Bio-based conversion of volatile fatty acids from waste streams to polyhydroxyalkanoates using mixed microbial cultures

Polyhydroxyalkanoates production from cheese whey under near-seawater salinity conditions

Treating saline streams presents considerable challenges due to their adverse effects on conventional biological processes, thereby leading to increased expenses in managing those side streams. With this in consideration, this study explores into the potential for valorizing fermented cheese whey (CW), a by-product of the dairy industry, into polyhydroxyalkanoates (PHA) using mixed microbial cultures (MMC) under conditions of near-seawater salinity (30 gNaCl/L). The selection of a PHA-accumulating MMC was successfully achieved using a sequential batch reactor operated under a feast and famine regime, with a hydraulic retention time of 14.5 h, a variable solids retention time of 3 and 4.5 days, and an organic loading rate (OLR) of 60 Cmmol/(L d). The selected culture demonstrated efficient PHA production rates and yields, maintaining robust performance even under high salinity conditions. During PHA accumulation, a maximum PHA content in biomass of 56.4 % wt. was achieved for a copolymer P(3HB-co-3HHx) with a 3HHx content of 7 %. Additionally, to asses the capacity of the culture to produce polymers with different compositions, valeric acid was supplemented to the real fermented feedstock which resulted in the production of terpolymers P(3HB-co-3HV-co-3HHx) with varied monomeric content and a higher maximum PHA content of 62 % wt. Additionally, this study highlights the potential utilization of seawater as alternative to freshwater for PHA production, thereby enhancing circular economy principles and promoting environmental sustainability.

Statistical modeling and optimization of volatile fatty acids production by anaerobic digestion of municipal wastewater sludge

Obtaining value-added products from renewable resources is limited by the lack of specific operating conditions optimized for the physico-chemical characteristics of the biomass and the desired end product. A mathematical model and statistical optimization were developed for the production of volatile fatty acids (VFAs) by anaerobic digestion of municipal sewage sludge. The experimental tests were carried out in triplicate and investigated a wide range of conditions: pH 9.5, 10.5, and 11.5; temperatures 25 °C, 35 °C, 45 °C, and 55 °C; primary sludge with organic loading (OL) of 10 and 14 g VS (volatile solids); and digested sludge with 4 and 6 g VS. Subsequently, a statistical search was performed to obtain optimal production conditions, then a statistical model of VFA production was developed and the optimal conditions were validated at pilot plant scale. The maximum VFA concentration predicted was 6975 mg COD (chemical oxygen demand)/L using primary sludge at 25 °C, initial OL of 14 g VS, and pH 10.5. The obtained third-degree model (r2 = 0.83) is a powerful tool for bioprocess scale-up, offering a promising avenue for sustainable waste management and biorefinery development.

Anaerobic acidification membrane bioreactor operating at acidic condition for treating concentrated municipal wastewater: Performance and implication

To address the low-carbon treatment requirements for municipal wastewater, a novel anaerobic acidification membrane bioreactor (AAMBR) was developed for recovering organic matter in terms of volatile fatty acids (VFAs). While the AAMBR successfully generated VFAs from municipal wastewater through forward osmosis (FO) membrane concentration, its operation was limited to a single pH value of 10.0. Here, performance of the AAMBR operating at acidic condition was evaluated and compared with that at alkaline condition. The findings revealed that the AAMBR with pH 5.0 efficiently transformed organic matter into acetic acid, propionic acid, and butyric acid, resulting in a VFAs yield of 0.48 g/g-CODfeed. In comparison with the AAMBR at pH 10.0, this study achieved a similar VFAs yield, a lower fouling tendency, a lower loss of nutrients and a lower controlling cost. In conclusion, this study demonstrated that a pH of 5.0 is optimal for the AAMBR treating municipal wastewater.

