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Towards advanced aqueous dye removal processes: A short review on the versatile role of activated carbon
Abstract
During the last decade, several physico-chemical and biological techniques have been developed to remove colour from textile wastewaters. Some of these techniques rely on and many will profit from activated carbon (AC). The role of AC is versatile: (1) it acts as a dye adsorbent, not only in straightforward adsorption processes but also in AC-enhanced coagulation and membrane filtration processes; (2) it generates strong oxidising agents (mostly, hydroxyl (�OH) radicals) in electrochemical dye oxidation; (3) it catalyses �OH production in advanced oxidation processes; (4) it catalyses anaerobic (azo) dye reduction and supports biofilm growth in microbial dye removal. This paper reviews the role of AC in dye decolourisation, evaluates the feasibility of each AC-amended decolourisation technique and discusses perspectives on future research.
... Due to growing environmental problems and the development of the textile industry, various treatment methods can be used to remove dyes from water, including physical, chemical, and biological processes [14][15][16]. Common techniques include coagulation and flocculation [17][18][19][20][21][22][23], membrane filtration [24][25][26][27][28][29], biological degradation [20,[30][31][32][33][34], advanced oxidation processes, and adsorption [35,36]. The adsorption process is widely special attention due to the high availability of the material from which it is made (chitin), its biodegradability, and the unique adsorption properties associated with the polycationic nature of its macromolecules. ...
... Due to growing environmental problems and the development of the textile industry, various treatment methods can be used to remove dyes from water, including physical, chemical, and biological processes [14][15][16]. Common techniques include coagulation and flocculation [17][18][19][20][21][22][23], membrane filtration [24][25][26][27][28][29], biological degradation [20,[30][31][32][33][34], advanced oxidation processes, and adsorption [35,36]. The adsorption process is widely special attention due to the high availability of the material from which it is made (chitin), its biodegradability, and the unique adsorption properties associated with the polycationic nature of its macromolecules. ...
In this work, various types of silica materials were used for the synthesis of chitosan–silica composites. The composites were obtained using the chitosan (Ch) immobilization process from an aqueous solution on various silica phases, i.e., amorphous diatomite (ChAD), crystalline diatomite (ChCD), mesoporous silica MCM-41 (ChMCM), and mesoporous silica SBA-15 (ChSBA). Textural, structural, morphological, and surface properties of the materials were determined by using various measurement techniques, i.e., low-temperature adsorption/desorption isotherms of nitrogen, X-ray diffraction (XRD), small-angle X-ray scattering (SAXS), potentiometric titration, high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The adsorption properties towards various anionic dyes, i.e., acid red 88 (AR88), acid orange 8 (AO8), and orange G (OG), were evaluated based on kinetic and equilibrium measurements. The ChSBA, ChAD, and ChMCM composites were characterized by relatively high adsorption capacities (am) for AR88, with values equal to 0.78, 0.71, and 0.69 mmol/g, respectively. These composites were also distinguished by the rapid AR88 adsorption rate, with the values of half-time parameter t0.5 equal to 0.35, 2.84, and 1.53 min, respectively. The adsorption equilibrium and kinetic data were analyzed by applying the generalized Langmuir isotherm and the multi-exponential equation (m-exp), respectively. An interaction mechanism between the dyes and the obtained materials was proposed.
... Polluted wastewater treatment is of utmost importance in removing pollutants using efficient materials or technologies before their discharge into surface water because pollutants pose a significant ecological threat worldwide [1][2][3]. The use of dyes is an important contributor to water pollution, presenting both a toxicological risk and an imminent danger to aquatic ecosystems and human lives [4][5][6]. ...
... Two characteristic peaks at 284.3 eV and 288.7 eV were observed in the C1s peaks of the high-resolution spectrum. These peaks were caused by the presence of hydroxide of water in the spacing between the layers and the bonding of the carbon of the CO 3 2− with the interlayer of LTHs, respectively [75]. O 1 s exhibits a single peak at 530.8 eV that corresponds to the M-OH (M=Ni/Co/Zn) and confirms that the -OH group of water molecules is absorbed on the surface of the NCZ LTHs. ...
... These dyes are non-biodegradable, persistent due to the fact of their synthetic origin and complex chemical properties and structures [2,3]. Discharge of these dyes into water bodies is deleterious to aquatic biodiversity [4,5], and they also possess negative effects on humans health [6][7][8][9][10]. Therefore, it is imperative to provide effective methods for removal of such toxins from the environment [10]. ...
... Discharge of these dyes into water bodies is deleterious to aquatic biodiversity [4,5], and they also possess negative effects on humans health [6][7][8][9][10]. Therefore, it is imperative to provide effective methods for removal of such toxins from the environment [10]. Though many conventional techniques have been employed to remove the harmful toxins from the effluents like reverse osmosis, ion exchange, micro-and ultra-filtration, oxidation, solvent extraction, and electrodialysis, but these methods are exorbitant and tedious [11,12], whereas treatment of colored compounds through adsorption was found to be most effective [13,14], as it has emerged as a promising and versatile water purification technique that can balance high pollutant removal efficiency and the possibility to treat large quantities of water as reported elsewhere [15][16][17]. ...
... Every method has disadvantages and advantages. However, in literature, the adsorption methods are dominating for the removal of those dyes from industries effluents [10][11]. Due to simple operation technic, economical, and efficiency, the adsorption method is better than other methods [12]. ...
The article presents low-cost activated charcoal as an adsorbent in the adsorption process for the removal of malachite green from aqueous solution by batch process. To find the optimum condition of the process, contact time, shaking rate, concentration of malachite green, and concentration of activated charcoal were examined. The malachite green was removed up to 98.9%. The adsorption isotherms were studied to check the performance of the adsorbent. Langmuir, Freundlich, Temkin, Hill De Boer, and Dubinin-Radushkevich adsorption isotherms were studied and compared to which one was suitable in the process. The adsorption process with the activated charcoal adsorbent followed suitably with the order of the Dubinin-Radushkevich > Langmuir > Hill De Boer> Temkin > Freundlich models. According to a kinetic study, the adsorption process was second order. In thermodynamic studies, we obtained negative values of ΔG, ΔS, and ΔH. The negative ΔH and ΔS values suggest that enthalpy contributes more than entropy in producing negative ΔG values. The negative ΔG values of malachite green adsorptions indicate that is a favorable and spontaneous process. The negative value of ΔH ensures the adsorption process is characterized as chemical adsorption and exothermic. The negative ΔS value indicates that randomness decreases at the solid-solution interface during the adsorption of MG by activated charcoal. The surface morphology of the Activated charcoal ensured the adsorption process. The results indicate that the adsorption process is exothermic, spontaneous, and favorable. So, activated charcoal might be useful for removing the malachite green dye from the aqueous solution.
... There are various types of available fillers, such as zeolites, carbon nanotubes, graphene oxide, and activated carbon, that can be used as additives in mixed matrix membrane preparations. As one of these versatile fillers, activated carbon is extensively used for water treatment processes to separate organic and inorganic pollutants from water, owing to its high surface area porosity and controllable pore structure [38,39]. Moreover, activated carbon has significant potential to reduce membrane fouling when integrated into polymeric materials [40]. ...
Ultrafiltration membrane technology holds promise for wastewater treatment, but its widespread application is hindered by fouling and flux reduction issues. One effective strategy for enhancing ultrafiltration membranes involves incorporating activated carbon powder. In this study, composite polyethersulfone (PES) ultrafiltration membranes were fabricated to include activated carbon powder concentrations between 0 and 1.5 wt.%, with carbon size fixed at 200 mesh. The ultrafiltration membranes were evaluated in terms of membrane morphology, hydrophilicity, pure water flux, equilibrium water content, porosity, average pore size, protein separation, and E-coli bacteria removal. It was found that the addition of activated carbon to PES membranes resulted in improvements in some key properties. By incorporating activated carbon powder, the hydrophilicity of PES membranes was enhanced, lowering the contact angle from 60° to 47.3° for composite membranes (1.0 wt.% of activated carbon) compared to the pristine PES membrane. Water flux tests showed that the 1.0 wt.% composite membrane yielded the highest flux, with an improvement of nearly double the initial value at 2 bar, without compromising bovine serum albumin rejection or bacterial removal capabilities. This study also found that the inclusion of activated carbon had a minor impact on the membrane’s porosity and equilibrium water content. Overall, these insights will be beneficial in determining the optimal concentration of activated carbon powder for PES ultrafiltration membranes.
... Dyes are water-soluble and so it is challenging to treat them with chemical or physical methods [3]. Many methods have been developed to treat these organic pollutants including adsorption, coagulation, advanced oxidation, membrane separation, photocatalytic and ozonation from industrial waste [4][5][6][7][8][9]. Among these, adsorption is the most economical and efficient method reported to date and many materials had been reported to act as adsorbents including coal, wood, rice husk, flash ash, activated carbon, cotton waste, clay, and other porous materials [10][11][12][13]. ...
Herein, we reported graphene oxide, as a suitable adsorbent for wastewater treatment to remove crystal violet dye from an aqueous solution. Crystal violet is used for various purposes including colouring, textile, pharmaceuticals etc. It has many harmful effects as it is non-biodegradable, toxic and carcinogenic in nature. So, it is very important to eradicate it from the water. Graphene oxide has been prepared by the modified Hummer's method and characterized by scanning electron micros-copy, Fourier-transform infrared spectroscopy and X-ray diffraction. Graphene oxide's removal efficiency depends on various factors including temperature, pH, and substrate concentration. The experimental data from batch studies is well substantiated with pseudo-second-order kinetics with an R 2 value of 0.98 and Temkin adsorption isotherm (R 2 : 0.94) with a Temkin constant (b T) value of 328 kJ/mol. It also closely fits the intraparticle diffusion model (R 2 : 0.99). The Langmuir adsorption capacity of graphene oxide was calculated to be 15.87 mg/g. The thermodynamic parameter study suggested that the adsorption process is exothermic and spontaneous in nature. Furthermore, a fixed bed column study was also conducted with a constant flow rate of 2.5 mL/min and bed height of 1 cm with a high concentration of crystal violet in a continuous mode of operation to evaluate its practical applicability and the area under the curve is found to be 4,701 cm 2 .
... [28] However, easy production and raw material availability make them costeffective over other porous materials. [29,30] The agro-waste is one of the alternatives to produce PACs employing physical or chemical approaches, including acid carbonization, N 2 activation, KOH/Na 2 CO 3 activation, etc. [31] Apart from being effective in pollutant removal, the PACs derived from agro-waste are economical due to the abundantly available agro-waste. [32] Wheat bran (WB) is one of the major agricultural byproducts with great potential for turning into a high-valueadded product such as PACs. ...
This work reports an efficient method for facile synthesis of hierarchically porous carbon (WB‐AC) utilizing wheat bran waste. Obtained carbon showed 2.47 mmol g⁻¹ CO2 capture capacity with good CO2/N2 selectivity and 27.35 to 29.90 kJ mol⁻¹ isosteric heat of adsorption. Rapid removal of MO dye was observed with a capacity of ~555 mg g⁻¹. Moreover, WB‐AC demonstrated a good OER activity with 0.35 V low overpotential at 5 mA cm⁻² and a Tafel slope of 115 mV dec⁻¹. It also exhibited high electrocatalytic HER activity with 57 mV overpotential at 10 mA cm⁻² and a Tafel slope of 82.6 mV dec⁻¹. The large SSA (757 m² g⁻¹) and total pore volume (0.3696 cm³ g⁻¹) result from N2 activation contributing to selective CO2 uptake, high and rapid dye removal capacity and superior electrochemical activity (OER/HER), suggesting the use of WB‐AC as cost effective adsorbent and metal free electrocatalyst.
