CO2 Buffer Research Articles

Shellfish CO2 excretion is modulated by seawater carbonate chemistry but largely independent of pCO2.

Four species of shellfish, blue mussel (Mytilus galloprovincialis), Pacific abalone (Haliotis discus hannai), zhikong scallops (Chlamys farreri), and Pacific oyster (Crassostrea gigas), were exposed to decoupled carbonate system variables to investigate the impacts of different seawater carbonate parameters on the CO2 excretion process of mariculture shellfish. Six experimental groups with two levels of seawater pH (pH 8.1 and pH 7.7) and three levels of total alkalinity (TA = 1000, 2300, and 3600μmol/kg, respectively) were established, while pH 8.1 and TA = 2300μmol/kg was taken as control. Results showed that the CO2 excretion rates of these tested shellfish were significantly affected by the change in carbonate chemistry (P < 0.05). At the same TA level, animals incubated in the acidified group (pH 7.7) had a lower CO2 excretion rate than those in the control group (pH 8.1). In comparison, at the same pH level, the CO2 excretion rate increased when seawater TA level was elevated. No significant correlation between the CO2 excretion rate and seawater pCO2 levels (P > 0.05) was found; however, a significant correlation (P < 0.05) between CO2 excretion rate and TA-DIC (the difference between total alkalinity and dissolved inorganic carbon) was observed. Blue mussel has a significantly higher CO2 excretion rate than the other three species in the CO2 excretions per unit mass of soft parts, with no significant difference observed among these three species. However, in terms of CO2 excretion rate per unit mass of gills, abalone has the highest CO2 excretion rate, while significant differences were found between each species. Our studies indicate that the CO2 buffering capacity impacts the CO2 excretion rate of four shellfish species largely independent of pCO2. Since CO2 excretion is related to acid-base balancing, the results imply that the effects of other carbonate parameters, particularly the CO2 buffering capacity, should be studied to fully understand the mechanism of how acidification affects shellfish. Besides, the species difference in gill to soft parts proportion may contribute to the species difference in responding to ocean acidification.

Novel pullulan-sodium alginate film incorporated with anthocyanin-loaded casein-carboxy methyl cellulose nanocomplex for real-time fish and shrimp freshness monitoring

This study fabricated novel smart colorimetric film from pullulan (P) and sodium alginate (SA) incorporated with anthocyanin (ACNs) loaded casein carboxymethylcellulose (CAS-CMC-ACNs) nanocomplex for the freshness monitoring of the fish and shrimp. The ACNs loaded nanocomplex exhibited large particle size (176.902 ± 4.641 nm) than CAS-CMC (155.454 ± 4.152 nm) nanocomplex without ACNs, and can be loaded in P/SA film with uniform distribution. The P/SA film incorporated with CAS-CMC-ACNs nanocomplex had a more compact structure, improved barrier properties, mechanical strength, and thermal stability than P/SA film incorporated with free ACNs, which could be attributed to hydrogen bonding among the components in the film matrix, as confirmed by SEM micrographs and FT-IR. Intriguingly, the composite film exhibited antibacterial effect against gram-negative bacteria E. coli (Escherichia coli) and gram-positive bacteria S. aureus (Staphylococcus aureus) with inhibition zone of 7 ± 0.283 mm and 8.6 ± 0.141 mm, and antioxidant effect. The composite film demonstrated a visible response to CO2 and pH buffer. Furthermore, the composite smart film demonstrated the potential to monitor the freshness of fish and shrimp stored at 25 °C for 24 h via a visual color change from pink to dark grey. The findings revealed that the fabricated film is an effective tool for evaluating the freshness of fish and shrimp.

#1001 Model-based profiling of bicarbonate supplementation during a hemodialysis cycle

