J. Rivera-Utrilla

Pharmaceuticals as emerging contaminants and their removal from water. A review

The main objective of this study was to conduct an exhaustive review of the literature on the presence of pharmaceutical-derived compounds in water and on their removal. The most representative pharmaceutical families found in water were described and related water pollution issues were analyzed. The performances of different water treatment systems in the removal of pharmaceuticals were also summarized. The water treatment technologies were those based on conventional systems (chlorine, chlorine dioxide, wastewater treatment plants), adsorption/bioadsorption on activated carbon (from lotus stalks, olive-waste cake, coal, wood, plastic waste, cork powder waste, peach stones, coconut shell, rice husk), and advanced oxidation processes by means of ozonation (O₃, O₃/H₂O₂, O₃/activated carbon, O₃/biological treatment), photooxidation (UV, UV/H₂O₂, UV/K₂S₂O₈, UV/TiO₂, UV/H₂O₂/TiO₂, UV/TiO₂/activated carbon, photo-Fenton), radiolysis (e-Beam, ⁶⁰Co, ¹³⁷Cs. Additives used: H₂O₂, SO₃²⁻, HCO₃⁻, CH₃₋OH, CO₃²⁻, or NO₃⁻), and electrochemical processes (Electrooxidation without and with active chlorine generation). The effect of these treatments on pharmaceutical compounds and the advantages and disadvantages of different methodologies used were described. The most important parameters of the above water treatment systems (experimental conditions, removal yield, pharmaceutical compound mineralization, TOC removal, toxicity evolution) were indicated. The key publications on pharmaceutical removal from water were summarized.

Activated carbon modifications to enhance its water treatment applications. An overview.

The main objective of this study was to list and compare the advantages and disadvantages of different methodologies to modify the surface of activated carbons (ACs) for their application as adsorbents to remove organic and inorganic pollutants from aqueous phase. These methodologies have been categorized into four broad groups: oxidation, sulfuration, ammonification, and coordinated ligand anchorage. Numerous investigations into the removal of metals from water have modified carbon surfaces to increase their content of acidic surface functional groups by using H(2)O(2), O(3) and HNO(3). Because these treatments can reduce the AC surface area, researchers are seeking alternative methods to modify and/or create surface functional groups without the undesirable effect of pore blockage. The nitrogenation or sulfuration of the AC surface can increase its basicity favoring the adsorption of organic compounds. The introduction of nitrogen or sulfur complexes on the carbon surface increases the surface polarity and, therefore, the specific interaction with polar pollutants. Different coordinated ligands have also been used to modify ACs, showing that coordinated ligand anchorage on the AC surface modifies its textural and chemical properties, but research to date has largely focused on the use of these modified materials to remove heavy metals from water by complexes formation.

Effects of non-oxidant and oxidant acid treatments on the surface properties of an activated carbon with very low ash content

Abstract An activated carbon obtained from olive stones and with very low ash content (0.10%) was treated with either HCl, HF or HNO3. The changes in surface area and porosity resulting from the acid treatments were studied by N2 and CO2 adsorption at 77 and 273 K, respectively and by mercury porosimetry. The changes in surface chemistry were studied by temperature-programmed desorption and Fourier transformed infrared spectroscopy. The treatments with HCl yielded activated carbons on which some chlorine remained chemisorbed, whereas the HF treatment did not fix any fluorine. Due to this, the HCl treatment had a slight effect on the microporosity of the samples. Moreover, the HF treatment increased the amount of CO-evolving surface groups. The treatment with HNO3 destroyed the pore walls to a large extent, fixing a large amount of oxygen surface groups. The nature and structure of the CO- and CO2-evolving groups will be discussed in detail.

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.

Optimization of conditions for the preparation of activated carbons from olive-waste cakes

Abstract An experimental design (Doehlert matrix) has been drawn up to optimize the experimental conditions of the preparation of activated carbon from olive-waste cakes. A series of activated carbons have been prepared by physical activation with steam. Adsorption of N2 (77 K), CO2 (273 K) and mercury porosimetry experiments have been carried out to determine the characteristics of all carbons prepared. Adsorption of iodine and methylene blue was used as a primary indicator of the adsorption capacity of these carbons. The experimental response varied between: 13–27% for the total yield (Y1), 115–490 mg/g for the adsorption of methylene blue (Y2), 741–1495 mg/g for the adsorption of iodine (Y3), 514–1271 m2/g for the BET surface area (Y4), 0.225–0.377 cm3/g for the micropore volume (Y5), 0.217–0.557 cm3/g for the volume of pores with a diameter greater than 3.7 nm (Y6) and 31.3–132 m2/g for the external surface area (Y7). The results obtained were exploited using response surface methodology. These responses have been represented and studied in all experimental regions of activation time and activation temperature, the most influential factors in activated carbon preparation. Optimization to obtain activated carbons with textural characteristics suitable to use in water treatment has been carried out. The optimal activated carbon is obtained when using 68 min as activation time and 1095 K as activation temperature.

