Carmen Gabaldón

Adsorption of Heavy Metals from Aqueous Solutions onto Activated Carbon in Single Cu and Ni Systems and in Binary Cu–Ni, Cu–Cd and Cu–Zn Systems

Single copper and nickel adsorption from aqueous solutions onto a granular activated carbon is reported. Metal removals increase on raising pH and temperature, and decrease on raising the initial metal concentration at constant carbon dose. The adsorption processes are modelled using the surface complex formation (SCF) Triple Layer Model (TLM) with an overall surface bidentate species. A dependence of the SCF constant on pH, initial molar metal/carbon ratio and temperature is observed, and a correlation for log Kads is determined. The SCF model successfully predicts copper and nickel removals in single metal solutions. Adsorption in the binary metal systems copper–nickel, copper–cadmium and copper–zinc is also reported, showing competitive adsorption effects.

Cadmium and zinc adsorption onto activated carbon: Influence of temperature, pH and metal/carbon ratio

The adsorption characteristics of cadmium and zinc onto a granular activated carbon were studied. Cadmium and zinc removals increased on raising pH and temperature, and decreased on raising the molar metal/carbon ratio. The adsorption processes were modelled using the surface complex formation (SCF) Triple Layer Model (TLM) with an overall bidentate species. A dependence of the SCF constant on pH, the molar metal/carbon ratio and temperature was observed, and a correlation for log K ads was determined. The SCF model successfully predicted cadmium and zinc removals.

Single and competitive adsorption of Cd and Zn onto a granular activated carbon

Single and competitive adsorption of cadmium and zinc onto granular activated carbon DARCO 12–20 mesh has been investigated. This activated carbon has been shown as an effective adsorbent for both metals. Cadmium and zinc removals increased with pH and decreased with molar metal/carbon ratio. Surface precipitation phenomena have been detected for the higher pHs and molar ratios. The adsorption process has been modelled on the surface complexation Triple Layer Model (TLM). For this purpose, the amphoteric nature of the activated carbon has been studied. Single metal adsorption data have been used to calibrate TLM parameters. A dependence of the adsorption constants on pH and molar metal/carbon ratio has been observed, and a correlation for log Kads has been determined. In the competitive system, the removal efficiency of the activated carbon decreased for both metals. The TLM model, using surface complexation constants determined from single adsorption experiments, successfully predicted cadmium and zinc removal from the two metal solutions.

Effect of pH, cation concentration and sorbent concentration on cadmium and copper removal by a granular activated carbon

The single adsorption of cadmium and copper from aqueous solutions has been investigated on Darco 12-20 mesh granular activated carbon for a wide range of experimental conditions: pH, metal concentration and carbon concentration. The results showed the efficiency of the activated carbon as sorbent for both metals. Metal removal increases on raising pH and carbon concentration, and decreases on raising the initial metal concentration. The adsorption processes have been modelled using the surface complex formation (SCF) Triple Layer Model (TLM) with a single surface bidentate species or with an overall surface species with fractional stoichiometry. Bidentate stoichiometry considering pH, metal concentration and carbon concentration dependencies successfully predicted cadmium and copper removals for all experimental conditions. The Freundlich isotherm has been also checked.

Performance evaluation of a biotrickling filter treating a mixture of oxygenated VOCs during intermittent loading

Laboratory scale-studies on the biodegradation of a 1:1:1 weight mixture of three oxygenated volatile organic compounds (VOCs), ethanol, ethyl acetate, and methyl-ethyl ketone (MEK) in a biotrickling filter (BTF) were carried out using two identically sized columns, filled with different polypropylene rings. The performance of the BTFs was examined for a period of 10 months applying several operational strategies. Similar performance was obtained for both supports. Intermittent flow rate of trickling liquid was shown beneficial to improve the removal efficiency (RE). Continuous feeding of VOC resulted in an excessive accumulation of biomass so high pressure drop was developed in less than 20-30 d of operation. Intermittent VOC loading with night and weekend feed cut-off periods passing dry air, but without addition of water, was shown as a successful operational mode to control the thickness of the biofilm. In this case, operation at high inlet loads (ILs) was extended for more than 75 d maintaining high REs and low pressure drops. Outlet emission concentrations lower than 100 mg Cm(-3) were obtained for ILs up to 100 g Cm(-3)h(-1) working at 15s of empty bed residence time. The most easily biodegradable compounds ethanol and ethyl acetate were used primarily than MEK. After a 3-wk-starvation period, the system performance was almost restored since the first d of operation, being the removal of the less biodegradable compound, MEK, partially deteriorated.