Abstract Background and Aims Bicarbonate is delivered to hemodialysis (HD) patients via diffusion following a concentration gradient across the dialyzer membrane. However, the concentration of bicarbonate in the dialysis fluid ([HCO3]d) is usually not individualized for the specific patient's conditions, as no clear guidelines are provided, which leads to suboptimal pre- and post-dialytic plasma bicarbonate concentrations ([HCO3]p) during each treatment cycle. We used a mathematical model to predict the outcomes of a week-long HD cycle with time-dependent [HCO3]d in 24 patients, tuning the [HCO3]d prescription to keep the simulated pre-dialytic [HCO3]p in the range 22-24 mEq/L throughout the week. The [HCO3]d profiles thus developed were then tested, and [HCO3]p during HD compared with those using a constant [HCO3]d in the same patients. Method The compartmental model (Pietribiasi et al PLOS ONE 2023) describes the transport of total CO2, O2, and total buffer base in arterial and mixed-venous blood (plasma and red blood cells), tissues (interstitial and intracellular fluid), and lung capillaries and alveoli, calculating derivate quantities such as bicarbonate concentration, pH, partial pressure of CO2. The patients underwent one week of standard HD with constant [HCO3}d (Week 1, [HCO3]d = 33.6 ± 1.8 mEq/L) consisting of 3 sessions (HD1, HD2, HD3) to estimate the baseline model parameters and, successively, an intervention week (Week 2), during which the model-derived [HCO3]d profiles were implemented. Each profile consisted of a single step increase after 2 hours of HD, the two values of [HCO3]d chosen for each session and patient according to the model's simulations. Blood samples for the blood gas analyzer were taken before and after each session, and each hour during HD2. Results [HCO3]p profiles in Week 2 showed a more linear increase compared those of Week 1 (Fig. 1). The efficacy of the response to the model-based treatment was different depending on whether the intervention aimed to decrease or increase pre-dialytic [HCO3]p during Week 2 (Fig. 2). In the group of patients attempting to decrease pre-dialytic [HCO3]p (Decrease group, n = 10, average [HCO3]d = 31.3 ± 1.5 mEq/L), a significant fraction of sessions achieved the target (60% across the whole week). In contrast, among the patients attempting to increase pre-dialytic [HCO3]p (Increase group, n = 6, average [HCO3]d = 35.3 ± 2.0 mEq/L), the model-based prescription was effective only in increasing post-dialytic concentration (20% of sessions achieved pre-dialytic targets). By comparison, during Week 1 only 30% and 10% of sessions were in the target range for Decrease and Increase groups, respectively. Patients for which we didn't want to alter pre-dialytic [HCO3]p were termed the Neutral group (n = 8, average [HCO3]d = 33.3 ± 2.1 mEq/L, 40% and 50% of sessions in the target [HCO3]p range in Week 1 and 2, respectively). Conclusion The model-based profiling intervention was only partially successful in achieving the targets for pre-dialytic [HCO3]p in Week 2. The reasons why pre-dialytic [HCO3]p were resistant to the model-based [HCO3]d in the Increase group are not clear, but it could be that the increase in the average [HCO3]d was too small (6-7% higher than Week 1). However, in the Decrease group a similar difference was sufficient to produce a more marked decrease in pre-dialytic [HCO3]p. The profiling of [HCO3]d was shown to be effective in reducing the time the patients spend at higher [HCO3]p. Nevertheless, our study demonstrated that, upon refinement, mathematical modeling can be used to develop individualized treatments to pilot the markers of the acid-base response to HD towards desired values.

Natural carbonation of portland cement with synthetic zeolite Y as a supplementary cementitious material

Risks associated with carbonation are a key limitation to greater replacement levels of ordinary portland cement (OPC) by supplementary cementitious materials (SCMs). The addition of pozzolanic SCMs in OPC alters the hydrate assemblage by forming phases like calcium-(alumina)-silicate-hydrate (C-(A)-S-H). The objective of the present study was to elucidate how such changes in hydrate assemblage influence the chemical mechanisms of carbonation in a realistic OPC system. Here, we show that synthetic zeolite Y (faujasite) is a highly reactive pozzolan in OPC that reduces the calcium content of hydration products via prompt consumption of calcium hydroxide from the evolving phase assemblage prior to CO2 exposure. Suppression of portlandite at moderate to high zeolite Y content led to a more damaging mechanism of carbonation by disrupting the formation of a passivating carbonate layer. Without this layer, carbonation depth and CO2 uptake are increased. Binders containing 12–18% zeolite Y by volume consumed all the calcium hydroxide from OPC during hydration and reduced the Ca/(Si+Al) ratio of the amorphous products to near 0.67. In these cases, higher carbonation depths were observed after exposure to ambient air with decalcification of C-(A)-S-H as the main source of CO2 buffering. Binders with either 0% or 4% zeolite Y contained calcium hydroxide in the hydrated microstructure, had higher Ca/(Si+Al) ratios, and formed a calcite-rich passivation layer that halted deep carbonation. Although the carbonated layer in the samples with 12% and 18% zeolite Y contained 70% and 76% less calcite than the OPC respectively, their higher carbonation depths resulted in total CO2 uptakes that were 12x greater than the OPC sample. Passivation layer formation in samples with calcium hydroxide explains this finding and was further supported by thermodynamic modeling. High Si/Al zeolite additives to OPC should be balanced with the calcium content for optimal carbonation resistance.

