Dyes are an important class of pollutants, and can even be identified by the human eye. Disposal of dyes in precious water resources must be avoided, however, and for that various treatment ...technologies are in use. Among various methods adsorption occupies a prominent place in dye removal. The growing demand for efficient and low-cost treatment methods and the importance of adsorption has given rise to low-cost alternative adsorbents (LCAs). This review highlights and provides an overview of these LCAs comprising natural, industrial as well as synthetic materials/wastes and their application for dyes removal. In addition, various other methods used for dye removal from water and wastewater are also complied in brief. From a comprehensive literature review, it was found that some LCAs, in addition to having wide availability, have fast kinetics and appreciable adsorption capacities too. Advantages and disadvantages of adsorbents, favourable conditions for particular adsorbate–adsorbent systems, and adsorption capacities of various low-cost adsorbents and commercial activated carbons as available in the literature are presented. Conclusions have been drawn from the literature reviewed, and suggestions for future research are proposed.
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▶ The system is cheap, efficient and fast for the removal of dyes from waters. ▶ Higher adsorption capacity is due to higher mesoporous volume of the adsorbent. ▶ The rate determining ...step of the adsorption process is particle diffusion.
A mesoporous carbon developed from waste tire rubber, characterized by chemical analysis, FTIR, and SEM studies, was used as an adsorbent for the removal and recovery of a hazardous azo dye, Acid Blue 113. Surface area, porosity, and density were determined. The adsorption of the dye over the prepared adsorbent and a commercial activated carbon was achieved under different pH, adsorbate concentration, sieve size, adsorbent dosage, contact time and temperature conditions. Langmuir and Freundlich adsorption isotherm models were applied and thermodynamic parameters were calculated. Kinetic studies indicated that the adsorption process follow first order kinetics and particle diffusion mechanisms are operative. By percolating the dye solution through fixed-bed columns the bulk removal of the Acid Blue 113 was carried out and necessary parameters were determined to find out the percentage saturation of both the columns. Recovery of the dye was made by eluting 0.1M NaOH through the column.
The adsorption features of multiwall carbon nanotubes (MWCNTs) with the magnetic properties of iron oxides have been combined in a composite to produce a magnetic adsorbent. Composites of ...MWCNT/nano-iron oxide were prepared, and were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and Fourier transform infrared spectroscopy (FTIR). XRD suggests that the magnetic phase formed is maghemite and/or magnetite. FESEM image shows nano-iron oxides attached to a network of MWCNTs. The adsorption capability of the composites was tested in batch and fixed bed modes. The composites have demonstrated a superior adsorption capability to that of activated carbon. The results also show that the adsorptions of Cr(III) on the composites is strongly dependent on contact time, agitation speed and pH, in the batch mode; and on flow rate and the bed thickness in the fixed bed mode. Along with the high surface area of the MWCNTs, the advantage of the magnetic composite is that it can be used as adsorbent for contaminants in water and can be subsequently controlled and removed from the medium by a simple magnetic process.
The effect of pH on the amount of Cr(III) adsorbed.
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► The MWCNT/nano-iron oxide magnetic composites were prepared and characterized. ► The composites show good adsorption capacity for chromium ions. ► The material could be used as a base for encapsulation in reverse osmoses systems.
Waste rubber tire has been used for the removal of pesticides from waste water by adsorption phenomenon. By applying successive chemical and thermal treatment, a basically cabonaceous adsorbent is ...prepared which has not only a higher mesopore, macropore content but also has a favorable surface chemistry. Presence of oxygen functional groups as evidenced by FTIR spectra along with excellent porous and surface properties were the driving force for good adsorption efficiency observed for the studied pesticides: methoxychlor, methyl parathion and atrazine. Batch adsorption studies revealed maximum adsorption of 112.0 mg g
−1, 104.9 mg g
−1 and 88.9 mg g
−1 for methoxychlor, atrazine and methyl parathion respectively occurring at a contact time of 60 min at pH 2 from an initial pesticide concentration of 12 mg/L. These promising results were confirmed by column experiments; thereby establishing the practicality of the developed system. Effect of various operating parameters along with equilibrium, kinetic and thermodynamic studies reveal the efficacy of the adsorbent with a higher adsorption capacity than most other adsorbents. The adsorption equilibrium data obey Langmuir model and the kinetic data were well described by the pseudo-first-order model. Applicability of Bangham’s equation indicates that diffusion of pesticide molecules into pores of the adsorbent mainly controls the adsorption process. Spontaneous, exothermic and random characteristics of the process are confirmed by thermodynamic studies. The developed sorbent is inexpensive in comparison to commercial carbon and has a far better efficiency for pesticide removal than most other adsorbents reported in literature.
