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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Lignin’s Indispensable role in orchestrating seed stone formation: Insights from jujuba, peach and pear with future prospective on pitless fruits

A hard endocarp (i.e., stone) inside fruit is a characteristic of drupe fruits such as jujube, peach, mango, etc. Hard stone significantly affects the quality and downstream processing of fruits. The complex aromatic polymer lignin deposition in the secondary cell wall determines stone hardness. Lignin comprises phenylpropanoid units formed by hydroxycinnamoyl alcohol, which includes coniferyl, sinapyl, and p-coumaroyl alcohols. Lignin biosynthesis pathway involves a series of complex enzymatic reactions initiated from phenylalanine ammonia lyase and ends up polymerizing lignin monomers by laccase and peroxidase enzymes. Phytohormones, particularly auxin, gibberellins, and Ca²⁺ signaling, further modulate endocarp lignification by regulating transcriptional networks and lignin biosynthetic genes, thereby fine-tuning secondary cell wall thickening and stone hardness in drupe fruits. Lignin biosynthesis is controlled by both structural genes and transcriptional regulators. The structural genes encoding lignin biosynthetic enzymes include LAC12–1, PAL2, C4H, C3H, CSE, CCoAOMT, F5H, CAD, and PRX1. In addition, several transcription factors regulating secondary cell wall and lignin deposition, such as MYB24, bZIP48, and bZIP33 play key regulatory roles. Conversely, delignification or suppression of stone formation is associated with transcription factors (Pistillata, MYB32, FUL, and REPLUMLESS) and post-transcriptional regulators, including miR397a, miR31-3p, and miR8-5p. Accurate alteration in the expression of these genes will result in the attainment of stoneless fruits for cheap and hazel-free downstream processing.

Fruit endocarp↗
DOE OSTI2021

Near-complete depolymerization of polyesters with nano-dispersed enzymes

Successfully interfacing enzymes and biomachinery with polymers affords on-demand modification and/or programmable degradation during the manufacture, utilization and disposal of plastics, but requires controlled biocatalysis in solid matrices with macromolecular substrates. Embedding enzyme microparticles speeds up polyester degradation, but compromises host properties and unintentionally accelerates the formation of microplastics with partial polymer degradation. Here we show that by nanoscopically dispersing enzymes with deep active sites, semi-crystalline polyesters can be degraded primarily via chain-end-mediated processive depolymerization with programmable latency and material integrity, akin to polyadenylation-induced messenger RNA decay. It is also feasible to achieve processivity with enzymes that have surface-exposed active sites by engineering enzyme-protectant-polymer complexes. Poly(caprolactone) and poly(lactic acid) containing less than 2 weight per cent enzymes are depolymerized in days, with up to 98 per cent polymer-to-small-molecule conversion in standard soil composts and household tap water, completely eliminating current needs to separate and landfill their products in compost facilities. Furthermore, oxidases embedded in polyolefins retain their activities. However, hydrocarbon polymers do not closely associate with enzymes, as their polyester counterparts do, and the reactive radicals that are generated cannot chemically modify the macromolecular host. This study provides molecular guidance towards enzyme-polymer pairing and the selection of enzyme protectants to modulate substrate selectivity and optimize biocatalytic pathways. Furthermore, the results also highlight the need for in-depth research in solid-state enzymology, especially in multi-step enzymatic cascades, to tackle chemically dormant substrates without creating secondary environmental contamination and/or biosafety concerns.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Desulfatiglans anilini Initiates Degradation of Aniline With the Production of Phenylphosphoamidate and 4-Aminobenzoate as Intermediates Through Synthases and Carboxylases From Different Gene Clusters

