Polyhydroxyalkanoates Bioplastics Research Articles

High-cell-density fed-batch strategy to manufacture tailor-made P(HB-co-HHx) by engineered Ralstonia eutropha at laboratory scale and pilot scale.

The transition towards a sustainable bioeconomy requires the development of highly efficient bioprocesses that enable the production of bulk materials at a competitive price. This is particularly crucial for driving the commercialization of polyhydroxyalkanoates (PHAs) as biobased and biodegradable plastic substitutes. Among these, the copolymer poly(hydroxybutyrate-co-hydroxyhexanoate) (P(HB-co-HHx)) shows excellent material properties that can be tuned by regulating its monomer composition. In this study, we developed a high-cell-density fed-batch strategy using mixtures of fructose and canola oil to modulate the molar composition of P(HB-co-HHx) produced by Ralstonia eutropha Re2058/pCB113 at 1-L laboratory scale up to 150-L pilot scale. With cell densities >100 g L-1 containing 70-80 wt% of PHA with tunable HHx contents in the range of 9.0-14.6 mol% and productivities of up to 1.5 g L-1 h-1, we demonstrate the tailor-made production of P(HB-co-HHx) at an industrially relevant scale. Ultimately, this strategy enables the production of PHA bioplastics with defined material properties on the kilogram scale, which is often required for testing and adapting manufacturing processes to target diverse applications.

Enrichment strategies for mixed cultures in valorisation of crude glycerol into polyhydroxyalkanoate bioplastics

This study investigated two different strategies for enrichment using crude glycerol and mixed culture. Coupled feeding allowed simultaneous supplies of glycerol and nutrients at start of feast, whereas uncoupled feeding postponed nutrient supply until start of famine. Adaptation of culture enriched by the uncoupled feeding strategy was faster with higher operational stability. This however resulted in low PHB content of 20% and yield of 0.137 mg PHB/mg glycerol in feast phase, cell growth at yield of 0.298 mgX/mg PHB in famine. With more abundance (29.2%) of PHA storing bacteria in culture enriched by the coupled feeding strategy as revealed from 16 S rRNA analysis, results showed that polymer storage was dominated in feast phase (max. PHB content of 68%, yield of 0.563 mg PHB/mg glycerol), leading to high cell growth yield of 0.745 mg X/mg PHB. PHB accumulation by the enriched culture from coupled feeding has achieved 82% PHB content with 1094 mg PHB/L.h volumetric productivity. Thus, the coupled feeding was more effective to enrich PHA storing culture for PHA production using crude glycerol via two-step process.

Sustainable bioconversion of synthetic plastic wastes to polyhydroxyalkanoate (PHA) bioplastics: recent advances and challenges

Millions of tons of chemical plastics are accumulated annually worldwide in terrestrial and marine environments due to inadequate recycling plants and facilities and low circular use. Their continuous accumulation and contamination of soil and water pose a severe threat to the environment and to human, animal and plant health. There is therefore an urgent need to develop effective eco-environmental strategies to overcome the significant environmental impacts of traditional plastic waste management practises (incineration, landfilling, and recycling). In recent years, reports on microbial strains equipped with the potential of degrading plastic materials, which can further be converted into usable products such as PHA bioplastics have sprung up, and these offer a possibility to develop microbial and enzymatic technologies for plastic waste treatment and then progressing plastics circularity. In this chapter, an overview of the reported microbial and enzymatic degradations of petroleum-based synthetic plastics, specifically polyethylene, polystyrene, polypropylene, polyvinyl chloride, polyurethane and polyethylene terephthalate, is detailed. Furthermore, the harvesting of depolymerization products to produce new PHA materials with high added industrial value can be considered as an innovative solution, helping to increase synthetic plastic recycling rate and creating new circular economy opportunities. Finally, the challenge of ending plastic pollution is still difficult, but sustainable, renewable, bio-based and completely biodegradable, PHA will hold enormous promise for replacing plastics made from petrochemicals.

