Effect of the organic loading rate on the production of polyhydroxyalkanoates in a multi-stage process aimed at the valorization of olive oil mill wastewater

Polyhydroxyalkanoates production from laboratory to industrial scale: A review

Environmental issues related to fossil-based plastics are getting the attention of the media and legislative authorities, addressing the need to improve the plastics' design, collection, and circular economy. In this regard, polyhydroxyalkanoates (PHAs) represent a promising alternative to the conventional polymers, given their biological origin, biodegradability, and biocompatibility. To date, their commercialization covers only a little percentage of the biodegradable plastic application, mainly due to their high cost. However, new production strategies are being investigated and patented, enhancing the PHA market competitiveness. This review tries to fill the gap about the critical investigation on innovative and up-to-date process strategies in PHA production field, deeply evaluating them from a plant-engineering point of view. Several aspects are considered regarding the reduction of the production costs and the increase in the overall PHA productivity and recovery. Among them, the feeding of pre-treated carbon sources derived from food and agro-industrial wastes, the use of mixed microbial cultures as convenient substitutes to the pure ones, and optimized downstream processes are widely discussed. The overlook of the topic is completed by evaluating the innovative technologies existing at pilot and industrial scale, able to achieve improved production yields. Finally, PHA economic and market current conditions are investigated.

Combined recovery of polyhydroxyalkanoates and reclaimed water in the mainstream of a WWTP for agro-food industrial wastewater valorisation by membrane bioreactor technology

The present study investigated the combined production of reclaimed water for reuse purposes and polyhydroxyalkanoates (PHA) from an agro-food industrial wastewater. A pilot plant implementing a two-stage process for PHA production was studied. It consisted of a mainstream sequencing batch membrane bioreactor (SBMBR) in which selection of PHA-accumulating organisms and wastewater treatment were carried out in, and a side-stream fed-batch reactor (FBR) where the excess sludge from the SBMBR was used for PHA accumulation. The performance of the SBMBR was compared with that of a conventional sequencing batch reactor (SBR) treating the same wastewater under different food to microorganisms' ratios (F/M) ranging between 0.125 and 0.650 kgCOD kgTSS-3 d-1. The SBMBR enabled to obtain very high-quality effluent in compliance with the relevant national (Italy) and European regulations (Italian DM 185/03 and EU, 2020/741) in the field of wastewater reclamation, whereas the performances in the SBR collapsed at F/M higher than 0.50 kgCOD kgTSS-1d-1. A maximum intracellular storage of 45% (w/w) and a production yield of 0.63 gPHA L-1h-1 were achieved when the SBMBR system was operated with a F/M ratio close to 0.50 kgCOD kgTSS-1d-1. This resulted approximately 35% higher than those observed in the SBR, since the ultrafiltration membrane avoided the washout of dispersed and filamentous bacteria capable of storing PHA. Furthermore, while maximizing PHA productivity in conventional SBR systems led to process dysfunctions, in the SBMBR system it helped mitigate these issues by reducing membrane fouling behaviour. The results of this study supported the possibility to achieve combined recovery of reclaimed water and high-value added bioproducts using membrane technology, leading the way for agro-food industrial wastewater valorization in the frame of a circular economy model.

The General Composition of Polyhydroxyalkanoates and Factors that Influence their Production and Biosynthesis

