High CO2 Concentration Research Articles

Simultaneous Biogas Upgrading and Valuable Chemical Production Using Homoacetogens in a Membrane Biofilm Reactor.

Biogas produced from anaerobic digestion usually contains impurities, particularly with a high content of CO2 (15-60%), thus decreasing its caloric value and limiting its application as an energy source. H2-driven biogas upgrading using homoacetogens is a promising approach for upgrading biogas to biomethane and converting CO2 to acetate simultaneously. Herein, we developed a novel membrane biofilm reactor (MBfR) with H2 and biogas separately supplied via bubbleless hollow fiber membranes. The gas-permeable hollow fibers of the MBfR enabled high H2 and CO2 utilization efficiencies (∼98% and ∼97%, respectively) and achieved concurrent biomethane (∼94%) and acetate (∼450 mg/L/d) production. High-throughput 16S rRNA gene amplicon sequencing suggested that enriched microbial communities were dominated by Acetobacterium (38-48% relative abundance). In addition, reverse transcription quantitative PCR of the functional marker gene formyltetrahydrofolate synthetase showed that its expression level increased with increasing H2 and CO2 utilization efficiencies. These results indicate that Acetobacterium plays a key role in CO2 to acetate conversion. These findings are expected to facilitate energy-positive wastewater treatment and contribute to the development of a new solution to biogas upgrading.

Direct Air Capture (DAC) for Achieving Net-Zero CO2 Emissions: Advances, Applications, and Challenges

Carbon dioxide (CO2), as the primary greenhouse gas, has significant impacts on global climate change, leading to severe and irreversible adverse consequences for ecosystems and human environments. To address the issue of excessive CO2 emissions, efforts in recent years have yielded significant progress in the development of clean energy sources and the promotion of carbon capture, utilization, and storage (CCUS) technologies. Conventional CO2 capture techniques are limited in addressing global atmospheric CO2 excess effectively, as they target only high-concentration CO2 emissions and require implementation at specific emission points. Direct air capture (DAC) technology has emerged as a promising solution due to its flexibility in deployment, avoidance of land competition, and ability to capture legacy CO2 emissions. Additionally, DAC offers opportunities for producing synthetic clean fuels, thereby reducing reliance on traditional fossil fuels and aiding in reducing greenhouse gas emissions. This study provides a comprehensive review of DAC technology, encompassing its principles, technological advancements, real-world applications, challenges, and future research directions. By offering insights into the current state and potential of DAC technology, this study aims to guide global efforts in scaling up DAC deployment, ultimately contributing to achieving global carbon neutrality or even negative emissions.

O-163 The effect of ambient exposure to air pollutants on live birth rates in frozen embryo transfer cycles

Abstract Study question Do air pollutants during oocyte retrieval (OPU) and frozen embryo transfer (FET) affect in vitro fertilization (IVF) outcomes? Summary answer Environmental exposure to increased concentrations of CO either on oocyte retrieval or embryo transfer day negatively influences clinical outcomes in FET cycles. What is known already Exposure to air pollution is linked to adverse perinatal outcomes and reduced fecundity, yet its effect on fertility and IVF cycles is inconclusive. Previous studies explored associations between air pollutant concentrations and IVF outcomes with conflicting results. Nevertheless, few assessed different pollutants’ effects either on oocyte retrieval or embryo transfer days on live birth rates. While Asian and American studies suggest that pollutants affect pregnancy rates, from European studies failed to show meaningful differences in live birth rates. Considering varying pollutant levels globally, we aimed to evaluate their impact on a European population’s fertility outcomes. Study design, size, duration A retrospective cohort study analysed 1960 FET cycles conducted by a university affiliated fertility center in Europe between January 2017 to December 2022. Participants/materials, setting, methods Daily average ambient concentrations of five air pollutants (PM2.5, NO, SO2, CO, and O3) were obtained from an urban air quality monitoring station on the day of oocyte retrieval and the day of FET. Tertiles (T1, T2, T3) of each pollutant served as cut-off levels. Multiple logistic regression analysis assessed associations between pollutant exposure and pregnancy outcomes, adjusted for confounders. Main results and the role of chance Overall pregnancy and live birth rates following FET were 52.55% and 40.71%, respectively. When analysis the results according to air pollutants on the day of FET, ambient exposure to CO was significantly associated with up to 36% lower live birth (T2, OR: 0.64, 95% CI: 0.49—0.84; T3, OR: 0.67, 95% CI: 0.51—0.88; both compared to T1). Higher CO concentrations on the FET day were positively associated with increased miscarriage rates of up to 75% (T2, OR: 1.75, 95% CI: 1.12—2.75; T3, OR: 1.63, 95% CI: 1.04—2.56; both compared to T1). Limitations, reasons for caution The retrospective nature of the study and the omission of various potential covariates including environmental and patient factors that could affect IVF outcomes, limit our findings. Exposure assessment exclusively considered specific IVF days, and reliance on data from one air quality station reduces accuracy. Caution advised when interpreting the results. Wider implications of the findings This study highlights the potential impact of air quality on IVF cycle outcomes. Further investigations are needed to determine vulnerable IVF cycle phases and clarify mechanisms underlying fertility impairment. Trial registration number not applicable

