Biosynthesis of polyhydroxyalkanoate from food waste oil by Pseudomonas alcaligenes with simultaneous energy recovery from fermentation wastewater

Waste to wealth: Polyhydroxyalkanoates (PHA) production from food waste for a sustainable packaging paradigm

The growing demand for sustainable food packaging and the increasing concerns regarding environmental pollution have driven interest in biodegradable materials. This paper presents an in-depth review of the production of Polyhydroxyalkanoates (PHA), a biodegradable polymer, from food waste. PHA-based bioplastics, particularly when derived from low-cost carbon sources such as volatile fatty acids (VFAs) and waste oils, offer a promising solution for reducing plastic waste and enhancing food packaging sustainability. Through optimization of microbial fermentation processes, PHA production can achieve significant efficiency improvements, with yields reaching up to 87 % PHA content under ideal conditions. This review highlights the technical advancements in using PHA for food packaging, emphasizing its biodegradability, biocompatibility, and potential to serve as a biodegradable alternative to petroleum-based plastics. However, challenges such as high production costs, mechanical limitations, and the need for scalability remain barriers to industrial adoption. The future of PHA in food packaging hinges on overcoming these challenges through further research and innovation in production techniques, material properties, and cost reduction strategies, along with necessary legislative support to promote widespread use.

Innovations in poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and nanocomposites for sustainable food packaging via biochemical biorefinery platforms: A comprehensive review

The substantial build-up of non-biodegradable plastic waste from packaging sector not only poses severe environmental threats but also hastens the depletion of natural petroleum-based resources. Presently, poly (3-hydroxybutyrate-co-3-hydroxy valerate) (PHBV), received enormous attention as ideal alternatives for such traditional petroleum-derived plastics based on their biocompatibility and superior mechanical properties. However, high cost of such copolymer, due to expensive nature of feedstock, inefficient microbial processes and unfavorable downstream processing strategies restricts its large-scale commercial feasibility in the packaging sector. This review explores merits and challenges associated with using potent agricultural and industrial waste biomasses as sustainable feedstocks alongside improved fermentation and downstream processing strategies for the biopolymer in terms of biorefinery concept. Despite PHBV's attractive properties, its inherent shortcomings like weak thermal stability, poor mechanical properties, processability difficulty, substantial hydrophobicity and comparatively higher water vapor permeability (WVP) demand the development of its composites based on the application. Based on this fact, the review assessed properties and potential applications of PHBV-based composite materials having natural raw materials, nanomaterials and synthetic biodegradable polymers. Besides, the review also enlightens sustainability, future prospects, and challenges associated with PHBV-based composites in the field of food packaging while considering insights about economic evaluation and life cycle assessment.

Expanding the utilization of alkane mixtures: Enhancing medium chain length polyhydroxyalkanoate production in Pseudomonas resinovorans through alkane monooxygenase overexpression

Medium chain length Polyhydroxyalkanoate (mcl-PHA) is a biodegradable bioplastic material with promising applications in various fields, including the medical, packaging, and agricultural industries. This mcl-PHA can be biosynthesized by microorganisms from various carbon sources, and notably, it can also be produced from alkane mixtures contained in pyrolysis oil derived from low-grade waste plastics. In this study, Pseudomonas resinovorans was engineered to overexpress alkane monooxygenase from Lysinibaillus fusiformis JJY0216, enhancing its ability to utilize alkanes as carbon sources and thereby increasing mcl-PHA production. The engineered strain, P. resinovorans JJY01, demonstrated a notable increase in cell dry weight (CDW) to 0.97 g/L and mcl-PHA production to 0.33 g/L from an optimized alkane mixture, achieving a 1.7-fold enhancement compared to the wild type. The PHA content reached 39.5 %, which is 3.1 times higher than the wild type. Further optimization through fed-batch cultivation resulted in P. resinovorans JJY01 achieving 5.65 g/L of CDW, 3.07 g/L of PHA, and a PHA content of 57.5 % within 96 h. In addition, produced mcl-PHA were characterized through various analytical techniques to assess their physical properties and monomer compositions, highlighting the potential of mcl-PHA produced by P. resinovorans JJY01 as a candidate for medical-grade biopolymers.

