Low CO2 Concentrations Research Articles

Pressure dependence of electrochemical CO2 reduction to ethanol in flow cell

The electroreduction of carbon dioxide (CO2RR) to ethanol is an ideal approach for using released CO2 and producing fuel. The impact of CO2 partial pressure (PCO2) on ethanol synthesis was significant but was not well understood. The present study investigates the pressure dependence of ethanol formation from 0.25 bar to 15 bar in a high-pressure flow cell. It displayed a volcano type. The PCO2 associated with the peak Faradaic efficiency (FE) of ethanol increased as the current density increased. The pressure peak values were 0.5 bar, 0.75 bar at 100, 200, and 300 mA cm−2, respectively. Ethanol formation kinetics was affected by adsorbate-adsorbate interactions and the physical blocking of active sites on catalysts with excess CO2. Besides, ethanol synthesis using the configured flue gas, i.e., low-concentration CO2 (VCO2 = 5–30%), was realized via system pressurization from 5 to 20 bar at 200 mA cm−2. By optimizing the combination of CO2 concentration and total pressure (Ptot), the fuel efficiency (FE) of ethanol was maximized to 26.5%. This study uncovers the ideal CO2 partial pressure for ethanol synthesis under industrial current densities, hence presenting potential industrial applications for utilizing flue gas directly in ethanol production.

Na-doped Li4SiO4 as an efficient sorbent for low-concentration CO2 capture at high temperature: Superior adsorption and rapid kinetics mechanism

Lithium silicate (Li4SiO4) sorbent has garnered attention in CO2 capture due to its high theoretical adsorption capacity and fast kinetics. However, its adsorption capacity and kinetics were hindered by low CO2 concentration. Improving adsorption performance of Li4SiO4 at low CO2 concentration has become the key to industrial application. In this work, high-activity Na-doped Li4SiO4 with controllable active substance Li3NaSiO4 was achieved. The influences of raw materials ratios on the CO2 adsorption performance were systematically investigated. When RLi/Si=4.05:1 and RNa/Si=0.15:1, the sample exhibited the highest adsorption capacity of 32.28 wt% with an equilibrium time of 29 min, and a superior stable capacity of 31.09 wt% in 15 cycles. Importantly, the double exponential fitting revealed that LiNaCO3 accelerated the ion diffusion rate and real-time adsorption processes showed Li3NaSiO4 expedited surface chemical reaction rate. Based on these, a novel Na2CO3 eutectic doping mechanism was proposed. The active substance Li3NaSiO4, generated through Na doping, along with its product formed from the reaction with CO2, molten LiNaCO3, acted synergistically to improve adsorption performance by accelerating surface chemical reaction rate and ion diffusion rate. Compared with other doped Li4SiO4, the sorbent prepared in this work demonstrated competitive adsorption performance, providing theoretical and technical support for the large-scale production of high-activity Li4SiO4.

Porous bi-functional ionic liquid-grafted metal–organic framework for diluted CO2 cycloaddition reaction

Direct utilization of low-concentration CO2 is of importance to mitigate the global warming and reduce energy consumption. Herein, a new bi-functional ionic liquid-grafted material was fabricated for CO2/N2 selectivity and diluted CO2 cycloaddition reaction. Following the preparation of 1-carboxymethyl-3-methoxy ethyl-imidazolium chloride ([CmMOEim]Cl) containing carboxyl and ether group, MIL-53(Al) was used for directly chemical grafting of the ionic liquid to obtain [CmMOEim]Cl@MIL-53(Al). CO2 capture capacity of [CmMOEim]Cl@MIL-53(Al) reached up to 70 cm3 CO2/g sorbent at 25 °C and 0.1 MPa, which was higher than that of two individual components. Cyclopropyl carbonate of 97 % yield was obtained at 110 °C, 3 MPa of initial 50 vol% CO2/N2 pressure and 4 h with 2.4 wt% [CmMOEim]Cl@MIL-53(Al)-0.4 under solventless and co-catalyst-free condition. Various terminal cyclocarbonates were synthesized with above 90 % yield. In addition, the heterogeneous catalyst was separated from reaction system by simple centrifugation and the yield of cyclopropyl carbonate was higher than 90 % after 12 cycles owing to the chemical grafting of [CmMOEim]Cl on MIL-53(Al).