Bioaugmentation of Thauera mechernichensis TL1 for enhanced polyhydroxyalkanoate production in mixed microbial consortia for wastewater treatment

Polyhydroxyalkanoate (PHA) is a fully biodegradable bioplastic. To foster a circular economy, the integration of PHA production into wastewater treatment facilities can be accomplished using mixed microbial consortia. The effectiveness of this approach relies greatly on the enrichment of PHA-accumulating microorganisms. Hence, our study focused on bioaugmenting Thauera mechernichensis TL1 into mixed microbial consortia with the aim of enriching PHA-accumulating microorganisms and enhancing PHA production. Three sequencing batch reactors-SBRctrl, SBR2.5%, and SBR25%-were operated under feast/famine conditions. SBR2.5% and SBR25% were bioaugmented with T. mechernichensis TL1 at 2.5%w/w of mixed liquor volatile suspended solids (MLVSS) and 25%w/w MLVSS, respectively, while SBRctrl was not bioaugmented. SBR2.5% and SBR25% achieved maximum PHA accumulation capacities of 56.3 %gPHA/g mixed liquor suspended solids (MLSS) and 50.2 %gPHA/gMLSS, respectively, which were higher than the 25.4 %gPHA/gMLSS achieved by SBRctrl. The results of quantitative polymerase chain reaction targeting the 16S rRNA gene specific to T. mechernichensis showed higher abundances of T. mechernichensis in SBR2.5% and SBR25% compared with SBRctrl in the 3rd, 17th, and 31st cycles. Fluorescence in situ hybridization, together with fluorescent staining of PHA with Nile blue A, confirmed PHA accumulation in Thauera spp. The study demonstrated that bioaugmentation of T. mechernichensis TL1 at 2.5%w/w MLVSS is an effective strategy to enhance PHA accumulation and facilitate the enrichment of PHA-accumulating microorganisms in mixed microbial consortia. The findings could contribute to the advancement of PHA production from wastewater, enabling the transformation of wastewater treatment plants into water and resource recovery facilities.

Influence of pH, Heat Treatment of Inoculum, and Selenium Oxyanions on Concomitant Selenium Bioremediation and Volatile Fatty Acid Production from Food Waste

Developing novel strategies to enhance volatile fatty acid (VFA) yield from abundant waste resources is imperative to improve the competitiveness of biobased VFAs over petrochemical-based VFAs. This study hypothesized to improve the VFA yield from food waste via three strategies, viz., pH adjustment (5 and 10), supplementation of selenium (Se) oxyanions, and heat treatment of the inoculum (at 85 °C for 1 h). The highest VFA yield of 0.516 g COD/g VS was achieved at alkaline pH, which was 45% higher than the maximum VFA production at acidic pH. Heat treatment resulted in VFA accumulation after day 10 upon alkaline pretreatment. Se oxyanions acted as chemical inhibitors to improve the VFA yield at pH 10 with non-heat-treated inoculum (NHT). Acetic and propionic acid production was dominant at alkaline pH (NHT); however, the VFA composition diversified under the other tested conditions. More than 95% Se removal was achieved on day 1 under all the conditions tested. However, the heat treatment was detrimental for selenate reduction, with less than 15% Se removal after 20 days. Biosynthesized Se nanoparticles were confirmed by transmission and scanning electron microscopy and and energy dispersive X-ray analyses. The heat treatment inhibited the presence of nonsporulating bacteria and methanogenic archaea (Methanobacteriaceae). High-throughput sequencing also revealed higher relative abundances of the bacterial families (such as Clostridiaceae, Bacteroidaceae, and Prevotellaceae) that are capable of VFA production and/or selenium reduction.

Production of polyhydroxyalkanoate (PHA) copolymer from food waste using mixed culture for carboxylate production and Pseudomonas putida for PHA synthesis

Production of polyhydroxyalkanoates (PHAs) with high concentration of carboxylate, that was accumulated from solid state fermentation (SSF) of food waste (FW), was tested using Pseudomonas putida strain KT2440. Mixed-culture SSF of FW supplied in a high concentration of carboxylate, which caused a high PHA production of 0.56 g PHA/g CDM under nutrients control. Interestingly, this high PHA fraction in CDM was almost constant at 0.55 g PHA/g CDM even under high nutrients concentration (25 mM NH₄⁺), probably due to high reducing power maintained by high carboxylate concentration. PHA characterization indicated that the dominant PHA building block produced was 3-hydroxybutyrate, followed by 3-hydroxy-2-methylvalerate and 3-hydroxyhenxanoate. Carboxylate profiles before and after PHA production suggested that acetate, butyrate, and propionate were the main precursors to PHA via several metabolic pathways. Our result support that mixed culture SSF of FW for high concentration carboxylate and P. putida for PHA production enables sustainable production of PHA in cost-effective manners.