... The idea behind this approach is that it can be easier to treat the wastewater of each dyeing process separately, targeting the treatment to its specific chemistry. This work focused on the adsorption of dyes on two types of adsorbent materials: activated carbons [70][71][72][73], already studied and used in traditional purification processes, and polyurethane foams (PUF) [74], explored as an alternative adsorbent. The preparation of the model dyeing solution used in the tanning process was replicated in our laboratory. ...
Wastewater production is a major environmental issue for the leather and textile industries: in a modern plant, several synthetic dyes are used in separated coloring batches whose wastewaters are usually mixed, diluted with other process water streams, and sent to a unique wastewater treatment plant. This includes specific physical and biochemical tertiary treatments to remove dyes efficiently. One of the main difficulties of these processes is the presence of multiple dyes, which cannot be treated with the same efficiency as a “wide-spectrum” process. This work explores the possibility of using conventional granular activated carbon (GAC) and a new polyurethane foam (PUF) for the adsorption of an acid red dye in the wastewater of a specific coloring batch of the tanning industry. The aim of this work is twofold: on the one hand, we aim to explore the performance of the new PUF sorbent; on the other hand, we aim to explore the possibility of using adsorption as an optimized pre-treatment for single-dye batches, which may take advantage of the presence of a single type of target dye and its higher concentration. The effluent is then sent to the wastewater treatment plant for further depuration.
... The efficiency of the process depends on the adsorption capacity and disposal of residual waste. Activated carbon is the most commonly used adsorbent for dyestuff removal and loss of 10-15% during reactivation [11]. Synthetic polymer materials have been used as adsorbents for dye removal but are not biodegradable and replace such limitations with natural biodegradable polymer materials. ...
This work synthesized eco-friendly silver hybridized polymer nanocomposite (Ag@PNC) via a free radical mechanism. The Ag@PNC consists of a network of starch grafted to vinyl acetate (VA), lactic acid (LA), and Methylmethacrylate (MMA), which was reinforced with silver nanoparticles (AgNPs). The effect of incorporation of AgNPs into composite and properties was studied using different techniques, i.e., FTIR, SEM, EDS, and TGA/DTG. The SEM analysis indicates that the pore size of the Ag@PNC decreased with the blending of AgNPs, increasing the composite adsorption capacity and thermal stability. The FTIR confirms the grafting of monomers on starch and thermal degradation and melting of the composite assessed by TGA/DTG. Further, the adsorption kinetics and isotherm data indicate that the pseudo-second-order (R 2 = 0.9898) and Langmuir adsorption isotherm (R 2 = 0.99829) are suitable for the composite with a maximum adsorption capacity of 561.2563 mg/g. These results indicate the potential of synthesized nanocomposite in water treatment at a low cost with efficient reusability.
... Although activated carbon is the adsorbent traditionally used to remove pollutants from aqueous solutions due to its large pore surface (with a controllable pore size), wide variety of surface functional groups, high efficiency, high adsorption rate and easy regeneration [22,23], research on the possibilities of using adsorbents derived from agrifood wastes has increased significantly in recent years [24][25][26]. ...
This paper describes a comparative study of the adsorption of methylparaben onto commercial activated carbon and olive stones activated by calcination at 300 °C and treatment with 1 M HCl. The influence of the initial concentration of methylparaben, adsorbent dose, stirring speed and pH on the adsorption capacity of methylparaben on both adsorbents was studied. To find out the isotherm model, the kinetic model and the mechanism that best describe the adsorption process on each adsorbent, the experimental equilibrium data were analyzed using six isotherm models (Langmuir, Freundlich, Elovich, Temkin, Jovanovic and Dubinin–Radushkevich), and the experimental kinetic data were analyzed using four kinetic models (pseudo-first order, pseudo-second order, Elovich and Avrami) and two mechanistic models (Weber–Morris and Boyd). For both adsorbents, the Langmuir model best describes the adsorption equilibrium, the kinetics of the process follow a pseudo-first-order model and boundary layer diffusion is the step that mainly controls the adsorption process. The adsorption capacity of methylparaben on activated carbon is about four times higher than that of activated olive stones. The addition of graphene oxide and reduced graphene oxide to both adsorbents increases their methylparaben adsorption capacity, to a greater extent in the case of graphene oxide, being that increase more important in activated carbon than in activated olive stones.
... Porous carbon materials have a highly developed pore structure [27], a large specific surface area [28], strong mechanical properties, high chemical stability, and many excellent physical properties [29,30], such as electrical conductivity, thermal conductivity, and thermal stability. Porous carbon materials can adsorb dyes efficiently as well as play a catalytic function in the degradation of dyes [31], which is a kind of adsorbent material that can be widely used in dye wastewater purification and has become popular among researchers in recent years [32,33]. The adsorption effect of porous carbon materials on dyes is mainly influenced by their pore structure and surface heteroatoms. ...
Biomass porous carbon is a low-cost, environmentally friendly material with no secondary pollution and has great potential in the field of dye pollutant adsorption. In this work, we used lignin, a renewable resource abundant in nature, to completely replace phenol and develop a lignin-based phenolic resin carbon (LPFC) adsorbent with high dye removal capacity, high recyclability, and low production cost. The samples were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy. Then the effects of adsorbent dosage (1 g/L, 2 g/L, 3 g/L, 4 g/L, and 5 g/L), temperature (30 °C, 45 °C, and 60 °C), initial dye concentration (100, 200, 300, 400, 500, 600, 700, and 800 mg/L), and pH (3, 4, 6, 8, 10, and 12) on the adsorption capacity were investigated during the adsorption process. The experimental results showed that the pore structure of LPFC was richer and more graphitized than that of phenolic resin carbon (PFC). The adsorption performance of LPFC on CR was better than that of PFC. The adsorption characteristics of LPFC were investigated from the adsorption isotherm and kinetic perspectives. The Langmuir isothermal adsorption model and the proposed second-order kinetic model were able to fit the adsorption data better. The adsorption process preferred monolayer adsorption, and the proposed second-order model predicted a maximum adsorption capacity of 425.53 mg/g. After five cycles, the removal of CR by LPFC only decreased from 92.1 to 79.2%. It can be seen that LPFC adsorbents have great potential in the field of wastewater treatment and can effectively realize the high-value application of lignin.
... Azo dyes are the most widely used by industry, reaching 35% (Argote-Fuentes et al., 2021). They contain aromatic and N=N groups (Mezohegyi et al., 2012). The dyes have high toxicity and can even bioaccumulate in the food chain (Robinson et al., 2001;El Gaini et al., 2009). ...
In this study, MgFe2O4 was successfully synthesized through the coprecipitation method using the precursors Fe(NO3)3·9H2O and Mg(NO3)2·6H2O. The MgFe2O4 product was characterized using XRD, SEM-EDS, VSM, UV-DRS, and FTIR. The catalyst was used for the photocatalytic degradation of Congo red dye under visible light irradiation. The variables of the photocatalytic degradation included solution pH, Congo red concentration, H2O2 concentration, and irradiation time. The MgFe2O4 synthesized has magnetic properties, with a saturation magnetization value of 17.78 emu/g and a band gap of 1.88 eV. A degradation efficiency of 99.62% was achieved under specific conditions, including a Congo red concentration of 10 mg/L, a solution pH of 6, an H2O2 concentration of 2.5 mM, and an irradiation time of 180 min. The degradation efficiency without H2O2 was observed to be 83.45%. The photocatalytic degradation of Congo red followed the pseudo-first-order kinetics model with a rate constant (k) of 0.0167 min-1 and a half-life (t1/2) of 41.49 min. The total organic carbon (TOC) removal of 84.58% indicated that the mineralization of Congo red had occurred. The effectiveness of photocatalytic degradation decreased from 99.62% to 94.50% (<5%) after five cycles of photocatalytic degradation. The results demonstrated that MgFe2O4 has a high Congo red dye degradation efficiency, can be regenerated, and is readily separated from the solution using a permanent magnet.
... Various adsorbents such as activated carbon, graphene, zeolites, polymers, metal oxides/hydroxides, waste-derived materials, and porous silica have been used for wastewater treatment (Abu-Nada et al., 2021;Rauf et al., 2007). In particular, carbonaceous materials have been widely utilized due to their exceptional properties, such as a large specific surface area, abundant pore structure, chemical stability, ease of physical and chemical modification, ability to be tuned for specific applications, and their ability to remove a variety of pollutants (Mezohegyi et al., 2012;S. Hijab, M, et al., 2008). ...
In this study, activated carbon (AC) obtained with apple peel was used for removal of Neutral Red (NR) from aqueous solutions. The characterization of AC was evaluated with the Brunauer-Emmett-Teller (BET), Fourier transform infrared spectra (FTIR), X-ray diffraction (XRD), and scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDX) analyses. Isotherm, kinetic, and thermodynamic parameters were determined for NR removal with AC. Eighteen isotherm models and eight kinetic models were analyzed for three temperatures and six initial dye concentrations. The experimental data best agree with the Langmuir model among the isotherm models, and the maximum adsorption capacity (qm) was calculated 142.857 mg/g at 318 K. It was determined that the pseudo-second-order (PSO) model was the best choice among the kinetic models with the highest correlation coefficients. The removal percentage of NR dye with AC obtained 82.13%, 84.79%, and 87.20% for 120 mg/L initial dye concentration at 298 K, 308 K, and 318 K, respectively. The negative free energy, enthalpy, and entropy values of adsorption obtained − 6386 J/mol, 46280 J/mol, and 165.48 J/mol.K for 20 mg/L NR concentration at 318 K, respectively. The results of this separation process shown spontaneous essence, and workability coinciding with the negative free energy and activation energy was found 13.651 kJ/mol. The assessment of the isotherm, kinetic, and thermodynamic results were evaluated with error functions. The highest correlation coefficient (R²) values and the lowest sum of squares (SS), sum of the square of error (SE), and mean square of error (MSE) values were determined with Langmuir isotherm and PSO kinetic models. This research showed that AC prepared from biomass can be used effectively for wastewater treatment using adsorption technique.
Graphical Abstract
... The main sources of dyes in wastewater are the textile industry and other sectors in which colorings are used, including food, plastics, printing, leather, and paper. Usually, 40-65 L of wastewater per kilogram of the finished product is discharged at each step of the textile manufacturing process (Mezohegyi et al., 2012). Dyes present in textile effluent display high visibility and resilience and have harmful effects (Ali et al., 2009). ...
Although rapid industrialization has made life easier for humans, several associated issues are emerging and harming the environment. Wastewater is regarded as one of the key problems of the 21st century due to its massive production every year and requires immediate attention from all stakeholders to protect the environment. Since the introduction of nanotechnology, bismuth-based nanomaterials have been used in variety of applications. Various techniques, such as hydrothermal, solvo-thermal and biosynthesis, have been reported for synthesizing these materials, etc. Among these, biosynthesis is eco-friendly, cost-effective, and less toxic than conventional chemical methods. The prime focuses of this review are to elaborate biosynthesis of bismuth-based nanomaterials via bio-synthetic agents such as plant, bacteria and fungi and their application in wastewater treatment as anti-pathogen/photocatalyst for pollutant degradation. Besides this, future perspectives have been presented for the upcoming research in this field, along with concluding remarks.
