A study of carbon dioxide sequestration has been performed in aqueous electric arc furnace (EAF) and ladle furnace (LF) slag suspensions, in leached hydrated-matrixes, and in leachates to estimate ...their intrinsic sequestration potential at ambient conditions (temperature of 20 ± 1 °C and atmospheric pressure). The CO2 sequestration was tested in aqueous suspensions of steel slags at a liquid-to-solid ratio of 10 kg/kg as well as in leached hydrated-matrixes and leachates isolated from these fresh slag suspensions after three consecutive leachings. The sequestration assays were performed at 20 °C with a flow rate of 5 mL/min of a CO2 concentration of 15.00 vol %. The results have revealed that the CO2 sequestration capacity of the LF slag suspension (24.7 g of CO2/100 g of slag) is 14 times superior to that of the EAF slag suspension. This greater CO2 sequestration capacity of the LF slag suspension may be associated in large part to its higher content of portlandite, which reacts with CO2 relative to the EAF slag suspension. Moreover, the separation of hydrated-matrixes and leachates significantly enhanced the CO2 sequestration capacity of EAF slag while a slight decrease was observed for the LF slags. This may be due to an obstruction of the CO2 binding sites of LF slag hydrated-matrixes following the accumulation of calcium carbonate. Taken together, these results suggest that EAF and LF slags could be used for the CO2 sequestration and given a good yield as well in aqueous suspension as in separated matrixes and leachates.
We report the advances in the principal structural and experimental factors that might influence the carbon dioxide (CO
2
) adsorption on natural and synthetic zeolites. The CO
2
adsorption is ...principally govern by the inclusion of exchangeable cations (countercations) within the cavities of zeolites, which induce basicity and an electric field, two key parameters for CO
2
adsorption. More specifically, these two parameters vary with diverse factors including the nature, distribution and number of exchangeable cations. The structure of framework also determines CO
2
adsorption on zeolites by influencing the basicity and electric field in their cavities. In fact, the basicity and electric field usually vary inversely with the Si/Al ratio. Furthermore, the CO
2
adsorption might be limited by the size of pores within zeolites and by the carbonates formation during the CO
2
chemisorption. The polarity of molecules adsorbed on zeolites represents a very important factor that influences their interaction with the electric field. The adsorbates that have the most great quadrupole moment such as the CO
2
, might interact strongly with the electric field of zeolites and this favors their adsorption. The pressure, temperature and presence of water seem to be the most important experimental conditions that influence the adsorption of CO
2
. The CO
2
adsorption increases with the gas phase pressure and decreases with the rise of temperature. The presence of water significantly decreases adsorption capacity of cationic zeolites by decreasing strength and heterogeneity of the electric field and by favoring the formation of bicarbonates. The optimization of the zeolites structural characteristics and the experimental conditions might enhance substantially their CO
2
adsorption capacity and thereby might give rise to the excellent adsorbents that may be used to capturing the industrial emissions of CO
2
.
A microbial consortium that degrades ethyl‐tert‐butyl ether (ETBE) as the sole source of carbon and energy under aerobic conditions was selected from a gasoline‐polluted soil. This consortium ...consists of a variety of microorganisms with a predominance of filamentous morphology. Degradation of ETBE was found to be solely related to bacterial activity. After prolonged cultivation followed by successive transfers, the consortium's degradation ability was improved and reached a specific degradation rate of 95 mg/gprotein/h (about 146 mg/gdry wt/h). This exceeds the previously reported rates in the literature for ETBE‐degrading microorganisms as pure or mixed cultures. Furthermore, a stoichiometric balance of chemical oxygen demand (COD) removal and oxygen uptake with ETBE removal provides indirect evidence of complete degradation. The consortium's activity was not inhibited by high ETBE concentrations (≤1,600 mg/L), and large inoculum sizes (≥120 mgprotein/L) were desirable for a faster and complete degradation of ETBE. The enriched consortium was also able to completely degrade methyl‐tert‐butyl ether (MTBE), tert‐amyl methyl ether (TAME), and tert‐butyl alcohol (TBA), both alone and in mixture with ETBE, without any measurable release of major degradation intermediates. In each case, MTBE and TAME exhibited the most significant resistance to degradation while TBA was rapidly degraded.
