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

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.

Effects of Extraction Methods on the Thermal Stability of Extracellular Polymeric Substances-Based Biomaterials from Wastewater Sludge

Various methods for recovering extracellular polymeric substances (EPS)-based biomaterials from wastewater sludge exist. However, the relationships between extraction methods and properties of biomaterials have not been fully explored. In this study, the thermal properties, including activation energy (AE) and thermal decomposition mechanism, of EPS-based biomaterials extracted by different methods have been determined by thermogravimetric analysis integrated with the deconvolution method. Simultaneously, the chemical properties of these biomaterials, such as the extraction yield, chemical composition, and functional groups, have been monitored to clarify the influences of extraction methods. Notably, proteins and humic-like substances have been found as the major components to determine thermal stability and AE. Moreover, the physicochemical method shows significant effects on enhancing extraction yield and AE, with the NaOH and heat methods proving to be outstanding by delivering the highest AE of 300 kJ/mol and a substantial char formation of 24%. The results have demonstrated the significant impact of extraction methods on the thermal stability of EPS-based biomaterials. Moreover, this finding provides insights into the linkages between the properties of EPS-based biomaterials and extraction methods to guide the selection of appropriate extraction methods tailored to specific applications, including flame-resistant materials.

Olivera E, Chamizo-Ampudia A. The Effectiveness of Polyhydroxyalkanoate (PHA) Extraction Methods in Gram-Negative Pseudomonas putida U

Bioplastics are emerging as a promising solution to reduce pollution caused by petroleum-based plastics. Among them, polyhydroxyalkanoates (PHAs) stand out as viable biotechnological alternatives, though their commercialization is limited by expensive downstream processes. Traditional PHA extraction methods often involve toxic solvents and high energy consumption, underscoring the need for more sustainable approaches. This study evaluated physical and chemical methods to extract PHAs from Pseudomonas putida U, a bacterium known to produce poly-3-hydroxyoctanoate P(3HO). Lyophilized cells underwent six extraction methods, including the use of the following: boiling, sonication, sodium hypochlorite (NaClO), sodium dodecyl sulfate (SDS), sodium hydroxide (NaOH), and chloroform. Physical methods such as boiling and sonication achieved yields of 70% and 60%, respectively, but P(3HO) recovery remained low (30-40%). NaClO extraction provided higher yields (80%) but resulted in significant impurities (70%). NaOH methods offered moderate yields (50-80%), with P(3HO) purities between 50% and 70%, depending on the conditions. Spectroscopic and analytical techniques (FTIR, TGA, NMR, GPC) identified 0.05 M NaOH at 60 °C as the optimal extraction condition, delivering high P(3HO) purity while minimizing environmental impact. This positions NaOH as a sustainable alternative to traditional halogenated solvents, paving the way for more eco-friendly PHA production processes.

Producing and Characterizing Polyhydroxyalkanoates from Starch and Chickpea Waste Using Mixed Microbial Cultures in Solid-State Fermentation

The environmental impact of plastic waste is a growing global challenge, primarily due to non-biodegradable plastics from fossil resources that accumulate in ecosystems. Biodegradable polymers like polyhydroxyalkanoates (PHAs) offer a sustainable alternative. PHAs are microbial biopolymers produced by microorganisms using renewable substrates, including agro-industrial byproducts, making them eco-friendly and cost-effective. This study focused on the isolation and characterization of PHA-producing microorganisms from agro-industrial waste, including chickpeas, chickpeas with bean residues, and starch. Screening via Sudan Black staining identified PHA-accumulating strains such as Brevibacillus sp., Micrococcus spp., and Candida krusei, among others. To assess the potential for PHA biosynthesis, solid-state fermentation (SSF) was conducted using agro-industrial waste as substrates, along with a mixed culture of the isolated microorganisms. The highest observed yield was a PHA accumulation of 13.81%, achieved with chickpeas containing bean residues. Structural and thermal characterization of the PHAs was performed using Fourier-transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). FTIR-ATR spectra indicated polyhydroxybutyrate (PHB), suggesting it as the synthesized PHA type. This study highlights the potential of agro-industrial waste for sustainable PHA production and eco-friendly bioplastics.

