Production Of Bio-based Chemicals Research Articles

Integrated Biphasic Electrochemical Oxidation of Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid

Production of biobased platform chemicals and polymers via electrochemical routes enables the direct utilization of electrical energy from renewable sources. To date, the integration of electrochemical conversions in process chains remains largely unexplored, and the reactions are often studied using synthetic solutions. This work demonstrates the biphasic electro-oxidation of hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) and couples the electrochemical oxidation with the biphasic dehydration of fructose to HMF. The integrated approach eradicates the intermediate HMF purification as the HMF-rich organic product phase is fed directly into the electrochemical flow-cell reactor. Here, HMF is extracted into the aqueous phase and oxidized to FDCA on a Ni(OH)2/NiOOH catalyst in a 0.1 M KOH solution at pH 13. The FDCA then remains in the aqueous phase, enabling direct recirculation of the HMF-containing organic phase. We demonstrate a FDCA yield of close to 80% with a feed from HMF synthesis. Further, we analyze the influence of the phase ratio (organic to aqueous) and current density for biphasic electrochemical oxidation. By adjusting the gap width, we were able to decrease the average cell voltage from 7 V down to 3 V at a current density of 30 mA cm–1. This work presents a promising integrated process for the synthesis of green platform chemicals and provides insight into biphasic solutions in electrochemical conversions.

Scalable aqueous-phase fabrication of reduced graphene oxide nanofiltration membranes by an integrated roll-to-roll (R2R) process

Economic fractionation of multicomponent biomass-derived streams is a key challenge in biobased fuels and chemicals production. Kraft black liquor (BL) is generated at ∼1 billion tons/yr globally from biomass pulping and contains ∼15 wt% total solids including lignin, hemicellulose fragments, and inorganics. Membrane-based BL concentration is attractive but challenged by low solute rejections and poor stability in BL, which combines alkaline pH (∼13), high dissolved solids content (15+ wt%) and high temperature (70–85 °C). Here we discuss the scaled fabrication and characterization of reduced graphene oxide (rGO) nanofiltration membranes by slot die coating on a roll-to-roll (R2R) with integrated vacuum filtration. We obtain high-quality 90 × 30 cm rGO membranes (referred to as “R2R-rGO membranes” in this work) with ∼100 nm average thickness supported on porous poly(ethersulfone) (PES) sheets, and an effective area of 2700 cm2. We present characterizations of their microstructure and uniformity as mapped over large areas by scanning electron microscopy (SEM), ellipsometry, adhesion test and X-ray photoelectron spectroscopy (XPS). The constructed ellipsometry model for the rGO membrane/PES substrate composite was successfully applied to 48 different locations of the R2R-rGO membranes. The R2R-rGO membranes showed >98% lignin rejection with a steady state flux of ∼12 LMH at 50 bar in a 15.7 wt% total solids (TS) kraft BL stream at 72 °C and 2–3 gal/min crossflow rates. Slot die coating on a R2R platform with integrated vacuum filtration can enable rapid fabrication of high-quality GO membranes at scale without organic solvents or volatile organic compounds.

Enhanced production of 5-hydroxymethyl-2-furfurylamine from biobased HMF by a robust triple mutant ω-transaminase biocatalyst in a betaine:malonic acid − water medium

5-Hydroxymethyl-2-furfurylamine (HMFA) is a key furan-based compound for manufacturing curing agents, additives, medicines and agrochemicals. It is also a good solvent for production of valuable biobased chemicals and biofuels. HMFA can be obtained by biological amination of 5-HMF by ω-transaminase (AT) from Aspergillus terreus. In this work, one stable triple mutant of AT ω-transaminase (HNILGD) was obtained via consensus mutagenesis. The half-life (t1/2) of the mutant AT ω-transaminase [G292D (glycine to aspartate), H210N (histidine to asparagine) I77L (isoleucine to leucine)] was 1.43- and 2.14-fold higher than that of the wild-type AT ω-transaminase at 35 °C and 50 °C, respectively. Recombinant E. coli containing HNILGD ω-transaminase could aminate high load of 5-HMF (800 mM) to HMFA in the aqueous media [HMFA yield 92 %, selectivity 100 %]. In deep eutectic solvent betaine:malonic acid (5 wt%), HNILGD cells converted 900 mM 5-HMF to HMFA with a yield of 97.4 %. Moreover, d-fructose was chemoenzymatically transformed to HMFA in the betaine:malonic acid − water. 36.0 g/L of d-fructose was dehydrated into 5-HMF (63.9 % yield) with betaine:malonic acid (5 wt%) at 180 °C for 1 h, and the formed 5-HMF was further aminated to HMFA by HNILGD cells with amine donor d-alanine (d-Ala-to-5-HMF molar ratio 16:1) at 35 °C and pH 8.0 after 24 h in betaine:malonic acid (5 wt%), obtaining a productivity of 0.433 g HMFA per g d-fructose [cal. 0.96 g HMFA/(g d-fructose-derived 5-HMF)]. A significant enhancement of HMFA production from biobased d-fructose-derived HMF by a robust triple mutant ω-transaminase biocatalyst was successfully developed in a betaine:malonic acid − water system.

