Low O2 Concentrations Research Articles

Preparation of AIE Functional Single-Chain Polymer Nanoparticles and Their Application in H2 O2 Detection through Intermolecular Heavy-Atom Effect.

Single-chain polymer nanoparticles (SCNPs) are soft matter constructed by intrachain crosslinks, with promising prospects in detection and catalysis. Herein, a fluorescent core (SCNPs) with aggregation-induced emission (AIE) is prepared, applying for H2 O2 detection through intermolecular heavy-atom effect. In detail, the SCNPs precursors are synthesized by ring-opening copolymerization. Then the SCNPs are prepared by intramolecularly cross-linking via olefin metathesis. Imitating the structure of AIE dots, SCNPs are encapsulated by H2 O2 -responsive polymers. Probably due to the stable secondary structure of SCNPs, the obtained micelles show stable fluorescence performance. Furthermore, as the heavy-atom, tellurium is introduced into the carriers to construct the heavy-atom effect. In this micelle-based system, the SCNPs act as the fluorescent core, and the stimuli-responsive polymer acts as the carrier and the fluorescent switch. The hydrophilicity of the tellurium-containing segment is affected by the concentration of H2 O2 , resulting in a change in the distance from the SCNPs, which ultimately leads to a change in the fluorescence intensity. Furthermore, tellurium is particularly sensitive to H2 O2 , which can detect low concentrations of H2 O2 . The SCNPs are merged with AIE materials, with the hope of exploring new probe designs.

Crossing and selection of Chlamydomonas reinhardtii strains for biotechnological glycolate production

As an alternative to chemical building blocks derived from algal biomass, the excretion of glycolate has been proposed. This process has been observed in green algae such as Chlamydomonas reinhardtii as a product of the photorespiratory pathway. Photorespiration generally occurs at low CO2 and high O2 concentrations, through the key enzyme RubisCO initiating the pathway via oxygenation of 1.5-ribulose-bisphosphate. In wild-type strains, photorespiration is usually suppressed in favour of carboxylation due to the cellular carbon concentrating mechanisms (CCMs) controlling the internal CO2 concentration. Additionally, newly produced glycolate is directly metabolized in the C2 cycle. Therefore, both the CCMs and the C2 cycle are the key elements which limit the glycolate production in wild-type cells. Using conventional crossing techniques, we have developed Chlamydomonas reinhardtii double mutants deficient in these two key pathways to direct carbon flux to glycolate excretion. Under aeration with ambient air, the double mutant D6 showed a significant and stable glycolate production when compared to the non-producing wild type. Interestingly, this mutant can act as a carbon sink by fixing atmospheric CO2 into glycolate without requiring any additional CO2 supply. Thus, the double-mutant strain D6 can be used as a photocatalyst to produce chemical building blocks and as a future platform for algal-based biotechnology.Key Points• Chlamydomonas reinhardtii cia5 gyd double mutants were developed by sexual crossing• The double mutation eliminates the need for an inhibitor in glycolate production• The strain D6 produces significant amounts of glycolate with ambient air only

