Combined Adsorption Process Research Articles

Degradation of ampicillin by combined process: Adsorption and Fenton reaction

When disposed incorrectly, antibiotics can cause complex effects on environmental matrices, such as bacterial resistance. In this context, the present work investigated the degradation and mineralization of the β -lactam antibiotic ampicillin (AMP) applying a combined treatment of Fenton reaction and adsorption onto granular activated carbon (GAC). Adsorption parameters of contact time (10–210 min) and GAC dosage (5–50 g L − 1 ) were evaluated, as well as adsorption kinetics. Both in Fenton reaction and combined process, the influence of H 2 O 2 and Fe + 2 concentrations were evaluated, using five combinations of H 2 O 2 /Fe + 2 : 300/60 μ M, 300/80 μ M, 400/70 μ M, 500/60 μ M and 500/80 μ M. Finally, because of the combined process, GAC regeneration was investigated in 3 cycles. Best adsorption conditions were determined as 150 minutes of contact time and GAC concentration of 20 g L −1 , reaching 57% of AMP removal and adsorbed amount of 0.58 mg g − 1 . All Fenton experimental conditions led to a complete degradation of AMP within 1 min, suggesting the generation rate of hydroxyl radicals was faster in the first minutes of reaction. In the combined process, similar results for degradation were found. A higher mineralization (83%) and GAC regeneration (85%) was reached at H 2 O 2 /Fe + 2 = 500 / 80 μ M, indicating the influence of H 2 O 2 and Fe + 2 concentrations. GAC regeneration efficiency for the 3 cycles were, respectively, 84%, 71% and 49%. Thus, the results demonstrate the combined process of Fenton reaction and GAC adsorption is a feasible treatment reaching high mineralization. • The combined process of adsorption and Fenton is a feasible treatment for effluents containing ampicillin reaching high mineralization. • Generation rate of hydroxyl radicals was faster in the first minutes of reaction. • Fenton promotes the granular activated carbon regeneration.

Interaction of Ca2+ and soil humic acid characterized by a joint experimental platform of potentiometric titration, UV–visible spectroscopy, and fluorescence spectroscopy

Rocky desertification has become a major environmental issue in the karst region of southwestern China. Karst rocky desertification was more severe in regions of limestone soil than in adjacent regions of other soils, despite the relatively higher soil organic matter (SOM) content in limestone soil. The underlying mechanism remains ambiguous. We speculated that the geochemical characteristics of limestone soils in the karst region plays an essential role, especially the high calcium content of limestone soil. To test this hypothesis, we collected limestone soil samples from a limestone soil profile in the southwestern China karst region and extracted humic acid (HA) from these limestone soil samples. We investigated the interaction of Ca2+ and three HA samples on a joint experimental platform, which consists of an automatic potentiometric titrator, a UV–visible spectrometer, and a Fluorescence spectrometer. HA solutions were titrated by Ca2+ and optical spectra of the HA solutions were monitored during the titration experiments. The results indicated that: (1) the interaction of Ca2+ and HA is a combined process of adsorption and complexation. Adsorption dominated the overall distribution behavior of Ca2+, which could be fit by Langmuir and Freundlich isotherm models. Complexation was distinguished only when the concentration of Ca2+ is low; (2) the changes of UV–visible spectroscopy and excitation–emission matrix fluorescence spectroscopy spectra of HA samples when they were binding with Ca2+ implied the apparent molecular size and structure of HA became larger and more complex; (3) the combination of Ca2+ and HA plays an important role in the SOM preservation of limestone soils but the stability of the Ca–HA association was relatively weak. The present study draws attention to maintaining the relatively higher Ca2+ concentration in limestone soils in ecologic restoration attempts in karst regions.

Fe-Cu Doped Multiwalled Carbon Nanotubes for Fenton-like Degradation of Paracetamol Under Mild Conditions.

A series of carbon nanotubes doped with Fe and/or Cu, Fe100−xCux/CNT (x = 0, 25, 50, 75 and 100) has been prepared by an easy method of wetness impregnation of commercial multiwalled carbon nanotubes previously oxidized with nitric acid. The wide characterization of the solids by different techniques demonstrates that the incorporation of Fe and Cu to the CNTs has been successfully produced. Fe100−xCux/CNT samples were tested as catalysts in the removal of paracetamol from aqueous solution by a combined process of adsorption and Fenton-like oxidation. Under mild conditions, 25 °C and natural pH of solution, i.e., nearly neutral, values of oxidation of paracetamol between 90.2% and 98.3% were achieved after 5 h of reaction in most of cases. Furthermore, with the samples containing higher amounts of copper, i.e., Cu100/CNT and Fe25Cu75/CNT, only 2 h were necessary to produce depletion values of 73.2% and 87.8%, respectively. The influence of pH and dosage of H2O2 on the performance has also been studied. A synergic effect between both Cu+/Cu2+ and Fe2+/Fe3+ in Fenton-like reaction was observed. These results demonstrate that Fe100−xCux/CNT are powerful Fenton-like catalyst for degradation of paracetamol from aqueous solution and they could be extended to the removal of other organic pollutants.