Impact of phosphorus limitation on medium-chain-length polyhydroxyalkanoate production by activated sludge

For a sustainable economy, biodegradable biopolymers polyhydroxyalkanoates (PHA) are desirable substitutes to petroleum-based plastics that contaminate our environment. Medium-chain-length (MCL) PHA bioplastics are particularly interesting due to their thermoplastic properties. To hamper the high cost associated to PHA production, the use of bacterial mixed cultures cultivated in open systems and using cheap resources is a promising strategy. Here, we studied the operating conditions favouring direct MCL accumulation by activated sludge, using oleic acid as a model substrate and phosphorus limitation in fed-batch bioreactors. Our results confirm the presence of PHA-accumulating organisms (PHAAO) in activated sludge able to accumulate MCL from oleic acid. A positive correlation between phosphorus (P) limitation and PHA accumulation was demonstrated, allowing up to 26% PHA/total biomass accumulation, and highlighted its negative impact on the MCL/PHA fraction in the polymer. Diversity analysis through 16S rRNA amplicon sequencing revealed a differential selection of PHAAO according to the P-limitation level. A differential behaviour for the orders Pseudomonadales and Burkholderiales at increasing P-limitation levels was revealed, with a higher abundance of the latter at high levels of P-limitation. The PHA accumulation observed in activated sludge open new perspectives for MCL-PHA production system based on P-limitation strategy applied to mixed microbial communities. KEY POINTS: • Direct accumulation of MCL-PHA in activated sludge was demonstrated. • MCL-PHA content is negatively correlated with P-limitation. • Burkholderiales members discriminate the highest P-limitation levels.

From waste to wealth: upcycling of plastic and lignocellulosic wastes to PHAs

AbstractOver the past fifty years, environmental pollution from non‐biodegradable petroleum‐based plastics has worsened and become a real threat to marine life and human health. Thus, solutions to plastic pollution are urgently needed for reducing the contamination of soil and water resources. Developing alternative biodegradable plastics derived from renewable resources is an emerging research focus that can alleviate the accumulation of plastic waste in the environment. Polyhydroxyalkanoates (PHAs) are promising biodegradable biopolymers for replacing plastics derived from fossil fuel resources. The large scale commercialization of PHAs is not yet feasible due to their high production cost, which is largely associated with the feedstock cost. Using readily available carbon sources from underutilized lignocellulosic biomass and non‐recyclable plastic wastes allows for feedstock cost reduction and for the production of value‐added PHA bioplastics, and this significantly contributes to the solution of plastic pollution in a circular economy approach. This review highlights the recent efforts for valorizing plastic and lignocellulosic wastes to produce PHAs through a biotechnological approach using a two‐step methodology. In the first step, plastic (PE, PP, PS, PET) and lignocellulosic (cellulose, hemicellulose, lignin) macromolecules are depolymerized and converted to smaller fragments/monomers, which will be utilized for the subsequent bio‐upcycling step via fermentation process to produce PHAs. Pyrolyzed plastic wastes and hydrolysates from lignocellulosic waste biomass will facilitate the transition from linear to circular economy, lower the production cost of PHAs, and contribute to the solution of plastic pollution in a practical, economical, and sustainable approach. © 2021 Society of Chemical Industry (SCI).

Conversion of Pine Sawdust into Polyhydroxyalkanoate Bioplastics

Conversion of Pine Sawdust into Polyhydroxyalkanoate Bioplastics

Production of methanol from biogas using methanotrophs for the application in a microbial fuel cell

Methane is available in abundance as natural and renewable gas. Methane-rich biogas has low power density so cannot be considered as a good substrate for the microbial fuel cell. The power density of methane-rich biogas can be increased by its conversion to methanol. Two-step strategy has been followed for the production of methanol from methane-rich biogas and its utilization in a microbial fuel cell. Methanol production using methanotrophs is an attractive way for the valorisation of waste-derived biogas. Besides this, methanotrophs have been used in converting the methane-rich biogas into a variety of bioproducts which include single cell protein, polyhydroxyalkanoate bioplastics, biodiesel, extracellular polysaccharides, propylene oxide, and human health supplements. This paper focusses on the biological conversion of methanol in which solid-state anaerobic digestate can be used for the isolation of methanotrophic bacterium. A fresh isolate possesses the characteristics which resembled to constrained methanotrophs from the methylocaldum genus. This freshly new isolated methanotroph evolved on purified methane or biogas and successful production of methanol is accomplished from the biogas. This study also deals with the effect of formate and various inhibitors of methanol dehydrogenase for the biological conversion of methanol and where the formate act as an electron donor. But isolate produced methanol without any electron donor with the help of phosphate. Moreover, isolate also produced methanol without methanol dehydrogenase inhibitor by the use of formate. The maximum quantity of methanol consists of an optimum quantity of formate and phosphate as a growth medium. This study reveals an efficient conversion of methanol from biogas using solid-state anaerobic digestate. The produced methanol will not go for the purification process and can be used directly in a microbial fuel cell for the power generation purpose.