Impact of the Birth Transition on Striated Muscle Function in Normal Development

Considerable changes are expected in the regulation of myocardial and limb skeletal muscle perfusion from the pre‐ to post‐natal condition based on changes in gravitational force, work load, and arterial O2 content. Yet the impact of birth on the growth and function of microvasculature in striated muscle is poorly understood. Our objective was to assess resting and maximal microvascular flow in the cardiac left ventricle (LV; with high workload before and after birth), and biceps femoris (BF; hindlimb muscle with little workload before birth). We hypothesized that resting flow in the fetus exceeds that in the neonate because of low fetal arterial O2 content, but that flow reserve is greater in the neonate in order to support ambulation. We expected this increase in reserve to be greater in skeletal than myocardial muscle.Fetuses (N=8) were instrumented at 130 d gestational age (dGA, birth is at 146 d) and studied exteriorized from the uterus at 135 dGA. Lambs (N=8) were instrumented 2 d after birth and studied at 5 d. Instrumentation included arterial, venous, and left atrial catheters for systemic pressure monitoring, arterial blood sampling, and drug delivery; and an inflatable occluder around the descending thoracic aorta. Myocardial perfusion (Q) in mL/min/g of tissue was assessed by transthoracic contrast echocardiography at rest, during adenosine‐induced hyperemia, and during combined hyperemia and increased perfusion pressure produced by transient constriction of the postductal aorta. Work was determined by the product of heart rate and perfusion pressure. Hindlimb BF muscle Q was assessed at rest, and during contractile work produced by electrostimulation (2 Hz, 10 mA). Differences were assessed by the Mann‐Whitney U‐test. One fetus and one lamb were excluded from analysis because of abnormal blood gasses at the time of study.At rest, LV myocardial Q was 2‐fold higher in fetuses than neonates (Fig 1A), as was Q normalized to work; whereas, O2 delivery was similar between groups (Fig 1B). Maximal flow during hyperemia followed a similar pattern, with fetal Q, as well as Q per work, exceeding that in the neonate by a factor of 7, whereas maximal O2 delivery per work was similar between age groups. Skeletal muscle (BF) flow in the fetus was highly variable both at rest and during exercise. Median resting Q, resting O2 delivery, and exercised flow were all at least 5‐fold higher in the fetus than neonate, however the difference only reached statistical significance for resting flow (Fig 1A,B). Exercise O2 delivery was similar between ages. Flow reserve was similar between the fetus and neonate in both myocardium and skeletal muscle (Fig 1C).At rest, elevated flow in the fetal LV supported similar levels of O2 delivery per work as found in the newborn. Surprisingly, there was a tendency for increased O2 delivery in the fetal skeletal muscle compared to the newborn; we speculate that this reflects differences in regulation of non‐nutritive flow between the ages studied. Overall, the results of this study suggest that despite the dramatically different physiological circumstances between the fetus and newborn, microvascular growth is regulated to preserve similar levels of flow reserve in both.

Study of ambient temperature oxidation in low metamorphic coal and the oxidation mechanism

In view of the problem where there is abnormal continuous CO exceedance in the tailgate corner without any sign of spontaneous combustion associated with the mining of low metamorphic coal seam, both desorption experiments and ambient temperature oxidation experiments were carried out, and the ambient temperature oxidation characteristics and its mechanism were studied. The results demonstrate that the original coal seam from which the experimental coal sample was taken, does not contain CO and CO2, and the coal sample can oxidize at ambient temperature. The O2 consumption rate, CO and CO2 production rate is not directly related to the particle size. Low O2 concentration can inhibit but not eliminate the ambient temperature oxidation. In addition to the active sites of coal itself, the ambient temperature oxidation reaction rate is also affected by the inhibitory substances produced by the reaction itself. R1(△CO/△O2), R2(△CO2/△O2) and R3(△CO/△CO2) indexes are mostly not affected by the changes of particle size, O2 concentration and oxidation rates, and the ambient temperature oxidation of coal is dominated by a single mechanism. The ambient temperature oxidation mechanism is also theoretically deduced. The research will have important significance for controlling the abnormal exceedance of CO.

Regulatory Crosstalk between Physiological Low O2 Concentration and Notch Pathway in Early Erythropoiesis.

Physiological low oxygen (O2) concentration (<5%) favors erythroid development ex vivo. It is known that low O2 concentration, via the stabilization of hypoxia-induced transcription factors (HIFs), intervenes with Notch signaling in the control of cell fate. In addition, Notch activation is implicated in the regulation of erythroid differentiation. We test here if the favorable effects of a physiological O2 concentration (3%) on the amplification of erythroid progenitors implies a cooperation between HIFs and the Notch pathway. To this end, we utilized a model of early erythropoiesis ex vivo generated from cord blood CD34+ cells transduced with shHIF1α and shHIF2α at 3% O2 and 20% O2 in the presence or absence of the Notch pathway inhibitor. We observed that Notch signalization was activated by Notch2R–Jagged1 ligand interaction among progenitors. The inhibition of the Notch pathway provoked a modest reduction in erythroid cell expansion and promoted erythroid differentiation. ShHIF1α and particularly shHIF2α strongly impaired erythroid progenitors’ amplification and differentiation. Additionally, HIF/NOTCH signaling intersects at the level of multipotent progenitor erythroid commitment and amplification of BFU-E. In that, both HIFs contribute to the expression of Notch2R and Notch target gene HES1. Our study shows that HIF, particularly HIF2, has a determining role in the early erythroid development program, which includes Notch signaling.

