Reactive Red 120 dye removal from aqueous solution by adsorption on nano-alumina

The adsorption of Reactive Red 120 dye from aqueous solutions by using nano-alumina has been investigated. The batch adsorption studies were carried out to determine the impact of pH, contact time, concentration of dye, and the adsorbent dose on adsorption process. The maximum adsorption efficiency was observed at pH 3. However with an increase of the adsorbent dose, the dye removal efficiency increased, while the amount of dye adsorbed per unit mass (mg/g) decreased. A pseudo-second-order model best described the adsorption kinetics of the specified dye onto nano-alumina. In this case the Langmuir isotherm model appeared to be most suitable. Findings of the present study reveal that nano-alumina can be an effective adsorbent for the removal of Reactive Red 120 from aqueous solutions.     

Removal of Congo Red from Aqueous Solutions by Spent Black Tea as Adsorbent

Herein we present spent black tea as an adsorbent for the removal of Congo red dye from aqueous solutions. The effects of various parameters such as pH, time, temperature, adsorbent dosage and adsorbate dosage on dye adsorption were investigated. Batch experiments were conducted using different amount of adsorbent material (2.5–1000 mg) at varying amounts of adsorbate (5–500 mg/L) at 35°C and different pH (1–13). A maximum dye removal of >80% was achieved with an adsorbent dose of 100 mg, adsorbate concentration of 5 mg/L under pH range of 6 within 5 min at room temperature. The experimental data were modeled by Langmuir, Freundlich and Temkin isotherms and conforms to both Langmuir and Freundlich isotherms but not to Temkin isotherm. The proposed spent black tea can be effectively used as a low cost adsorbent for the removal of Congo red dye.     

Atrazine removal using adsorption and electrochemical regeneration

This paper demonstrates the removal of atrazine using a novel carbon-based adsorbent to below 1.0 microg l(-1) and its subsequent electrochemical regeneration in a simple electrochemical cell. Effective electrochemical regeneration can be achieved with a treatment time as low as 20 min over a number of adsorption/regeneration cycles using laboratory-prepared solutions. The results suggest that electrochemical modification of the particulate surface on electrochemical regeneration can result in adsorptive capacities three times greater than originally achieved.     

Removal of textile basic dye from aqueous solutions using sawdust as bio‐adsorbent

The ability of low cost bio‐adsorbent sawdust to remove basic dye (methylene blue) from aqueous solution is investigated using it in two different forms: in raw form and in chemically treated (with sulphuric acid) form. The effect of contact time, dye concentration, adsorbent dose and the kinetics of adsorption were studied in batch experiments. At neutral pH and 4?gm/l of chemically activated and raw sawdust adsorbents, removal of 98.12% and 97.18% of methylene blue dye (at 100?mg/l concentration) from the aqueous solution, was the best result obtained during study. An average percentage removal difference of less than 5%, between two adsorbents was achieved under different conditions in the experiments. The data fit well in Freundlich isotherm.     

Arsenic (V) removal from aqueous system using adsorbent developed from a high iron-containing fly ash

A novel adsorbent for arsenic (V) removal from wastewater was developed through simple chemical processes using a special iron-abundant fly ash. In the synthesis process, the inherent iron in the fly ash was rearranged and loaded on the surface of the fly ash by dissolution and precipitation processes. The adsorbent (HIOFAA) was characterized by XRD, FT-IR, SEM, LPS and BET surface area. The results showed that porous amorphous FeOOH was loaded on the surface of HIOFAA successfully. The BET surface area of HIOFAA was 22 times of those of the original fly ash, and furthermore, the mean particle size of HIOFAA increased 3 times compared to the raw fly ash, thus effectively accelerated the solid/liquid separation after the adsorptive treatment. The adsorption isotherm data could be well described by Langmuir isotherm model, and the adsorption capacity for arsenic removal was 19.46 mg g^− 1. Accordingly, it is believed that the adsorbent developed in this study is effective for arsenic polluted wastewater treatment.     