Crystal-Defect-Induced Longer Lifetime of Excited States in a Metal-Organic Framework Photocatalyst to Enhance Visible-Light-Mediated CO2 Reduction.

We report the structural defects in Zr-metal-organic framework (MOFs) for achieving highly efficient CO2 reduction under visible light irradiation. A series of defective Zr-MOF-X (X = 160, 240, 320, or 400) are synthesized by acid-regulated defect engineering. Compared to pristine defect-free Zr-MOF (NNU-28), N2 uptake increases for Zr-MOF-X synthesized with the HAc modulator, producing a larger pore space and Brunauer-Emmett-Teller surface area. The pore size distribution demonstrates that defective Zr-MOF-X exhibits mesoporous structures. Electrochemistry tests show that defective Zr-MOF-X possesses a more negative reduction potential and a higher photocurrent responsive signal than that of pristine NNU-28. Consequently, the defective samples exhibit a significantly higher efficiency in the photoreduction of CO2 to formate. Transient absorption spectroscopies manifest that structural defects modulate the excited-state behivior of Zr-MOF-X and improve the photogenerated charge separation of Zr-MOF-X. Furthermore, electron paramagnetic resonance and in-suit X-ray photoelectron spectroscopy provide additional evidence of the high photocatalytic performance exhibited by defective Zr-MOF-X. Results demonstrate that structural defects in Zr-MOF-X also improve the charge transfer, producing abundant Zr(III) catalytically active sites, exhibiting a slower decay process than defect-free Zr-MOF. The long-lifetime Zr(III) species in defective Zr-MOF-X are fully exposed to a high-concentration CO2 atmosphere, thereby enhancing the photocatalytic efficiency of CO2 reduction.

Kinetic assessment of pulp mill-derived lime mud calcination in high CO2 atmosphere

The chemical pulping of biomass involves the recycling of calcium through the calcination of lime mud, which is mostly comprised of calcium carbonate (CaCO3). Lime mud decomposes under elevated temperatures to generate calcium oxide (CaO) and carbon dioxide (CO2), the kinetics of which are strongly influenced by the CO2 partial pressure and temperature. Oxy-fuel combustion and electrified lime kilns for lime mud calcination are intriguing methods to decarbonize this highly polluting operation within the biomass pulping industry. However, the high CO2 concentration in oxy-fuel and electrified calcination processes alters the kinetics and overall reactivity of lime mud. For the first time, a model-fitting method is used to determine the kinetic parameters for lime mud calcination under a wide range of temperatures (550 °C–1250 °C) and under different concentrations of CO2 (0 %, 15 %, 50 %, and 90 %). A kinetic model is developed that accurately predicts the reaction rates as a function of temperature and CO2 concentration. The apparent activation of energy for lime mud calcination is elevated under a high CO2 environment. Relative to inert gas (N2, Ar), the temperature window for calcination is much smaller under high CO2 environments. The presence of Na in lime mud does not seem to affect calcination under a high CO2 environment. Finally, particle size variation does not have a significant effect on calcination under a high CO2 environment.