Polyhydroxyalkanoates (PHAs) have been a current research topic for many years. PHAs are biopolymers produced by bacteria under unfavorable growth conditions. They are biomaterials that exhibit a variety of properties, including biocompatibility, biodegradability, and high mechanical strength, making them suitable for future applications. This review aimed to provide general information on PHAs, such as their structure, classification, and parameters that affect the production process. In addition, the most commonly used bacterial strains that produce PHAs are highlighted, and details are provided on the type of carbon source used and how to optimize the parameters for bioprocesses. PHAs present a challenge to researchers because a variety of parameters affect biosynthesis, including the variety of carbon sources, bacterial strains, and culture media. Nevertheless, PHAs represent an opportunity to replace plastics, because they can be produced quickly and at a relatively low cost. With growing environmental concerns and declining oil reserves, polyhydroxyalkanoates are a potential replacement for nonbiodegradable polymers. Therefore, the study of PHA production remains a hot topic, as many substrates can be used as carbon sources. Both researchers and industry are interested in facilitating the production, commercialization, and application of PHAs as potential replacements for nonbiodegradable polymers. The fact that they are biocompatible, environmentally biodegradable, and adaptable makes PHAs one of the most important materials available in the market. They are preferred in various industries, such as agriculture (for bioremediation of oil-polluted sites, minimizing the toxicity of pollutants, and environmental impact) or medicine (as medical devices). The various bioprocess technologies mentioned earlier will be further investigated, such as the carbon source (to obtain a biopolymer with the lowest possible cost, such as glucose, various fatty acids, and especially renewable sources), pretreatment of the substrate (to increase the availability of the carbon source), and supplementation of the growth environment with different substances and minerals). Consequently, the study of PHA production remains a current topic because many substrates can be used as carbon sources. Obtaining PHA from renewable substrates (waste oil, coffee grounds, plant husks, etc.) contributes significantly to reducing PHA costs. Therefore, in this review, pure bacterial cultures (Bacillus megaterium, Ralstonia eutropha, Cupriavidus necator, and Pseudomonas putida) have been investigated for their potential to utilize by-products as cheap feedstocks. The advantage of these bioprocesses is that a significant amount of PHA can be obtained using renewable carbon sources. The main disadvantage is that the chemical structure of the obtained biopolymer cannot be determined in advance, as is the case with bioprocesses using a conventional carbon source. Polyhydroxyalkanoates are materials that can be used in many fields, such as the medical field (skin grafts, implantable medical devices, scaffolds, drug-controlled release devices), agriculture (for polluted water cleaning), cosmetics and food (biodegradable packaging, gentle biosurfactants with suitable skin for cosmetics), and industry (production of biodegradable biopolymers that replace conventional plastic). Nonetheless, PHA biopolymers continue to be researched and improved and play an important role in various industrial sectors. The properties of this material allow its use as a biodegradable material in the cosmetics industry (for packaging), in the production of biodegradable plastics, or in biomedical engineering, as various prostheses or implantable scaffolds.

Producing volatile fatty acids and polyhydroxyalkanoates from foods by-products and waste: A review

Dairy products, extra virgin olive oil, red and white wines are excellent food products, appreciated all around the world. Their productions generate large amounts of by-products which urge for recycling and valorization. Moreover, another abundant waste stream produced in urban context is the Organic Fraction of Municipal Solid Wastes (OFMSW), whose global annual capita production is estimated at 85 kg. The recent environmental policies encourage their exploitation in a biorefinery loop to produce Volatile Fatty Acids (VFAs) and polyhydroxyalkanoates (PHAs). Typically, VFAs yields are high from cheese whey and OFMSW (0.55-0.90 g_{COD_VFAs}/g_COD), lower for Olive Mill and Winery Wastewaters. The VFAs conversion into PHAs can achieve values in the range 0.4-0.5 g_PHA/g_VSS for cheese whey and OFMSW, 0.6-0.7 g_PHA/g_VSS for winery wastewater, and 0.2-0.3 g_PHA/g_VSS for olive mill wastewaters. These conversion yields allowed to estimate a huge potential annual PHAs production of about 260 M tons.

Valorization of Brewery Waste through Polyhydroxyalkanoates Production Supported by a Metabolic Specialized Microbiome

Simple Summary

Raw brewers’ spent grain, a by-product of beer production, is produced at a large scale and is usually used as animal feed or is landfilled. However, its composition shows that this feedstock has the potential for other applications, such as bioplastics production (e.g., polyhydroxyalkanoates). In this way, the aim of this work was to assess the use of raw brewers’ spent grain for polyhydroxyalkanoates production, adding new value to this feedstock. The results confirm the potential of raw brewers’ spent grain to produce polyhydroxyalkanoates, as the population was enriched in the microorganisms able to accumulate these biopolymers. These results will contribute to society’s knowledge and competence via the development of a treatment process for brewery waste of both environmental (productive waste treatment) and economic interest (production of biopolymers), which will certainly attract its application to the brewery industry worldwide.