Removal of quinol from aqueous solution by adsorption onto Fe(III)/Cr(III) hydroxide and application to real effluent treatment

The adsorption capacity of ‘waste’ Fe(III)/Cr(III) hydroxide for removal of quinol at varying agitation time, quinol concentration, adsorbent dose, pH and temperature was investigated by batch method. The Langmuir isotherm was found to represent the equilibrium sorption data well and the adsorption capacity was found to be 24.4 mg g^?1 and 28.2 mg g^?1 for untreated and pre‐treated adsorbent, respectively. Adsorption followed second‐order kinetics. Adsorption was maximum and uniform in the pH range 4.0–10.0 and 6.0–10.0 for untreated and pre‐treated adsorbent, respectively. The adsorption was endothermic in nature. Application of the adsorbent to the treatment of real effluent was demonstrated.     

Study on the adsorption of Neutral Red from aqueous solution onto halloysite nanotubes

Halloysite nanotubes (HNTs), a low-cost available clay mineral, were tested for the ability to remove cationic dye, Neutral Red (NR), from aqueous solution. Natural HNTs used as adsorbent in this work were initially characterized by XRD, FT-IR, TEM and BET. The effect of adsorbent dose, initial pH, temperature, initial concentration and contact time were investigated. Adsorption increased with increase in adsorbent dose, initial pH, temperature and initial concentration. The equilibrium data were well described by both the Langmuir and Freundlich isotherm models. The maximum adsorption capacity was 54.85, 59.24 and 65.45 mg/g at 298, 308 and 318 K, respectively. Batch kinetic experiments showed that the adsorption followed pseudo-second-order kinetic model with correlation coefficients greater than 0.999. Thermodynamic parameters of ΔG⁰, ΔH⁰ and ΔS⁰ indicated the adsorption process was spontaneous and endothermic. The results above confirmed that HNTs had the potential to be utilized as low-cost and relatively effective adsorbent for cationic dyes removal.     

Effective removal of effluent organic matter (EfOM) from bio-treated coking wastewater by a recyclable aminated hyper-cross-linked polymer

Effluent organic matter (EfOM) is a complex matrix of organic substance mainly from bio-treated sewage effluent and is considered as the main constraint to further advanced treatment. Here a recyclable aminated hyper-cross-linked polymeric adsorbent (NDA-802) featured with aminated functional groups, large specific surface area, and sufficient micropore region was synthesized for effective removal of EfOM from the bio-treated coking wastewater (BTCW), and its removal characteristics was investigated. It was found that hydrophobic fraction was the main constituent (64.8% of DOC) in EfOM of BTCW, and the hydrophobic-neutral fraction had the highest SUVA level (7.06 L mg^?1 m^?1), which were significantly different from that in the domestic wastewater. Column adsorption experiments showed that NDA-802 exhibited much higher removal efficiency of EfOM than other polymeric adsorbents D-301, XAD-4, and XAD-7, and the efficiency could be readily sustained according to continuous 28-cycle batch adsorption–regeneration experiments. Moreover, dissolved organic matter (DOM) fractionation and excitation-emission matrix (EEM) fluorescence spectroscopy study indicated that NDA-802 showed attractive adsorption preference as well as high removal efficiency of hydrophobic and aromatic compounds. Possibly ascribed to the presence of functional aminated groups, relatively large specific surface area and micropore region of the unique polymer, NDA-802 possesses high and sustained efficiency for the removal of EfOM, and provides a potential alternative for the advanced treatment.     

Enhanced mitigation of para-chlorophenol using stratified activated carbon adsorption columns

The adsorptive removal of toxic para-chlorophenol using activated carbon adsorption columns is a proven effective engineering process. This paper examined the possibility to stratify an adsorbent bed into layers, in order to enhance the adsorption process performance in terms of increased column service time and adsorbent bed saturation. Four different types of fixed-bed adsorption columns are used and compared under the same operating conditions, but with the variation of column geometry and activated carbon particle size stratification. The Type 3 column - a cylindrical column with particle stratification packing, is found to be the most efficient choice, as the extent of column service time and adsorbent bed saturation are the largest. This could eventually decrease the frequency of adsorbent replacement/regeneration and hence reduce the operating cost of the fixed-bed adsorption process. The Homogeneous Surface Diffusion Model (HSDM) was applied successfully to describe the dynamic adsorption of para-chlorophenol onto Filtrasorb 400 (F400) activated carbon in different types of columns. The Redlich-Peterson isotherm model equation, an experimentally derived external mass transfer correlation and a constant surface diffusivity are used in the HSDM. The optimised surface diffusivity of para-chlorophenol is found to be 1.20E-8 cm²/s, which is in good agreement with other phenolics/F400 carbon diffusing systems in literature.     