An analysis of carbonation was carried out with the aqueous fresh red mud suspension at a liquid-to-solid ratio of 10 kg/kg, as well as in the leached-hydrated matrixes and leachates isolated from ...this red mud suspension after three successive leachings, to evaluate their intrinsic carbonation potential at ambient conditions (temperature of 20 ± 1 °C and atmospheric pressure). The carbonation assays were performed at 20 °C using a CO2 concentration of 15.00 vol% at a flow rate of 5 mL/min. The red mud matrix has a great leaching capacity of Na−(hydr)oxide, which is the principal hydroxide that seems to be implicated in the carbonation of leachates that have half-carbonation capacity of red mud. Moreover, the carbonation of the red mud suspension also involves a portlandite-containing matrix. The carbonation of the red mud suspension and leachates implicates a complete neutralization of their content in Ca− and Na−(hydr)oxides. Although the leached hydrated-matrixes seem to be partially carbonated, it preserves a carbonation capacity near to that of leachate after three successive leachings. Moreover, three leached hydrated-matrixes and leachates have a carbonation capacity (7.09 g of CO2/100 g of red mud) higher than the carbonation capacity obtained for the red mud suspension, which is evaluated to 4.15 g of CO2/100 g of red mud. Taken together, these results suggest that the carbonation of the red mud may be enhanced by the use of leached hydrated-matrixes and leachates obtained from multiple leaching.
This review presents a summary of the main interactions that occur during the carbon dioxide (CO
2) adsorption at the surface of steel slags with basic (CaO, MgO), amphoteric (Al
2O
3, Cr
2O
3, TiO
...2, MnO, iron oxides) and acidic (SiO
2) oxides. The high content of metal oxides in steel slags gives them a great potential to adsorb CO
2, reaching a saturation value of about 0.25
kg of CO
2/kg of slag. CO
2 is physisorbed and chemisorbed on the most of metal oxide types. Generally, the CO
2 physisorption on the basic and amphoteric metal oxides involves an electrostatic interaction between the CO
2 and the cation from the oxides while the CO
2 chemisorption rather implicates the basic sites that acts as the electron donor, and which are associated with O
2− ions localized at surface defects. These interactions result in the formation of carbonates (monodentates or unidentates and bidentates). The affinity of oxides for the CO
2 and the carbonate formation principally depend of the strength and number of basic sites at their surface and varies as following: basic oxides
>
amphoteric oxides
>
acidic oxides. The basic metal oxides generally represent the best electron donors and thus the best CO
2 adsorbents due to the high basicity and their great number of reaction sites. Hence, it appears that the surface structure of basic and amphoteric metal oxides which may favour their interaction with the CO
2, as well as their basicity is the determinant factor contributing to the formation of carbonate species. The molecular analysis of CO
2 adsorption on steel slag metal oxides will provide useful data to identify rate-controlling mechanisms and should be considered for the development of new effective methods for the capture of atmospheric CO
2 emissions released from industries.
The ‘earthy' and ‘muddy' off-flavours in pond-reared fish are due to the presence of geosmin or 2-methylisoborneol in the flesh of the fish. Similar off-flavours have been reported in fish raised in ...recirculating aquaculture systems (RAS); however, little information is available regarding the cause of these off-flavours. Our hypothesis was that earthy and muddy off-flavour compounds, found previously in pond-raised fish, are also responsible for off-flavours in fish raised in RAS. In this preliminary study, we examined water, biofilms in RAS and fillets from cultured arctic charr known to have off-flavours and requiring depuration using instrumental solid-phase microextraction procedure and gas chromatograph-mass spectrometry (GC-MS) and human sensory analyses. Geosmin was present in the samples taken from the biofilter and on the side walls of the tanks. Two-methylisoborneol was only found in low levels in the samples. The GC-MS results indicated the presence of geosmin in the fillets (705 ng kg⁻¹), but lower levels were found in the water (30.5 ng L⁻¹). Sensory analyses also detected an earthy flavour (i.e., geosmin presence) in the fillets, and, therefore, it appears that geosmin is the main compound responsible for the off-flavour in RAS. Further studies are being performed to identify the microorganisms responsible for geosmin production in RAS.