Application of Immersed Membrane Bioreactor for Semi-Continuous Production of Polyhydroxyalkanoates from Organic Waste-Based Volatile Fatty Acids

Volatile fatty acids (VFAs) appear to be an economical carbon feedstock for the cost-effective production of polyhydroxyalkanoates (PHAs). The use of VFAs, however, could impose a drawback of substrate inhibition at high concentrations, resulting in low microbial PHA productivity in batch cultivations. In this regard, retaining high cell density using immersed membrane bioreactor (iMBR) in a (semi-) continuous process could enhance production yields. In this study, an iMBR with a flat-sheet membrane was applied for semi-continuous cultivation and recovery of Cupriavidus necator in a bench-scale bioreactor using VFAs as the sole carbon source. The cultivation was prolonged up to 128 h under an interval feed of 5 g/L VFAs at a dilution rate of 0.15 (d^-1), yielding a maximum biomass and PHA production of 6.6 and 2.8 g/L, respectively. Potato liquor and apple pomace-based VFAs with a total concentration of 8.8 g/L were also successfully used in the iMBR, rendering the highest PHA content of 1.3 g/L after 128 h of cultivation. The PHAs obtained from both synthetic and real VFA effluents were affirmed to be poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with a crystallinity degree of 23.8 and 9.6%, respectively. The application of iMBR could open an opportunity for semi-continuous production of PHA, increasing the feasibility of upscaling PHA production using waste-based VFAs.

Perceiving biobased plastics as an alternative and innovative solution to combat plastic pollution for a circular economy

Plastic waste from fossil-based sources, including single-use packaging materials, is continuously accumulating in landfills, and leaching into the environment. A 2021 UN Environment Programme (UNEP) report suggests that the plastic pollution is likely to be doubled by 2030, posing a major challenge to the environment and the overall global plastic waste management efforts. The use of biobased plastics such as polyhydroxyalkanoates (PHAs) as a biodegradable substitute for petroleum-based plastics could be a feasible option to combat this issue which may further result in much lower carbon emissions and energy usage in comparison to conventional plastics as additional advantages. Though recent years have seen the use of microbes as biosynthetic machinery for biobased plastics, using various renewable feedstocks, the scaled-up production of such materials is still challenging. The current study outlays applications of biobased plastics, potential microorganisms producing biobased plastics such as Cupriavidus necator, Bacillus sp., Rhodopseudomonas palustris, microalgae, and mixed microbial cultures, and inexpensive and renewable resources as carbon substrates including industrial wastes. This review also provides deep insights into the operational parameters, challenges and mitigation, and future opportunities for maximizing the production of biobased plastic products. Finally, this review emphasizes the concept of biorefinery as a sustainable and innovative solution for biobased plastic production for achieving a circular bioeconomy.

Conceptual system for sustainable and next-generation wastewater resource recovery facilities

Shifting the concept of municipal wastewater treatment to recover resources is one of the key factors contributing to a sustainable society. A novel concept based on research is proposed to recover four main bio-based products from municipal wastewater while reaching the necessary regulatory standards. The main resource recovery units of the proposed system include upflow anaerobic sludge blanket reactor for the recovery of biogas (as product 1) from mainstream municipal wastewater after primary sedimentation. Sewage sludge is co-fermented with external organic waste such as food waste for volatile fatty acids (VFAs) production as precursors for other bio-based production. A portion of the VFA mixture (product 2) is used as carbon sources in the denitrification step of the nitrification/denitrification process as an alternative for nitrogen removal. The other alternative for nitrogen removal is the partial nitrification/anammx process. The VFA mixture is separated with nanofiltration/reverse osmosis membrane technology into low-carbon VFAs and high-carbon VFAs. Polyhydroxyalkanoate (as product 3) is produced from the low-carbon VFAs. Using membrane contactor-based processes and ion-exchange techniques, high-carbon VFAs are recovered as one-type VFA (pure VFA) and in ester forms (product 4). The nutrient-rich fermented and dewatered biosolid is applied as a fertilizer. The proposed units are seen as individual resource recovery systems as well as a concept of an integrated system. A qualitative environmental assessment of the proposed resource recovery units confirms the positive environmental impacts of the proposed system.