Immobilization of heavy metals from aqueous solutions using polyacrylamide grafted hydrous tin (IV) oxide gel having carboxylate functional groups

A new adsorbent containing a carboxylate group has been prepared by the surface modification of a polyacrylamide grafted hydrous tin (IV) oxide gel. The product exhibits a very high adsorption potential for Pb(II), Hg(II) and Cd(II). The effect of initial metal ion concentration, adsorbent dose, pH, concentration of light metal ions, and temperature on metal removal has been studied. The process follows a first-order rate kinetics. The intraparticle diffusion of metal ions through pores in the adsorbent was shown to be the main rate limiting step. The equilibrium data fit well with the Langmuir adsorption isotherm. The selectivity order of the adsorbent is Pb(II) > Hg(II) > Cd(II). Adsorption rate constants and thermodynamic parameters were also presented to predict the nature of adsorption. The method was applied on synthetic wastewaters. Acid regeneration has been tried for several cycles with a view to recover the adsorbed metal ions and also to restore the sorbent to its original state.     

Electrochemical regeneration of field spent GAC from two water treatment plants

The effectiveness of on-site thermal regeneration of field-spent granular activated carbon (GAC) from two municipal drinking water facilities was compared with bench-scale electrochemical regeneration, a novel regeneration technology. The regeneration method was evaluated using aqueous natural organic material (NOM) adsorption, iodine number analysis, and surface area analysis. In contrast to the large electrochemical regeneration efficiencies reported in the literature for GAC loaded with phenolics and other individual organic compounds, the electrochemical reactor tested was only able to regenerate 8-15% of the NOM adsorption capacity of the field spent GAC. In contrast, thermal reactivation achieved up to 103% regeneration efficiency. To more accurately assess the efficiency of regeneration processes for water treatment applications, GAC should be loaded in continuous-flow columns and not batch rectors. The iodine number analysis yielded higher efficiency values, however it did not give an accurate estimate of the regeneration efficiency. The small changes in GAC pore size distribution were consistent with the low electrochemical regeneration efficiencies. These low efficiencies appear to be related to the low reversibility of NOM adsorption and to pH-induced adsorbate desorption being the primary mechanism for this type of electrochemical regeneration system.     

Remediation of pharmaceutical contaminated water by use of magnetic functionalized metal organic framework. Physicochemical study of doxycycline adsorption

The presence of pharmaceutical pollutant, doxycycline (DOC) in water and waste streams has negative impact on the environment. In this research, metal organic framework was synthesized and functionalized by potassium nickel ferrocyanide (KNiFC). After characterisation, the functionalized adsorbent was used for removal of DOC from aqueous solutions. The adsorbent containing 80% of KNiFC exhibited the high adsorption capacity of 100 mg/g. The adsorption process was kinetically fast and the equilibration was established within 30 min. The used adsorbent retained 90% of its initial capacity after regeneration. The magnetic susceptibility of the adsorbent measured by VSM technique was 35 emu/g and sufficient for separation of the used adsorbent by external magnetic field. Isotherm models including Langmuir, Freundlich, Tempkin, Redlich‐Peterson, and Sips were applied to correlate the experimental equilibrium data. To evaluate the fitness of the isotherm equations error analysis methods, residual root mean square error and average relative error were used.     

The characterization of metal oxide - Mangifera indica L. matrix and its potential as scavenger of heavy metal pollutant

Widespread pollution by heavy metals requires an efficient, cheap and eco-friendly removal technique. This paper reports the use of discarded leaves of Mangifera indica L. modified to enhance their adsorption efficiency in the removal of heavy metal pollutant. The adsorbent was then characterized through X-ray diffraction study, Fourier transform infrared spectroscopy and application to mathematical models. The adsorption process was found to fit the Langmuir’s isotherm model and pseudo-first-order kinetic model. The intra-particle diffusion model was found to be the rate limiting step for the adsorption process. Its rapid kinetics, high hydrophilicity, and easy regenerability with mild mineral acid (like 0.005 M HCl) make this adsorbent suitable for the fixed bed column technique.     