Enrichment performance and salt tolerance of polyhydroxyalkanoates (PHAs) producing mixed cultures under different saline environments

The key to the resource recycling of saline wastes in form of polyhydroxyalkanoates (PHA) is to enrich mixed cultures with salt tolerance and PHA synthesis ability. However, the comparison of saline sludge from different sources and the salt tolerance mechanisms of salt-tolerant PHA producers need to be clarified. In this study, three kinds of activated sludge from different salinity environments were selected as the inoculum to enrich salt-tolerant PHA producers under aerobic dynamic feeding (ADF) mode with butyric acid dominated mixed volatile fatty acid as the substrate. The maximum PHA content (PHAm) reached 0.62 ± 0.01, 0.62 ± 0.02, and 0.55 ± 0.03 g PHA/g VSS at salinity of 0.5%, 0.8%, and 1.8%, respectively. Microbial community analysis indicated that Thauera, Paracoccus, and Prosthecobacter were dominant salt-tolerant PHA producers at low salinity, Thauera, NS9_marine, and SM1A02 were dominant salt-tolerant PHA producers at high salinity. High salinity and ADF mode had synergistic effects on selection and enrichment of salt-tolerant PHA producers. Combined correlation network with redundancy analysis indicated that trehalose synthesis genes and betaine related genes had positive correlation with PHAm, while extracellular polymeric substances (EPS) content had negative correlation with PHAm. The compatible solutes accumulation and EPS secretion were the main salt tolerance mechanisms of the PHA producers. Therefore, adding compatible solutes is an effective strategy to improve PHA synthesis in saline environment.

Investigating the efficiency of a two-stage anaerobic-aerobic process for the treatment of confectionery industry wastewaters with simultaneous production of biohydrogen and polyhydroxyalkanoates

The scope of the current study was to investigate the efficiency of a two-stage anaerobic-aerobic process for the simultaneous treatment and valorization of selective wastewater streams from a confectionary industry. The specific wastewater (confectionary industry wastewater, CIW) was a mixture of the rinsing eluting during washing of the cauldrons in which jellies and syrups were produced, and contained mainly readily fermentable sugars, being thus of high organic load. The first stage of the process was the dark fermentation (DF) of the CIW in continuous, attached-biomass systems, in which the effect on hydrogen yields and distribution of metabolites were studied for different packing materials (ceramic or plastic), hydraulic retention times, HRTs (12 h-30 h) and feed substrate concentration (20 g COD/L- 50 g COD/L). In the second stage, the effectiveness of the aerobic treatment of the DF effluents was evaluated in terms of the reduction of the organic load and the production of polyhydroxyalkanoates (PHAs) through an enriched mixed microbial culture (MMC). The MMC was developed in a continuous draw and fill system, in which the accumulation potential of PHAs was studied. It was shown that the hydrogen production rates decreased for increasing substrate concentration and HRTs, with a maximum of 12.70 ± 0.35 m3 H2/m3 initial CIW achieved for the lowest HRT and feed concentration and using ceramic beads as packing material. Butyrate, acetate and lactate were the main metabolites generated in all cases, in different ratios. The distribution of metabolites during DF was shown to highly affect the efficiency of the second process in terms of both the reduction of organic load and the PHAs yields. The highest removal of organic load achieved after 48 h of aerobic treatment was 84.0 ± 0.9 %, whereas the maximum PHAs yield was 21.46 ± 0.13 kg PHAs/m3 initial CIW.

Unlocking the potential of spent coffee grounds via a comprehensive biorefinery approach: production of microbial oil and carotenoids under fed-batch fermentation

The valorization of renewable feedstock to produce a plethora of value-added products could promote the transition towards a circular bioeconomy. This study presents the development of cascade processes to bioconvert spent coffee grounds (SCGs) into microbial oil and carotenoids employing sustainable practices. The stepwise recovery of crude phenolic extract and coffee oil was carried out using green or recyclable solvents, i.e., aqueous ethanol and hexane. Palmitic acid (43.3%) and linoleic acid (38.9%) were the major fatty acids in the oil fraction of SCGs. The LC-MS analysis of crude phenolic extracts revealed that chlorogenic acid dominated (45.7%), while neochlorogenic acid was also detected in substantial amounts (24.0%). SCGs free of coffee oil and phenolic compounds were subjected to microwave-assisted pretreatment under different irradiations and solvents to enhance subsequent enzymatic saccharification. Microwave/water pretreatment at 400 W, followed by enzymatic hydrolysis with proteases, hemicellulases, and cellulases, at 50 g/L initial SCGs, led to satisfying overall yields of cellulose (75.4%), hemicellulose (50.3%), and holocellulose (55.3%). Mannan was the most extractable polysaccharide followed by galactan and arabinan. SCGs hydrolysate was used in fed-batch bioreactor fermentations with Rhodosporidium toruloides to produce 24.0 g/L microbial oil and carotenoids of 432.9 μg/g biomass.