The anaerobic degradation of aniline was studied in the sulfate-reducing bacterium Desulfatiglans anilini. Our aim was to identify the genes and their proteins that are required for the initial activation of aniline as well as to characterize intermediates of this reaction. Aniline-induced genes were revealed by comparison of the proteomes of D. anilini grown with different substrates (aniline, 4- aminobenzoate, phenol, and benzoate). Most genes encoding proteins that were highly abundant in aniline- or 4-aminobenzoate-grown D. anilini cells but not in phenol- or benzoate-grown cells were located in the putative gene clusters ani (aniline degradation), hcr (4-hydroxybenzoyl-CoA reductase) and phe (phenol degradation). Of these putative gene clusters, only the phe gene cluster has been studied previously. Based on the differential proteome analysis, four candidate genes coding for kinase subunits and carboxylase subunits were suspected to be responsible for the initial conversion of aniline to 4-aminobenzoate. These genes were cloned and overproduced in E. coli. The recombinant proteins were obtained in inclusion bodies but could be refolded successfully. Two subunits of phenylphosphoamidate synthase and two carboxylase subunits converted aniline to 4-aminobenzoate with phenylphosphoamidate as intermediate under consumption of ATP. Only when both carboxylase subunits, one from gene cluster ani and the other from gene cluster phe, were combined, phenylphosphoamidate was converted to 4-aminobenzoate in vitro, with Mn 2+ , K + , and FMN as co-factors. Thus, aniline is degraded by the anaerobic bacterium D. anilini only by recruiting genes for the enzymatic machinery from different gene clusters. We conclude, that D. anilini carboxylates aniline to 4-aminobenzoate via phenylphosphoamidate as an energy rich intermediate analogous to the degradation of phenol to 4-hydroxybenzoate via phenylphosphate.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Data for Valorization of Miscanthus x giganteus for Sustainable Recovery of Anthocyanins and Enhanced Production of Sugars

The increased awareness for eco-friendliness and sustainability has shifted the interest of stakeholders from synthetic colors to natural plant-based pigments. In this study, purple stemmed Miscanthus x giganteus was evaluated as a source of anthocyanins. Hydrothermal pretreatment was studied as a green, chemical-free process for recovering maximum anthocyanins in the pretreatment liquor. The highest recovery of 94.3 ± 1.5% w/w of the total anthocyanin concentration was obtained for a temperature and time combination of 170 °C and 10 min. The pretreatment also improved the enzymatic digestibility of the biomass and led to a 2.1-fold increase in the overall recovery of glucose (70.6 ± 0.5% w/w) at the end of 72 h. The sugar monomers obtained after the enzymatic hydrolysis of the pretreated biomass could be used for the production of biofuels or biochemicals in an integrated biorefinery based on purple-stemmed miscanthus. Overall, this study demonstrates that the clean pretreatment method developed could lead to an additional product stream (rich in anthocyanins) along with its effect in reducing the recalcitrance of miscanthus biomass.

Biomass Analytics↗
DOE OSTI2020

Ammonia Fiber Expansion (AFEX) Pretreatment of Lignocellulosic Biomass

Lignocellulosic materials are plant-derived feedstocks, such as crop residues (e.g., corn stover, rice straw, and sugar cane bagasse) and purpose-grown energy crops (e.g., miscanthus, and switchgrass) that are available in large quantities to produce biofuels, biochemicals, and animal feed. Plant polysaccharides (i.e., cellulose, hemicellulose, and pectin) embedded within cell walls are highly recalcitrant towards conversion into useful products. Ammonia fiber expansion (AFEX) is a thermochemical pretreatment that increases accessibility of polysaccharides to enzymes for hydrolysis into fermentable sugars. These released sugars can be converted into fuels and chemicals in a biorefinery. Here, we describe a laboratory-scale batch AFEX process to produce pretreated biomass on the gram-scale without any ammonia recycling. The laboratory-scale process can be used to identify optimal pretreatment conditions (e.g., ammonia loading, water loading, biomass loading, temperature, pressure, residence time, etc.) and generates sufficient quantities of pretreated samples for detailed physicochemical characterization and enzymatic/microbial analysis. The yield of fermentable sugars from enzymatic hydrolysis of corn stover pretreated using the laboratory-scale AFEX process is comparable to pilot-scale AFEX process under similar pretreatment conditions. This paper is intended to provide a detailed standard operating procedure for the safe and consistent operation of laboratory-scale reactors for performing AFEX pretreatment of lignocellulosic biomass.

09 BIOMASS FUELS↗
DOE OSTI2021

Self-Assembling Metabolon Enables the Cell Free Conversion of Glycerol to 1,3-Propanediol

Cell free biocatalysis is showing promise as a replacement or complement to conventional microbial biocatalysts due to the potential for achieving high yields, titers, and productivities. However, there exist several challenges that need to be addressed before its broader industrial adoption is achieved. New paradigms and innovative solutions are needed to overcome these challenges. In this study we demonstrate high levels of glycerol conversion to 1,3-propanediol using a self-assembling metabolic pathway leveraging the arraying strategy (protein scaffolds) used by thermophilic cellulolytic bacteria to assemble their biomass degrading enzymes. These synthetic metabolons were capable of producing 1,3-PDO at a yield more than 95% at lower glycerol concentration and close to 70% at higher concentrations at a higher productivity rate than the equivalent microbial strain. One of the benefits of our approach is the fact that no enzyme purification is required, and that the assembly of the complex is accomplished in vivo before immobilization, while product formation is conducted in vitro. We also report the recovery of enzymatic activity upon fusion enzymes binding to these protein scaffolds, which could have broader applications when assembling arrayed protein complexes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Water-soluble saponins accumulate in drought-stressed switchgrass and may inhibit yeast growth during bioethanol production