Carbonic anhydrase immobilized on Zn(II)-geopolymer membrane for CO2 capture

Inorganic membranes are widely used in water filtration and gas separation due to their many advantages. In this work, we proposed an innovative approach for enzyme immobilization using a geopolymer based tubular inorganic membrane (GM) as a carrier. The GM has abundant mesopores, excellent mechanical strength and strong stability for continuous flow systems in biocatalysis field, and carbonic anhydrase (CA) was successfully loaded into this mesoporous membrane using adsorption-crosslinking method, relying on the excellent ion exchange capacity of geopolymers and large number of hydroxyl groups naturally present in the membrane's mesopores. The results of the immobilization experiments showed that the immobilized enzyme composite membrane (GZnM-CA) could achieve 63.7% enzyme recovery. This is a significant improvement over the enzyme recoveries obtained on organic membranes which are typically less than 50%. In stability tests, the membrane retained more than 90.0% relative activity after 10 consecutive uses. In the CO2 capture assay, the CO2 capture efficiency developed dramatically under the catalytic of GZnM-CA. To our delight, the membrane has excellent separation capability for CO2 gas mixtures, especially at low CO2 concentrations, achieving 99.90% CO2 removal rate, and this result can be maintained for a long period of time in a pH = 8.0 environment.

Facile synthesis of polymer-derived K, Ti co-doped Li4SiO4-based sorbent for efficient and stable post-combustion CO2 capture

Li4SiO4-based sorbent has received considerable attention in the past decade due to its attractive intrinsic merits for post-combustion CO2 capture. To meet the practical applications, the development of Li4SiO4-based sorbent with more higher capture performances by an easy preparation route is desired. In this work, a facile and novel polymer-derived ceramic strategy (PDCs) was used to yield the high-performance Li4SiO4-based sorbent. The phase evolution and microstructure development of Li4SiO4 during the polymer-to-ceramic conversion were investigated. The CO2 capture performances of obtained Li4SiO4 sorbent were studied by comparing with other methods. To further improve its capture performances, Ti(EtO)4-K2CO3 were doped in Li4SiO4, and the enhancement mechanism was surveyed. Results indicate that high-purity Li4SiO4 sorbent with high adsorption properties can be prepared by PDCs route at 700 ℃, and it possessed similar synthesis and adsorption kinetics with the Li4SiO4 prepared by sol–gel method. The 5 mol% Ti doping exhibited a dual enhancement of adsorption capacity and cyclic stability for Li4SiO4 sorbent. Especially, due to the positive synergistic effect of the K, Ti co-doping, the obtained K/5TE-PDCs-Li4SiO4 sorbent showed ultra-high adsorption capacity (0.303 gCO2/gsorbent), ultra-fast adsorption rate (0.219 gCO2/(gsorbent·min)) and ultra-stable cycling performance at a low CO2 concentration (15 vol%). These efficient and stable CO2 capture performances prove the huge potential of polymer-derived K, Ti co-doped Li4SiO4-based sorbent for practical industrial applications.

