Influence Of Different CO2 Concentrations Research Articles

Effect of CO2 Concentration and Liquid to Gas Ratio on CO2 Absorption from Simulated Biogas Using Monoethanolamine Solution

In industrial scale, removal of CO2 by chemical absorption from raw biogas represents an imperative treatment and the cutting-edge technology towards improvement of its quality and heat value. In this work, CO2 absorption studies were conducted in an absorption column packed with Sulzer metal gauze packing with simulated biogas absorbed using 30 wt. % of monoethanolamine (MEA) solution. Experimental works were conducted to determine the influence of different CO2 concentrations in feed gas (30 % and 40 %) and L/G ratio (0.6 and 0.7) and subsequently assessed in terms of CO2 absorption efficiency along the column. The results showed that 30 % CO2 in feed gas has higher removal efficiency as compared to 40 % CO2 with the ability to remove 94 % CO2 during the process. In addition, the CO2 absorption studied on the L/G ratio proved that CO2 removal was improved at higher L/G ratio of 0.7.

Influence of CO2 concentration on the performance of MgO cement mixes

This paper investigated the influence of different CO2 concentrations on the microstructural and mechanical development of reactive MgO cement (RMC) concrete. Combination of various analyses revealed the enhancement of hydrated magnesium carbonate (HMC) phases with relatively superior micro-mechanical properties as the CO2 concentration increased from ambient (~0.04%) to accelerated (5–20%) levels. The higher CO2 diffusion within samples cured under 5–20% CO2 increased the compressive strength by ~5 times. While samples cured under 20% CO2 revealed high early strengths, the formation of a dense HMC layer on the sample exterior led to limitations on further CO2 diffusion. Use of 5% CO2 produced comparable strengths as 20% CO2 at 28 days, highlighting the potential of using lower concentrations. Samples cured under 10% CO2 revealed the best performance at 28 days, thereby defining this environment as the most favorable condition for the development of microstructural and mechanical properties of RMC concrete.

The influence of different CO2 concentrations on the biochemical and molecular response of two isolates of Dunaliella sp. (ABRIINW-CH2 and ABRIINW-SH33)

Biological capture of CO2 using microalgae is promising approach for mitigation of excess carbon. The aim here was to study the influence of different CO2 (10, 20, and 30% v/v) concentrations as a carbon source on two indigenous isolates of Dunaliella sp. (ABRIINW-CH2 and ABRIINW-SH33) under adjusted pH. Algal growth improved at elevated concentrations of CO2. Resistance response patterns to elevated CO2 concentrations in contents of all the storage products, proline, malondialdehyde (MDA), H2O2, and enzymatic antioxidant activities were different in the studied isolates at different CO2 concentrations. The protein and lipids were high at 10% CO2 concentration, but carbohydrates decreased at 10% CO2 concentration, followed by decrease in protein and lipids and increase in the amount of carbohydrates at 20 and 30% CO2 concentrations. MDA and H2O2 increased significantly at 20 and 30% CO2 concentrations in both isolates, but since MDA in ABRIINW-SH33 isolate was less than that in ABRIINW-CH2 isolate, ABRIINW-SH33 had a higher tolerance to high CO2 concentrations. The increases in catalase (CAT), polyphenol oxidase (PPO), superoxide dismutase (SOD), and proline are the signs of oxidative stress under elevated CO2 concentrations as well as the antioxidative responses in the isolates. In addition, quantitative real-time (qRT)–polymerase chain reaction (PCR) analysis confirmed the biochemical results that elevated CO2 concentration inducted expression of SOD and CAT genes in both isolates under elevated CO2 concentrations. The results clearly showed that two isolates indicated different resistance patterns in response to elevated CO2 concentrations. The molecular and biochemical markers obtained from this study are the basic information that can be used in microalgae strain selection and improvement for CO2 capturing.