Biological export production controls upper ocean calcium carbonate dissolution and CO2 buffer capacity.

Marine biogenic calcium carbonate (CaCO3) cycles play a key role in ecosystems and in regulating the ocean's ability to absorb atmospheric carbon dioxide (CO2). However, the drivers and magnitude of CaCO3 cycling are not well understood, especially for the upper ocean. Here, we provide global-scale evidence that heterotrophic respiration in settling marine aggregates may produce localized undersaturated microenvironments in which CaCO3 particles rapidly dissolve, producing excess alkalinity in the upper ocean. In the deep ocean, dissolution of CaCO3 is primarily driven by conventional thermodynamics of CaCO3 solubility with reduced fluxes of CaCO3 burial to marine sediments beneath more corrosive North Pacific deep waters. Upper ocean dissolution, shown to be sensitive to ocean export production, can increase the neutralizing capacity for respired CO2 by up to 6% in low-latitude thermocline waters. Without upper ocean dissolution, the ocean might lose 20% more CO2 to the atmosphere through the low-latitude upwelling regions.

Constraining activity and growth substrate of fungal decomposers via assimilation patterns of inorganic carbon and water into lipid biomarkers.

Fungi are among the few organisms on the planet that can metabolize recalcitrant carbon (C) but are also known to access recently produced plant photosynthate. Therefore, improved quantification of growth and substrate utilization by different fungal ecotypes will help to define the rates and controls of fungal production, the cycling of soil organic matter, and thus the C storage and CO2 buffering capacity in soil ecosystems. This pure-culture study of fungal isolates combined a dual stable isotope probing (SIP) approach, together with rapid analysis by tandem pyrolysis-gas chromatography-isotope ratio mass spectrometry to determine the patterns of water-derived hydrogen (H) and inorganic C assimilated into lipid biomarkers of heterotrophic fungi as a function of C substrate. The water H assimilation factor (αW) and the inorganic C assimilation into C18:2 fatty acid isolated from five fungal species growing on glucose was lower (0.62% ± 0.01% and 4.7% ± 1.6%, respectively) than for species grown on glutamic acid (0.90% ± 0.02% and 7.4% ± 3.7%, respectively). Furthermore, the assimilation ratio (RIC/αW) for growth on glucose and glutamic acid can distinguish between these two metabolic modes. This dual-SIP assay thus delivers estimates of fungal activity and may help to delineate the predominant substrates that are respired among a matrix of compounds found in natural environments.IMPORTANCEFungal decomposers play important roles in food webs and nutrient cycling because they can feed on both labile and more recalcitrant forms of carbon. This study developed and applied a dual stable isotope assay (13C-dissolved inorganic carbon/2H) to improve the investigation of fungal activity in the environment. By determining the incorporation patterns of hydrogen and carbon into fungal lipids, this assay delivers estimates of fungal activity and the different metabolic pathways that they employ in ecological and environmental systems.

Desalination brines as a potential vector for CO2 sequestration in the deep sea

Freshwater scarcity, driven by population growth and climate change, is increasingly mitigated by seawater desalination, globally. As an energy-intensive process, desalination is a substantial source of atmospheric CO2. Nevertheless, desalination may hold a potential for ocean-based atmospheric carbon removal. Here we describe, for the first time, the carbonate chemistry of desalination brines near the submerged marine outfalls of a large desalination plant, their unique CO2 buffering capacity, and potential for deep sea carbon sequestration. We show that reverse osmosis acts as a carbon concentration factory and that the high-density brine plumes could create a vector for long-term CO2 removal to the deep sea below the seasonal thermocline. At present desalination capacity, we estimate that Desalination Assisted Carbon Concentration (DACC) and Carbon Dioxide Removal (CDR) could potentially remove 3.8 Mton CO2/year globally, with a negligible contribution to ocean acidification. This mechanism partially mitigates the high carbon print associated with desalination. SynopsisDesalination reject brines pose environmental challenges upon disposal to sea, but due to their unique properties, may become an opportunity for long-term carbon sequestration.