Cobalt-silver catalyst with low metal content for highly efficient synthesis of methyl glycolate through synergistic effect

The Co-Agx/TiO2 catalysts with low mass content of Co and Ag were synthesized through the impregnation method and investigated for dimethyl oxalate (DMO) hydrogenation to methyl glycolate (MG). Remarkably, the Co-Ag0.7/TiO2 catalyst with an Ag concentration of 0.7 wt%, exhibited an impressive yield of MG of ∼94.4 %, surpassing the yields of MG obtained with Co/TiO2 (∼54 %) and Ag0.7/TiO2 (∼69 %) catalysts. Various characterizations elucidated that the exceptional catalytic performance of Co-Ag0.7/TiO2 can be ascribed to the synergy between Co and Ag, resulting in the formation of AgCoO2 as high active site can improve the adsorption and activation of DMO and H2 on catalyst surface. Additionally, the doping of a small amount of Ag regulated the contents of Lewis acidic and Brønsted acidic sites, leading to a high conversion of DMO and selectivity of MG. Furthermore, the excellent MG yield and long-term stability (at least 200 h) facilely obtained over our catalyst under mild reaction conditions guarantee a feasible prospect in the industrial application. This study not only unraveled the superior performance of the Co-Ag synergistic catalyst, but also carried significant implications for developing catalysts with low-content in DMO hydrogenation to MG.

Nanocrystalline sodium mordenite as an efficient low-concentration CO2 adsorbent

Systematic control of the crystal size and morphology of zeolites to enhance their CO2 adsorption performance is of great importance from both environmental and economic perspectives. Here we report the seeded synthesis of sodium mordenite (Na-MOR) with a Si/Al ratio of 4.9 and an average crystal length and width of 70 and 40 nm, respectively, using γ-aminobutyric acid as a crystal growth inhibitor in the absence of any organic structure-directing agent (OSDA). This nanozeolite shows an unprecedented CO2 capacity of 1.58 mmol g−1 under dynamic direct air capture (DAC) conditions at 25 °C, which is approximately 40 % greater than the value (1.15 mmol g−1) of the best zeolite adsorbent (an unidentified OSDA-directed Na-MOR (Si/Al = 5.0) zeolite with Na+ enrichment in 8-ring side pockets), mainly due to its nanocrystalline nature. It has also been characterized by much faster CO2 adsorption kinetics (ca. 5 vs. 50 min equilibration time) compared to a commercial Na-MOR zeolite with Si/Al = 5.0. Our study paves the way for developing a more efficient zeolite-based DAC adsorbent.

Recycled materials and secondary processes controlled the chemical and isotopic compositions of bubbling gases discharged from two adjacent geothermal springs in the Northern Luzon Arc

Gas emissions from hydrothermal systems can serve as indicators of subsurface activity. In addition to gas sources, hydrothermal gas geochemistry is strongly influenced by secondary processes that occur during/after hydrothermal circulation. Here, we observed statistically significant differences in the geochemical characteristics (except for helium isotopes) of bubbling gases discharged from two adjacent vents in the Northern Luzon Arc. Helium (3He/4He = 4.25–7.09 Ra) in both vents was controlled by mixing between mantle and crustal components, where about 74% of helium was contributed by the mantle. Differences in N2/Ar ratios (∼ 300–330) of the two neighboring springs are attributed to subducted materials and seawater mixing (contributing ∼2.5% N2 and Ar), rather than phase separation in the reaction zone. Specifically, Ar was mainly supplied by atmospheric components that dissolved in the percolated seawater with only 8%–9% contributed by the excess radiogenic 40Ar. Excess N2 relative to Ar was mainly supplied by the decomposition of subducted materials (83%–92%) of the South China Sea plate beneath the Philippine Sea Plate. The Lutao gases showed low CO2 concentrations (0.07–22.2 mmol/mol), despite the high 3He/4He ratios indicating a significant contribution of magmatic components. Magmatic CO2 may have been largely consumed by the high Ca Lutao vent fluids via carbonate precipitation in the reaction zone. Alternatively, stable carbon isotope compositions (δ13C) indicate that Lutao CO2 may be supplied by microbial oxidation of alkanes (e.g., CH4 with concentrations of 14.6–173 mmol/mol in the samples), with fractionation factor ΔCO2–CH4 ranging from −15‰ to −25‰ and conversion rates of <10%. Up to 65% of the CO2 in the 2016 samples experienced secondary calcite precipitation in the discharge zone. Our results indicate that recycled subducted materials could potentially affect the geochemical characteristics of gases discharged from arc-volcanic systems. In addition, the influence of secondary processes needs to be considered before tracing the sources of hydrothermal fluids and/or gases, especially in shallow-water hydrothermal systems.