The effect of pre-industrial and predicted atmospheric CO2 concentrations on the development of diazotrophic and non-diazotrophic cyanobacterium: Dolichospermum circinale and Microcystis aeruginosa

Photoautotrophs are capable of consuming high quantities of CO2, yet scant research exists examining the influence of different CO2 concentrations on the growth of freshwater diazotrophic or non-diazotrophic cyanobacteria. In this study, we cultured two cyanobacteria taxa (Dolichospermum circinale and Microcystis aeruginosa) within controlled atmospheric CO2 chambers at pre-industrial, and post-industrial concentrations. Biovolume and chlorophyll a (Chl-a) differed as a consequence of the adjusted CO2 gradients. Significantly higher biovolume measurements were observed in the elevated CO2 treatment for the diazotrophic species in the initial experiment. However, a follow-up experiment, with a corrected culture replenishment regime showed Chl-a measurements were greater for the diazotrophic and non-diazotrophic species in the elevated CO2 treatment. Increasing CO2 presents a risk to already compromised eutrophic and hyper-eutrophic ecosystems, and we reason increasing CO2 concentrations could affect photosynthetic performance and CO2 assimilation of surface dwelling cyanobacteria. Further experimental work is required to establish ecological thresholds for freshwater ecosystems, as pH levels showed a measurable reduction within the elevated CO2 treatments. As cyanobacteria species may respond quite differently to future CO2 concentrations similar comparative studies should be carried out that focus on CO2 dynamics and pH. The findings of the study indicate diazotrophic cyanobacteria growth in particular may benefit from elevated atmospheric CO2 concentrations.

Model for practical carbonation depth prediction for high volume fly ash concrete and recycled aggregate concrete

Abstract The reuse of industrial residue streams such as fly ash (FA) or waste materials such as recycled concrete aggregate (RCA) can be beneficial both from an economic and an ecological point of view. Extensive research, investigating different properties of these concrete types, has been carried out so far. However, durability remains a key property ensuring sustainable application of these materials in the construction sector that still needs more research to be fully understood. The main objective of this study was to evaluate the application of widely used models for carbonation depth prediction—defined for ordinary Portland cement concrete with natural aggregate (NAC)—to high volume FA concrete (HVFAC) and recycled aggregate concrete (RAC). The research presented in this paper was conducted in two steps. First, an experimental programme was designed to provide better understanding of the influence of different CO2 concentrations on the carbonation process kinetics in HVFAC, RAC and NAC. This was performed using accelerated carbonation tests (CO2 concentrations of 1%, 2%, 4% and 16%) and natural carbonation tests (duration 21 and 48 months). Furthermore, a database of previously published results of HVFAC and NAC carbonation depths was made in order to analyse the application of carbonation depth prediction defined by Tuutti and given in the fib Model Code 2010. It was shown that the existing models, providing the relationship between accelerated test results and natural carbonation depth, are applicable to NAC and RAC but not to HVFAC. Modifications of the above mentioned models were proposed in order to enable a more accurate and reliable prediction of the HVFAC carbonation depth under natural exposure conditions.

Methane from CO2: Influence of different CO2 concentrations in the flush gas on the methane production in BMP tests

The influence of carbon dioxide (CO2) in the headspace gas on the specific methane (CH4) production of blank samples with just inoculum during Biochemical Methane Potential (BMP) tests was studied. The headspace of the bottles had been flushed with 15 different ratios of CO2 and N2 prior to incubation, while they were treated otherwise identically. The results revealed that the CH4 yield increased linearly with higher ratio of CO2 in the flush gas reaching a 30% higher yield at pure CO2 relative to pure N2 headspace conditions. However, a slightly distinct lag is noticeable during the initial phase of the degradation process at high ratios of CO2, hypothesizing a reversible disturbance of the biocenosis. Further experiments and analyses need to be performed to elucidate the underlying mechanisms.

The effect of CO2 concentration in neuroectoderm commitment of mouse embryonic stem cells

The goal of coaxial methods is to direct pluripotent stem cells toward specific phenotypes, limiting the appearance of tumorigenic or apoptotic cells. Beside culture medium components, other parameters, such as incubator atmosphere composition, temperature or pH of the culture medium, may have an influence on culture progression. In this study, the influence of different CO2 concentrations (1·5 and 5%) was analyzed in the commitment of D3 mouse embryonic stem cells to a neuroectodermal lineage. Real-time polymerase chain reaction (PCR) experiments showed that the expression level of three neuroectoderm marker genes (Neurofilament middle, Nestin and Acetylcholine esterase) was three times higher at 1·5% CO2 than at 5%, suggesting a favored commitment to neuroectoderm at low CO2 concentration. No change was observed in the expression of other markers such as Oct4, Nanog (pluripotency), Sox1 (neuroectoderm and gonads) and Pax6 (neuroectoderm and definitive endoderm) at the two CO2 conditions. Markers for primitive endoderm (Amnionless), mesendoderm (Brachyury) and germinal lineage (Vasa) were not detected. The percentage of cells in the G0 phase of cell cycle is slightly higher in cells growing at 1·5%CO2. Therefore, incubation in the presence of 1·5%CO2 seems to favor neuroectoderm commitment of mouse D3-cells modulating cell cycle progression.