Effect of oxidative torrefaction on particulate matter emission from agricultural biomass pellet combustion in comparison with non-oxidative torrefaction

Torrefaction could improve the fuel properties and reduce the operating costs. However, the particulate matter (PM) emission behavior during the torrefied pellet combustion remains unknown. In this work, cotton stalk was torrefied at a temperature of 220–300 °C with a O2 concentration of 0–21%. The torrefied pellet was burned out and PM emission behavior was investigated using a Dekati low-pressure impactor. The results show that oxidative torrefaction leads to notable decreases of H/C and O/C ratios, which makes the fuel properties similar to coals. The heating value is significantly improved and sensitive to the torrefaction temperature. Both non-oxidative and oxidative torrefaction give rise to considerable increase in the yield of PM10. The main composition of PM1 changed from KCl to K2SO4 due to the substantial release of Cl during torrefaction. Meanwhile, Ca and K contents in PM1-10 are generally high, implying that the presence of oxygen can facilitate the transformation of alkali and alkaline-earth metals into coarse particles. The torrefaction temperature at around 260 °C with a low O2 concentration of 0–6% are the optimal torrefaction operation conditions to produce good quality torrefied cotton stalk pellet with respect to high heating value and low PM emission in later combustion application.

Mixotrophic Cultivation of Microalgae Using Biogas as the Substrate.

Biogas utilization through biotechnology represents a potential and novel technology. We propose the microalgal mixotrophic cultivation to convert biogas to microalgae-based biodiesel, in which methanotroph was co-cultured to convert CH4 to organic intermediate (and CO2) for microalgal mixotrophic growth. This study constructed a co-culture of Methylocystis bryophila (methanotroph) and Scenedesmus obliquus (microalgae) with biogas feeding. Compared with the single culture of S. obliquus, higher microalgal biomass but a lower chlorophyll concentration was observed. The organic metabolism-related genes were upregulated, verifying microalgal mixotrophic growth. The stoichiometric calculation of M. bryophila culture shows that M. bryophila tends to release organic matter rather than grow under a low O2 content. M. bryophila rarely grew under five different light intensities, indicating that M. bryophila acts as a biocatalyst in the co-culture. The organic intermediate released by methanotroph increased the maximum biomass of microalgal culture, accelerated nitrogen absorption, accumulated more monounsaturated fatty acids, and improved the adaptation to light. The co-culture of microalgae and methanotroph may provide new opportunities for microalgae-based biodiesel production using biogas as a substrate.

Study on the formation of ultrafine particulate matter (PM) during char combustion in a wet oxy-combustion atmosphere

In this study, the effect of H2O on the formation of ultrafine particulate matter (PM) in an oxy-combustion atmosphere with various O2 contents of 21%, 27%, and 33% was investigated in a high-temperature drop tube furnace at 1800 K. The combustion-generated ultrafine PM was collected by a 14-stage electrical low-pressure impactor for analyzing the mass- and number-based particle size distribution (PSD). The element composition of ultrafine PM was identified using inductively coupled plasma mass spectrometry. The results indicated that all the primary peaks of the mass- and number-based PSD of ultrafine PM were located nearby 0.2 μm under various O2/CO2/H2O atmospheres. As H2O content increased, both the mass and the number yield of ultrafine PM decreased initially and then increased, with an inflection point at 5% H2O content. The inhibitory effects of 5% H2O content on the formation of ultrafine PM at 21%, 27% and 33% O2 contents were −12.3%, −28.5%, and −33.5%, respectively, while the promoting effects of 30% H2O content were 105.4%, 54.0%, and 7.0%, respectively. Thus, the yield of ultrafine PM in the oxy-combustion atmosphere with low O2 content fluctuates more with the increase of H2O, and was more sensitive to H2O. Moreover, with the increase of H2O and O2 content, the average mass of ultrafine PM exhibited an enlarged tendency. And high H2O content (30%) evidently favored the enrichment of alkali and alkaline earth metals (e.g. Na, K, Ca and Mg), as well as Fe in PM0.1, whereas the volatilization of Si and Al was suppressed.