Untargeted metabolomics elucidated biosynthesis of polyhydroxyalkanoate by mixed microbial cultures from waste activated sludge under different pH values

Waste activated sludge has been frequently used as mixed substrate to produce polyhydroxyalkanoate (PHA). However, insufficient research on microbial metabolism has led to difficulties in regulating PHA accumulation in mixed microbial cultures (MMCs). To explore the variation of functional genes during domestication and the effect of different pH conditions on metabolic pathways during PHA accumulation, MMCs were domesticated by adding acetate and propionate with aerobic dynamic feeding strategy for 60 days. As the domestication progressed, the microbial community diversity declined and PHA-producing bacteria, Brevundimonas, Dechloromonas and Hyphomonas, were enriched. Through bacterial function prediction by PICRUSt the gene rpoE involved in starvation resistance of bacteria was enriched after the domestication. The pH value of 8.5 was the best condition for PHA accumulation in MMCs, under which a maximum PHA content reached 23.50% and hydroxybutyric (HB)/hydroxyvaleric (HV) reached 2.22. Untargeted metabolomics analysis exhibited that pH conditions of 7 and 8.5 could promote the up-regulation of significant differential metabolites, while higher alkaline conditions caused the inhibition of metabolic activity. Functional annotation showed that pH condition of 8.5 significantly affected Pyrimidine metabolism, resulting in an increase in PHA production. Regarding the pathways of PHA biosynthesis, acetoacetate was found to be significant in the metabolism of hydroxybutyric, and the alkaline condition could restrain the conversion from hydroxybutyric (HB) to the acetoacetate to protect PHB accumulation in MMCs compared with neutral condition. Taken together, the present results can advance the fundamental understanding of metabolic function in PHA accumulation under different pH conditions.

Cascading Beta-oxidation Intermediates for the Polyhydroxyalkanoate Copolymer Biosynthesis by Metabolic Flux using Co-substrates and Inhibitors

Polyhydroxyalkanoates (PHAs) are biopolymers that are produced within the microbial cells in the presence of excess carbon and nutrient limitation. Different strategies have been studied to increase the quality and quantity of this biopolymer which in turn can be utilized as biodegradable polymers replacing conventional petrochemical plastics. In the present study, Bacillus endophyticus, a gram-positive PHA-producing bacterium, was cultivated in the presence of fatty acids along with beta-oxidation inhibitor acrylic acid. A novel approach for incorporating different hydroxyacyl groups provided using fatty acids as co-substrate and beta-oxidation inhibitors to direct the intermediates to co-polymer synthesis was experimented. It was observed that higher fatty acids and inhibitors had a greater influence on PHA production. The addition of acrylic acid along with propionic acid had a positive impact, giving 56.49% of PHA along with sucrose which was 1.2-fold more than the control devoid of fatty acids and inhibitors. Along with the copolymer production, the possible PHA pathway functional leading to the copolymer biosynthesis was hypothetically interpreted in this study. The obtained PHA was analyzed by FTIR and ¹H NMR to confirm the copolymer production, which indicated the presence of poly3hydroxybutyrate-co-hydroxyvalerate (PHB-co-PHV), poly3hydroxybutyrate-co-hydroxyhexanoate (PHB-co-PHx).

Fermentative bioconversion of food waste into biopolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) using Cupriavidus necator

Dependency on plastic commodities has led to a recurrent increase in their global production every year. Conventionally, plastic products are derived from fossil fuels, leading to severe environmental concerns. The recent coronavirus disease 2019 pandemic has triggered an increase in medical waste. Conversely, it has disrupted the supply chain of personal protective equipment (PPE). Valorisation of food waste was performed to cultivate C. necator for fermentative production of biopolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). The increase in biomass, PHBV yield and molar 3-hydroxy valerate (3HV) content was estimated after feeding volatile fatty acids. The fed-batch fermentation strategy reported in this study produced 15.65 ± 0.14 g/L of biomass with 5.32 g/L of PHBV with 50% molar 3HV content. This is a crucial finding, as molar concentration of 3HV can be modulated to suit the specification of biopolymer (film or fabric). The strategy applied in this study addresses the issue of global food waste burden and subsequently generates biopolymer PHBV, turning waste to wealth.

