Initial CO2 Concentration Research Articles

Investigation of a biosystem based on Arthrospira platensis for air revitalisation in spacecrafts: Performance evaluation through response surface methodology

Arthrospira platensis is featured as a promising microalgae candidate for the development of the biosystems for air revitalisation in spacecrafts and life support in space. An enhanced configuration of a sparged type photobioreactor (PBR), containing 5 L of A. platensis culture, which was equipped with an external LED lighting tube around the reactor, was used in this study. The PBR was operated under dynamic conditions (0.5 L/min) with synthetic air containing CO2 (400, 900, 1400 ppm) and other gas traces (NO2 1 ppm, SO2 2.5 ppm, acetic acid vapours 1 ppm), at various light intensities (1.5, 2.5, 3.5 klux), according to an experimental design. The removal of gas traces (NO2, SO2 and acetic acid vapours) was below the detection limit (e.g. above 90% removal efficiency), while the removal of CO2 ranged between 69% and 85%, depending on the initial CO2 concentration and the light intensity. Thus, the system is able to roughly decrease the contaminant concentration from 1 ppm to below 0.1 ppm for NO2, 2.5 ppm to below 0.1 ppm for SO2, 1 ppm to below 1 ppb for acetic acid vapours and from 1400 ppm to 370 or from 400 ppm to 60 ppm for CO2. The system performance was thus subject to mathematical modelling and optimization in terms of CO2 removal efficiency and CO2 elimination capacity, which were also corroborated with the power consumption for illumination.

Electro-assisted adsorption of Cs(I) and Co(II) from aqueous solution by capacitive deionization with activated carbon cloth/graphene oxide composite electrode

In this study, a new composite of activated carbon cloth/graphene oxide (ACC/GO) was prepared, characterized and used as electrode material for the electro-assisted adsorptive removal of Co2+ and Cs+ from aqueous solution. The ACC/GO composite was synthesized by a vacuum filtration method, and characterized by cyclic voltammetry and various surface characterization methods. Effect of applied voltage and initial concentration of Co2+ and Cs+ on their removal efficiency was examined. The kinetics and isotherms of Co2+ and Cs+ adsorption were investigated to explain the adsorption mechanism. At 0 V, the removal efficiency of Co2+ and Cs+ was 10.1% and 21.4%; at 1.2 V, electro-assistance increased the removal efficiency of Co2+ and Cs+ to 40.8% and 39.7%, respectively. Moreover, ACC/GO composite electrode had higher adsorption capacity compared to the pristine ACC electrode, due to its higher specific surface area and more oxygen-containing functional groups. The maximum adsorption capacity of Co2+ and Cs+ was 16.7 mg g−1 and 22.9 mg g−1, respectively at 1.2 V and 20 mg L−1 by ACC/GO composite electrode. The modeling and experimental results demonstrated that the removal mechanism involved in physical adsorption, chemical adsorption, and electro-adsorption. Overall, the prepared ACC/GO composite electrode had high capacitive deionization performance in removing heavy metal ions from wastewater.

Efficient removal of CO2 from indoor air using a polyethyleneimine-impregnated resin and its low-temperature regeneration

Aminated adsorbents are efficient in capturing high concentrations of CO2, while their efficiency in air purifier for the removal of low concentrations of CO2 from indoor air remains unclear. In this study, a polyethyleneimine-impregnated resin (PEI-MR10) was prepared and used to remove indoor CO2, and its regeneration at low temperatures was evaluated. PEI loading narrowed the pore size distribution but increased the average pore size of the PEI-MR10. The PEI-MR10 with small particle size (0.250–0.425 mm) exhibited higher adsorption capacity and faster adsorption rate than the bigger one. The PEI-MR10 was able to remove all CO2 during the first 2 h with an initial CO2 concentration of 1000 ppm. Under variable indoor conditions, the adsorbed amounts of CO2 could maintain high values from 90 to 136 mg/g. At a relative humidity of 50%, the adsorbed amount on the PEI-MR10 for 1000 ppm CO2 reached 128.4 mg/g. In consideration of real application in air purifier, a cost-effective regeneration method using ambient air was adopted, and the spent PEI-MR10 was regenerated at low temperatures no more than 70 °C. The desorption efficiency of CO2 increased with increasing temperatures, and the best regeneration was obtained at 70 °C. The adsorbed amount of CO2 on the first-regenerated PEI-MR10 decreased significantly, but the adsorbent maintained stable adsorption capacity of about 80 mg/g after three adsorption-regeneration cycles. This study demonstrated that PEI-MR10 was an effective adsorbent for CO2 removal from indoor air.

