Search

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) is a biodegradable polymer with excellent thermal and mechanical properties comparable to fossil-based plastics. Scaling up the production of this polymer could provide a viable solution for reducing the use of fossil-based materials. However, its current production capacities are limited, with only a few facilities implementing the process at pilot or semi-industrial scales. The primary challenge lies in the high production costs, with 40% of the expenses attributed to the feedstock used for fermentation. Additionally, the energy required for sterilization in processes using pure methanotrophic cultures further reduces its economic viability. In this study, the economic aspects of the PHBV production process were assessed at an industrial level (100,000 t/y PHBV), using cheap and renewable substrates such as valeric acid and methane. A mixed methanotrophic consortium was used to reduce the need for sterility. The techno-economic analysis was based on estimating both fixed investment and operating costs. Then, a sensitivity analysis was performed to analyse the effect that the polymer content has on the final selling price: the initial biomass concentration was set to 30 g L-1, and the PHBV content was considered to be 20, 30, 40, 50 and 70% wt on a dry weight basis. The results revealed that increasing the polymer content beyond 40% wt led to a more competitive PHBV selling price, thus opening significant market opportunities. [ABSTRACT FROM AUTHOR]

Thanks to their properties, fossil fuel-based plastics are widely used daily (for industrial, domestic and environmental applications). However, they are not biodegradable, and their end of life is the cause of one of the most dangerous pollution in the world. Plastic, if recovered, can be recycled or used to recover energy, but it is not possible to recover all the tons of waste produced, so some end up in landfills. Therefore all non-recycled and non-collected plastic can take up to a thousand years to degrade. So the scientific idea is to produce biodegradable plastic capable of replacing conventional plastics. One possible solution is the poly(3-Hydroxybutyrate) (PHB) of the polyhydroxyalkanoates (PHA) family. PHB is a biopolymer accumulated in intracellular granules, under unfavourable growth conditions, by many prokaryotes and can be extracted with eco-friendly solvents. In particular, the extraction phase consists of the disruption of the cells and the subsequent separation of the biopolymer from the non-biopolymeric material (non-PHB). Currently, solvent extraction is the most used method for PHB recovery because it guarantees a high recovery yield and keeps the characteristics of the extracted biopolymer almost unaltered. In this study, the extraction of PHB with eco-friendly solvents was investigated. Simulations were carried out using 1,2-propylene carbonate as the solvent and acetone as the anti-solvent. Two process schemes were analyzed, without and with the recirculation of solvents (by distillation) and with two different types of biomass (wet and dry). The present work aims to study the final recovery yield in different operating conditions and the influence of PHB solubility on the process. The simulation results confirm the importance of solubility for optimizing the extraction process and underline the problem related to the lack of data in the literature. [ABSTRACT FROM AUTHOR]

Polyhydroxyalkanoates (PHAs) are biobased and biodegradable polymers that may be considered to replace fossil-based materials. However, their widespread deployment is slowed down because of the high production cost and their low quality. Using methane during the generation of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB-co-HV) could reduce the production costs, which are usually owed to the carbon source used, and enhance the performance of the material. In fact, the properties of PHB-co-HV make it more suitable than the most common homopolymer, named poly(3-hydroxybutyrate) (PHB), for many applications since it is more flexible, has a wider thermal processing range, a lower crystallinity and permeability to water. In this work, the production of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) was simulated using an innovative process scheme consisting of two bioreactors working in series equipped with a gas recycling unit, which was designed to increase the methane mass transfer from the gas to the liquid. During the first step, a Methylocystis dominated culture was grown on ammonia and methane to reach a high cell concentration; then, the cells were moved to the second bioreactor and subjected to nutrients starvation to favour the metabolic pathway addressed to the accumulation of PHB-co-HV. The effect of the variation of valeric acid concentration (100-400 ppm), which was used as co-substrate, on the fraction of PHB-co-HV stored in the cells and the percentage of 3-hydroxyvalerate (3-HV) was investigated: results showed that the highest the valeric acid concentration, the lower the total polymer content and the higher the HV fraction accumulated. [ABSTRACT FROM AUTHOR]

Poly(3-hydroxybutyrate) (PHB) is a thermoplastic polyester that can be synthesised by many bacteria under unfavourable growth conditions. Among all its properties, biodegradability is the most attractive since it makes PHB a potential alternative to non-biodegradable plastics. However, the current market penetration of this polymer is limited by the high production costs, which accounts for approximately 40% of the total price, and the complexity in scaling-up the biological process. In this work, an innovative approach is presented, simulating the production of PHB through a double stage aerobic fermentation in which a Methylocystis strain grows and accumulates PHB granules. The effects of the reactor geometry on PHB yields were investigated in terms of aspect ratio (A), which was varied in the range 5-16 both at constant volume and variable volume: in the first case, the working volume was kept constant at 100 L and the diameter of the reactor was varied in the range 0.2-0.3 m; in the second case, the working volume was varied between 100 and 340L, keeping constant the diameter at 0.3 m. The effect of the geometry on transition parameters was evaluated as well. Results show that a maximum transition superficial gas velocity (Ut) of 0.05 ms-1 was obtained at A=16; while the productivity of PHB ranged between 0.12 and 0.25 kgm-3d-1 . [ABSTRACT FROM AUTHOR]