Seamless reconstruction and spatiotemporal analysis of satellite-based XCO2 incorporating temporal characteristics: A case study in China during 2015–2020

Carbon dioxide (CO2) is a crucial greenhouse gas, and its concentration and spatiotemporal characteristics are among the principal sources of uncertainty in global warming assessments. Satellite remote sensing is a widely adopted, high-accuracy approach for monitoring atmospheric CO2. However, limited swath width and cloud cover significantly reduce satellite observation coverage. This study addresses the temporal changes in CO2 concentration and utilizes a machine learning-based fusion of multiple data sources to generate daily, full-coverage, 0.05° spatial resolution column-averaged CO2 concentration data for China from 2015 to 2020. Ten-fold cross-validation yielded a determination coefficient R2 of 0.97, root mean square error of 0.92 ppm, and mean absolute error of 0.59 ppm. Compared to other datasets, this study’s dataset exhibits superior accuracy and spatiotemporal detail. Using the produced CO2 concentration data in this study, we conducted a spatiotemporal analysis of CO2 concentrations in China. The results indicate that, in general, the Western region exhibits a higher growth rate in CO2 concentration than the Eastern and Central regions, with areas of lower CO2 concentration experiencing higher growth rates while regions with higher CO2 concentration have lower growth rates. Moreover, the highest increase in CO2 concentration occurred in 2016, with a substantial decrease in CO2 concentration growth observed in 2018. Notably, the reduction in CO2 concentration in the Qinghai-Tibet Plateau region during the summer is considerably smaller than in other regions, possibly due to atmospheric transport from the Indian Peninsula.

Influence of IAA and ABA on maize stem vessel diameter and stress resistance in variable environments.

The plasticity of the xylem and its associated hydraulic properties play crucial roles in plant acclimation to environmental changes, with vessel diameter (Dv) being the most functionally prominent trait. While the effects of external environmental factors on xylem formation and Dv are not fully understood, the endogenous hormones indole-3-acetic acid (IAA) and abscisic acid (ABA) are known to play significant signalling roles under stress conditions. This study investigates how these hormones impact Dv under various environmental changes. Experiments were conducted in maize plants subjected to drought, soil salinity, and high CO2 concentration treatments. We found that drought and soil salinity significantly reduced Dv at the same stem internode, while an elevated CO2 concentration can mitigate this decrease in Dv. Remarkably, significant negative correlations were observed between Dv and the contents of IAA and ABA when considering the different treatments. Moreover, appropriate foliar application of either IAA or ABA on well-watered and stressed plants led to a decrease in Dv, while the application of corresponding inhibitors resulted in an increase in Dv. This finding underscores the causal relationship between Dv and the levels of both IAA and ABA, offering a promising approach to manipulating xylem vessel size.

Analysis and comparison of the membrane-cryogenic hybrid process and multistage membrane process for pre-combustion carbon capture based on the superstructure method

The feed in pre-combustion carbon capture has a high CO2 concentration and high pressure, which gives membrane technology and membrane-based hybrid technology a strong separation driving force. Because the membrane-cryogenic hybrid method can inexpensively achieve the high CO2 purity and recovery, it offers a novel approach in addition to traditional separation methods. Nevertheless, it is uncommon to consider the combination of membrane materials and processes. Furthermore, investigations comparing multistage membrane processes with membrane-cryogenic hybrid processes under identical conditions are lacking. Therefore, this paper establishes separately the membrane-cryogenic hybrid processes and multistage membrane process by the superstructure method, which considers the number of membrane stage, membrane material type, and operating parameters simultaneously. The optimal process structures for three-stage membrane, cryogenic-membrane process, and membrane-cryogenic process are investigated and compared. The influences of membrane price and electricity price on the CO2 capture cost are also investigated. Results shows that the CO2 capture cost of cryogenic + membrane process is the lowest (11.69 $/t CO2) of the studied processes at 96 % CO2 purity and 90 % CO2 recovery. The system structure of the cryogenic + membrane process varies with CO2 purity and recovery. Electricity price has a more important impact on the CO2 capture cost than membrane price under the optimized conditions.

Effects of CO₂ on the occurrence of decompression sickness: review of the literature.