Abstract

Raw brewers’ spent grain (BSG), a by-product of beer production and produced at a large scale, presents a composition that has been shown to have potential as feedstock for several biological processes, such as polyhydroxyalkanoates (PHAs) production. Although the high interest in the PHA production from waste, the bioconversion of BSG into PHA using microbial mixed cultures (MMC) has not yet been explored. This study explored the feasibility to produce PHA from BSG through the enrichment of a mixed microbial culture in PHA-storing organisms. The increase in organic loading rate (OLR) was shown to have only a slight influence on the process performance, although a high selectivity in PHA-storing microorganisms accumulation was reached. The culture was enriched on various PHA-storing microorganisms, such as bacteria belonging to the Meganema, Carnobacterium, Leucobacter, and Paracocccus genera. The enrichment process led to specialization of the microbiome, but the high diversity in PHA-storing microorganisms could have contributed to the process stability and efficiency, allowing for achieving a maximum PHA content of 35.2 ± 5.5 wt.% (VSS basis) and a yield of 0.61 ± 0.09 Cmmol_PHA/Cmmol_VFA in the accumulation assays. Overall, the production of PHA from fermented BSG is a feasible process confirming the valorization potential of the feedstock through the production of added-value products.

From Organic Wastes and Hydrocarbons Pollutants to Polyhydroxyalkanoates: Bioconversion by Terrestrial and Marine Bacteria

The use of fossil-based plastics has become unsustainable because of the polluting production processes, difficulties for waste management sectors, and high environmental impact. Polyhydroxyalkanoates (PHA) are bio-based biodegradable polymers derived from renewable resources and synthesized by bacteria as intracellular energy and carbon storage materials under nutrients or oxygen limitation and through the optimization of cultivation conditions with both pure and mixed culture systems. The PHA properties are affected by the same principles of oil-derived polyolefins, with a broad range of compositions, due to the incorporation of different monomers into the polymer matrix. As a consequence, the properties of such materials are represented by a broad range depending on tunable PHA composition. Producing waste-derived PHA is technically feasible with mixed microbial cultures (MMC), since no sterilization is required; this technology may represent a solution for waste treatment and valorization, and it has recently been developed at the pilot scale level with different process configurations where aerobic microorganisms are usually subjected to a dynamic feeding regime for their selection and to a high organic load for the intracellular accumulation of PHA. In this review, we report on studies on terrestrial and marine bacteria PHA-producers. The available knowledge on PHA production from the use of different kinds of organic wastes, and otherwise, petroleum-polluted natural matrices coupling bioremediation treatment has been explored. The advancements in these areas have been significant; they generally concern the terrestrial environment, where pilot and industrial processes are already established. Recently, marine bacteria have also offered interesting perspectives due to their advantageous effects on production practices, which they can relieve several constraints. Studies on the use of hydrocarbons as carbon sources offer evidence for the feasibility of the bioconversion of fossil-derived plastics into bioplastics.

Effect of the organic loading rate on the PHA-storing microbiome in sequencing batch reactors operated with uncoupled carbon and nitrogen feeding

Over the last years, in a search for sustainable and biodegradable alternatives to petrol-based plastics, biotechnological applications turned to the potentialities of mixed microbial cultures (MMC) for producing polyhydroxyalkanoates (PHAs). Under a feast and famine regime, an uncoupled carbon (C) and nitrogen (N)-feeding strategy may be adopted by dosing the C-source at the beginning of the feast and the N-source at the beginning of the famine in order to stimulate a PHA storage response and microbial growth. Even though this strategy has been already successfully applied for the PHA production, very few information is to date available regarding the MMC operating in these systems and the influence of Organic Loading Rate (OLR) on their selection and enrichment. To fill the gap, this study investigated the effect of the OLR on the selection of PHA-accumulating microorganisms in a sequencing batch reactor (SBR) operated with an uncoupled C and N feeding strategy. The SBR cycle length was set at 12 h and four OLRs values (4.25, 8.50, 12.75 and 18 gCOD L^-1 d^-1) were tested by changing the concentration of the feeding solution, made of a synthetic mixture of acetic (85% of the overall COD) and propionic (15%) acids. The PHA-storage yield increased by increasing the OLR (up to 0.69 COD/COD at 12.75 gCOD L^-1 d^-1) but significantly decreased (0.27 COD/COD) at 18 gCOD L^-1 d^-1 concomitantly with a longer feast phase and a lower PHA content in the biomass at the end of the feast phase. The selective pressure induced by the applied OLRs strongly influenced the microbiome composition revealing a high content of putative PHA-storing bacteria, such as Rhodobacter, Thauera and Paracoccus, in the SBR operated at OLRs 4.25, 8.50 and 12.75 g COD L^-1 d^-1 (up to 97.4% of total reads) and a low content (5.4%) in the SBR at 18 g COD L^-1 d^-1where the predominance of genus Nitrinicola was instead observed.

