Improving polyhydroxyalkanoates production in phototrophic mixed cultures by optimizing accumulator reactor operating conditions

TL;DR

This study optimizes conditions for PHA production in phototrophic mixed cultures, achieving higher yields and using waste substrates, with implications for sustainable bioplastic manufacturing.

Contribution

It identifies optimal acetate concentrations and light intensities for enhanced PHA production and demonstrates the use of fermented cheese whey as a substrate.

Findings

High PHA yields achieved at low acetate and specific light intensities.

PHA content increased from 15% to 30% in less than 4 hours.

First demonstration of using fermented cheese whey for PHA production.

Abstract

Polyhydroxyalkanoates (PHAs) production with phototrophic mixed cultures (PMCs) has been recently proposed. These cultures can be selected under the permanent presence of carbon and the PHA production can be enhanced in subsequent accumulation steps. To optimize the PHA production in accumulator reactors, this work evaluated the impact of 1) initial acetate concentration, 2) light intensity, 3) removal of residual nitrogen on the culture performance. Results indicate that low acetate concentration (<30CmM) and specific light intensities around 20W/gX are optimal operating conditions that lead to high polyhydroxybutyrate (PHB) storage yields (0.83+-0.07 Cmol-PHB/Cmol-Acet) and specific PHB production rates of 2.21+-0.07 Cmol-PHB/Cmol X d. This rate is three times higher than previously registered in non-optimized accumulation tests and enabled a PHA content increase from 15 to 30% in less than 4h. Also, it was shown for the first time, the capability of a PMC to use a real waste, fermented cheese whey, to produce PHA with a hydroxyvalerate (HV) content of 12%. These results confirm that fermented wastes can be used as substrates for PHA production with PMCs and that the energy levels in sunlight that lead to specific light intensities from 10 to 20W/gX are sufficient to drive phototrophic PHA production processes.