Inhalation of high concentrations of carbon dioxide (CO₂) at atmospheric pressure can be toxic with dose-dependent effects on the cardiorespiratory system or the central nervous system. Exposure to both hyperbaric and hypobaric environments can result in decompression sickness (DCS). The effects of CO₂ on DCS are not well documented with conflicting results. The objective was to review the literature to clarify the effects of CO₂ inhalation on DCS in the context of hypobaric or hyperbaric exposure. The systematic review included experimental animal and human studies in hyper- and hypobaric conditions evaluating the effects of CO₂ on bubble formation, denitrogenation or the occurrence of DCS. The search was based on MEDLINE and PubMed articles with no language or date restrictions and also included articles from the underwater and aviation medicine literature. Out of 43 articles, only 11 articles were retained and classified according to the criteria of hypo- or hyperbaric exposure, taking into account the duration of CO₂ inhalation in relation to exposure and distinguishing experimental work from studies conducted in humans. Before or during a stay in hypobaric conditions, exposure to high concentrations of CO₂ favors bubble formation and the occurrence of DCS. In hyperbaric conditions, high CO₂ concentrations increase the occurrence of DCS when exposure occurs during the bottom phase at maximum pressure, whereas beneficial effects are observed when exposure occurs during decompression. These opposite effects depending on the timing of exposure could be related to 1) the physical properties of CO₂, a highly diffusible gas that can influence bubble formation, 2) vasomotor effects (vasodilation), and 3) anti-inflammatory effects (kinase-nuclear factor and heme oxygenase-1 pathways). The use of O₂-CO₂ breathing mixtures on the surface after diving may be an avenue worth exploring to prevent DCS.

Effects of high concentration of CO2 and/or Cd stress on endogenous hormones and organic acids contents in rice (Oryza sativaL.) seedling roots

Effects of high concentration of CO2 and/or Cd stress on endogenous hormones and organic acids contents in rice (Oryza sativaL.) seedling roots

STUDY ON KINETICS OF BIOMASS PYROLYSIS IN THE FIXED BED. 2. ANALYSIS OF THE RESULTS OF CALCULATING THE THERMAL DECOMPOSITION OF DIFFERENT TYPES OF SOLID FUEL

Using the constructed non-stationary model of the dynamics of the release of volatile substances in a fixed bed [1], extensive numerical studies on three types of biomass pyrolysis Wood Birch, Wood quebracho and Bagasse were performed in order to determine the light gas composition satisfactorily coinciding with experimental data. As a result of research, the following composition of light gas (in mass fractions) was determined for the first time: CO = 0.464, CO2 = 0.101, H2 = 0.01, H2O = 0.23, C6H6.2O0.2 = 0.058, and C1.16H4 = 0.137, which differs from the light gas composition given in modern sources copies [2−4] (in mass fractions): CO = 0.396, CO2 = 0.209, H2 = 0.019, H2O = 0.249, and C6H6.2O0.2 = 0.127 [3], also CO = 0.46, CO2 = 0.08, H2 = 0.015, H2O = 0.23, C6H6.2O0.2 = 0.058, and CH4 = 0.157 [2]. Obtained calculation results for Wood quebracho with refined composition of light gas in terms of dry mass at a temperature of 800 °С: H2 = 15.56 %, CO2 = 7.134 %, CO = 51.4 %, C1.16H4 = 23.71 % (CH4 = 16.6 %, C2H4 = 7.46 %), and C6H6.2O0.2 = 2.21 % — agree satisfactorily with the experimental data. At the exit from the retort, mixed pyrolysis gas composition changes little over time and differs in the values of the gas components from the pyrolysis gases compositions obtained in the elementary volumes of the retort. This discrepancy is explained by the fact that the initial gas mixture contains components obtained at low temperatures with a high content of H2 and CO2 and a low concentration of CO and C1.16H4. Bibl. 20, Fig. 11, Tab. 4.

Magnetite geochemistry as a proxy for metallogenic processes: A study on sulfide-mineralized mafic–ultramafic intrusions peripheral to the Kunene Complex in Angola and Namibia

AbstractTrace element concentrations in magnetite are dictated by the petrogenetic environment and by the physico-chemical conditions during magmatic, hydrothermal, or sedimentary processes. This makes magnetite chemistry a useful tool in the exploration of ore-forming processes. We describe magnetite compositions from Ni-Cu-(PGE)-sulfide mineralized rocks from seven mafic–ultramafic intrusions peripheral to the Mesoproterozoic AMCG (anorthosite-mangerite-charnockite-granite) suite of the Kunene Complex of Angola and Namibia to investigate metallogenic processes through the geochemical characterization of Fe-oxides, which were analyzed in-situ via Electron Probe Microanalysis (EPMA), and Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS). We identified magmatic magnetite, segregated from both a silicate liquid and an immiscible sulfide liquid. Elements like Cr, Co and V suggest that the sulfide-related magnetite segregated from a relatively primitive Fe-rich monosulfide solid solution (MSS). Secondary Cr-rich magnetite appears in intrusions with abundant chromite or Cr-spinel. Two types of hydrothermal magnetite were identified, related to the pervasive replacement of sulfides and a late-stage, low-T fluid circulation event. Magnetite replacing sulfides is associated with serpentinized ultramafic rocks and is preferentially observed in the intrusions with the highest base and precious metal tenors. The high concentration of Ni, Co, Cu, Pd, As and Sb in these grains is corroborated by the identification of micron-size PGE mineral inclusions. We infer that serpentinization during hydrothermal fluid circulation was accompanied by desulphurization of sulfides with metal remobilization and reconcentration to generate magnetite carrying Pd microinclusions. We suggest that the highly serpentinized ultramafic rocks in the Kunene Complex region may become a possible target for economic Ni-Cu-(PGE) mineralization.