Removal of 2,4,6-trichlorophenol and natural organic matter from water supplies using PAC in floc-blanket reactors

The objective of this study was to evaluate the addition of powdered activated carbon (PAC) to upflow floc-blanket reactors for the adsorption of natural and synthetic organic chemicals. A 15.5-1. bench-scale floc-blanket reactor was operated with PAC addition for the adsorption of 2,4,6-trichlorophenol (TCP) and natural organic matter from one groundwater and two surface waters under laboratory and field conditions, respectively. Influent TCP concentrations ranged from 21 to 415 μg/l. The PAC doses ranged from 2 to 12 mg/l. While the hydraulic residence time in the floc-blanket reactor varied from 15 to 30 min, the carbon residence time ranged from 9 to 34 h. This is due to the high solids concentration in the floc blanket, which ranged from 1200 to 8700 mg/l. Comparison between the extent of TCP adsorption through the floc-blanket reactor and the equilibrium adsorption isotherms of TCP on PAC showed that the maximum adsorption capacity of PAC for TCP was utilized in the reactor. However, this study showed that the maximum adsorptive capacity of the carbon in a continuous process is dependent on the influent adsorbate concentration. This was in agreement with isotherm studies conducted with varying initial TCP concentration. The maximum PAC adsorption capacity for natural organic matter was also achieved in the floc-blanket reactor.     

Removal of anionic dye Congo red from aqueous solution by raw pine and acid-treated pine cone powder as adsorbent: equilibrium, thermodynamic, kinetics, mechanism and process design

Pine cone a natural, low-cost agricultural by-product in Australia has been studied for its potential application as an adsorbent in its raw and hydrochloric acid modified form. Surface study of pine cone and treated pine cone was investigated using Fourier transform infrared (FTIR) and scanning electron microscopy (SEM). The modification process leads to increases in the specific surface area and decreases mean particle sizes of acid-treated pine cone when compared to raw pine cone biomass. Batch adsorption experiments were performed to remove anionic dye Congo red from aqueous solution. It was found that the extent of Congo red adsorption by both raw pine cone biomass and acid-treated biomass increased with initial dye concentration, contact time, temperature but decreased with increasing solution pH and amount of adsorbent of the system. Overall, kinetic studies showed that the dye adsorption process followed pseudo-second-order kinetics based on pseudo-first-order and intra-particle diffusion models. The different kinetic parameters including rate constant, half-adsorption time, and diffusion coefficient were determined at different physico-chemical conditions. Equilibrium data were best represented by Freundlich isotherm model among Langmuir and Freundlich adsorption isotherm models. It was observed that the adsorption was pH dependent and the maximum adsorption of 32.65 mg/g occurred at pH of 3.55 for an initial dye concentration of 20 ppm by raw pine cone, whereas for acid-treated pine cone the maximum adsorption of 40.19 mg/g for the same experimental conditions. Freundlich constant 'n' also indicated favourable adsorption. Thermodynamic parameters such as ?G(0), ?H(0), and ?S(0) were calculated. A single-stage batch absorber design for the Congo red adsorption onto pine cone biomass also presented based on the Freundlich isotherm model equation.     

Novel heterocyclic chitosan‐based Schiff base: evaluation as adsorbent for removal of methyl orange from aqueous solution

A Schiff base has been made by reacting chitosan with 2‐hydroxy quinoline‐3‐carbaldehyde in the presence of acetic acid. The synthesized compound was characterized by FTIR, TGA, XRD and SEM techniques. The Schiff base was evaluated for removal of anionic dye from aqueous solution using methyl orange as model dye. Influences of initial dye concentration, pH and contact time on the extent of adsorption were investigated. The adsorption data fits best with Freundlich isotherm model and the maximum adsorption capacity was found to be 55.55 mg/g. The kinetic study indicated second‐order adsorption. The thermodynamic parameters showed the adsorption to be endothermic and non‐spontaneous. Desorption studies indicated the reusability of the compound as adsorbent material.     