Providing Insights into the Markets for Bio-Based Materials with BioMAT

Knowledge-based policy making in the field of bio-based economy needs two elements: (i) a monitoring system for assessing the historical developments of bio-based industry and (ii) foresight capacities to provide prospects for the bio-based industry in the future and how it can contribute to achieving different targets. However, significant knowledge gaps in both areas exist, especially regarding the markets of bio-based materials in general and bio-based chemicals in particular. Against this background, a new consistent framework for the representation of the value chains of bio-based materials in the EU and its Member States is developed, i.e., BioMAT. This article aims to present the BioMAT database which (i) is used to track historical developments in the markets for bio-based chemicals and the demand for feedstocks and (ii) enables the construction of the BioMAT model to make future projections. The developed BioMAT database compilation procedure is described in detail. Results reveal that the production of bio-based chemicals in the EU reached 43 million tons or 14% of the total output volume of the organic chemical industry in 2018. The main application of bio-based chemicals is biofuels, followed by agrochemicals and surfactants. The main feedstocks are plant oils and starch.

Optimisation of alkaline pretreatment of spent coffee grounds for microbial oil production by Cryptococcus curvatus

In a world of finite resources, the transition to a sustainable post-fossil resources economy is essential. Within this concept, spent coffee grounds (SCGs) could be used for the production of bio-based chemicals, biopolymers and value-added products. Lipids and phenolics were initially extracted from SCGs. Alkaline pretreatment of the remaining SCGs solids has been optimised in this study via Central Composite Design to maximise lignin removal and overall sugar to polysaccharide conversion yield. The optimal SCGs pretreatment conditions were 0.06% (w/v) NaOH and 99.5 °C resulting in 35.7% lignin removal at 60 min pretreatment duration with low glucan and hemicellulose losses (ca. 2.5%). Enzymatic hydrolysis of the remaining SCGs alkaline pretreated solids resulted in 79.4% glucan, 74.5% mannan and 54.8% hemicellulose hydrolysis yield. The SCGs hydrolysate was used as fermentation feedstock in bioreactor cultures of Cryptococcus curvatus resulting in 36.1 g/L microbial oil with 0.25 g/g yield and 0.41 g/(L∙h) productivity. The total dry weight reached 62.7 g/L corresponding to 57.5% (w/w) intracellular lipid content. The microbial oil was rich in oleic acid (55.6%) followed by palmitic acid (18.9%) and stearic acid (14.0%). The proposed process led to the production of 7.81 g microbial oil per 100 g antioxidant- and oil-free SCGs.

Increasing the atom economy of glucose fermentation for bioethanol production in Rubisco-based engineered Escherichia coli

Feedstock accounts for a major portion of bio-based chemical production. While tremendous progress has been made in cellulosic ethanol production over the last few decades, direct conversion of CO2 to biofuels has been under-investigated. Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) is an enzyme that can fix CO2 by catalyzing the carboxylation. A Rubisco-based Escherichia coli has been constructed that is capable of simultaneously converting glucose and CO2 to bioethanol. Practically homo-fermentative ethanol production can be achieved by FB295A (E. coli BL21(DE3) Δzwf ΔldhA Δfrd ΔpflB harboring pdc, adhB, rbcLS, and prk) in 60 h where the bioethanol yield, concentration, percentage/fermentation product, and CO2 emission/ethanol production were 2.3 ± 0.2 mol/molglucose, 256 ± 19 mM, 100 %, and 0.13 ± 0.02 molCO2/molEtOH, respectively. By a subculture to the second generation, the overall fermentation time was shortened within 30 h and therefore, the bioethanol productivity was improved to 7.1 ± 0.5 mmol⋅L−1⋅h−1 while maintaining an apparent ethanol yield of 2.4 ± 0.1 mol/molglucose. The performance of FB295A reached 100 % theoretical for in situ CO2 recycling. This study presents a new bioethanol production pathway based on in situ CO2 recycling.