Pseudomonas rhizophila S211 as a microbial cell factory for direct bioconversion of waste cooking oil into medium-chain-length polyhydroxyalkanoates

The present study examines the use of waste cooking oil (WCO) as a substrate for medium-chain-length polyhydroxyalkanoates (mcl-PHA) production by Pseudomonas rhizophila S211. The genome analysis revealed that the S211 strain has a mcl-PHA cluster (phaC1ZC2DFI) encoding two class II PHA synthases (PhaC1 and PhaC2) separated by a PHA depolymerase (PhaZ), a transcriptional activator (PhaD) and two phasin-like proteins (PhaFI). Genomic annotation also identified a gene encoding family I.3 lipase that was able to hydrolyze plant oils and generate fatty acids as favorable carbon sources for cell growth and PHA synthesis via β-oxidation pathway. Using a three-variable Doehlert experimental design, the optimum conditions for mcl-PHA accumulation were achieved in 10% of WCO-based medium with an inoculum size of 10% and an incubation period of 48 h at 30 °C. The experimental yield of PHA from WCO was 1.8 g/L close to the predicted yield of 1.68 ± 0.14 g/L. Moreover, 1H nuclear magnetic resonance spectroscopy analysis confirmed the extracted mcl-PHA. Overall, this study describes P. rhizophila as a cell factory for biosynthesis of biodegradable plastics and proposes green and efficient approach to cooking oil waste management by decreasing the cost of mcl-PHA production, which can help reduce the dependence on petroleum-based plastics.

Facilitating effects of the synergy with zero-valent iron and peroxysulfate on the sludge anaerobic fermentation system: Combined biological enzyme, microbial community and fermentation mechanism assessment

This study evaluated a synergetic waste activated sludge treatment strategy with environmentally friendly zero-valent iron nanoparticles (Fe0) and peroxysulfate. To verify the feasibility of the synergistic treatment, Fe0, peroxysulfate, and the mixture of peroxysulfate and Fe0 (synergy treatment) were added to different sludge fermentation systems. The study demonstrated that the synergy treatment fermentation system displayed remarkable hydrolysis performance with 435.50 mg COD/L of protein and 197.67 mg COD/L of polysaccharide, which increased 1.13-2.85 times (protein) and 1.12-1.49 times (polysaccharide) for other three fermentation system. Additionally, the synergy treatment fermentation system (754.52 mg COD/L) exhibited a well acidification performance which was 1.35-41.73 times for other systems (18.08-557.27 mg COD/L). The synergy treatment fermentation system had a facilitating effect on the activity of protease, dehydrogenase, and alkaline phosphatase, which guaranteed the transformation of organic matter. Results also indicated that Comamonas, Soehngenia, Pseudomonas, and Fusibacter were enriched in synergy treatment, which was beneficial to produce SCFAs. The activation of Fe0 on peroxysulfate promoting electron transfer, improving the active groups, and increasing the enrichment of functional microorganisms showed the advanced nature of synergy treatment. These results proved the feasibility of synergy treatment with Fe0 and peroxysulfate to enhance waste activated sludge anaerobic fermentation.

Potato Peel Waste as an Economic Feedstock for PHA Production by Bacillus circulans

Polymers of hydroxy alkanoates (PHA), also known as biodegradable, biocompatible plastic, are potential alternatives to petrochemical-based plastics. PHA is synthesized by microbes in their cytoplasm in the form of inclusion bodies in stress conditions such as nitrogen, oxygen, and phosphorus with excessive amounts of carbon. Sugar extracted from potato peel in the form of hydrolysate was employed as a carbon source for PHA production after acidic hydrolysis. The acid hydrolysis conditions are optimized for dilute acid concentrations and temperatures. The highest sugar-yielding condition (2% 15 min at 121 ℃) was used for submerged fermentation for PHA production by Bacillus circulans MTCC 8167. Fourier transform infrared spectroscopy, nuclear magnetic resonance, and differential scanning calorimetry were used for polymer characterization. Gas chromatography coupled with mass spectrometry confirmed the monomers such as hexadecenoic acid 3-hydroxy, methyl esters, pentadecanoic acid 14 methyl esters, and tetradecanoic acid 12- methyl esters. Crotonic acid assay was used for quantification of PHA and it was found highest (0.232 ± 0.04 g/L) at 37 °C and 36 h of incubation. Hence, potato peel waste could be a potential feedstock for waste to valuable production.