A plant wide simulation of polyhydroxyalkanoate production from wastewater and its conversion to methyl crotonate

This work simulates the production of methyl crotonate from various industrial wastewaters. In the upstream process, wastewater is fermented into volatile fatty acids which are then converted into polyhydroxyalkanoates (PHA) by means of mixed microbial cultures. In the downstream, PHA undergoes a series of thermolysis and esterification reactions to produce methyl crotonate. The origin of the wastewater was found to have a great influence on the composition of the PHA with the effluent of a candy bar factory producing a high polyhydroxybutyrate/polyhydroxyvalerate ratio of 86/14 in favour of methyl crotonate production. It was observed that the use of intracellular polyhydroxybutyrate, instead of purified, significantly lowers the number of separation steps and yet reduces the methyl crotonate recovery by only 20 %. An operating pressure higher than 18 bar led to more transesterification of polyhydroxybutyrate, producing byproducts instead of methyl crotonate. Finally, a 3 h reaction was found sufficient for completion of polyhydroxybutyrate conversion.

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.

Pure cultures for synthetic culture development: Next level municipal waste treatment for polyhydroxyalkanoates production

Polyhydroxyalkanoates (PHAs), as bio-based plastics, promise a transition from petroleum products to green and sustainable alternatives. However, their commercial production is yet impeded by high production costs. In this study, we assessed synthetic culture in mono and co-culture modes for bacterial PHA production. It was demonstrated that volatile fatty acids (VFAs) derived from food waste and primary sludge are cheap carbon sources for maintaining high production yields in the synthetic cultures. The maximum obtained PHA was 77.54 ± 5.67% of cell dried weight (CDW) (1.723 g/L) from Cupriavidus necator and 54.9 ± 3.66% of CDW (1.088 g/L) from Burkholderia cepacia. The acquired results are comparable to those in literature using sugar substrates. Comparatively, lower PHA productions were obtained from the co-cultivations ranging between 36-45 CDW% (0.39-0.48 g/L). Meanwhile, the 3-hydroxyvalerate content in the biopolymers were increased up to 21%.

Current state of the art biotechnological strategies for conversion of watermelon wastes residues to biopolymers production: A review

Poly-3-hydroxyalkanoates (PHA) are biodegradable and compostable polyesters. This review is aimed to provide a unique approach that can help think tanks to frame strategies aiming for clean technology by utilizing cutting edge biotechnological advances to convert fruit and vegetable waste to biopolymer. A PHA manufacturing method based on watermelon waste residue that does not require extensive pretreatment provides a more environmentally friendly and sustainable approach that utilizes an agricultural waste stream. Incorporating fruit processing industry by-products and water, and other resource conservation methods would not only make the manufacturing of microbial bio-plastics like PHA more eco-friendly, but will also help our sector transition to a bioeconomy with circular product streams. The final and most critical element of this review is an in-depth examination of the several hazards inherent in PHA manufacturing.

Advances in downstream processes and applications of biological carboxylic acids derived from organic wastes

Recovering carboxylic acids derived from organic wastes from fermentation broth is challenging. To provide a reference for future study and industrial application, this review summarized recent advances in recovery technologies of carboxylic acids including precipitation, extraction, adsorption, membrane-based processes, etc. Meanwhile, applications of recovered carboxylic acids are summarized as well to help choose suitable downstream processes according to purity requirement. Integrated processes are required to remove the impurities from the complicated fermentation broth, at the cost of loss and expense. Compared with chemical processes, biological synthesis is better options due to low requirements for the substrates. Generally, the use of toxic agents, consumption of acid/alkaline and membrane fouling hamper the sustainability and scale-up of the downstream processes. Future research on novel solvents and materials will facilitate the sustainable recovery and reduce the cost of the downstream processes.