The production, recovery, and valorization of polyhydroxybutyrate (PHB) based on circular bioeconomy

As an energy-storage substance of microorganisms, polyhydroxybutyrate (PHB) is a promising alternative to petrochemical polymers. Under appropriate fermentation conditions, PHB-producing strains with metabolic diversity can efficiently synthesize PHB using various carbon sources. Carbon-rich wastes may serve as alternatives to pure sugar substrates to reduce the cost of PHB production. Genetic engineering strategies can further improve the efficiency of substrate assimilation and PHB synthesis. In the downstream link, PHB recycling strategies based on green chemistry concepts can replace PHB extraction using chlorinated solvents to enhance the economics of PHB production and reduce the potential risks of environmental pollution and health damage. To avoid carbon loss caused by biodegradation in the traditional sense, various strategies have been developed to degrade PHB waste into monomers. These monomers can serve as platform chemicals to synthesize other functional compounds or as substrates for PHB reproduction. The sustainable potential and cycling value of PHB are thus reflected. This review summarized the recent progress of strains, substrates, and fermentation approaches for microbial PHB production. Analyses of available strategies for sustainable PHB recycling were also included. Furthermore, it discussed feasible pathways for PHB waste valorization. These contents may provide insights for constructing PHB-based comprehensive biorefinery systems.

Physicochemical cell disruption of Bacillus sp. for recovery of polyhydroxyalkanoates: future bioplastic for sustainability

Polyhydroxybutyrate (PHB) is known for wide applications, biocompatibility, and degradability; however, it cannot be commercialized due to conventional recovery using solvents. The present study employed mechanical cell-disruption methods, such as Pestle and mortar, sonication, and glass bead vortexing, for solvent-free extraction of PHA from Bacillus sp. Different time intervals were set for grinding (5, 10, 15 min), sonicating (1, 3 and 5 min), and vortexing (2, 5 and 8 g glass beads with 5, 10 and 15 min each) hence studying their effect on cell lysis to release PHA. Tris buffer containing phenylmethyl sulfonyl fluoride (PMSF) (20 mM Tris-HCl, pH 8.0, 1 mM PMSF) was employed as a lysis buffer to study its action over Bacillus cells. Its presence was checked with the above methods in cell lysis. Sonicating cells for 5 min in the presence of lysis buffer achieved a maximum PHA yield of 45%. Cell lysis using lysis buffer yielded 35% PHA when vortexing with 5 g glass beads for 15 min. Grinding cells for 15 min showed a maximum yield of 34% but lacked a lysis buffer. The overall results indicated that the action of lysis buffer and physical extraction methods improved PHA yield by %. Therefore, the study sought to evaluate the feasibility of applying laboratory methods for cell disruption. These methods can showcase possible opportunities in large-scale applications. The polymer yield results were compared with standard sodium hypochlorite extraction. Confirmation of obtained polymers as polyhydroxy butyrate (PHB) was made through FTIR and 1HNMR characterization.

Quantification of the Monomer Compositions of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and Poly(3-hydroxyvalerate) by Alkaline Hydrolysis and Using High-Performance Liquid Chromatography

With the growing interest in bioplastics, there is an urgent need to develop rapid analysis methods linked to production technology development. This study focused on the production of a commercially non-available homopolymer, poly(3-hydroxyvalerate) (P(3HV)), and a commercially available copolymer, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(3HB-co-3HV)), through fermentation using two different bacterial strains. The bacteria Chromobacterium violaceum and Bacillus sp. CYR1 were used to produce P(3HV) and P(3HB-co-3HV), respectively. The bacterium Bacillus sp. CYR1 produced 415 mg/L of P(3HB-co-3HV) when incubated with acetic acid and valeric acid as the carbon sources, whereas the bacterium C. violaceum produced 0.198 g of P(3HV)/g dry biomass when incubated with sodium valerate as the carbon source. Additionally, we developed a fast, simple, and inexpensive method to quantify P(3HV) and P(3HB-co-3HV) using high-performance liquid chromatography (HPLC). As the alkaline decomposition of P(3HB-co-3HV) releases 2-butenoic acid (2BE) and 2-pentenoic acid (2PE), we were able to determine the concentration using HPLC. Moreover, calibration curves were prepared using standard 2BE and 2PE, along with sample 2BE and 2PE produced by the alkaline decomposition of poly(3-hydroxybutyrate) and P(3HV), respectively. Finally, the HPLC results obtained by our new method were compared using gas chromatography (GC) analysis.