Initial Land Use/Cover Distribution Substantially Affects Global Carbon and Local Temperature Projections in the Integrated Earth System Model

AbstractInitial land cover distribution varies among Earth system models, an uncertainty in initial conditions that can substantially affect carbon and climate projections. We use the integrated Earth System Model to show that a 3.9 M km2 difference in 2005 global forest area (9–14% of total forest area) generates uncertainties in initial atmospheric CO2 concentration, terrestrial carbon, and local temperature that propagate through a future simulation following the Representative Concentration Pathway 4.5. By 2095, the initial 6 ppmv uncertainty range increases to 9 ppmv and the initial 26 PgC uncertainty range in terrestrial carbon increases to 33 PgC. The initial uncertainty range in annual average local temperature of −0.74 to 0.96 °C persists throughout the future simulation, with a seasonal maximum in Dec‐Jan‐Feb. These results highlight the importance of accurately characterizing historical land use and land cover to reduce overall initial condition uncertainty.

The effect of microorganisms on soil carbonate recrystallization and abiotic CO2 uptake of soil

Desert ecosystems with a high soil pH are considered as a sink for atmospheric CO2. Although high CO2-uptakevia chemical processes is the major CO2-uptake process in saline and alkaline soil, microorganisms may affect the exchange of inorganic carbon between the soil solution and the solid phase. Some studies related to microbial processes on carbonate formation have been published, but seldom focus on saline and alkaline soils. To determine the microbial effects on the inorganic C flux and CaCO3 recrystallization, sterile and non-sterile Solonchak samples were incubated in a 14CO2-labelled atmosphere at two CO2 concentrations (0.2% and 2%). The 14C activity was measured in the soil solution, air, and in CaCO3 after 2, 7, 21, 92 and 197 days. The 14C in dissolved organic carbon in the sterile and non-sterile soils was below 5% of the 14C input. 14C trapping in CaCO3 increased with the decrease of the 14C remaining in the gaseous CO2. Carbonate recrystallization increased logarithmically with time (R2 > 0.96). A two percent initial CO2 concentration lead to higher CaCO3 recrystallization (5–50 × 10−3% of initial CaCO3) compared to a 0.2% initial CO2 concentration (0.8–7 × 10−3% of initial CaCO3) from 2 to 197 days. CaCO3 recrystallization (% of initial CaCO3) in the sterile Solonchak was higher by 10% to 190% than the non-sterile Solonchak, indicating that the microorganisms decreased the 14C trapping of CaCO3 by 4–23% from 2 to 197 days. We assume that microorganisms grew on the carbonate surface like a coating. This must have retarded the carbonate recrystallization. We concluded that the soil CO2 concentration is the most important factor for CaCO3 recrystallization. The presence of microorganisms strongly decreased the CaCO3 recrystallization. CaCO3 recrystallization process including CO2 in soil water could be the abiotic CO2 uptake from the atmosphere by saline and alkaline soil.

Development of computational fluid dynamics model for two initial CO2 concentration in circulating fluidized bed reactor

Nowadays, the global warming is considered as a world problem because it influences the environment by increasing the average temperature of earth surface. One of the greenhouse gases that release from human activities and fossil fuels combustion in industry is CO2. Several technologies are applied to reduce the CO2 emission to atmosphere. In this study, the aim is to capture the CO2 by solid sorbent adsorption with potassium carbonate supported on gamma alumina using full loop circulating fluidized bed reactor in commercial computational fluid dynamics program, ANSYS FLUENT. This study focuses on the effect of initial CO2 concentrations from cement industry and power plant on CO2 removal efficiency. Besides, the solid volume fraction profile is also considered. The simulation results showed the hydrodynamics in circulating fluidized bed reactor that the solid sorbent was high at the reactor wall and low at the reactor center. In addition, the independent input variables were investigated which were percentage of K2CO3 loading on sorbent and gas velocity. The increasing of K2CO3 loading on sorbent and the decreasing of gas velocity increased the CO2 capture efficiency.