The impact of biomass withdrawal strategy on the biomass selection and polyhydroxyalkanoates accumulation of mixed microbial cultures

The production of polyhydroxyalkanoates (PHA) by mixed microbial cultures (MMC) has been studied as an alternative to pure cultures in order to reduce the price of PHA through use of open systems and low-cost substrates, such as agro-industrial sub-products. However, the widespread applicability of this process depends on the optimization of operational factors impacting PHA productivity. This study addresses the impact of biomass withdrawal strategy on the performance of MMC selection reactors and consequently on biomass productivity and global PHA productivity. Two selection reactors were operated in parallel under similar conditions, except for the timing of biomass withdrawal, at the end of the famine phase (Reactor 1, R1) versus at the end of the feast phase (Reactor 2, R2) at an organic loading rate of 100 Cmmol.L^-1.d^-1 and solids retention time of 4 days. The biomass selected in both conditions had similar PHA storing capacity as shown by the similar yields of PHA per substrate obtained in the accumulation assays; however, R1 reached a higher biomass productivity (about 4-fold higher than R2). This study demonstrated that removing the excess biomass at the end of the famine phase resulted in a much higher global PHA productivity and that the key parameter affecting the global PHA productivity of the 2-stage system was the volumetric biomass productivity. Results obtained provide important insight into how MMC systems can be best operated to maximize PHA productivity.

From Residues to Added-Value Bacterial Biopolymers as Nanomaterials for Biomedical Applications

Bacterial biopolymers are naturally occurring materials comprising a wide range of molecules with diverse chemical structures that can be produced from renewable sources following the principles of the circular economy. Over the last decades, they have gained substantial interest in the biomedical field as drug nanocarriers, implantable material coatings, and tissue-regeneration scaffolds or membranes due to their inherent biocompatibility, biodegradability into nonhazardous disintegration products, and their mechanical properties, which are similar to those of human tissues. The present review focuses upon three technologically advanced bacterial biopolymers, namely, bacterial cellulose (BC), polyhydroxyalkanoates (PHA), and γ-polyglutamic acid (PGA), as models of different carbon-backbone structures (polysaccharides, polyesters, and polyamides) produced by bacteria that are suitable for biomedical applications in nanoscale systems. This selection models evidence of the wide versatility of microorganisms to generate biopolymers by diverse metabolic strategies. We highlight the suitability for applied sustainable bioprocesses for the production of BC, PHA, and PGA based on renewable carbon sources and the singularity of each process driven by bacterial machinery. The inherent properties of each polymer can be fine-tuned by means of chemical and biotechnological approaches, such as metabolic engineering and peptide functionalization, to further expand their structural diversity and their applicability as nanomaterials in biomedicine.

A novel strategy for triacylglycerides and polyhydroxyalkanoates production using waste lipids

Lipids are one of the main components of the organic matter present in the effluents of the food-processing industry. These waste streams can be biotransformed into valuable triacylglycerides (TAGs) and polyhydroxyalkanoates (PHAs), precursors of biofuels and biomaterials alternative to petroleum-based products. These compounds are yielded by mixed microbial cultures, and considering that both TAG and PHA accumulators may coexist within the community, it seems crucial to define those operational strategies that might control the selection of the dominant metabolic pathways (TAG or PHA accumulation). In this work, residual fish-canning oil was used as a carbon source in a two-stage process (culture selection and intracellular compounds accumulation) in which the substrate was simultaneously hydrolyzed in these two stages without the need for a previous fermentation unit. It was pretended to maximize preferential TAG or PHA storage in the accumulation reactor by the imposition of certain selective pressures in the enrichment one. Uncoupling C and N feedings and limiting nitrogen availability in the medium, allowed to maximize PHA production (82.3 wt% of PHAs, 0.80 Cmmol_PHA/Cmmol_S). Besides, when low pH in the famine phase was considered as additional selective pressure, it was possible to shift the ratio TAG:PHA from 4:96 obtaining 43.0 wt% of TAGs (0.67 Cmmol_TAG/Cmmol_S). Therefore, this novel and simplified process demonstrated versatility and efficiency in the storage of TAGs and PHAs from a unique residual feedstock and using an open culture proving that product selection can be harnessed if choosing the right operational conditions in the enrichment stage.