Abstract Background Developing economically viable pathways to produce renewable energy has become an important research theme in recent years. Lignocellulosic biomass is a promising feedstock that can be converted into second-generation biofuels and bioproducts. Global warming has adversely affected climate change causing many environmental changes that have impacted earth surface temperature and rainfall patterns. Recent research has shown that environmental growth conditions altered the composition of drought-stressed switchgrass and directly influenced the extent of biomass conversion to fuels by completely inhibiting yeast growth during fermentation. Our goal in this project was to find a way to overcome the microbial inhibition and characterize specific compounds that led to this inhibition. Additionally, we also determined if these microbial inhibitors were plant-generated compounds, by-products of the pretreatment process, or a combination of both. Results Switchgrass harvested in drought (2012) and non-drought (2010) years were pretreated using Ammonia Fiber Expansion (AFEX). Untreated and AFEX processed samples were then extracted using solvents (i.e., water, ethanol, and ethyl acetate) to selectively remove potential inhibitory compounds and determine whether pretreatment affects the inhibition. High solids loading enzymatic hydrolysis was performed on all samples, followed by fermentation using engineered Saccharomyces cerevisiae . Fermentation rate, cell growth, sugar consumption, and ethanol production were used to evaluate fermentation performance. We found that water extraction of drought-year switchgrass before AFEX pretreatment reduced the inhibition of yeast fermentation. The extracts were analyzed using liquid chromatography–mass spectrometry (LC–MS) to detect compounds enriched in the extracted fractions. Saponins, a class of plant-generated triterpene or steroidal glycosides, were found to be significantly more abundant in the water extracts from drought-year (inhibitory) switchgrass. The inhibitory nature of the saponins in switchgrass hydrolysate was validated by spiking commercially available saponin standard (protodioscin) in non-inhibitory switchgrass hydrolysate harvested in normal year. Conclusions Adding a water extraction step prior to AFEX-pretreatment of drought-stressed switchgrass effectively overcame inhibition of yeast growth during bioethanol production. Saponins appear to be generated by the plant as a response to drought as they were significantly more abundant in the drought-stressed switchgrass water extracts and may contribute toward yeast inhibition in drought-stressed switchgrass hydrolysates.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Bimetallic Metal–Organic Framework Fe/Co-MIL-88(NH 2 ) Exhibiting High Peroxidase-like Activity and Its Application in Detection of Extracellular Vesicles

Metal–organic frameworks (MOFs) have many attractive features, including tunable composition, rigid structure, controllable pore size, and large specific surface area, and thus are highly applicable in molecular analysis. Depending on the MOF structure, a high number of un-saturated metal sites can be exposed to catalyze chemical reactions. In the present work, we report that by using both Co(II) and Fe(III) to prepare the MIL-88(NH 2 ) MOF, we can produce the bimetallic MOF that can catalyze the conversion of 3,3', 5,5"-tetramethylbenzidine (TMB) to a color product through reaction with H 2 O 2 at a higher reaction rate than the monometallic Fe-MIL-88(NH 2 ). The Michaelis constants (K m ) of the catalytic reaction for TMB and H 2 O 2 are 3-5 times smaller, and the catalytic constants (k cat ) are 5-10 times higher than those of the horse-radish peroxidase (HRP), supporting ultrahigh peroxidase-like activity. These values are also much more superior to those of the HRP-mimicking MOFs reported previously. Interestingly, the bimetallic MOF can be coupled with glucose oxidase (GOx) to trigger the cascade enzymatic reaction for highly sensitive detection of extracellular vesicles (EVs), a family of important biomarkers. Through conjugation to the aptamer that recognizes the marker protein on EV surface, the MOF can help isolate the EVs from biological matrices, which are subsequently labeled by GOx via antibody recognition. The cascade enzymatic reaction between MOF and GOx enables detection of EVs at a concentration as low as 7.8 × 10 4 particles/ml. Further, the assay can be applied to monitor EV secretion by cultured cells, and also can successfully detect the different EV quantities in the sera samples collected from cancer patients and healthy controls. Overall, we prove that the bimetallic Fe/Co-MIL-88(NH 2 ) MOF, with its high peroxidase-activity and high biocompatibility, is a valuable tool deployable in clinical assays to facility disease diagnosis and prognosis.

