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

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Title: Soybean Molasses as a Feedstock for Polyhydroxyalkanoates (PHA) Production by Mixed Microbial Cultures: Effects of the Organic Loading Rate.
Authors: Barroso, Andressa Gomes1 (AUTHOR) andressagb@usp.br, Augusto, Isabela Mehi Gaspari2 (AUTHOR), Rodrigues, José Alberto Domingues3 (AUTHOR), Oliveira, Guilherme Henrique Duarte1 (AUTHOR)
Source: Journal of Polymers & the Environment. Aug2026, Vol. 34 Issue 8, p1-14. 14p.
Subject Terms: Polyhydroxyalkanoates, Molasses, Biopolymers, Fermentation, Mixed culture (Microbiology), Poly-beta-hydroxybutyrate, Batch reactors
Abstract: 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. [ABSTRACT FROM AUTHOR]
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Description
Abstract: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. [ABSTRACT FROM AUTHOR]
ISSN:15662543
DOI:10.1007/s10924-026-03906-3