Acid hydrolysis of Solanum tuberosum periderm for accumulation of polyhydroxyalkanoates in Pseudomonas putida MTCC 2475

Polyhydroxyalkanoates are a class of biodegradable, biocompatible polymers composed of polyesters of R-hydroxyalkanoic acids and deposited intracellularly by a variety of microorganisms which have potential to serve as alternative to commercial plastic. Bioplastics are gaining attention due to sustainability, biodegradability, biocompatibility, and lower carbon footprint. Nevertheless, the commercialization of PHA is predominantly hindered by the elevated production expenses arising primarily from the use of a pure sugar substrate. Our study has established a feasible method for bioplastic formation applying Pseudomonas putida MTCC 2475 and Solanum tuberosum periderm as a carbon source. To optimize the sugar yield response surface methodology was used, which released 69.34% ± 0.25% reducing sugar. PHA production experiments were performed in hydrolysate containing media as well as commercial sugar containing mineral salt media. After 48 h of fermentation of using this sugar, a biomass concentration of 2.19 gL-1, with a PHA production of 0.60 gL-1 (28.71% ± 0.55%) was obtained which was comparatively similar with synthetic media (2.56 gL-1 cell dry weight and 29.97% ± 0.45% PHA). Furthermore, the monomers of PHA produced by hydrolysate were characterized using Gas chromatography-mass spectrometry, Fourier transform infrared spectroscopy, differential scanning calorimetry, and nuclear magnetic resonance. This investigation has identified three distinct monomers of medium-chain PHAs, namely, methyl 3-Hydroxydodecanoate, 3-Hydroxytetradecanoate, and Hexadecanoic acid 3-Hydroxy methyl esters. Hence this study concludes a sustainable production of bioplastics from S. tuberosum periderm waste.

Resource recovery and valorization of food wastewater for sustainable development: An overview of current approaches

The food processing industry is one of the world's largest consumers of potable water. Agri-food wastewater systems consume about 70% of the world's fresh water and cause at least 80% of deforestation. Food wastewater is characterized by complex composition, a wide range of pollutants, and fluctuating water quality, which can cause huge environmental pollution problems if discharged directly. In recent years, food wastewater has attracted considerable attention as it is considered to have great prospects for resource recovery and reuse due to its rich residues of nutrients and low levels of harmful substances. This review explored and compared the sources and characteristics of different types of food wastewater and methods of wastewater treatment. Particular attention was paid to the different methods of resource recovery and reuse of food wastewater. The diversity of raw materials in the food industry leads to different compositional characteristics of wastewater, which determine the choice and efficiency of wastewater treatment methods. Physicochemical methods, and biological methods alone or in combination have been used for the efficient treatment of food wastewater. Current approaches for recycling and reuse of food wastewater include culture substrates, agricultural irrigation, and bio-organic fertilizers, recovery of high-value products such as proteins, lipids, biopolymers, and bioenergy to alleviate the energy crisis. Food wastewater is a promising substrate for resource recovery and reuse, and its valorization meets the current international policy requirements regarding food waste and environment protection, follows the development trend of the food industry, and is also conducive to energy conservation, emission reduction, and economic development. However, more innovative biotechnologies are necessary to advance the effectiveness of food wastewater treatment and the extent of resource recovery and valorization.

Enhanced poly(3-hydroxybutyrateco-3-hydroxyvalerate) production from high-concentration propionate by a novel halophile Halomonas sp. YJ01: Detoxification of the 2-methylcitrate cycle

As a carbon substrate, propionate can be used to synthesize poly(3-hydroxybutyrateco-3-hydroxyvalerate) [PHBV] biopolymer, but high concentrations can inhibit PHBV production. Therefore, novel PHBV producers that can utilize high propionate concentrations are needed. Here, a novel halophile, Halomonas sp. YJ01 was applied to PHBV production via a propionate-dependent pathway, and optimal culture growth conditions were determined. The maximum poly(3-hydroxybutyrate) [PHB] content and yield in the presence of glucose were 89.5 wt% and 5.7 g/L, respectively. This strain utilizes propionate and volatile fatty acids (VFAs) for PHBV accumulation. Multiple genes related to polyhydroxyalkanoate (PHA) synthesis were identified using whole-genome annotation. The PHBV yield and 3HV fraction obtained by strain YJ01 utilizing 15 g/L propionate were 0.86 g/L and 29 mol%, respectively, but in cultures with glucose-propionate, it decreased its copolymer dry weight. This indicates that propionyl-CoA was converted to pyruvate through the 2-methylcitrate cycle (2MCC), which reduced propionate detoxification for the strain.