... The main sources of dyes in wastewater are the textile industry and other sectors in which colorings are used, including food, plastics, printing, leather, and paper. Usually, 40-65 L of wastewater per kilogram of the finished product is discharged at each step of the textile manufacturing process (Mezohegyi et al., 2012). Dyes present in textile effluent display high visibility and resilience and have harmful effects (Ali et al., 2009). ...
Persistent contaminants in wastewater effluent pose a significant threat to aquatic life and are one of the most significant environmental concerns of our time. Although there are a variety of traditional methods available in wastewater treatment, including adsorption, coagulation, flocculation, ion exchange, membrane filtration, co-precipitation and solvent extraction, none of these have been found to be significantly cost-effective in removing toxic pollutants from the water environment. The upfront costs of these treatment methods are extremely high, and they require the use of harmful synthetic chemicals. For this reason, the development of new technologies for the treatment and recycling of wastewater is an absolute necessity. Our way of life can be made more sustainable by the synthesis of adsorbents based on biomass, making the process less harmful to the environment. Biopolymers offer a sustainable alternative to synthetic polymers, which are manufactured by joining monomer units through covalent bonding. This review presents a detailed classification of biopolymers such as pectin, alginate, chitosan, lignin, cellulose, chitin, carrageen, certain proteins, and other microbial biomass compounds and composites, with a focus on their sources, methods of synthesis, and prospective applications in wastewater treatment. A concise summary of the extensive body of knowledge on the fate of biopolymers after adsorption is also provided. Finally, consideration is given to open questions about future developments leading to environmentally friendly and economically beneficial applications of biopolymers.
... 3) the concentration of the heavy metal; 4) the temperature and pH of the solution; and 5) time exposure of the contaminated solution to AC [12,[83][84][85]. After treatment, high-quality effluents can be obtained. ...
The increase in the level of iron concentration in drinking water due to natural and anthropogenic activities has become a major problem imposing a severe risk to human wellness. Mining and associated activities have qualitative and quantitative effects on the water regimes in and around the mines. People residing in the mining areas of Odisha, India, confronted a typical problem of iron contamination in water. Almost 60% of the surface water and 50% of the drinking water constitutes iron ions more than the permissible limit established by World Health Organization (W.H·O) i.e. 0.3 mg/L has been noted. Excessive iron accumulation may cause severe health problems such as hemochromatosis, diseases related to the heart and central nervous system, cirrhosis of the liver, diabetes, nausea, etc. Available literature has been incorporated on iron remediation by adsorption technology. This technology has been widely accepted because it offers economic and environmental benefits such as low cost, availability, profitability, ease of operation, and high removal efficacy. Thus the feasibility of activated carbon prepared from various agro-wastes for eradication of iron ions by batch and fixed-bed adsorption has been critically reviewed in this paper.
... 28 It should be noted, however, that activated carbon is a structurally rich material and its interactions with gases and liquids under various environmental parameters are not limited to physisorption. 29 Activated carbon can be commercially obtained in various macroscopic forms including powdered, granulated and fibrous. The term activated carbon indicates that material synthesis conditions involved aggressive heating of carbonaceous material in an inert environment, which induces pyrolytic decomposition and carbonization, followed by "activation", which is a subsequent aggressive heating step in the presence of an oxidant (CO2 or steam, for example). ...
Electrosurgery procedures produce airborne contaminants including volatile organic compounds (VOCs). The effectiveness of commercial grade activated carbon at removing toluene, a typical VOC, from the air in an enclosed simulated operating room when interfaced with an air recirculation device was tested. The concentration of toluene in the air was measured using gas sensitive semiconductor VOC sensors. When the air recirculation device containing activated carbon was turned on, the concentration of toluene in the air decayed exponentially. When the device was off, the toluene concentration reduced much more slowly. After 130 min., a VOC sensor placed near the air recirculation device showed VOC reductions of approximately 30% when the device is on and less than 1% when the device is off. Changing the activated carbon filter after 22 h of constant use showed an abrupt increase in the rate of toluene removal.
... On that account, the protection of the earth's water resources becomes vital and has been facilitated through the development of effective and efficient separation and purification techniques. So far, the reported techniques for the treatment of dye-contaminated aquatic sources include sorption, flocculation, electrolysis, photocatalysis, and biodegradation [8][9][10][11]. Among these methods, sorption is the simplest and most efficient one adopted for these purposes [12]. ...
Environmental pollution has been a reality for many decades, with its contamination intensifying daily due to rapid urbanization and the ever-increasing world population. Dyes, and especially synthetic ones, constitute a category of pollutants that not only affect the quality of water but also exhibit high toxicity toward living organisms. This study was thoroughly planned to explore the removal of two toxic dyes, namely the methylene blue (MB) and methyl orange (MO) compounds from contaminated aqueous media. For this purpose, we designed and synthesized two new composite materials based on ammonium-functionalized Zr4+ MOF (MOR-1 or UiO-66-NH3+) and naturally occurring sorbents, such as bentonite and clinoptilolite. The composite materials displayed exceptional sorption capability toward both MB+ and MO− ions. A key finding of this study was the high efficiency of the composite materials to simultaneously remove MB+ and MO− under continuous flow conditions, also showing regeneration capability and reusability, thus providing an alternative to well-known mixed bed resins.
... In recent years, significant efforts have been made to develop new materials to improve water quality. The application of activated carbon for dyes removal has been the subject of much research due to its many economic advantages [13,14]. The performance efficiency is highly dependent on the physical properties and the functional groups of the activated carbon [15,16]. ...
A significant environmental concern is posed by wastewater containing dyes. When dealing with a polluted medium, adsorption is a beneficial method for the removal of contaminants. This study used argan nutshell as a precursor to synthesize activated carbon via chemical activation with Na 2 CO 3 at 600 °C. The prepared activated carbon (Na@Ac) was characterized using Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET), and zeta potential measurements. The results showed that the prepared activated carbon has a high surface area (1543 m ² /g) and microporous structure. Furthermore, many parameters for Rhodamine B (RhB) dye removal efficiency, including pH, initial pollutant concentration, and temperature, were optimized by response surface methodology (RSM) with a central composite design. Based on the RSM, the best efficiency was 96.84% for the removal of RhB at pH 5, temperature 20 °C, and initial concentration 33.2 mg/L. The kinetic of RhB dye adsorption onto Na@Ac was effectively explained by a pseudo-second-order model, with a maximum uptake capacity of 35.9 mg/g. Moreover, Density functional theory (DFT) calculations were used to understand the adsorption mechanism of the RhB dye onto the Na@Ac. Based on the DFT calculations, hydrogen bonding and π-π interactions may be preferred mechanisms of RhB dye adsorption onto Na@Ac. The Na@Ac could be a promising adsorbent for the removal of Rhodamine B from polluted wastewater.
... The key impact of dyes in the environment are death of microorganisms in soil and staining of water bodies, thus removing dyes from the industrial effluent is of paramount importance. Several treatment technologies have been employed to process these environmental toxic effluents, including solvent extraction, reverse osmosis, membrane separation, and coagulation-flocculation (Mezohegyi et al., 2012). Some authors used graphene-based adsorbents for adsorption of dyes from waters. ...
Water scarcity has been felt in many countries and will become a critical issue in the coming years. The release of toxic organic and inorganic contaminants from different anthropogenic activities, like mining, agriculture, industries, and domestic households, enters the natural waterbody and pollutes them. Keeping this in view in combating the environmental crises, removing pollutants from wastewater is one of the ongoing environmental challenges. Adsorption technology is an economical, fast, and efficient physicochemical method for removing both organic and inorganic pollutants, even at low concentrations. In the last decade, graphene and its composite materials have become the center of attraction for numerous applications, including wastewater treatment, due to the large surface area, highly active surface, and exclusive physicochemical properties, which make them potential adsorbents with unique physicochemical properties, like low density, chemical strength, structural variability, and the possibility of large-scale fabrications. This review article provides a thorough summary/critical appraisal of the published literature on graphene-, GO-, and rGO-based adsorbents for the removal of organic and inorganic pollutants from wastewater. The synthesis methods, experimental parameters, adsorption behaviors, isotherms, kinetics, thermodynamics, mechanisms, and the performance of the regeneration-desorption processes of these substances are scrutinized. Finally, the research challenges, limitations, and future research studies are also discussed. Certainly, this review article will benefit the research community by getting substantial information on suitable techniques for synthesizing such adsorbents and utilizing them in water treatment and designing water treatment systems.
... 30 It should be noted, however, that activated carbon is a structurally rich material, and its interactions with gases and liquids under various environmental parameters are not limited to physisorption. 31 In general, the structural features of activated carbon are complex and vary based on preparation conditions. These features include pore size and chemical composition. ...
Electrosurgery procedures produce airborne contaminants including volatile organic compounds (VOCs). The effectiveness of commercial grade activated carbon at removing toluene, a typical VOC, from the air in an enclosed simulated operating room (OR) when interfaced with an air recirculation device was tested. The concentration of toluene in the air was measured using gas sensitive semiconductor VOC sensors. When the air recirculation device containing activated carbon was turned on, the concentration of toluene in the air decayed exponentially. When the device was off, the toluene concentration reduced much more slowly. After 130 min, a VOC sensor placed near the air recirculation device showed VOC reductions of approximately 30% when the device is on and less than 1% when the device is off. Changing the activated carbon filter after 22 h of constant use showed an abrupt increase in the rate of toluene removal.
CB[8]-based supramolecular assembly, i.e., 2CB[8]·[ZnCl4]·4H2O (1) (CB[8] = cucurbit[8]uril), was synthesized under solvothermal condition in the presence of [ZnCl4]²⁻ anions as a structure inducer. 1 was applied as a high-efficiency absorbent to remove the commonly used dye amaranth (AMR) and an antibacterial drug of broad-spectrum sulfadiazine sodium (SFZ) from the aqueous solution. It showed an excellent removal rate and could remove 96.08% and 96.21% for AMR and SMZ, respectively. The adsorption behaviors were investigated using FT-IR. The differences in IR spectra revealed that the formation of inclusion complexes is the main driving force of adsorption. The phenyl and sulfonyl or sulfone moieties of AMR and SFZ entered the cavity of CB[8] in 1, and the adsorption mechanism could be due to the formation of inclusion complexes of AMR and SFZ in the CB[8] cavities of 1. This work illustrates the application prospects of CB[8]-based supramolecular assembly in environmental protection.
Polluting species released in industrial-colored effluents contaminate water, degrading its quality and persisting in the aquatic environment; therefore, it must be treated for safe discharge or onsite reuse/recycling to ensure a fresh water supply. This review has the principal goal of facilitating understanding of some important issues concerning wastewater (WW) treatment systems, mainly based on a coagulation–flocculation step, as follows: (i) the significance of and facilities offered by specialized treatment processes, including the coagulation–flocculation step as a single or associated step (i.e., coagulation–flocculation followed by sedimentation/filtration or air flotation); (ii) the characteristics of industrial-colored WW, especially WW from the textile industry, which can be reduced via the coagulation–flocculation step; (iii) primary and secondary groups of hybrid materials and their characteristics when used as coagulants–flocculants; (iv) the influence of different process operating variables and treatment regimens on the efficiency of the studied treatment step; and (v) the benefits of using hybrid materials in colored WW treatment processes and its future development perspectives. The consulted scientific reports underline the benefits of applying hybrid materials as coagulants–flocculants in colored textile WW treatment, mainly fresh, natural hybrid materials that can achieve high removal rates, e.g., dye and color removal of >80%, heavy metals, COD and BOD of >50%, or turbidity removal of >90%. All of the reported data underline the feasibility of using these materials for the removal of colored polluting species (especially dyes) from industrial effluents and the possibility of selecting the adequate one for a specific WW treatment system.