Association among polydisperse aerodynamic size of bioaerosols, biodiversity and urbanization in kindergartens

The aerodynamic sizes of bioaerosols may significantly affect their behaviors, respiratory deposition and biodiversity. The respirable bacterial size, biodiversity, and human-associated bacteria (HAB) related bioaerosols were evaluated at three kindergartens in Taiwan. Kindergartens A, B, and C were in urban, semi-urban, and rural areas, respectively. A six-stage viable Andersen cascade impactor was used to collect bioaerosols and to determine their size distributions. The geometric mean diameter (GMD), geometric standard deviation (GSD), heat maps, and uniformity were used to evaluate the association of bacteria characteristics. A BD Phoenix-100 automated interpretation system was used to identify the airborne bacteria species.The results revealed that 1425 colonies of the sampled airborne bacteria contained 63 species in 29 genera, and overall, 63.0% were HABs. The most abundant phylum was Actinobacteria (56.6 ± 22.2%) and Firmicutes (31.6 ± 22.3%), and from the taxonomic analysis, both airborne Micrococcus and the Staphylococcus aureus are the dominant genus. All the bacteria aerodynamic particle size distributions were polydisperse distributions. The heat map and uniformity analysis had revealed most of the sampled bioaerosols distributed between 1.1–3.3 μm, and most of the polydisperse airborne Streptococcus spp. had a size in the respirable range, due to urbanization, they have potentially contributed to respiratory risk in the kindergartens. The Shannon diversity index (H) and inverse Simpson diversity index (D) of the bioaerosols in urban kindergarten were negatively correlated with GMD and GSD. The Pearson correlations revealed that the kindergarten in the rural area, with a higher temperature, a lower relative humidity, and a lower CO2 concentration than the others, tended to have the largest H and D values (P < 0.05). Multiple and stepwise regression revealed that bioaerosol aerodynamic size was statistically significantly correlated with H (P = 0.001) and D values (P = 0.002). This study sheds light on the characteristics of bioaerosols and their associations with microbiome.

Dynamic breakthrough performance of low concentration CO2 adsorption in fixed-bed column with porous amino acid ionic liquid composites

Low concentration carbon dioxide (CO2) capture from air or confined spaces currently faces significant challenges, such as relatively poor dynamic adsorption breakthrough performance and cyclic stability. In our previous work, functionalized ionic liquid (IL) tetraethylammonium glycine ([N2222][Gly]) and porous molecular sieve (SBA-15) were combined to synthesize porous amino acid IL composite 60 wt% [N2222][Gly]@SBA-15 with microporous and ultra-microporous structures, which provide a new pathway for low concentration CO2 capture. In order to further obtain the dynamic CO2 adsorption breakthrough performance of this material under simulated actual working conditions, the effects of temperatures, relative humidity (RH) and CO2 concentrations on CO2 adsorption and desorption breakthrough performance of 60 wt% [N2222][Gly]@SBA-15 in a fixed-bed column were systematically studied in this work. The results indicated that CO2 adsorption capacity is up to 1.81 mmolCO2/g-adsorbent at 298.15 K, 1 bar and 0 % RH under 1 vol% CO2-containing gas mixture balanced with N2 and reaches 2.44 mmolCO2/g-adsorbent at 15 % RH due to the mechanism change of CO2 reaction with primary amine from 2: 1 under dry gas to 1: 1 stoichiometry in the presence of moisture. Moreover, the adsorbent maintains good cyclic adsorption-desorption performance. Further, CO2 adsorption breakthrough behaviors were well fitted by Avrami kinetic model, and the CO2 adsorption rate of 60 wt% [N2222][Gly]@SBA-15 was controlled by intra-particle diffusion. This work implied that IL-modified adsorbents have great potentials for low concentration CO2 capture applications.

