial enrichment, as derived from our previous research on synthetic
medium, was validated using an agro-industrial waste stream in this study. The microbial
enrichment obtained could accumulate maximum up to 77% PHA of cell dry weight within
5 h, which is currently the best result obtained on real agro-industrial waste streams,
especially in terms of biomass specific efficiency. Biomass in this enrichment included
both Plasticicumulans acidivorans, which was the main PHA producer, and a flanking pop-
ulation, which exhibited limited PHA-producing capacity. The fraction of P. acidivorans in
the biomass was largely dependent on the fraction of volatile fatty acids in the total soluble
COD in the wastewater after acidification. Based on this observation, one simple equation
was proposed for predicting the PHA storage capacity of the enrichment. Moreover, some
crucial bottlenecks that may impede the successful scaling-up of the process are discussed.