Examination of Adsorption Abilities of Natural and Acid Activated Bentonite for Heavy Metals Removal from Aqueous Solutions

The effect of the initial concentration of Cr, Co, Cu, Ni, and Pb metal ions from multicomponent solutions on the sorption capacity of natural and acid activated bentonite was examined in this paper. The acid activation was performed by using hydrochloric and sulfuric acid at different concentrations. The results of adsorption research have shown that bentonite can be effectively used as an adsorbent for the removal of metal ions from multicomponent solutions. Acid activation of bentonite changes the structure and content of individual oxides, increases the porosity and the number of available spots for the adsorption process. For this reason, the bentonite removal efficiency increased after acid activation for all heavy metals tested. With increased acid concentration, the degree of bentonite adsorption increased, and sulfuric acid rather than chloric acid showed better results in removal efficiency.

Optimization upstream CO2 deliverable with downstream algae deliverable in quantity and quality and its impact on energy consumption

Algae CO2 biofixation provides a promising opportunity due to earn carbon credits and valuable end uses. For balancing technology, energy and economy issues in practical utilization, this approach quantitively interprets the contradictions from upstream CO2 source with a wide range of initial concentration to downstream CO2 biofixation product including edible algae and algal biomass. The influence of upstream CO2 deliverable on algal quantity and quality have been assessed, and the influence of CO2 concentration on CO2 transport mode choice has been also assessed coupling the transportation distance. In downstream algal fixation, quantitively relationship of algal growth have been established. The assessment discovered that direct energy consumptions complied with logarithmic relationship with specific productivities while both direct energy and indirect energy consumption complied with linear relationship with protein content. According to sensitive uncertainty analysis, initial CO2 concentration is a critical parameter to influence significantly energy consumption in upstream CO2 deliverables and algal quality while the contents of protein and specific productivity are the critical sensitive parameters in downstream algae deliverables. Potential modification systems are achieved for significantly reducing energy consumption by improving specific productivity and carbon abundance with low protein content in algae.

Intensification of CO₂ capture by monoethanolamine solution containing TiO2 nanoparticles in a rotating packed bed

This study investigates the mass transfer intensification in the absorption of carbon dioxide (CO₂) into a monoethanolamine (MEA) solution enhanced by TiO2 nanoparticles in a typical rotating packed bed (RPB). The overall volumetric gas phase mass transfer coefficients (KGa) were investigated in a counter-current RPB with blade packings. The effects of TiO2 and MEA concentrations, rotational speed, initial concentration of CO₂, gas and liquid flow rates on KGa were specified. The rotational speed had positive effects on KGa. It is deduced that TiO2 nanoparticles led to enhanced CO₂ capture efficiency of over 26.9 % and enhancement in KGa from 7.5%–96.1% for MEA based TiO2 suspension in comparison with MEA solution without nanoparticles. Therefore, TiO2 nanoparticles can augment the mass transfer coefficient and intensify the CO₂ absorption, even in a high-efficiency equipment like a high gravity RPB.

Carbon Dioxide Adsorption on Grafted Nanofibrous Adsorbents Functionalized Using Different Amines

Of late, the demand for new CO2 adsorbents with high adsorption capacity and stability is growing very fast. Nanofibrous adsorbents are potential materials for such application with most attempts made on carbon nanofibers. In this study, a series of electrospun nanofibrous adsorbents containing amines were prepared using a 3-stage promising approach and tested comparatively for CO2 capture. The preparation of adsorbents involved electrospinning of syndiotactic polypropylene (s-PP) solution, radiation-induced grafting (RIG) of glycidyl methacrylate (GMA) onto electrospun nanofibers, and functionalization of poly-GMA grafted s-PP nanofibrous mats with different amines, including ethanolamine (EA) diethylamine (DEA) and triethylamine (TEA). The effect of different amination parameters: namely, amine concentration, reaction time, temperature, and degree of grafting (DG) on the degree of amination (DA), was evaluated. The nanofibrous mats containing amine were tested for CO2 adsorption in a fixed bed column operated under various parameters such as amine density, amine type, initial CO2 concentration and temperature. The adsorbents recorded CO2 adsorption capacities of 2.87, 2.06 and 0.94 mmol/g for EA-, DEA- and TEA-containing adsorbents, respectively, at 30° C using initial CO2 concentration of 15%. This was coupled with the same order of high amine efficiency of 75, 57, and 31%. Results demonstrated that the nanofibrous adsorbent containing amine had strong potential for CO2 capture application.