Fungal diversity and mycotoxins detected in maize stored in silo-bags: a review.

Silo-bags are hermetic storage systems that inhibit fungal growth because of their atmosphere with low humidity, as well as low pH and O2 concentrations, and a high CO2 concentration. If a silo-bag with stored maize loses its hermetic nature, it favors the development of fungi and the production of mycotoxins. To the best of our knowledge, this is the first review on the diversity of fungal species and mycotoxins that were reported in maize stored under the environmental conditions provided by silo-bags. The genera Penicillium, Aspergillus and Fusarium were found more frequently, whereas Acremonium spp., Alternaria sp., Candida sp., Cladosporium sp., Debaryomyces spp., Epiconum sp., Eupenicillium spp., Eurotium sp., Eurotium amstelodami, Hyphopichia spp., Hyphopichia burtonii, Moniliella sp., Wallemia sp. and genera within the orden Mucorales were reported less recurrently. Despite finding a great fungal diversity, all of the studies focused their investigations on a small group of toxins: fumonisins (FBs), aflatoxins (AFs), deoxynivalenol (DON), zearalenone (ZEA), patulin (PAT), toxin T2 (T2) and ochratoxin (OT). Of the FBs, fumonisin B1 and fumonisin B2 presented higher incidence percentages, followed by fumonisin B3 . Of the AFs, the only one reported was aflatoxin B1. The mycotoxins DON, ZEA and OT were found with lower incidences, whereas PAT and T2 were not detected. Good management practices of the silo-bags are necessary to achieve a hermetically sealed environment, without exchange of gases and water with the external environment during the storage period. © 2022 Society of Chemical Industry.

Try or Die: Dynamics of Plant Respiration and How to Survive Low Oxygen Conditions.

Fluctuations in oxygen (O2) availability occur as a result of flooding, which is periodically encountered by terrestrial plants. Plant respiration and mitochondrial energy generation rely on O2 availability. Therefore, decreased O2 concentrations severely affect mitochondrial function. Low O2 concentrations (hypoxia) induce cellular stress due to decreased ATP production, depletion of energy reserves and accumulation of metabolic intermediates. In addition, the transition from low to high O2 in combination with light changes—as experienced during re-oxygenation—leads to the excess formation of reactive oxygen species (ROS). In this review, we will update our current knowledge about the mechanisms enabling plants to adapt to low-O2 environments, and how to survive re-oxygenation. New insights into the role of mitochondrial retrograde signaling, chromatin modification, as well as moonlighting proteins and mitochondrial alternative electron transport pathways (and their contribution to low O2 tolerance and survival of re-oxygenation), are presented.

Effect of the Oxygen Concentration and Temperature on Thermal Decomposition of N2O in an Inert Gas.

Nitrous oxide (N2O) is one of the greenhouse gases that contribute to global warming. But, there are few methods for controlling N2O directly. It is essential to reduce N2O to solve environmental problems. In this study, we investigate the O2 concentration dependence of N2O decomposition under an argon-based gas mixture in a high-temperature thermal reactor. The gas concentrations are calculated using CHEMKIN. The results confirm that more N2O is converted to N2 or NO at lower O2 concentrations. Therefore, the conversion process is hindered by increasing the O2 concentration. We propose a modified parameter of N2O decomposition, and it is employed in the CHEMKIN calculations. With the modified parameter, the experimental results are in a similar tendency to the calculated results.