Effect of bicarbonate on hydrogen generation by Zero-Valent iron and its impact on generation of acetic acid by seven different inocula

This study demonstrates the substantial role of bicarbonate within a zero-valent iron (ZVI) system in hydrogen evolution, demonstrating that heightened concentration levels notably enhance hydrogen output. The acetic acid performance production of seven different inocula was examined when exposed to ZVI and CO2 as the sole carbon source, separately. Along the seven inocula, river and constructed wetland sludges show the highest production rates at 300 mg/L day−1 and 269 mg/L day−1, respectively. Acetobacterium levels significantly rose in CO2-enriched environments, particularly in river and wetland sludges. Moreover, bacteria attached to ZVI showed accelerated hydrogen consumption and acetic acid production compared to their freely suspended or ZVI-detached counterparts when hydrogen was primarily added externally. This study highlighted the positive effect of high concentrations of soluble CO₂, which acted both as a reactant with ZVI for hydrogen production and as a substrate for homoacetogens, leading to high acetic acid generation.

Influence of CO2 and Dust on the Survival of Non-Resistant and Multi-Resistant Airborne E. coli Strains.

The airborne transmission of bacterial pathogens poses a significant challenge to public health, especially with the emergence of antibiotic-resistant strains. This study investigated environmental factors influencing the survival of airborne bacteria, focusing on the effects of different carbon dioxide (CO2) and dust concentrations. The experiments were conducted in an atmospheric simulation chamber using the non-resistant wild-type E. coli K12 (JM109) and a multi-resistant variant (JM109-pEC958). Different CO2 (100 ppm, 800 ppm, 3000 ppm) and dust concentrations (250 µg m-3, 500 µg m-3, 2000 µg m-3) were tested to encompass a wide range of CO2 and dust levels. The results revealed that JM109-pEC958 exhibited greater resilience to high CO2 and dust concentrations compared to its non-resistant counterpart. At 3000 ppm CO2, the survival rate of JM109 was significantly reduced, while the survival rate of JM109-pEC958 remained unaffected. At the dust concentration of 250 µg m-3, JM109 exhibited significantly reduced survival, whereas JM109-pEC958 did not. When the dust concentration was increased to 500 and 2000 µg m-3, even the JM109-pEC958 experienced substantially reduced survival rates, which were still significantly higher than those of its non-resistant counterpart at these concentrations. These findings suggest that multi-resistant E. coli strains possess mechanisms enabling them to endure extreme environmental conditions better than non-resistant strains, potentially involving regulatory genes or efflux pumps. The study underscores the importance of understanding bacterial adaptation strategies to develop effective mitigation approaches against antibiotic-resistant bacteria in atmospheric environments. Overall, this study provides valuable insights into the interplay between environmental stressors and bacterial survival, serving as a foundational step towards elucidating the adaptation mechanisms of multi-resistant bacteria and informing strategies for combating antibiotic resistance in the atmosphere.