Aerobic degradation of ethyl
tert-butyl ether (ETBE), Methyl
tert-butyl ether (MTBE) and
tert-amyl methyl ether (TAME), as tertiary-substrates, was studied in a continuous upflow fixed-bed reactor ...(UFBR) using an external oxygenator and sintered glass rings as biomass carriers. The UFBR has been shown to be an effective system for the simultaneous and continuous long-term degradation of the three-oxygenates mixture as sole source of carbon and energy. Therefore, the oxygenates feed concentration must be related in conjunction with the hydraulic retention time “HRT” and vice versa. The permissible feed concentration of both MTBE and TAME to achieve more than 99% removal efficiency is about 80
mg
L
−1 at a constant HRT of 24
h. The same performance can be obtained if the HRT kept at a value equal or above to 15
h for a feed concentration of about 80
mg
L
−1 of both MTBE and TAME. However, the ETBE removal efficiency was always greater than 99% whatever the ETBE concentration feed (between 10 and 100
mg
L
−1 at a constant HRT of 24
h) and the HRT (between 24 and 13
h at a constant concentration feed of about 80
mg
L
−1) tested in this study. The highest ETBE, MTBE and TAME removal rates achieved throughout the UFBR runs, with efficiency better than 99%, were 140±5, 132±2 and 135±2
mg
L
−1
d
−1, respectively. No metabolic intermediates including
tert-butyl alcohol (TBA),
tert-butyl formate (TBF) and
tert-amyl alcohol (TAA) were detected in the effluent during all the reactor runs. Furthermore, based on the chemical oxygen demand balance, all the removed oxygenates were completely metabolized. The results of this study suggest that the higher resistance to biodegradation exhibited by the MTBE and the TAME is probably due to the steric hindrance for the attacking enzyme(s); and the major limiting step to the oxygenate degradation maybe the accessibility and the cleavage of the ether bond, but not the assimilation of their major metabolites such as TBA, TBF and TAA. These results were concomitant with the batch tests using the reactor's immobilized biomass as inoculum.
This review presents a summary of the main interactions that occur during the carbon dioxide (CO2) adsorption at the surface of steel slags with basic (CaO, MgO), amphoteric (Al2O3, Cr2O3, TiO2, MnO, ...iron oxides) and acidic (SiO2) oxides. The high content of metal oxides in steel slags gives them a great potential to adsorb CO2, reaching a saturation value of about 0.25 kg of CO2/kg of slag. CO2 is physisorbed and chemisorbed on the most of metal oxide types. Generally, the CO2 physisorption on the basic and amphoteric metal oxides involves an electrostatic interaction between the CO2 and the cation from the oxides while the CO2 chemisorption rather implicates the basic sites that acts as the electron donor, and which are associated with O2- ions localized at surface defects. These interactions result in the formation of carbonates (monodentates or unidentates and bidentates). The affinity of oxides for the CO2 and the carbonate formation principally depend of the strength and number of basic sites at their surface and varies as following: basic oxides > amphoteric oxides > acidic oxides. The basic metal oxides generally represent the best electron donors and thus the best CO2 adsorbents due to the high basicity and their great number of reaction sites. Hence, it appears that the surface structure of basic and amphoteric metal oxides which may favour their interaction with the CO2, as well as their basicity is the determinant factor contributing to the formation of carbonate species. The molecular analysis of CO2 adsorption on steel slag metal oxides will provide useful data to identify rate-controlling mechanisms and should be considered for the development of new effective methods for the capture of atmospheric CO2 emissions released from industries.
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