Transcriptional regulation in key metabolic pathways of Actinobacillus succinogenes in the presence of electricity

The potential of renewable energy application via direct electrode interaction for the production of bio-based chemicals is a promising technology. The utilization of extracellular energy in pure culture fermentations aims in intracellular redox balance regulation in order to improve fermentation efficiency. This work evaluates the impact of a bioelectrochemical system in succinic acid fermentation and the metabolic response of Actinobacillus succinogenes. The metabolic pathway regulation of A. succinogenes was evaluated via RNA expression of the key enzymes that participate in TCA cycle, pyruvate metabolism and oxidative phosphorylation. The genes that were significantly overexpressed in BES compared to non-BES were phosphoenolpyruvate carboxykinase (0.4-fold change), inorganic pyrophosphatase (2.3-fold change) and hydrogenase (2.2-fold change) and the genes that were significantly underexpressed were fumarase (−0.94-fold change), pyruvate kinase (−6.9-fold change), all subunits of fumarate reductase (−2.1 to −1.17-fold change), cytochromes I and II (−1.25 and −1.02-fold change, respectively) and two C4-carboxylic acid transporters.

Increasing lysine level improved methanol assimilation toward butyric acid production in Butyribacterium methylotrophicum

BackgroundMethanol, a promising non-food fermentation substrate, has gained increasing interest as an alternative feedstock to sugars for the bio-based production of value-added chemicals. Butyribacterium methylotrophicum, one of methylotrophic-acetogenic bacterium, is a promising host to assimilate methanol coupled with CO2 fixation for the production of organic acids, such as butyric acid. Although the methanol utilization pathway has been identified in B. methylotrophicum, little knowledge was currently known about its regulatory targets, limiting the rational engineering to improve methanol utilization.ResultsIn this study, we found that methanol assimilation of B. methylotrophicum could be significantly improved when using corn steep liquor (CSL) as the co-substrate. The further investigation revealed that high level of lysine was responsible for enhanced methanol utilization. Through the transcriptome analysis, we proposed a potential mechanism by which lysine confers improved methylotrophy via modulating NikABCDE and FhuBCD transporters, both of which are involved in the uptake of cofactors essential for enzymes of methanol assimilation. The improved methylotrophy was also confirmed by overexpressing NikABCDE or FhuBCD operon. Finally, the de novo synthetic pathway of lysine was further engineered and the methanol utilization and butyric acid production of B. methylotrophicum were improved by 63.2% and 79.7%, respectively. After an optimization of cultivation medium, 3.69 g/L of butyric acid was finally achieved from methanol with a yield of 76.3%, the highest level reported to date.ConclusionThis study revealed a novel mechanism to regulate methanol assimilation by lysine in B. methylotrophicum and engineered it to improve methanol bioconversion to butyric acid, culminating in the synthesis of the highest butyric acid titer reported so far in B. methylotrophicum. What’s more, our work represents a further advancement in the engineering of methylotrophic-acetogenic bacterium to improve C1-compound utilization.Graphical

Integrative omics analyses of the ligninolytic Rhodosporidium fluviale LM-2 disclose catabolic pathways for biobased chemical production