Synergetic Cu0 and Cu+ on the surface of Al2O3 support enhancing methanol steam reforming reaction

The methanol steam reforming (MSR) reaction was a crucial pathway for hydrogen production, with Cu-based catalysts widely applied. It was established that the isolated Cu0-site path and Cu+-site path were responsible for methanol conversion. However, a “Seesaw Effect” existed between the activation of *CH3O and the formation of CO2. Specifically, Cu0 site favored *CH3O activation but facilitated the reverse water gas shift (RWGS) process. Conversely, Cu+ site suppressed CO and promoted CO2 formation but had a reduced ability for *CH3O dehydrogenation. In this work, a Cu0-Cu+ synergy path was proposed, Cu0 sites activate CH3OH into *CH2O, and the subsequent conversion of *CH2O is catalyzed over the Cu+ site. Characterization and calculation results demonstrated that this synergy path subtly avoids two rate-determining steps (*CH3O → *CH2O on Cu+ sites and bi-*CHOO → *CO2 on Cu0 site). The migration of *CH2O from the Cu0 site to Cu+ sites was a critical step in constructing a synergy path. Moreover, MSR performance was governed by the quantity of synergy sites (Cu0/Cu+) and the amount of matched Cu0-Cu+ sites, both of which could be adjusted by varying the Cu loading (1–20%). An optimal 9% Cu enhanced the synergy interaction, with a Cu0/Cu+ ratio of 1.2 and the highest amount of Cu0-Cu+ sites (609.4 μmol/g), giving rise to high methanol conversion and low CO concentration. The discovery in this work provided theoretical guidance for constructing high-performance Cu-based catalysts.

Are Ecological Risk Indices for Trace Metals Relevant for Characterizing Polluted Substrates in the Katangese Copperbelt (DR Congo) and for Assessment of the Performance of Remediation Trials?

This study aims to contribute to the characterization of Katangese Copperbelt’s (DR Congo) mining wastes and soils polluted with trace metals, using pollution indices and direct concentration measurements. This study also evaluated the use of these indices in assessing the success of remediation projects. Data from previous studies and samples collected from six types of discharge and one polluted soil were used to address the first objective. Soil and plant samples were collected at Kipushi and Penga Penga for the second objective. The results reveal very high concentrations of As, Cd, Co, Cu, Mn, Pb, and Zn in all mine tailings and polluted soils, compared with local references. The degree of contamination (DC) values (from 72 to 5440) and potential ecological risk (RI) values (from 549 to 162,091) indicate very high-risk situations associated with polluted discharges and soils. Regarding revegetation trials, the results show lower concentrations and RIs in tree rhizospheres compared with unamended areas at both sites. However, trace metal concentrations are higher in tree rhizospheres compared with local references, and RI values are in the considerable risk range for Penga Penga (RI = 533) and in the very high range (>1500) for Kipushi. Bioconcentration factor values are below 1, indicating low accumulation in roots, wood, and leaves, and low risk of contamination of the trophic chain. In this context, it seems that the pollution indices used are suitable for characterizing pollution and prioritization for remediation. However, their seems unsuitable for assessing the effectiveness of phytotechnology processes based on metal stabilization. Direct plant performance measurements combined with direct measurements of metals in substrates and plants to assess transfer and efficiency are more appropriate.

Dialkyl Carbonate Synthesis Using Atmospheric Pressure of CO2.

Dialkyl carbonates (DRCs) are valuable compounds widely used in the industry. The synthesis of DRC from CO2 has attracted interest as an alternative to the current method, which uses phosgene. However, the reported approaches for DRC synthesis from CO2 requires high-pressure and high-concentration CO2, resulting in elevated costs associated with CO2 purification and manufacturing facilities. In this report, we present an environmentally friendly method for producing DRC from low-concentration and low-pressure CO2 via a dehydration condensation approach without the use of halogenated alkylating agents. This method involves the formation of monoalkyl carbonate [BASE-H][ROC(O)O] using a strong organic base and alcohols, tetraalkyl orthosilicates as dehydrating agents, and CeO2 as the catalyst. Using the method, 39 and 30% of diethyl carbonate yields were accomplished with only 100 and 15 vol % CO2 (CO2/N2 = 15:85) gas bubbling at atmospheric pressure, even under reaction conditions with no large excess of either CO2, alcohol, or dehydration agent.

Relevance and prediction of N2O in small-scale multi-fuel biomass furnaces using primary NOx reduction measures

The relevance of the greenhouse gas N2O was investigated in two small-scale biomass combustion plants, a 30-kW fixed bed and a 70-kW moving grate furnace, both of which use double air staging. Furthermore, the 70-kW furnace was simulated with ideal reactor models, applying a detailed nitrogen chemistry mechanism to gain insights into N2O formation mechanisms that occur during double air-staged combustion.The experimental and simulated results confirm the existence of correlations between CO, NOx and N2O. For all investigated fuels, N2O reached the highest levels (increase of up to 300 %) when high CO and low NOx concentrations were present. Therefore, caution is advised when looking for minimum NOx emissions, due to the risk of having high N2O emissions, an aspect which is often overlooked.A deeper analysis of the N2O formation mechanisms revealed that N2O is mainly generated from HCN in the oxidation zone and it is thermally dissociated at high temperatures. Finally, a comparison between the results of both plants showed that the concern about high N2O emissions at minimum NOx concentrations is not a reactor-specific problem; therefore, it is necessary to ensure that CO and N2O are kept at a low level during NOx reduction with primary measures.