Soil properties and not high CO2 affect CH4 production and uptake in periodically waterlogged arable soils

Several studies related to CH4 cycling focus on the effect of elevated atmospheric CO2 levels on soil methanogenesis and methanotrophy. However, periodically waterlogged soils are characterized by much higher CO2 concentrations, while aggregates forming in arable soils due to traditional cultivation may be a natural CH4 source for low-affinity methanotrophs. We present a comprehensive laboratory investigation into both methanogenesis and methanotrophy in three different soils under ambient and high CO2 concentrations. The tested materials were agricultural soils widely distributed in Europe: Eutric Cambisol, Haplic Podzol and Mollic Gleysol with determined properties: Corg, Ntot, clay, silt, sand, pH, NO3−, NH4+. We conducted two independent experiments on methanogenesis (flooded conditions) and methanotrophy (non-flooded conditions). All samples for both studies were divided into three sets which differed in the initial CO2 concentration in headspace: ambient CO2 (0.03% v/v ± 0.005), and two high CO2 levels (5% ± 0.4 and 10% ± 0.5 v/v CO2). Moreover, 1% (v/v) of CH4 was added to all sets prepared for the methanotrophy test since low-affinity methanotrophy in the tested soils had been reported previously. Gas concentrations (CH4, CO2, O2) in headspace were measured using gas chromatography method. We observed that the examined soils differed in their ability to produce CH4 as follows: Haplic Podzol = Eutric Cambisol > Mollic Gleysol, as well as to consume CH4: Mollic Gleysol > Haplic Podzol > Eutric Cambisol. The CH4 emissions started faster in Gleysol, but the final CH4 concentration and CH4 production rate in this soil were significantly lower than in the two other soils. The CH4 uptake rate significantly differed among the tested soils. The MANOVA confirmed the significance of the soil-type factor in determining both process rates, whereas the effect of CO2 level and the interaction between both factors were not significant. The amount of consumed O2 during CH4 oxidation was also characteristic for examined soil, but did not differ significantly between CO2 variants. CH4 production and consumption in three different soils (Eutric Cambisol, Haplic Podzol and Mollic Gleysol) collected from periodically waterlogged arable fields were more strongly affected by soil properties than by high CO2 concentration. In contrast, the high CO2 level significantly decreased CO2 production accompanying tested the CH4-related processes.

Optimization of an innovative composited material for effective monitoring and removal of cobalt(II) from wastewater

A newly designed composite adsorbent (CpAD), ultra-trace detection ability and a superior adsorption capability to that novel material, was fabricated by functional ligand (3-(((5-ethoxybenzenethiol)imino)methyl)–salicylic acid) combining with mesoporous silica. The resultant CpAD was maintained a high surface area with ordered porosity even after successful ligand anchoring. The application of cobalt (Co(II)) detection and adsorption was measured at an optimum experimental protocol with exhibition of significant color visualization. The experiment conditions were optimized based on contact time, solution pH, initial Co(II) concentration and diverse competing metal ions. The CpAD was able to detect the low level Co(II) ion as the detection limit was 0.39 μg/L. The data were clarified that the CpAD was not affected with the existing competing ions and the signal intensity and specific color was observed only toward the Co(II) ion. When used as an adsorbent, the CpAD was demonstrated a very quick adsorption property for the removal of Co(II) ions. The adsorption capability approaches 185.23 mg/g, which is one of the highest capabilities of today's materials. The data also revealed that the removal capabilities of the CpAD for Co(II) ions depended on the material functionality and initial concentration of Co(II) ions. The elution of Co(II) ions from the saturated composite adsorbent was desorbed successfully with 0.30 M HCl. The regenerated adsorbent that remained maintained the high selectivity to Co(II) ions and exhibited almost the same adsorption capacity as that of the original adsorbent. The highest percentage adsorption of Co(II) exceeds 96% in the presence of competing ion, indicating that the CpAD is one of the very suitable composite adsorbent in environmental pollution management.

