The objective of the present study was to analyse the behaviour of activated carbon with different chemical and textural properties in nitroimidazole adsorption, also assessing the combined use of ...microorganisms and activated carbon in the removal of these compounds from waters and the influence of the chemical nature of the solution (pH and ionic strength) on the adsorption process. Results indicate that the adsorption of nitroimidazoles is largely determined by activated carbon chemical properties. Application of the Langmuir equation to the adsorption isotherms showed an elevated adsorption capacity (
X
m
=
1.04–2.04
mmol/g) for all contaminants studied. Solution pH and electrolyte concentration did not have a major effect on the adsorption of these compounds on activated carbon, confirming that the principal interactions involved in the adsorption of these compounds are non-electrostatic. Nitroimidazoles are not degraded by microorganisms used in the biological stage of a wastewater treatment plant. However, the presence of microorganisms during nitroimidazole adsorption increased their adsorption on the activated carbon, although it weakened interactions between the adsorbate and carbon surface. In dynamic regime, the adsorptive capacity of activated carbon was markedly higher in surface water and groundwater than in urban wastewaters.
The present study aimed to analyze the behavior of different activated carbons in the adsorption and removal of bisphenol A (2−2-bis-4-hydroxypheniyl propane) from aqueous solutions in order to ...identify the parameters that determine this process. Two commercial activated carbons and one prepared in our laboratory from almond shells were used; they were texturally and chemically characterized, obtaining the surface area, pore size distribution, mineral matter content, elemental analysis, oxygen surface groups, and pH of the point of zero charge (pHPZC), among other parameters. Adsorption isotherms of bisphenol A and adsorption capacities were obtained. The capacity of the carbons to remove bisphenol A was related to their characteristics. Thus, the adsorption of bisphenol A on activated carbon fundamentally depends on the chemical nature of the carbon surface and the pH of the solution. The most favorable experimental conditions for this process are those in which the net charge density of the carbon is zero and the bisphenol A is in molecular form. Under these conditions, the adsorbent−adsorbate interactions that govern the adsorption mechanism are enhanced. Influences of the mineral matter present in the carbon samples and the solution chemistry (pH and ionic strength) were also analyzed. The presence of mineral matter in carbons reduces their adsorption capacity because of the hydrophilic nature of the matter. The presence of electrolytes in the solution favor the adsorption process because of the screening effect produced between the positively charged carbon surface and the bisphenol A molecules, with a resulting increase in adsorbent−adsorbate interactions.
The main objectives of this study were: (1) to investigate the decomposition and mineralization of nitroimidazoles (Metronidazole MNZ, Dimetridazole DMZ, and Tinidazole TNZ) in waste and drinking ...water using gamma irradiation; (2) to study the decomposition kinetics of these nitroimidazoles; and (3) to evaluate the efficacy of nitroimidazole removal using radical promoters and scavengers. The results obtained showed that nitroimidazole concentrations decreased with increasing absorbed dose. No differences in irradiation kinetic constant were detected for any nitroimidazole studied (0.0014–0.0017
Gy
−1). The decomposition yield was higher under acidic conditions than in neutral and alkaline media. Results obtained showed that, at appropriate concentrations, H
2O
2 accelerates MNZ degradation by generating additional HO
; however, when the dosage of H
2O
2 exceeds the optimal concentration, the efficacy of MNZ degradation is reduced. The presence of t-BuOH (HO
radical scavenger) and thiourea (HO
, H
and e
aq
− scavenger) reduced the MNZ irradiation rate, indicating that degradation of this pollutant can take place
via two pathways: oxidation by HO
radicals and reduction by e
aq
− and H
. MNZ removal rate was slightly lower in subterranean and surface waters than in ultrapure water and was markedly lower in wastewater. Regardless of the water chemical composition, MNZ gamma irradiation can achieve i) a decrease in the concentration of dissolved organic carbon, and ii) a reduction in the toxicity of the system with higher gamma absorbed dose.