Effect of flow rate on removal of pesticides.
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► A novel carbon is developed by a cost effective method from waste rubber tire. ► We used this for the removal of pesticides-an environmentally hazardous pollutant. ► The carbon exhibited admirable efficiency w.r.t capacity, kinetics and cost. ► Physisorption and pore diffusion are the characteristics of the adsorption system. ► A comparative analysis showed the carbon is efficient for the removal of pesticides.
Effect of pH on adsorption of Congo red over bottom ash and deoiled soya.
The present investigation assesses the applicability of waste materials—bottom ash and deoiled soya—for the removal of the ...colorant Congo red from wastewaters. The adsorption characteristics and dye removal efficiency of adsorbents have been determined by investigating factors such as effect of pH, effect of concentration of the dye, amount of adsorbents, contact time, and temperature. Langmuir, Freundlich, Tempkin, and Dubinin–Radushkevich isotherm models have been used to evaluate the ongoing adsorption. With the help of adsorption isotherm data different thermodynamic parameters such as free energy; enthalpy, and entropy have been calculated. The estimated free energy has been obtained as −21.52
kJ
mol
−1 for bottom ash and −16.88
kJ
mol
−1 for deoiled soya. On the basis of pseudo-first-order and pseudo-second-order kinetic equations different kinetic parameters have been obtained. Column operations depicted good adsorptive tendencies for Congo red with 96.95% and 97.14% saturation of dye on bottom ash and deoiled soya, respectively. Regeneration of the saturated columns has been made by eluting NaOH solution and more than 90% dye has been recovered in both cases.
The hexavalent chromium, Cr(VI), biosorption by raw and acid-treated
Oedogonium hatei were studied from aqueous solutions. Batch experiments were conducted to determine the biosorption properties of ...the biomass. The optimum conditions of biosorption were found to be: a biomass dose of 0.8
g/L, contact time of 110
min, pH and temperature 2.0 and 318
K respectively. Both Langmuir and Freundlich isotherm equations could fit the equilibrium data. Under the optimal conditions, the biosorption capacities of the raw and acid-treated algae were 31 and 35.2
mg Cr(VI) per g of dry adsorbent, respectively. Thermodynamic parameters showed that the adsorption of Cr(VI) onto algal biomass was feasible, spontaneous and endothermic under studied conditions. The pseudo-first-order kinetic model adequately describe the kinetic data in comparison to second-order model and the process involving rate-controlling step is much complex involving both boundary layer and intra-particle diffusion processes. The physical and chemical properties of the biosorbent were determined and the nature of biomass–metal ions interactions were evaluated by FTIR analysis, which showed the participation of
COOH,
OH and
NH
2 groups in the biosorption process. Biosorbents could be regenerated using 0.1
M NaOH solution, with up to 75% recovery. Thus, the biomass used in this work proved to be effective materials for the treatment of chromium bearing aqueous solutions.