Effect of Oxygen and Carbon Dioxide Concentration on the Quality of Minikiwi Fruits after Storage

The rapid increase in the production of hardy kiwi fruit (A. arguta) since the beginning of the 21st century has required the development of new cultivation technologies and postharvest handling procedures in order to extend the supply and transport of the fruit to distant markets. Fruit storage focuses on the inhibition of ripening processes regulated by ethylene activity or respiration. Both of these are effectively regulated by appropriate concentrations of O2 and CO2 in the atmosphere surrounding the fruit. In this study, the effect of the concentration of both gases in the cold room on the physico-chemical indices of fruit quality, i.e., mass loss, firmness, soluble solids and monosaccharides content, titratable acidity and acid content, and color of the peel was evaluated. Studies have shown that high CO2 concentrations inhibit ripening processes more effectively than low O2 concentrations. Softening of berries as well as an increase in soluble solid contents was recorded during the first 4 weeks of storage in the fruit. However, the increase in monosaccharides was fairly stable throughout the study period. The increase in soluble solids content as well as the loss of acidity were more strongly determined by CO2 than O2, although the acid content in a 10% CO2 atmosphere did not change. Additionally, the fruits were greener after storage in 10% CO2, but the weakness was skin dulling and darkening. The results indicate that the use of high CO2 concentrations (5–10%) effectively inhibits ripening processes in fruit. After 12 weeks of storage, the fruit was still not suitable for direct consumption, which suggests that the storage period can be extended further.

Photochemistry of HOSO2 and SO3 and Implications for the Production of Sulfuric Acid.

Sulfur trioxide (SO3) and the hydroxysulfonyl radical (HOSO2) are two key intermediates in the production of sulfuric acid (H2SO4) on Earth's atmosphere, one of the major components of acid rain. Here, the photochemical properties of these species are determined by means of high-level quantum chemical methodologies, and the potential impact of their light-induced reactivity is assessed within the context of the conventional acid rain generation mechanism. Results reveal that the photodissociation of HOSO2 occurs primarily in the stratosphere through the ejection of hydroxyl radicals (•OH) and sulfur dioxide (SO2). This may decrease the production rate of H2SO4 in atmospheric regions with low O2 concentration. In contrast, the photostability of SO3 under stratospheric conditions suggests that its removal efficiency, still poorly understood, is key to assess the H2SO4 formation in the upper atmosphere.

Modeling the time evolution of the dissociation fraction in low-pressure CO2 plasmas

The time evolution of the CO2 dissociation fraction in pulsed discharges is studied through kinetic modeling. The simulations are compared against experimental data obtained in pulsed DC glow and radio-frequency discharges, operated with currents of about 40 mA and powers of 40 W, sustained under low gas pressures (< 600 Pa). The model is used to analyse the experimental trends associated with different pulsed configurations, namely different combinations of pulse duration and delay between pulses. The results validate the chemical module used in this work and reveal the importance of electronically excited states, in particular CO(a3Π), to describe the evolution of CO2(X1Σ+) and CO(X1Σg+) densities. In particular, it is shown that CO(a3Π) can promote CO2 formation for increasing concentrations of O2 due to bimolecular reactions such as CO(a3Π) + O2(X3Σg−) → CO2(X1Σ+) + O(3P). At the same time, for low concentration of O2 the CO2 dissociation fraction can be stimulated through CO(a3Π) + CO2(X1Σ +) → 2CO(X1Σg+) + O(3P). It is also found that the pulse parameters influence the concentration of O2(X3Σg−) by favouring or limiting oxygen atomic recombination during the afterglow. Overall, this work addresses reaction mechanisms often overlooked in the CO2 plasma-based reforming literature, while confirming that electronically excited states play a key role in describing the dissociation fraction in CO2 plasmas operated under low pressure conditions.

Identifying Site-Specific Superoxide and Hydrogen Peroxide Production Rates From the Mitochondrial Electron Transport System Using a Computational Strategy.

Mitochondrial reactive oxygen species (ROS) play important roles in cellular signaling; however, certain pathological conditions such as ischemia/reperfusion (I/R) injury disrupt ROS homeostasis and contribute to cell death. A major impediment to developing therapeutic measures against oxidative stress-induced cellular damage is the lack of a quantitative framework to identify the specific sources and regulatory mechanisms of mitochondrial ROS production. We developed a thermodynamically consistent, mass-and-charge balanced, kinetic model of mitochondrial ROS homeostasis focused on redox sites of electron transport chain complexes I, II, and III. The model was calibrated and corroborated using comprehensive data sets relevant to ROS homeostasis. The model predicts that complex I ROS production dominates other sources under conditions favoring a high membrane potential with elevated nicotinamide adenine dinucleotide (NADH) and ubiquinol (QH2) levels. In general, complex I contributes to significant levels of ROS production under pathological conditions, while complexes II and III are responsible for basal levels of ROS production, especially when QH2 levels are elevated. The model also reveals that hydrogen peroxide production by complex I underlies the non-linear relationship between ROS emission and O2 at low O2 concentrations. Lastly, the model highlights the need to quantify scavenging system activity under different conditions to establish a complete picture of mitochondrial ROS homeostasis. In summary, we describe the individual contributions of the electron transport system complex redox sites to total ROS emission in mitochondria respiring under various combinations of NADH- and Q-linked respiratory fuels under varying workloads.