The main objective of this study was to analyze the effectiveness of technologies based on the use of ozone and activated carbon for the removal of nitroimidazoles from water, considering them as ...model of pharmaceutical compounds. A study was undertaken of the influence of the different operational variables on the effectiveness of each system studied (O
3, O
3/activated carbon), and on the kinetics involved in each process. Ozone reaction kinetics showed that nitroimidazoles have a low reactivity, with
k
O
3
values <350
M
−1
s
−1 regardless of the nitroimidazole and solution pH considered. However, nitroimidazoles have a high affinity for HO
radicals, with radical rate constant (
k
HO) values of around 10
10
M
−1
s
−1. Among the nitroimidazole ozonation by-products, nitrate ions and 3-acetyl-2-oxazolidinone were detected. The presence of activated carbon during nitroimidazole ozonation produces (i) an increase in the removal rate, (ii) a reduction in the toxicity of oxidation by-products, and (iii) a reduction in the concentration of dissolved organic matter. These results are explained by the generation of HO
radicals at the O
3–activated carbon interface.
This paper presents a new procedure to optimize the geometric parameters of a n-type coaxial HPGe detector. It is based on a statistical technique called “Design of Experiments” (DoE). This technique ...aims to identify the most influential parameters and to determine the optimal configuration. In this work, The effects of each parameter on the detector responses have been investigated by a fractional factorial design. Only the most influential factors contributing to the detector response have been selected. Precise modeling of these factors was then performed using a full factorial design. Based on the results obtained from this design, the full energy peak efficiencies according to the geometric parameters were modeled by a multiple-linear regression. These models have been statistically validated by analysis of variance (ANOVA). The optimal combination of the geometric parameters has been identified using the desirability function approach, which is a useful tool to optimize multi-response problems. A verification test was performed to validate the results obtained. It was observed that the relative deviation found between experimental and simulated values was less than 5%.
•Optimization of geometrical dimensions of an HPGe detector.•Application of Monte Carlo simulation and “Design of Experiments” technique.•Investigating influence of each detector parameter on the FEPE.•Achieving good agreement between the measured and the simulated results.
Hydrophobic interactions govern the adsorption of nitroimidazoles on activated carbons. A model that combines external mass transport and intraparticle diffusion was applied, achieving an adequate ...fit to the experimental data.
The adsorption kinetics of four nitroimidazoles, Dimetridazole (DMZ), Metronidazole (MNZ), Ronidazole (RNZ) and Tinidazole (TNZ), were studied on three activated carbons: two commercial carbons from Sorbo-Norit (S) and Merck (M) and a third prepared by chemical activation of petroleum coke (C). Experimental data of the corresponding adsorption kinetics were analyzed by applying pseudo-first and pseudo-second-order models and a general diffusion model. Application of pseudo-first and pseudo-second-order kinetic models verified the following: (i) The kinetic model used that better predicts the adsorption rates depends of both the adsorbent and adsorbate studied. (ii) Nitroimidazole adsorption rate decreases in the order MNZ
>
DMZ
>
RNZ
>
TNZ; therefore, in the case of MNZ, molecular size does not appear to be a determining factor in the process. (iii) Nitroimidazole adsorption rate on carbons increases in the order C
<
S
<
M, which is related to the increase in carbon hydrophobicity. Hence, in general, hydrophobic interactions appear to govern the kinetics of the adsorption process. Finally, a general diffusion model was applied that combines external mass transport and intraparticle diffusion, achieving an adequate fit to the experimental data. There are notable differences among the diffusivity values for the different nitroimidazoles that do not appear to be exclusively related to carbon textural parameters or adsorbate size. Therefore, adsorbent and adsorbate chemical characteristics are highly important to establish the adsorption mechanism of nitroimidazoles on activated carbons.
This paper studies the uranium content and uranium isotopic disequilibria as a tool to identify hydrogeochemical processes from 52 groundwater samples in the province of Granada (Betic Cordillera, ...southeastern Spain). According to the geological complexity of the zone, three groups of samples have been considered. In Group 1 (thermal waters; longest residence time), the average uranium content was 2.63 ± 0.16 μg/L, and 234U/238U activity ratios (AR) were the highest of all samples, averaging 1.92 ± 0.30. In Group 2 (mainly springs from carbonate aquifers; intermediate residence time), dissolved uranium presented an average value of 1.34 ± 0.13 μg/L, while AR average value was 1.38 ± 0.25. Group 3 comes from pumping wells in a highly anthropized alluvial aquifer. In this group, where the residence time of the groundwater is the shortest of the three, average uranium content was 5.28 ± 0.26 μg/L, and average AR is the lowest (1.17 ± 0.12). In addition, the high dissolved uranium value and the low AR brought to light the contribution of fertilizers (Group 3). In the three groups, 235U/238U activity ratios were similar to the natural value of 0.046. Therefore, 235U detected in the samples comes from natural sources. This study is completed with the determination of major ions and physicochemical parameters in the groundwater samples and the statistical analysis of the data by using the Principal Component Analysis. This calculation indicates the correlation between uranium isotopes and bicarbonate and nitrate anions.