Environmental quality in sixty primary and secondary school classrooms in London

Poor environmental quality in school classrooms can have a detrimental impact on children's health, nevertheless, the association between air pollutants and physical features of classrooms is poorly understood. We monitored particulate matter (PM), carbon dioxide (CO2) and thermal comfort in sixty classrooms across ten London primary and secondary schools using similar equipment to produce a comparable dataset. The overall research objective was to understand the association of classroom air quality with occupancy levels, floor types, classroom locations, classroom volume, ventilation types and different year groups. Average in-classroom PM10 (29 ± 20), PM2.5 (10 ± 2) and PM1 (5 ± 2 μg m-3) during occupied hours were ∼150 % (PM10) and 110 % (PM2.5) higher compared to non-occupied hours. PM10 concentration was reduced by 30 % for dual (mechanical + natural) compared to natural ventilation only; the corresponding reduction was slightly lower for PM2.5 (28 %) and PM1 (20 %). PM10 almost doubled for wooden floored classrooms compared with those having carpets. During high occupancy (>26 occupants), the average CO2 (935 ± 453 ppm) was ∼140 % higher than non-occupancy. The average CO2 in classrooms occupied by younger children (reception and year one) was ∼190 % higher than those with older children (years eight and nine). 68 % of classrooms exceeded the minimum recommended levels of 40 % relative humidity. Low PM10 concentrations coincided with low CO2 concentrations in classrooms across all schools. These findings highlight the importance of simultaneously addressing both thermal comfort and the resuspension of PM10 to achieve comprehensive improvements in classroom air quality. Classroom settings where indoor environment is likely to be compromised can also be identified and addressed.

Ionic Pairs-Engineered Fluorinated Covalent Organic Frameworks Toward Direct Air Capture of CO2.

The covalent organic frameworks (COFs) possessing high crystallinity and capability to capture low-concentration CO2 (400ppm) from air are still underdeveloped. The challenge lies in simultaneously incorporating high-density active sites for CO2 insertion and maintaining the ordered structure. Herein, a structure engineering approach is developed to afford an ionic pair-functionalized crystalline and stable fluorinated COF (F-COF) skeleton. The ordered structure of the F-COF is well maintained after the integration of abundant basic fluorinated alcoholate anions, as revealed by synchrotron X-ray scattering experiments. The breakthrough test demonstrates its attractive performance in capturing (400ppm) CO2 from gas mixtures via O─C bond formation, as indicated by the in situ spectroscopy and operando nuclear magnetic resonance spectroscopy using 13C-labeled CO2 sources. Both theoretical and experimental thermodynamic studies reveal the reaction enthalpy of ≈-40kJmol-1 between CO2 and the COF scaffolds. This implies weaker interaction strength compared with state-of-the-art amine-derived sorbents, thus allowing complete CO2 release with less energy input. The structure evolution study from synchrotron X-ray scattering and small-angle neutron scattering confirms the well-maintained crystalline patterns after CO2 insertion. The as-developed proof-of-concept approach provides guidance on anchoring binding sites for direct air capture (DAC) of CO2 in crystalline scaffolds.

A Study of the Antioxidizing and Inhibiting Effects of the Alcoholic Extract of Sage Salvia Officinalis on Microorganisms