BackgroundLignin is an attractive alternative for producing biobased chemicals. It is the second major component of the plant cell wall and is an abundant natural source of aromatic compounds. Lignin degradation using microbial oxidative enzymes that depolymerize lignin and catabolize aromatic compounds into central metabolic intermediates is a promising strategy for lignin valorization. However, the intrinsic heterogeneity and recalcitrance of lignin severely hinder its biocatalytic conversion. In this context, examining microbial degradation systems can provide a fundamental understanding of the pathways and enzymes that are useful for lignin conversion into biotechnologically relevant compounds.ResultsLignin-degrading catabolism of a novel Rhodosporidium fluviale strain LM-2 was characterized using multi-omic strategies. This strain was previously isolated from a ligninolytic microbial consortium and presents a set of enzymes related to lignin depolymerization and aromatic compound catabolism. Furthermore, two catabolic routes for producing 4-vinyl guaiacol and vanillin were identified in R. fluviale LM-2.ConclusionsThe multi-omic analysis of R. fluviale LM-2, the first for this species, elucidated a repertoire of genes, transcripts, and secreted proteins involved in lignin degradation. This study expands the understanding of ligninolytic metabolism in a non-conventional yeast, which has the potential for future genetic manipulation. Moreover, this work unveiled critical pathways and enzymes that can be exported to other systems, including model organisms, for lignin valorization.

INFLUENCE OF BIOMASS PRETREATMENT ON SUBSEQUENT PYROLYSIS AND HYDRODEOXYGENATION IN BIO-BASED TRANSPORT FUELS AND CHEMICALS PRODUCTION: A CRITICAL REVIEW

The present article aims to review the influence of various biomass pretreatments on the production of bio-based transportation fuel and chemicals via pyrolysis and hydrodeoxygenation (HDO). The article includes the influence of different thermochemical pretreatments such as dry torrefaction (DT), wet torrefaction (WT), steam explosion treatment (SET), hot water extraction (HWE), acid treatment (ACT), and alkali treatment (AKT) on bio-oil yield and bio-oil properties. HDO primarily includes dehydration, hydrogenolysis, decarbonylation, and hydrogenation. HDO can be classified based on stages (single and two-stage HDO), reaction pressure (high and low), and hydrogen presence (ex situ and in situ). The recent developments, advantages, and drawbacks associated with different types of HDO processes have been included. The article includes recent studies on designing various catalysts based on HDO conversion of different bio-oil compositions or selective model compounds to targeted bio-based products. The various biomass pretreatments impact the concentration of certain families of organic compounds present in bio-oil. Hence, the present review article also includes recommendations of specific biomass pretreatments for various HDO catalysts designed for selective model compounds or different bio-oil compositions. Few praiseworthy techno-economic analysis (TEA) studies on the influence of different biomass pretreatments on the minimum selling price (MSP) of bio-based products obtained at various production stages have been discussed.

Bamboo as a Cost-Effective Source of Renewable Carbon for Sustainable Economic Development in Low- and Middle-Income Economies

Low- and middle-income countries have tremendous potential for renewable energy production, including production of renewable carbon from locally prolific crops. In this work, bamboo endemic to West Africa (Bambusa vulgaris) was studied as a feedstock for the production of renewable sugars as the gateway to the local production of biofuels and bio-based chemical products. The effectiveness of delignification and amorphization pretreatments was evaluated, with the observation that quantitative (97 ± 4%) sugar yields could be obtained with a rapid initial hydrolysis rate (82 ± 4 mg g−1 h−1) but only when amorphization was performed following delignification. Experimental measurements and further characterization using 13C solid state nuclear magnetic resonance (NMR) helped establish the importance of amorphization and delignification and explained why the order of these treatments determined their effectiveness. The economics of the bamboo-based process were compared with those projected for corn stover, selected as a well-studied benchmark crop. Because of the higher bamboo growth rate compared with corn stover and the effectiveness of the pretreatment, the projected net present value (NPV) of the bamboo biorefinery was positive ($190 MM, U.S.), whereas the corn biorefinery projected to negative NPV (−$430 MM, U.S.). A socially sustainable framework for deployment of a bamboo biorefinery in a low- or middle-income economy was then proposed, guided by the principle of local ownership and stakeholder buy-in. The findings presented here motivate further investment in development of bamboo cultivation and conversion to sugars as a rapid route to decarbonization of low- and middle-income economies.