A dynamic botanical air purifier (DBAP) with activated carbon root-bed for reducing indoor carbon dioxide levels

Indoor Air Quality (IAQ), is important in buildings because it can affect an occupant’s health and productivity. Carbon Dioxide (CO2) is a main indicator of IAQ. 4 decades ago, researchers discovered the potential for indoor plants to remediate indoor air pollutants via photosynthesis. This study investigates the CO2 removal rate when a Maranta Leuconeura is paired with activated carbon (AC), as well as a mechanical ventilation system that draws air into its root-bed making it an active system (DBAP). The results were compared to passive systems i.e plant with AC, potting soil etc. The study was conducted in a 0.7 m3 Plexiglas chamber with initial CO2 concentrations of 1500±100 ppm while initial temperatures ranged between 24 ± 2°C for a duration of 6 hours continuously. Results showed, the DBAP reduced CO2 levels by 40.90% while a passive plant with AC only, was able to lower CO2 levels by 15.20%. The other passive systems did not reduce CO2 levels. All systems were able to raise humidity and reduce temperature in the chamber, with the exception of the DBAP, which slightly increased the temperature in the chamber.

In situ diamond anvil cell (DAC) experiments on equilibrated carbonate–CO2–H2O interaction under elevated temperature and pressure

The carbonate–CO2–H2O interaction in a closed system under burial conditions was simulated in diamond anvil cell (DAC) with an in situ Raman spectroscopy. Experiments were performed in \({\text{H}}_{2} {\text{CO}}_{3}\) solution at acidic pH (≈ 5.6), 20–260 °C, and atmospheric pressure to about 400 MPa. Pressure was first solely increased to separately evaluate the pressure effect on carbonate dissolution/precipitation. Then temperature and pressure were increased together alike in the burial process, to monitor the dissolution/precipitation tendency of carbonate during burial. A continuous dissolution was observed for both limestone and dolostone when solely increasing pressure. A rapid dissolution and then continuous precipitation were observed when increasing temperatures and pressures simultaneously. These observations indicate that pressure has a positive effect (prograde solubility), while temperature has a negative effect (retrograde solubility) on CO2 solubility and carbonate dissolution. In case of low initial CO2 content as our experiments revealed, the increase in solid carbonate volume and a counterbalance decrease in porosity caused merely by increasing burial depth are minor (< 0.23%). The porosity decrease of dolostone was likely less than that of limestone at smaller burial depth (< 1.5 km), and notable at bigger burial depth. This work may help to improve our understanding on carbonate reservoir porosity evolution during burial.

Removal of CO2 in a multistage fluidized bed reactor by amine impregnated activated carbon: optimization using response surface methodology

Carbon dioxide (CO2) is the major component of greenhouse gas. Increase in concentration of CO2 in the atmosphere leads to global warming. To remove the CO2 from waste flue gas a four-stage counter-current multistage fluidized bed adsorber was developed and operated in continuous bubbling fluidization regime for the two-phase system. This paper describes the optimum condition for CO2 removal efficiency in a multistage fluidized bed reactor using amine impregnated activated carbon. Response surface methodology with central composite design was used to determine the effect of three variables on the response. The variables are inlet concentration of CO2 in ppm (ranging from 3000 to 20,000), impregnation ratio of monoethanol amine (ranging from 0.2 to 0.6) and weir height in mm (20–60). The response was CO2 removal efficiency. The factor which was most influential has been identified from the analysis of variance. The optimum CO2 removal efficiency for the amine impregnated activated carbon (MEA-AC) was found to be 95.17%, at initial concentration of CO2 7312.85 ppm, chemical impregnation ratio of 0.31, and weir height 48.65 mm. From the experiment, the CO2 removal efficiency was found to be 95.97% at the same operating conditions. The predicted response was found to relevance with experimental data.