Objectives: A study of the antioxidizing and inhibiting effects of the sage salvia officinalis on microorganisms. Methods: Chemical constituents of sage leaves the percentage of the 98% ethanol extract of sage was 5.8% prepared in concentrations of 50, 100, 150 and 200 mg/ml, Antioxidizing and inhibiting effects on microorganisms, and sensory characteristics of the sage added biscuits. Results: Scanning electron microscope images, the structure of powder sage leaves which appear as long tubes and round crystals, Hight percent concentration of minerals carbon and oxygen while low concentrations of (Zn, Al, Na, Mg, Si, K, Co, Ca, and Ce) were also found. the percentage of the moisture, protein, fat and ash (11.09, 6.89, 13.14, 9.64) % respectively, the inhibition effect of sage leaves ethanol extract prepared in concentrations of 50, 100, 150 and 200 mg/ml on three bacteria and fungi species of disc method. maximum effect on all three bacteria species Escherichia coli, Staphylococcus aureus and Pseudomonas sp. was found with the concentration 50 and 100 mg/ml. compared with 150 and 200 mg/ml. It has been found that the 150 mg/ml concentration has the most inhibition effect on the three species of fungi studied Aspergillus niger, A. carbonarius, A. flavus. All extract concentration inhibited A. flavus, it was that the antioxidant activity, iron ion bonding, reducing power and the ability capture the hydrogen peroxide of sage ethanol extract increases with high concentrations. Peroxide values decreased with increased sage added biscuits percentage (0, 0.5, 0,75 and 1) w/w% in stored for periods. However, the sensory characteristics of the sage added biscuits samples were good and close to the standard biscuit control. Conclusions: Finally, we conclude that the sage plant has medicinal and nutritional benefits due to its antioxidant and antimicrobial activity.

Woody biomass waste derivatives in decarbonised blast furnace ironmaking process

Modern ironmaking process relies significantly on fossil-related fuels, which ultimately results in the enormous CO2 emitted into the atmosphere. Biomass of plant origin, as a carbon-neutral energy source, has been considered as an alternative to fossil-based reducing agents such as coke. This study aims to investigate the potential of three woody biomass waste derivatives produced from biomass waste pyrolysis and gasification, namely charcoal, bio-oil, and bio-syngas, as the reducing agents in blast furnace. A model based on heat and mass balance and Gibbs free energy minimisation is proposed to simulate an ironmaking process with assistance of these derivatives. The effects of specific composition of biomass waste derivatives on process operation, CO2 emissions, and coke replacement are explored. Also the effects of H2-rich gas produced from biomass waste gasification on the blast furnace operation are estimated. Results indicate that reactions of woody biomass waste derivatives in blast furnace are complex and greatly dependent on composition. When charcoal has a higher carbon content, lower CO2 concentration is found from the top gas. The higher content of hydrogen in bio-oil will inhibit further reduction in CO2 emissions. Bio-syngas with H2/CO ratio of 1.3 proves to have a remarkable potential to reduce CO2 emissions. From the aspects of available biomass waste resources across the world, woody biomass waste derivatives as reducing agents are more suitable for countries with the limited pig iron production. This study provides a reference on the future of moving forward the decarbonised ironmaking by using woody biomass waste derivatives.

Assessment of Effects of Carbon Dioxide Exposure on Sleep Stability in Insomnia Using the Envelope Analysis

Objectives: Insomnia is a common sleep disorder, and various strategies have been explored for its treatment. One of the methods involves the administration of carbon dioxide (CO&lt;sub&gt;2&lt;/sub&gt;) at bedtime, as the CO&lt;sub&gt;2&lt;/sub&gt; increment exerts a sedative effect on the central nervous system. We aimed to assess the effect of CO&lt;sub&gt;2&lt;/sub&gt; on sleep quality in patients with insomnia using the coefficient of variation of the envelope (CVE) analysis, a novel analytical method. Methods: In this randomized, double-blind, sham-controlled crossover trial, 24 adults with sleeping difficulties underwent level 1 polysomnography. Two interventions involved exposure to either 2% low-concentration CO&lt;sub&gt;2&lt;/sub&gt; gas or room air. CVE analysis was performed to assess the stability of the delta band. Morphological variations in delta waves can be quantitatively monitored using the envelope analysis, which assesses the effect of manipulations on sleep that may otherwise elude detection. Results: Exposure to CO&lt;sub&gt;2&lt;/sub&gt; improved the total sleep time (TST) (&lt;i&gt;p&lt;/i&gt;=0.010) and total arousal index (TAI) (&lt;i&gt;p&lt;/i&gt;=0.011). The CVE analysis showed a distinct distribution between the experimental and sham-controlled groups. Moreover, correlations between the TST and CVE (r=0.41) and those between the TAI and CVE (r=0.40) were observed. Conclusions: This study is the first to evaluate the effects of CO&lt;sub&gt;2&lt;/sub&gt; exposure on sleep stability in patients with insomnia. The CVE analysis implies the possibility of sleep stabilization by CO&lt;sub&gt;2&lt;/sub&gt; administration and suggests a link between enhanced sleep maintenance and sleep stability.