Characterization of Polyhydroxyalkanoates Produced at Pilot Scale From Different Organic Wastes

Polyhydroxyalkanoates (PHAs) production at pilot scale has been recently investigated and carried out exploiting different process configurations and organic wastes. More in detail, three pilot platforms, in Treviso (North-East of Italy), Carbonera (North-East of Italy) and Lisbon, produced PHAs by open mixed microbial cultures (MMCs) and different organic waste streams: organic fraction of municipal solid waste and sewage sludge (OFMSW-WAS), cellulosic primary sludge (CPS), and fruit waste (FW), respectively. In this context, two stabilization methods have been applied, and compared, for preserving the amount of PHA inside the cells: thermal drying and wet acidification of the biomass at the end of PHA accumulation process. Afterward, polymer has been extracted following an optimized method based on aqueous-phase inorganic reagents. Several PHA samples were then characterized to determine PHA purity, chemical composition, molecular weight, and thermal properties. The polymer contained two types of monomers, namely 3-hydroxybutyrate (3HB) and 3-hydroxyvalerate (3HV) at a relative percentage of 92.6-79.8 and 7.4-20.2 w/w, respectively, for Treviso and Lisbon plants. On the other hand, an opposite range was found for 3HB and 3HV monomers of PHA from Carbonera, which is 44.0-13.0 and 56.0-87.0 w/w, respectively. PHA extracted from wet-acidified biomass had generally higher viscosity average molecular weights (M v ) (on average 424.8 ± 20.6 and 224.9 ± 21.9 KDa, respectively, for Treviso and Lisbon) while PHA recovered from thermally stabilized dried biomass had a three-fold lower M v .

A framework based on fundamental biochemical principles to engineer microbial community dynamics

Microbial communities are complex but there are basic principles we can apply to constrain the assumed stochasticity of their activity. By understanding the trade-offs behind the kinetic parameters that define microbial growth, we can explain how local interspecies dependencies arise and shape the emerging properties of a community. If we integrate these theoretical descriptions with experimental 'omics' data and bioenergetics analysis of specific environmental conditions, predictions on activity, assembly and spatial structure can be obtained reducing the a priori unpredictable complexity of microbial communities. This information can be used to define the appropriate selective pressures to engineer bioprocesses and propose new hypotheses which can drive experimental research to accelerate innovation in biotechnology.

Waste to bioplastics: How close are we to sustainable polyhydroxyalkanoates production?

Increased awareness of environmental sustainability with associated strict environmental regulations has incentivized the pursuit of novel materials to replace conventional petroleum-derived plastics. Polyhydroxyalkanoates (PHAs) are appealing intracellular biopolymers and have drawn significant attention as a viable alternative to petrochemical based plastics not only due to their comparable physiochemical properties but also, their outstanding characteristics such as biodegradability and biocompatibility. This review provides a comprehensive overview of the recent developments on the involved PHA producer microorganisms, production process from different waste streams by both pure and mixed microbial cultures (MMCs). Bio-based PHA production, particularly using cheap carbon sources with MMCs, is getting more attention. The main bottlenecks are the low production yield and the inconsistency of the biopolymers. Bioaugmentation and metabolic engineering together with cost effective downstream processing are promising approaches to overcome the hurdles of commercial PHA production from waste streams.

Recent developments in Polyhydroxyalkanoates (PHAs) production - A review

Polyhydroxyalkanoates (PHAs) are inevitably a key biopolymer that has the potential to replace the conventional petrochemical based plastics that pose jeopardy to the environment globally. Even then the reach of PHA in the common market is so restricted. The economy of PHA is such that, even after several attempts the overall production cost seems to be high and this very factor surpasses PHAs usage when compared to the conventional polymers. The major focus of the review relies on the synthesis of PHA from Mixed Microbial Cultures (MMCs), through a 3-stage process most probably utilizing feedstocks from waste streams or models that mimic them. Emphasis was given to the works carried out in the past decade and their coherence with each and every individual criteria (Aeration, Substrate and bioprocess parameters) such that to understand their effect in enhancing the overall production of PHA.