Sorption of carbon dioxide by chickpeas packaged in modified atmospheres

Modified atmospheres (MAs) with high CO2 concentrations are used for packaging several commodities with different purposes, including as an alternative method for pest control. When used in gas-tight flexible packages, sorption by the commodity produces a vacuum effect that causes the package to adopt a random shape and makes it impossible to reshape it without opening the package. Other than storage problems in retail storehouses, sorption can affect the amount of gas inside the packages needed for pest control. This study reports the amount of CO2 sorption by chickpeas packaged with different MAs and the negative pressure produced due to the decrease in the partial pressure of the gas. Trials were conducted in 710 mL semi-rigid plastic containers filled up to 24%, 48% and 96% of their capacity (filling ratios). Three MAs (90%, 70% and 50% CO2 with a residual of 3%, 6% and 10% O2, respectively, and balanced by N2) were used during 24 h, 48 h, 240 h and 384 h of exposure at 20 °C. The maximum sorption (1.28 g CO2/kg of chickpea) was obtained with the lower filling ratio (24%) and with an initial concentration of 90%. Sorption decreased with the decline in the initial CO2 concentration and with the rise in the filling ratio. The time needed to reach the equilibrium sorption varied between 141 h and 27 h, depending on the initial CO2 concentration and the filling ratio of chickpeas. The vacuum effect produced inside the containers by sorption produced a negative pressure that increased with the increase in the filling ratio and the initial CO2 concentration. Whether the amount of CO2 available in packages after gas sorption is still effective for controlling chickpea pests remains to be tested.

Performance of dry water- and porous carbon-based sorbents for carbon dioxide capture

Carbon dioxide is the primary greenhouse gas that has a strong impact on global warming. Several technologies have been developed for capturing CO2 to mitigate the greenhouse effect. The objective of this research was to investigate the performance of several sorbents based on dry water and porous carbon materials for capturing CO2. Seven sorbents were prepared and comparatively evaluated for their CO2 capture capabilities: (i) Conocarpus biochar (CBC); (ii) commercial activated carbon (CAC); (iii) normal dry water (NDW); (iv) K2CO3-treated CBC (TCBC); (v) K2CO3-modified dry water (MDW); (vi) MDW and 2% TCBC (MDWTCBC); and (vii) MDW and 2% activated carbon (MDWCAC). The sorption process was carried out with initial CO2 concentration of 5.7%, temperature of 25 °C, feed gas flow rate of 0.5 l min−1 and a pressure of 1.0 bar. The pure CO2 was mixed with O2 or N2 to achieve the desired inlet concentration of CO2. The CO2 adsorption capacity and partition coefficient (PC) of the tested sorbents were evaluated at 5% and 100% breakthrough (BT). The results showed a longer breakthrough and equilibrium adsorption times for CO2 when mixed with N2 than with O2. Among all sorbents, both CAC and CBC showed enhanced CO2 capture performance with equilibrium (100% BT) adsorption capacities of 239 and 197 mg g−1, respectively (in terms of PC: 1.0 × 10−3 and 7.9 × 10−4 mol kg−1 Pa−1, respectively). In contrast, the performance of TCBC and the dry water-based sorbents was far lower than CAC or CBC. The CO2 adsorption data fitted well to the non-linearized form of the pseudo-first-order kinetic model. The Fourier-transform infrared spectral patterns indicated that the reaction of CO2 molecules with the hydroxyl groups of sorbents is possible through the formation of chemisorbed CO2 species. It could be concluded that the activation process did not play a role in increasing the CO2 capture performance in order to form new active sorption sites. However, Conocarpus biochar can be used as efficient sorbent for CO2 capture with a better performance than other materials tested previously (e.g., activated carbon).