Thiol-functionalised mesoporous silica-coated magnetite nanoparticles for high efficiency removal and recovery of Hg from water

The preparation and testing of thiol-functionalised silica-coated magnetite nanoparticles (TF-SCMNPs) is described. The characteristics of these particles are assessed at different stages in the production process using X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR), and a magnetometer. The particles were found to be almost spherical with a uniform mesoporous structure with a pore size of ∼2.1 nm. The particles were strongly responsive to an external magnetic field making separation from solution possible in less than 1 min. The adsorption characteristics of the particles were quantified in a series of isotherm experiments using Hg(II) solution concentrations between 40 and 1000 μg l⁻¹ at adsorbent concentrations of 4 and 8 mg l⁻¹. The adsorption capacity was higher than for other commonly used adsorbents with 90% of Hg(II) removed during the first 5 min and equilibrium in less than 15 min. Both the Langmuir and Freundlich isotherm models were applied to the isotherm data and the maximum adsorption capacity was achieved when the ratio of adsorbent to adsorbate was low. Both temperature and pH had an effect on adsorption but when the TF-SCMNPs were used for removal of Hg(II) from tap water and bottled water, which contained other ions, there appeared to be no interference. Hg(II) could be successfully desorbed using thiourea in a 3 M HCl solution; this did not result in the destruction of the nanoparticles and they could subsequently be reused without loss of their activity in repetitive adsorption tests.     

Phosphorus removal by acid mine drainage sludge from secondary effluents of municipal wastewater treatment plants

Acid mine drainage (AMD) sludge, a waste product from coal mine water treatment, was used in this study as an adsorbent to develop a cost-effective treatment approach to phosphorus removal from municipal secondary effluents. Batch tests were carried out to study the effects of pH, temperature, concentration, and contact time for phosphorus removal from wastewater. Batch tests were followed by continuous flow tests using a continuous stirred tank reactor (CSTR). Adsorption of orthophosphate onto AMD sludge particles followed the Freundlich isotherm model with an adsorption capacity ranging from 9.89 to 31.97 mg/g when the final effluent concentration increased from 0.21 to 13.61 mg P/L. P adsorption was found to be a rather rapid process and neutral or acidic pH enhanced phosphorus removal. Based on a thermodynamic assessment, P adsorption by AMD sludge was found to be endothermic; consequently, an increase in temperature could also favor phosphorus adsorption. Results from batch tests showed that leaching of metals common to AMD sludges was not likely to be a major issue of concern over the typical pH range (6-8) of secondary wastewater effluents. CSTR tests with three types of water (synthetic wastewater, river water, and municipal secondary effluent) illustrated that P adsorption by AMD sludge was relatively independent of the presence of other ionic species. In treating municipal secondary effluent, a phosphorus removal efficiency in excess of 98% was obtained. Results of this study indicated that it was very promising to utilize AMD sludge for phosphorus removal from secondary effluents and may be relevant to future efforts focused on the control of eutrophication in surface waters.     

Mineralisation of coloured aqueous solutions by ozonation in the presence of activated carbon

The degradation of organic matter in coloured solutions of different classes of dyes by ozonation in the presence of activated carbon is investigated. The kinetics of the decolourisation and mineralisation of three different dyes solutions (CI Acid Blue 113, CI Reactive Red 241 and CI Basic Red 14) were studied in a laboratory scale reactor by three different processes: adsorption on activated carbon, oxidation with ozone and ozonation in the presence of activated carbon. The mineralisation of the solutions was followed by measuring the total organic carbon (TOC). Under the experimental conditions used in this work, activated carbon was not capable of completely removing the colour of the solutions in reasonable time. On the other hand, ozonation quickly decolourised all the solutions, but satisfactory removal of TOC was never achieved by this process. The combination of activated carbon with ozone enhanced the decolourisation of the solutions and especially the mineralisation of the organic matter. Activated carbon acts both as an adsorbent and as a catalyst in the reaction of ozonation. The surface chemistry of the activated carbon is an important parameter; it was observed that basic samples improve TOC removal. The main conclusions of this work were validated by treating a real textile effluent collected after the conventional biological treatment.     

Kinetics of a reactive dye adsorption onto dolomitic sorbents

A novel wastewater treatment technique has been investigated, for reactive dye removal, in batch kinetic systems. These experimental studies have indicated that charred dolomite has the potential to act as an adsorbent for the removal of Brilliant Red reactive dye from aqueous solution. The effect of initial dye concentration, adsorbent mass:liquid volume ratio, and agitation speed on dye removal have been determined with the experimental data mathematically described using empirical external mass transfer and intra-particle diffusion models. The experimental data show conformity with an adsorption process, with the removal rate heavily dependent on both external mass transfer and intra-particle diffusion.