Thermo-chemical conversion of cucumber peel waste for biobased energy and chemical production

Thermo-chemical conversion of cucumber peel waste for biobased energy and chemical production

Mind the Pulp: Environmental and economic assessment of a sugar beet pulp biorefinery for biobased chemical production

Sugar beet pulp, a byproduct from sugar beet refining, is used by farmers as fertilizer or sold as animal feed. Both options underestimate the potential of sugar beet pulp as a platform to produce specialty and bulky chemicals as a promising pathway for sustainable biochemicals – mind the pulp. This study proposes a biorefinery concept to produce food additives (pectin-derived oligosaccharides) and bulky chemicals (terephthalic acid). Since the biorefinery has a low technology readiness level (TRL = 1), it is relevant to evaluate the feasibility of this biorefinery concept to provide guidance (at an early stage) on the environmental and economic advantages and limitations. For this purpose, the life cycle assessment and techno-economic assessment frameworks are used to assess the environmental impact and economic performance of the biobased terephthalic acid, respectively. Moreover, environmental impacts are accounted for in economic terms using different monetary valuation methods (environmental prices, Ecovalue12, and Ecotax). The environmental impact of biobased terephthalic acid was higher in most impact categories than the fossil counterpart, depending on the selected allocation approach (mass vs economic). The economic feasibility of the proposed biorefinery is highly dependent on the pectin-derived oligosaccharides market price and the valorization of byproducts (humins and levulinic acid). The selection of the monetary valuation method is critical for monetizing environmental impacts when comparing biobased against fossil-based alternatives.

Segregationally stabilised plasmids improve production of commodity chemicals in glucose-limited continuous fermentation

BackgroundThe production of chemicals via bio-based routes is held back by limited easy-to-use stabilisation systems. A wide range of plasmid stabilisation mechanisms can be found in the literature, however, how these mechanisms effect genetic stability and how host strains still revert to non-productive variants is poorly understood at the single-cell level. This phenomenon can generate difficulties in production-scale bioreactors as different populations of productive and non-productive cells can arise. To understand how to prevent non-productive strains from arising, it is vital to understand strain behaviour at a single-cell level.The persistence of genes located on plasmid vectors is dependent on numerous factors but can be broadly separated into structural stability and segregational stability. While structural stability refers to the capability of a cell to resist genetic mutations that bring about a loss of gene function in a production pathway, segregational stability refers to the capability of a cell to correctly distribute plasmids into daughter cells to maintain copy number. A lack of segregational stability can rapidly generate plasmid-free variants during replication, which compromises productivity.ResultsCitramalate synthase expression was linked in an operon to the expression of a fluorescent reporter to enable rapid screening of the retention of a model chemical synthesis pathway in a continuous fermentation of E. coli. Cells without additional plasmid stabilisation started to lose productivity immediately after entering the continuous phase. Inclusion of a multimer resolution site, cer, enabled a steady-state production period of 58 h before a drop in productivity was detected. Single-cell fluorescence measurements showed that plasmid-free variants arose rapidly without cer stabilisation and that this was likely due to unequal distribution of plasmid into daughter cells during cell division. The addition of cer increased total chemical yield by more than 50%.ConclusionsThis study shows the potential remains high for plasmids to be used as pathway vectors in industrial bio-based chemicals production, providing they are correctly stabilised. We demonstrate the need for accessible bacterial ‘toolkits’ to enable rapid production of known, stabilised bacterial production strains to enable continuous fermentation at scale for the chemicals industry.

Genetic Code Expansion in Pseudomonas putida KT2440.

Pseudomonas putida KT2440 is an emerging microbial chassis for biobased chemical production from renewable feedstocks and environmental bioremediation. However, tools for studying, engineering, and modulating protein complexes and biosynthetic enzymes in this organism are largely underdeveloped. Genetic code expansion for the incorporation of unnatural amino acids (unAAs) into proteins can advance such efforts and, furthermore, enable additional controls of biological processes of the strain. In this work, we established the orthogonality of two widely used archaeal tRNA synthetase and tRNA pairs in KT2440. Following the optimization of decoding systems, four unAAs were incorporated into proteins in response to a UAG stop codon at 34.6-78% efficiency. In addition, we demonstrated the utility of genetic code expansion through the incorporation of a photocross-linking amino acid, p-benzoyl-l-phenylalanine (pBpa), into glutathione S-transferase (GstA) and a chemosensory response regulator (CheY) for protein-protein interaction studies in KT2440. This work reported the successful genetic code expansion in KT2440 for the first time. Given the diverse structure and functions of unAAs that have been added to protein syntheses using the archaeal systems, our research lays down a solid foundation for future work to study and enhance the biological functions of KT2440.