The effect of total alkalinity on growth performance and calcification in juvenile Pacific abalone Haliotis discus hannai

A 45-day trial was conducted to study the effect of seawater total alkalinity (TA) level up- and downregulation on the growth performance and calcification of Haliotis discus hannai Ino, while seawater pH was maintained at pHNBS = 8.1. Although seawater was not acidified, the results showed that TA downregulation caused a significant reduction (P < 0.05) in the somatic tissue growth of juvenile abalone, while TA upregulation significantly increased growth performance (P < 0.05). Similar to the impacts of pH reduction, TA downregulation also induces a decline in CO2 buffering capacity, which may be the reason why somatic tissue growth was reduced, as lowered CO2 buffering capacity was reported to shift the acid-base balancing of abalone. Parts of the periostracum layer weremissing and exposed the inner shell layers of the individuals from the TA-downregulated group. Scanning electron microscopy (SEM) results showed calcium carbonate densely deposited onto the inner shell in the control and TA-upregulated groups, while sparsely deposited calcium carbonate was observed in the TA-downregulated group. The C: N ratio in the shell of individuals from the TA-downregulated group was significantly lower than that of the other two groups, indicating that less inorganic carbon was added to the shell. As a result, abalone grew lighter and thinner shells in TA-downregulated seawater. Although seawater was not acidified, TA downregulation also caused a reduction in the calcium carbonate saturation state (Ω), which induced the erosion of the surface shell and the interruption of calcium carbonate generation. In conclusion, although seawater pH remained at ambient levels, the lowered CO2 buffering capacity and Ω induced by seawater TA downregulation also showed a detrimental effect on the growth and calcification of Pacific abalone. The impact of ocean acidification on the growth of abalone should not be assessed using only seawater pH and/or pCO2 but rather taking into account all of carbonate chemistry, particularly the CO2 buffering capacity. Abalone cultivation is suggested to be carried out in seawater with a higher level of CO2 buffering capacity and Ω, which can be achieved through integrated culture with seaweed or increasing the seawater TA level.

Disentangling the impact of Atlantic Niño on sea-air CO2 flux

Atlantic Niño is a major tropical interannual climate variability mode of the sea surface temperature (SST) that occurs during boreal summer and shares many similarities with the tropical Pacific El Niño. Although the tropical Atlantic is an important source of CO2 to the atmosphere, the impact of Atlantic Niño on the sea-air CO2 exchange is not well understood. Here we show that the Atlantic Niño enhances (weakens) CO2 outgassing in the central (western) tropical Atlantic. In the western basin, freshwater-induced changes in surface salinity, which considerably modulate the surface ocean CO2 partial pressure (pCO2), are the primary driver for the observed CO2 flux variations. In contrast, pCO2 anomalies in the central basin are dominated by the SST-driven solubility change. This multi-variable mechanism for pCO2 anomaly differs remarkably from the Pacific where the response is predominantly controlled by upwelling-induced dissolved inorganic carbon anomalies. The contrasting behavior is characterized by the high CO2 buffering capacity in the Atlantic, where the subsurface water mass contains higher alkalinity than in the Pacific.

Towards the determination of carbon dioxide retention in earthen materials

Thanks to its hygroscopic properties, raw earth can passively buffer indoor humidity. The high sorption properties of clay minerals present in earth also attract other molecules, such as carbon dioxide (CO2), this can potentially lead to indoor CO2 buffering. It would improve air quality in buildings and their resilience towards mechanised ventilation systems. However, there is currently no protocol to evaluate this potential. This paper aims to present a innovative methodology based on thermogravimetric (TG) and calorimetric (DSC) analysis to characterise the interactions between clay and CO2 at the microscopic scale by focusing on the dry state. Results show a CO2 adsorption capacity of 134 mg/kg at 5000 ppm at 35 °C associated with a reversible physisorption process and provides first evidence of a passive CO2 regulation capacity of the indoor air. Determination of the adsorption enthalpies as a function of the amount adsorbed revealed high values (from −74 kJ/mol to −40 kJ/mol) which are characteristic of a strong energetic heterogeneity of the material.

