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<p>Polyhydroxyalkanoates (PHA) are fully biodegradable polyesters synthesized by microorganisms from renewable carbon sources, including agro-industrial residues. Soy molasses, a carbohydrate-rich by-product of soybean processing, can be fermented to produce organic acids suitable for PHA production. The established process to produce PHA using mixed microbial cultures (MMC) comprises three stages: acidogenic fermentation, microbial enrichment and PHA accumulation. This study investigated PHA production by MMC through the application of different organic loading rates (OLR) in the enrichment stage in a sequential batch reactor (SBR). The nominal OLR values applied were 2.0, 3.5 and 7.0&#xa0;kg <sub>COD</sub> m⁻³ d⁻¹. Among the evaluated conditions, the best measured OLR for selecting PHA-producing MMC was 6.78 ± 0.37&#xa0;kg <sub>COD</sub> m⁻³ d⁻¹, based on stability in the enrichment reactor (F/F, 0.15 ± 0.06) and maximum volumetric PHA productivity (0.15&#xa0;g <sub>PHA</sub> L⁻¹ h⁻¹) in the accumulation assay. Biomass from the best conditions was also evaluated in an accumulation stage with acidified soy molasses fortified with its main organic acids (lactic, valeric, acetic, and butyric), at a concentration of 79&#xa0;kg <sub>COD</sub> m<sup>− 3</sup>. When using fortified molasses as a substrate, productivity increased to 0.38&#xa0;g <sub>PHA</sub> L⁻¹ h⁻¹, with a yield of 0.48&#xa0;g <sub>COD−PHA</sub> g <sub>COD−dosed</sub>⁻¹ (soluble COD), demonstrating a positive effect of high substrate concentration on accumulation performance. The biopolymer produced was a PHBV copolymer, with proportions of 3-hydroxybutyrate (HB) to 3-hydroxyvalerate (HV) ranging from 82:18 to 88:12 (mass basis) under non-fortified conditions, changing to 65:35 (mass basis) when fortified molasses was used.</p>

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Soybean Molasses as a Feedstock for Polyhydroxyalkanoates (PHA) Production by Mixed Microbial Cultures: Effects of the Organic Loading Rate

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月11日

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  • Andressa Gomes Barroso,
  • Isabela Mehi Gaspari Augusto,
  • José Alberto Domingues Rodrigues,
  • Guilherme Henrique Duarte Oliveira

摘要

Polyhydroxyalkanoates (PHA) are fully biodegradable polyesters synthesized by microorganisms from renewable carbon sources, including agro-industrial residues. Soy molasses, a carbohydrate-rich by-product of soybean processing, can be fermented to produce organic acids suitable for PHA production. The established process to produce PHA using mixed microbial cultures (MMC) comprises three stages: acidogenic fermentation, microbial enrichment and PHA accumulation. This study investigated PHA production by MMC through the application of different organic loading rates (OLR) in the enrichment stage in a sequential batch reactor (SBR). The nominal OLR values applied were 2.0, 3.5 and 7.0 kg COD m⁻³ d⁻¹. Among the evaluated conditions, the best measured OLR for selecting PHA-producing MMC was 6.78 ± 0.37 kg COD m⁻³ d⁻¹, based on stability in the enrichment reactor (F/F, 0.15 ± 0.06) and maximum volumetric PHA productivity (0.15 g PHA L⁻¹ h⁻¹) in the accumulation assay. Biomass from the best conditions was also evaluated in an accumulation stage with acidified soy molasses fortified with its main organic acids (lactic, valeric, acetic, and butyric), at a concentration of 79 kg COD m− 3. When using fortified molasses as a substrate, productivity increased to 0.38 g PHA L⁻¹ h⁻¹, with a yield of 0.48 g COD−PHA g COD−dosed⁻¹ (soluble COD), demonstrating a positive effect of high substrate concentration on accumulation performance. The biopolymer produced was a PHBV copolymer, with proportions of 3-hydroxybutyrate (HB) to 3-hydroxyvalerate (HV) ranging from 82:18 to 88:12 (mass basis) under non-fortified conditions, changing to 65:35 (mass basis) when fortified molasses was used.