36 MATERIALS SCIENCE↗
DOE OSTI2022

MSW Decontamination: Methods to Improve Biofuel Yields

MSW is usually contaminated with a variety of undesirable materials (food, chemicals, glass, metal) that can impact downstream applications such as conversion to biofuels. This presentation will showcase two decontamination methods using either a detergent wash or an organic solvent extraction to demonstrate up to 30% increase in biofuel precursor yields for plastic and paper MSW. The economics of the two decontamination methods will also be presented.

09 BIOMASS FUELS↗
DOE OSTI2025

Integrating catalytic fractionation and microbial funneling to produce 2-pyrone-4,6-dicarboxylic acid and ethanol

Replacing biorefinery designs that use stepwise fractionation, depolymerization, and conversion processes with designed tandem process steps can greatly reduce a biorefinery's operating costs and environmental impact. Reductive Catalytic Fractionation (RCF) is a highly efficient lignin-first approach that combines biomass fractionation and lignin depolymerization to generate a hydrogenolysis oil and pulp. The oil is composed of a complex mixture of phenolic monomers, dimers, and oligomers. Intergrating this chemical deconstruction process with microbial funneling of phenolics can simplify the product mixture and make high-value products. We applied RCF to poplar biomass in a biomass-to-bioproduct processing chain in which the phenolics were funneled to 2-pyrone-4,6-dicarboxylic acid (PDC) by an engineered strain of Novosphingobium aromaticivorans DSM12444. The pulp was enzymatically digested and the glucose and xylose was funneled to ethanol by an engineered strain of Saccharomyces cerevisiae GLBRCY945. By combining biomass fractionation and lignin depolymerization we removed a costly processing step that directly translated into a 29% reduction in the minimum selling price of PDC. This work combines experimentation with process modeling of an integrated biorefinery design to show how utilizing tandem process steps can significantly reduce operating expenses and environmental impact of upgrading lignocellulosic biomass to a portfolio of high value products.

Sener, Canan [Great Lakes Bioenergy Research Cente↗
DOE OSTI2024

Mechanical and biochemical recovery of landfill waste in an underserved community

Historically in the United States, waste collected for recycling has been sold and shipped to processors in China. In 2013 and 2018, China introduced the Green Fence and National Sword policies which restricts the import of contaminated materials and banned the import of many recyclables. The cost of recycling in the United States has increased following these policy changes, which has led to many communities reducing their recycling programs or halting them altogether. Rural and underserved communities that don’t have resources to afford sophisticated recycling programs have been heavily impacted. Previous work at INL demonstrated that MSW is a potentially viable feedstock for both biochemical and thermochemical conversion. The goal of this project is to assess preprocessing tools that can produce consistent feedstocks that meet conversion specifications, remove problematic contaminants, and reduce the amount of waste that is landfilled. Municipal solid waste was collected from an underserved community in southeast Idaho, contaminants were characterized, and mechanically separated into two discrete fractions. The unit operations identified during mechanical separation trials will be mobilized to on-site with a goal of 50% recovery of paper and plastic waste.

09 - BIOMASS FUELS↗
DOE OSTI2020

Carbon Utilization: Electrochemical Approach Using Novel Catalyst and System Integration

The environmental footprint from power generation can be mitigated by capturing emitted carbon dioxide (CO2) and converting it to value-added fuel sources. A multitude of different fuels can be produced from CO2 depending on the chemical reaction catalysts. Typically, these pathways can be developed electrochemically, or through hydrogenation. In recent years the electrochemical reduction of CO2 has grown exponentially, as it has shown potential to decrease atmospheric pollution and provide an additional means of on-demand electricity storage. Formic acid (FA) in particular has industrial applications such as in fuel cells or as a hydrogen storage medium, and requires a lower thermodynamic energy input than any other fuel produced for electrochemical CO2 reduction. However, product selectivity remains a challenge for conventional electrocatalysts, making FA production efficiencies above 50% difficult. To address the challenge of catalytic selectivity, UK CAER employs enzymatic catalysts to facilitate the FA production and minimize unwanted byproducts. Our process couples the catalyst with a charge mediator which is necessary to shuttle electrons, and an electrolyte pH buffer to prevent the catalyst from degrading. Presently, production efficiencies have approached 60% at a rate of over 10 mM FA/hour. System design considerations (flow rate, bulk volume) will also be discussed.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2020