Biosorption is the effective method for the removal of heavy metal ions from wastewaters. Results are presented showing the sorption of Pb(II) from solutions by biomass of commonly available, ...filamentous green algae
Spirogyra sp. Batch experiments were conducted to determine the biosorption properties of the biomass and it was observed that the maximum adsorption capacity of Pb(II) ion was around 140
mg
metal/g of biomass at pH 5.0 in 100
min with 200
mg/L of initial concentration. Temperature change in the range 20–40
°C affected the adsorption capacity and the nature of the reaction was found to be endothermic in nature. Uptake kinetics follows the pseudo-second-order model and equilibrium is well described by Langmuir isotherm. Isotherms have been used to determine thermodynamic parameters of the process, viz., free energy change, enthalpy change and entropy change. Various properties of the algae, as adsorbent, explored in the characterization part were chemical composition of the adsorbent, thermal analysis by TGA, surface area calculation by BET method, surface morphology with scanning electron microscope images and surface functionality by FTIR. FTIR analysis of algal biomass revealed the presence of amino, carboxyl, hydroxyl and carbonyl groups, which are responsible for biosorption of metal ions. The results indicated that the biomass of
Spirogyra sp. is an efficient biosorbent for the removal of Pb(II) from aqueous solutions.
The biosorption of cadmium(II) ions on
Oedogonium sp. is studied in a batch system with respect to initial pH, algal dose, contact time and the temperature. The algal biomass exhibited the highest ...cadmium(II) uptake capacity at 25
°C, at the initial pH value of 5.0 in 55
min and at the initial cadmium(II) ion concentration of 200
mg
L
−1. Biosorption capacity decreased from 88.9 to 80.4
mg
g
−1 with an increase in temperature from 25 to 45
°C at this initial cadmium(II) concentration. Uptake kinetics follows the pseudo-second-order model and equilibrium is well described by Langmuir isotherm. Isotherms have been used to determine thermodynamic parameters of the process, viz., free energy change, enthalpy change and entropy change. FTIR analysis of algal biomass revealed the presence of amino, carboxyl, hydroxyl and carbonyl groups, which are responsible for biosorption of metal ions. Acid pretreatments did not substantially increase metal sorption capacity but alkali like NaOH pretreatment slightly enhanced the metal removal ability of the biomass. During repeated sorption/desorption cycles at the end of fifth cycle, Cd(II) sorption decreased by 18%, with 15–20% loss of biomass. Nevertheless,
Oedogonium sp. appears to be a good sorbent for removing metal Cd(II) from aqueous phase.
Among various water purification and recycling technologies, adsorption is a fast, inexpensive and universal method. The development of low-cost adsorbents has led to the rapid growth of research ...interests in this field. The present protocol describes salient features of adsorption and details experimental methodologies for the development and characterization of low-cost adsorbents, water treatment and recycling using adsorption technology including batch processes and column operations. The protocol describes the development of inexpensive adsorbents from waste materials, which takes only 1-2 days, and an adsorption process taking 15-120 min for the removal of pollutants. The applications of batch and column processes are discussed, along with suggestions to make this technology more popular and applicable.
Natural biological suppression of soil-borne diseases is a function of the activity and composition of soil microbial communities. Soil microbe and phytopathogen interactions can occur prior to crop ...sowing and/or in the rhizosphere, subsequently influencing both plant growth and productivity. Research on suppressive microbial communities has concentrated on bacteria although fungi can also influence soil-borne disease. Fungi were analyzed in co-located soils 'suppressive' or 'non-suppressive' for disease caused by Rhizoctonia solani AG 8 at two sites in South Australia using 454 pyrosequencing targeting the fungal 28S LSU rRNA gene. DNA was extracted from a minimum of 125 g of soil per replicate to reduce the micro-scale community variability, and from soil samples taken at sowing and from the rhizosphere at 7 weeks to cover the peak Rhizoctonia infection period. A total of ∼ 994,000 reads were classified into 917 genera covering 54% of the RDP Fungal Classifier database, a high diversity for an alkaline, low organic matter soil. Statistical analyses and community ordinations revealed significant differences in fungal community composition between suppressive and non-suppressive soil and between soil type/location. The majority of differences associated with suppressive soils were attributed to less than 40 genera including a number of endophytic species with plant pathogen suppression potentials and mycoparasites such as Xylaria spp. Non-suppressive soils were dominated by Alternaria, Gibberella and Penicillum. Pyrosequencing generated a detailed description of fungal community structure and identified candidate taxa that may influence pathogen-plant interactions in stable disease suppression.
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