Explosive eruptions at Stromboli volcano (Italy): a comprehensive geochemical view on magma sources and intensity range

A comprehensive understanding of the processes that occur during magmatic storage and pre-eruptive ascent—and of their associated timescales—is critical to identifying potential precursory signals, and to developing robust volcano early-warning systems. Stromboli’s persistent activity comprises continuous degassing and explosive activity that ranges from hourly, low-intensity “normal” activity to occasional, more violent, paroxysmal activity. While the magma source processes that drive normal and paroxysmal activity are reasonably constrained, eruptive activity intermediate in magnitude and intensity (i.e., major explosions) remains elusive in terms of classification, source region, and pre-eruptive timescales. Here, we investigate the 19 July 2020 major explosion that geophysical parameters place at the upper limit of the major explosions field, close to small-scale paroxysms such as the 2003 and 2007 events. The geochemical signatures of matrix glass, olivine, melt inclusions, and embayments—integrated with gas measurements—highlight important differences in eruption source, ascent behaviour, and pre-eruptive timescales of the studied event when compared to paroxysms. Melt inclusion volatile contents identify that magma rise begins from a slightly shallower source (~9.5 km below sea level, b.s.l.) than for paroxysms (11.4 km b.s.l.), with the activation of a shallower ponding zone at 5–6 km b.s.l.. This, in combination with intermediate matrix glass compositions, suggests complex ascent behaviour, characterised by CO2 buffering in the deep ponding region and magma self-mixing in the shallower zone. Fe–Mg-diffusion modelling in olivine indicates a system perturbation starting ~20–25 days before eruption onset, in agreement with the timescale of volcanic gas CO2/SO2 ratio changes observed in the plume, and significantly shorter than that observed prior to paroxysms (~4 months). The geochemical dataset provides insights into the processes controlling the steady-state conditions and the broad spectra in eruption magnitude and intensity at Stromboli and bears important implications for eruption forecasting.

Emissions and CO2 Concentration—An Evidence Based Approach

The relation between CO2 emissions and atmospheric CO2 concentration has traditionally been treated with more or less complex models with several boxes. Our approach is motivated by the question of how much CO2 must necessarily be absorbed by sinks. This is determined by accepted measurements and the global carbon budget. Observations lead to the model assumption that carbon sinks, similar to oceans or the biosphere, are linearly dependent on CO2 concentration on a decadal scale. In particular, this implies the falsifiable hypothesis that oceanic and biological CO2 buffers have not significantly changed in the past 70 years and are not saturated in the foreseeable future. A statistical model with two parameters is built from the global carbon budget and two testable assumptions. This model explains the relation between CO2 emission and historical CO2 concentration data very well. The model gives estimates of the natural emissions, the pre-industrial CO2 equilibrium concentration levels, the half-life time of an emission pulse, and the future CO2 concentration level from a given emission scenario. It is validated by an ex-post forecast of the last 20 years. The important result is that, with the stated polices emission scenario of the International Energy Agency (IEA), the future CO2 concentrations will not rise above 475 ppm. The model is compared with the carbon module of the Bern model, mapping their complex impulse response functions (IRFs) to a single time variant absorption parameter.

Mathematical modelling of bicarbonate supplementation and acid-base chemistry in kidney failure patients on hemodialysis.

Acid-base regulation by the kidneys is largely missing in end-stage renal disease patients undergoing hemodialysis (HD). Bicarbonate is added to the dialysis fluid during HD to replenish the buffers in the body and neutralize interdialytic acid accumulation. Predicting HD outcomes with mathematical models can help select the optimal patient-specific dialysate composition, but the kinetics of bicarbonate are difficult to quantify, because of the many factors involved in the regulation of the bicarbonate buffer in bodily fluids. We implemented a mathematical model of dissolved CO2 and bicarbonate transport that describes the changes in acid-base equilibrium induced by HD to assess the kinetics of bicarbonate, dissolved CO2, and other buffers not only in plasma but also in erythrocytes, interstitial fluid, and tissue cells; the model also includes respiratory control over the partial pressures of CO2 and oxygen. Clinical data were used to fit the model and identify missing parameters used in theoretical simulations. Our results demonstrate the feasibility of the model in describing the changes to acid-base homeostasis typical of HD, and highlight the importance of respiratory regulation during HD.

