I. Bautista-Toledo

Adsorption of zinc, cadmium, and copper on activated carbons obtained from agricultural by-products

Abstract Adsorption studies of Zn2+, Cd2+, and Cu2+ from aqueous solutions at 293 K and 313 K on three activated carbons are reported. These carbons were obtained by activation of almond shells, olive stones, and peach stones by heating in CO2 at 1123 K. From these isotherms some adsorption parameters have been determined. The influence of the solution pH on the adsorption processes has been studied. The extent of adsorption in the presence of Cl−, CN−, SCN−, or EDTA has been also investigated. The adsorptive behaviour of these activated carbons is explained on the basis of their chemical nature and porous texture.

Removal of nitroimidazole antibiotics from aqueous solution by adsorption/bioadsorption on activated carbon.

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.

Influence of the oxygen surface complexes of activated carbons on the adsorption of chromium ions from aqueous solutions : effect of sodium chloride and humic acid

Adsorption of Cr(III) and Cr(VI) on activated carbons from aqueous solutions has been studied. A commercial activated carbon, then treated with HNO3 to introduce surface oxygen complexes, and subsequently heated up to 873 K in N2 to eliminate some of the above complexes, gave the three samples used. Adsorption of both Cr(III) and Cr(Vl) was enhanced by the presence of surface oxygen complexes of acid type on the activated carbon. The effect of the presence of NaCl and humic acid in the chromium solution on the adsorption capacity of the activated carbons has also been studied.

Bioadsorption of Pb(II), Cd(II), and Cr(VI) on activated carbon from aqueous solutions

The bioadsorption of Pb(II), Cd(II), and Cr(VI) using bacteria and activated carbon has been studied. Preliminary studies yielded the chemical and textural characterization of the carbons. The adsorption of bacteria on the activated carbons modified their surface characteristics, reducing the volume of pores and the pH of the point of zero charge, with a resulting increase in the density of the negative charge of their surface. The adsorption of the above metals was studied in both static and dynamic conditions and in the absence and presence of bacteria (Escherichia coli). The presence of bacteria in aqueous solution enhances the adsorption of Pb(II) and Cd(II) and reduces the adsorption of Cr(VI). These results can be explained by changes in the surface charge density of the carbons when bacteria are adsorbed, and by considering the structural and chemical characteristics of the bacterial cell walls. Investigation of the effect of electrolytes on the bioadsorption of these metals showed, in general, a resulting reduction in the amount of metal adsorbed, mainly in the presence of divalent cations. According to the divalent cation bridging theory, these results derive from competition between the Pb(II) or Cd(II) cations and the electrolyte cations for the negatively charged functional groups of extracellular polymeric substances.

Removal of pharmaceutical compounds, nitroimidazoles, from waters by using the ozone/carbon system.

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.

Removal of lead from water by activated carbons

Abstract Studies about the removal of lead from aqueous solutions by activated carbons are described. These activated carbons were prepared from almond shells, olive stones, and peach stones. A commercial one was also used in this study. The adsorption isotherms of lead on those activated carbons at 298 K have been obtained. From these isotherms some adsorption parameters have been calculated. The lead removal process in dynamic regimen has also been studied by using different columns of activated carbon. In order to know the operational parameters for optimum removal, the breakthrough curves of column tests carried out at different experimental conditions were obtained. From these curves the characteristics of each column were determined.

Influence of support surface properties on activity of bacteria immobilised on activated carbons for water denitrification

Denitrification of water under anaerobic conditions was carried out by Escherichia coli supported or immobilised on different activated carbons and silica. Results were compared with those obtained when bacteria was used alone or mixed with activated carbons. Denitrification took place in two steps: reduction of nitrate to nitrite, and its subsequent reduction to dinitrogen. The process required an external carbon source that in this case was ethanol. Results obtained in the denitrification process were related to characteristics of activated carbon that favoured bacteria adsorption and to the final pHPZC of the activated carbon–bacteria complex. In addition, a large macropore volume also allowed the bacteria to grow during the process. The presence of Cd(II) and Cr(VI) ions negatively affected the denitrification process. However, their influence on the removal of nitrite ions was smaller if the bacteria were supported on activated carbon.

Regeneration of ortho-chlorophenol-exhausted activated carbons with liquid water at high pressure and temperature

A study was undertaken of the regeneration of three activated carbons exhausted with ortho-chlorophenol. The regeneration process was carried out using liquid water at 623 K and 150 atm in the absence of oxygen. The efficiency of this procedure was analyzed by determining the rate and amount of ortho-chlorophenol adsorbed in successive adsorption-regeneration cycles. The present procedure showed a much greater efficiency than that reported for chemical and/or thermal regeneration. Effects of this regeneration on the adsorption kinetics, adsorption capacity and textural characteristics of the carbon were investigated. The increase in adsorption capacity of the regenerated carbon compared with that of the original carbon seems mainly due to the opening of porosity during the regeneration treatment.

Adsorption/bioadsorption of phthalic acid, an organic micropollutant present in landfill leachates, on activated carbons.

This study investigated the adsorption of phthalic acid (PA) in aqueous phase on two activated carbons with different chemical natures, analyzing the influence of: solution pH, ionic strength, water matrix (ultrapure water, ground water, surface water, and wastewater), the presence of microorganisms in the medium, and the type of regime (static and dynamic). The activated carbons used had a high adsorption capacity (242.9 mg/g and 274.5 mg/g), which is enhanced with their phenolic groups content. The solution pH had a major effect on PA adsorption on activated carbon; this process is favored at acidic pHs. PA adsorption was not affected by the presence of electrolytes (ionic strength) in solution, but was enhanced by the presence of microorganisms (bacteria) due to their adsorption on the carbon, which led up to an increase in the activated carbon surface hydrophobicity. PA removal varies as a function of the water type, increasing in the order: ground water<surface water≈ultrapure water<wastewater. The effectiveness of PA adsorption was lower in dynamic than in static regime due to the shorter adsorbent-adsorbate contact time in dynamic regime.

Removal of tinidazole from waters by using ozone and activated carbon in dynamic regime.

The main objective of the present study was to analyze the efficacy of technologies based on ozone and activated carbon in dynamic regime to remove organic micropollutants from waters, using the antibiotic tinidazole (TNZ) as a model compound. Results obtained in static regime show that the presence of activated carbon (GAC) during tinidazole ozonation: (i) increases its removal rate, (ii) reduces oxidation by-product toxicity, and (iii) reduces the concentration of dissolved organic matter. Study of the ozone/activated carbon system in dynamic regime showed that ozonation of tinidazole before the adsorption process considerably improves column performance, increasing the volume of water treated. It was observed that the efficacy of the treatment considerably increased with a shorter contact time between TNZ and O(3) streams before entering the column allowing a much higher volume of TNZ solution to be treated compared with the use of activated carbon alone, and reducing by 75% the amount of activated carbon required per unit of treated water volume. TNZ removal by the O(3)/GAC system is lower in natural waters and especially in wastewaters, than in ultrapure water. The toxicity results obtained during TNZ treatment with O(3)/GAC system showed that toxicity was directly proportional to the concentration of TNZ in the effluent, verifying that oxidation of the organic matter in the natural waters did not increase the toxicity of the system.