Cadmium and Copper Removal by a Granular Activated Carbon in Laboratory Column Systems

Single and competitive removal of Cd and Cu from aqueous solutions by using Darco 12–20 mesh granular activated carbon in column systems has been investigated. Seven experiments modifying the initial pH and the flow rate were performed. Results showed the efficiency of activated carbon as a sorbent for both metals. pH is shown to be the decisive parameter on metal removal in the column; metal removal increases when the influent pH value is raised. The influence of the flow rate for the experimental conditions is negligible. Batch adsorption and column data are compared. Column modeling assuming local equilibrium and rate-controlled pore diffusion was performed.

Diagnosis of boron, fluorine, lead, nickel and zinc toxicity in citrus plantations in Villarreal, Spain

In the late 1980s, citrus plantations in the area of Villarreal (Spain) showed injuries similar to those previously reported for boron and fluorine toxicity. The area was affected by the disposal of industrial wastewater, mainly from ceramic industries. Conjunctive uses of surface water, groundwater and wastewater for irrigation had taken place. A survey was conducted at 25 orchards to assess leaves and soil for their boron, fluorine, lead, nickel and zinc contents. Wastewater and groundwater were also analyzed to corroborate the presence of these pollutants. The results showed that both boron and fluorine contents were greater than those reported as excess at the most part of the orchards included in the study. Heavy metals toxicity effects were not confirmed. Boron pollution was attributed to industrial wastewater spills and fluorine contamination from atmospheric pollution.

Modeling of copper fixed-bed biosorption from wastewater by Posidonia oceanica

Biosorption of copper from aqueous solutions by Posidonia oceanica was investigated in batch and fixed-bed experiments. Batch experiments were conducted to evaluate the removal equilibrium at pH 5.0 and 6.0; experimental data were fitted to Langmuir model with maximum uptake capacities of 56.92 and 85.78 mg g(-1), respectively. Five column experiments were carried out at different feed concentrations. Breakthrough times and continuous sorption isotherm were obtained from breakthrough curves. Differences among batch and continuous isotherms were observed; the maximum uptake capacity in dynamic conditions was found in 56.70 mg g(-1) for final pH between 5.0 and 5.5. The biosorbent was regenerated with HCl. Hydrodynamic axial dispersion was estimated by tracing experiments at different velocities using LiCl as tracer. A mass transport model including convection-dispersion and sorption processes was successfully applied to breakthrough curve modeling. Results indicate that P. oceanica can be used as an effective biosorbent for copper removal.

Morphological Similarity and Ecological Overlap in Two Rotifer Species

Co-occurrence of cryptic species raises theoretically relevant questions regarding their coexistence and ecological similarity. Given their great morphological similitude and close phylogenetic relationship (i.e., niche retention), these species will have similar ecological requirements and are expected to have strong competitive interactions. This raises the problem of finding the mechanisms that may explain the coexistence of cryptic species and challenges the conventional view of coexistence based on niche differentiation. The cryptic species complex of the rotifer Brachionus plicatilis is an excellent model to study these questions and to test hypotheses regarding ecological differentiation. Rotifer species within this complex are filtering zooplankters commonly found inhabiting the same ponds across the Iberian Peninsula and exhibit an extremely similar morphology—some of them being even virtually identical. Here, we explore whether subtle differences in body size and morphology translate into ecological differentiation by comparing two extremely morphologically similar species belonging to this complex: B. plicatilis and B. manjavacas. We focus on three key ecological features related to body size: (1) functional response, expressed by clearance rates; (2) tolerance to starvation, measured by growth and reproduction; and (3) vulnerability to copepod predation, measured by the number of preyed upon neonates. No major differences between B. plicatilis and B. manjavacas were found in the response to these features. Our results demonstrate the existence of a substantial niche overlap, suggesting that the subtle size differences between these two cryptic species are not sufficient to explain their coexistence. This lack of evidence for ecological differentiation in the studied biotic niche features is in agreement with the phylogenetic limiting similarity hypothesis but requires a mechanistic explanation of the coexistence of these species not based on differentiation related to biotic niche axes.

Performance of a Pilot-Scale Biotrickling Filter in Controlling the Volatile Organic Compound Emissions in a Furniture Manufacturing Facility

Abstract A 0.75-m3 pilot-scale biotrickling filter was run for over 1 yr in a Spanish furniture company to evaluate its performance in the removal of volatile organic compounds (VOCs) contained in the emission of two different paint spray booths. The first one was an open front booth used to manually paint furniture, and the second focus was an automatically operated closed booth operated to paint pieces of furniture. In both cases, the VOC emissions were very irregular, with rapid and extreme fluctuations. The pilot plant was operated at an empty bed residence time (EBRT) ranging from 10 to 40 sec, and good removal efficiencies of VOCs were usually obtained. When a buffering activated carbon prefllter was installed, the system performance was improved considerably, so a much better compliance with legal constraints was reached. After different shutdowns in the factory, the period to recover the previous performance of the biotrickling reactor was minimal. A weekend dehydration strategy was developed and implemented to control the pressure drop associated with excessive biomass accumulation.