Element composition of several marine macrophytes (Crimea, Black Sea) and correlations with the element abundances in sediments and seawater

The study of the element accumulation in marine plants against the backdrop of permanently increasing environmental pollution is of particular importance due to the participation of these plants in biogeochemical cycles. The element abundances are highly variable and depend on both the macrophyte species and environment. The purpose of this study was to analyze the elemental composition of widespread marine plants of different taxonomic affiliations collected in the same area of the Black Sea coast. The contents of 74 elements in three species of lower (red, brown, green algae) and one species of higher plants (seagrass) were analyzed using inductively coupled plasma mass spectrometry. High contents of most elements were found in the red alga Ceramium ciliatum and in rhizomes of the seagrass Zostera noltei. In C. ciliatum, high metal bioaccumulation factors were found, which are dependent also on their concentration in the environment. Compared to the higher plant, all the macroalgae accumulated increased amounts of As and I. The seagrass proved to be a good concentrator of Mo and Sb, and relatively high contents of Mn, Co, Ni, Zn, Cd and Ir were registered in its leaves. High contents of Mg, S, Ge, Se and Ta were found in the green alga Ulva rigida, and elevated levels of Al, As, Sr, Zr, Ru, Rh, Pd, Ag, Ba and Re were noted in the brown alga Gongolaria barbata. The enrichment factors for most elements in the sediments were well above 1 with respect to both the local Late Pleistocene sediments and the upper continental crust. The strength of correlations between the element contents in the plants and sediments was found to decrease with the specific surface area growth and appeared to have a lower asymptotic limit of the sediments–seawater correlation strength.

Are physiological and ecosystem-level tipping points caused by ocean acidification? A critical evaluation

Abstract. Ocean acidification (OA) is predicted to cause profound shifts in many marine ecosystems by impairing the ability of calcareous taxa to calcify and grow and by influencing the physiology of many others. In both calcifying and non-calcifying taxa, ocean acidification could further impair the ability of marine life to regulate internal pH and thus metabolic function and/or behaviour. Identifying tipping points at which these effects will occur for different taxa due to the direct impacts of ocean acidification on organism physiology is difficult because they have not adequately been determined for most taxa nor for ecosystems at higher levels. This is due to the presence of both resistant and sensitive species within most taxa. However, calcifying taxa such as coralline algae, corals, molluscs, and sea urchins appear to be most sensitive to ocean acidification. Conversely, non-calcareous seaweeds, seagrasses, diatoms, cephalopods, and fish tend to be more resistant or even benefit from the direct effects of ocean acidification, though the effects of ocean acidification are more subtle for these taxa. While physiological tipping points of the effects of ocean acidification either do not exist or are not well defined, their direct effects on organism physiology will have flow-on indirect effects. These indirect effects will cause ecological tipping points in the future through changes in competition, herbivory, and predation. Evidence for indirect effects and ecological change is mostly taken from benthic ecosystems in warm temperate–tropical locations in situ that have elevated CO2. Species abundances at these locations indicate a shift away from calcifying taxa and towards non-calcareous taxa at high-CO2 concentrations. For example, lower abundance of corals and coralline algae and higher covers of non-calcareous macroalgae, often turfing species, are often found at elevated CO2. However, there are some locations where only minor changes or no detectable changes occur. Where ecological tipping points do occur, it is usually at locations with naturally elevated mean pCO2 concentrations of 500 µatm or more, which also corresponds to just under that concentration where the direct physiological impacts of ocean acidification are detectable in the most sensitive taxa in laboratory research (coralline algae and corals). Collectively, the available data support the concern that ocean acidification will most likely cause ecological change in the near future in most benthic marine ecosystems, with tipping points in some ecosystems as low as 500 µatm pCO2. However, further research is required to more adequately quantify and model the extent of these impacts in order to accurately project future marine ecosystem tipping points under ocean acidification.