The present study conducted a successful green synthesis of zinc oxide nanoparticles (ZnO NPs) from the aqueous solution of Salvadora persica leaf extract as a capping agent. The environmental application of the synthesized ZnO NP was understood from the methyl orange (MO) dye removal investigation. The morphology, chemical composition, crystallinity, optical property, and isothermal behaviour of synthesized NPs were characterized by scanning electron microscopy (SEM), energy-dispersive spectroscopy, Fourier transform infrared (FTIR), X-ray diffraction (XRD), and UV-visible spectroscopy (UV-Vis). The UV-Vis absorption band was found at 365 nm, and the XRD analysis confirmed the crystallinity of the ZnO NP and the particle sizes were in the range of 32–68 nm. The FTIR bands confirm the presence of bioactive compounds. SEM images showed the formation of hexagonal and rod-shaped NPs. The findings suggested that the shape of the synthesized ZnO NPs has a major influence on the removal of MO from water. The results revealed that a maximum MO removal of 68% was obtained with an amount of 0.05 g of ZnO NPs at pH 5. This research demonstrates a green method of preparing various ZnO NPs with a remarkable efficiency towards the removal of MO dye.
The accumulation of non-biomass wastes, including anthracite, asphalt/asphaltene, synthetic polymers, petroleum coke, and tire wastes, contributes to environmental pollution. Utilizing these waste resources as precursors for activated carbon production emerges as an economical and sustainable strategy for energy storage and environmental remediation. This review (explicitly from 2010 to 31 December 2022) comprehensively explores recent advancements in employing these waste materials for activated carbon synthesis. The study highlighted textural characteristics such as surface chemistry, surface area, microstructures, and mesostructures and their impact on the functionality of activated carbon. Examining various precursors, asphalt-based activated carbons exhibited superior mean specific surface area (2715.73 m2g─1) and pore volume (1.6078 cm3g─1), surpassing other reported sources. Anthracite-based activated carbon stood out with a specific capacitance of 433 Fg─1, demonstrating excellent energy storage potential. In wastewater treatment, asphalt-based activated carbons display a remarkable qmax of 1113 mgg─1, while waste tire-based activated carbon exhibited a strong gaseous compound removal capacity of 475 mgg─1. Despite widespread application in wastewater treatment, the investigation notes a gap in utilizing these activated carbons for energy storage. The activated carbon derived from these non-biomass sources emerges as a promising material with commendable properties in volume and pore sizes, surface area, surface behavior, and functional groups. The review guides researchers toward an economical approach for producing non-biomass-derived activated carbons with exceptional physicochemical characteristics and adsorption capacity. It concludes by critically evaluating current knowledge gaps, synthesizing challenges, and offering recommendations for future research endeavors.
Dyes are complex unsaturated aromatic compounds used as coloring agents in different industries like textile, paper, tannery, photography, etc. The dye industries have sprouted like mushrooms with inappropriate dye effluent treatment technologies. Thus, the current situation demands effective and sustainable wastewater treatment methods. This review article covers the classification of dye, the impact of dye effluent on humans and its environment, the drawbacks of treatment approaches, the making of value-added products, and energy production from dye effluents. This review discussed various regular technologies that had already been applied; the advanced and sustainable physicochemical and biological approaches (hybrid constructed wetland, advanced oxidation method, nano photocatalysis, and ceramic membrane filtration) will be implemented in the future by reviewing. Though the recent technologies obtained are successful, the several downsides like high operating costs, the use of chemicals, secondary pollutant production, the need for adequate equipment, high electricity consumption, membrane fouling, scalability, and sludge disposal are the headache of the researchers. Among those technologies, the approaches like microbial remediation, phytoremediation, constructed wetland (MFC-CW), and fungal remediation are sustainable solutions in terms of treatment and resource recovery from dye effluent. The primary goal of this review article is to spread ideas about traditional and advanced treatment technologies to scientists and researchers currently engaged in dye effluent management.
Water is an indispensable natural resource and is the most vital substance for the existence of life on earth. However, due to anthropogenic activities, it is being polluted at an alarming rate which has led to serious concern about water shortage across the world. Moreover, toxic contaminants released into water bodies from various industrial and domestic activities negatively affect aquatic and terrestrial organisms and cause serious diseases such as cancer, renal problems, gastroenteritis, diarrhea, and nausea in humans. Therefore, water treatments that can eliminate toxins are very crucial. Unfortunately, pollution treatment remains a difficulty when four broad considerations are taken into account: effectiveness, reusability, environmental friendliness, and affordability. In this situation, protecting water from contamination or creating affordable remedial techniques has become a serious issue. Although traditional wastewater treatment technologies have existed since antiquity, they are both expensive and inefficient. Nowadays, advanced sustainable technical approaches are being created to replace traditional wastewater treatment processes. The present study reviews the sources, toxicity, and possible remediation techniques of the water contaminants.
Dye pollution is a significant environmental catastrophe, and it has so far proven to be challenging to purify dye-contaminated water effectively. Metal–organic frameworks (MOFs) have potential of removing dyes from wastewater but effectively addressing the simultaneous removal of multiple dyes remains a challenging task. In-MOF, synthesized in the round-bottom flask, sealed glass tubes, and under microwave conditions, exhibits excellent adsorption for cationic dyes. The identification and characterization of In-MOF were accomplished using several analytical techniques, including Powder X-ray diffraction, Fourier-transform infrared spectroscopy, Brunauer–Emmett–Teller analysis, Thermogravimetric analysis, Scanning electron microscope, Energy-dispersive X-ray spectroscopy, Elemental analysis, and Density functional theory for structure elucidation. In-MOF exhibits outstanding dye removal efficiency for Methylene Blue (MB: 98%; 18.6 mg/g), Azure A (AZA: 99%; 22.4 mg/g), Azure B (AZB: 98%; 17.2 mg/g), Toluidine Blue O (TOLO: 99%; 20.6 mg/g), Rhodamine B (RHB: 82%; 8.8 mg/g), and Congo red (CR: 93%; 14.2 mg/g) individually. Moreover, In-MOF demonstrates remarkable selectivity towards MB removal even in the presence of RHB. The kinetics of adsorption and reusability tests for MB indicate consistent removal capacity for the initial three cycles, but a significant decline of up to 52% is observed by the sixth cycle. These findings establish In-MOF as a promising candidate for industrial applications due to its high removal efficiency and practical synthetic approach.
Spartina alterniflora, as an invasive alien species, has been studied in terms of its potential use in immobilization and synergistic photocatalysis against dye contaminants for the first time. Microscopic characterization and Fourier transform infrared (FTIR) spectroscopy results confirmed the presence of abundant 3D wormhole-like pore structures and active functional groups (-OH, -NH2, CO, Si-O-Si). Moreover, the existence of SiO2 was connected the metal oxides with polar groups, which could proceed entire reaction procedure subsequently. Transition metal oxides (such as Fe2O3, TiO2, MnO2 and NiO) contained in photocatalysts might effectively promote the organics decomposition by the visible light excitation. The highest dye removal efficiency of 92.03% could be reached with the addition of 0.02 g photocatalyst. The capture experiment confirmed that the h+ was the dominant active substance during the photocatalytic degradation process. Density functional theory (DFT) calculations verified that the functional groups (-COOH, -OH and -NH2) were exceptional adsorption sites for catalyst, and the calculated adsorption energy were all negative with the order of SRHH-NH2 (-2.712688 eV) < SRHH-OH (-2.075601 eV) < SRHH-COOH (-1.283141 eV), which confirmed that interface interaction effectively bound cationic dyes through the formation of hydrogen bonds at the catalysts-water interface, further accelerating the reaction rate of the entire photocatalytic reduction of dye molecules. Therefore, this work provides a feasible synthesis of natural photocatalysts using solid waste, which suggests excellent adsorption and photocatalysis properties for the treatment of organic industrial pollutant.
A hetero-Fenton zeolite-supported Fe3O4 catalyst was synthesized using a simple impregnation–precipitation method. The structure, morphology, and components of the catalyst were characterized using various analytical methods (XRD, SEM, and ICP-MS). Subsequently, the catalyst was used to degrade the azo dye methylene blue (MB), via a heterogeneous photo-Fenton process under UV irradiation in an aqueous solution. This study investigated the influence of different parameters on MB decolorization efficiency, such as the initial concentration of hydrogen peroxide, amount of catalyst, initial dye concentration, and reusability of the catalyst. The removal efficiency was nearly 100% within only 5 min with an initial concentration of methylene blue of 50 mg L⁻¹ under the following experimental conditions: a pH solution of 3, a catalyst of 0.6 g L⁻¹, an H2O2 concentration of 66 mg L⁻¹, and a UV lamp power of 6 W. Moreover, the Fe3O4/zeolite A catalyst (Fe/ZA) showed good stability in the photo-Fenton degradation of methylene blue after four consecutive cycles, implying that the Fe/ZA catalyst could be a potential wastewater treatment option. Furthermore, the findings of the reaction kinetics study demonstrate that the kinetics of the dye removal reaction can be fitted using the Langmuir–Hinshelwood model for heterogeneous catalytic reactions.
The textile, leather, paint and other industries discharge lots of dyes in their effluent which can cause major impact to environment and human life. Therefore, it becomes necessary to eliminate the dye from the effluent before its discharge and reuse. Several procedures for the removal and inactivation of dyes have been proposed over past but the adsorption has gained popularity due to its efficiency and operational ease. Use of the biochars as an adsorbent is gaining attention due to their low cost, availability and high adsorption capability. The current study focuses on the removal of Basic Fuchsin (BF) dye through adsorption using Jamun (Syzyum Cumini) seed powder biochar as an adsorbent. The biochar was characterized through various analyses such as: XRD, EDS, FTIR, TGA and SEM. Adsorption was studied by varying the parameters such as pH, contact duration, temperature, adsorbent dose, and temperature. Further, the isotherm, kinetic, and thermodynamic studies were also performed to understand the adsorption mechanism. The maximum adsorption capacity for BF dye was found with Jamun seed biochar produced at 500?C. The study reveals that the biochar manufactured from Jamun seed power has significant potential for elimination of BF dye from wastewater.