Towards biodegradable polyhydroxyalkanoate production from wood waste: Using volatile fatty acids as conversion medium

Production of polyhydroxyalkanoate (PHA) via mixed microbial consortia is a potential economic alternative responding to the current demand for functional greener materials to replace traditional petroleum-basedpolymers. The goal of this study was to synthesize PHA using volatile fatty acids (VFAs) obtained from the co-fermentation of pretreated wood waste and sewage as carbon source. High PHA yield of 0.71 g COD PHA/g COD VFAs and PHA content of 50.3 g PHA/100 g VSS were obtained at VFAs ratio (even:odd) of 88:12 after seven cycles cultivation. Even acids were more suitable for accumulating PHA as the preferred carbon source than odd acids, resulting in 3-hydroxybutyrate being the main monomer. PHA production achieved to the highest value of about 2639 mg COD/L at 1400 mg COD/L VFAs concentration. The bacterial genera displayed a highly diverse of the microbial community for the synthesis of PHA.

Recovery of polyhydroxyalkanoates (PHAs) from wastewater: A review

Polyhydroxyalkanoates (PHAs) are biopolyesters accumulated as carbon and energy storage materials under unbalanced growth conditions by various microorganisms. They are one of the most promising potential substitutes for conventional non-biodegradable plastics due to their similar physicochemical properties, but most important, its biodegradability. Production cost of PHAs is still a great barrier to extend its application at industrial scale. In order to reduce that cost, research is focusing on the use of several wastes as feedstock (such as agro-industrial and municipal organic waste and wastewater) in a platform based on mixed microbial cultures. This review provides a critical illustration of the state of the art of the most likely-to-be-scale-up PHA production processes using mixed microbial cultures platform and waste streams as feedstock, with a particular focus on both, upstream and downstream processes. Current pilot scale studies, future prospects, challenges and developments in the field are also highlighted.

High rate selection of PHA accumulating mixed cultures in sequencing batch reactors with uncoupled carbon and nitrogen feeding

The selection and enrichment of a mixed microbial culture (MMC) for polyhydroxyalkanoates (PHA) production is a well-known technology, typically carried out in sequencing batch reactors (SBR) operated under a feast-famine regime. With a nitrogen-deficient carbon source to be used as feedstock for PHA synthesis, a nutrient supply in the SBR is required for efficient microbial growth. In this study, an uncoupled carbon (C) and nitrogen (N) feeding strategy was adopted by dosing the C-source at the beginning of the feast and the N-source at the beginning of the famine, at a fixed C/N ratio of 33.4 g COD/g N and 12 h cycle length. The applied organic loading rate (OLR) was increased from 4.25 to 8.5 and finally to 12.725 g COD/L d. A more efficient selective pressure was maintained at lower and intermediate OLR, where the feast phase length was shorter (around 20 % of the whole cycle length). However, at the higher OLR investigated, the PHA content in the biomass reached a value of 0.53 g PHA/g VSS at the end of the feast phase, as a consequence of the increased C-source loaded per cycle. Moreover, 2nd stage PHA productivity was 2.4 g PHA/L d, 1.5 and 3.0-fold higher than those obtained at lower OLR. The results highlight the possibility of simplifying the process by withdrawing the biomass at the end of the feast phase directly to downstream processing, without a need for the intermediate accumulation step.

Production of polyhydroxyalkanoates and enrichment of associated microbes in bioreactors fed with rice winery wastewater at various organic loading rates

This study aimed to explore the production of polyhydroxyalkanoates (PHA) and selection of PHA-accumulating microorganisms in bioreactors fed with rice winery wastewater at various organic loading rates (OLRs). The substrate utilization, sludge properties, PHA synthesis and microbial community structure of three sequencing batch reactors were monitored. The results show the highest PHA yield (0.23 g/g) was achieved in one of the three reactors with an OLR of 2.4 g COD/L/d, in which Zoogloea was the most dominant PHA-accumulating microorganism. To quantify the PHA production and track the population changing profiles of the PHA-accumulating microorganisms in the long-term reactor operation, the Activated Sludge Model No. 3 was modified with two different heterotrophic microorganisms responding differently with the same substrate. The modeling results indicate that a moderate OLR (>2.4 gCOD/L/d) was beneficial for PHA production. The results are useful for understanding the PHA production from industrial wastewaters and selection of PHA-accumulating microorganisms.