One-Pot Approach to Fe2+ /Fe3+ -Based MOFs with Enhanced Catalytic Activity for Fenton Reaction.

Smart theragnostic nanoplatforms exhibit great promise in clinical tumor treatment. The Fe-based Fenton reaction in tumor sites may generate reactive oxygen species to kill cancer cells with negligible side effects on normal tissues. However, its efficiency and duration are limited by the low intracellular concentration of H2 O2 , weak acidicity of tumor tissue, and low catalytic activity of conventional Fenton reagents. Herein, a facile strategy is proposed to efficiently overcome these obstacles. An efficient enzymatic/Fenton-starvation nanoreactor PMs loaded with glucose oxidase and perfluoropentane (PGPMs) is constructed through synthesizing methoxy-PEG-carboxymethy-modified iron (Fe2+ /Fe3+ )-based metal-organic frameworks (PMs), followed by loading glucose oxidase (GOx) and perfluoropentane (PFP). PGPMs accumulating in the tumor tissue exhibit tumor microenvironment-responsive biodegradable behavior and unusual catalytic activity for Fenton reaction advantageous over Fe3+ -based MOFs. Meanwhile, encapsulation of GOx into PGPMs further significantly increases the catalytic activity for Fenton reaction and also induces starvation therapy. PGPMs also exhibit considerable capabilities of ultrasound and tumor microenvironment-responsive T2 MR imaging applicable for contrast-enhanced diagnosis. Both in vitro and in vivo studies demonstrate the great diagnostic and therapeutic potentials of this nanoreactor in tumor.

Microaerobic Lifestyle at Nanomolar O2 Concentrations Mediated by Low-Affinity Terminal Oxidases in Abundant Soil Bacteria.

ABSTRACTHigh-affinity terminal oxidases (TOs) are believed to permit microbial respiration at low oxygen (O2) levels. Genes encoding such oxidases are widespread, and their existence in microbial genomes is taken as an indicator for microaerobic respiration. We combined respiratory kinetics determined via highly sensitive optical trace O2 sensors, genomics, and transcriptomics to test the hypothesis that high-affinity TOs are a prerequisite to respire micro- and nanooxic concentrations of O2 in environmentally relevant model soil organisms: acidobacteria. Members of the Acidobacteria harbor branched respiratory chains terminating in low-affinity (caa3-type cytochrome c oxidases) as well as high-affinity (cbb3-type cytochrome c oxidases and/or bd-type quinol oxidases) TOs, potentially enabling them to cope with varying O2 concentrations. The measured apparent Km (Km(app)) values for O2 of selected strains ranged from 37 to 288 nmol O2 liter−1, comparable to values previously assigned to low-affinity TOs. Surprisingly, we could not detect the expression of the conventional high-affinity TO (cbb3 type) at micro- and nanomolar O2 concentrations but detected the expression of low-affinity TOs. To the best of our knowledge, this is the first observation of microaerobic respiration imparted by low-affinity TOs at O2 concentrations as low as 1 nM. This challenges the standing hypothesis that a microaerobic lifestyle is exclusively imparted by the presence of high-affinity TOs. As low-affinity TOs are more efficient at generating ATP than high-affinity TOs, their utilization could provide a great benefit, even at low-nanomolar O2 levels. Our findings highlight energy conservation strategies that could promote the success of Acidobacteria in soil but might also be important for as-yet-unrevealed microorganisms.IMPORTANCE Low-oxygen habitats are widely distributed on Earth, ranging from the human intestine to soils. Microorganisms are assumed to have the capacity to respire low O2 concentrations via high-affinity terminal oxidases. By utilizing strains of a ubiquitous and abundant group of soil bacteria, the Acidobacteria, and combining respiration kinetics, genomics, and transcriptomics, we provide evidence that these microorganisms use the energetically more efficient low-affinity terminal oxidases to respire low-nanomolar O2 concentrations. This questions the standing hypothesis that the ability to respire traces of O2 stems solely from the activity of high-affinity terminal oxidases. We propose that this energetically efficient strategy extends into other, so-far-unrevealed microbial clades. Our findings also demonstrate that physiological predictions regarding the utilization of different O2 concentrations based solely on the presence or absence of terminal oxidases in bacterial genomes can be misleading.