Discharge of untreated water may cause serious health diseases. There have been studies on effluent concentration from wastewater treatment plants of pharmaceutical and personal care product industries. In this paper, the authors have reviewed the concentration of water discharged through the surface water and effluent of wastewater treatment plants, and secondary sludge treatment. Significant compounds with their maximum concentration and removal efficiency are reviewed, and the method applied is then compared with previous results. Challenges to design instruments and techniques to decrease the concentration of endocrine-disrupting compounds from the effluent and, to reduce the toxicity of EDs in drinkable water and aquatic environments are discussed. Personal care products (PCPs), endocrine-disrupting compounds (EDCs), pharmaceuticals (PhACs), and their transformation products are examples of emerging contaminants (ECs) whose inclusion at trace levels in treated wastewater is affecting human health and the aquatic ecosystem. Despite advancements in treatment technologies, the design of existing treatment plants is often unsuitable for removing these ECs, and there are few published health standards that guide the treatment of these pollutants. Many new ECs are introduced into the environment without being detected. This paper reviews existing research that provides reliable and quantitative information on PhACs, PCPs, and EDCs, and their concentrations in surface water, groundwater, drinking water, and treated wastewater, as well as the removal efficiency of different treatment processes for different emerging pollutants, with a focus on recent studies regarding the fate and behavior of the contaminants in wastewater treatment plants and the environment.
This research aims to create an alternating polyketone with the advantage of having its cationic groups in one and four alternating places for increased functionality. Simple condensation polymerization between terephthaldehyde and 2,5-hexane dione yielded a new polyarylidene ketone (PAK). Fourier-transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), X-ray diffraction, UV-Visible absorbance, fluorescence, and SEM studies were used to assess the physicochemical properties of the resultant polymer. The results demonstrate that the polymer is amorphous, has good thermal stability, and emits a red color. It can also be utilized as a dye adsorbent in an aqueous solution, with remarkable adsorption selectivity for the cationic dye methylene blue (MB). The effectiveness of PAK as an adsorbent was calculated as a function of pH, dosage, and initial dye concentration; the highest dye removal percentage of 96% was achieved at pH 10, 50 mg dosage and initial dye concentration of 20 ppm. The study of kinetics and isotherms was also carried out. The pseudo-second-order model was more adapted to the kinetic data, while the Freundlich and Langmuir models were better suited to the PAK equilibrium data. According to the kinetics and isotherms analyses, the adsorption behavior was a favorable chemisorption process. The findings of this study suggest that PAK could be used as an adsorption filter for MB dyeing wastewater decolorization. It also has excellent metal ion removal capabilities with various metals (Zn ²⁺ , Cu ²⁺ , Ni ²⁺ , Co ²⁺ , Cd ²⁺ , and Fe ³⁺ ). PAK is selective for Fe (III) and Cu (II); the polymers' ion adsorption is not based on ion exchange but on chelating process.
A ternary arrow down dual S-scheme nano photocatalyst ZnIn2S4/Bi2O2CO3/ZnFe2O4 composed of microspheres of ZnIn2S4, layered Bi2O2CO3, and magnetic ZnFe2O4 has been prepared for RhB degradation. The ZnIn2S4/Bi2O2CO3/ZnFe2O4 degraded 99.8% of RhB in 90 min, and its photocatalytic activity toward RhB degradation was highest as compared to pure ZnIn2S4 (36.38%), Bi2O2CO3 (19.56%), ZnFe2O4 (16.65%) and binary Bi2O2CO3/ZnFe2O4 (43.82%) composite. The Langmuir–Hinshelwood kinetics model was found for RhB degradation for all photocatalysts. The rate constant of the ZnIn2S4/Bi2O2CO3/ZnFe2O4 hybrid photocatalyst was 0.177 min−1, which is 12.73, 29.84, and 38.06 times greater than pure ZnIn2S4, Bi2O2CO3, and ZnFe2O4, respectively. UV–Vis, EIS, and PL measurements indicate that the synergistic effect is brought on by an expanded range of light absorption, lower charge separation resistance, and decreased recombination of e−/h+ pairs. The significant decrease in photocatalytic activity with radical scavengers established that •O2−, •OH, and h+ were the active free radicals, and •O2− was the leading one during the degradation of RhB. The dual S-scheme electron transfer mechanism has been proposed because lesser energy electrons and holes were destroyed, and charge carriers with higher redox potentials were retained. The photocatalysts' good magnetic separation and photostability were confirmed after four reuse cycles and maintained 87% degradation efficiency.
Membrane technology utilizing ultrafiltration (UF) processes has emerged as the most widely used and cost-effective simple process in many industrial applications. The industries like textiles and petroleum refining are promptly required membrane based UF processes to alleviate the potential environmental threat caused by the generation of various wastewater. At the same time, major limitations such as material selection as well as fouling behavior challenge the overall performance of UF membranes, particularly in wastewater treatment. Therefore, a complete discussion on material design with structural property relation and separation performance of UF membranes is always exciting. This state-of-the-art review has exclusively focused on the development of UF membranes, the material design, properties, progress in separation processes, and critical challenges. So far, most of the review articles have examined the UF membrane processes through a selected track of paving typical materials and their limited applications. In contrast, in this review, we have exclusively aimed at comprehensive research from material selection and fabrication methods to all the possible applications of UF membranes, giving more attention and theoretical understanding to the complete development of high-performance UF systems. We have discussed the methodical engineering behind the development of UF membranes regardless of their materials and fabrication mechanisms. Identifying the utility of UF membrane systems in various applications, as well as their mode of separation processes, has been well discussed. Overall, the current review conveys the knowledge of the present-day significance of UF membranes together with their future prospective opportunities whilst overcoming known difficulties in many potential applications.
Environmental contamination due to organic pollutants including organic dyes (e. g., methylene blue (MB)) and paraquat (i. e., methyl viologen (MV)) has become a serious problem. Herein, the removal for toxic cations of methylene blue (MB⁺) and methyl viologen (MV²⁺) has been realized by a three‐dimensional (3D) anionic microporous metal‐organic framework, namely [Me2NH2][In(TDC)2] ⋅ 1.5DMA ⋅ H2O (FJSM‐InMOF). FJSM‐InMOF is capable of selectively adsorbing MB⁺ in the presence of various dyes due to the effects of size‐exclusion and charge‐matching. Particularly, the strategy of combining adsorption and photocatalytic degradation realizes the thorough treatment of MB⁺, which has been rarely reported. The adsorbent material can be easily regenerated and reused. Moreover, FJSM‐InMOF exhibits a high capacity and rapid kinetics towards more toxic MV²⁺. This work poses a new way for the selective removal of cationic organic pollutants and highlights the significance of combining different methods for the decontamination of organic pollutants.
Virtually all the known physicochemical and biological techniques have been explored for treatment of extremely recalcitrant dye wastewater; none, however, has emerged as a panacea. A single universally applicable end-of-pipe solution appears to be unrealistic, and combination of appropriate techniques is deemed imperative to devise technically and economically feasible options. An in-depth evaluation of wide range of potential hybrid technologies delineated in literature along with plausible analyses of available cost information has been furnished. In addition to underscoring the indispensability of hybrid technologies, this article also endorses the inclusion of energy and water reuse plan within the treatment scheme, and accordingly proposes a conceptual hybrid dye wastewater treatment system.
Ozonation was found to be effective for the decolorization of solutions, but has only a slight effect on TOC removal. On the other hand, adsorption on activated carbon improves the TOC removal, but the progressive uptake of the organic contaminants during the adsorption process decreases its removal efficiency. Decolorization, mineralization, and ozone consumption of colored solutions were evaluated under continuous operation in a column by three different processes: ozonation, adsorption on a fixed activated carbon bed, and ozonation in the presence of the activated carbon bed. The introduction of an ozone flow in a fixed activated carbon bed enhances both the decolorization of the solutions and mainly the mineralization of the organic matter, even when the activated carbon was previously partially saturated. Activated carbon acts both as an adsorbent and as a catalyst in the ozonation of colored solutions. The column configuration plays an important role in the performance of this system. The configurations in series and with activated carbon in the upper part of the column showed the highest colour and TOC removal for dye solutions.The results obtained clearly show that the combination of ozone and activated carbon is a promising technique for the final treatment of colored effluents. Practical applicability of this process was validated by treating two industrial textile effluents, collected after two different biological treatments.
Electrocoagulation (EC) is an efficient method for textile wastewater treatment. Researches are mainly focused on the technical performance of this process, while its economic aspect has been usually neglected. This paper deals with a simplified operating cost analysis for the treatment of a textile wastewater by EC using iron and aluminium electrode materials. The effects of various parameters such as wastewater conductivity and pH, current density and operating time, on the operating cost have been discussed for two electrode materials, separately.
Activated carbons can be used as catalyst supports or as catalysts on their own. An example of the latter case is the oxidative dehydrogenation of ethylbenzene (ODE), which can be of industrial relevance. In this work, a systematic study of the influence of the texture of the activated carbon in the ODE reaction is carried out. Starting from the same material, two types of experiments were made, the first where the porosity of the catalyst was enlarged by carbon gasification and the second where it was partially blocked by carbon deposition. All the carbon catalysts were characterised by nitrogen adsorption at 77 K (textural properties) and TPD (surface chemical properties) before and after reaction, and their performances in the ODE were evaluated. The results show that the texture effects are important up to a certain pore size; for larger pore sizes, the surface chemistry controls catalyst performance.
The application of catalytic ozonation processes for the decolourisation and mineralisation of coloured aqueous solutions was studied. One acid azo dye, CI Acid Blue 113, and two reactive dyes, CI Reactive Yellow 3 and CI Reactive Blue 5, with azo and anthraquinone chromophores, respectively, were used as representative textile dyes. The catalytic activities of activated carbon, cerium oxide and a ceria-activated carbon composite were evaluated in the removal of the selected dyes. In all cases, with an initial dye concentration of 50 mg/L, a complete decolourisation was achieved by single ozonation in short reaction times (less than 10 min). The ceria-activated carbon composite allowed the highest removal of total organic carbon. For dye concentrations of 50 mg/L, mineralisation degrees of 100%, 98% and 97% were achieved with the composite after 2 h of reaction, respectively for CI Reactive Blue 5, CI Acid Blue 113 and CI Reactive Yellow 3. The activity of the catalyst containing cerium was affected by the presence of carbonate and bicarbonate ions due to their scavenging effect towards hydroxyl radicals; for example the mineralisation degree of CI Reactive Blue 5 (C0 = 300 mg/L) after 120 min of reaction was only 63%, contrasting with the value of 85% obtained in the absence of carbonates. All the catalytic systems were evaluated in the treatment of textile effluents, collected before or after conventional biological treatment. Catalytic ozonation was proven to be effective when used as tertiary treatment for bio-treated effluents.
The catalytic performance of 3 wt.% copper supported on carbon nanofibers (CNFs) in liquid phase oxidation has been tested using a batch stirred tank microreactor in order to determine the decolorization and total organic carbon (TOC) removal efficiency in washing textile wastewater (WTW). A preliminary study was carried out in a temperature range of 120–160 °C and two oxygen partial pressure of 6.3 and 8.7 bar. TOC removal and toxicity reduction were as high as 74.1% and 43%, respectively at 140 °C and 8.7 bar, after 180 min reaction. The main intermediates detected in raw wastewater were decanoic acid, methyl ester and 1,2-benzenedicarboxylic acid, and have been degraded by means of Cu/CNF catalyst. Application of CWAO to the treatment of a textile effluent at 160 °C and 8.7 bar of oxygen partial pressure showed that the use of a Cu/CNF catalyst significantly improves the TOC and color removal efficiencies and it can be considered as an option for a pretreatment step in the treatment of these industrial effluents.
