Strategies for PHA production by mixed cultures and renewable waste materials
ABSTRACT Production of polyhydroxyalkanoates (PHA) by mixed cultures has been widely studied in the last decade. Storage of PHA by mixed microbial cultures occurs under transient conditions of carbon or oxygen availability, known respectively as aerobic dynamic feeding and anaerobic/aerobic process. In these processes, PHA-accumulating organisms, which are quite diverse in terms of phenotype, are selected by the dynamic operating conditions imposed to the reactor. The stability of these processes during long-time operation and the similarity of the polymer physical/chemical properties to the one produced by pure cultures were demonstrated. This process could be implemented at industrial scale, providing that some technological aspects are solved. This review summarizes the relevant research carried out with mixed cultures for PHA production, with main focus on the use of wastes or industrial surplus as feedstocks. Basic concepts, regarding the metabolism and microbiology, and technological approaches, with emphasis on the kind of feedstock and reactor operating conditions for culture selection and PHA accumulation, are described. Challenges for the process optimization are also discussed.
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- "For this category of food products, as their shelf life is short, there is no need for long-lasting packaging materials, making biodegradable materials interesting environmental-friendly solu- tions. Among the different biodegradable materials commercially available, poly(hydroxy-3-butyrate-co-3-valerate) (PHBV), is a bacterial polyester presenting the advantage of being bio-sourced and potentially prepared from food industry by-products (Serafim et al., 2008). Its main drawbacks are its high cost (3–5 D /kg, Chanprateep, 2010) and its barrier properties which are too high to fit respiring products needs (Shogren, 1997). "
ABSTRACT: Abstract Lignocellulosic fibres obtained by dry grinding of three different solid agro-residues, i.e. wheat straw, brewing spent grains and olive mills, were compared regarding their potential use as fillers in poly(3-hydroxybutyrate-co-valerate) (PHBV) for food packaging applications. Differences found in their composition might have influenced their grinding ability, as observed with the difference of sizes, i.e. 109 μm, 148 μm and 46 μm, respectively. Thereafter, composites structure was characterized regarding their morphology, fibre/matrix interaction, matrix molecular weight and crystallization behaviour. Poor fibre/matrix adhesion, degradation of PHBV polymer chains, and decrease of PHBV’s crystallinity were evidence. Consequently, mechanical properties were degraded in presence of the fibres. Water vapour transfer rate of composites was increased with wheat straw fibres introduction while it was decreased for olive mills-based materials. Regarding the food packaging applications, PHBV/wheat straw fibres composites appeared as promising materials to reach the requirements of respiring food products, whereas PHBV/olive mills composites would be more adapted for water sensitive products.Industrial Crops and Products 07/2015; 69:110 - 122. DOI:10.1016/j.indcrop.2015.01.028 · 2.84 Impact Factor
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- "For example, it has been recently demonstrated that sustainable packaging materials can be obtained by designing composite structures from constituents all derived from food industry by-products in order to fulfil mass transfer properties requirements for an optimal preservation of a targeted food type . Among the matrices used for the preparation of biocomposites, polyhydroxy-co-3-butyrate-co-3-valerate (PHBV), a bacterial aliphatic copolyester, has been reported to be produced from food industry by-products  and to provide a complete biodegradability in composting, backyard or landfill conditions, as well as recyclability  . In addition, PHBV is easily process-able using either extrusion or injection processes   . "
ABSTRACT: The present work aims at investigating the impact of wheat straw fibres (WSF) size, morphology and content on the process-ability and functional properties (mechanical properties and water vapour permeability) of PHBV-based composites. For that purpose, three types of fibres obtained by successive grindings (from the micrometric up to the millimetric scale) were used. It was shown that the highest possible filler level was all the more high when decreasing fibre size (over 50wt% in the case of micrometric fibres), due to reduced film heterogeneity and improved fibre wetting by the polymer. As regards functional properties, increasing fibre size and/or content led to a significant degradation of ultimate tensile properties, while the Young’s modulus was not significantly affected. At the same time, water vapour transmission rate was significantly increased from 11 up to 110 g.m-2.day-1, which could extend the applicability of PHBV/WSF composites as food packaging materials to respiring fresh products.Composites Part A Applied Science and Manufacturing 02/2015; 72. DOI:10.1016/j.compositesa.2015.02.006 · 3.01 Impact Factor
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- "To lower the final price of polymers, complex waste could be used, for example, fermented sugar cane molasses, palm oil mill effluents, industrial wastewaters, and brewery wastewater (Serafim et al., 2008). Besides these substrates, crude glycerol generated as a by-product during biodiesel production has acquired importance during the last years, as reviewed by da Silva et al. (2009). "
ABSTRACT: Polyhydroxyalkanoates (PHAs) can be produced by microorganisms and are a biodegradable alternative to fossil-fuel based plastics. Currently, the focus is on reducing production costs by exploring alternative substrates for PHAs production, and on producing copolymers which are less brittle than monomers. Accordingly, this study used a substrate consisting of wastewater from waste-glycerol fermentation, supplemented with different amounts of acetic and propionic acids. These substrates were used to feed mixed microbial communities enriched from activated sludge in a sequencing batch reactor. A reactor supplemented with 2 mL of acetic acid produced 227.8 mg/L of a homopolymer of hydroxybutyrate (3HB); 4 mL of acetic acid produced 279.8 mg/L 3HB; whereas 4 mL of propionic acid produced 673.0 mg/L of a copolymer of 3HB and 3HV (hydroxyvalerate). Ribosomal Intergenic Spacer Analysis (RISA) was used to show the differences between the communities created in the reactors. Thauera species predominated in biomass that produced 3HB; Paracoccus denitrificans in the biomass that produced 3HB-co-3HV. Because P. denitrificans produced the more desirable copolymer, it may be advantageous to promote its growth in PHAs-producing reactors by adding propionate.Brazilian Journal of Microbiology 08/2014; 45(2):395-402. DOI:10.1590/S1517-83822014000200005 · 0.45 Impact Factor