Sustainable biohydrogen production by dark fermentation using carbon monoxide as the sole carbon and energy source

Abstract This study evaluated the kinetics of biomass growth, biohydrogen production and substrate utilization using carbon monoxide as the sole carbon and energy source. Experiments were conducted at different initial CO concentration in the range 1.8–5.12 mmol/L over a period of 144 h in order to assess the effect of CO concentration on biomass growth, substrate utilization and H2 production. Complete utilization (100%) of CO was achieved up to an initial concentration of 3.8 mmol/L and it gradually decreased to 84.5% for 4.4 mmol/L and 83.7% for 5.12 mmol/L. The experimental results of CO utilization were fitted to substrate utilization kinetic models reported in the literature, and it followed a modified Gompertz model. A maximum yield of H2 on CO was found to be 70.8% and a maximum H2 production of 29.9 mmol/L was obtained for an initial CO concentration of 5.12 mmol/L. The experimental results on biohydrogen production matched well with the values predicted using the modified Gompertz model. Furthermore, the experimental data on specific growth rate of the ananerobic biomass at different H2 concentration was fitted to different product inhibition models and the best fit was obtained with Aiba model. This study showed product inhibition on both specific growth rate of biomass and H2 production due to H2 accumulation in the gas phase. A very good correlation between the experimental specific growth rate and the Han-Levenspiel model predicted values were obtained with a high determination coefficient (R2) value of more than 0.96.

Nickel and cobalt adsorption on hydroxyapatite: a study for the de-metalation of electronic industrial wastewaters

In the present study, the Ni(II) and Co(II) adsorption efficiency and selectivity, as well adsorption mechanisms on a stoichiometric hydroxyapatite (HAP) surface have been investigated. Characterization studies (N2 adsorption/desorption and X-ray powder diffraction (XRPD) analyses) and adsorption tests under various operative conditions provided detailed information about the use of HAP in the de-metalation of wastewaters containing Ni and Co as polluted metal species. The sorption capacity of HAP has been evaluated by static batch adsorption tests varying initial concentration of Ni(II) and Co(II) species (from ca. 0.25 to 4.3 mM), contact time (from 15 min to 24 h), and pH (from 4 to 9) operative parameters. Proposed mechanisms of adsorption of Ni(II) and Co(II) on HAP surface are ion-exchange and surface complexation; a partial contribution of chemical precipitation from bulk solution should be considered at pH 9. In addition, adsorption isotherms of Ni(II) and Co(II) on HAP have been collected at 30 °C and pH 4 and modeled by employing different equations. The maximum sorption capacities have been quantified as 0.317 mmol $${\text{g}}_{{{\text{HAP}}}}^{{ - 1}}$$ (18.6 mg $${\text{g}}_{{{\text{HAP}}}}^{{ - 1}}$$ ) and 0.382 mmol $${\text{g}}_{{{\text{HAP}}}}^{{ - 1}}$$ (22.5 mg $${\text{g}}_{{{\text{HAP}}}}^{{ - 1}}$$ ) for Ni(II) and Co(II), respectively. Selectivity to Co and Ni in the adsorption process on HAP has also been investigated; HAP has higher affinity towards Co than Ni species (Co:Ni = 2.5:1, molar ratio).

Enhanced CO2 sorption capacity of amine-tethered fly ash residues derived from co-firing of coal and biomass blends

Co-firing of coal and biomass blends provides a promising route for clean energy utilization with high efficiency and mitigated pollutants emission. However, the technology meets an important challenge in effective utilization of the co-firing fly ashes. Efforts have been made to valorize the co-firing fly ash residues as potential CO2 sorbents. To achieve enhanced CO2 sorption performance, the samples were modified with tetraethylenepentamine (TEPA). Effects of amine loading, CO2 sorption temperature, initial CO2 concentration and gas flow rate on CO2 sorption behaviors of the amine-tethered sorbents were investigated. The desired sorbent with 25% TEPA loading presented the highest CO2 sorption capacity of 1.19 mmol CO2/g when tested under 60 °C and 15%CO2 with a total gas flow rate of 1200 ml min−1. The effects of regeneration temperature and ramping rate on sorbent regeneration performance were demonstrated. The maximum sorbent regeneration efficiency of 97.2% was achieved under the regeneration condition of 110 °C and 5 °C min−1. CO2 sorption capacity of the amine-tethered sorbent kept stable within 5 repeated cycles. These findings indicate that the amine-tethered sorbent could be a good candidate for on-site CO2 capture from flue gas in co-firing power plants.