Long-term alkaline volatile fatty acids production from waste streams: Impact of pH and dominance of Dysgonomonadaceae

Alkaline co-fermentation of primary sludge and external organic waste (OW) was studied to elucidate the influence of substrate ratios and long-term system robustness and microbial community dynamics using batch and semi-continuous reactors. Volatile fatty acid (VFA) production increased with increasing OW fraction in the substrate due to synergistic effects of co-degradation. VFA production at pH 10 increased up to 30,300 mgCOD/L (yield of 630 mg COD/gVS_fed) but reduced over time to ≈10,000 mgCOD/L. Lowering pH to 9 led to the restoration of VFA production with a maximum of 32,000 mg COD/L (676 mg COD/g VS_fed) due to changes in microbial structure. VFA was composed mainly of acetic acid, but propionic acid increased at pH 9. The microbial community was dominated by Bacillaceae (34 ± 10%) and Proteinivoracales_uncultured (16 ± 11%) at pH 10, while Dysgonomonadaceae (52 ± 8%) was enriched at pH 9. The study demonstrated a zero-waste strategy that turns organic wastes into bio-based products.

Polyhydroxyalkanoates Production by Mixed Microbial Culture under High Salinity

The fishing industry produces vast amounts of saline organic side streams that require adequate treatment and disposal. The bioconversion of saline resources into value-added products, such as biodegradable polyhydroxyalkanoates (PHAs), has not yet been fully explored. This study investigated PHA production by mixed microbial cultures under 30 gNaCl/L, the highest NaCl concentration reported for the acclimatization of a PHA-accumulating mixed microbial culture (MMC). The operational conditions used during the culture-selection stage resulted in an enriched PHA-accumulating culture dominated by the Rhodobacteraceae family (95.2%) and capable of storing PHAs up to 84.1% wt. (volatile suspended solids (VSS) basis) for the highest organic loading rate (OLR) applied (120 Cmmol/(L.d)). This culture presented a higher preference for the consumption of valeric acid (0.23 ± 0.03 CmolHVal/(CmolX.h)), and the 3HV monomer polymerization (0.33 ± 0.04 CmmolHV/(CmmolX.h) was higher as well. As result, a P(3HB-co-3HV)) with high HV content (63% wt.) was produced in the accumulation tests conducted at higher OLRs and with 30 gNaCl/L. A global volumetric PHA productivity of 0.77 gPHA/(L.h) and a specific PHA productivity of 0.21 gPHA/(gX.h) were achieved. These results suggested the significant potential of the bioconversion of saline resources into value-added products, such as PHAs.

Production of polyhydroxyalkanoates by three novel species of Marinobacterium

Several species of novel marine bacteria from the genus Marinobacterium, including M. nitratireducens, M. sediminicola, and M. zhoushanense were found to be capable of producing polyhydroxyalkanoates (PHA) using sugars and volatile fatty acids (VFAs) as the carbon source. M. zhoushanense produced poly-3-hydroxybutytate (PHB) from sucrose, achieving a product titer and PHB content of 2.89 g/L and 64.05 wt%, respectively. By contrast, M. nitratireducens accumulated 3.38 g/L PHB and 66.80 wt% polymer content using butyrate as the substrate. A third species, M. sediminicola showed favorable tolerance to propionate, butyrate, and valerate. The use of 10 g/L valerate yielded 3.37 g/L poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), with a 3-hydroxyvalerate (3 HV) monomer content of 94.75 mol%. Moreover, M. sediminicola could be manipulated to produce PHBV with changeable polymer compositions by feeding different mixtures of VFAs. Our results indicate that M. sediminicola is a promising halophilic bacterium for the production of PHA.

Diversifying the products from the organic fraction of municipal solid waste (OFMSW) by producing polyhydroxyalkanoates from the liquid fraction and biomethane from the residual solid fraction

This study describes the diversification of products obtainable from the organic fraction of municipal solid waste (OFMSW) by producing polyhydroxyalkanoates (PHA) from the liquid fraction and biomethane from the residual solid fraction. OFMSW samples were taken during the 2021 season from two full field scale plants treating wastes. After solid/liquid (S/L) separation, 80% of initial organic acids (OAs) were released in the liquid stream. OAs were then used as feed for PHA production and residual solid cakes were tested for biomethane production. Complete mass balance and energy balance were calculated. PHAs production was of 115 ± 23 (n = 6) g kg^{- 1} OFMSW (TS) and residual biomethane of 219 ± 3 g kg^{- 1} OFMSW TS, (n = 6). Energy balance indicated that nearly 40% of OFMSW energy was recovered as products. This value was lower than that obtained previously when AD was performed before OAs separation (i.e. 64%).