Active carbon fiber was used as electrodes to treat several simulated dyeing wastewater and factual textile-dyeing wastewater from a textile-dyeing operation at Shanghai. This method was found to be quite effective and highly competitive in contrast with Fenton's reagent. Several operating variables, such as voltage, pH and salt added were studied to ascertain their respective effect on the treatment efficacy. According to the experiment, nearly all the wastewater's chromaticity removals were higher than 90%, with COD removals within ca. 40–80%.
The surface chemistry of a commercial activated carbon with a slightly basic nature was modified by appropriate treatments in order to obtain two additional samples, respectively with acidic and basic properties, without changing its textural parameters significantly. Different techniques (N2 adsorption at 77 K, temperature programmed desorption, and determination of acidity, basicity, and pH at the point of zero charge) were used to characterize the adsorbents. Kinetic and equilibrium adsorption data of a selected textile reactive dye (Rifafix Red 3BN, C.I. reactive red 241) on the mentioned materials were obtained at the pH values of 2, 7, and 12. The kinetic curves are fitted using the second-order model. The respective rate constants seem to diminish progressively with the initial concentration for the more diluted solutions tested, reaching a constant value at higher concentrations, which depends on the experimental system under consideration (adsorbent and pH). In general, the Langmuir model provides the best fit for the equilibrium data. The different uptakes obtained are discussed in relation to the surface chemical properties of the adsorbents. It is shown that the adsorption of the reactive (anionic) dye on the basic sample (prepared by thermal treatment under H2 flow at 700 °C) is favored. This conclusion is explained on the basis of the dispersive and electrostatic interactions involved. Moreover, it is also shown that the optimal adsorption condition for all the activated carbons tested corresponds to solution pH values not higher than the pHpzc of the adsorbents, which may be interpreted by taking into account the electrostatic forces present.
A feasibility study was carried out in the laboratory for the sequential anaerobic/aerobic treatment of textile wastewater. The process units consisted of an anaerobic UASB (upflow anaerobic sludge blanket) reactor and a SCAS (semi-continuous activated sludge) reactor. A contact-sorption layer with GAC (granular activated carbon) was provided at the bottom of the conventional UASB reactor. The raw textile wastewater first passed through the GAC bed and then through the sludge bed. By means of the GAC bed, the top-layer granular sludge was protected from toxicants. Biological regeneration of GAC, which was enhanced via a recycle flow, was demonstrated. The combined GAC-UASB and SCAS treatments allowed a stable performance and a COD (chemical oxygen demand) and colour removal of 98 and 95 %, respectively.
Treatment of textile dyeing wastewaters by conventional methods have recently proved to be inadequate. Such methods consist of various combinations of biological, physical and chemical methods including coagulation/flocculation and carbon adsorption. The study described herein is an investigation of the treatability of a commonly used azo dye in the textile dyeing and finishing operations, Reactive Black 5, by an advanced oxidation process, to achieve an acceptable degree of destruction of the target pollutant. The research was focused on a UV/H2O2 oxidation process, where the individual effects of H2O2 concentration, initial dye concentration, and alkalinity under neutral pH on the pseudo-first order reaction rate constant were investigated. Relative removal rates of color with respect to chemical oxygen demand and total organic carbon in dye-distilled water mixture were compared; effect of bicarbonate alkalinity at neutral pH was tested. Pseudo-first order reaction rate constants and electrical energy requirements per order of magnitude removal were determined.
In an ozone-containing water a suspension of a few milligrams per liter of activated carbon (AQ or carbon black (CB) initiates a radical-type chain reaction that then proceeds in the aqueous phase and accelerates the transformation of O3 into secondary radicals, such as hydroxyl radicals (°OH). This results in an Advanced Oxidation Process (AOP) that is similar to an O3-based AOP involving application of H2O2 or UV-irradiation. We have studied these phenomena by observing the effect of suspensions of AC and CB on the rate of transformation of O3 in lakewater and in well-characterized solutions. In addition, the stoichiometric yield factor of the AC-catalyzed conversion of O3, into °OH has been shown to be comparable to that which is achieved by a slower process in the absence of AC. This comparison has been based on the measured depletion of an O3-resistant organic °OH probe that was added as a trace reference compound and that competed with a kinetic excess of solutes that controlled the lifetime of °OH. The AC-catalyzed transformation of O3 into °OH for creating an O3-based AOP may be of practical interest to water utilities as an alternative to extended reaction times, to hydrogen peroxide addition, or to UV-catalyzed transformation of O3. We propose the name “Carbozone Process” for this new type of AOP.
This study was to investigate the ozone oxidation of textile wastewaters in a fluidized or fixed granular activated carbon (GAC) bed. Experiments were conducted to examine the effects of various operating variables on the treatment efficiencies of the combined ozonation and activated carbon adsorption. Ozonation was found to provide very efficient regeneration of exhausted GAC in the reactor, avoiding the costly ex situ GAC regeneration. It was also observed that the GAC acts not only as an adsorbent, but also as a catalyst in promoting ozone oxidation. The combined ozonation and GAC adsorption offers strong synergistic effects on the textile wastewater treatment. A generalized kinetic model consisting of multiple steps of ozonation and adsorption was proposed in this work to represent the combined process. The proposed adsorption/ozonation/desorption mechanism and the generalized kinetic model were shown to describe very well the combined treatment process.
Active carbon fiber was used as electrodes to treat several simulated dyeing wastewater and factual textile-dyeing wastewater from a textile-dyeing operation at Shanghai. This method was found to be quite effective and highly competitive in contrast with Fenton's reagent. Several operating variables, such as voltage, pH and salt added were studied to ascertain their respective effect on the treatment efficacy. According to the experiment, nearly all the wastewater's chromaticity removals were higher than 90%, with COD removals within ca. 40–80%.
The sorption of three acid dyes, namely, Acid Red 114, Polar Yellow and Polar Blue RAWL, onto activated carbon, has been studied. Equilibrium isotherms have been measured for three single component systems (AB, AR, AY) and one binary component system (AB+AY). The isotherms were determined by shaking 0.05 g activated carbon, particle size range 500–710 μm, with 0.05 dm3 dye solution of initial concentrations from 10 to 250 mg/dm3. A constant temperature agitating 400-rpm shaking water bath was used and the temperature maintained at 20±2°C. A contact time of 21 days was required to achieve equilibrium. Analysis of data has been carried out in two stages. (a) In single component analysis, the experimental isotherm data were analysed using Langmuir, Freundlich, Redlich-Peterson, Temkin and Dubinin-Radushkevich equations for each individual dye. The monolayer adsorption capacities are 101.0 mg Acid Red per g carbon, 100.9 mg Acid Blue per g carbon and 128.8 mg Acid Yellow per g carbon. (b) In multicomponent analysis, one binary system has been analysed using an extended form of the Langmuir equation. The correlation between theoretical data and experimental data only had limited success due to competitive and interactive effects between the dyes and dye-surface interactions.
The effect of powdered activated carbon (PAC) addition on the performance of a membrane-coupled anaerobic bioreactor (MCAB) was investigated in terms of membrane filterability and treatability through a series of batch and continuous microfiltration (MF) experiments. In both batch and continuous MF of the digestion broth, a flux improvement with PAC addition was achieved, especially when a higher shear rate and/or a higher PAC dose were applied. Both the fouling and cake layer resistances decreased continuously with increasing the PAC dose up to 5 g/L. PAC played an important role in substantially reducing the biomass cake resistance due to its incompressible nature and higher backtransport velocities. PAC might have a scouring effect for removing the deposited biomass cake from the membrane surface while sorbing and/or coagulating dissolved organics and colloidal particles in the broth. The chemical oxygen demand and color in the effluent were much removed with PAC addition, and the system was also more stable against shock loading.
The oxidation reaction of the cobalt(II) complex [Co(edta)]2− to [Co(edta)]− (edta4− = ethylenediaminetetraacetate ion) occurred efficiently by hydrogen peroxide or peroxodisulfate with activated carbon (AC) in aqueous media of pH 4.7, where the AC acts as a catalyst of the electron-transfer mediator. The oxidation reaction constitutes a chain reaction comprising the AC/AC+ cycle, in which the oxidation reaction is initiated by an electron-transfer from AC to hydrogen peroxide or peroxodisulfate to make radicals of AC+ and OH•, or SO4−•. These radicals could rapidly oxidize [Co(edta)]2− to [Co(edta)]−. The rate of the oxidation reaction is of first-order with respect to the concentrations of hydrogen peroxide (or peroxodisulfate) and the AC amounts added, and of zero-order to [Co(edta)]2− under the conditions. Further, the rate was unrelated to the dissolved O2. In the case of hydrogen peroxide, it could be decomposed by the AC, even in the absence of [Co(edta)]2−, according to the first-order with respect to the hydrogen peroxide concentration; the rate constant was 2-fold of the rate constant in the presence of [Co(edta)]2−. However, in the case of peroxodisulfate, no appreciable decomposition of the S2O82− was found in the absence of [Co(edta)]2−, and the decomposition rate in the presence of [Co(edta)]2− was 104-fold faster than the rate of hydrogen peroxide decomposition under the same conditions. Consequently, it is concluded that the AC acts in a way similar to iron(II) ion in the Fenton-reagent.
Activated carbons, prepared from low-cost mahogany sawdust and rice husk have been utilized as the adsorbents for the removal of acid dyes from aqueous solution. An acid dye, Acid Yellow 36 has been used as the adsorbate. Results show that a pH value of 3 is favourable for the adsorption of acid dye. The isothermal data could be well described by the Langmuir and Freundlich equations. Kinetic parameters of adsorption such as the Langergren pseudo-first-order constant and the intraparticle diffusion rate constant were determined. For the present adsorption process, intraparticle diffusion of dye molecule within the particle has been identified to be rate limiting. The adsorption capacities of sawdust carbon (SDC) and rice husk carbon (RHC) were found to be 183.8 mg and 86.9 mg per g of the adsorbent respectively. The results indicate that SDC and RHC could be employed as low-cost alternatives to commercial activated carbon in wastewater treatment for the removal of acid dyes.
The regeneration of three commercial activated carbons by thermal desorption with liquid water at 320°C and 150 atm, in the absence of oxygen, was investigated. The efficiency of this procedure was evaluated by measuring the rate and the amount of substance retained in successive cycles of adsorption–regeneration. The efficiency of the treatment was found to be very high. The study was conducted with the adsorption of two compounds differing greatly in their molecular sizes: phenol and an azo dye (direct red 79 C.I. 29065). In all three carbons a slight increase in the adsorptive power was observed with respect to the original carbons; this is attributed to the cleaning or opening of closed pores. The carbons exhausted with phenol showed the greatest difficulty in regenerating because part of the phenol may be chemically adsorbed. The effect of the treatment on the textural and chemical characteristics of the original carbons was also investigated using N2 adsorption isotherms, mercury porosimetry, pycnometry, scanning electron microscopy and acid-base titration. The alterations found were not very significant, except for a slight increase in the true density, total pore volume and the acidity of the treated carbons.
This contribution deals with the study of hollow fibre membrane dead-end microfiltration combined with powdered activated carbon sorption used in removing of organic dyes from wastewater. Adsorption characteristics of model reactive dye OSTAZIN RED on powdered activated carbon were studied. Adsorption isotherms and kinetics were measured from which followed, that adsorption of this dye on activated carbon is favourable, however the time to reach an equilibrium is around 7 days. From hybrid separation process characteristics measurements it resulted that the activated carbon does not foul this type of membrane and the permeate flux is recovered after membrane backflush. A simple mathematical model describing dynamic sorptive process in microfiltration system is presented and discussed.