The rate of biodegradation of PHA bioplastics in the marine environment: A meta-study

There is a reasonably extensive body of literature recording mass loss of polyhydroxyalkanoates (PHAs) (a class of biodegradable plastics) in the natural marine environment. However, to date, this research has been very disparate. Thus, it remains unclear what the timeframe for the biodegradation of such marine biodegradable plastics actually is. The aim of this work was to determine the rate of biodegradation of PHA in the marine environment and apply this to the lifetime estimation of PHA products. This provides the clarification required as to what ‘marine biodegradation of PHA’ means in practicality and allows the risks and benefits of using PHA to be transparently discussed. It was determined that the mean rate of biodegradation of PHA in the marine environment is 0.04–0.09 mg·day−1·cm−2 (p = 0.05) and that, for example, a PHA water bottle could be expected to take between 1.5 and 3.5 years to completely biodegrade.

Commercialization of bacterial cell factories for the sustainable production of polyhydroxyalkanoate thermoplastics: progress and prospects.

Ubiquitous conventional plastics, generally manufactured from finite, nonsustainable fossil fuels are non-biodegradable wonder entities but their ill effect on Mother Nature has subsequently raised major environmental concerns like their safe disposal, solid waste management and several potential hazards. Such concerns have fuelled initiatives for research globally towards development of sustainable and eco-friendly bioplastics. The new generation of plastics called 'bioplastics' are polymers of long chain of repeating monomer units that are classified as photodegradable, semi-biodegradable, chemically synthesized and polyhydroxyalkanoates (PHAs). The commonly emerged novel bioplastics are polyesters of hydroxyalkanoates (HAs) called PHAs, which are lipoidic storage materials found in the cytosol of vast and diverse forms of bacteria. Among 150 different PHAs known so far, poly- 3-hydroxybutyrate is the most common and comprehensively characterized PHA. Interestingly, PHAs are only completely biodegradable plastics with material properties comparable to conventional plastics that can be achieved by regulating the co-monomers incorporation into PHAs backbone. PHA bioplastics are exploited in the form of user-friendly goods viz. films, absorbable sutures, bone plates, drug carriers, etc. Besides advantages, such useful entity(s) has major shortcomings as well like high production cost compared to conventional plastics. Precisely, in PHAs production, about fifty percent of the overall price is due to the carbon substrates. Consequently, exploring novel cost-effective substrates is a major compulsion for successful commercialization of this bioplastic, which is anticipated to reduce the cost of production as a result of advancing and intensifying research work. This review presents an insight and patent developments in the field of PHAs bioplastics.

BiotecVisions 2013, March

BiotecVisions 2013, March

PHA Bioplastics, Biochemicals, and Energy from Crops

Large scale production of polyhydroxyalkanoates (PHAs) in plants can provide a sustainable supply of bioplastics, biochemicals, and energy from sunlight and atmospheric CO(2). PHAs are a class of polymers with various chain lengths that are naturally produced by some microorganisms as storage materials. The properties of these polyesters make them functionally equivalent to many of the petroleum-based plastics that are currently in the market place. However, unlike most petroleum-derived plastics, PHAs can be produced from renewable feedstocks and easily degrade in most biologically active environments. This review highlights research efforts over the last 20 years to engineer the production of PHAs in plants with a focus on polyhydroxybutryrate (PHB) production in bioenergy crops with C(4) photosynthesis. PHB has the potential to be a high volume commercial product with uses not only in the plastics and materials markets, but also in renewable chemicals and feed. The major challenges of improving product yield and plant fitness in high biomass yielding C(4) crops are discussed in detail.