Enhancement of biosynthesis of polyhydroxyalkanoates (PHA) from Taihu blue algae by adding by-product acetic acid

As an easily obtained organic waste, by-product acetic acid could be an appropriate co-substrate with blue algae wastes (increase C/N ratio of substrates) for co-fermentation of PHA production. However, there are still acrylic acid and other chemicals in by-product acetic acid, which could cause severe inhibition for fermenting microorganisms during PHA production process. The current study represented that alkali pretreatment (pH level of 12) is a more favorable method compared with thermal pretreatment (80 ℃ for 30 min) for breaking cell walls of blue algae. It seemed that there was no synergistic effect of the combination of thermal and alkali pretreatment methods (temperature of 80 ℃ and pH level of 12). Optimal parameters during electro-fenton process for removal of inhibitors in by-product acetic acid were under current of 0.5 A, pH level of 3 and reaction time of 120 min. Both the highest dry weight of PHA and PHA concentration were achieved by applying blue algae and by-product acetic acid (after pretreatment) as co-substrates (mixed ratio of 3:1, stirring speed of 200 r/min, 24 h), indicating that using by-product acetic acid (after pretreatment) as co-substrate could increase C/N ratio and promote PHA production successfully. The current study could offer new insights for improving PHA production by co-fermentation.

Recovery of polyhydroxyalkanoates (PHAs) polymers from a mixed microbial culture through combined ultrasonic disruption and alkaline digestion

PHAs are a form of cellular storage polymers with diverse structural and material properties, and their biodegradable and renewable nature makes them a potential green alternative to fossil fuel-based plastics. PHAs are obtained through extraction via various mechanical, physical and chemical processes after their intracellular synthesis. Most studies have until now focused on pure cultures, while information on mixed microbial cultures (MMC) remains limited. In this study, ultrasonic (US) disruption and alkaline digestion by NaOH were applied individually and in combination to obtain PHAs products from an acclimated MMC using phenol as the carbon source. Various parameters were tested, including ultrasonic sound energy density, NaOH concentration, treatment time and temperature, and biomass density. US alone caused limited cell lysis and resulted in high energy consumption and low efficiency. NaOH of 0.05-0.2 M was more efficient in cell disruption, but led to PHAs degradation under elevated temperature and prolonged treatment. Combining US and NaOH significantly improved the overall process efficiency, which could reduce energy consumption by 2/3rds with only minimal PHAs degradation. The most significant factor was identified to be NaOH dosage and treatment time, with US sound energy density playing a minor role. Under the semi-optimized condition (0.2 M NaOH, 1300 W L^-1, 10 min), over 70% recovery and 80% purity were achieved from a 3 g L^-1 MMC slurry of approximately 50% PHAs fraction. The material and thermal properties of the products were analyzed, and the polymers obtained from US + NaOH treatments showed comparable or higher molecular weight to previously reported results. The products also exhibited good thermal stability and rheological properties, compared to the commercial standard. In conclusion, the combined US and NaOH method has the potential in real application as an efficient process to obtain high quality PHAs from MMC, and cost-effectiveness can be further optimized.

Genomic insights into the metabolic potential of a novel lignin-degrading and polyhydroxyalkanoates producing bacterium Pseudomonas sp. Hu109A