The adsorption of two commercial dyes and phenol from water on activated carbons was investigated at 30°C. The carbons were prepared from bagasses and were activated by steam with different extents of burn-off by varying the temperature in the range of 750–840°C. Pore structures of the carbons were characterized by the t-plot method based on N2 adsorption isotherms. Three simplified models including the pseudo-first-order equation, pseudo-second-order equation, and intraparticle diffusion models were used to test the adsorption kinetics. It was shown that the adsorption of dyes could be best fitted by the intraparticle diffusion model; the kinetic parameter was calculated and correlated with the extent of burn-off of the carbons. Neither of the three models had a preference for describing the adsorption of phenol, presumably due to its combined control of chemisorption and intraparticle diffusion.
The mineralization of an azo dye Acid Red 14 (AR14) by the photoelectro-Fenton (PEF) process was studied in an undivided electrochemical reactor with a RuO2/Ti anode and an activated carbon fiber (ACF) cathode able to electrochemically generate H2O2. Anodic oxidation and UV irradiation of AR14 were also examined as comparative experiments. Results indicate that the electro-Fenton process yielded about 60–70% mineralization of AR14, while the photoelectro-Fenton could mineralize AR14 more effectively (more than 94% total organic carbon (TOC) removal) even at low current densities assisted with UV irradiation after 6h electrolysis. The mineralization current efficiency (MCE) of the PEF process increased with the increasing AR14 concentrations. In addition, the initial solution pH ranging from 1.49 to 6.72 had little influence on the TOC removal probably due to the formation of organic carboxylic acids which balanced the pH increase caused by the cathodic generation of hydrogen gas. The ACF cathode showed a long-term stability during multiple experimental runs for degradation of AR14, indicating its good potential for practical application in treating refractory organic pollutants in aqueous solutions.
This review analyses the literature from the early 1990s until the beginning of 2003 and covers the use of carbon nanotubes (CNT) and nanofibers as catalysts and catalysts supports. The article is composed of three sections, the first one explains why these materials can be suitable for these applications, the second describes the different preparation methods for supporting metallic catalysts on these supports, and the last one details the catalytic results obtained with nanotubes or nanofibers based catalysts. When possible, the results were compared to those obtained on classical carbonaceous supports and explanations are proposed to clarify the different behaviors observed.
The photocatalysts of Fe-ACF/ compositeswere prepared by the sol-gel method and characterized by BET, XRD, SEM, and EDX. It showed that the BET surface area was related to adsorption capacity for each composite. The SEM results showed that ferric compound and titanium dioxide were distributed on the surfaces of ACF. The XRD results showed that Fe-ACF/ composite only contained an anatase structure with a Fe mediated compound. EDX results showed the presence of C, O, and Ti with Fe peaks in Fe-ACF/ composites. From the photocataytic degradation effect, on activated carbon fiber surface modified with Fe (Fe-ACF/) could work in the photo-Fenton process. It was revealed that the photo-Fenton reaction gives considerable photocatalytic ability for the decomposition of methylene blue (MB) compared to non-treated ACF/, and the photo-Fenton reaction was improved by the addition of . It was proved that the decomposition of MB under UV (365 nm) irradiation in the presence of predominantly accelerated the oxidation of to and produced a high concentration of OH radicals.
The removal efficiency of activated carbon Filtrasorb 400 (F-400) towards three highly used reactive dyes in the textile industry was investigated. In this work, the adsorption capacities for the anionic reactive dyes, namely; Remazol Reactive Yellow, Remazol Reactive Black and Remazol Reactive Red were determined. The adsorption capacity data showed a high removal ability for the three reactive dyes and a distinguished ability for R. Yellow. The high adsorption capacities for F-400 were attributed to the net positive surface charge during the adsorption process. Surface acidity, surface basicity, H+ and OH− adsorption capacities and pHZPC for F-400 were estimated and compared with other reported values.
A novel process for regenerating activated carbon based on high active species (O3, OH, HO2, O2 and RO, etc.) generated by dielectric barrier discharge (DBD) oxidation was proposed. The method was assayed with granular activated carbon (GAC) exhausted with azo dye acid orange 7. The regeneration efficiency of this technique was evaluated, and the regeneration efficiencies could reach over 73% after five continuous regeneration cycles. The effects of DBD on the adsorption rate, the texture characteristic, the surface chemistry, and the adsorption capacity of GAC samples after different regeneration cycles were investigated. The adsorption rate remained stable after multi-successive regeneration cycles. The analysis of texture of GAC samples showed that the specific surface area and pore volume decreased after DBD regeneration cycles except for the first regeneration sample. It was observed that DBD also resulted in the increase of carboxylic functional groups of GAC's surface. Furthermore, all adsorption equilibrium isotherms fitted the Freundlich model fairly well, which demonstrated DBD plasma did not appear to modify adsorption process but to shift the equilibrium towards lower adsorption concentrations.
Studies were undertaken for the removal of colour from different types of syn- thetic dye solutions by using powdered activated carbon (PAC) and bentonite clay (BC) as adsorbents. The different types of dyes (direct, mordant and basic) studied were Direct Orange, Eriochrome Black T and Malachite Green. The synthetic dye solutions behaved differently with the two adsorbents. The effect of adsorption by PAC and the further addition of a very small dose of a coagu- lant polyaluminium chloride (PAlC) on the settling and/or reuse of adsorbents used was studied. PAC and BC, though effective adsorbents, remained sus- pended in the solution for a long time. PAlC not only enhanced dye removal, but also formed a sludge that settled very quickly and which could also be reused effectively for dye removal.
Anatase TiO2 photocatalysts supported with the ordered mesoporous carbon, CMK-3, were synthesized by the incorporation of TiO2 into CMK-3 followed by heating at 700°C. The structural properties of the TiO2 on CMK-3 were investigated by X-ray diffraction, nitrogen physisorption and electron microscopy techniques. In particular, TiO2 was observed both inside and the external surface of CMK-3. The photocatalytic activity of TiO2 on CMK-3 under UV-light exhibited higher efficiency in removing the Rhodamine 6G dye solution than the commercial photocatalyst P25 and TiO2 on activated carbon. It was attributed to the synergistic effect of large surface area adsorption provided by mesoporous CMK-3 and the distinctive location of TiO2 on the external surface of CMK-3.
This paper presents a review of catalytic ozonation and methods of enhancing molecular ozone reactions in water treatment. It is also an attempt to propose general ideas about mechanisms governing catalytic ozone reactions. Catalytic ozonation is a new means of contaminants removal from drinking water and wastewater. Its application is mainly limited to laboratory use. However, due to successful results further investigation is to be carried out. The majority of models proposed represent more of a speculative approach to the problem than a hypothesis based on experimental data. It is therefore useful to provide a summary of the accomplishments concerning catalytic ozonation and methods of enhancing molecular ozone reactions that were published so far. A survey of the application of several homo- and heterogeneous catalysts, their activity and the parameters influencing the efficiency of catalytic systems is presented here as a short overview, the aim of which is to raise awareness of possible new approaches to water purification.
The study was concerned primarily with characterization of the NF45 membrane. Its pure water permeability, the mass transfer coefficient of NaCl, and the mean radius of the membrane pores were determined. Experiments run with five pure dye solutions and an industrial dye pulp solution confirmed the potential of nanofiltration membrane separation for the treatment of textile dye plant effluent. The effects of such significant parameters as initial solution concentration, transmembrane pressure, and type of dye on two fundamental characteristics of nanofiltration (flux and separation factor) were studied.
The conversion of wood into bio-fuels and bio-chemicals is technically feasible. Wood valorization processes include fractionation, pyrolysis, hydrolysis, fermentation, and gasification. Fast pyrolysis utilizes wood biomass to produce a product that is used both as an energy source and a feedstock for chemical production. The bio-oils from wood pyrolysis were composed of a range of cyclopentanone, methoxyphenol, acetic acid, methanol, acetone, furfural, phenol, formic acid, levoglucosan, guaiocol, and their alkylated phenol derivatives. When wood is rapidly heated in a reduced oxygen environment, the feeding material does not combust but rather becomes a synthetic gas (syngas), a combination of hydrogen (H2) and carbon monoxide (CO). Wood can be converted by hydrolysis into sugars and subsequently fermentation of sugars.
The anaerobic reduction of azo dye Acid Orange 7 (AO7) was investigated in a continuous upflow packed-bed reactor (UPBR) containing biological activated carbon (BAC). Preliminary batch experiments using graphite proved the catalytic effect of using a solid electron mediator in the reactor. Before the start of continuous experiments, AO7 adsorption studies were done to control adsorption effects on initial decolorization rates. In a continuous UPBR-BAC system, high azo dye conversion rates were achieved during very short space times (τ) up to 99% in 2.0 min. In order to know which are the crucial and most influencing properties of BAC in AO7 reduction, other materials (graphite and alumina) with different properties were also tested in UPBRs. The results show that both electron-mediating capability and specific surface area of activated carbon contribute to higher reduction rates. Compared to other continuous and biological processes treating azo dyes, UPBR-BAC seems to be a very effective and promising system for anaerobic azo dye degradation.
This study aims at testing several activated carbons for the catalytic wet air oxidation (CWAO) of phenol solutions. Two commercial activated carbons were used both as received and modified by treatment with either HNO3, (NH4)2S2O8, or H2O2 and by demineralisation with HCl. The activated carbons were characterised by measuring their surface area, distribution of surface functional groups and phenol adsorption capacity. The parent and treated activated carbons were then checked for CWAO using a trickle bed at 140 °C and 2 bar of oxygen partial pressure. The treatments increase the acidic sites, mostly creating lactones and carboxyls though some phenolic and carbonyl groups were also generated. Only (NH4)2S2O8 treatment yields a significant decrease in surface area. CWAO tests show that catalytic activity mainly depends on the origin of the activated carbon. The modifications generally had a low impact on phenol conversion, which correlates somewhat with the increase in the acidity of the carbons. Characterisation of the used activated carbon evidences that chemisorbed phenolic polymers formed through oxidative coupling and oxygen radicals play a major role in the CWAO over activated carbon.
The anaerobic biodegradability of some commercially important colorants was investigated in upflow stirred packed-bed reactors (USPBR) containing biological activated carbon (BAC) system. Decolorization with very high reduction rates took place in the case of azo dyes. At least 80% of conversion was achieved for these dyes at a space time (τ) of 2.0 min or higher corresponding to a residence time of about 1.8 min at the most. On the contrary, nonazo xanthene dye was not converted in the anaerobic bioreactor system. A simple model was proposed to predict azo dye decolorization involving both heterogeneous catalysis and biological degradation. Adsorption studies for the dyes revealed that their adsorption affinity to activated carbon is not the key factor in the reduction process. Results from voltammetric experiments show that a correlation exists between electrochemical characteristic and anaerobic biodegradability of different azo dyes in the continuous USPBR-BAC catalytic system.