Replication Origin Deletion Enhances Poly(3-Hydroxybutyrate-co-3-Hydroxyvalerate) Synthesis in Haloarchaea.

Although the use of multiple replication origins for chromosome replication has been widely characterized in haloarchaea, whether it is possible to manipulate the chromosome copy number by their genetic engineering is not known, and how it would affect the cell functioning is poorly understood. Here, we demonstrate that deletion of the three active chromosomal origins in Haloferax mediterranei remarkably reduces its DNA amounts and ploidy numbers. Consequently, the mutant strain H. mediterranei Δ123 is more sensitive to UV and mitomycin C. Surprisingly, the cell size increases by 21.2%, and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) production in shake flask culture enhances from 7.23 to 8.11 g/L in ΔEPSΔ123, although there is also a decrease in cell growth. In this mutant, the chromosomal copy number decreases, whereas the pha-encoding pHM300 megaplasmid copy number increases. Moreover, our transcriptome analysis reveals that the genes involved in primary metabolisms are significantly downregulated in ΔEPSΔ123, whereas those responsible for starch utilization and precursor supplying for PHBV monomers are upregulated. This indicates that more energy and carbon flux is redirected from primary metabolism to PHBV synthesis, thereby enhancing its PHBV accumulation. These findings may therefore provide a rational design to enhance PHBV synthesis by simply tuning the replication origins to modulate the chromosome/megaplasmid copy number ratio and subsequently influence cellular metabolism and physiological functions. IMPORTANCE The haloarchaeon Haloferax mediterranei is a potential producer of PHBV (100% biodegradable plastic) from inexpensive carbon sources. We previously reported that H. mediterranei possessed three active chromosomal origins and, when these origins were deleted, a dormant origin was activated to initiate the replication of chromosome. In this context, in the present study, we first found a close connection between replication initiation and PHBV accumulation. We describe the potential industrial advantages of the strain H. mediterranei ΔEPSΔ123, which includes the enlargement of cell volume by 21.2% and enhancement of PHBV production by 11.2%. We further reveal the possible mechanism that contributes to the greater PHBV production in the ΔEPSΔ123 strain. Overall, we provide here a conceptual advance in the field of synthetic biology by modulating chromosome replication to improve the production of bio-based chemicals.

Metal sulfate-catalyzed methanolysis of cellulose at high solid loadings: Heterogeneous degradation kinetics and levulinate synthesis

Increasing efforts have been devoted to the production of bio-based chemicals from high solid content of renewable biomass to pursue optimal process efficiency and economics. In this study, the preparation of methyl levulinate (ML) by metal sulfate-catalyzed methanolysis from high solid content of cellulose was investigated. When the cellulose loading was 15%, 38.67% of ML yield can be obtained under the optimum reaction conditions. Al2(SO4)3 can be reused more than five times while maintaining high activity in the process. The characterization of cellulose particles confirmed that cellulose particles shrunk over the reaction time. The heterogeneous degradation kinetics of high solid content of cellulose in methanol could be explained by a shrinking core model. High solid loadings led to a decrease of the reaction rate constants of methanolysis. Using cellulose with a small particle size can improve the methanolysis reaction rate. The study also proposed comprehensive reaction pathways for ML production from high solid content of cellulose. To elucidate the methanolysis mechanism, an assessment of density functional theories for the calculation of glucose methanolysis at the molecular level is presented. All these results can inspire the development of ML synthesis technology through methanolysis from renewable biomass with high solid loadings.