Magnetic clay as catalyst applied to organics degradation in a combined adsorption and Fenton-like process

In this work, a magnetic sepiolite composite was prepared by chemical co-precipitation method and firstly applied as both adsorbent and catalyst for the removal of bisphenol A (BPA) through a heterogeneous Fenton process. The composite was characterized by XPS, XRD, SEM and TEM techniques. The results of the kinetics study indicate that BPA (50 mg·L−1) can be adsorbed onto the composite via electrons transfer as well as π-π interaction, and then be completely degraded at pH 6.0 within 30 min after the addition of H2O2 (1000 mg·L−1). The analysis of FTIR confirms that the degradation occurred through a combined process of adsorption and oxidation. BPA was pre-concentrated and fixed onto the composite surface and then degraded in-situ by hydroxyl radicals, which were generated through the interaction between H2O2 and surface active sites. To investigate the stability and regeneration properties of the catalyst, the powder composite was extruded into a small cylindrical sample and loaded in a fixed-bed reactor, which was operated under continuous-flow condition. The BPA removal efficiency after 4 h remained at 87%, while the leaching of Fe ions gradually increased. Further, degradation tests in different real waters including tap water and municipal wastewater spiked with BPA (50 μg·L−1) reveal that the influence of real matrix on the oxidation ability was very little. The findings of this study confirm the composite as a promising material for the catalytic removal of organics via the coupled adsorption-oxidation process.

Comparing fine particulate iron hydroxide adsorbents for the removal of phosphate in a hybrid adsorption/ultrafiltration system

The use of micro-sized iron hydroxide adsorbents in mixed reactors is a promising technique for the removal of inorganic contaminants from wastewater within minutes of contact time. This study focusses on phosphate adsorption onto fine fraction granular ferric hydroxide (µGFH) and iron oxy(hydr)oxide agglomerates (IOAs) in a reactor with submerged ultrafiltration (UF) membrane. The performance of the hybrid adsorption/UF membrane system was evaluated for various adsorbents and phosphate concentrations, residence times and concentrations of co-existing ions. The membrane was not fouled at the experimental conditions used (up to 6.3 g/L adsorbent).Phosphate loadings of 20 and 60 mg P/g Fe (36.1 and 108.3 mol P/mol Fe) were reached for µGFH and IOAs, respectively (C0(P) = 4.5 mg/L, deionized water at pH 8, C(Fe) = 0.6 g/L). A shortened residence time of 15 min in the reactor led to a decrease in final loading of 6 mg/g compared to 30 min residence time (54 mg/g compared to 60 mg/g). An extension to 60 min did not result in higher loadings. An increase in adsorbent (IOA) concentration from 0.1 to 0.3 mg/L resulted in an increase of phosphate removal (27 to 35%). Simultaneously, loadings decreased from 50 to 35 mg/g. The application of the developed process for the treatment of artificial secondary effluent resulted in an increase of 87 and 60% in treated volumes until breakthrough (50%) for µGFH and IOAs, respectively, compared to deionized water. Thus, the combined process of adsorption and particle separation using a submerged membrane can be well adjusted according to water composition, initial pollutant concentrations and desired removals.

Combined adsorption process and photocatalytic degradation of some commercial herbicides over N-doped TiO2 particles supported on recyclable magnetic hexagonal mesoporous silica

ABSTRACTMagnetic hexagonal mesoporous silica (magnetic HMS) containing N-doped TiO2 was prepared by hydrothermal method and used for the removal of trifluralin, 2,4-dichlorophenoxyacetic acid, and glyphosate herbicides at the presence and absence of UV/visible lights. The prepared samples were found as efficient for the removal of the herbicides and easily recyclable after treatment by UV irradiation. A red shift effect by nitrogen doping was also observed in the prepared samples resulting photocatalytic activity at the presence of visible light. Kinetic studies indicated that the photodegradation followed as the first order and kUV ≈ 10kvis. The results also showed synergetic effects between the adsorption of herbicides on the surface of magnetic HMS and photoreactions over N-doped TiO2 species.