Interactive effect of crude glycerin concentration and C:N ratio on polyhydroxyalkanoates accumulation by mixed microbial cultures modelled with Response Surface Methodology

Response Surface Methodology (RSM) was used to investigate how the crude glycerin concentration and the carbon to nitrogen (C:N) ratio in the culture medium affect four indicators of polyhydroxyalkanoates (PHAs) accumulation by mixed microbial cultures (MMC): the observed coefficient of active-biomass yield (Y_obs,BA), the observed coefficient of PHA yield (Y_obs,PHA), the PHA content in biomass (X_PHA) and the volumetric productivity (Pr_V). The C:N ratio had the largest effect on Y_obs,BA and Y_obs,PHA. When the C:N ratio was increased, Y_obs,BA decreased and Y_obs,PHA increased, regardless of the concentration of crude glycerin in the culture medium. The C:N ratio also had the largest effect on the PHA content, whereas volumetric productivity was strongly affected by both the C:N ratio and the crude glycerin concentration. The optimal conditions for PHA accumulation were a crude glycerin concentration of 8954 mg COD/L with a C:N ratio of 15.9 mg C/mg N-NH₄, which gave a Y_obs,BA of 0.29 mg COD_BA/mg COD, a Y_obs,PHA of 0.28 mg COD_PHA/mg COD, a X_PHA of 55.6% VSS and a Pr_V of 757.3 mg COD_PHA/L⋅d (550.0 mg PHA/L⋅d). The accumulated PHAs consisted mainly of 3-hydroxybutyrate. By using RSM, it was possible to predict crude glycerin concentrations and C:N ratios not tested here that will allow desirable values of PHA content in biomass or PHA productivity, which can be useful for designing PHA production with MMC.

The Next Generation of Sustainable Food Packaging to Preserve Our Environment in a Circular Economy Context

Packaging is an essential element of response to address key challenges of sustainable food consumption on the international scene, which is clearly about minimizing the environmental footprint of packed food. An innovative sustainable packaging aims to address food waste and loss reduction by preserving food quality, as well as food safety issues by preventing food-borne diseases and food chemical contamination. Moreover, it must address the long-term crucial issue of environmentally persistent plastic waste accumulation as well as the saving of oil and food material resources. This paper reviews the major challenges that food packaging must tackle in the near future in order to enter the virtuous loop of circular bio-economy. Some solutions are proposed to address pressing international stakes in terms of food and plastic waste reduction and end-of-life issues of persistent materials. Among potential solutions, production of microbial biodegradable polymers from agro-food waste residues seems a promising route to create an innovative, more resilient, and productive waste-based food packaging economy by decoupling the food packaging industry from fossil feed stocks and permitting nutrients to return to the soil. To respond to the lack of tools and approach to properly design and adapt food packaging to food needs, mathematical simulation, based on modeling of mass transfer and reactions into food/packaging systems are promising tools. The next generation of such modeling and tools should help the food packaging sector to validate usage benefit of new packaging solutions and chose, in a fair and transparent way, the best packaging solution to contribute to the overall decrease of food losses and persistent plastic accumulation.

Challenges of scaling-up PHA production from waste streams. A review

The search for new materials that replace fossil fuel-based plastics has been focused on biopolymers with similar physicochemical properties to fossil fuel-based plastics, such as Polyhydroxyalkanoates (PHA). The present paper reviews the challenges of scaling-up PHA production from waste streams during the period from 2014 to 2016, focusing on the feasibility of the alternatives and the most promising alternatives to its scaling-up. The reviewed research studies mainly focus on reducing costs or obtaining more valuable polymers. In the future, the integration of PHA production into processes such as wastewater treatment plants, hydrogen production or biodiesel factories could enhance its implementation at industrial scale.

Fast method for the determination of short-chain-length polyhydroxyalkanoates (scl-PHAs) in bacterial samples by In Vial-Thermolysis (IVT)

A new method based on the GC-MS analysis of thermolysis products obtained by treating bacterial samples at a high temperature (above 270°C) has been developed. This method, here named "In-Vial-Thermolysis" (IVT), allowed for the simultaneous determination of short-chain-length polyhydroxyalkanoates (scl-PHA) content and composition. The method was applied to both single strains and microbial mixed cultures (MMC) fed with different carbon sources. The IVT procedure provided similar analytical performances compared to previous Py-GC-MS and Py-GC-FID methods, suggesting a similar application for PHA quantitation in bacterial cells. Results from the IVT procedure and the traditional methanolysis method were compared; the correlation between the two datasets was fit for the purpose, giving a R² of 0.975. In search of further simplification, the rationale of IVT was exploited for the development of a "field method" based on the titration of thermolyzed samples with sodium hydrogen carbonate to quantify PHA inside bacterial cells. The accuracy of the IVT method was fit for the purpose. These results lead to the possibility for the on-line measurement of PHA productivity. Moreover, they allow for the fast and inexpensive quantification/characterization of PHA for biotechnological process control, as well as investigation over various bacterial communities and/or feeding strategies.