•Natural uranium isotopic ratios have been calculated and used as a prospecting tool in hydrogeochemical processes in groundwater samples.•Anthropogenic contribution to the presence of uranium has been found.•234U/238U activity ratio has demonstrated to be a key factor to distinguish different geological environments.•A statistical study has been performed and some chemical processes that take place in water have been remarked.
Traces of 131I, 134Cs and 137Cs were measured after the Fukushima nuclear accident between 23 March and 13 April 2011 in southeast Spain. The movement of the radioactive cloud toward southeast Spain ...was reconstructed based on the backward and forward trajectory cluster analyses. Polar maritime air masses which had originated over North America transported the radioactive plume toward the southeast Spain. Aerosols, rainwater, vegetables and cheese were analyzed to determine the radioactive risk. The highest concentrations of 131I, 134Cs and 137Cs in air samples were 2.63 ± 0.12 mBq/m3; 0.10 ± 0.03 mBq/m3; 0.09 ± 0.02 mBq/m3, respectively. After precipitation on April 3rd, the maximum concentrations of 131I, 134Cs and 137Cs were detected in rainwater samples, 1.10 ± 0.16 mBq/L; 0.022 ± 0.003 mBq/L; 0.05 ± 0.03 mBq/L, respectively. As a consequence, 131I was transferred to the human food chain, and found in chard and goat cheese, 0.97 ± 0.20 Bq/kg and 0.52 ± 0.08 Bq/kg, respectively. The traces of 131I, 134Cs and 137Cs detected in the different samples were so low, that there is no impact on human health or the environment in Spain after the Fukushima nuclear accident.
► Fission products were detected in southeast Spain after Fukushima nuclear accident. ► There is no radioactive risk for the Spanish population after the accident. ► The trajectory cluster analyses demonstrate the transport of the radioactive plume. ► Bulk deposition and air masses play an important role in the transport of nuclides.
This research is focused on studying the preferred source regions and the pathways of the air masses with high particulate concentrations impacting on the activity concentrations of 7Be and 210Pb ...aerosols in Granada atmosphere. For this purpose, three different source-receptor methods have been used: Cluster Analysis, Potential Source Contribution Function (PSCF), and Concentration Weighted Trajectory (CWT). Air filter samples were weekly collected and analysed in Granada university (Spain 37.177N, 3.598 W, 687m a.s.l.) during 12 years (2006–2017) for the activity concentration of 7Be, and during 5 years (2010–2014) for the one of 210Pb. The time series of the collected data indicate that the concentration of both radiotracers present a cyclical and seasonal pattern, in association with their origins and atmospheric conditions. Clustering analysis showed that the air masses arriving to Granada can be classified as: (1) tropical continental air masses coming from the Mediterranean Sea, (2) tropical and warm polar maritime air masses produced over the Atlantic Ocean, and (3) continental air masses originated over Europe and Northern Africa. The PSCF and CWT methods confirmed that the main source areas of 7Be are located in the Atlantic coast of southern Morocco, and Northern Africa. On the other hand, southern France and the Algerian desert were found to be the main region sources of 210Pb. In addition, the Mediterranean Basin has been postulated as a strong source region for 7Be and 210Pb. Furthermore, the PSCF and CWT models show that the regions with larger 7Be/210Pb ratios are located in the Atlantic Ocean, due to frequent stratospheric intrusions specially during the winter months.
•A seasonal pattern of 7Be and 210Pb was identified in Granada, Spain.•Back trajectory analysis was used to identify the origin and pathway of air masses.•Potential sources regions of 7Be and 210Pb activity were investigated.•Granada is affected by Mediterranean Sea, Atlantic Ocean, and Sahara.•Mediterranean basin is the main source common of 210Pb and 7Be.
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