The Role of Evolving Interfacial Substrate Properties on Heterogeneous Cellulose Hydrolysis Kinetics

Interfacial enzyme reactions require formation of an enzyme–substrate complex at the surface of a heterogeneous substrate, but often multiple modes of enzyme binding and types of binding sites complicate analysis of their kinetics. Excess heterogeneous substrate is often used as a justification to model the substrate as unchanging, but using the study of the enzymatic hydrolysis of insoluble cellulose as an example, we argue that reaction rates are dependent on evolving substrate interfacial properties. We hypothesize that the relative abundance of binding sites on cellulose where hydrolysis can occur (productive binding sites) and binding sites where hydrolysis cannot be initiated or is inhibited (nonproductive binding sites) contribute to rate limitations. We show that the initial total number of productive binding sites (the productive binding capacity) determines the magnitude of the initial burst phase of cellulose hydrolysis, while productive binding site depletion explains overall hydrolysis kinetics. Furthermore, we show that irreversibly bound surface enzymes contribute to the depletion of productive binding sites. Our model shows that increasing the ratio of productive to nonproductive binding sites promotes hydrolysis, while maintaining an elevated productive binding capacity throughout conversion is key to preventing hydrolysis slowdown.

09 BIOMASS FUELS↗
DOE OSTI2020

Expression of the Trichoderma reesei expansin-like protein, swollenin, in poplar results in biomass with improved sugar release by enzymatic hydrolysis

Ethanol production from lignocellulosic biomass has been considered an alternative to corn-based ethanol and fossil fuel. However, the secondary cell wall structure prevents efficient degradation of cellulose. Expression of cell wall degrading enzymes has been suggested as one solution to generate suitable feedstocks for lignocellulosic ethanol production. Swollenin (SWO), originating from Trichoderma reesei, disrupts cellulose structure with low-level hydrolytic activity to the glucan chain. Previously, characterization of T. reesei SWO has been carried out in multiple microorganisms and tobacco. This study heterologously overexpressed T. reesei SWO in hybrid poplar (Populus tremula × alba), a promising feedstock for biofuel production, under the control of either the constitutive Cauliflower Mosaic Virus 35S (CaMV 35S) promoter or the putative vascular tissue specific Subterranean Clover Stunt Virus S7 (SCSV) promoter. Transgenic poplar lines with high or moderate SWO expression level showed abnormal growth and reduced biomass production, along with increased glucose and reduced lignin contents. Increased cellulose crystallinity was observed in two transgenic events. This study also investigated the effect of in planta SWO expression on cellulose saccharification efficiency and found that transgenic events improved glucan conversion rates compared to wild type poplar. The results suggest SWO-overexpressing transgenic poplar lines could be a potential feedstock for ethanol production.

09 BIOMASS FUELS↗
DOE OSTI2022

Carbohydrate-aromatic interface and molecular architecture of lignocellulose

Abstract Plant cell walls constitute the majority of lignocellulosic biomass and serve as a renewable resource of biomaterials and biofuel. Extensive interactions between polysaccharides and the aromatic polymer lignin make lignocellulose recalcitrant to enzymatic hydrolysis, but this polymer network remains poorly understood. Here we interrogate the nanoscale assembly of lignocellulosic components in plant stems using solid-state nuclear magnetic resonance and dynamic nuclear polarization approaches. We show that the extent of glycan-aromatic association increases sequentially across grasses, hardwoods, and softwoods. Lignin principally packs with the xylan in a non-flat conformation via non-covalent interactions and partially binds the junction of flat-ribbon xylan and cellulose surface as a secondary site. All molecules are homogeneously mixed in softwoods; this unique feature enables water retention even around the hydrophobic aromatics. These findings unveil the principles of polymer interactions underlying the heterogeneous architecture of lignocellulose, which may guide the rational design of more digestible plants and more efficient biomass-conversion pathways.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Solid–liquid separation of lignocellulosic sugars from biomass by rotating ceramic disc filtration