Demonstration of a Top-Lit Updraft Based Pyrolytic Burner with Low Emission Operation and Automatic Process Control

In this study, a small-scale (4.7 kWfuel) biomass burner based on “top-lit updraft” (TLUD) technology with automatic process control was developed for process heat generation. The combustion experiments were performed using wood pellets to gain more insights on the process, its repeatability and the behaviors of the emitted gaseous and particulate emissions under different combustion phases. The emission values were compared with similar small-scale combustion technologies as well as the emission limits defined in official regulations. The results showed that the average emissions (based on standardized 13 vol. % O2 content in the dry flue gas (STP)) over the entire process from start-up to switch-off were 29.4 mg/m3 for CO, 80 mg/m3 for NOx, and 3.6 mg/m3 for total particle matter (TPM) measured within the hot gas. These results were below the official limits for wood-fueled small-scale systems. The developed process control approach resulted in very low residual O2 content in the flue gas (approx. 2 vol. %), high flue gas temperatures and repetition accuracy. Thus, the process offers potential for further development in terms of process control, scale-up, and application in different areas.

Influence of air staging strategies on flue gas sensible heat losses and gaseous emissions of a wood pellet boiler: An experimental study

An effective air staging strategy is of great importance for achieving low emissions and sensible heat losses through flue gas extraction. In cases where a commercially available system needs to be optimised, often the only viable measure is the modification of process parameters. In this work, the aim is to (1) Discover a combination of the most suitable process parameters based on a multi-criteria decision-making method and (2) To unveil relevant correlations between the two process parameters under study (PA/SA ratio and excess air), emissions and combustion temperatures. A modified commercial small-scale hot water wood pellet boiler was installed into a laboratory heating system. Nine different cases have been addressed within a parametric study, differing in the PA/SA ratio and overall excess air. Emissions, temperatures inside the combustion chamber and the flow rate of air entering the combustion chamber were measured. A low PA/SA ratio of 0.53 (54.7% reduction from factory settings), combined with a low O2 concentration in the flue gases of 5.26% (39.8% reduction from factory settings), and the elimination of infiltration air resulted in a simultaneous reduction of NOx and CO emissions by 14.4% and 93.9% respectively and a flue gas sensible heat loss reduction of 31.6%.

Spectroelectrochemical investigation of the glyoxal oxidase activation mechanism

Glyoxal oxidase (GLOX) is an extracellular source of H2O2 in white-rot secretomes, where it acts in concert with peroxidases to degrade lignin. It has been reported that GLOX requires activation prior to catalytic turnover and that a peroxidase system can fulfill this task. In this study, we verify that an oxidation product of horseradish peroxidase, the radical cation of 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid), is an activator for GLOX. A spectroelectrochemical cell was used to generate the activating radical species, to continuously measure its concentration, and to simultaneously measure the catalytic activity of GLOX based on its O2 consumption. The results show that GLOX can undergo multiple catalytic turnovers upon activation and that activity increases with the activator concentration. However, we also found that the ABTS cation radical can serve as an electron acceptor which becomes visible in the absence of O2. Furthermore, GLOX activity is highly restrained by the naturally occurring, low O2 concentration. We conclude that GLOX is indeed an auxiliary enzyme for H2O2 production in white-rot secretomes. Its turnover rate is strongly regulated by the availability of O2 and the radical generating activity of peroxidases present in the secretome, which acts as a feedback loop for GLOX activity.