Frustrated Lewis pairs on facet-engineered CeO2 boost the conversion of low-concentration CO2 into cyclic ureas with assistance of diamine platforms

The development of efficient processes for value-added utilization of low-concentration CO2 is an on-going challenge. In this work, we present a sequential system based on diamine platforms for the direct utilization of low-concentration sources of CO2 (≤15%) in the production of cyclic ureas. Specifically, the low-concentration CO2 is captured by ethylenediamine to form ethylenediamine carbamate (EDA-CA), which subsequently undergoes the intramolecular dehydration to give ethyleneurea (EU) in the presence of frustrated Lewis pairs (FLPs) on the facet-engineered CeO2. Remarkably, the productivity of EU obtained from EDA-CA in the sequential system (9.5 mmol·gcat−1·h−1) is ∼4 times higher compared to the traditional catalytic system (2.4 mmol·gcat−1·h−1) using ethylenediamine and pure CO2 (3 MPa). Density functional theory calculations demonstrated that the FLPs on facet-engineered CeO2 significantly reduce the energy barrier for the nucleophilic attack of N-containing segment towards the carbonyl carbon in EDA-CA (rate-limiting step), ultimately optimizing the intramolecular cyclization efficiency of EDA-CA. This work not only provides an innovation tandem approach that enables the production of cyclic ureas from low-concentration CO2, but also opens up a promising avenue for the direct utilization of low-concentration CO2 for value-added applications in the future.

The study of novelty nutrients supplementary scheme and methodology on advanced carbon sequestration of microalgae

Microalgae has great potential in carbon sequestration and production of biofuel even with a low concentrations of CO2. In this paper, an Andrews based microalgae growth kinetic model and a novel and multiple nutrient supplementary scheme that significantly extends the carbon sequestration period and enhances growth rates of microalgae are proposed. First, the correlation between nutrient concentration and microalgal growth is constructed experimentally. The advanced growth kinetic model incorporating nitrogen and phosphorus consumption is developed. Then, the optimum cultivation conditions including initial nutrients concentration, nutrients supplementary interval and daily nutrients supplementary quantities are obtained in the conical flask reactor. The findings led to a novel nutrient supplementation strategy that initiates with a 0.2BC concentration, followed by a 0.3BC addition at 100 h, with subsequent supplements every 72 h. After adopting this supplementary strategy, the microalgae growth rate is increased by 42.9 % and the carbon sequestration rate is increased by 56.2 % compared with that of the original microalgae cultivation method in one cultivation cycle. Finally, the universal microalgae nutrients supplementary model is proposed in a piecewise model. It can be concluded from the model that in the first cultivation period, microalgae needs a higher affinity for nutrients and after nutrients supplementary, the sensitivity to nutrient inhibition is reduced. The paper is significantly helpful to improve the sustainability of the microalgae growth rate and the carbon sequestration rate.

