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Background <p>Polyhydroxyalkanoates (PHAs) are promising bio-based and biodegradable polymers that can contribute to the transition towards a circular bioeconomy, particularly when produced from renewable feedstocks. Nevertheless, the use of mixed microbial cultures (MMC) and real agri-food residues poses challenges related to substrate variability, process stability and control of polymer composition. In this study, a three-stage process was investigated to produce poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) from agri-food residues. The process consisted of: (i) acidogenic fermentation of cattle slurry and corn residues to generate a carboxylic acid (CA)-rich stream; (ii) microbial selection under feast–famine conditions to enrich PHA-accumulating microorganisms; and (iii) PHA accumulation in a fed-batch reactor. Two operational setups, differing in the pretreatment type, were compared to evaluate possible effects on PHA production: setup 1 used centrifuged fermentate, whereas setup 2 included an additional 0.22-µm filtration step.</p> Results <p>Acidogenic fermentation produced up to 18.6&#xa0;gCOD/L of CAs, mainly acetic, butyric and propionic acids, with production strongly influenced by substrate ratio, hydraulic retention time and pH. The CA-rich fermented liquid was used to select MMC enriched with PHBV-accumulating microorganisms and to tune the PHBV composition during the subsequent accumulation phase. In setup 1, storage yield (mean 0.33 ± 0.23 gCOD<sub>PHA</sub>/gCOD<sub>CA</sub>), PHA titre (mean 0.81 ± 0.33&#xa0;g/L) and intracellular PHA contents (4.0–21.0% w/w of cell dry weight) remained relatively low, likely due to the use of unfiltered fermentation effluent. In setup 2, the introduction of a filtration step and improved microbial selection led to higher and more stable conversion of CAs into PHAs, reaching mean storage yields of 0.78 ± 0.27 gCOD<sub>PHA</sub>/gCOD<sub>CA</sub>, mean PHA titre of 1.70 ± 0.44&#xa0;g/L and intracellular PHA values up to 57.0% w/w. The hydroxyvalerate (HV) monomer content showed temporal variability, ranging from 14.0–32.0% w/w in setup 1 and from 13.0–35.0% w/w in setup 2, with values generally within or close to the target range required to improve polymer flexibility and processability. Microbial community analysis revealed a marked reduction in genus richness following feedstock filtration and the progressive dominance of specialised PHA-storing genera, indicating effective selection pressure under feast–famine operation and supporting the observed improvements in polymer accumulation.</p> Conclusions <p>Overall, the results indicate that MMC-based PHBV production from agri-food residues can achieve polymer contents comparable to those reported for similar systems using complex substrates, while highlighting the importance of feedstock pretreatment and process control. The study provides insights into the integration of acidogenic fermentation with MMC-based PHA production, and identifies operational aspects that require further optimisation to enhance process robustness and product consistency.</p>

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Process optimisation for polyhydroxyalkanoates production with tailored hydroxyvalerate content from agri-food residues using mixed microbial cultures

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年5月14日

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  • Giovanna Pesante,
  • Claudia Magonara,
  • Alessia Zucca,
  • Elvis Montagnese,
  • Davide Bertasini,
  • Gaia Salvatori,
  • Lionel Nguemna Tayou,
  • Luca Di Leva,
  • Marianna Villano,
  • David Bolzonella

摘要

Background

Polyhydroxyalkanoates (PHAs) are promising bio-based and biodegradable polymers that can contribute to the transition towards a circular bioeconomy, particularly when produced from renewable feedstocks. Nevertheless, the use of mixed microbial cultures (MMC) and real agri-food residues poses challenges related to substrate variability, process stability and control of polymer composition. In this study, a three-stage process was investigated to produce poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) from agri-food residues. The process consisted of: (i) acidogenic fermentation of cattle slurry and corn residues to generate a carboxylic acid (CA)-rich stream; (ii) microbial selection under feast–famine conditions to enrich PHA-accumulating microorganisms; and (iii) PHA accumulation in a fed-batch reactor. Two operational setups, differing in the pretreatment type, were compared to evaluate possible effects on PHA production: setup 1 used centrifuged fermentate, whereas setup 2 included an additional 0.22-µm filtration step.

Results

Acidogenic fermentation produced up to 18.6 gCOD/L of CAs, mainly acetic, butyric and propionic acids, with production strongly influenced by substrate ratio, hydraulic retention time and pH. The CA-rich fermented liquid was used to select MMC enriched with PHBV-accumulating microorganisms and to tune the PHBV composition during the subsequent accumulation phase. In setup 1, storage yield (mean 0.33 ± 0.23 gCODPHA/gCODCA), PHA titre (mean 0.81 ± 0.33 g/L) and intracellular PHA contents (4.0–21.0% w/w of cell dry weight) remained relatively low, likely due to the use of unfiltered fermentation effluent. In setup 2, the introduction of a filtration step and improved microbial selection led to higher and more stable conversion of CAs into PHAs, reaching mean storage yields of 0.78 ± 0.27 gCODPHA/gCODCA, mean PHA titre of 1.70 ± 0.44 g/L and intracellular PHA values up to 57.0% w/w. The hydroxyvalerate (HV) monomer content showed temporal variability, ranging from 14.0–32.0% w/w in setup 1 and from 13.0–35.0% w/w in setup 2, with values generally within or close to the target range required to improve polymer flexibility and processability. Microbial community analysis revealed a marked reduction in genus richness following feedstock filtration and the progressive dominance of specialised PHA-storing genera, indicating effective selection pressure under feast–famine operation and supporting the observed improvements in polymer accumulation.

Conclusions

Overall, the results indicate that MMC-based PHBV production from agri-food residues can achieve polymer contents comparable to those reported for similar systems using complex substrates, while highlighting the importance of feedstock pretreatment and process control. The study provides insights into the integration of acidogenic fermentation with MMC-based PHA production, and identifies operational aspects that require further optimisation to enhance process robustness and product consistency.