Effects of CO2 on the Phenanthrene Adsorption Capacity of Carbonaceous Materials

Three-ring polycyclic aromatic hydrocarbons (PAHs), and phenanthrene (Phe) in particular, are the main pollutants found in the waste flue gases from organic material combustion in energy generation processes. Quantitatively, the most abundant gaseous contaminant emitted in these processes is CO2. Therefore, the aim of this paper has been to study the influence of different CO2 concentrations on the phenanthrene adsorption in a postcombustion cleanup process when carbonaceous materials are used to remove low concentrations of phenanthrene from a hot exhaust gas stream. Adsorption isotherms were obtained using CO2 and phenanthrene concentrations in the ranges of 0−30% and 0.025−3.2 ppmv, respectively. The process temperature was fixed to 150 °C in all runs. All the obtained isotherms were properly fitted to the Freundlich adsorption model and their parameters determined by regression analyses. A negative influence of CO2 in phenanthrene adsorption capacity was observed, probably due to a competitive effect between CO2 and phenanthrene for the adsorption sites within the carbonaceous material. However, it was found that high CO2 concentrations did not affect the phenanthrene adsorption more negatively than low CO2 concentrations. It was thus concluded that the most suitable carbonaceous materials for phenanthrene abatement in flue gases were those having a wide pore distribution with a high average micropore diameter. The development of mesoporosity in adsorbents promotes phenanthrene adsorption because it favors both the access of phenanthrene molecules into the micropores and the phenanthrene multilayer adsorption. Finally, the Yoon and Nelson mathematical model was applied to simulate the breakthrough curves. This model was able to predict the adsorption breakthrough in all the runs. Nevertheless, problems arose when trying to fit breakthrough curves at relative concentrations higher than 70% in those adsorbents with narrow micropore distributions.

Combined Carbon Dioxide Inhibition and Oxygen Limitation of the Growth of Pseudomonas fragi 72 in Batch and Continuous Culture

The effect of CO2 inhibition and O2 limitation on the growth of Pseudomonas fragi strain 72 was studied in carbon and/or energy limited continuous culture using citric acid as the growth substrate. The influence of different CO2 concentrations on the maximal growth capacity, estimated as the dilution rate at which the culture density begins to fall (D b) or the dilution rate at which biomass output rate is maximal (D m), was demonstrated together with the differences in influence of CO2 inhibition and O2 limitation, on the steady-state characteristics of the culture. The combined effect of CO2 inhibition and O2 limitation was measured. Comparative studies made in batch cultures suggested that continuous culture was more sensitive to change than the batch culture. The maximum specific growth rate of the organism decreased when the CO2 concentration was increased. However, the results from the continuous cultures revealed a plateau in the curve of D b versus CO2 concentration (between 3·5 % and 12 % CO2). This plateau could not be seen from the μmax determinations (batch). Unlike O2 limitation the CO2 inhibition did not disturb the regularity of the curves of the steady-state characteristics. Two levels of O2 limitation were indicated from the curve of biomass versus dilution rate, a minor one, slightly reducing the biomass concentration of the culture and a major one, significantly reducing the biomass. An O2 concentration of 5 % of the incoming gas (dissolved oxygen tension in the culture: 3–5 %) had no effect on the steady-state characteristics of the culture, while 0·4 % O2 significantly affected the curve of biomass versus dilution rate (dissolved oxygen tension 0–0·4 %). The combined effect of oxygen limitation and 12 % CO2, further altered the steady-state characteristics and the biomass curve started to decrease at very low dilution rates. Thus, the two inhibitory agents co-operated and their joint growth restricting effect was considerably stronger than the strongest agent alone. The question whether the restricting effect of the two together should be regarded as ‘synergistic’ or ‘additive’, is still open to discussion even though some evidence was obtained which suggested the former.

Grain Growth and Carbohydrate Content in Spring Wheat at Different CO2-Concentrations

Spring wheat plants cultivated in a controlled environment cabinet were investigated in respect to the influence of different CO2 concentrations on grain growth and carbohydrate content. Treatment with 1500 vpm CO2 from 2 weeks before anthesis till maturity increased the carbohydrate content of the stalk but not of the grain yield. A treatment with 1500 vpm CO2 during the whole growth period significantly increased the number of grains per ear and grain yield per ear but grain weight after this treatment was significantly lower.