Ambient carbon dioxide concentration correlates with SARS-CoV-2 aerostability and infection risk

An improved understanding of the underlying physicochemical properties of respiratory aerosol that influence viral infectivity may open new avenues to mitigate the transmission of respiratory diseases such as COVID-19. Previous studies have shown that an increase in the pH of respiratory aerosols following generation due to changes in the gas-particle partitioning of pH buffering bicarbonate ions and carbon dioxide is a significant factor in reducing SARS-CoV-2 infectivity. We show here that a significant increase in SARS-CoV-2 aerostability results from a moderate increase in the atmospheric carbon dioxide concentration (e.g. 800 ppm), an effect that is more marked than that observed for changes in relative humidity. We model the likelihood of COVID-19 transmission on the ambient concentration of CO2, concluding that even this moderate increase in CO2 concentration results in a significant increase in overall risk. These observations confirm the critical importance of ventilation and maintaining low CO2 concentrations in indoor environments for mitigating disease transmission. Moreover, the correlation of increased CO2 concentration with viral aerostability need to be better understood when considering the consequences of increases in ambient CO2 levels in our atmosphere.

Carbonation of Recycled Concrete Aggregates for New Concrete and Concrete Fines to Make Cement-Free Hollow Blocks

Mineral carbonation provides a way to increase the recycling of concrete waste in added-value products, and contributes to the principles of the circular economy. At present, most concrete waste is still downcycled. The high water absorption of recycled concrete aggregates, among other factors, impedes their recycling in the concrete industry. The quality of coarse recycled concrete aggregates (RCA) can, however, be enhanced by carbonation. Even when starting with high-grade RCA obtained from a selective demolition process, the carbonation process can decrease the water absorption of the RCA to as low as 3.0%. Concrete with a 50% replacement rate of carbonated RCA can be produced without a significant compressive strength reduction. The research further shows that carbonation can be performed at atmospheric pressure and low CO2 concentrations (e.g., 10%). The recycled concrete fines (RCF, 0–4 mm) in combination with 25% stainless steel slag were used to make zero-cement hollow blocks (39 × 19 × 9 cm) by carbonation curing without using any hydraulic binder. The hollow blocks have a compressive strength of 15.4 MPa at the lab scale. Both technologies were demonstrated on a pilot scale. In both processes, CO2 is immobilized in the resulting construction product. The developed production processes use less primary raw materials and cause less greenhouse-gas emissions than the production of traditional concrete products.

Multiscale effects of radial mixing on mixotrophic microalgal growth and macromolecular synthesis in tubular bubble-column photobioreactors

Extremophillic microalga Chlorella sorokiniana is grown mixotrophically in a 5 L externally-illuminated tubular bubble-column photobioreactor with an external light intensity of 10,500 lx (≈195 μmol-photons.m−2.s−1) at atmospheric (0.04 %), 1 %, 2 %, 3 %, 4 %, and 5 % CO2 concentrations, with acetic acid and urea as the organic carbon and nitrogen sources, respectively, for 6–8 days. Two different setups are employed: one permits axial air flow, and another promotes radial mixing of algal particles, dissolved CO2 and nutrients along with axial sparging. We show that radial mixing increases biomass yields by reducing both photo-limitation and photo-inhibition up to CO2 concentrations <3 %, above which substrate (CO2) inhibition necessitates lower reactor mixing. Radial mixing increases the lipid yield from 1.06 and 1.61 g/L to 1.27 and 1.78 g/L at 2 % and 3 % CO2, respectively, in nitrogen-limited cases, resulting in a 10–20 % increase. We show that complete reactor mixing, facilitated by the dual effects of branched (radial) and axial sparger, is preferred only in the absence of substrate (CO2) inhibition. Subsequently, we stratify the tubular photobioreactor design strategy into two regimes based on CO2 inlet concentrations. In one regime (for inlet CO2 < 3 %), we recommend the deployment of branched sparger to facilitate both radial and axial mixing simultaneously, thereby creating a well-mixed reactor at lower CO2 concentrations. In the other regime (for inlet CO2 > 3 %), axial sparging alone is recommended since complete mixing of CO2 increases substrate inhibition by reducing the reactor pH below 7.5.