Anaerobic reduction of two textile azo dyes (Orange II and Reactive Black 5) was investigated in upflow stirred packed-bed reactors (USPBRs) with biological activated carbon (BAC) system. The bioreactors were prepared with tailored activated carbons (ACs) having different textural properties and various surface chemistries. A kinetic model proposed previously was able to describe the catalytic azo reduction in all cases. Decolourisation with very high reduction rates took place in the case of each AC. Best dye removals were ensured by the AC having the highest surface area: conversion values above 88% were achieved in the case of both azo dyes at a space time of 0.23 min or higher, corresponding to a very short hydraulic residence time of about 0.30 min at the most. The decolourisation rates were found to be significantly influenced by the textural properties of AC and moderately affected by its surface chemistry. The results confirmed the catalytic effects of carbonyl/quinone sites and, in addition, delocalized π-electrons seemed to play a role in the catalytic reduction in the absence of surface oxygen groups.
The anaerobic decolourisation of azo dye Acid Orange 7 (AO7) was studied in a continuous upflow stirred packed-bed reactor (USPBR) filled with biological activated carbon (BAC). Special stirring of BAC and different biodegradation models were investigated. The application of appropriate stirring in the carbon bed resulted in an increase of azo dye bioconversion up to 96% in 0.5 min, compared to unstirred reactor system with ensuring high dye degradation rates at very short space times. In addition, USPBR provided much more reproducible data to make kinetic modeling of AO7 biodegradation. First-order, autocatalytic and Michaelis–Menten models were found to describe the decolourisation process rather well at lower initial dye concentration. AO7 showed significant inhibition effect to biomass beyond inlet dye concentrations of 300 mg L−1. Expanding Michaelis–Menten kinetics by a substrate inhibition factor resulted in a model giving good fitting to experimental points, independently on the initial colourant concentration. Processing at very low hydraulic residence time together with higher initial dye concentration resulted in toxicity to bacteria.
Continuous catalytic wet air oxidation (CWAO) was investigated as a suitable precursor for the biological treatment of industrial wastewater that contained phenols (phenol, o-cresol, 2-chlorophenol and p-nitrophenol), aniline, sulfolane, nitrobenzene or sodium dodecylbenzene sulfonate (DBS). Seventy-two-hour tests were carried out in a fixed bed reactor in trickle flow regime, using a commercial activated carbon (AC) as catalyst. The temperature and total pressure were 140 °C and 13.1 bar, respectively. The influence of hydroxyl-, methyl-, chloride-, nitro-, sulfo- and sulfonic-substituents on the oxidation mechanism of aromatic compounds, the occurrence of oxidative coupling reactions over the AC, and the catalytic activity (in terms of substrate elimination) were established. The results show that the AC without any supported active metal behaves bifunctionally as adsorbent and catalyst, and is active enough to oxidate phenol, o-cresol, 2-chlorophenol and DBS, giving conversions between 30 and 55% at the conditions tested. The selectivity to the production of carbon dioxide was considerable with total organic carbon (TOC) abatement between 15 and 50%. The chemical oxygen demand (COD) reduction was between 12 and 45%. In turn, aniline, sulfolane, p-nitrophenol and nitrobenzene conversions were below 5% and there was almost no TOC abatement or COD reduction, which shows the refractory nature of these compounds.
The waste slurry generated in fertilizer plants and slag (blast furnace waste) have been converted into low-cost adsorbents, activated carbon and activated slag, respectively, and these are utilized for the removal of malachite green (a basic dye) from wastewater. In the batch experiments, parameters studied include the effect of pH, sorbent dosage, adsorbate concentration, temperature, and contact time. Kinetic studies have been performed to have an idea of the mechanistic aspects and to obtain the thermodynamic parameters of the process. The uptake of the dye is greater on carbonaceous material than on activated slag. Sorption data have been correlated with both Langmuir and Freundlich adsorption models. The presence of anionic surfactants does not affect the uptake of dye significantly. The mass transfer kinetic approach has been applied for the determination of various parameters necessary for the designing of fixed-bed contactors. Chemical regeneration has been achieved with acetone in order to recover the loaded dye and restore the column to its original capacity without dismantling the same.
In this paper, we present a mathematical model for a continuous, integrated advanced oxidation process consisting of single-component adsorption, UV photocatalytic mineralization, and draft tube transport. The model is developed and employed as part of a strategy to determine optimal values of selected process design parameters and to identify suitable process operating conditions that may lead to an overall robust performance. An optimization-based algorithm is presented and applied to the design of a water purification system utilizing a composite titanium dioxide/activated carbon photocatalyst adsorbent immobilized on a silica substrate for the degradation of reactive red (RR) dye. A sensitivity analysis is performed to identify qualitative trends implicit in the proposed mathematical model and to measure the robustness of the resulting design over a range of process operating conditions.
A commercial activated carbon, Industrial React FE01606A, without impregnation of any metal, was used as a catalyst in the wet oxidation of three dyes commonly found in textile wastewaters, Orange G, Methylene Blue, and Brilliant Green. Runs were carried out in a three phase fixed-bed reactor by feeding concurrently an aqueous phase containing 1000 mg/L of the dye and an oxygen gas flow rate of 90 mL/min. Temperature was set to 160 °C, and the pressure in the reactor was fixed to 16 bar. The catalyst showed high catalytic activity in dye conversion and color removal. The catalyst kept stable during the time tested on stream (200 h). Total decolorization is obtained at short residence times, but some refractory organic intermediates are obtained (mineralization achieved an asymptotic value about 40−60% depending on the dye). The toxicity of the inlet and outlet effluent was measured by the Microtox bioassay, and the oxidation intermediates identified and quantified explained the obtained toxicity evolution.
The decomposition of ozone in water at different solution pHs in the absence or presence of activated carbons with different surface chemistries and textural properties was investigated. Activated carbon acts as a catalyst in the decomposition of ozone into radical species, significantly accelerating this process. Homogeneous and heterogeneous decomposition of ozone were described by second-order kinetic models. In general, both homogeneous and heterogeneous ozone-decomposition rates increase with solution pH. Textural and surface chemical features of the activated carbon play a role in the catalytic decomposition of ozone. Heterogeneous ozone decomposition is enhanced by activated carbon with high surface area and basicity. Despite the mild oxidation undergone by the activated carbon samples during ozonation, no strong deactivation occurs.
The treatment of textile waste water is commonly carried out using biological (mainly aerobic) and physico-chemical systems. However, anaerobic bioreactors can be used to at least partially treat these effluents and provide a number of significant advantages. The most attractive feature for the treatment of textile effluents is the decolourisation of many dyes under the reducing conditions present in an anaerobic reactor. Laboratory-scale results on this particular topic are here reviewed. A second major advantage of anaerobic processing is its ability to treat wastestreams with high organic loads such as the effluents from the desizing and scouring operations currently employed in the textile manufacturing industry. Reports on successful, full-scale and pilot-scale plants are also reviewed and some limitations are discussed. © 1998 Society of Chemical Industry
The efficiency and cost-effectiveness of H2O2/UV for the complete decolorization and mineralization of wastewater containing high concentrations of the textile dye Reactive Black 5 was examined. Oxidation until decolorization removed 200–300 mg g−1 of the dissolved organic carbon (DOC). The specific energy consumption was dependent on the initial dye concentration: the higher concentration required a lower specific energy input on a weight basis (160 W h g−1 RB5 for 2.1 g L−1 versus 354 W h g−1 RB5 for 0.5 g L−1). Biodegradable compounds were formed, so that DOC removal could be increased by 30% in a following biological stage. However, in order to attain 800 mg g−1 overall mineralization, 500 mg g−1 of the DOC had to be oxidized in the H2O2/UV stage. A cost analysis showed that although the capital costs are much less for a H2O2/UV stage compared to ozonation, the operating costs are almost double those of ozonation. Thus, while H2O2/UV can compete with ozonation when the treatment goal only requires decolorization, ozonation is more cost-effective in this case when mineralization is desired. Copyright © 2006 Society of Chemical Industry
A series of TiO2/ACF samples were prepared by sol–gel-adsorption method and were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD) and nitrogen adsorption. SEM showed that calcined temperature had an important influence on final structure morphologies of TiO2 films. XRD analysis implied that all samples presented anatase structure, carbon surfaces located under TiO2 film could influence the crystalline degree of TiO2. Nitrogen adsorption measurement indicated that some pores located in activated carbon fiber (ACF) were covered by TiO2 film. Photocatalytic degradations of methyl orange solution and acid fuchsine solution showed that dye compounds could be removed rapidly from water by TiO2/ACF samples because of dual functions: absorption of ACF and photocatalytic degradation of TiO2 film, and there was a matched relation between pore diameter of immobilized sample and molecular size of dye compound.
The effect of the electrochemical treatment (galvanostatic electrolysis in a filter-press electrochemical cell) on the surface chemistry and porous structure of a granular activated carbon (GAC) has been analyzed by means of temperature-programmed desorption and N2 (at 77 K) and CO2 (at 273 K) adsorption isotherms. The anodic and cathodic treatments, the applied current (between 0.2 and 2.0 A) and the type of electrolyte (NaOH, H2SO4 and NaCl) have been studied as electrochemical variables. Both anodic and cathodic treatments lead to an increase in the surface oxygen groups. A suitable choice of the electrochemical variables allows a selective modification of the amount and the nature of the surface oxygen groups of the GAC. In general, the electrochemical treatment does not modify significantly the textural properties of the GAC. However, an increase in the porosity of the activated carbon occurs during the cathodic treatment in oxygen-saturated solutions. This result is interpreted as a consequence of carbon gasification driven by reaction with peroxide species generated by electroreduction of oxygen. The anodic treatment in NaCl produces oxidation degrees comparable to those achieved by classical chemical oxidations.
Nineteen solvents were evaluated in batch tests involving the desorption of a representative organic adsorbate (phenol) from activated carbon. Three of the better solvents which also possess complete miscibility with water (acetone, dimethylformamide, methanol) were tested further in fixed-bed runs. The effects of solvent temperature and solvent flow rate on phenol desorption were evaluated. In addition, the recovery of phenol adsorption capacity by an activated carbon bed operated cyclically using a sequence of phenol adsorption, desorption with methanol, and rinsing with water was determined. It was found that solvent temperature and flow rate are not critical variables. Solvent volume and type were the most important factors in phenol desorption. A modest volume of methanol restored 88% of the fixed-bed adsorption capacity for phenol after 1 regeneration, and the capacity essentially leveled off after 5 regenerations at a value of 81% of the capacity of fresh carbon. Methanol regeneration is effective, easy to perform and offers convenient solvent recovery. Thus, it is an attractive alternative to thermal regeneration methods.
The adsorption of acid dyes (Acid Blue 9, Acid Blue 74, Acid Orange 10, and Acid Orange 51), direct dyes (Direct Black 19, Direct Yellow 11, and Direct Yellow 50), and basic dyes (Basic Brown 1 and Basic Violet 3) on a highly mesoporous activated carbon fiber (Y-ACF) obtained from pitch containing yttrium acetylacetonate was investigated in terms of size of dye molecules, and pore size and surface charge of the activated carbon fiber. The results were compared with that on a microporous activated carbon fiber (A-20). The high amounts of sterically small size of acid dyes and basic dyes were adsorbed on both Y-ACF and A-20. The amounts of direct dyes, which are large in one or two dimensions of molecular structures, adsorbed on a mesoporous Y-ACF were much higher than those on microporous A-20. The adsorbed amounts of direct dyes decreased with increasing pH in alkaline pH, in which the ζ potentials of Y-ACF show negative values. From these results, we can suggest that the adsorption of dyes on activated carbon fiber varies greatly by changing pore size and surface charge of activated carbon fiber.