PHA bioplastic: A value‐added coproduct for biomass biorefineries

AbstractThe petroleum industry has optimized profits by producing value‐added coproducts, such as plastics and chemicals, in addition to primary liquid fuels. A similar coproduct strategy applied to biorefineries processing cellulosic biomass to liquid fuels and/or energy would transform a technology that is marginally economic, depending on oil prices, to a sustainable business with enhanced revenue streams from multiple coproducts. The challenge is finding a biobased coproduct that is compatible with a biorefinery scenario and where markets warrant its production on a similar scale as liquid fuels and/or energy. Polyhydroxyalkanoate (PHA) bioplastics represent a coproduct that would be entirely compatible with either production of liquid fuels by hydrolyzing the residual biomass after PHA extraction or by alternative thermochemical processes. PHA bioplastics possess properties making them suitable replacements for many of the applications currently served by petroleum‐based plastics, thus providing tremendous market potential. Proof‐of‐concept technology for production of these plastics in several crops of agronomic interest has been demonstrated. In this review, we show that the potential for developing biomass‐based biorefineries producing liquid fuels and a value‐added coproduct is both real and realizable. Examples using switchgrass producing PHA bioplastics as a coproduct are described. © 2009 Society of Chemical Industry and John Wiley & Sons, Ltd.

The Greenhouse Gas Emissions and Fossil Energy Requirement of Bioplastics from Cradle to Gate of a Biomass Refinery

Polyhydroxyalkanoates (PHA) are promising eco-friendly bioplastics that can be produced from cellulosic ethanol biorefineries as value-added coproducts. A cradle-to-factory-gate life cycle assessment is performed with two important categories: the greenhouse gas (GHG)emissions and fossil energy requirement per kg of bioplastics produced. The analysis indicates that PHA bioplastics contribute clearly to the goal of mitigating GHG emissions with only 0.49 kg CO(2-e) being emitted from production of 1 kg of resin. Compared with 2-3 kg CO(2-e) of petrochemical counterparts, it is about 80% reduction of the global warming potential. The fossil energy requirement per kg of bioplastics is 44 MJ, lowerthan those of petrochemical counterparts (78-88 MJ/kg resin). About 62% of fossil energy is used for processing utilities and wastewater treatment, and the rest is required for raw materials in different life cycle stages.

Metabolic carbon fluxes and biosynthesis of polyhydroxyalkanoates in Ralstonia eutropha on short chain fatty acids.

Short chain fatty acids such as acetic, propionic, and butyric acids can be synthesized into polyhydroxyalkanoates (PHAs) by Ralstonia eutropha. Metabolic carbon fluxes of the acids in living cells have significant effect on the yield, composition, and thermomechanical properties of PHA bioplastics. Based on the general knowledge of central metabolism pathways and the unusual metabolic pathways in R. eutropha, a metabolic network of 41 bioreactions is constructed to analyze the carbon fluxes on utilization of the short chain fatty acids. In fed-batch cultures with constant feeding of acid media, carbon metabolism and distribution in R. eutropha were measured involving CO2, PHA biopolymers, and residual cell mass. As the cells underwent unsteady state metabolism and PHA biosynthesis under nitrogen-limited conditions, accumulative carbon balance was applied for pseudo-steady-state analysis of the metabolic carbon fluxes. Cofactor NADP/NADPH balanced between PHA synthesis and the C3/C4 pathway provided an independent constraint for solution of the underdetermined metabolic network. A major portion of propionyl-CoA was directed to pyruvate via the 2-methylcitrate cycle and further decarboxylated to acetyl-CoA. Only a small amount of propionate carbon (<15% carbon) was directly condensed with acetyl-CoA for 3-hydroxyvalerate. The ratio of glyoxylate shunt to TCA cycle varies from 0 to 0.25, depending on the intracellular acetyl-CoA level and acetic acid in the medium. Malate is the node of the C3/C4 pathway and TCA cycle and its decarboxylation to dehydrogenation ranges from 0.33 to 1.28 in response to the demands on NADPH and oxaloacetate for short chain fatty acids utilization.