Polyhydroxybutyrate (PHB) is a possible sustainable alternative to fossil-based plastic, today the cause of one of the primary forms of pollution in the world, since it is biodegradable, recyclable and compostable. Furthermore, PHB can be accumulated in several bacterial strains as a product of their metabolic activity. Solvent extraction (SE) is the most used technique, thanks to the high recovery yields and purity, to extract PHB from bacteria. In particular, a two-step SE is required: the accumulated PHB in the bacterial biomass is firstly dissolved in a solvent to obtain a mixture rich in PHB; then, an anti-solvent is added to reduce the total solubility allowing the biopolymer to precipitate and to be recovered from the residual biomass. However, despite its wide application, the SE technique is characterised by several limitations, such as the high cost and the use of halogenated solvents (i.e. chloroform). In this work, a non-halogenated based extraction process for PHB recovery from wet bacterial biomass is proposed. Simulations were carried out using butyl acetate (BA) as solvent and hexane (HEX) as anti-solvent. The process scheme also includes a distillation column and a cooling system (when necessary) to recover both the solvent and the anti-solvent. The effects of the PHB solubility during the precipitation step and the solvent recovery on process performance were investigated. The recovery yield was higher than 90% and increased as the solubility decreased. The simulation results highlighted that the proposed strategy is an effective and sustainable alternative to conventional processes for PHB recovery. [ABSTRACT FROM AUTHOR]

Polyhydroxyalkanoates (PHAs) are a very promising alternative to traditional plastic materials since they are biobased and can degrade in soil, water, and sediments. Among all the existing PHAs, Poly-3-hydroxybutyrate (PHB) is the most well-known homopolymer. However, to the current state, PHAs represent only about 2% of the total bioplastics produced because their diffusion on a large scale is still limited due to their high market price. Techno-economic assessments showed that raw materials, such as sugars and oils account for up to 40% of the total costs. In this work, an innovative PHB production process scheme is presented. The expensive carbon sources are replaced by methane, which is cheap, abundant, and can be found as natural gas and in the biogas derived from the anaerobic digestion, thus allowing an integrated biorefinery. Process simulations were carried out to estimate the Poly-3-hydroxybutyrate production yields. Two aerobic fermentations were simulated into 400L semi-continuous reactors: the first for biomass growth in the presence of micro and macronutrients; the second for the PHB accumulation in a nutrient-deprived medium. Since both the biomass growth and PHB accumulation reactions take place in the liquid phase, the mass transfer from a gas to a liquid need to be maximised to increase biopolymer production. In this context, the effects of the superficial gas velocity (Ug) on the mass transfer rates and PHB yields were assessed. Several values of Ug, in the range 0.004 to 0.027 m s-1, that does not limit the viability of the cells, were tested. The PHB production increased with the superficial gas velocity. [ABSTRACT FROM AUTHOR]

The increasing need for biodegradable polymers demands efficient and environmentally friendly extraction methods. In this study, a simple and sustainable method for extracting polyhydroxybutyrate (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate (PHB-co-HV) from Methylocystis hirsuta and a mixed methanotrophic consortium with different biopolymer contents was presented. The extraction of biopolymers with 1,3-dioxolane was initially investigated by varying the biomass-to-solvent ratio (i.e., 1:2 w v -1 , 1:4 w v -1 , 1:6 w v -1 , 1:8 w v -1 and 1:10 w v -1 ) and extraction time (6, 8 and 10 h) at the boiling point of the solvent and atmospheric pressure. Based on the results of the preliminary tests, and only for the most efficient biomass-to-solvent ratio, the extraction kinetics were also studied over a time interval ranging from 30 min to 6 h. For Methylocystis hirsuta , the investigation of the extraction time showed that the maximum extraction was reached after 30 min, with recovery yields of 87% and 75% and purities of 98.7% and 94% for PHB and PHB-co-HV, respectively. Similarly, the extraction of PHB and PHB-co-HV from a mixed methanotrophic strain yielded 88% w w -1 and 70% w w -1 recovery, respectively, with 98% w w -1 purity, at a biomass-to-solvent ratio of 6 in 30 min.