Integrating Torrefaction of Pulp Industry Sludge with Anaerobic Digestion to Produce Biomethane and Volatile Fatty Acids: An Example of Industrial Symbiosis for Circular Bioeconomy

Industrial symbiosis, which allows the sharing of resources between different industries, could help to improve the overall feasibility of bio-based chemicals production. In that regard, this study focused on integrating the torrefaction of pulp industry sludge with anaerobic digestion. More specifically, anaerobic digestion (AD) of pulp sludge-derived torrefaction condensate (TC) was studied to evaluate the biomethane and volatile fatty acid (VFA) potential. The torrefaction condensate produced at 275 and 300 °C was used in AD. The volatile solid content (VS) was 6.69 and 9.01% for the condensate produced at 275 and 300 °C, respectively. The organic fraction of TC mainly contained acetic acid, 2-furanmethanol, and syringol. The methane yield was in the range of 481–772 mL/g VS for the mesophilic and 401–746 mL/g VS for the thermophilic process, respectively. The VFA yield was in the range of 1.1 to 3.4 g/g VS for mesophilic and from 1.5 to 4.7 g/g VS in thermophilic conditions, when methanogenesis was inhibited. Finally, pulp sludge TC is a feasible feedstock to produce platform chemicals like VFA. However, at higher substrate loading, signs of process inhibition were observed because of the relatively increasing concentration of microbial inhibitors

Valorization of cheese whey to lactobionic acid by a novel strain Pseudomonas fragi and identification of enzyme involved in lactose oxidation

BackgroundEfficient upgrading of inferior agro-industrial resources and production of bio-based chemicals through a simple and environmentally friendly biotechnological approach is interesting Lactobionic acid is a versatile aldonic acid obtained from the oxidation of lactose. Several microorganisms have been used to produce lactobionic acid from lactose and whey. However, the lactobionic acid production titer and productivity should be further improved to compete with other methods.ResultsIn this study, a new strain, Pseudomonas fragi NL20W, was screened as an outstanding biocatalyst for efficient utilization of waste whey to produce lactobionic acid. After systematic optimization of biocatalytic reactions, the lactobionic acid productivity from lactose increased from 3.01 g/L/h to 6.38 g/L/h in the flask. In batch fermentation using a 3 L bioreactor, the lactobionic acid productivity from whey powder containing 300 g/L lactose reached 3.09 g/L/h with the yield of 100%. Based on whole genome sequencing, a novel glucose dehydrogenase (GDH1) was determined as a lactose-oxidizing enzyme. Heterologous expression the enzyme GDH1 into P. putida KT2440 increased the lactobionic acid yield by 486.1%.ConclusionThis study made significant progress both in improving lactobionic acid titer and productivity, and the lactobionic acid productivity from waste whey is superior to the ever reports. This study also revealed a new kind of aldose-oxidizing enzyme for lactose oxidation using P. fragi NL20W for the first time, which laid the foundation for further enhance lactobionic acid production by metabolic engineering.Graphical

Fabrication of Z-scheme CdS/H5PMo10V2O40/g-C3N4 for the photocatalytic depolymerization of lignin into aromatic monomers

As the most abundant resource composed of aromatic groups in nature, lignin harbors significant potential for the production of bio-based fuels and chemicals. In recent years, solar-driven photocatalysis with its mild, low cost and environmental benign, has been employed for lignin depolymerization. Herein, we designed a Z-scheme CdS/H5PMo10V2O40/g-C3N4 (CdS/HPA-2/CN) photocatalyst via hydrothermal method for the photocatalytic depolymerization of lignin. The prepared CdS/HPA-2/CN presents a nanoflower-like morphology with the average diameter of ∼600 nm. With the presence of electron-mediated HPA-2, CdS/HPA-2/CN exhibits the enhanced separation and transfer capacity of photogenerated charge carriers through Z-scheme mechanism. Result shows that the total yield (Y) of vanillin and vanillic acid from lignin depolymerization over optimized CdS/HPA-2/CN can reach to 32.7 mg/g lignin in DMF/formic acid (v/v = 40/10) for 4 h. Reusability experiment of optimized CdS/HPA-2/CN displays that Y (26.5 mg/g lignin) can still reach to 81.0% of initial one after three cycles. Qualitative analysis of depolymerized products reveals that most components are aromatic compounds with the dominant products of vanillin and vanillic acid. Evidence also shows that photocatalysis promotes the reaction and small molecular products increased significantly after depolymerization. In addition, mechanism experiments and electron spin resonance tests exhibit that h+, ·O2− and ·OH took part in lignin depolymerization together and the effect sequence was ·O2− > ·OH > h+. In this work, as an electron mediator, HPA-2 provides the inspiration for construction of Z-scheme heterojunction, and CdS/HPA-2/CN exhibits enormous potential in lignin depolymerization by photocatalysis.