In many biomass conversion processes, the separation of cellulosic sugars from residual, lignin-rich solids is a critical step, and achieving high recovery yields of sugars by conventional tangential crossflow and vacuum filtration is challenged by the presence of biomass solids, which rapidly foul filters, resulting in decreased throughput. Considering the performance limitations of traditional filtration methods, dynamic filtration, which generates high shear at the membrane surface to decrease fouling, is emerging as a viable alternative for demanding solid–liquid separations. For high solids separations, there is little available information regarding the performance, limitations, and energy consumption of dynamic filtration. To that end, here we characterized the performance of a dynamic filtration module, specifically a rotating ceramic disc (RCD) filter, for the aseptic recovery of cellulosic sugars from biomass solids following pretreatment and enzymatic hydrolysis. We show how RCD rotational velocity and percent biomass solids impact the filter throughput. Additionally, we used computational fluid dynamics (CFD) simulations to estimate the shear rate at the membrane surface and to visualize hydrodynamic profiles within the module. With the combined CFD simulations and experimental results, we estimated the energy demand and operating expenses for a viable dynamic filtration system operating with a lignocellulosic feed slurry. Our results indicate that an RCD filter can achieve ≥95% recovery of sugars and produce a retentate slurry containing 12 wt% insoluble solids with low energy consumption (a 2.2-fold improvement over cross-flow filtration) and low operating costs ($\$$0.06 per kg sugars). These results show a viable path towards operationally reliable, energy efficient, and cost-effective separations of sterilized cellulosic sugars from biomass solids and highlight the potential of dynamic filtration systems for challenging solid–liquid separations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Aqueous buffer solution-induced crystallization competes with enzymatic depolymerization of pre-treated post-consumer poly (ethylene terephthalate) waste

In this paper, the complex relationship between kinetics and substrate morphology during enzymatic depolymerization of melt processed poly(ethylene terephthalate) (PET) is explored and the effects of competing transformations are analyzed. Extruded PET substrates from post-consumer recycled PET (RPET) bottles flakes subjected to enzymatic depolymerization are examined to reveal increases in crystallinity from ~10% post-extrusion to >30% after 3 days of depolymerization as well as increases in glass transition temperature (T g ) from ~66°C to > 80°C. Further investigation into this behavior shows that post-extrusion RPET substrates do not exhibit changes in crystallinity when subjected to dry annealing at 65°C in an oven over 7 days, but they do experience annealing in depolymerization buffer solution with no enzymes at 65°C within 3 days. This difference may be attributed to plasticization of PET in the presence of water, also known as solvent induced crystallization. The impact of this plasticized annealing behavior is demonstrated by subjecting RPET substrates to increasing enzyme-to-substrate loads. As enzyme load increases, overall conversion of substrates increases despite crystallinity also increasing to similar levels regardless of the initial enzyme loading. The competition between depolymerization and crystallization suggests that the rate at which PET substrates are depolymerized at the operational temperature is integral to achieving high conversion to monomeric product. This, in turn, also suggests that savings from lowered enzyme loadings may be more detrimental than helpful in pursuing the most cost-effective recycling systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Integration of pH Control into Chi.Bio Reactors and Demonstration with Small-Scale Enzymatic Poly(ethylene terephthalate) Hydrolysis

Small-scale bioreactors that are affordable and accessible would be of major benefit to the research community. In previous work, an open-source, automated bioreactor system was designed to operate up to the 30 mL scale with online optical monitoring, stirring, and temperature control, and this system, dubbed Chi.Bio, is now commercially available at a cost that is typically 1–2 orders of magnitude less than commercial bioreactors. In this work, we further expand the capabilities of the Chi.Bio system by enabling continuous pH monitoring and control through hardware and software modifications. For hardware modifications, we sourced low-cost, commercial pH circuits and made straightforward modifications to the Chi.Bio head plate to enable continuous pH monitoring. For software integration, we introduced closed-loop feedback control of the pH measured inside the Chi.Bio reactors and integrated a pH-control module into the existing Chi.Bio user interface. We demonstrated the utility of pH control through the small-scale depolymerization of the synthetic polyester, poly(ethylene terephthalate) (PET), using a benchmark cutinase enzyme, and compared this to 250 mL bioreactor hydrolysis reactions. The results in terms of PET conversion and rate, measured both by base addition and product release profiles, are statistically equivalent, with the Chi.Bio system allowing for a 20-fold reduction of purified enzyme required relative to the 250 mL bioreactor setup. Through inexpensive modifications, the ability to conduct pH control in Chi.Bio reactors widens the potential slate of biochemical reactions and biological cultivations for study in this system, and may also be adapted for use in other bioreactor platforms.

09 BIOMASS FUELS↗