Lignin is the most abundant heterogeneous aromatic polymer present on planet Earth and is recalcitrant to degradation due to its complex structure, therefore, imposing a challenge to biorefinery procedures. Identifying new microbial strains with the potential to valorize lignin into useful compounds is indispensable to achieving green sustainable consumption. In this study, a novel Pseudomonas strain designated as Hu109A was isolated from the termite gut and the genome was sequenced and analyzed further. The genome contains a circular chromosome with the size of 5,131,917 bp having a GC content of 62.6% and 4698 genes. Genome annotation reveals that the strain possesses lignin-oxidizing enzymes such as DyP-type peroxidases, laccase, dioxygenase, and aromatic degradation gene clusters. The genome also contains O-methyltransferases which function in accelerating the lignin degradation by methylating the free hydroxyl phenolic compounds which in high concentration can inhibit the lignin peroxidase. Furthermore, the genome exhibits two gene clusters encoding the enzymes related to polyhydroxyalkanoates (PHA) synthesis. Pseudomonas strains are generally assumed to produce medium chain length PHAs (mcl-PHAs) only, however, strain Hu109A contains both Class II PHA synthase genes involved in mcl-PHAs and Class III PHA synthase gene involved in short-chain length PHAs (scl-PHAs). Gas Chromatography-Mass Spectrometry (GC-MS) analysis showed that using 1 g/L lignin as the sole carbon source, the maximum production of PHA observed was 103.68 mg/L, which increased to 186 mg/L with an increase in lignin concentration to 3 g/L. However, PHA production while using glucose as the sole carbon source was significantly lower than the lignin source, and maximum production was 125.6 mg/L with 3 g/L glucose. The strain Hu109A can tolerate a broad range of solvents including methanol, isopropanol, dimethylformamide, and ethanol, revealing its potential for industrial applications.

Upgrading cardoon biomass into Polyhydroxybutyrate based blends: A holistic approach for the synthesis of biopolymers and additives

Cardoon, Cynara cardunculus L. represents a biorefinery crop with a great potential in the bioplastic field. This work investigates the valorization of different cardoon components into high added value products, finally recombined into novel upgraded bioplastics. Bioprocesses for Polyhydroxybutyrate (PHB) and medium-chain-length Polyhydroxyalkanoates (mcl-PHA) production were set up starting from root inulin and seed oil respectively, highlighting the effect of process conditions on polymer properties. The ternary blend, in which the PHB polymer matrix was added with mcl-PHA and epoxidized cardoon oil, evidenced a synergic effect of both additives in modulating PHB structural and thermal properties, promoted by the physical interaction occurring among the components. This proof-of concept frames the paper in the holistic approach of circular economy applied to bioplastic production.

Migration and transformation of main components during perishable waste bio-drying process

Bio-drying can significantly reduce the moisture content of waste. The factors, functional microorganisms, and the transformation of main components were investigated during bio-drying of perishable waste. This study provides a scientific basis for the improvement of the bio-drying process and the necessity for secondary pollutant control. Reaction temperature and microbial biomass were main factors during the bio-drying process. The ideal bio-drying conditions included an initial temperature above 20 °C, intermittent ventilation, and appropriate microbial inoculation. The main microorganisms included Alcaligenes, Aquamicrobium, and Brevundimonas. From each gram of the carbonaceous, nitrogenous, sulfur-containing compounds, and phosphorus-containing substances in the perishable waste, approximately 0.74 g, 0.66 g, 0.40 g, and 0.94 g, respectively, were transferred as gas-phase products; consisting mainly of ammonia and volatile organic compounds: 2-heptanone, dimethyl heptanone, and benzene. In the leachate, the respective amounts of the carbonaceous, nitrogenous, sulfur-containing compounds, and phosphorus-containing substances were 3.20 × 10^-3 g, 4.08 × 10^-3 g, 0.33 g, and 9.52 × 10^-3 g, while those of the residual substances remaining in solid were 0.26 g, 0.33 g, 0.28 g, and 0.05 g.

Optimization of Propagation Medium for Enhanced Polyhydroxyalkanoate Production by Pseudomonas oleovorans

Polyhydroxyalkanoates (PHAs) represent a promising alternative to commercially used petroleum-based plastics. Pseudomonas oleovorans is a natural producer of medium-chain-length PHA (mcl-PHA) under cultivation conditions with nitrogen limitation and carbon excess. Two-step cultivation appears to be an efficient but more expensive method of PHA production. Therefore, the aim of this work was to prepare a minimal synthetic medium for maximum biomass yield and to optimize selected independent variables by response surface methodology (RSM). The highest biomass yield (1.71 ± 0.04 g/L) was achieved in the optimized medium containing 8.4 g/L glucose, 5.7 g/L sodium ammonium phosphate and 35.4 mM phosphate buffer. Under these conditions, both carbon and nitrogen sources were completely consumed after 48 h of the cultivation and the biomass yield was 1.7-fold higher than in the conventional medium recommended by the literature. This approach demonstrates the possibility of using two-stage PHA cultivation to obtain the maximum amount of biomass and PHA.