Removal of fluoride by effectively using spent cation exchange resin

Spent strongly acidic cation exchange resin was effectively used for the removal of trace concentration of fluoride ions. For this purpose, the spent resins were pulverized into fine powders to be used together with inorganic coagulation agent consisting of iron, aluminum, and calcium in batchwise operation. Prior to this operation, the pulverized resins were loaded with Zr(IV) ions to develop adsorption sites which effectively and selectively adsorb fluoride ions over other coexisting anionic species such as chloride and sulfate ions. The fluoride uptake capacity of the Zr(IV)-loaded resin powder was negligibly affected by the coagulation agent. This combined process of adsorption and coagulation was proven to be used for at least six repeated cycles of adsorption followed by desorption using dilute alkaline solution without lowering the uptake capacity for fluoride ion. Quantitative removal of trace concentration of fluoride was successfully achieved from actual waste plating solution by this process.

Evaluation of the mercaptobenzothiazole degradation by combined adsorption process and Fenton reaction using iron mining residue

ABSTRACT The present study investigated the degradation of mercaptobenzothiazole (MBT), evaluating homogeneous and heterogeneous systems. An iron mineral residue from the desliming step of iron mining was used as a source in the Fenton-like reaction (advanced oxidation process). A granulometric analysis of the residue was performed and yielded fractions with high hematite (Fe2O3) and low quartz content in sieves from 74 to below 44 mm. In this particle size range, the hematite content from 58.9% to 67.4% and the Brunauer-Emmett-Teller area from 0.1345 to 1.3137 m2 g−1 were obtained. The zeta potential curves as a function of pH were obtained for the residue, the MBT solution and mixtures thereof. The adsorption of MBT in the residue and its degradation through the Fenton-like reaction were investigated. Adsorption tests and the Fenton-like reaction were carried out, where the MBT species and the residue are oppositely charged, yielding, respectively, 10% MBT adsorption on the surface of the residue and 100% MBT degradation by the Fenton-like reaction at pH 3, hydrogen peroxide concentration of 25 mg L−1, residue concentration of 3 g L−1, 200 rpm and 25°C, from a 100 mg L−1 MBT solution. MBT degradation was found to occur mainly by the heterogeneous Fenton-like process.

On the textural and crystalline properties of Fe-carbon xerogels. Application as Fenton-like catalysts in the oxidation of paracetamol by H2O2

A series of five Fe-carbon xerogels has been prepared by a sol-gel modified method of polymerization of resorcinol and formaldehyde, iron being incorporated in the form of ferrous acetate. Some modifications, such as the monomer used, the use of a surfactant and the step of addition of the ferrous acetate have been done in order to study their influence on the textural and crystalline properties of the final solids obtained. Fe-carbon xerogels have been characterized by N2 adsorption, mercury porosimetry, thermal analysis, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and inductively coupled plasma mass spectrometry (ICP-MS). All samples contain micropores, with the exception of that prepared in the presence of an anionic surfactant. However, they are mainly meso- and/or macropores samples, the ratio of mesopore to macropore volume depending on the synthesis conditions. The amounts of iron in the samples, as well as the crystalline phases formed are also different. Fe-carbon xerogels were tested as catalysts in the removal of paracetamol from aqueous solution by a combined process of adsorption and Fenton-like oxidation under mild conditions, 25 °C and pH nearly neutral. Values of oxidations of paracetamol between 78 and 95% were achieved after 5 h of reaction, and the 90% of paracetamol was removed after only 37 min with two of the catalysts. The activity seems to be correlated with the high dispersion of small nanoparticles of iron, mainly present as zero-valent iron.

Potential of Melaleuca diosmifolia as a novel, non-conventional and low-cost coagulating adsorbent for removing both cationic and anionic dyes

The potential of dried twigs of Melaleuca diosmifolia as a novel biosorbent for removing three cationic dyes, methylene blue (MB), acridine orange (AO) and malachite green (MG), and an anionic dye, eriochrome black T (EB) was evaluated in a batch adsorption process. Notably, the biosorbent removed 77–99% of both cationic and anionic dyes in a wide ranging pH of 2–10, and the reactions were endothermic. The dye adsorption equilibria were rapidly attained within 3h. The monolayer adsorption capacity of the sorbent added at 5gL−1 was 119.05, 126.8, 116.28 and 94.34mgg−1 for MB, AO, MG and EB, respectively. The water extract obtained from the plant material induced fast decolourization of both categories of dyes followed by gradual flocculation, indicating its potential as a natural coagulant. Gas chromatographic analysis also indicated that the main electrostatic attraction between 1,8-cineole, 1-p-methene-8-thiol and furfural compounds of the biomaterial, and dye molecules resulted in the formation of initial supramolecular complexes which further progressed into strong aggregates, leading to precipitation of dye–biomaterial complexes. Subsequently, the overall complex mechanism of dye removal was confirmed to be a combined process of adsorption and coagulation. Consistent with the batch studies, using selected plant material in real environmental water samples also resulted in effective dye removal, highlighting its potential for use in wastewater treatment.