Combined Strategies to Boost Polyhydroxyalkanoate Production from Fruit Waste in a Three-Stage Pilot Plant

The full-scale implementation of polyhydroxyalkanoate (PHA) production using mixed microbial cultures (MMCs) has been limited by the low PHA global productivity and overall process yield. This work aimed to demonstrate, at a pilot scale, that by combining different effective operating conditions, it is possible to boost the PHA production performance when using fruit waste as a substrate. The organic loading rate (OLR) and pH of the acidogenic reactor were successfully used as tuning parameters to obtain a high fermentation yield (0.74 gCOD.gCOD(-1)) and a fermentate rich in butyrate, resulting in enhanced PHA production steps. A biomass highly enriched in PHA-storing microorganisms was selected as a result of uncoupling the carbon to the nitrogen feeding. The biomass concentration attained a notable value (7.83 g-L-1) as a response to the high OLR (8.7 gCOD.L-1.d(-1)) imposed. In the PHA accumulation assays, the culture selected at the optimal OLR in the selection reactor achieved a high storage yield (0.98 gCOD.gCOD(-1)), and the continuous feeding strategy led to a maximum PHA content of 80.5% (g-basis). The high global productivity (8.1 g-PHA.L-1.d(-1)) and overall process yield (0.45 gCOD.gCOD(-1)) are, to the best of the authors' knowledge, the highest values reported for MMC using a real feedstock at pilot scale. These results demonstrate the importance of combining different effective strategies to maximize the process performance, a promising result toward the full-scale implementation of PHA production from wastes and MMC.

Automated summary

This research demonstrated the importance of combining different effective strategies to maximize the performance of PHA production from fruit waste as a substrate. The results showed enhanced PHA production steps by tuning parameters like organic loading rate (OLR) and pH of the acidogenic reactor. The study achieved high global productivity and overall process yield, making it a promising step towards full-scale implementation of PHA production from wastes and MMC.