Adsorption of some substituted phenols on activated carbons from a bituminous coal

Adsorption at 298 K of phenol, p-cresol, m-chlorophenol, m-aminophenol, and p-nitrophenol from aqueous solutions on activated carbons obtained from an original and a demineralized bituminous coal has been studied. The adsorption capacity of the activated carbons depended on the surface area and porosity of the carbon, the solubility of the phenolic compound, and the hydrophobicity of the substituent. The relative affinity of the phenolic compound toward the surface of the carbon was related to the electron donor-acceptor complexes formed between the basic sites on the surface of the carbon and the aromatic ring of the phenol. The adsorption capacity of the carbon depended on the solution pH. As a result, the adsorption capacity began to decrease at a pH value that depended on the difference between the external and internal surface charge density, as measured by electrophoresis and pH measurement of the slurry, respectively.

Ozonation of 1,3,6-naphthalenetrisulphonic acid catalysed by activated carbon in aqueous phase

This paper presents experimental results of the ozonation of a model aromatic sulphonic compound, 1,3,6-naphthalenetrisulphonic acid (NTS), in the presence of different activated carbons with different physical and chemical surface properties. Carbons used were commercial activated carbons (Ceca AC40, Norit, Merck, Witco, Ceca GAC, Filtrasorb 400, Sorbo) with or without demineralisation pre-treatment. Carbon samples were texturally and chemically characterised using N 2 adsorption isotherms, mercury porosimetry, pHPZC, selective neutralisation and elemental analysis. Results show that NTS was degraded by ozone at a faster rate in the presence of activated carbon, especially in the case of Sorbo, Ceca GAC and Norit carbons, which display catalytic activity, probably by enhancing ozone decomposition in aqueous phase in highly oxidative species. These catalytic properties seem to be favoured by both the basicity of the carbon surface and the higher macropore volume. Dissolved total organic carbon from the NTS degradation compounds was removed in the presence of activated carbon through both the catalytic activity of activated carbon to mineralise organic matter and the adsorption of these organic compounds on activated carbon.

Regularities in the temperature-programmed desorption spectra of CO2 and CO from activated carbons

Temperature-programmed desorption (TPD) spectra of CO and CO2 have been obtained under vacuum or helium flow with activated carbons from different origins and oxidized in various ways. In particular, a special form of TPD, called Intermittent TPD, has been applied to one of the carbon samples (prepared from almond shells and oxidized with nitric acid) in order determine the variation of the apparent activation energy of desorption Ed as the coverage of the surface decreases. Regularities appeared in the set of results obtained: There are common features in TPD profiles of carbons from different origins and histories. This finding is confirmed by a re-examination of numerous CO and CO2 spectra found in the literature, including results obtained under ultra-vacuum. These regularities are interpreted by the existence of the same superficial entities (various oxygen groups with different environments).

Adsorption of p-nitrophenol on an activated carbon with different oxidations

An activated carbon prepared from olive stones has been modified through oxidation by nitric acid or sodium hypochlorite. These treatments introduced large amounts of oxygen groups, which were characterized by mass-spectrometry, temperature-programmed desorption (DTP–MS). Both CO2- and CO-evolving groups were created by these oxidation treatments. A part of these oxidized samples was then outgassed under vacuum up to 823 K in order to remove most of the CO2-evolving groups from their surface. Oxidized samples have a smaller surface area than the original sample. The subsequent partial outgassing increases the surface area which, however, does not reach the value it had before oxidation. p-Nitrophenol (PNP) adsorption isotherms from aqueous solutions were determined at 298 K for the original, oxidized, and partly outgassed samples. The results confirm the presence of an intermediate plateau at low equilibrium PNP concentration (at about 10 mg/l). The relative effects of textural versus surface chemistry on PNP uptakes are then discussed. The presence of CO-evolving groups showed no influence on PNP uptakes. The conclusion is that models in which carbonylic groups are basic adsorption sites for substituted phenols can be ruled out for the entire isotherm of PNP obtained with the original carbon. These models are also unlikely for PNP adsorption on oxidized and partly outgassed samples.

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.