Regulated strategies of cold-adapted microorganisms in response to cold: a review

There are a large number of active cold-adapted microorganisms in the perennial cold environment. Due to their high-efficiency and energy-saving catalytic properties, cold-adapted microorganisms have become valuable natural resources with potential in various biological fields. In this study, a series of cold response strategies for microorganisms were summarized. This mainly involves the regulation of cell membrane fluidity, synthesis of cold adaptation proteins, regulators and metabolic changes, energy supply, and reactive oxygen species. Also, the potential of biocatalysts produced by cold-adapted microorganisms including cold-active enzymes, ice-binding proteins, polyhydroxyalkanoates, and surfactants was introduced, which provided a guidance for expanding its application values. Overall, new insights were obtained on response strategies of microorganisms to cold environments in this review. This will deepen the understanding of the cold tolerance mechanism of cold-adapted microorganisms, thus promoting the establishment and application of low-temperature biotechnology.

Nature-Based Units as Building Blocks for Resource Recovery Systems in Cities

Cities are producers of high quantities of secondary liquid and solid streams that are still poorly utilized within urban systems. In order to tackle this issue, there has been an ever-growing push for more efficient resource management and waste prevention in urban areas, following the concept of a circular economy. This review paper provides a characterization of urban solid and liquid resource flows (including water, nutrients, metals, potential energy, and organics), which pass through selected nature-based solutions (NBS) and supporting units (SU), expanding on that characterization through the study of existing cases. In particular, this paper presents the currently implemented NBS units for resource recovery, the applicable solid and liquid urban waste streams and the SU dedicated to increasing the quality and minimizing hazards of specific streams at the source level (e.g., concentrated fertilizers, disinfected recovered products). The recovery efficiency of systems, where NBS and SU are combined, operated at a micro- or meso-scale and applied at technology readiness levels higher than 5, is reviewed. The importance of collection and transport infrastructure, treatment and recovery technology, and (urban) agricultural or urban green reuse on the quantity and quality of input and output materials are discussed, also regarding the current main circularity and application challenges.

Burkholderia sacchari (synonym Paraburkholderia sacchari): An industrial and versatile bacterial chassis for sustainable biosynthesis of polyhydroxyalkanoates and other bioproducts

This is the first review presenting and discussing Burkholderia sacchari as a bacterial chassis. B. sacchari is a distinguished polyhydroxyalkanoates producer strain, with low biological risk, reaching high biopolymer yields from sucrose (0.29 g/g), and xylose (0.38 g/g). It has great potential for integration into a biorefinery using residues from biomass, achieving 146 g/L cell dry weight containing 72% polyhydroxyalkanoates. Xylitol (about 70 g/L) and xylonic acid [about 390 g/L, productivity 7.7 g/(L.h)] are produced by the wild-type B. sacchari. Recombinants were constructed to allow the production and monomer composition control of diverse tailor-made polyhydroxyalkanoates, and some applications have been tested. 3-hydroxyvalerate and 3-hydroxyhexanoate yields from substrate reached 80% and 50%, respectively. The genome-scale reconstruction of its metabolic network, associated with the improvement of tools for genetic modification, and metabolic fluxes understanding by future research, will consolidate its potential as a bioproduction chassis.

Bioaugmentation as a strategy for tailor-made volatile fatty acid production

This study aimed to develop a novel strategy for tailor-made volatile fatty acid (VFA) composition. For this purpose, the mixed microbial culture was bioaugmented by Propionibacterium acidipropionici. Anaerobic sequencing batch reactors were operated with cheese wastewater under alkali pH. While the maximum propionic acid production almost four times increased (3779 ± 201 mgCOD_eq propionic acid/L in the bioaugmented reactor and 942 ± 172 mgCOD_eq propionic acid/L in the control reactor), there was no significant difference in VFA composition. The gene copy number of P.acidipropionici increased 20 times after the bioaugmentation. Furthermore, the gene copy number of P.acidipropionici was positively correlated with total VFA and isovaleric acid concentration. The relative abundance of family Flavobacteriaceae increased in the bioaugmented reactor, which might be caused by the syntrophic relation between Flavobacteriaceae and P. acidipropionici. The cycle analysis results showed that the shorter cycle (6h) could ensure the same efficiency.