Methanation of CO2 over High Surface Nickel/Aluminates Compounds Prepared by a Self-Generated Carbon Template

Catalytic gas-phase hydrogenation of CO2 into CH4 was tested under three different nickel/aluminate catalysts obtained from precursors of hexaaluminate composition (MAl16O19, M = Mg, Ca, Ba). These catalysts were prepared using a carbon template method, where carbon is self-generated from a sol-gel that contains an excess of citric acid and the Al and M salts (Ba2+, Ca2+, Mg2+) by two-step calcination in an inert/oxidizing atmosphere. This procedure yielded Ni particles decorating the surface of a porous high surface area matrix, which presents a typical XRD pattern of aluminate structure. Ni particles are obtained with a homogeneous distribution over the surface and an average diameter of ca 25–30 nm. Obtained materials exhibit a high conversion of CO2 below 500 °C, yielding CH4 as a final product with selectivity &gt;95%. The observed trend with the alkaline earth cation follows the order NiBaAlO-PRx &gt; NiCaAlO-PRx &gt; NiMgAlO-PRx. We propose that the high performance of the NiBaAlO sample is derived from both an appropriate distribution of Ni particle size and the presence of BaCO3, acting as a CO2 buffer in the process.

Activity and Selectivity of Bimetallic Catalysts Based on SBA-15 for Nitrate Reduction in Water

Nitrate from the application of nitrogen-based fertilizers in intensive agriculture is a notorious waste product, though it lacks cost-effective solutions for its removal from potential drinking water resources. Catalytic reduction appears to be a promising technique for converting nitrates to benign nitrogen gas. Mesoporous silica SBA-15 is a frequently used catalyst support that has large surface areas and highly ordered nanopores. In this work, mesoporous silica SBA-15 bimetallic catalysts for nitrate reduction were investigated. The catalyst was optimized for the selection of promoter metal (Sn and Cu), noble metal (Pd and Pt) and loading ratios of these metals at different temperatures and reduction conditions. The catalysts prepared were characterized by FT-IR, N2 physisorption, XRD, SEM, and ICP. All catalysts showed the presence of cylindrical mesoporous channels and uniform pore structures that remained even after metals loading. In the presence of a CO2 buffer, the catalysts 4Pd-1Cu/SBA-15 and 1Pt-1Cu/SBA-15 reduced at 100?C under H2 and 1Pd-1Cu/SBA-15 reduced at 200°C under H2 demonstrated very high nitrate conversion. Furthermore, the forementioned Pd catalysts had higher N2 selectivity (88% - 87%) compared to Pt catalyst (80%). Nitrate conversion by the 4Pd-1Cu/SBA-15 catalyst was significantly decreased to 81% in the absence of CO2.

Indoor CO2 buffering potential of clay-based building materials

To mitigate the anthropogenic greenhouse gas emissions from the operational energy consumption in buildings, increasingly high-performance envelopes are developed. A reduction in indoor air renewal is observed that leads to a higher pollutant concentration in the built environment. Particular attention was given to CO2, an anthropogenic gas that has consequences on the Indoor Air Quality (IAQ) and the health of occupants. Developing a passive regulation system appears to be a promising solution for improving IAQ and reducing the energy consumption of ventilation systems. For that purpose, earth-based materials present interesting characteristics through the presence of clay minerals and their microstructure. In this context, this paper aims at presenting a novel experimental method to assess the CO2 retention potential of natural earth plasters. The method uses a thermogravimetric device (TGA/DSC) associated with a gas mixer and humid air generator. The mass variation resulting from the interaction of the increasing CO2 content could thereby be measured and analysed. Results show the important role of reversibility in the phenomenon: the majority of the captured CO2 being released when the CO2 concentration drops. It also highlights the role of the relative humidity on the retention capacity. As the retention of CO2 is lower when the material is wet, the water molecules may occupy part of the adsorption sites and react themselves with the CO2. This experiment provides the first values and thus evidence of the CO2 retention capacity and passive regulation potential of this material.

Determination of carbonation resistance of concrete through a combination of cement content and tortuosity

The underlying motivation of the study is to understand the effect of CO2 buffering capacity and pore structure characteristics on the rate of carbonation of concrete. An investigation on the influence of different parameters of concrete on the rate of carbonation of 11 concrete mixes made using PC (Portland cement) and six different SCMs (Supplementary cementitious materials) is presented in this work. Compressive strength and various transport properties (oxygen permeability, porosity, resistivity and sorptivity) of concrete are measured after 28 days of curing. Concrete samples are subjected to accelerated carbonation conditions (2.5% CO2, 60% R.H. and 20 °C temperature) for 60 days after the end of the curing and preconditioning period. No notable correlation is observed between the rate of carbonation and measured parameters of concrete. A pragmatic approach to measure the carbonation resistance of concrete is proposed by means of a carbonation resistance factor derived using the tortuosity and cement content of concrete. The carbonation resistance factor could be effectively used to compare concrete mixes containing different SCMs for their carbonation resistance providing an alternative to tedious and time-consuming carbonation tests.