The composition analysis and preliminary cultivation optimization of a PHA-producing microbial consortium with xylose as a sole carbon source

This work aimed at using xylose as sole substrate, and combining feast-famine process with Nile blue staining as well as denaturing gradient gel electrophoresis (DGGE) analysis to screen polyhydroxyalkanoate (PHA)-producing bacteria from waste activated sludge (WAS). Composition changes of the microbial consortium during domestication were analyzed by DGGE, and the results indicated that there were mainly four classes of bacteria in the final stable system, which were γ-Proteobacteria, Cellvibrio sp., an uncultured bacterium and Pseudomonas sp., respectively. After preliminary optimization, the optimal conditions for the microbial consortium to produce PHA were also obtained as follows: temperature 33°C, pH 8, xylose concentration 2.4g/L, C/N ratio 160 and C/P ratio 125. The final PHA accumulation was up to 31% of dry cell weight (DCW), compared to 23.8% of the original consortia. Though our process is at the very beginning and the PHA yield is relatively low, producing PHA from xylose by using microbial consortia is a promising way to save the PHA production cost.

Batch and Continuous Flow Adsorption of Phenolic Compounds from Olive Mill Wastewater: A Comparison between Nonionic and Ion Exchange Resins

The goals of this work were (i) to compare two anion ion exchange resins (IRA958 Cl and IRA67) and a nonionic resin (XAD16) in terms of phenolic compounds adsorption capacity from olive mill wastewater and (ii) to compare the adsorption capacity of the best resin on columns of different length. The ion exchange resins performed worse than nonionic XAD16 in terms of resin utilization efficiency (20% versus 43%) and phenolic compounds/COD enrichment factor (1.0 versus 2.5). The addition of volatile fatty acids did not hinder phenolic compounds adsorption on either resin, suggesting a noncompetitive adsorption mechanism. A pH increase from 4.9 to 7.2 did not affect the result of this comparison. For the best performing resin (XAD16), an increase in column length from 0.5 to 1.8 m determined an increase in resin utilization efficiency (from 12% to 43%), resin productivity (from 3.4 to 7.6 gsorbed  phenolics/kgresin), and phenolics/COD enrichment factor (from 1.2 to 2.5). An axial dispersion model with nonequilibrium adsorption accurately interpreted the phenolic compounds and COD experimental curves.

Fate of β-hexachlorocyclohexane in the mixed microbial cultures (MMCs) three-stage polyhydroxyalkanoates (PHA) production process from cheese whey

This work aimed to study the fate and effect of β-hexachlorocyclohexane (β-HCH) during several steps of PHA production and purification, by using an artificially contaminated cheese whey (CW) as the feedstock. Most of β-HCH (around 90%) was adsorbed on CW solids and it was removed after the acidogenic fermentation step, when residual CW solids are separated along with anaerobic biomass from the liquid-phase. Purification steps also contributed strongly to the removal of residual β-HCH; overall, the PHA production process removed about 99.9% of initial β-HCH content. Moreover, it has been shown that β-HCH has neither detrimental effect on acidogenic fermentation nor on PHA accumulation, that were performed by using unacclimated mixed microbial cultures.

Production of polyhydroxyalkanoate (PHA) by Ralstonia eutropha JMP 134 with volatile fatty acids from palm oil mill effluent as precursors

The highest volatile fatty acids (VFAs) concentration from palm oil mill effluent (POME) treated by anaerobic fermentation was achieved for a 1-day process when the main acids used were acetic, propionic and butyric acids. Polyhydroxyalkanoate (PHA) production with VFAs from POME as precursors in the fed-batch mode has advantages over batch mode, both in terms of its productivity and 3HV (3-hydroxyvalerate) composition in the produced polymer. With the fed batch, the productivity increased to 343% and contained more 3HV than those of the batch. The structures of the PHA were identified by different methods and they supported each other; the resulting products consisted of functional groups of 3HB (3-hydroxybutyrate) and 3HV.