Submarine Groundwater Discharge in the Northern Bohai Sea, China: Implications for Coastal Carbon Budgets and Buffering Capacity

AbstractSubmarine groundwater discharge (SGD) has been widely recognized as an important source of dissolved nutrients in coastal waters and affects nutrient biogeochemistry. In contrast, little information is available on SGD impacts on coastal carbon budgets. Here, we assessed the SGD and associated carbon (dissolved inorganic carbon [DIC] and total alkalinity [TA]) fluxes in Liaodong Bay (the largest bay of the Bohai Sea, China) and discussed their border implications for coastal DIC budget and buffering capacity. Based on 223Ra and 228Ra mass balance models, the SGD flux was estimated to be (0.92–1.43) × 109 m3 d−1. SGD was the largest contributor of DIC, accounting for 55%–77% of the total DIC sources. The low ratio (&lt;1) of SGD‐derived TA to DIC fluxes and negative correlation between radium isotopes and pH in seawater implied that SGD would potentially reduce seawater pH in Liaodong Bay. Combining the groundwater carbon data in Liaodong Bay with literature data, we found that the SGD‐derived DIC flux off China was 4–9 times greater than those from rivers. By analyzing the TA/DIC ratios in groundwater along the Chinese coast and related carbon fluxes, SGD was thought to partially reduce the CO2 buffer capacity in receiving seawater. These results obtained at the bay scale and national scale suggest that SGD is a significant component of carbon budget and may play a critical role in modulating coastal buffering capacity and atmospheric CO2 sequestration.

Carbonation of cement paste with GGBFS: Effect of curing duration, replacement level and [formula omitted] concentration on the reaction products and [formula omitted] buffer capacity

Uncertainties related to durability of concrete arise when Portland Cement (PC) is combined with supplementary cementitious materials, urging a more thorough understanding of the deterioration mechanisms. This paper focusses on carbonation, specifically the effect of replacement level of PC by ground granulated blast-furnace slag (GGBFS), curing duration and CO2 concentration on the reaction products and CO2 buffer capacity. The experimental test program included the determination of the hydration degree of PC, the reaction degree of GGBFS and an analysis of the reaction products by Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy. ATR-FTIR spectra of cement paste powders showed a delay in calcium silicate hydrate (C-S-H) decalcification upon carbonation in case of 40wt% GGBFS by increasing the curing period from 3 to 7 and 28 days. However for 70wt% GGBFS, C-S-H decalcification was quick and irrespective of the curing period whereas in neat PC, C-S-H decalcification was minimal. When comparing elevated and natural CO2 concentrations, portlandite contents and the formed CaCO3 polymorphs were comparable while the carbonate content and C-S-H decalcification lack resemblance suggesting different carbonation stages. ATR-FTIR spectra from the exposed surface towards the centre showed a systematic agreement between the peak area of carbonates and the colour change boundary by phenolphthalein. The spectra also suggested the transformation of aragonite to calcite during ongoing carbonation of mixes with 70wt% GGBFS and 40wt% GGBFS cured for 3 days. The use of phenolphthalein to distinguish carbonation does not reflect the heterogeneous composition of the microstructure of (partially) carbonated areas.

Interactions of Tris with rutile surfaces and consequences for in vitro bioactivity testing

Tris(hydroxymethyl)aminomethane (Tris) has been used as the buffer in bioactivity testing for over two decades and has become a standard choice for the scientific community. While it is believed to be non-interacting, the extent of its interactions with titanium oxide surfaces has not been systematically studied. Here, we use experimental (zeta potential measurements) and computational (molecular dynamics) approaches to evaluate the interaction of Tris with a rutile surface and how it affects the adsorption of other molecules relevant in biomedical in vitro testing. We show that the interaction of Tris with the rutile surface is strong and significantly affects the interaction of other organic residues with the surface. These strong interactions are compounded by the Tris concentration in the in vitro testing protocol, which is much higher compared to other components. Our findings indicate that the kinetics observed in in vitro tests will be strongly influenced by the presence of Tris as a buffering agent when compared to the natural CO2 buffer in blood. These results reveal that considering the so-far neglected active role of Tris in in vitro testing is critically needed and that in vitro protocols using CO2 partial pressure as the buffering agent should yield more reliable results.